Aspects of GnRH neurobiology conserved across vertebrate forms

The decapeptide gonadotropin-releasing hormone (GnRH) came into prominence because of its roles in releasing luteinizing hormone and follicle-stimulat ing hormone and promoting reproductive behavior. At least three aspects of GnRH neurobiology have features which may be universal among vertebrates. F irst, the GnRH neuronal migration from the olfactory placode into the basal forebrain appears to hold true for forms ranging from fish to humans. Seco nd, for proper agonist activity in the anterior pituitary, GnRH must be rel eased in a pulsatile fashion. Since GT-1 neuronal cell cultures can demonst rate pulsatile release, it must be concluded that GnRH neuronal networks th emselves can manage this type of pulsatility. Using a neuronal mathematical model with "minimalist" assumptions, we demonstrated that a network of ide ntical neurons can achieve this self-organizing property without the use of , or spontaneous appearance of, "pacemaker cells." Indeed, since many param eter combinations worked, and since no information about species identity o r chemical cell type is provided to the model, this conclusion could apply across many vertebrate forms and, perhaps, even for other neuroendocrine ce ll types. Third, Fernald and colleagues (this issue of General and Comparat ive Endocrinology) have demonstrated remarkable effects of social context o n GnRH expression in fish. Reviewed here are some data in musk shrews sugge sting that behavioral and social stimuli can also modify GnRH neurons in ma mmals. Therefore, although GnRH neuronal mechanisms are adapted to meet spe cies-typical variations in environment and physiology, some of the importan t features of this system appear to be widely conserved. (C) 1998 Academic Press.