Neurophysiological analysis on neuronal circuits related to thermoregulatory actions of central gonadotropin releasing hormone.

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To clarify the neuronal circuits related central actions of gonadotropin releasing hormone (GnRH) on thermoregulation, neuronal circuits in the preoptic area (POA) in the hypothalamus, central grey (CG) and ventral tegmental area (VTA) in the midbrain, and septal area (SA) were investigated in detail using rats. 1.Stimulation and dislocation experiment : Electrical or chemical stimulations in the CG elicited skin vasodilations. On the other hand electrical or chemical stimulations in the VTA elicited skin vasoconstrictions. When the CG was cut by Haras-type knife, vasodilations which had been induced by the local thermal stimulation in the POA were disappeared. By the dislocation in the caudal VTA, peripheral skin vessels dilated spontaneously. 2.Electrophysiological experiment : The extracellular neuronal actions in the POA which retrogradely responded to electrical stimulations in the VTA were recorded. The warm-sensitive neurons in the POA, which responded to the local warming, tended to show responses with a slow conduction velocity. The warm-sensitive neurons which responded antegradely to the electrical stimulations in the SA showed four types of responses; 44% were facilitated, 13% inhibited, 18% inhibited after facilitation and 25% facilitated after inhibition by the electrical stimulation in the SA. These results indicated that there were two efferent neuronal circuits from POA related to thermoregulatory skin vasomotions; one is the inhibitory circuit to the VTA and the other is the facilitatory circuit to the CG. Majority of the POA neurons concerning thermoregulatory vasomotions were also shown to respond facilitatorily to the electrical stimulations in SA. The further investigations focused on POA-SA area using slice specimen may give more information to the central effects of GnRH on thermoregulation.