Sex-Specific Gene Expression in the Mouse Nucleus Accumbens Before and After Cocaine Exposure

Abstract

The nucleus accumbens plays a major role in the response of mammals to cocaine. In animal models and human studies, the addictive effects of cocaine and relapse probability have been shown to be greater in females. Sex-specific differential expression of key transcripts at baseline and after prolonged withdrawal could underlie these differences. To distinguish between these possibilities, gene expression was analyzed in four groups of mice (cycling females, ovariectomized females treated with estradiol or placebo, and males) 28 days after they had received seven daily injections of saline or cocaine. As expected, sensitization to the locomotor effects of cocaine was most pronounced in the ovariectomized mice receiving estradiol, was greater in cycling females than in males, and failed to occur in ovariectomized/placebo mice. After the 28-day withdrawal period, RNA prepared from the nucleus accumbens of the individual cocaine- or saline-injected mice was subjected to RNA sequencing analysis. Baseline expression of 3% of the nucleus accumbens transcripts differed in the cycling female mice compared with the male mice. Expression of a similar number of transcripts was altered by ovariectomy or was responsive to estradiol treatment. Nucleus accumbens transcripts differentially expressed in cycling female mice withdrawn from cocaine exhibited substantial overlap with those differentially expressed in cocaine-withdrawn male mice. A small set of transcripts were similarly affected by cocaine in the placebo- or estradiol-treated ovariectomized mice. Sex and hormonal status have profound effects on RNA expression in the nucleus accumbens of naive mice. Prolonged withdrawal from cocaine alters the expression of a much smaller number of common and sex hormone-specific transcripts.

Identifying roles for peptidergic signaling in mice

“…When the locomotor response to cocaine was tested, cocaine was administered by intraperitoneal (i.p.) injection, and open field ambulations were recorded for 45 min on successive days or after a brief withdrawal period; cocaine injections were 10 mg/kg except for day 2, which was 20 mg/kg (32,33).…”

“…We tested the response of Pam Emx1-cKO/cKO mice to 4 injections of cocaine, 4 d of abstinence, and a final injection of cocaine ( Fig. 3B) (33). No difference was observed in the response of WT and Pam Emx1-cKO/cKO mice to the initial administration of saline (day 1).…”

“…DESeq2 analysis of differential expression was performed on the counts data, yielding 1,063 transcripts with P < 0.05; when outliers were eliminated (33), the number of differentially expressed transcripts dropped to 555. When depicted as a volcano plot, the vast majority of over 14,000 transcripts with average fragments per kilobase of transcript per million mapped reads (FPKM) > 1 were clustered near the origin, with a WT/knockout ratio within the 0.5 to 2.0 range (log 2 [ratio] −1 to +1) and a DESeq2 P value > 0.05. and Pam Emx1-cKO/cKO , n = 24.…”

Prospects for finding the mechanisms of sex differences in addiction with human and model organism genetic analysis

“…Gene expression analyses in reward‐related regions over time following drug exposure show mechanisms that underlie drug response, drug‐seeking and drug‐taking . Differential gene expression analysis in the mouse nucleus accumbens before and after prolonged cocaine withdrawal have showed profound effects of sex and hormonal status in drug naïve states and fewer differentially expressed genes unique to each sex, post‐cocaine exposure . Sex‐specific differences in the brain tissue transcriptome in drug‐naive vs postdrug exposure states indicate genes that mediate sex differences in the initial response to cocaine administration and those involved in withdrawal.…”

“…132,133 Differential gene expression analysis in the mouse nucleus accumbens before and after prolonged cocaine withdrawal have showed profound effects of sex and hormonal status in drug naïve states and fewer differentially expressed genes unique to each sex, post-cocaine exposure. 134 Sex-specific differences in the brain tissue transcriptome in drug-naive vs postdrug exposure states indicate genes that mediate sex differences in the initial response to cocaine administration and those involved in withdrawal. RNA expression differences have also been demonstrated in the NAc of adult male and female C57BL/6J mice following binge ethanol drinking sessions that was strongly influenced by sex.…”