Multiple Forms of GnRH Are Released from Perifused Medial Basal Hypothalamic/preoptic Area (MBH/POA) Explants in Birds

Both chicken gonadotropin-releasing hormones I and II (cGnRH I and II) were detected in abundant quantity by radioimmunoassay of extracts of Japanese quail medial basal hypothalamic/preoptic area (MBH/POA) fragments that included the median eminence (ME) region. However, in radioimmunoassayed extracts of Japanese quail ME alone, the concentration of cGnRH I greatly exceeded that of cGnRH II (approximately 450 pg/ME vs < 10 pg/ME). Likewise, cGnRH I and II were released into perifusates from quail an turkey MBH/POA explants maintained in short-term perifusion. Release of both forms occurred whether or not explants included the ME region, i.e., from quail POA explants did not include the ME or from turkey MBH/POA explants from which the ME region had been dissected out. This indicates that neuropeptides released from areas other than the ME can be a major source of neuropeptides detected in perifusates. Further, release of cGnRH I was altered following the addition of norepinephrine to perfusion media, whereas cGnRH II release was unaffected, again, whether or not explants included the ME. These results demonstrate that the release of neurohemoral substances from perifused explants cannot be assumed to represent regulated secretion from the ME.