Testosterone differentially modulates the display of agonistic behavior and dominance over opponents before and after adolescence in male Syrian hamsters

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.