Adolescent Social Isolation Reprograms the Medial Amygdala: Transcriptome and Sex Differences in Reward

Abstract

Adolescence is a sensitive window for reward-and stress-associated behavior. Although stress during this period causes long-term changes in behavior in males, how females respond is relatively unknown. Here we show that social isolation stress in adolescence, but not adulthood, induces persistent but opposite effects on anxiety-and cocaine-related behaviors in male vs. female mice, and that these effects are reflected in transcriptional profiles within the adult medial amygdala (meA). By integrating differential gene expression with co-expression network analyses, we identified crystallin mu (Crym), a thyroid-binding protein, as a key driver of these transcriptional profiles. Manipulation of Crym specifically within adult meA neurons recapitulates the behavioral and transcriptional effects of social isolation and re-opens a window of plasticity that is otherwise closed. Our results establish that meA is essential for sex-specific responses to stressful and rewarding stimuli through transcriptional programming that occurs during adolescence. INTRODUCTION:In many mammals, sex differences in behavior are required for the perpetuation of the species and are expressed as differences in mating and reproductive strategies. Individual variations in reproductive strategies are known to be dependent on e n v i r o n m e n t a l f a c t o r s a n d r e l y o n programming mediated by experiencedependent plasticity (Bergan et al., 2014). Stressful and rewarding stimuli are two key factors that may be especially important for encoding these strategies to optimize sexual behaviors and maximize reproductive success . However, very little is known about the brain region-specific m o l e c u l a r p r o c e s s e s u n d e r l y i n g t h e programming of such strategies.Adolescence is a sensitive period for programming reward-associated behaviors particularly in males (Sisk, 2016;Walker et al., 2019) and a time of heightened responsiveness to rewarding and stressful Statistical Analysis of Behavioral DataAll behaviors were analyzed using a 2-way ANOVA or a Kruskall-Wallis non-parametric test depending on the significance of a Levene's test for homogeneity of variance. If an interaction was identified, a Tukey post-hoc analysis was conducted to determine specific differences between groups. If an effect was identified via Kruskall-Wallis, follow-up Mann-Whitney tests were run to determine specific differences between groups. Chi-square tests were used to determine differences in the distribution of behavioral phenotypes within a group (marble burying and CPP). Pearson's Chi Squared tests were used to account for the lack of representation of all categories across groups. All analyses were conducted using SPSS Statistical Software, V25 (IBM, Armonk, NY). Cocaine Injections and Tissue Collection for RNA-seqOn P80, animals were divided into 8 groups of males and 8 groups of females: GH + chronic cocaine/saline; SI + chronic cocaine /saline; GH + acute cocaine/saline; SI + acute cocaine/saline. In total, 200 animals were utlilized. F...

Social Isolation Stress in Adolescence, but not Adulthood, Produces Hypersocial Behavior in Adult Male and Female C57BL/6J Mice

“…In these studies, we separated animals at PD 28, which is consistent with a well-established adolescent isolation paradigm commonly used in male rats (Butler et al, 2014a , 2016 ; Skelly et al, 2015 ). However, others have isolated animals earlier in adolescence; for example, Walker and colleagues separated C57BL/6J males and females from PD 22–42 and did not find that isolation during this period increased EPM open arm time (Walker et al, 2020 ). Given the rapid shifts in hormonal and neuroendocrine profiles across adolescence and puberty in rodents, slight differences in the onset of isolation could potentially have significant long-term behavioral implications (Walker et al, 2019 ).…”

Individual differences in social play behaviour predict alcohol intake and control over alcohol seeking in rats

“…Shown are the average + SEM levels of weekly alcohol intake per group. Post hoc pairwise comparisons: ** or *** significant difference between adolescent water and adolescent alcohol (p < 0.01 or p < 0.001, respectively); # significant difference between low and high playing rats (p < 0.05) play deprivation was shown to result in augmented cocaine and alcohol self-administration (Baarendse et al 2014;Lesscher et al 2015) and enhanced cocaine-, amphetamine-and alcohol-induced conditioned place preference in adulthood (Walker et al 2020;Whitaker et al 2013). Moreover, children who engage(d) more in outdoor play show improved self-regulation and conflict resolution skills (Tremblay et al 2015).…”

“…For example, treatment with low doses of alcohol enhances social play behaviour in rats (Trezza et al 2009;Varlinskaya et al 2001Varlinskaya et al , 2010Varlinskaya and Spear 2002). Moreover, play deprivation in rats has been shown to result in enhanced sensitivity for cocaine selfadministration (Baarendse et al 2014) and for cocaine-, amphetamine-and alcohol-induced conditioned place preference (Walker et al 2020;Whitaker et al 2013). Also, play deprivation augmented alcohol consumption in adulthood (Lesscher et al 2015).…”

Long-Term Impacts of Post-weaning Social Isolation on Nucleus Accumbens Function

“…Interestingly, the few studies investigating isolation in females found that SI-R has no effect on cocaine CPP at a low dose [2 mg/kg; ( 81 )]. However, this effect may be dose, species and/or isolation-type specific as others have shown that resocialization after aSI decreases preference for cocaine at a higher dose [7.5 mg/kg; ( 84 )] in mice. Similarly, SI-R increases preference for ethanol in male rats ( 79 ).…”

“…The key driver genes identified in the Walker et al ( 121 ) ranged in biological functions and display sex-specific expression across multiple treatments groups. A full list of key driver genes identified in the PFC, NAc and VTA is published in Walker et al ( 84 ). Overall, the authors observed a greater transcriptional response to acute and chronic cocaine in the NAc of aSI males but not females, with very little overlap in the cocaine-induced differentially expressed genes (DEGs).…”