Genes, Brain and Behavior (2005) 4: 31–44
Copyright
#
Blackwell Munksgaard 2004
Changes in gene expression within the nucleus
accumbens and striatum following sexual experience
K. C. Bradley†,‡, M. B. Boulware†, H. Jiang§,
R. W. Doerge§, R. L. Meisel‡,¶ and
P. G. Mermelstein*,†
†
Department of Neuroscience, University of Minnesota,
Minneapolis, MN, ‡ Graduate Neuroscience Program, §Department of Statistics and ¶Department of Psychological Sciences,
Purdue University, West Lafayette, IN, USA
*Corresponding author: P. G. Mermelstein, Department of
Neuroscience, University of Minnesota, 6-145 Jackson Hall,
321 Church Street, SE, Minneapolis, MN 55455, USA.
E-mail: [email protected]
Sexual experience, like repeated drug use, produces longterm changes including sensitization in the nucleus
accumbens and dorsal striatum. To better understand the
molecular mechanisms underlying the neuroadaptations
following sexual experience, we employed a DNA microarray approach to identify genes differentially expressed
between sexually experienced and sexually naı̈ve female
hamsters within the nucleus accumbens and dorsal striatum. For 6 weeks, a stimulus male was placed in the home
cage of one-half of the hormonally primed, ovariectomized
female hamsters. On the seventh week, the two experimental groups were subdivided, with one half paired with
a stimulus male. In comparison with sexually naı̈ve animals, sexually experienced hamsters receiving a stimulus
male on week 7 exhibited an increase in a large number of
genes. Conversely, sexually experienced female hamsters
not receiving a stimulus male on week 7 exhibited a reduction in the expression of many genes. For directional
changes and the categories of genes regulated by the
experimental conditions, data were consistent across the
nucleus accumbens and dorsal striatum. However, the
specific genes exhibiting changes in expression were disparate. These experiments, among the first to profile
genes regulated by female sexual behavior, will provide
insight into the mechanisms by which both motivated
behaviors and drugs of abuse induce long-term changes
in the mesolimbic and nigrostriatal dopamine pathways.
Keywords: Dopamine, female sexual behavior, hamster, microarray, nucleus accumbens, real-time PCR, sensitization, striatum
Received 23 April 2004, revised 30 June 2004, accepted for
publication 6 July 2004
doi: 10.1111/j.1601-183X.2004.00093.x
The rewarding effects of many drugs of abuse are correlated with increased neurotransmission within the mesolimbic and nigrostriatal dopamine systems (Cadoni & Di Chiara
1999; Dietze & Kuschinsky 1994; Guix et al. 1992; Kuczenski
et al. 1991; Nisell et al. 1997; Pierce & Kalivas 1997;
Pontieri et al. 1995; Tanda et al. 1997). Increased activity
within these functionally distinct dopamine systems
(Di Chiara et al. 1992; Hyman 1996; Self & Nestler 1995)
enduringly alters the excitability of nucleus accumbens
(NAc) and dorsal striatum (dSTR) projection neurons, a
process termed sensitization (Cadoni et al. 2000; Kalivas
et al. 1992; Kuczenski et al. 1997; Paulson & Robinson
1991; Pierce & Kalivas 1995). The process of sensitization
results in the alteration of gene-expression patterns within
neurons of the NAc and dSTR (Berke & Hyman 2000; Nestler
2001).
Similar changes in neuronal activity are believed to occur in
response to sexual behavior. Extracellular dopamine levels in
the NAc and dSTR increase during sexual interactions in
female rats (Becker et al. 2001; Mermelstein & Becker
1995; Pfaus et al. 1995) and hamsters (Kohlert & Meisel
1999; Kohlert et al. 1997; Meisel et al. 1993), with multiple
sexual behavior tests augmenting both the presynaptic
release of dopamine (Kohlert & Meisel 1999) and the
responsiveness of the postsynaptic neurons, as seen by
increased c-Fos expression (Bradley & Meisel 2001). As with
drug addiction, the NAc and dSTR appear to modulate
specific and distinct aspects of female sexual behavior
(Becker et al. 2001; Jenkins & Becker 2001). These
observations suggest that, like drugs of abuse, sexual
experience sensitizes neurons in the nigrostriatal and
mesolimbic dopamine pathways.
Although research is beginning to focus on the long-term
changes in gene expression, dendritic morphology and
synaptic plasticity that accompany drug addiction (Li et al.
2003; Robinson & Kolb 1997, 1999; Robinson et al. 2001;
Yao et al. 2004), little is known about the molecular and
cellular mechanisms that accompany behaviorally induced
sensitization. Thus, using DNA microarray technology,
we compared alterations in gene expression within the
NAc and dSTR of female hamsters that were either
sexually naı̈ve or experienced following a test session in
which a male stimulus animal was either absent or present.
Prior sexual experience was found to alter the expression levels of a number of functionally distinct groups of
transcripts.
31
Bradley et al.
Materials and methods
Animals
Female Syrian hamsters, approximately 50 days of age, were
delivered from Charles River Laboratories (Kingston, NY).
Adult male Syrian hamsters were from Harlan Laboratories
(Indianapolis, IN). The female hamsters were individually
housed, while three to four males were housed in plastic
cages (50 40 20 cm). The animal colony room was maintained on a 14L : 10D light schedule (lights off between 0130 h
and 2330 h) at a constant temperature of 22 C. Food and
water were available ad libitum. Of note, all procedures used
in this study were in accordance with National Institutes of
Health Guidelines for the Care and Use of Laboratory Animals and approved by the Purdue Animal Care and Use
Committee.
In brief, the microarray experiment compared changes in
gene expression within the NAc and dSTR of female hamsters. Two separate runs were performed, allowing cross
comparisons between separate trials. Following behavioral
manipulation, the NAc and dSTR were separately isolated
and brain tissue from five to six hamsters/trial run was
pooled within each of the four test conditions. The isolated
mRNA was processed for hybridization onto eight individual
gene chips (4 conditions 2 brain regions). With replication,
there were approximately 45 animals and 16 gene chips
used.
Sexual experience
Approximately 1 week after the females arrived, they were
bilaterally ovariectomized under sodium pentobarbital
anesthesia (8.5 mg/100 g body weight, intraperitoneally).
After a 1-week recovery period, the female hamsters were
divided into two groups. Once a week for 6 weeks, one
group of females received sexual experience with an adult
male; the second group remained sexually naı̈ve. Male hamsters were sexually experienced via their use in other behavioral experiments. The pairing of partners was rotated every
week so that an individual male and female were only paired
together once during the successive weeks of sexual behavior testing.
During these 6 weeks, all female hamsters, whether or not
they were exposed to a stimulus male, were hormonally
primed with a series of estradiol benzoate and progesterone
injections. For the 2 days before the sexual experience test,
females received a daily injection (subcutaneous) of 10 mg of
estradiol benzoate in 0.1 ml of cottonseed oil. On the day of
the test, female hamsters were injected with 500 mg of progesterone in 0.1 ml of cottonseed oil. At 4–5 h after progesterone administration, a male hamster was placed in the
home cage of the experimental female for 10 min, thereby
avoiding issues regarding extended sexual behavior tests
affecting termination of sexual receptivity.
During sexual activity, the latency to initiate lordosis
(immobility with dorsoflexion of the back) and the cumulative
32
amount of time that the female assumed the sexual receptive posture were measured. Those hormonally primed
females not receiving sexual experience remained in their
home cages.
Sexual behavior testing
During week 7, estradiol benzoate and progesterone injections were again administered to all of the female hamsters.
Half of the sexually experienced and naı̈ve females were
arbitrarily chosen and tested for sex behavior by placing an
adult male in their home cage. The remaining females, both
experienced and naı̈ve, were left undisturbed. The 10-min
sex behavior tests were again analyzed for latency to initiate
lordosis and the cumulative amount of time the female maintained the posture. In addition, the number of mounts and
intromissions (including ejaculation) by the male was
recorded. The occurrence of intromission (with and without
ejaculation) was determined from the gross motor pattern of
the mounting male, as described previously (Bunnell et al.
1977). A measure of copulatory efficiency by the males,
referred to as hit rate (the proportion of total mounts that
included intromission), was derived from these measures. Of
note, using an ANOVA statistical analysis, there were no differences in female behavior during the previous 6 weeks
between the two groups of sexually experienced animals
(P > 0.05).
Following this protocol, we generated four different treatment groups for our mRNA analysis. The first group consisted of those females that received 6 weeks of sexual
experience and were again sexually active during the
seventh week (experience/sex, or E/S). Female hamsters in
the second group had no experience with a stimulus male
until having sex on the seventh week for the first time (no
experience/sex, NE/S). The third group received 6 weeks of
sexual experience but were not paired with a stimulus male
for sex on week 7 (experience/no sex, E/NS), while the fourth
group had no sexual experience across all 7 weeks (no
experience/no sex, NE/NS). Each treatment group contained
five to six female hamsters.
Tissue collection
Three hours after exposure to the stimulus male on week 7,
the female hamsters were decapitated and their brains were
rapidly removed. Those females not tested for sexual behavior on week 7 were killed at the same time point. A 2 mm
coronal section encompassing the NAc and dSTR was isolated, and stainless steel tubing (inside diameter ¼ 2.27 mm)
was used to collect bilateral punches of the NAc and dSTR. It
should be noted that owing to its small size, the 2 mm slice
of the NAc slightly extended beyond the boundaries of that
region. As a result, part of the bed nucleus of the stria
terminalis was dissected out with the NAc. The tissue
punches were submerged in RNAlater solution (Ambion
RNA Diagnostics, Austin, TX) and stored at 20 C until use.
Genes, Brain and Behavior (2005) 4: 31–44
Sexual experience-induced gene expression
Tissue preparation and hybridization to
oligonucleotide microarrays
All procedures for tissue preparation and hybridization followed the methods described in the Affymetrix GeneChip
Expression Analysis Manual (Affymetrix, Santa Clara, CA). To
obtain enough tissue for the RNA-isolation procedure, the
punches of the five to six animals in each treatment group
were pooled across each brain region. Total RNA from the
pooled NAc and pooled dSTR was isolated using the RNeasy
Total RNA Isolation kit (Qiagen, Valencia, CA), followed by
isolation of poly(Aþ) mRNA from the total RNA solution using
an Oligotex Direct mRNA kit (Qiagen). The poly(Aþ) mRNA
was converted to double-stranded cDNA (Gibco BRL SuperScript Choice System; Invitrogen, Carlsbad, CA) using a T7(dT)24 primer. The cDNA was cleaned using a phase-lock gel
system, extracted with phenol : chloroform, ethanol precipitated and then used as template to synthesize biotinylated
cRNA (BioArray High Yield RNA Transcript Labeling Kit; Enzo
Diagnostics, Famingdale, NY). Following cleanup (RNeasy
Mini kit; Qiagen), the in vitro transcribed cRNA was quantified by spectrophotometry. For each treatment group, 5 mg
of fragmented, biotin-labeled cRNA was hybridized to a single Affymetrix rat neurobiology U34 chip. The microarrays
were washed, stained with streptavidin–phycoerythrin and
then scanned with a probe array scanner. While hamster
RNA was probed against a rat chip, signal intensities were
comparable to other studies performed at the Affymetrix
facility using rat tissue.
Microarray gene-expression analysis
On the basis of the experimental design and the focus on
behavioral sensitization, we performed two comparisons in
which a single variable was altered between two treatment
groups. They were as follows:
Comparison
Goal
(I) E/S vs. NE/S
To determine whether prior sexual experience
alters mRNA transcription following a sexual
encounter
To determine whether prior sexual experience
alters mRNA transcription when no stimulus
male is presented
(II) E/NS vs. NE/NS
Bioconductor (http://www.bioconductor.org) was employed to
decode the gene-expression measurements at the probe level
for the purpose of gaining gene-expression intensities. A constant normalization method was carried out at the probe level for
all the probes on a chip using the intensity of the NE/NS dSTR
chip as a reference to equate the background levels of the chips
and eliminate non-biological influences.
The Affymetrix chips contain multiple (approximately 16–20)
unique sequences for each gene, termed the perfect match
(PM) set, and for each a paired control in which a single
nucleotide is altered so that a mismatch (MM) occurs. We
Genes, Brain and Behavior (2005) 4: 31–44
analyzed data at the probe level. For example, if there are 20
probe pairs for one gene, with eight chips there are 160
separate observations for that gene. There are multiple statistical methods available for analyzing Affymetrix GeneChips;
we employed a linear modeling approach (Chu et al. 2002) in
which data are analyzed using two measurements: PM only
and the PM–MM difference. The only notable difference in
our analysis from that proposed by Chu et al. (2002) is that
because each chip contained a separate experimental
condition, it was treated as a fixed factor in the mixed model.
A linear model for the log2-transformed gene-expression
measurements was also employed. A simple ANOVA model at
the probe level was set up for each gene:
log2 ðyij Þ ¼ þ Ai þ Pj þ "ij ;
where i ¼ 1, . . . , 8, j ¼ 1, . . . , n (n is the number of probe
pairs, generally an integer between 16 and 20), yij is the
normalized gene-expression measurement (PM or PM–
MM) on array i and probe level j and A and P represent the
array and probe effects, respectively. The random normal
error is denoted as eij with mean 0 and variance s2. When
the data were analyzed using the PM/MM difference, if the
intensity for more than half of the probe pairs was greater for
the MM vs. the PM, then the gene was excluded from
analysis.
Replication
As mentioned, we were required to combine tissue from five
to six animals in order to have sufficient cRNA to probe a
single chip. Although this necessitated more effort, it carried
the advantage of minimizing the effect of any potential
outlier. Furthermore, to test whether the effects of the
experimental treatments were reproducible, the entire
protocol was replicated on a new set of animals, generating
a second pool of cRNA for hybridization. The first run was
defined as Trial A, the second as Trial B. As described below,
only genes which exhibited significant changes both within
and across trials were considered altered by the experimental
treatment. This crossover comparison technique has been
previously tested by Affymetrix and is currently their
suggested method of sample assessment as it minimizes
false positives.
Because the entire experiment was replicated (Trials A and
B), four pair-wise comparisons were generated for each of
the two comparisons (I and II). For example, in comparison
(I), we analyzed:
1
2
3
4
experience/sex
experience/sex
experience/sex
experience/sex
(A)
(A)
(B)
(B)
vs.
vs.
vs.
vs.
no
no
no
no
experience/sex
experience/sex
experience/sex
experience/sex
(A)
(B)
(A)
(B)
In comparing individual genes between two chips,
probabilities of 0.05 were considered differentially expressed
in that single analysis. However, using the crossover
33
Bradley et al.
approach, only those genes that exhibited significant differences in expression for all four, or three out of the four
comparisons (with the fourth comparison not significantly
different), were considered by this study as altered via the
testing conditions.
Real-time polymerase chain reaction
To verify the accuracy of the microarray experiments, realtime polymerase chain reaction (PCR) was employed. In
these studies, the relative expression of five example
genes, microtubule-associated protein 2 (MAP2), copper,
zinc superoxide dismutase (SOD), extracellular signal-related
kinase 3 (ERK3), syntaxin 6 and tyrosine hydroxylase (TH),
was compared in striatal tissue taken from experience/sex
and no experience/sex animals. For this analysis, tissue
punches of the dSTR were taken from a third set of animals
(Trial C) undergoing similar experimental procedures as those
in Trials A and B. Punches from two female hamsters for
each treatment group were combined and homogenized
using a tissue tearer. These genes were selected based
upon results from the microarray data, in which we observed
bidirectional responses: expression of two genes that went
up with sexual experience (MAP2 and syntaxin 6), two that
went down (SOD and TH) and one that did not change
(ERK3). In independent experiments, glyceraldehyde-3-phosphate (GAPDH) expression indicated only an 8% difference
between cDNA samples; therefore, the PCR data are presented unadjusted.
Total RNA was extracted from the homogenate, followed
by the synthesis of cDNA, using the procedures outlined in
Groth and Mermelstein (2003). For each treatment condition,
2 mg of total RNA was used in the reverse transcription step.
The single-stranded cDNA was amplified by real-time PCR
through the addition of 1 ml of cDNA template to a 0.2 ml thinwalled, low-profile PCR tube containing 10.0 ml of 2
DyNAmo master mix (modified Tbr DNA polymerase, SYBR
Green I, optimized PCR buffer, 5 mM MgCl2 and dNTP mix
including dUTP; MJ Research, Waltham, MA), 1.0 ml of upper
primer (20 mM stock solution), 1.0 ml of lower primer (20 mM)
and 7.0 ml of diethyl pyrocarbonate (DEPC)-treated water. To
ensure that extraneous DNA did not contaminate the PCR,
water was used as a control template. Real-time PCR amplification was performed using a DNA Engine Opticon 2 thermal cycler (MJ Research). For each of the PCRs, cDNA
template was first linearized via a 10 min incubation at
95 C. The PCR consisted of a 15 second step to 94 C, a
20 second annealing step, followed by a 28 second extension
step at 72 C, for 45 cycles. After each cycle, SYBR green
fluorescence was measured. For MAP2, the annealing temperature was 58 C, 58.5 C for syntaxin 6, 59.3 C for SOD,
59.8 C for ERK3 and 61 C for TH. The plate read for MAP2
was at 78 C, 79.2 C for syntaxin 6, 81.1 C for SOD, 82.3 C
for ERK3 and 85 C for TH. Optimal PCR amplification protocols were empirically determined before the experimental
34
runs. Following real-time amplification, PCR products were
separated using agarose (1.5%) gel electrophoresis and
visualized using ethidium bromide. Gels were imaged and
processed using an Eastman Kodak (Rochester, NY) 1D system (version 3.5.3), to determine whether the PCR product
for each reaction was of the expected size.
All primers used for PCR were synthesized by Qiagen.
The upper and lower primers for MAP2 were 50 -TGGGTGGAC
ACTCAAGATGA-30 (nucleotides 4242–4261) and 50 -AAGGTCT
TGGGAGGGAAGAA-30 (nucleotides 4694–4713), yielding a predicted size of 471 bp. Upper and lower primers for syntaxin 6
were 50 -CCAGGGATTGTTCCAGAGAT-30 (nucleotides 209–228)
and 50 -ACCGCGAAGAGGATGGCTAT-30 (nucleotides 858–877),
yielding a predicted product size of 668 bp. Primers for SOD
were 50 -TCTAAGAAACATGGCGGTCC-30 (nucleotides 257–276)
and 50 -CAGTTAGCAGGCCAGCAGAT-30 (nucleotides 549–568),
yielding a predicted size of 311 bp. Primers for ERK3 were
50 -TGGTAACCAATCCTTCAGAAAG-30 (nucleotides 703–724)
and 50 -AAGGTCTTGGGAGGGAAGAA-30 (nucleotides 951–972),
for a predicted product size of 269 bp. Primers used for TH
were 50 -ACAGCCCAAGGGCTTCAGAA-30 (nucleotides 38–57)
and 50 -CCTCGAAGCGCACAAAATAC-30 (nucleotides 401–420),
yielding a predicted size of 382 bp. Primers for GAPDH
were 50 -ACCACAGTCCATGCCATCAC-30 (nucleotides 566–588)
and 50 -TCCACCACCCTGTTGCTGTA-30 (nucleotides 998–1017),
yielding a predicted size of 451 bp.
Real-time PCR data analysis
For each of the five genes probed, two separate real-time
PCRs per each treatment group were performed for each
run. The duplicate samples for each gene were to assure the
reliability of the determinations within a single experiment.
The cycle number at which the emitted fluorescence
reached 10 standard deviations above baseline [threshold
cycle, c(t)] was averaged across the duplicate samples for
each run. A difference of greater than one cycle was considered to reflect a change in mRNA levels between the E/S
and NE/S. The real-time PCR experiments were then
repeated (Run 2) with the same pool of cDNA in order to
verify results from the initial run (Run 1) for adequate comparison with the microarray data.
Results
Sexual behavior measures
The lordosis latencies and durations during the test for sexual behavior on week 7 were compared between the experience/sex and the no experience/sex groups. The statistical
analysis showed no significant difference (P > 0.05) between
the average (SEM) lordosis latencies (experience/sex
37 6 seconds; no experience/sex 31 5 seconds); however, females in the no experience/sex group had assumed
lordosis for a significantly, although only slightly, longer
Genes, Brain and Behavior (2005) 4: 31–44
Sexual experience-induced gene expression
duration than had the females in the experience/sex group
(t23 ¼ 2.289; P ¼ 0.032). The average lordosis duration
during the 10-min test was 526 7 seconds for the experience/sex group and 550 8 seconds for the no experience/
sex group. Sexual experience did not affect any parameters
related to male sexual behavior, including the number of
mounts (21 2 vs. 20 2), intromissions (38 3 vs. 44 3)
or hit rate (0.64 0.02 vs. 0.69 0.03).
Changes in gene expression detected by DNA
microarrays
The Affymetrix rat neurobiology GeneChip, containing
probes for 1200 genes, was used to probe changes in gene
expression broadly in the NAc and dSTR following sexual
behavior testing and previous sexual experience. Although
we used hamster tissue against a rat chip, the internal positive and negative controls on the U34 chip were as expected.
Moreover, this cross-species hybridization approach has
been validated (Chismar et al. 2002). Within the NAc, 40
genes were found to exhibit increased expression in E/S
animals when compared with NE/S animals (Table 1). Within
the dSTR, 43 genes exhibited increased expression and 13
exhibited decreased expression across the same behavioral
paradigm.
The relative increase in gene expression found within
sexually experienced animals was dependent upon the final
exposure to a stimulus male. Within the NAc, only one gene
was found to exhibit increased expression vs. 22 displaying
decreased expression, when E/NS animals were compared
with NE/NS counterparts. A similar trend was observed in
the dSTR, with 21 genes exhibiting increased and 83 showing decreased expression.
The majority of transcripts that were altered in the NAc
and dSTR were classified as genes encoding channels,
receptors, neurotransmission-regulating proteins or signaling
molecules (Table 2). For the categories of genes regulated by
sexual experience and sexual testing, the data were fairly
consistent across brain regions. Yet, the specific genes
exhibiting changes in expression were distinct. Summarized
in Tables 3 and 4 are the complete list of genes altered within
both brain regions following the two behavioral conditions.
Similar changes in gene expression detected by
real-time PCR and microarray analysis
To verify the data obtained in the microarray analysis, we
utilized real-time PCR to measure mRNA levels for five
model genes in the dSTR for hamsters in the E/S and NE/S
conditions. The increases or decreases in mRNA levels found
using real-time PCR mirrored the changes in gene expression
detected by the microarray approach for four of the five
genes (Fig. 1). As observed using DNA microarrays, sexual
experience was found to upregulate MAP2, downregulate
TH and SOD and not change ERK3 expression following
presentation of a stimulus male. The expression levels
observed using real-time PCR for syntaxin 6, though, were
not similar to the microarray data. The DNA microarrays
suggested an increase in syntaxin 6 expression, whereas
real-time PCR suggested a relative decrease. The 80% consistency between techniques suggests that the microarray
data should prove useful as a launching point for further
studies.
Discussion
By probing changes in gene expression utilizing a microarray
technique, we have putatively identified a group of proteins
that may underlie the regulation of sensitization and withdrawal following sexual experience. Accordingly, the goals of
the study were to enable the generation of new hypotheses
that will address the roles of these candidate proteins in the
aforementioned processes. Many of the genes that are regulated by female sexual behavior can be grouped into specific
biochemical pathways. Interestingly, several of these pathways have also been implicated in mediating the effects of
drug addiction, suggesting that both motivated behaviors and
pharmacological agents induce long-lasting changes in basal
ganglia physiology through common mechanisms.
Female hamsters were chosen as the animal model
because they maintain a relatively immobile sexual receptive
posture (i.e. lordosis) in contrast to the active pattern of
sexual behavior of other rodents, male and female. Because
these experiments are correlative in nature, the female hamster is an ideal model, as issues regarding increased motor
behavior are minimized. However, this necessitated hybridizing hamster RNA to gene sequences from the rat genome.
The PM sequences on the rat gene chip could potentially be
a ‘mismatch’, limiting our ability to detect additional changes
in gene expression. This did not compromise our results
regarding the changes we did detect.
The timing at which the animals were killed relative to their
behavioral treatment limits the scope of our results. The time
point for killing of the animals following sexual behavior testing
Table 1: Changes in gene expression within the dorsal striatum and nucleus accumbens resulting from previous sexual experience
Nucleus accumbens
Sex on test day: experience vs. no experience
No sex on test day: experience vs. no experience
Genes, Brain and Behavior (2005) 4: 31–44
Dorsal striatum
Increase
Decrease
Increase
Decrease
40
1
0
22
43
21
13
83
35
Bradley et al.
Table 2: Number of genes exhibiting altered expression between sexually naı̈ve vs. experienced female hamsters (separated by class)
Gene classification
Channels
Signal transduction
Neurotransmission
Transcription factors
Receptors
Cytoskeleton/adhesion
Others
Sex on test day
No sex on test day
Nucleus accumbens
Dorsal striatum
Nucleus accumbens
Dorsal striatum
3
7
8
4
10
4
4
2
7
6
1
4
0
3
10
9
7
2
14
4
15
16
16
18
3
33
5
14
(3 h) was chosen in order to maximize the magnitude of
activity-dependent gene expression with minimal mRNA
degradation. This time point should have allowed us to
detect changes in both immediate-early gene expression
and those genes whose expression is somewhat slower in
onset. As a result though, this picture of gene expression is
only a snapshot in time; lost in this approach are the dynamic
changes in gene expression in the intervening periods. A
long-term goal of this research is to compare the impact of
behavioral experience on the molecular and cellular plasticity
of NAc and dSTR neurons with the impact of effects of
administration of drugs of abuse. Until a time course for
both responses to behavioral and drug experience is established, we will have to rely on less complete data for comparisons.
Sexual interactions activate the ascending dopamine
pathways (Becker et al. 2001; Bradley & Meisel 2001;
Kohlert & Meisel 1999; Kohlert et al. 1997; Meisel et al.
1993; Mermelstein & Becker 1995; Pfaus et al. 1995), with
multiple sexual behavior tests accentuating these neuronal
responses (Bradley & Meisel 2001; Kohlert & Meisel 1999).
These changes parallel the neuroadaptations that have been
reported with repeated drug exposure (Nestler 2001). Sexually
experienced animals showed relative increases in activitydependent gene expression following exposure to a stimulus
male, whereas if no male was presented during the last week
of testing, a notable decrease in gene expression was observed.
Relatively unidirectional changes have been reported previously
in the striatum; thus this result is with precedent (Yuferov et al.
2003). Possibly, like drugs of abuse, sexual experience ‘primes’
this region, altering both the signaling pathways and the
expression of transcription factors that regulate gene expression.
Anticipatory effects may play an important role as well,
allowing for heightened gene expression with an expected
reward-generating behavior and diminished responses
when the stimulus (i.e. male) is absent. Interestingly, in
sexually experienced animals, the set of genes with
increased expression following exposure to a male was
distinct from the group of genes that decreased in
expression when no male was present. This implies that
there is not one set of genes that responds to sexual
behavior, increasing expression when stimulation is present
36
and decreasing expression when it is absent. But in fact,
these are disparate conditions which result in completely
different patterns of gene expression. Furthermore, while
the gene-expression patterns were similar between the
NAc and dSTR, the specific genes altered by the
experimental manipulations differed. The fact that we see
sexual experience affecting the same biochemical
pathways in the NAc and dSTR, though through the
regulation of different signaling molecules, seems to
underscore the importance of these pathways in the
sensitization of the mesolimbic and nigrostriatal dopamine
systems. Described below are the changes observed in
selected families of genes and the possible implications in
activity-dependent plasticity.
Changes in channels
Within both the NAc and dSTR, the expression of voltagegated Naþ and Kþ channels was dependent upon sexual
experience, suggesting possible changes in the regulation
of electrical activity. Within the dSTR, several a1 subunits
comprising voltage-dependent calcium channels also
exhibited changes in expression. Intriguingly, a1C, the
principal subunit of the L-type calcium channels that are
responsible for cyclic AMP response element (CRE)-dependent and other forms of gene expression (Dolmetsch et al.
2001; Graef et al. 1999; Liu & Graybiel 1996; Weick et al.
2003), displayed increased expression in sexually experienced animals following a test with a stimulus male and
decreased expression when the male hamster was absent.
The directional effects on a1C expression suggest in the
dSTR a progressive feedback loop, whereby stimuli triggering heightened/reduced periods of gene expression induce
changes that make these neurons more/less responsive to
future stimulations. Interestingly, the opposite response may
occur in the NAc.
Changes in signal transduction
In both the NAc and dSTR, alterations in the expression of
the G-protein Gao were observed, albeit in opposite directions (Tables 2 and 3). Interestingly, changes in Go mRNA
following sensitizing treatments of cocaine have also been
reported (Nestler et al. 1990). Other genes encoding for
Genes, Brain and Behavior (2005) 4: 31–44
Sexual experience-induced gene expression
Table 3: Genes differentially expressed in the nucleus accumbens resulting from previous sexual experience
Gene classification
Channels
Signal transduction
Kinases/phosphatases
Tyrosine kinase signaling
G-protein coupled signaling
Ca2þ signaling
Neurotransmission
Neurotransmitter release
Neurotransmitter uptake
Neuropeptides
Neurotrophic factors
Transcription factors
Receptors
GenBank
accession number
Gene descriptions
M81784_at
AF083341_s_at
AJ007627_at
U92897_s_at
X12589cds_s_at
Kþ channel
Ca2þ-activated Kþ channel 1
ELK channel 2
Voltage-dependent Kþ channel (Kv4.3)
Voltage-dependent Kþ channel
M55417exon_s_at
D14591_s_at
M64300_at
M82824_s_at
U69109_s_at
M17526_at
M1756_g_at
M13707_at
M55417exon_s_at
L09119_g_at
L04739cds_s_at
L05557cds_g_at
X59949cds_s_at
U51898_at
Creatine kinase B
MAP kinase kinase (MEK)
Extracellular signal-related kinase (ERK2)
Neurofibromatosis protein I
Ca2þ-dependent tyrosine kinase
GTP-binding protein (Gao)
GTP-binding protein (Gao)
Protein kinase C type I
Protein kinase Cg
Neurogranin/RC3
Plasma membrane Ca2þ ATPase, isoform 1
Plasma membrane Ca2þ ATPase, isoform 2
Nitric oxide synthase
Ca2þ-independent phospholipase A2
AB003991_g_at
X06655_at
U14398_g_at
U26402_at
AF041373_s_at
L35558_s_at
S68944_i_at
S68944_r_at
X63253cds_s_at
D49653_s_at
X17012mRNA_s_at
L15305_s_at
M34643_at
Z14117cds_i_at
SNAP-25A
Major synaptic vesicle protein p38
Synaptotagmin IV
Synaptotagmin V
Clathrin assembly protein, short form
Glutamate/aspartate transporter
Naþ/Cl–-dependent neurotransmitter transporter
Naþ/Cl–-dependent neurotransmitter transporter
Serotonin transporter
Leptin
Insulin-like growth factor II
Glial-derived neurotrophic factor
Neurotrophin 3
Platelet-derived growth factor, B chain precursor
X06769cds_g_at
S66024_g_at
U75398_s_at
U53450cds_at
c-fos
CREM
Krox-24
Jun dimerization protein 1
L08496cds_s_at
X55246_at
AF020756_s_at
AF001423_at
M36418_s_at
D13871_s_at
U01227_s_at
S79903mRNA_g_at
S60953_s_at
U25650_f_at
GABAA receptor, d subunit
Inhibitory glycine receptor, a1 subunit
P2x2 receptor 3
N-Methyl-D-aspartate receptor, 2A subunit
Glutamate receptor A
Glut 5 protein
Serotonin receptor 3
m-Opioid receptor
trkCTK þ 39
Neurotrophin receptor (p75LNTR), precursor
Genes, Brain and Behavior (2005) 4: 31–44
Test day sex
Test day no sex
Experience vs.
no experience
Experience vs.
no experience
Decrease
Decrease
Increase
Increase
Increase
Increase
Decrease
Decrease
Increase
Decrease
Decrease
Decrease
Increase
Increase
Increase
Decrease
Increase
Increase
Increase
Decrease
Increase
Increase
Increase
Decrease
Decrease
Decrease
Increase
Increase
Decrease
Increase
Increase
Increase
Decrease
Decrease
Increase
Increase
Increase
Increase
Increase
Increase
Increase
Decrease
Increase
Decrease
Increase
Increase
Decrease
37
Bradley et al.
U71089cds_at
M31174_g_at
X62295cds_s_at
AJ002942cds_at
CXC chemokine receptor 1
c-erbA-a-2-related protein
Vascular type-1 angiotensin II receptor
Retinoic acid receptor b2
Increase
Increase
Increase
Cytoskeleton/adhesion
X59149_at
U16845_at
AB013130_at
S82649_r_at
AF007583_at
Neural cell adhesion molecule L1
Neurotrimin
Synaptopodin
Neuronal activity-regulated pentraxin (Narp)
Acetylcholinesterase-associated collagen
Increase
Increase
Increase
Increase
Increase
Others
L13192_f_at
AF044201_at
D13125_at
L18889_at
L27867_at
S68809_s_at
U90448_at
Brain factor 2
Neural membrane protein 35
Neural visinin like Ca2þ-binding protein 2
Calnexin
Neurexophilin
S100 alpha
CXC chemokine LIX
Decrease
Decrease
Increase
Increase
Decrease
Decrease
Increase
Increase
signal transduction machinery that exhibited changes in
expression within the NAc include MEK and ERK2, members
of the mitogen-activated protein kinase (MAPK) signaling pathway (Cano & Mahadevan 1995), protein kinase C (for which
similar changes are observed following cocaine self-administration; Thomas et al. 2001) and nitric oxide synthase. Within
the dSTR, genes encoding for several MAPK signaling proteins, as well as components of calmodulin signaling (CaMdependent protein kinases and calcineurin), were altered with
sexual experience. Notably, each of these signaling cascades
will lead to changes in gene expression (Deisseroth et al.
2003; Groth et al. 2003). These data are consistent with
recent findings that activity-dependent gene expression alters
the same signaling machinery initially recruited to trigger
changes in mRNA production (Groth & Mermelstein 2003).
cant decrease in the expression of the immediate-early gene
c-fos (Curran & Morgan 1995). This change in c-fos is consistent with the relative unidirectional change in gene expression within this region during the E/NS treatment.
Conversely, animals within the E/S group exhibited heightened expression of the cyclic AMP-response element modulator (CREM) isoform cyclic AMP early repressor (ICER),
known to interact with cyclic AMP response element binding
protein (CREB) and inhibit CRE-dependent transcription
(Lonze & Ginty 2002; Stehle et al. 1993), suggesting a
negative-feedback loop. Within the dSTR, an increased
expression of the R-Smad, Smad2, was observed in E/S
animals. Smad2 is part of a class of proteins important for
mediating the cellular responses to transforming growth
factor-b (Derynck & Zhang 2003; Reguly & Wrana 2003).
Changes in neurotransmission
Changes in receptors
In both the NAc and dSTR, a variety of SNARE proteins were
found to be regulated by sexual experience, suggesting that
changes in neurotransmission may underlie sensitization.
Increased expression of the dopamine transporter within the
dSTR of E/NS animals is also of significant interest. A variety of
neurotrophins and tissue growth factors were also found regulated by sexual experience, similar to findings in research on
drug addiction. Neurotrophins have been found to facilitate the
development of behavioral sensitization to psychostimulants,
as infusion of neurotrophins into the mesolimbic circuit potentiates the response to cocaine (Horger et al. 1999; Pierce et al.
1999) and amphetamine (Hoane et al. 1999; Martin-Iverson
et al. 1994). The significance that several tissue growth factors
were also found to be differentially expressed is a particularly
interesting topic to be addressed in future studies.
One striking aspect of the data was the number of receptors
within the dSTR that exhibited changes in expression with
sexual experience. Expression of a number of glutamate
receptors was altered following either sex or no sex before
killing. Interestingly, repeated exposure to drugs has also
been reported to produce functional changes in glutamate
neurotransmitter systems (Kalivas & Duffy 1998; Pierce et al.
1996; Reid & Berger 1996; Reid et al. 1997). Similarly, glutamate receptor stimulation is necessary for sensitization, as
pretreatment with various glutamate receptor antagonists
will prevent the development of sensitization (Kalivas &
Alesdatter 1993; Karler et al. 1991; Stewart & Druhan 1993;
Wolf & Khansa 1991).
Along with changes in glutamate receptors, there were
alterations in many other receptor classes, including GABAA
subunits and GABAB receptors, acetylcholine receptor subunits, D1 and D4 dopamine receptors, neurotrophin receptors
and the neuron-specific, IP3 type I receptor. While changes in
channel expression were less frequent in the NAc, sexual
experience did alter the expression of glutamate N-methyl-D-
Changes in transcription factors
Several transcription factors of note were altered by our
experimental conditions. Within the NAc, not providing a
partner to sexually experienced animals resulted in a signifi-
38
Genes, Brain and Behavior (2005) 4: 31–44
Sexual experience-induced gene expression
Table 4: Genes differentially expressed in the dorsal striatum resulting from previous sexual experience
Gene classification
Channels
Signal transduction
Kinases/phosphatases
Tyrosine kinase
signaling
G-Protein
coupled signaling
Ca2þ signaling
GenBank
accession number
Gene descriptions
M91808_at
U37147_at
M27223_at
M22253_at
M26643_at
U79568_s_at
M32867_at
M27159cds_s_at
J04731_at
M59211_at
M59313_at
M22412_at
AF081366_s_at
X83581cds_at
AF055477_at
U31815_s_at
U31816_s_at
D38101_s_at
D13985_at
Z56277_i_at
Z56277_i_at
U12623_at
AF048828_at
Naþ channel b1 subunit
Naþ channel b2 subunit
Naþ channel
Naþ channel 1
Voltage-sensitive Naþ channel a subunit
Voltage-dependent Naþ channel PN1
Kþ channel 1
Kþ channel (Kv2)
Kþ channel 2
Kþ channel (Kv3.2b)
Kþ channel (Kv3.2c)
Putative Kþ channel protein
ATP-regulated Kþ channel 2.1
Inward rectifier 9
Ca2þ channel a1B subunit
Ca2þ channel a1C subunit
Ca2þ channel a1S subunit
2þ
L-Type voltage-dependent Ca
channel a1 subunit
–
Cl channel 1
Cl– channel 5
Cl– channel 5
Cyclic nucleotide gated cation channel
Voltage-dependent anion channel 1
D28560_g_at
X73653_at
AJ000556cds_at
M64301_at
U73142_at
AF055291mRNA_at
AF075382_at
M17526_at
M17526_g_at
U88324_at
U88324_g_at
M18332_s_at
X04139_s_at
M25350_s_at
M91590_at
AF007758_g_at
AB004267_at
M16112_g_at
S83194_s_at
L09119_g_at
M31809_at
U04934_s_at
AF061726_s_at
AF085195_at
Phosphodiesterase I
Tau protein kinase I
Janus protein tyrosine kinase 1
Extracellular signal-related kinase 3
p38 MAP kinase
Signal transducer and activator of transcription 4 (STAT4)
Suppressor of cytokine signaling 2 (SOCS-2)
GTP-binding protein (Gao)
GTP-binding protein (Gao)
G protein, b1 subunit
G protein, b1 subunit
Protein kinase C, zeta subspecies
Protein kinase C, 3 subunit
cAMP phosphodiesterase 4
barrestin 2
Synuclein 1
Ca2þ/calmodulin-dependent protein kinase Ib2
Ca2þ/calmodulin-dependent protein kinase II, b subunit
Ca2þ/calmodulin-dependent protein kinase IV
C kinase substrate calmodulin-binding protein 3
Calcineurin Ab
Naþ/Ca2þ exchanger
Calpain p94
Nitric oxide synthase III
Test day sex
Test day no sex
Experience vs. Experience vs.
no experience no experience
Decrease
Increase
Decrease
Decrease
Decrease
Decrease
Decrease
Increase
Decrease
Increase
Decrease
Decrease
Decrease
Decrease
Decrease
Increase
Increase
Increase
Increase
Decrease
Increase
Decrease
Decrease
Increase
Increase
Decrease
Decrease
Increase
Increase
Increase
Increase
Increase
Increase
Decrease
Decrease
Decrease
Decrease
Decrease
Increase
Increase
Decrease
Increase
Increase
Decrease
Increase
Increase
Decrease
Decrease
Increase
Decrease
Decrease
Neurotransmission
Genes, Brain and Behavior (2005) 4: 31–44
39
Bradley et al.
Neurotransmitter synthesis M10244_at
X57573_at
Neurotransmitter release AB003991_g_at
L20821_at
U56815_at
AF033109_g_at
U26402_at
Neurotransmitter uptake
S56141_s_at
S68944_r_at
S76145_s_at
L00603_at
Neuropeptides
D00698_s_at
X16703_i_at
X16703_r_at
E05551cds_s_at
X87157_at
Neurotrophic factors
AF023087_s_at
D64085_g_at
M54987_at
Z14117cds_i_at
Cytokines
M22899_at
M26744_at
AJ222813_s_at
U77777_s_at
Transcription factors
Receptors
40
Tyrosine hydroxylase
Glutamic acid decarboxylase
SNAP-25A
Syntaxin 4
Syntaxin 6
Syntaxin 8
Synaptotagmin 5
Naþ-dependent neurotransmitter transporter
Naþ/Cl–-dependent neurotransmitter transporter
Dopamine transporter
Vesicular monoamine transporter
Insulin-like growth factor I
Insulin-like growth factor II
Insulin-like growth factor II
Vasoactive intestinal polypeptide
Neurotensin endopeptidase
Nerve growth factor-induced factor A
Fibroblast growth factor 5
Corticotropin-releasing hormone
Platelet-derived growth factor B precursor
Interleukin 2
Interleukin 6
Interleukin 18 precursor
Interferon-g-inducing factor a precursor (interleukin 18)
Decrease
Increase
Increase
Increase
Decrease
Decrease
Increase
Increase
Decrease
Decrease
Increase
Decrease
Decrease
Increase
Decrease
Increase
Decrease
Increase
Increase
Decrease
Decrease
Increase
Decrease
Decrease
Decrease
X17053cds_s_at
U75398_s_at
AF030088UTR#1_at
AB017912_at
Immediate-early serum-responsive JE gene
Krox-24
Activity and neurotransmitter-induced early gene 3
Smad2
Increase
X51991_at
U95368_at
S55933_i_at
AB016161cds_i_at
AB016161UTR#1_g_at
D50671_at
X17184_at
M83561_s_at
U08256_at
S39221_at
U08259_r_at
U11418_s_at
M61099_at
X96790_at
U12336_at
X74835cds_at
M16409_at
AF020756_s_at
U47031_at
X57281_at
M64867_at
J05276cds_at
U20907_at
S46131mRNA_r_at
S46131mRNA_s_at
X66022mRNA#1_s_at
U22830_at
D12498_s_at
GABAA receptor a3 subunit
GABAA receptor r subunit
GABAA receptor a4 subunit
GABAB receptor 1D
GABAB receptor 1D
GABA receptor, rho-3 subunit
Glutamate receptor 1 (AMPA)
Glutamate receptor (kainate), subunit 5–2
Glutamate receptor, d2 subunit
N-Methyl-D-aspartate receptor
N-Methyl-D-aspartate receptor, 2C subunit
N-Methyl-D-aspartate receptor 1
Metabotropic glutamate receptor 1 (mGLUR 1)
Metabotropic glutamate receptor 7B (mGLUR7B)
Nicotinic acetylcholine receptor, a9 subunit
Nicotinic acetylcholine receptor d subunit
Muscarinic acetylcholine receptor 4
P2x2 receptor 3
P2x4 receptor
Glycine receptor
Serotonin receptor
Serotonin 1 A receptor
Serotonin 4 receptor (long)
Dopamine D1 receptor
Dopamine D1 receptor
Dopamine D4 receptor
P2y receptor
Fibroblast growth factor receptor 1
Increase
Decrease
Increase
Decrease
Increase
Increase
Decrease
Decrease
Decrease
Increase
Decrease
Increase
Decrease
Decrease
Increase
Increase
Decrease
Decrease
Decrease
Decrease
Decrease
Decrease
Increase
Increase
Decrease
Decrease
Increase
Increase
Increase
Decrease
Decrease
Decrease
Decrease
Increase
Genes, Brain and Behavior (2005) 4: 31–44
Sexual experience-induced gene expression
Cytoskeleton/adhesion
Others
S54008_i_at
D12524_at
S60953_s_at
S62933_i_at
L26110_at
S49003_s_at
U92469mRNA_s_at
Z14118cds_at
U15211_at
U15211_at
AF014365_i_at
AF014365_s_at
AF016296_at
AJ132230_at
M90065UTR#1_s_at
M64698_s_at
U03390_at
Fibroblast growth factor receptor 1b
c-kit trk receptor
trkCTK þ 39
trkCTK þ 14
Transforming growth factor receptor 1b
Growth hormone receptor, short
Gonadotropin-releasing hormone receptor
Platelet-derived growth factor receptor a
Retinoic acid receptor a2
Retinoic acid receptor a2
CD44
CD44
Neuropilin
Bradykinin B1 receptor
Angiotensin II receptor
Inositol 1,4,5-trisphosphate receptor
Protein kinase C receptor
K00512_at
K03242_at
S74265_s_at
U30938_at
U59801_at
S58528_at
S58529_at
U88572_at
Myelin basic protein
Increase
Schwann cell peripheral myelin
Increase
Microtubule-associated protein 2, high molecular weight
Microtubule-associated protein 2
Increase
Integrin aM
Integrin, a5 subunit
Integrin, b3 subunit
Increase
AMPA receptor interacting protein (GRIP)
U66478_at
U45965_at
D14048_g_at
D26112_s_at
U38373_s_at
U20194_at
D25233UTR#1_at
D25233cds_at
D50093_s_at
L18889_at
L23088_at
L25527_at
M25157mRNA_i_at
AF025671_s_at
S45812_s_at
S68135_s_at
U49930_g_at
X04979_at
X06656_at
X13016_at
X60769mRNA_at
AF013985_at
M84725_at
D26154cds_at
U68562mRNA#2_s_at
AF065432_s_at
AF065433_at
Z11834_at
Mothers against dpp, 1 homolog
Macrophage inflammatory protein 2 precursor
SP120
Fas antigen
Huntingtin-associated protein 1A
Complement C8b
Retinoblastoma protein
Retinoblastoma protein
Prion protein
Calnexin
P-Selectin
E-Selectin 1
Cu, Zn superoxide dismutase
Caspase 2
Monoamine oxidase A
Glucose transporter 1
ICE-like cysteine protease (Lice)
Apolipoprotein E
Connexin 43
MRC OX-45 surface antigen
Silencer factor B
CD40 ligand
Neuronal protein 25
RB109
Chaperonin 60 and chaperonin 10
Bcl-2 related ovarian death gene, BOD-M
Bcl-2 related ovarian death gene, BOD-L
Brain-4
Genes, Brain and Behavior (2005) 4: 31–44
Decrease
Decrease
Increase
Decrease
Decrease
Decrease
Decrease
Decrease
Decrease
Increase
Decrease
Decrease
Decrease
Increase
Decrease
Decrease
Increase
Decrease
Decrease
Decrease
Decrease
Decrease
Decrease
Increase
Increase
Decrease
Decrease
Increase
Decrease
Decrease
Increase
Increase
Decrease
Decrease
Decrease
Decrease
Decrease
Increase
Increase
Increase
Increase
Decrease
Decrease
Increase
Decrease
Increase
Decrease
Increase
Decrease
Decrease
Increase
41
Changes in other interesting genes
2
PCR data (cycle difference)
Decreased expression in Increased expression in
E/S vs. NE/S
E/S vs. NE/S
Bradley et al.
1
0
–1
–2
Consistent with
Microarray?
MAP2
Syn6
ERK3
SOD
TH
Yes
No
Yes
Yes
Yes
Figure 1: Real-time polymerase chain reaction (PCR)
analysis of five genes differentially regulated by sexual
experience. The prediction from the microarray data is that
following a sexual encounter, sexually experienced female
hamsters in relation to sexually naı̈ve animals exhibit increased
mRNA for MAP2 and syntaxin 6, no change in ERK3 and a
decrease in superoxide dismutase (SOD) and tyrosine
hydroxylase (TH). The real-time PCR data were consistent for
all but syntaxin 6.
aspartate (NMDA) and a-amino-3-hydroxy-5-methylisoxazoleproprionic acid (AMPA) receptor subunits, GABAA subunits,
neurotrophin receptors and the m-opioid receptor, amongst
others. The data suggest that a multitude of signaling pathways
may contribute to long-term changes in striatal plasticity, consistent with current models of addiction (Chao & Nestler 2004).
Changes in genes encoding cytoskeleton/adhesion
proteins
One characteristic of repeated drug exposure is the enduring hypersensitivity to the locomotor activating and
rewarding effects of the drugs (Paulson & Robinson
1991; Valadez & Schenk 1994). Structural modifications
in neural circuitry, i.e. alterations in the patterns of synaptic connectivity, mediate these persistent alterations in
behavior (Chang & Greenough 1984; Robinson & Kolb
1997). Similarly, sexual experience increased mRNA
expression of neuronal activity regulated pentraxin (Narp),
an immediate-early gene product that is used as a marker
to detect neuritic sprouting (Tsui et al. 1996), and synaptopodin, an actin-associated protein in neuronal dendrites
(Deller et al. 2000a,b; Mundel et al. 1997), whose expression is amplified during hippocampal long-term potentiation (Yamazaki et al. 2001). Within the dSTR, expression of
MAP2, which plays a critical role in neuronal structure and
synaptic plasticity (Sanchez et al. 2000), was found to
increase in E/S and decrease in E/NS animals.
42
By utilizing DNA microarray techniques to profile genes regulated by sex behavior, we not only detected expression
changes for transcripts that have been already implicated in
behavioral sensitization by drugs of abuse but also uncovered
the regulation of many genes that have not yet been established in mediating neuronal plasticity. For example, within
the dSTR, alterations in the expression of caspase 2, calpain
p94, SP120 and the Fas antigen were observed. Classically,
these genes are known to be involved in neurodegenerative
processes. However, a role for these proteins in structural
plasticity (e.g. remodeling of the synaptical cytoskeleton) is
beginning to emerge (Chan & Mattson 1999). Another intriguing change was in SOD, which exhibited decreased
expression in E/S vs. NE/S animals. SOD is important in diverse
aspects of neuronal physiology, spanning between neuroprotection and maintenance of calcineurin signaling (Michiels et al.
1994; Wang et al. 1996). Potentially, many of the ‘other’ genes
regulated by sexual experience will be found to play essential
roles in neuronal plasticity in the future.
Conclusion
Collectively, the findings of this study will aid in the elucidation of mechanisms by which natural motivated behaviors
sensitize the mesolimbic and nigrostriatal dopamine pathways and, thus, provide new insights into the mechanisms
underlying addiction. Utilizing such an approach will hopefully
help others to examine activity-dependent transcription and
the role it plays in regulating long-term changes in basal
ganglia function.
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Acknowledgments
Special thanks to Melissa McCurley for her help with tissue
collection. This research was supported by NIH grants
DA13680 (RLM) and NS41302 (PGM) and a University of Minnesota Biomedical Genomics award.
Genes, Brain and Behavior (2005) 4: 31–44