Kalynn M. Schulz

Developmental stress is a well-established risk factor for mental health disorders, yet the neural mechanisms underlying these outcomes remain incompletely understood. Inhibitory brain networks, particularly within the amygdala, are disrupted by stress and implicated in stress-related psychopathologies. Using a rodent model, the current study investigated the isolated and combined effects of prenatal and adolescent stress on adult social interactions and GABAergic neurons surrounded by perineuronal nets (PNNs) in the basolateral amygdala (BLA). Male and female rats were exposed to chronic variable stressors (CVS) prenatally (PS), during adolescence (AS), or during both prenatal and adolescent periods (PS+AS). In adulthood, all animals were tested for social behavior with same-sex weight-matched partners, and brains were collected for identification of BLA inhibitory neurons (GAD67 staining) and PNNs ( Wisteria Floribunda Agglutinin staining). For social behavior, AS alone robustly increased social investigation in adulthood relative to non-stressed (NS) controls and animals exposed to combined PS+AS. PS+AS subjects did not significantly differ from NS controls, suggesting that prenatal stress exposure prevented adolescent stress-induced increases in adult social investigation. An analogous data pattern was observed in the BLA. AS alone decreased the number GAD67+ neurons surrounded by PNNs (co-labeled) relative to NS controls and subjects exposed to combined PS+AS. When the percentage of total GAD67+ neurons co-labeled with PNNs was assessed, both PS alone and AS alone reduced the proportion of GAD67+ neurons surrounded by PNNs, whereas combined PS+AS had no effect. Overall, these data suggest that prenatal stress exposure prevents adolescent stress-induced disruptions to perineuronal nets surrounding inhibitory neurons in the BLA, potentially conferring resilience to adolescent stress-induced changes in inhibitory function and social behavior. Highlights: Adolescent stress exposure increased social investigation in adulthood. Adolescent stress decreased the number of BLA cells co-labeled with GAD67 and WFA. Prenatal or adolescent stress decreased the proportion of inhibitory neurons with PNNs. When preceded by prenatal stress, effects of adolescent stress were not observed.

The current study investigated the influence of testosterone on agonistic behavior and dominance over an opponent before and after adolescence in male Syrian hamsters (Mesocricetus auratus), and tested the hypothesis that shifts in behavioral responsiveness to testosterone occur across adolescent development. We predicted that testosterone-dependent modulation of attacks decreases following puberty, and that flank marking behavior in response to testosterone increases following puberty. Prepubertal (14 days of age) and adult subjects (52–62 days of age) were gonadectomized and immediately implanted with testosterone propionate (TP) or vehicle pellets. Fourteen days later, agonistic behaviors were assessed in a neutral arena with age-matched testosterone-treated opponents. TP treatment increased attacks and dominance over an opponent in prepubertal but not adult males, supporting the hypothesis that testosterone-dependent modulation of aggression decreases following puberty. TP increased flank marking behavior in adults, but failed to increase flank marking in prepubertal subjects, supporting the hypothesized increase in testosterone-dependent modulation of flank marking after puberty. Thus, we provide here evidence that changes in agonistic responses to steroid hormones occur across puberty and adolescence in male rodents, much like the well-established shifts in neuroendocrine and reproductive behavioral responses to steroid hormones that occur pre- to post-pubertally. These findings may have implications for early pubertal timing and increased risk for externalizing symptoms and aggressive behavior in humans.

The current study investigated the influence of testosterone on agonistic behavior and dominance over an opponent before and after adolescence in male Syrian hamsters ( Mesocricetus auratus) . We hypothesized that testosterone-dependent modulation of agonistic behavior would be greater following adolescent development. To test this hypothesis, prepubertal (14 days of age) and adult subjects (52-62 days of age) were gonadectomized and immediately implanted with testosterone or vehicle pellets. Fourteen days later, agonistic behavior was assessed in a neutral arena with age-matched testosterone-treated opponents. Flank marking was also assessed separately in response to male odors alone. Our hypothesis predicted that testosterone would modulate agonistic behavior and dominance over an opponent in adult but not in prepubertal subjects, however, only flank marking behavior followed the predicted data pattern. During both social interaction and scent tests, testosterone increased flank marking behavior in adults, but failed to increase flank marking in prepubertal subjects. Contrary to our predictions, testosterone treatment increased prepubertal subject attacks, decreased submissive tail-up displays, and facilitated prepubertal subject dominance over opponents. In adults, testosterone increased paws-on investigation and flank marking during social interactions. Taken together, these data indicate that some, but not all aspects of agonistic behavior are sensitive to the activational effects of testosterone prior to adolescence, and that activational effects of testosterone differ substantially between prepubertal and adult males. Our results may have implications for early pubertal timing and increased risk for externalizing symptoms and aggressive behavior in humans. Highlights: Testosterone increased attacks and decreased submissive displays in prepubertal males Testosterone increased dominance over opponents in prepubertal males Prepubertal males displayed more attacks and submissive behaviors than adults overall Testosterone increased flank marking behavior only in adult males

Early pubertal onset during adolescence is consistently linked with increased risk of anxiety and depression in girls. Although estradiol tends to have anxiolytic effects in adulthood, whether sensitivity to estradiol’s anxiolytic actions increases during adolescence is not clear. Using a rodent model, the current study tested the hypothesis that a shift in sensitivity to the anxiolytic effects of estradiol occurs during adolescence. To test this hypothesis, prepubertal and adult C57BL/6 female mice were ovariectomized, implanted with vehicle- or estradiol-filled silastic capsules, and behavioral tested one week later in the open field and elevated zero maze. Our hypothesis predicted that estradiol would decrease anxiety-related behavior to a greater extent in adults than in adolescent females, however, our results did not support this hypothesis. In the open field, estradiol implants significantly decreased anxiety-like behavior in adolescent females (relative to vehicle) and had little to no effect on the behavior of adults. These data suggest that adolescence is associated with a downward shift in sensitivity to the anxiolytic effects of estradiol on behavior in the open field. In contrast, although estradiol treatment did not influence anxiety-like responses in the elevated zero maze in early adolescent or adult females, adolescent females displayed significantly higher levels of anxiety-like behavior than adults. These findings demonstrate that substantial changes in anxiety-related behavior occur during adolescence, including a context-dependent shift in behavioral responsiveness to estradiol.