The GABAergic system: A possible component of estrogenic feedback on gonadotropin secretion in rainbow trout (Oncorhynchus mykiss).

In teleost fish, GTH secretion is controlled by a large number of neuroendo crine factors at the central level and steroid feedback represents an effic ient process to synchronize the activity of all the systems involved along the brain-pituitary-gonad axis. Estrogen effects are mediated by specific n uclear receptors that act as transcription factors to regulate the expressi on of target genes. In order to understand the neuroendocrine mechanisms in volved in the estrogen feedback on GTH secretion, we need, as a first step, to know the nature of target cells at the pituitary and central levels. In rainbow trout, some estrogen receptors expressing cells are identified but the nature of a large number of them remains unknown. In this paper, we ex plain our strategy to identify the central target of estrogen using both in situ hybridization and immunohistochemistry. We focused our attention on G ABA neurons of which the distribution, in some central areas, exactly overl aps with that of estrogen receptors expressing cells.