Meeting Abstract

103.5  Tuesday, Jan. 7 09:15  Glucocorticoid responses to adrenocorticotropic hormone (ACTH) in red-sided garter snakes, Thamnophis sirtalis: Effects of sex and season DAYGER, CA*; LUTTERSCHMIDT, DI; Portland State University cdayger@pdx.edu

Many studies have demonstrated that vertebrate stress responses are often context-dependent. We recently showed that low body condition is associated with greater sensitivity to capture stress and exogenous corticosterone during the spring mating season in female red-sided garter snakes (Thamnophis sirtalis). In contrast, body condition does not appear to be related to stress responsiveness in male snakes, although capture stress does not consistently increase corticosterone concentrations in the spring compared to fall. Together, these data suggest that sex differences and seasonal variation in adrenal sensitivity and/or competency may be driving the context-dependent nature of stress responses. To test this hypothesis, we collected male and female garter snakes from a den site in Manitoba, Canada where snakes aggregate during the spring mating season and in the fall before descending underground for winter dormancy. Blood samples were collected immediately upon capture and 1 and 4 hours after treatment with either vehicle or 0.1 IU/g adrenocorticotropic hormone (ACTH). ACTH treatment elicited a significant increase in plasma corticosterone at the 1-hour sampling time in both sexes and seasons. The mean integrated corticosterone response was significantly lower in the spring compared to fall in males but not females, suggesting that adrenal sensitivity to ACTH is suppressed in males during spring mating. Females remained highly sensitive to ACTH regardless of season. Preliminary analyses indicate that corticosterone responses to ACTH do not vary with body condition in either sex. These studies examining variation in responses to ACTH challenge will help illuminate the physiological mechanisms underlying the context-dependency of stress responsiveness.