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Nucleus accumbens neuronal maturation differences in young rats bred for low versus high
voluntary running behavior
Michael D. Roberts1*, Ryan G. Toedebusch1*, Kevin D. Wells2*, Joseph M. Company1*, Jacob D.
Brown3*, Clayton L. Cruthirds1*, Alexander J. Heese1*, Conan Zhu1*, George E. Rottinghaus1*,
Thomas E. Childs1*, Frank W. Booth1,3,4,5*†
Affiliations
Department of Biomedical Sciences, College of Veterinary Medicine; 2Division of Animal
Sciences; 3Department of Medical Pharmacology and Physiology; 4Dalton Cardiovascular
Research Center; 5Department of Nutrition and Exercise Physiology, University of Missouri,
Columbia, MO USA 65211

1

Author Contributions
M.D.R. outlined the experiments, helped procure funding, performed bioinformatics and drafted
the manuscript. F.W.B. procured funding, conceived and maintained the selective breeding
model and helped draft the manuscript. R.G.T., J.M.C. and K.D.W. critically assisted with
RNA-seq bioinformatics and helped draft the manuscript. G.E.R. performed H.P.L.C. methods
and helped draft the manuscript. A.J.H. and C.Z. critically assisted with I.H.C. and writing of
the manuscript. R.G.T., J.M.C., J.D.B. and T.E.C. assisted in tissue collection, data analysis,
and/or writing of the manuscript.

Running title: Accumbens characteristics of low and high running rats
Key words: nucleus accumbens; exercise; gene expression
†

Corresponding author information:
Frank W. Booth
University of Missouri-Columbia, Department of Biomedical Sciences
E102 Veterinary Medicine Bldg
1600 E Rollins
Columbia, MO 65211
Phone: 573-882-6652
Fax: 573-884-6890
E-mail: boothf@missouri.edu

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KEY POINTS SUMMARY
•

Selective-breeding experiments with laboratory rodents have demonstrated the
heritability of voluntary exercise.

•

We performed RNA-sequencing and bioinformatics analyses of the reward and pleasure
hub in the brain – the nucleus accumbens – in rats selectively-bred for low voluntary
running (LVR) versus high voluntary running (HVR).

•

The discovery of unique genes and ‘cell cycle’-related gene pathways between lines
guided our hypothesis that neuron maturation may be lower in LVR rats.

•

Testing of this hypothesis revealed that the LVR line inherently possessed less mature
medium spiny neurons and less immature neurons compared to their high voluntary
running counterparts. However, minimal running in LVR rats appeared to rescue and/or
reverse these effects.

•

Neuron maturation in the nucleus accumbens is related to low running voluntary behavior
in our model; this allows researchers to understand potential neural mechanisms that
underlie the motivations for low physical activity behavior.

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ABSTRACT
We compared the nucleus accumbens (NAc) transcriptomes of generation 8 (G8), 34day-old rats selectively-bred for low (LVR) versus high voluntary running (HVR) behaviors in
rats that never ran (LVRnon-run and HVRnon-run), as well as in rats after six days of voluntary wheel
running (LVRrun and HVRrun). In addition, the NAc transcriptome of wild-type Wistar rats were
compared. The purpose of this transcriptomics approach was to generate testable hypotheses as
to possible NAc features which may be contributing to running motivation differences between
lines. Ingenuity Pathway Analysis and Gene Ontology analyses suggested that ‘cell cycle’related transcripts and the running-induced plasticity of dopamine-related transcripts were lower
in LVR versus HVR rats. From these data, a hypothesis was generated that LVR rats might have
less NAc neuron maturation than do HVR rats. Follow-up immunohistochemistry in G9-10
LVRnon-run rats suggested that the LVR line inherently possessed less mature medium spiny
(Darpp-32-positive) neurons (p < 0.001) and less immature (Dcx-positive) neurons (p < 0.001)
compared to their G9-10 HVR counterparts. However, voluntary running wheel access in our
G9-10 LVRs uniquely increased their Darpp-32-positive and Dcx-positive neuron densities. In
summary, NAc cellularity differences and/or the lack of running-induced plasticity in dopamine
signaling-related transcripts may contribute to low voluntary running motivation in LVR rats.

Key words: exercise; gene expression; central nervous system
Abbreviations: NAc, nucleus accumbens; G, generation; RNA-seq, RNA deep-sequencing;
RPKM, reads per kilobase per million mapped reads; HVRrun, HVR 34 day-old 6-day runners;
LVRrun, LVR 34 day-old 6-day runners; HVRnon-run, HVR 34 day-old non-runners; LVR non-run,
LVR 34 day-old non-runners; CTL, control Wistar rats; IPA, Ingenuity Pathway Analysis; GO,
Gene Ontology.

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INTRODUCTION
Understanding the neuro-molecular basis for voluntary exercise behaviors is imperative.
Accelerometry measurement suggests that over 90% of Americans that are 12 years old and
older fail to meet U.S. physical activity guidelines (Troiano et al., 2008). This statistic is
troubling given that lifetime physical inactivity accelerates the secondary aging of numerous
organ systems which leads to a diminished quality of life and an increased risk for chronic
disease and premature mortality (Booth et al., 2011). A recent genome-wise association study of
772 twins found that additive genetic factors explained 47% of the variance for time spent
performing moderate-to-vigorous intensity physical activity and 31% of the variance in the time
spent being sedentary (Hoed et al., 2013). Thus, low and high levels of voluntary physical
activity likely have a partial genetic basis.
The mesolimbic dopaminergic pathway in the midbrain and basal forebrain, specifically
the nucleus accumbens (NAc), plays a major role in determining voluntary running behavior in
rodents (Waters et al., 2008; Knab et al., 2009; Knab & Lightfoot, 2010; Knab et al., 2012).
Furthermore, Salamone and Correa (Salamone & Correa, 2012) contend that the NAc acts as a
‘gate’, ‘filter’, and/or ‘amplifier’ of information passing through from various cortical or limbic
areas to various motor areas of the brain, and suggest that the NAc participates in a variety of
behavioral processes related to aspects of motivation. A selective breeding model was first
developed by Garland to study the neurobiology of mice that voluntarily run high nightly
distances (HVR mice) compared to control mice (Swallow et al., 1998). Rhodes et al. (Rhodes
et al., 2003) examined brain activity patterns of HVR mice versus control lines through c-fos
staining and determined that high neuron activation in the NAc differentiated running motivation
between the HVR and control lines. Altered dopaminergic profiles also exist between the HVR
lines and control lines (Rhodes et al., 2001; Rhodes & Garland, 2003; Mathes et al., 2010),
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which further suggest that NAc dopaminergic signaling is involved with voluntary exercise
motivation. Beyond the HVR murine model of Garland and co-workers, other rodent data
similarly suggests that NAc dopaminergic signaling plays an integral role in voluntary physical
activity behaviors (Knab et al., 2009; Greenwood et al., 2011). Finally, genetic factors are
known to be involved in both motivation and ability to engage in voluntary wheel running in
rodents (Garland et al., 2011).
We recently developed a unique selective breeding model for rats that voluntarily run low
(LVR) or high (HVR) nightly distances in voluntary running wheels (Roberts et al., 2013). In
the current study, we sought to examine the NAc transcriptome in generation 8 (G8) 34-day-old
rats selectively bred for low (LVR) versus high voluntary running (HVR) behaviors, and tested
in subgroups of those that never ran (LVRnon-run and HVRnon-run), as well as after six days of
voluntary wheel running (LVRrun and HVRrun). In addition, wild-type Wistar (CTL) rats were
tested. Importantly, the purpose of this ‘omics’ approach was to generate testable hypotheses as
to which possible NAc features may be contributing to running motivation differences between
lines. In the current study, RNA-seq and bioinformatic analyses from the G8 LVR and HVR rats
directed hypothesis-driven follow-up immunohistochemistry experiments in G9-10 rats, which
suggested that NAc neuronal maturation differences exist between LVR and HVR rats. Our
newly generated hypothesis from these data are that LVR rats inherently possess less NAc
neuron maturation than HVR rats which, in turn, may suppress the development of voluntary
wheel running reward. Likewise, while G9-10 HVR and LVR rats possessed similar NAc
dopamine levels, the lack of running-induced plasticity in dopamine-signaling-related mRNAs in
the G8 LVR versus G8 HVR rats may be one culprit for low running motivation in the former
line type. More in depth discussion of these results are presented in greater detail herein.

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MATERIALS AND METHODS
NAc RNA isolation from Generation 8 (G8) HVR and LVR rats and cDNA library preparation
for RNA-sequencing
All animal procedures outlined below were approved by the University of Missouri’s
Animal Care and Use Committee. Our selective breeding model to generate LVR and HVR rats
is described elsewhere (Roberts et al., 2013). In brief, we reported that G8 HVR rats voluntarily
ran ~5 times longer distances than G8 LVR rats; an effect which is mostly explained by betweenline differences in time spent in running wheels versus running pace. In the current study, G8
LVR and HVR rats were weaned at 21 days of age, and then randomly divided into two groups
at 28 days old, composed of: a) those that voluntarily ran in wheels with bicycle computers for 6
days between the ages of 28-34 days old (LVRrun and HVRrun); and b) those that never ran in
wheels (LVRnon-run and HVRnon-run). Wild-type Wistar rats (CTL) that were never exposed to
voluntary running wheels, were purchased from Charles River Laboratories (Rayleigh, NC) for
this experiment. Food (Formulab Diet 5008, Purina) and water were provided ad libitum
throughout the entirety of the experiment for all rats.
At 34 days of age between 1700-1900, up to two hours prior to the dark cycle, rats were
administered an intraperitoneal injection of a lethal dose of sodium pentobarbital (60 mg/kg body
mass). This sacrificial time point was chosen as a ‘basal’ observational time-point in order to
avoid running-induced line-type differences in NAc mRNAs that likely could exist during and in
the hours following the dark cycle. Further, 34 days is the time when rats end the 6-day period
of voluntary wheel running for the selection process. Brains were quickly removed and NAc
tissue was extracted from seven (4 male, 3 female) G8 HVRnon-run rats, eight (4 male, 4 female)
G8 LVRnon-run rats, six G8 (3 male, 3 female) HVRrun rats, six (3 male, 3 female) G8 LVRrun rats,

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and four (2 male, 2 female) CTL rats using a 2-mm punch tool and brain sectioning apparatus
(Braintree Scientific, Braintree, MA). Tissue plugs from 2 mm-thick coronal brain slices, which
were visibly identified as being NAc per a rat brain atlas published by Paxinos and Watson
(Paxinos & Watson, 1998), were placed in Trizol and were stored at -80°C until processing.
During tissue processing, samples were lysed in Trizol using a high-speed shaking apparatus
(Tissuelyser LT, Qiagen) with RNase-free stainless steel beads. RNA was subsequently
separated according to manufacturer’s instructions, and isolated/DNase treated with columns
(Macherey-Nagel, Bethlehem, PA, USA). High RNA integrity of each sample was confirmed
using BioAnalyzer 2100 automated electrophoresis system (Bio-Rad) prior to cDNA library
construction. cDNA library preparation was performed at the University of Missouri DNA Core
as previously described (Roberts et al., 2013).
Illumina sequencing of NAc cDNA and statistical analyses of RNA-seq data. RNA-seq
procedures occurred at the University of Missouri DNA Core and are described in more detail
elsewhere (Rustemeyer et al., 2011; Roberts et al., 2013). Differential gene expression patterns
were analyzed for annotated genes between the HVRrun and LVRrun rats using reads per kilobase
per million mapped reads (RPKM) values. Our strategy to assess NAc mRNAs differentially
expressed between G8 HVR and LVR rats for hypothesis-generating purposes is presented in
Figure 1. We previously reported that 35 NAc transcripts exhibited line-type specificity between
G8 HVRnon-run and LVRnon-run (Roberts et al., 2013). However, it is possible that many of these
transcripts could be normalized after 6 days of running, making these less probable line typespecific gene candidates (as in Fig. 1C). Thus, we deemed an mRNA to be an inherent line-type
NAc candidate if it met the following thresholds: 1) the G8 HVRrun/ G8 LVRrun fold-change
value was greater than ±1.25-fold (Student t-test p < 0.01); and 2) subsequent analysis of this

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mRNA candidate differed between the HVRnon-run and LVRnon-run groups at a p < 0.05 confidence
level regardless of fold-change value. Transcripts that met the aforementioned HVRrun/LVRrun
and HVRnon-run/LVRnon-run thresholds were considered more representative, intrinsic line-type
candidate genes (Fig. 1B) and were also compared to control Wistar rats to further validate their
line-type specificity (not depicted in Fig. 1).

<Insert Fig 1 here>

Note that a false discovery rate threshold of q < 0.10 proved to be too stringent to detect
line-type NAc transcriptomic differences with and/or without running. While a ±1.25-fold cutoff (p < 0.01) threshold may seem statistically liberal compared to other publications using 1.5to-2.0 fold-change cut-offs to examine transcriptomic differences between treatments (Heruth et
al., 2012; Song et al., 2012; Zhang et al., 2012), we contend that subtle mRNA differences exist
within the NAc between the HVR and LVR rats given that: a) our model is a physiological/in
vivo model whereby rats are being observed in a ‘basal’ state, and b) only 8 transcripts differed at
a ±1.5 fold change threshold in our previous publication when solely comparing the HVRnon-run
versus LVRnon-run groups (Roberts et al., 2013). Of note, RNA-seq analyses were also performed
in the current study at a relatively early generation of selective breeding to identify early NAc
gene changes that occur prior to potential compensatory gene changes which may occur in later
generations and, thus, could confound data interpretation.

Bioinformatics of RNA-seq data

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Ingenuity Pathway Analysis (IPA; Ingenuity Systems Inc., Redwood, CA, USA) was
used to examine NAc gene networks that: a) differed between HVRrun and LVRrun, but were
similar between HVRnon-run and LVRnon-run rats (line-type differences likely due to running in Fig.
1a and b differed between runner (HVRrun and LVRrun) as well as between non-runner (HVRnonrun

and LVRnon-run) rats (inherent line-type differences as in Fig. 1b). Past literature has also

attributed differences in voluntary running behavior to differences in NAc dopamine signaling
(Knab & Lightfoot, 2010; Mathes et al., 2010; Greenwood et al., 2011; Knab et al., 2012;
Roberts et al., 2012; Roberts et al., 2013). Therefore, a list of dopamine signalling-related
transcripts was constructed using the Gene Ontology (GO) Consortium database
(http://www.geneontology.org) in order to examine if these gene expression patterns differed
between LVR and HVR lines with or without 6 days of voluntary wheel running. Pathways for
dopamine-related genes included the dopamine receptor- signaling pathway (GO ID: 0007212),
adenylate cyclase-activating dopamine receptor pathway (GO ID: 0007191), adenylate cyclaseinhibiting dopamine receptor pathway (GO ID: 0007191), and/or the negative regulation of
dopamine receptor signaling pathway (GO ID: 0060160).

Western blotting confirmation of line-type-specific targets yielded by G8 RNA-seq analyses in
female G10-G11 LVR and HVR rats
Western blotting of one of the gene candidates was performed in 35-day old female G10G11 LVRrun/non-run and HVRrun/non-run rats (n = 6-7 per line and activity group). The Cadm4 gene
was validated through Western blotting (Figure 2) due to it being the sole NAc inherent line-type
gene candidate that was most highly expressed on an RPKM basis and also associated with
neuronal synaptogenesis, as discussed in subsequent sections below.

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Briefly, 15-20 mg of NAc tissue was removed from brain and homogenized on ice in
RIPA buffer [50 mM Tris-HCl (pH 8.0), 150 mM NaCl, 1% NP-40, 0.5% sodium deoxycholate,
1% SDS, 1x protease inhibitor cocktail] using a Tissuelyser at 20 Hz for 1 min. The homogenate
was centrifuged at 12,000xg for 10 minutes and the resultant supernatant was obtained for
Western blotting. Protein concentrations were obtained using the BCA assay (Pierce
Biotechnology, Rockford, IL) and 60 µg of protein in loading buffer was loaded onto 18% SDSPAGE gels. Proteins were transferred onto PVDF membranes and all blots were incubated with
Ponceau S (Sigma) to verify equal loading in all lanes. Primary antibodies [rabbit polyclonal
Cadm4 at 1:1,000 (Abcam, Cambridge, MA, USA)], that had been diluted in Tris-buffered saline
+ Tween20 with 5% bovine serum albumin and applied to membranes overnight at 4°C, HRPconjugated secondary antibody (1:2,000; Cell Signaling), were applied for 1 hour at room
temperature, and ECL substrate (Pierce Biotechnology) was then applied for 5 minutes prior to
exposure. Band densitometry was performed through the use of Kodak 4000R Imager and
Molecular Imagery Software (Kodak Molecular Imaging Systems, New Haven, CT) and
statistical analyses on band densities were performed using a two-way [line-type (LVR vs. HVR)
x activity (run vs. non-run)] analysis of variance with Holm-Sidak post-hoc analyses when
appropriate.

Follow-up NAc tissue immunohistochemistry experiments in female G9-G10 LVR and HVR rats
from hypotheses derived from G8 RNA-seq analyses
Based upon resultant IPA gene network differences between lines of ‘cancer, cell cycle,
cellular growth and proliferation’, we hypothesized that LVR rats might have fewer mature
medium spiny neurons (MSN). This hypothesis was tested by an independent
immunohistochemical (IHC) analyses for dopamine- and cAMP-regulated neuronal
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phosphoprotein (Darpp-32)-positive neurons, as well as for NAc doublecortin (Dcx)-positive
neurons in female G9-G10 LVR and HVR rats. Dcx is highly expressed by immature neurons in
the adult cortex, and upon differentiation, gradually decreases to undetectable levels (Brown et
al., 2003). The stain was for total Darpp-32 protein that is prominently expressed in
differentiated striatal MSNs, composing 95% of neurons in the NAc (Arlotta et al., 2008), which
was thus used as a molecular marker of mature/differentiated NAc MSNs in the current study.
Briefly, coronal brain slices from 39-40-day old female G10 HVRrun (n = 7) and G10
LVRrun (n = 7) rats that voluntarily ran for 10-12 days from were used for IHC. Coronal brain
slices from age-matched G9 female LVRnon-run (n = 7) and G10 female HVRnon-run rats (n = 6)
were also examined for Dcx- and Darpp-32-positive NAc neurons. Of note, brains were
obtained 2-3 hours into their dark/running cycle for the purpose of examining if distance ran on
the night of sacrifice correlated with c-fos-positive neurons in the NAc and other brain areas
(data not included). This differed from the G8 NAc samples obtained for RNA-seq 2 hours prior
to the dark/running cycle. However, it is likely that NAc MSN and Dcx neuron densities do not
transiently fluctuate between light and dark cycles.
It is also import to note that while these animals were 4-5 days older than the G8 animals
interrogated for RNA-seq: a) these animals were still similarly pre-pubescent as posited from
previous literature (Zanato et al., 1994); and b) Dcx protein expression is long-lasting in
premature neurons and gradually declines upon differentiation as previously mentioned.
Additionally, brains from the G8 animals were not preserved for IHC and, given that IHC
experiments were done as a post-hoc analysis, G9-10 animals that were ~40 days of age were
used due to convenience of sampling as opposed to 35 days of age. In spite of these minor
differences, potential line type differences observed in NAc Dcx-positive and Darpp-32-positive

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neurons between the 39-40-day old HVRrun and LVRrun rats logically provided us with a good
representation of what likely occurred in G8 35-day old HVRrun and LVRrun rats.
IHC procedures were performed similar to those described by Rhodes et al. (Rhodes et
al., 2003). Briefly, rats were sacrificed and were transcardially perfused with freshly made 4%
paraformaldehyde (PFA, wt/vol) in phosphate-buffered saline (PBS, pH 7.4). Brains were
subsequently removed, post-fixed in 4% PFA overnight, and incubated in 30% sucrose (wt/vol)
in PBS for 2 d. Thereafter, brains were removed from the 30% sucrose solution, wrapped in
parafilm, and stored until coronal slicing. Multiple frozen 40 µm coronal sections containing the
NAc (Bregma +1.00 mm) were obtained using a cryostat (Leica) and each slice was placed in
24-well plates containing cryoprotectant solution (30% sucrose, 30% [wt/vol] ethylene glycol,
and 10% [wt/vol] polyvinylpryrrolidone in PBS, pH 7.4). Following long-term storage and prior
to assaying, the free-floating sections were thoroughly washed in PBS and blocked in 10%
normal goat serum for 2 h. IHC for Dcx (1:100 rabbit anti-Dcx, Abcam) and pan Darpp-32
(1:100 rabbit anti-Darpp-32, Cell Signaling) were subsequently performed on serial NAc
sections in PBS containing 1.5% normal goat serum and 0.2% Triton X-100, and sections were
incubated with the primary antibody solution for 2 d at 4°C. Sections were subsequently
incubated with biotinylated goat anti-rabbit secondary antibody (1:400, Vector Labs,
Burlingame, CA) in PBS containing 0.2% Triton X-100 for 2 h at room temperature followed by
incubation with ABC Elite kit reagents for 1 h (Vector Labs). Finally, sections were stained with
diaminobenzidine + nickel solution through peroxidase reaction for 5 min. Section staining from
all animals was performed simultaneously in order to avoid potential assay-assay variations in
staining. It should be noted that multiple coronal brain slices containing the NAc were collected
per animal. Per the methods of Rhodes et al. (Rhodes et al., 2003), one brain representative NAc

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section was immunostained. In order to standardize between-animal NAc sections, we ensured
that there was morphological similarity of the following visual landmarks: 1) the orientation of
the corpus collosum; 2) the initial presence of the lateral ventricle; and 3) the presence of the
anterior commissure which exists within the NAc core.
Microscopic images sections were captured by an Olympus BX60 photomicroscope at
10x magnification (Olympus, Melville, NY, USA), and photographed with Spot Insight digital
camera (Diagnostic Instruments, Sterling Heights, MI, USA). Dcx-positive and Darpp-32positive neurons from all samples were counted using Image J software (National Institutes of
Health). Statistical analyses on Dcx-positive and Darpp-32-positive neurons were performed
using a two-way [line-type (HVR vs. LVR) x activity (run vs. non-run)] analysis of variance
with Holm-Sidak post-hoc analyses when appropriate.

NAc tissue dopamine in female G9-G10 LVR and HVR rats as a follow-up to G8 RNA-seq
analyses
In order to examine if dopamine concentrations were different between lines, NAc
dopamine concentrations were determined in: a) G10-11 LVRnon-run and HVRnon-run rats 1-2 hours
prior to their dark cycle; and b) G10-11 LVRrun and HVRrun 1-2 hours prior to their running dark
cycle as well as 2-3 hours into their dark cycle. Approximately 15-20 mg of NAc tissue was
stereotactically removed from 35-day old G10-G11 LVRrun/non-run and HVRrun/non-run rats and
homogenized on ice in 0.1M perchloric acid, 0.001% EDTA (wt/vol) using a Tissuelyser at 20
Hz for 1 minute. The homogenate was centrifuged at 12,000 x g for 10 minutes and the resultant
supernatant was obtained for dopamine analysis using high performance liquid chromatography
(HPLC) with electrochemical detection. Briefly, the system consisted of an ESA isocratic pump
and a Thermo Separations Products Spectra system AS3500 auto sampler with a 4-channel ESA
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Coularray Model 5600 detection system. Coularray settings were 25mV, 150mV, 250mV, and
800 mV. A Phenomenex 250 x 4.60 mm, 5 µm, Prodigy reversed phase column was used with a
mobile phase consisting of 75 nM sodium hydrogen phosphate, 1.7 mM 1-octanesulfaonic acid,
100 µL/L triethylamine, 25 µM (500 µL of 100 mM EDTA/2L, 5% acetonitrile adjusted to pH
3.0 with phosphoric acid) being pumped at 1 ml/min. The system was controlled and data
acquired and processed using the CoulArray software on a Pentium-based computer. Dopamine
primary standard (1,000 ppm, Sigma) was prepared in 1:1 acetonitrile: water, working dopamine
standards (500 and 100 ppb) were prepared in 1:1 acetonitrile: water, and dopamine retention
was found to be at 8.3 min. Statistical analyses on NAc tissue dopamine content were performed
using a two-way [line-type (HVR vs. LVR) x activity (run vs. non-run vs. run during dark
cycle)] analysis of variance with Holm-Sidak post-hoc analyses when appropriate.

RESULTS
Characterization of RNA-seq data from G8 LVR and HVR rats
The total number of reads as well as the percentage of reads aligned to the reference
genome is presented in Table 1. To assure that there was uniform tiling across the reference
genome, tiled reads from each sample were visualized using NexGen v2.2 software (data not
shown).
<Insert Table 1 here>

Chen et al. (Chen et al., 2011) recently used laser capture microdissection to isolate NAc
neurons for subsequent RNA-seq analysis, and sequencing results yielded high enrichments for
glutamic acid decarboxylase 1 (Gad1) and Gad2 transcripts (RPKM, log2 values of 7-8), which
encode enzymes in NAc MSNs to produce GABA. Our current RNA-seq data demonstrates that
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all samples were similarly enriched for Gad1 and Gad2 suggesting that NAc MSNs were indeed
present within the assayed brain plugs (Fig. 3A&B). The high correlation between RPKM
values from a sampled rat versus the mean RPKM values from all of the 31 rats also demonstrate
a high reliability of transcript detection using our current RNA-seq methods (Fig. 3C). Specific
differentially expressed transcripts were verified by RT-PCR (Table 2).

<Insert Table 2 here>

94 of 107 NAc mRNA differences between G8 LVRrun versus G8 HVRrun rats were likely due to 6d running differences
RNA-seq differences between G8 LVR and HVR rats with or without running are
summarized in Figure 4.

<Insert Fig. 4 here>

Total 6-day running distances (3.6 km vs. 33.7 km) and times (121 min vs. 1,071 min)
were significantly less in the LVRrun versus HVRrun rats (p < 0.001; data not shown). Using the
aforementioned thresholds (HVRrun/LVRrun > ±1.25-fold, unadjusted p-value < 0.01), we
determined that 107 NAc mRNAs were differentially-expressed between LVRrun and HVRrun rats
Of these 107 transcripts, only 13 were also differentially expressed between LVRnon-run and
HVRnon-run rats, making them inherent/intrinsic line-type NAc mRNA candidates (Fig. 1b,
discussed in the next section). Thus, the 94 remaining transcripts that were differentially
expressed after 6 days of running between LVRrun and HVRrun rats (Fig. 1a) were likely a

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consequence of drastic voluntary running differences (top 10 up- and down-regulated are
presented in Table 3). No sex differences were noted for any of the 107 transcripts (data not
shown).

<Insert Table 3 here>

Only 6 of 13 inherent line-type NAc mRNA candidates were exclusive to the G8 LVR or G8 HVR
rats with or without running when compared to CTL rats
As mentioned in the preceding paragraph, 13 differentially expressed NAc mRNAs
existed between LVR and HVR rats regardless of running (Table 4). While most of the 13
transcripts had RPKM values that were relatively low (< 2.0), Cadm4, Retsat, Slc37a4 and
Tmem119 were relatively highly expressed (> 8.0) in both lines. Importantly, only 6 of these 13
NAc mRNAs were exclusive from CTL rats to either the LVR or HVR line-type (HVR & CTL >
LVR: Cadm4, Capg; LVR > HVR & CTL: Tmem119; LVR & CTL > HVR: Pcdhb3, Pcdhga1,
Pcdhb8]. This list is distinguished from the 35 previous candidates in our recent publication
(Roberts et al., 2013) only examining HVRnon-run and LVRnon-run rats mainly due to the fact that
most of the previously reported candidates were normalized between lines after 6 days of
running.

<Insert Table 4 here>

Western blotting confirmation of Cadm4 as line type-specific gene in G10-11 rats

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Due to the relatively high NAc enrichment of Cadm4 on an RPKM basis, and its role in
synaptogenesis, this protein was interrogated between lines in later generations in order to
confirm our RNA-seq findings at the protein level. Remarkably, NAc Cadm4 protein was
expressed to a lesser extent in LVRnon-run rats compared to HVRnon-run rats (p = 0.03), and tended
to be lower in the LVRrun versus HVRrun rats from generations 10-11 (p = 0.065; Fig. 2),
supporting its differential directionality in RNA-seq Table 4). Thus, this finding gave us further
confidence in interpreting our RNA-seq data for hypotheses generating purposes.

Hypothesis generation through bioinformatics of G8 LVR and HVR NAc transcriptome
differences
Interestingly, the top associated gene network, as identified by IPA, as down-regulated in
LVRrun versus HVRrun rats from the 94 differentially expressed NAc mRNAs included ‘cellular
assembly and organization, cellular function and maintenance, cell cycle’. When considering the
13 transcripts that differed between lines independent of voluntary wheel running, the top
associated down-regulated network in LVRnon-run versus HVRnon-run rats included ‘cancer, cell
cycle, cellular growth and proliferation’ (network score: 20, 7/35 molecules differentially
expressed: ↑Cadm4, ↑Capg, ↑Ggcx, ↑Restat, ↑Slc37a4, ↓Pcdhga1, ↓Tmem119). Others have
previously found that voluntary running increases cell proliferation and survival of new cells
within the subgranular zone of the mouse hippocampus (van Praag et al., 1999; Olson et al.,
2006). However no reports, to our knowledge, suggest that voluntary running affects
neurogenesis in the NAc. Thus, we hypothesized that these resultant networks may indicate that
NAc neuron maturation differed between lines, and follow-up experiments described below were
performed in order to test our newly generated hypotheses.

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RNA-seq-guided IHC experiments suggest LVRnon-run rats possess less immature and medium
spiny neurons in the NAc compared to HVRnon-run rats
Following the aforementioned line type differences discovered through IPA analysis, we
next performed IHC methods to assay the number of Dcx-positive NAc neurons in G9-10
LVRrun/non-run and HVRrun/non-run rats in order to determine if there was a line-type difference in the
number of immature neurons. Remarkably, LVRnon-run rats possessed 3.8-fold less Dcx-positive
NAc neurons compared to HVRnon-run rats (p < 0.001; Fig. 5A). LVRnon-run rats also possessed
6.3-fold less Darpp-32-positive NAc neurons compared to HVRnon-run rats (p < 0.001; Fig. 5B).
Contrary to the non-runner rats, LVRrun rats possessed 2.3-fold more Dcx-positive NAc
neurons compared to HVRrun rats (p < 0.001; Fig. 5A). Likewise, LVRrun rats possessed a
similar number of Darpp-32-positive NAc neurons compared to HVRrun rats (p < 0.001; Fig. 5B).
HVRrun rats possessed significantly less Dcx-positive and Darpp-32-positive cells compared to
HVRnon-run rats, respectively (p < 0.05; Fig. 5A/B). Conversely, LVRrun rats possessed
significantly more Dcx-positive and Darpp-32-positive cells compared to LVRnon-run rats (p <
0.05, Fig 3A/B).
Given that Dcx and Darpp-32 represent markers of immature neurons and
mature/differentiated MSNs, respectively, these findings suggest that substantial differences in
NAc neuronal maturation exist between the LVR and HVR lines types depending upon running
status; a finding which is discussed in greater detail in later paragraphs.

<Insert Fig 5 here>

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Of the HVR and LVR runners analyzed for NAc MSNs, we find correlations exist for the
following relationships:
1) HVRs: More NAc MSNs are associated with less total distances run prior to sacrifice (r =
-0.58 when excluding 1 outlier; Fig. 6a)
2) LVRs: More NAc MSNs are strongly associated with less total distances run prior to
sacrifice (r = -0.92; Fig. 6b)

<Insert Fig. 6 here>

Running induces plasticity in dopamine-related transcripts in HVR versus LVR rats despite linetype similarities in NAc tissue dopamine content
We had hypothesized prior to our RNA-seq analysis that more dopamine-related genes
would be up-regulated within the NAc of LVR (LVRrun and LVRnon-run) and CTL rats versus
HVR (HVRrun and HVRnon-run). Only three of the 30 mRNAs designated by Gene Ontology as
dopamine-related transcripts statistically differed (p < 0.05) between LVRnon-run and HVRnon-run
rats (LVR > HVR: Gna11, Oprd1; HVR > LVR: Slc6a3; Table 5). Similarly, only four of the 30
dopamine-related transcripts statistically differed between LVRrun and HVRrun rats after 6 days of
running (LVR > HVR: Adcy6, Arpp19; HVR > LVR: Oprd1, Oprm1; Table 5). Interestingly, 6
days of running altered 16 of these transcripts within the HVR line (HVRrun versus HVRnon-run
rats, Table 5), while only 1 of these 30 transcripts (Huntingtin; Htt) were altered between LVRrun
versus LVRnon-run rats, suggesting a running-acquired plasticity in dopamine-related NAc
mRNAs in HVR versus LVR rats.
<Insert Table 5 here>

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Interestingly, NAc tissue dopamine content was similar between lines when examining
G10-11 LVR versus HVR rats prior to or 2-3 h during the dark cycle; this finding suggests that
running-induced alterations in dopamine-related transcripts within the HVR line were
independent of running-induced increases in NAc dopamine content at the time period measured
(Fig. 7).

<Insert Fig. 7 here>

DISCUSSION
RNA- seq provides an unbiased measure of the presence and prevalence of transcripts
from known and unknown genes (Mortazavi et al., 2008). Therefore, our undertaken
experimental approach consisted of two phases: a) using RNA-seq and bioinformatics in order to
develop hypotheses that delineate NAc characteristics which may differentiate running
motivations between our unique model of LVR and HVR rats; and b) performing follow-up
experiments in later generations of these rats in order to test these hypotheses. Our newly
generated hypotheses from these experiments are illustrated in Fig. 8, with more in depth
discussions of our findings are presented below.

<Insert Fig 6 here>

NAc medium spiny neurons are lower in LVRnon-run versus HVRnon-run rats, whereas minimal
running in the LVR line normalizes these differences

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IHC experiments were performed in later LVR and HVR generations as a result of IPA
analysis suggesting that the top down-regulated NAc gene network in LVRnon-run versus HVRnonrun

rats included ‘cancer, cell cycle, cellular growth and proliferation’. A novel observation was

that LVRnon-run rats possessed 6.3-fold less mature NAc MSN with the Darpp-32 marker and 3.8fold less immature NAc MSN neurons with the Dcx marker, as compared to HVRnon-run rats.
Thus, MSN density is innately diminished in the LVR versus HVR line, as well as less Dcxpositive neurons that are able to potentially differentiate into MSNs. Lee et al. (Lee et al., 2006)
have shown that increases in dendritic spine density in dopaminoceptive NAc MSNs are linked
to long-lasting addictive behaviors. Hence, LVR rats not exposed to voluntary running may
possess a diminished motivation to voluntarily run due to less NAc MSNs.
However, minimal running in the LVRrun versus HVRrun normalized the aforementioned
line-type differences that existed in non-runners by: a) normalizing MSN density between lines,
and b) increasing the number of Dcx-positive neurons in LVRrun compared to HVRrun rats.
Indeed, these findings are now difficult to reconcile. However, we posit that allowing LVR rats
to partake in minimal running at a young age is associated with promotion of MSN
differentiation and/or stimulation of striatal cytogenesis. Striatal cytogenesis has been shown to
occur in juvenile rats weighing 200-250 g (Mao & Wang, 2001); these being older than the rats
tested herein. Interestingly, glutamate release in the striatum has been shown to occur in rodents
during treadmill exercise (Meeusen et al., 1997), and glutamate-NMDA receptor signaling has
been linked to promoting striatal neurogenesis (Luk et al., 2003). Hence, this may be the
underlying mechanism whereby voluntary running potentially increases NAc MSN and Dcx
neuron densities in the LVR line.

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HVRrun rats, after 6 days of voluntary running, possessed significantly less Darpp-32positive cells relative to HVRnon-run rats, indicating decreased mature MSN. In contrast to
running-induced increases in Dcx-positive and Darpp-32-positive cells within the LVR line, the
high volumes of running in HVRrun decreased these markers for neuronal developmental stage
relative to HVRnon-run. A recent review by Corty and Freeman (Corty & Freeman, 2013) gives
one potential explanation. They describe that during neuronal development, transient and
unnecessary neuronal-neuronal connections often occur. They indicate that selective axonal and
dendritic pruning takes place in order to achieve neural circuit refinement, and as a result,
programmed cell death follows. Thus, our speculation is that programmed cell death could be
one potential cause for the decrease in MSN density in the NAc of our HVR after 6 days of
running from 28-34 days of age, with the LVR line lagging in their relative neuronal
development.
When examining correlations between Darpp-32-positive neurons and running distances
in HVR and LVR rats, we report that modest-to-strong negative associations exist between lower
total distances run prior to sacrifice and a greater density of Darpp-32-positive neurons in HVR
(r = -0.58 with the exclusion of 1 outlier) and LVR rats (r = -0.92). While these correlations
were performed on a limited number of rats, these findings may suggest one of multiple
possibilities: 1) a possible inhibitory effect of MSNs on voluntary running distances in the LVR
line; and/or 2) an anti-differentiation and/or apoptotic effect of running on MSNs; note, however,
that the latter is precluded by the lack of up-regulated pro-apoptosis pathways in the LVR line
per RNA-seq analysis. With regards to the former, NAc MSNs in the may send inhibitory
signals to the globus pallidus, which is a known regulator of voluntary movement (Smith &
Bolam, 1990). Hence, future experiments manipulating NAc MSN number in our HVR and
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LVR animals, via localized neurotoxin injections, will yield critical information on this possible
relationship.

The expression of a number of dopamine-related mRNAs is amplified between HVRrun versus
HVRnon-run rats, but is mostly similar between LVRrun versus LVRnon-run rats despite similarities in
NAc dopamine tissue content between lines
A relationship between striatal dopaminergic signaling and voluntary running behavior is
well established (Garland et al., 2011), although transcriptomic analyses documenting this
relationship has been previously limited to the examination of few select NAc mRNAs; the sole
exception being the recent publication by Mathes et al. (Mathes et al., 2010) where only HVR
and control mouse lines were compared. Our current transcriptomic analyses unveil additional
numerous dopamine-related transcript differences that exist between and within the LVR and
HVR lines with or without 6 days of voluntary running. Only 3 dopamine-related transcripts
innately differed between LVRnon-run and HVRnon-run rats. However, 16/30 dopamine-related
mRNAs differed between HVRrun versus HVRnon-run rats compared to only 1/30 between LVRrun
versus LVRnon-run rats. This finding confirms and expands what Knab et al. (Knab et al., 2009),
Greenwood et al. (Greenwood et al., 2011), and our own data examining Drd1/2/5 NAc mRNA
expression patterns in G5-6 HVRrun versus LVRrun rats via real-time PCR (unpublished findings)
have similarly reported, which is that high levels of wheel running in rodents produces plasticity
in the mRNA expression of dopamine-related genes within the NAc. We posit that upregualtion
of the dopaminergic signaling pathway at the transcriptome level could play a positive reinforcer
for greater voluntary running. However, according to Mathes et al. (Mathes et al., 2010) and
Swallow et al. (Swallow et al., 1998), replication of these results in additional selection lines of

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LVR and HVR are potentially required in order to differentiate between an actual selection
response from possible effects of genetic drift.
Unexpectedly, and contrary to prior data by Mathes et al. (Mathes et al., 2010) who
reported that HVR versus control mice expressed more NAc tissue dopamine which drove the
increased expression of dopamine-related transcripts, NAc dopamine differences did not exist
between our LVR and HVR lines. Potential explanations could be that the running-induced
plasticity of dopamine-related transcripts within our HVR line may be due to: a) a given genetic
architecture within the HVR line which predisposes them to differentially regulate dopaminerelated transcripts in response to voluntary running without differences in dopamine levels, or b)
a species difference between our animals and the Garland’s HVR mice. Notwithstanding, the
plasticity of dopamine-related genes within the HVR line could play some role in the progressive
increase in daily distances of voluntary running that occurs in the initial weeks of accessibility to
running wheels.

Conclusions
While the current study provides a plethora of data which potentially explain differences
in voluntary exercise motivation, a limitation to the current study is that the HVR and LVR
transcriptomes were analyzed in a snapshot fashion early in the rodents’ lives.
Nonetheless, the current study illustrates very novel and potentially important concepts
including: a) that NAc MSN maturation differences may partially be responsible for differences
in voluntary running motivation between the HVR and LVR lines; b) that voluntary running
early in life is able to induces plasticity in neuron populations and mRNA expression profiles.
Specifically, LVR rats exhibit a lack of plasticity in dopamine-related transcripts, which could

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also interfere with the acquisition of voluntary exercise reward in these animals with low
voluntary running activity.

COMPETING INTERESTS
All authors disclose no competing interests.

AUTHOR CONTRIBUTIONS
M.D.R.: designed the study, assisted in most aspects of the study and primarily drafted the
manuscript
R.G.T.: assisted in data procurement, data analysis and writing of the manuscript
K.D.W.: assisted in data procurement, data analysis and writing of the manuscript
J.P.B.: assisted in data procurement, data analysis and writing of the manuscript
J.M.C.: assisted in data procurement, data analysis and writing of the manuscript
C.L.C.: assisted in data procurement, data analysis and writing of the manuscript
A.J.H.: critically assisted with I.H.C. and writing of the manuscript
C.Z.: critically assisted with I.H.C. and writing of the manuscript
G.E.R.: performed H.P.L.C. methods and helped draft the manuscript
T.E.C.: assisted in data procurement, data analysis and writing of the manuscript
F.W.B.: procured College of Veterinary Medicine Grant for RNA-seq experiments, helped
design the study, and assisted in writing of the manuscript

FUNDING
Partial funding for this project was obtained from a grant awarded to F.W.B. by the
College of Veterinary Medicine at the University of Missouri, NIH T32-AR048523 (M.D.R.)

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and AHA 11PRE7580074 (J.M.C.). This project was also largely supported by funds donated
through the College of Veterinary Medicine’s Development Office.

ACKNOWLEDGEMENTS
We graciously thank Dr. Charlotte Tate for her past conversations with F.W.B., which
helped guide the development of the HVR and LVR model.

TRANSLATABLE PERSPECTIVES
Understanding the neural and molecular mechanisms that regulate voluntary exercise
motivation is crucial due to the fact that most adolescents and adults do not engage in regular
physical activity (Troiano et al., 2008), and therapies are needed to correct this physical activity
motivational deficiency. While the current study offers no immediate ‘cure’ to lowered
voluntary exercise motivation, the transcriptomic evaluations and follow-up experiments
comparing the LVR and HVR lines herein continues to contribute to our understanding of the
neuro-molecular basis for voluntary exercise behaviors.

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FIGURE LEGENDS
Figure 1. Experimental strategy to assess influential NAc mRNAs differentially expressed
between generation 8 HVR and LVR rats.

1a) No inherent difference, but acquired difference with voluntary running. 1b) Inherent
difference is maintained after 6 days of voluntary running. 1c) Inherent difference is lost after 6
days of voluntary running. NAc transcripts from HVR and LVR sitters (HVRnon-run and LVR nonrun) were also compared to age-matched control (CTL) Wistar rats to provide further evidence for
line-type differences.

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Figure 2. Western blotting confirmation of NAc Cadm4 as a line-type-specific gene

G10-11 HVR

G10-11 LVR

NAc Cadm4 protein (AU)

46 kD
2.0
1.5
1.0
0.5

p = 0.065

*

1.09

1.00

0.93
0.69

0.0
Non-run

Run

All animals were female and were 35 days of age, and HVRrun and LVRrun animals spent 6 days
in a voluntary running wheel (n = 6-7 per bar). Symbols: *, p < 0.05.

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Figure 3. Enrichment of a NAc MSN-specific mRNA marker in all groups as well as the
reliability of RNA-seq measurements

Gad2 mRNA
(RPKM)

B

C
250
200
150
100
50
0
250
200
150
100
50
0

1000

Rat 1 RPKM values

Gad1 mRNA
(RPKM)

A

800
600
r= 0.994

400
200
0
0

200

400

600

800

1000

Mean RPKM for all rats

All groups presented high amounts of Grd1 (panel A) and Grd2 (panel B), respectively, which is
indicative of NAc MSNs as previously shown by Chen et al. (Chen et al., 2011). Panel C
demonstrates a high correlation of RPKM values from a single rat compared to RPKM average
values from all rats demonstrating high reliability from the RNA-seq data.

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Figure 4. Differentially expressed genes (DEGs) in HVRrun and LVRrun and similar or inherently
different between HVRnon-run and LVRnon-run rats as well as CTL rats in RNA-seq analysis.

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Figure 5. Differences in NAc immature neurons (Dcx+) and MSNs (Darpp-32+) between G9-10
LVR and HVR rats

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Line-type differences in NAc Dcx-positive (panel a) and Darpp-32-positive neurons (panel c),
which are indicative of immature neurons and mature/differentiated MSNs, respectively. Panels
B and D show representative NAc micrographs of Dcx-positive and Darpp-32-positive cell
staining, respectively. All animals were female and were 39-40 days of age, and HVRrun and
LVRrun animals spent ~10-12 days in a voluntary running wheel (n = 6-7 per bar). Symbols: **,
p < 0.01; ***, p < 0.001.

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Figure 6. Correlations between NAc IHC measures and 10-d running distance in G9-10 LVRand HVR- runner rats
Total distance run 10
days prior to the night
of sacrifice (km)

a

200

HVR run

*

160

HVRs
120

r = -0.58 (* is not included)
r = 0.06 (* is included)

80
40
0
0

200

400

600

800

1000

1200

1400

b

Total distance run 10
days prior to the night
of sacrifice (km)

NAc Darpp-32+ neurons
12

LVR run

10
8

LVRs

6

r = -0.92

4
2
0
0

200

400

600

800

1000

1200

1400

NAc Darpp-32+ neurons

Negative associations exist between 10-d running distances and NAc MSN density in HVR (panel a)
and LVR runners (panel b). Note that one HVR runner was excluded from analysis due to it being an
outlier (* in panel a). However, r-values are presented for both the inclusion and exclusion of this animal.

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Figure 7. NAc tissue dopamine content between G10-11 LVR and HVR lines

G10-11 HVR

NAc dopamine
(mg/mg tissue)

6

G10-11 LVR
NS

NS

NS

5
4
3
2
1
0
Non-run

Run

1-2 h prior to running/dark cycle

Run
2-3 h into running
/dark cycle

No significant differences (NS) existed between LVRnon-run and HVRnon-run rats 1-2 hours prior to
the running/dark cycle (p = 0.28), LVRrun and HVRrun rats 1-2 hours prior to the running/dark
cycle (p = 0.28), or LVRrun and HVRrun rats 2-3 hours into the running/dark cycle (p = 0.72). All
animals were female and were 35 days of age, and HVRrun and LVRrun animals spent 6 days in a
voluntary running wheel (n = 6-7 per bar).

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Figure 8. Summary figure of new hypotheses developed from current observations between the
LVR and HVR lines

Hypotheses on neuron development between lines: the inherent up-regulation of ‘cell-cycle’related transcripts in the HVR and LVR line and the higher densities of Dcx- and Darpp-32positive neurons indicates that MSN development is inherently greater in the HVR line.
However, voluntary running reverses these trends (MSNs: HVR = LVR; Dcx-positive neurons:
LVR > HVR). Methamphetamine administration to rodents, which increases striatal dopamine
levels, has been shown to decrease striatal neurogenesis. Hence, high pulsatile dopamine
secretions into the NAc on a nightly basis due to high running may be the mechanism whereby
HVRs experience a decrease in MSN density (refs. in text). Conversely, glutamate-NMDA
receptor signaling is linked to an increase in striatal neurogenesis (refs. in text). Hence, this may
be the mechanism whereby voluntary running in LVRs increases NAc Dcx- and Darpp-32positive neurons.
Hypotheses on MSN function between lines: Initially, we hypothesized that less inherent MSN
density in LVR versus HVR non-runners may lead to the lack of voluntary running reward.
However, there were negative associations between running distance and Darpp-32-positive

39
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neurons in the HVR and LVR runners (Fig 4a/b). Hence, we speculate that a greater MSN
density may inhibit efferent targets which lead to a decreased motivation for voluntary running.
Abbreviations: DA – dopamine; MSN – medium spiny neuron

40
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Table 1. RNA-seq reads mapped to reference library
Reads aligned to
Total annotated
Group
Total reads
reference library
transcripts expressed*
LVRnon-run
32,807,065
89.3%
17,438
HVRnon-run
34,273,956
88.6%
17,919
LVRrun
29,667,774
89.2%
17,764
HVRrun
25,423,774
88.7%
17,506
CTL
25,932,949
87.5%
17,962
According to Chen et al. (Chen et al., 2011), 20-30 million total reads per sample in the nucleus accumbens are sufficient to provide
gene expression data that correlate well with microarray and RT-PCR data.
Symbols: * = RPKM > 0 in all animals within each group as performed by Song et al. (Song et al., 2012).

41

Table 2. Validation of selected RNA-seq transcripts by RT-PCR.

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Transcript
name
Cadm4
Ggcx
Oprm1
Sgk1

RNA-seq
Fold change P value
2.1
0.007
1.5
0.000
1.5
0.010
1.5
0.009

RT-PCR
Fold change P value
3.5
0.009
1.6
0.001
1.6
0.002
1.7
0.04

Cell adhesion molecule 4 (Cadm4) promotes the formation of presynaptic terminals and induces functional synapses in the central
nervous system by functioning in cell-cell adhesion. It was intrinsically different between LVR and HVR both in non-running and in
voluntary running rats. It had a RPKM > 34 for all group means.
Gamma-glutamyl carboxylase (Ggcx) converts reduced hydroquinone form of vitamin K to vitamin K epoxide. It was intrinsically
different between LVR and HVR both in non-running and in voluntary running rats. It had RPKM > 2.5 for all group means.
Opioid receptor mu 1 (Oprm1) is the principal target of endogenous opioid peptides and opioid analgesic agents, such as betaendorphin and enkephalins, which exercise increases in the brain. It had a RPKM > 1.3 for all group means.
Serum- and glucocorticoid-inducible kinase-1 (Sgk1) expression plays an important role in cellular stress response, suggesting its
involvement in the regulation of processes such as cell survival and neuronal excitability. It had RPKM > 27 for all group means.

42

Table 3. Top ten up- and down-regulated NAc transcripts between HVRrun versus LVRrun but were similar HVRnon-run versus LVRnonrun rats (scenario in Fig 1A)
HVRrun
RPKM
avg

Transcript

LVRrun
RPKM
avg

HVRrun/
LVRrun

pvalue

HVRnon-run
RPKM avg

LVR non-run
RPKM avg

HVRnonrun/
LVRnon-

pvalue

run

Up-regulated in HVRrun and LVRrun but were similar HVRnon-run and LVRnon-run
Downloaded from J Physiol (jp.physoc.org) by guest on April 21, 2014

2.30↑ vs

Follistatin (Fst), mRNA
Serum/glucocorticoid regulated kinase 1
(Sgk1), mRNA
Dymeclin (Dym), mRNA

HVRnr

1.37

1.68

0.002

1.41

1.59

-1.13

0.449

41.20

26.97

1.53

0.009

31.52↑ vs CTL

27.59↑ vs CTL

1.14

0.380

1.67

1.47

0.000

1.81

1.89

-1.04

0.678

2.56

1.45

0.002

2.76

2.64

1.05

0.520

HVRnr

1.65

1.44

0.000

1.89

1.83

1.04

0.693

4.58

3.17

1.44

0.002

4.83

3.62

1.33

0.062

HVRnr

8.34

1.40

0.009

8.03↑ vs CTL

7.95↑ vs CTL

1.01

0.938

1.68

1.21

1.38

0.004

1.41

1.38

1.02

0.818

4.47

1.36

0.004

4.80

4.62

1.04

0.778

1.63

1.36

0.006

1.71

1.46

1.17

0.073

2.46↑ vs
HVRnr

Protocadherin gamma subfamily A8
(Pcdhga8), mRNA
Protocadherin gamma subfamily A11
(Pcdhga11), mRNA
HAUS augmin-like complex, subunit 4
(Haus4), mRNA
Zinc finger protein 189 (Zfp189), mRNA
Solute carrier family 38, member 10
(Slc38a10), mRNA
Leucine rich repeat containing 8 family,
member C (Lrrc8c), mRNA
Transmembrane protein 38A (Tmem38a),
mRNA

3.71↑ vs
HVRnr

2.39↑ vs

11.66↑ vs

6.09↑ vs
HVRnr

↑ vs

2.21

HVRnr

Down-regulated in HVRrun and LVRrun but were similar HVRnon-run and LVRnon-run
Steroid receptor RNA activator 1 (Sra1), noncoding RNA
Bcl2 modifying factor (Bmf), mRNA

1.93↓ vs
HVRnr

3.02↓ vs
HVRnr

2.67

-1.39

0.001

2.60

2.73

-1.05

0.706

4.21

-1.39

0.002

4.44

4.14

1.07

0.538

43

Zinc finger protein 408 (Znf408), mRNA

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PREDICTED: Rattus norvegicus zinc finger
CCCH type, antiviral 1-like
(LOC100365858), miscRNA
PREDICTED: Rattus norvegicus SRY-box
containing gene 9 (LOC100361122), mRNA
Patatin-like phospholipase domain containing
7 (Pnpla7), mRNA
ADAM metallopeptidase with
thrombospondin type 1 motif, 4 (Adamts4),
mRNA
RTEL1-TNFRSF6B readthrough, non-coding
RNA
3-hydroxy-3-methylglutaryl-CoA synthase 2
(mitochondrial) (Hmgcs2), mRNA
Keratin 2 (Krt2), mRNA

1.56↓ vs

2.22

-1.42

0.001

2.16

2.04

1.06

0.357

HVRnr

1.77

-1.43

0.003

1.66

1.73

-1.04

0.748

2.53

3.66

-1.45

0.007

3.31

3.40

-1.03

0.844

HVRnr

2.17

-1.45

0.004

2.05

1.94

1.05

0.327

12.38

18.08

-1.46

0.005

15.08

16.99

-1.13

0.317

2.07

3.83

-1.85

0.006

2.92

3.43

-1.17

0.311

HVRnr

5.83

-1.85

0.002

4.57↓ vs CTL

5.34

-1.17

0.204

1.10

2.05

-1.87

0.002

1.29

1.77

-1.37

0.093

HVRnr

1.23↓ vs

↓ vs

1.49

3.15↓ vs

These transcripts were the top ten up- and down-regulated NAc transcripts from the 94 transcripts that were differentially expressed in
HVRrun versus LVRrun rats; likely a result of more running in HVRrun rats.
Abbreviations: HVRrun = HVR 34 day-old 6-day runners, LVRrun = LVR 34 day-old 6-day runners, HVRnon-run = HVR 34 day-old nonrunners, LVR non-run = LVR 34 day-old non-runners, CTL = control Wistar rats
Symbols: ↑ vs CTL = transcript in HVRnon-run or LVR non-run rats was higher than in CTL rats (p < 0.05); ↓ vs CTL = transcript in
HVRnon-run or LVR non-run rats was lower than in CTL rats (p < 0.05); ↑ vs HVRnon-run or LVRnon-run = transcript in HVRrun or LVRrun is
greater than HVR non-run or LVR non-run rats, respectively (p < 0.05); ↓ vs HVRnon-run or LVRnon-run = transcript in HVRrun is less than
HVR non-run rats (p < 0.05).

44

Table 4. Differentially expressed NAc transcripts between HVRrun versus LVRrun as well as HVRnon-run versus LVRnon-run rats
Transcript

HVRrun
RPKM
avg

LVRrun
RPKM
avg

HVRrun/
LVRrun

pvalue

HVRnon-run
RPKM avg

LVR non-run
RPKM
avg

HVRnonrun/
LVRnon-

pvalue

run

Downloaded from J Physiol (jp.physoc.org) by guest on April 21, 2014

PREDICTED: Rattus norvegicus EG212225
protein-like (LOC100365310), miscRNA
PREDICTED: Rattus norvegicus EG212225
protein-like (LOC100360855), miscRNA
Cell adhesion molecule 4 (Cadm4), mRNA
Capping protein (actin filament), gelsolin-like
(Capg), mRNA
PREDICTED: Rattus norvegicus DEAD/H (AspGlu-Ala-Asp/His) box polypeptide 11 (CHL1-like
helicase homolog, S. cerevisiae) (Ddx11), mRNA
Gamma-glutamyl carboxylase (Ggcx), mRNA
Retinol saturase (all trans retinol 13,14 reductase)
(Retsat), mRNA
PREDICTED: Rattus norvegicus similar to
RIKEN cDNA 4632415K11 (RGD1308461),
mRNA
Solute carrier family 37 (glucose-6-phosphate
transporter), member 4 (Slc37a4), mRNA
Protocadherin beta 3 (Pcdhb3), mRNA
Transmembrane protein 119 (Tmem119), mRNA
Protocadherin gamma subfamily A1 (Pcdhga1),
mRNA
Protocadherin beta 8 (Pcdhb8), mRNA

2.60

1.01

2.57

0.002

3.06

1.41

2.17

0.004

3.96

1.61

2.47

0.003

4.93

2.07

2.39

0.002

70.10

33.84

2.07

0.007

65.95

CTL

1.64

0.034

2.10

1.20

1.76

0.004

2.24

1.31↓ vs CTL

1.71

0.011

2.34

1.41

1.66

0.007

2.69

1.38

1.95

0.001

3.71

2.49

1.49

0.000

3.33

2.71

1.23

0.048

23.89

16.25

1.47

0.001

23.82

17.91

1.33

0.045

3.61

2.70

1.34

0.003

3.25

2.86

1.13

0.048

8.80

1.31

0.001

9.94

8.80

1.13

0.030

2.38
14.28↑ vs

-1.33

0.001

CTL

-1.33

0.007

11.50↑ vs
HVRnr

↓ vs CTL

40.11↓ vs

1.80

2.59

-1.44

0.008

11.06

16.27

-1.47

0.002

10.70

1.03

1.54

-1.50

0.000

1.12↓ vs CTL

1.61

-1.44

0.006

1.91

3.03

-1.58

0.001

1.72↓ vs CTL

2.66

-1.54

0.000

1.79

Abbreviations: HVRrun = HVR 34 day-old 6-day runners, LVRrun = LVR 34 day-old 6-day runners, HVRnon-run = HVR 34 day-old nonrunners, LVR non-run = LVR 34 day-old non-runners, CTL = control Wistar rats.
Symbols: ↑ vs CTL = transcript in HVRnon-run or LVR non-run rats was higher than in CTL rats (p < 0.05); ↓ vs CTL = transcript in
HVRnon-run or LVR non-run rats was lower than in CTL rats (p < 0.05); ↑ vs HVRnr or LVRnr = transcript in HVRrun or LVRrun is greater

45

than HVR non-run or LVR non-run rats, respectively (p < 0.05); ↓ vs HVRnr or LVRnr = transcript in HVRrun is less than HVR non-run rats (p
< 0.05).

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46

Table 5. Dopamine signalling-related NAc mRNA expression differences between HVR and LVR lines

Downloaded from J Physiol (jp.physoc.org) by guest on April 21, 2014

mRNA

HVRrun RPKM
avg

LVRrun RPKM
avg

HVRrun/
LVRrun

pvalue

HVRnon-run RPKM
avg

LVR non-run RPKM
avg

Adcy5
Adcy6
Arpp19
Cav2
Caly
Cdnf
Drd1
Drd2
Drd3
Drd4
Drd5
Dtnbp1
Flna
Gna11
Gna12
Gna15
Gnal
Gnaq
Gnas
Gnao1
Htt
Klf16
Lrrk2
Nsg1
Oprd1*
Oprm1
Palm
Rgs9
Slc6a3
Slc9a3r1

26.21↑ vs HVRnr
4.07
107.05↑ vs HVRnr
7.02↓ vs HVRnr
142.02
0.36
81.54↑ vs HVRnr
59.03↑ vs HVRnr
0.54
ND
↑ vs HVRnr
1.22
11.64
1.59↓ vs HVRnr
15.95↑ vs HVRnr
72.63↓ vs HVRnr
2.04
71.17↑ vs HVRnr
33.91
54.31
105.13↑ vs HVRnr
0.80
41.93↑ vs HVRnr
17.70↑ vs HVRnr
177.37
3.10↑ vs HVRnr
2.05
82.97
129.27↑ vs HVRnr
0.10↓ vs HVRnr
20.79

21.21
4.68
82.12
8.51
142.84
0.38
65.53
50.26
0.64
ND
1.07
11.66
1.98
15.92
77.26
2.11
61.86
33.15
57.70
100.23
0.69↓ vs LVRnr
40.12
14.76
170.84
2.50
1.35
84.47
107.27
0.09
23.78

1.24
-1.15
1.30
-1.22
-1.01
-1.08
1.24
1.17
-1.20
ND
1.13
-1.01
-1.25
1.00
-1.06
-1.03
1.15
1.02
-1.06
1.05
1.15
1.05
1.20
1.04
1.24
1.52
-1.02
1.21
1.10
-1.15

0.08
0.02
0.03
0.06
0.90
0.83
0.06
0.15
0.34
ND
0.41
0.97
0.07
0.97
0.16
0.80
0.07
0.49
0.44
0.30
0.06
0.45
0.09
0.31
0.02
0.01
0.63
0.16
0.63
0.07

20.30
4.58
76.93
8.53
138.85↓ vs CTL
0.23
58.32
45.29↓ vs CTL
0.71
ND
0.92
11.65
2.80
12.86
80.81
2.05
57.67
31.73
55.54↓ vs CTL
89.96
0.72
36.45↓ vs CTL
13.34
161.51↓ vs CTL
2.03
1.88
88.52
97.37
0.16
21.83

21.80
4.84
82.71↓ vs CTL
7.87
135.83↓ vs CTL
0.35
60.44↓ vs CTL
47.72
0.54
ND
0.99
11.46
2.10
15.37
83.07
2.10
59.44
33.53
56.46
102.82
0.84
38.36↓ vs CTL
14.75
161.57↓ vs CTL
2.64
1.48
84.94
101.51
0.10
23.35

47

HVRnonrun/
LVRnon-run
-1.08
-1.06
-1.08
1.08
1.02
-1.56
-1.03
-1.06
1.30
ND
-1.09
1.01
1.32
-1.20
1.03
-1.02
1.03
1.05
-1.02
-1.15
1.16
-1.05
-1.11
1.00
-1.32
1.27
1.04
1.04
1.58
-1.08

pvalue
0.36
0.55
0.54
0.28
0.71
0.22
0.77
0.53
0.32
ND
0.56
0.62
0.15
0.02
0.57
0.86
0.74
0.24
0.71
0.24
0.20
0.37
0.31
0.99
0.01
0.16
0.64
0.69
0.03
0.49

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This gene list was constructed according to gene ontology (GO) dopamine receptor signaling pathway (GO ID: 0007212), adenylate
cyclase-activating dopamine receptor pathway (GO ID: 0007191), adenylate cyclase-inhibiting dopamine receptor pathway (GO ID:
0007191), and/or the negative regulation of dopamine receptor signaling pathway (GO ID: 0060160) lists.
Abbreviations: HVRrun = HVR 34 day-old 6-day runners, LVRrun = LVR 34 day-old 6-day runners, HVRnon-run = HVR 34 day-old nonrunners, LVR non-run = LVR 34 day-old non-runners, CTL = control Wistar rats; ND = not detected.
Symbols: * = cited as different between HVRnon-run versus LVR non-run rats in prior publication (Roberts et al., 2013); ↑ vs CTL =
transcript in HVRnon-run or LVR non-run rats was higher than in CTL rats (p < 0.05); ↓ vs CTL = transcript in HVRnon-run or LVR non-run
rats was lower than in CTL rats (p < 0.05); ↑ vs HVRnon-run or LVRnon-run = transcript in HVRrun or LVRrun is greater than HVR non-run or
LVR non-run rats, respectively (p < 0.05); ↓ vs HVRnon-run or LVRnon-run = transcript in HVRrun is less than HVR non-run rats (p < 0.05).

48