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

Abstract

In teleost fish, GTH sécrétion is controiled by a large number of neuroendocrine factors at the central level and steroid feedback represents an efficient process to synchronize the activity of ail the Systems involved along the brain-pituitary-gonad axis. Estrogen effects are mediated by spécifie nuclear receptors that act as transcription factors to regulate the expression of target gènes. In order to understand the neuroendocrine mechanisms involved in the estrogen feedback on GTH sécrétion, 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 explain our strategy to identify the central target of estrogen using both in situ hybridization and immunohistochemistry. We focused our attention on GABA neurons of which the distribution, in some central areas, exactly overlaps with that of estrogen receptors expressing cells.

Sex steroid regulation of glutamate decarboxylase mRNA expression in goldfish brain is sexually dimorphic

“…Consequently, GABAergic neurones have been shown to be the primary targets for steroid feedback on lutropin release, by modulating GABA release and GAD mRNA expression (McCarthy 1995; Herbison 1997). Recent data from rainbow trout suggest a role for GABAergic neurones as target cells for oestrogen feedback on lutropin release also in fish, because oestradiol receptors are present in GABAergic, but not in GnRH neurones (Anglade et al . 1998).…”