63.3 Friday, Jan. 6 In vivo Microdialysis Reveals Dynamics of Estradiol Production in the Avian Hippocampus RENSEL, M.A.*; SALWICZEK, L.; HSIAO, C.F.; XIA, S.; REMAGE-HEALEY, L.; SCHLINGER, B.; Univ. of California, Los Angeles email@example.com
Steroids act on the brain after their synthesis and secretion by peripheral organs or by their synthesis in the brain itself. Estrogens, synthesized in the brain due to neural expression of the enzyme aromatase, play a crucial role in the activation of neural circuits controlling reproductive and non-reproductive behaviors as well as in sensory processing. Songbirds are particularly useful models to study neuroestrogens because they express high levels of aromatase in the brain. Recent studies using newly developed in vivo microdialysis procedures show that estradiol levels fluctuate rapidly in a higher-order auditory region (NCM) of the zebra finch brain in response to auditory input, functionally enhancing neural responses to conspecific song. Here we describe studies using in vivo microdialysis to examine estradiol levels in the zebra finch hippocampus (HP), a brain region important for the formation and maintenance of spatial memory. In songbirds, the HP contains a distinct population of aromatase-producing neurons and, in zebra finches, estrogens improve spatial memory capability. We found that estradiol was indeed reliably detectable in the HP of awake, behaving zebra finches. Furthermore, peripheral injections of estradiol transiently increased HP levels of estradiol whereas retrodialysis into the HP of an aromatase inhibitor markedly decreased estradiol levels. HP levels of estradiol were unchanged by stimuli that elevate levels in the nearby NCM, suggesting that estrogens do not diffuse readily across brain regions. We are currently assessing HP estradiol levels as birds perform spatial memory tasks. In vivo microdialysis provides a powerful tool for the investigation of steroid-brain interactions in the awake and freely-behaving animal.