Abstract
Accumulating evidence suggests that up to three different molecular species of GnRH peptides encoded by different paralogs of gnrh genes are expressed by anatomically distinct groups of GnRH neurons in the brain of one vertebrate species. They are called gnrh1, gnrh2, and gnrh3. Recent evidence from molecular, anatomical, and physiological experiments strongly suggests that each GnRH system functions differently. Here, we review recent advancement in the functional studies of the three different GnRH neuron systems, mainly focusing on the electrophysiological analysis of the GnRH-green fluorescent protein (GFP) transgenic animals. The introduction of GFP-transgenic animals for the electrophysiological analysis of GnRH neurons greatly advanced our knowledge on their anatomy and electrophysiology, especially of gnrh1 neurons, which has long defied detailed electrophysiological analysis of single neurons because of their small size and scattered distribution. Based on the results of recent studies, we propose that different electrophysiological properties, especially the spontaneous patterns of electrical activities and their time-dependent changes, and the axonal projections characterize the different functions of GnRH1-3 neurons; GnRH1 neurons act as hypophysiotropic neuroendocrine regulators, and GnRH2 and GnRH3 neurons act as neuromodulators in wide areas of the brain.
Highlights
The conventional hypophysiotropic GnRH system, which expresses gnrh1 gene product, consists of neurons in the basal hypothalamic and/or preoptic area (POA) and project their axons to the median eminence or directly to the pituitary and facilitates the release of gonadotropins from the pituitary
It is clear that the two extrahypothalamic systems are not directly involved in the control of gonadotropin release from the pituitary, which is the main function of the hypothalamic/POA GnRH1 system
We have been suggesting that the terminal nerve (TN)-GnRH3 system, and probably the midbrain GnRH2 system as well, function as neuromodulators that regulate the excitability of other neurons in wide areas of the brain simultaneously [1,2,3]
Summary
Accumulating evidence suggests that up to three different molecular species of GnRH peptides encoded by different paralogs of gnrh genes are expressed by anatomically distinct groups of GnRH neurons in the brain of one vertebrate species. They are called gnrh, gnrh, and gnrh. We review recent advancement in the functional studies of the three different GnRH neuron systems, mainly focusing on the electrophysiological analysis of the GnRH-green fluorescent protein (GFP) transgenic animals. The introduction of GFP-transgenic animals for the electrophysiological analysis of GnRH neurons greatly advanced our knowledge on their anatomy and electrophysiology, especially of gnrh neurons, which has long defied detailed electrophysiological analysis of single neurons because of their small size and scattered distribution.
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