Activation of Both CB1 and CB2 Endocannabinoid Receptors Is Critical for Masculinization of the Developing Medial Amygdala and Juvenile Social Play Behavior

Abstract

Juvenile social play behavior is a shared trait across a wide variety of mammalian species. When play is characterized by the frequency or duration of physical contact, males usually display more play relative to females. The endocannabinoid system contributes to the development of the sex difference in social play behavior in rats. Treating newborn pups with a nonspecific endocannabinoid agonist, WIN55,212-2, masculinizes subsequent juvenile rough-and-tumble play behavior by females. Here we use specific drugs to target signaling through either the CB1 or CB2 endocannabinoid receptor (CB1R or CB2R) to determine which modulates the development of sex differences in play. Our data reveal that signaling through both CB1R and CB2R must be altered neonatally to modify development of neural circuitry regulating sex differences in play. Neonatal co-agonism of CB1R and CB2R masculinized play by females, whereas co-antagonism of these receptors feminized rates of male play. Because of a known role for the medial amygdala in the sexual differentiation of play, we reconstructed Golgi-impregnated neurons in the juvenile medial amygdala and used factor analysis to identify morphological parameters that were sexually differentiated and responsive to dual agonism of CB1R and CB2R during the early postnatal period. Our results suggest that sex differences in the medial amygdala are modulated by the endocannabinoid system during early development. Sex differences in play behavior are loosely correlated with differences in neuronal morphology.

Sex differences in juvenile play behavior differ among rat strains

“…We were surprised to find a lack of sex differences among Sprague‐Dawley subjects in either test, as almost all published studies have documented sex differences in this strain (Argue & McCarthy, ; Argue et al, ; Casto et al, ; Edelmann et al, ; Hotchkiss et al, ; Jessen et al, ; Krebs‐Kraft et al, ; Kurian et al, ; Olesen et al, ; Olioff & Stewart, ; Stockman & McCarthy, ; Wood et al, ), with the exception of Himmler et al () and those that found female‐biased sex differences (Field et al, ; Madden & Zup, ; Mychasiuk et al, ; Wood et al, ). However, the context in which our rats played differed in at least one way from that used in any of these previous studies.…”

“…However, the context in which our rats played differed in at least one way from that used in any of these previous studies. Many tested play in larger groups (Argue et al, ; Casto et al, ; Edelmann et al, ; Jessen et al, ; Krebs‐Kraft et al, ; Kurian et al, ; Olesen et al, ), some tested subjects in a novel environment (Argue & McCarthy, ; Argue et al, ; Krebs‐Kraft et al, ; Olioff & Stewart, ; Stockman & McCarthy, ; Wood et al, ), and others isolated subjects prior to testing (Hotchkiss et al, ; Wood et al, ). Therefore, Sprague‐Dawley males may be particularly sensitive to those environmental factors.…”

“…Among studies using Long‐Evans rats, approximately half report sex differences; although all of these sex differences are male‐biased, they range from males playing slightly more to about twice as much as females (Meaney & McEwen, ; Meaney, Dodge, & Beatty, ; Meaney, Stewart, Poulin, & McEwen, ; Parent & Meaney, ; Pellis & Pellis, ; Thor & Holloway, ). In contrast, most studies in Sprague‐Dawley rats have reported sex differences, at least in the summed frequency of all play behaviors (Argue & McCarthy, ; Argue et al, ; Casto, Ward, & Bartke, ; Edelmann, Demers, & Auger, ; Hotchkiss, Ostby, Vandenbergh, & Gray, ; Jessen, Kolodkin, Bychowski, Auger, & Auger, ; Krebs‐Kraft, Hill, Hillard, & McCarthy, ; Kurian, Bychowski, Forbes‐Lorman, Auger, & Auger, ; Olesen, Jessen, Auger, & Auger, ; Olioff & Stewart, ; Stockman & McCarthy, ; Wood, Bannoura, & Johanson, ), even when 24 hr isolation periods are used and subjects are tested with only one stimulus animal (Hotchkiss et al, ; Wood et al, ). Sprague‐Dawley rats seem to have more dramatic sex differences, with many finding that males play more than three times than females (Casto et al, ; Hotchkiss et al, ; Jessen et al, ; Kurian et al, ; Olesen et al, ; Stockman & McCarthy, ).…”

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

“…We then leveraged the sex-specific behavioral effects of adolescent SI to investigate underlying transcriptional mechanisms. We focused on meA because of its known sex differences in size (Hines et al, 1992), transcription (Chen et al, 2019), development (De Lorme et al, 2012, mechanisms of sexual differentiation (Argue et al, 2017;Krebs-Kraft et al, 2010;Nugent et al, 2009;Zehr et al, 2006), importance in sex-specific reward-associated behaviors (Chen et al, 2019;Li et al, 2017;Unger et al, 2015) and sensitivity to adolescent stress (Cooke et al, 2000;Hodges et al, 2019). Additionally, while evidence suggests that meA is an important regulator of drug sensitivity in females (Rudzinskas et al, 2019), very little is known about males (Knapska et al, 2007).…”

Microglial elimination of dopamine D1 receptors defines sex-specific changes in nucleus accumbens development and social play behavior during adolescence

“…4 A behavioral hallmark of adolescence is increased peer-centered social interaction. 2,5 Neuropeptides commonly associated with social behavior, like oxytocin, endocannabinoids, and opioids, have been demonstrated to modulate social behavior when manipulated locally in the amygdala, NAc, and VTA, in rodents, [6][7][8][9][10][11] as well as intra-nasally in humans. 12 Interestingly, access to social experience can be used in lieu of addictive drugs to induce conditioned place preference, operant conditioning, or maze performance, 13,14 and social interactions can modulate addiction-like behaviors, acting to enhance or diminish drug-seeking behaviors in difference contexts.…”