65.2 Saturday, Jan. 5 Real-time measurement of hippocampal corticosterone in a songbird RENSEL, M.A.*; KOSARUSSAVADI, S.; SCHLINGER, B.A.; Univ. of California, Los Angeles; Univ. of California, Los Angeles; Univ. of California, Los Angeles email@example.com
Traditional models of steroid hormone action assume release from distinct endocrine glands into the bloodstream. However, recent studies indicate that tissues such as the brain are capable of synthesizing some steroids de novo, providing a means of local regulation independent of the periphery. The steroid hormone corticosterone (CORT) is produced in the adrenal glands and potentially within the brain, and is an important mediator of physiological and behavioral responses to stress in addition to numerous other functions. Most studies of CORT focus on measurement of circulating hormone levels as a proxy for levels at target tissues, but less is known about the actual amounts of hormone that reach these targets. The goals of the current study were to 1) validate the real-time measurement of CORT in brain tissue using in-vivo microdialysis in a songbird, the zebra finch, 2) determine whether the circadian pattern of CORT commonly found in the bloodstream is present in the hippocampus, an important site for negative feedback of the hypothalamic-pituitary-adrenal axis, and 3) assess whether hippocampal CORT levels are elevated in a matter similar to that seen in the bloodstream in response to a standard handling stress paradigm. We reliably measured CORT in the hippocampus of awake zebra finches. Baseline levels over the course of 24 hours were cyclical, with significantly depressed levels during the night, a time when levels in the bloodstream are also low. Future studies will examine endogenous fluctuations in CORT that may occur during cognitive tasks such as the formation and recall of spatial memory.