Abstract
It was found previously that 1) analgesia (acupuncture analgesia) caused by low frequency stimulation of the acuppuncture point was produced finally by the serotonergic and noradrenergic descending pain inhibitory systems (DPIS) and 2) the dopaminergic neurons of the arcuate nucleus (ARN) of the hypothalamus play a role as the more proximal part of the DPIS. In present experiment, the relation bteween ARN and serotonergic descending system had been investigated. Analgesia, measured by tail flick test of rats, produced by stimulation of ARN was abolished by electrical lesion of the ventromedial nucleus of the hypothalamus (HVM) . The lesions of the upper or lateral parts of the HVM did not influence on the stimulation-produced analgesia of the ARN (ARN-SPA) . Evoked potential was produced in the HVM by stimulation of the ARN. Analgesia was produced by stimulation of the HVM. Like ARN-SPA, this analgesia 1) was limitted during stimulation, 2) did not exhibit the individual variations of the effectiveness which was observed in acupuncture analgesia, and 3) was not influenced by hypophysectomy or intraperitoneal 1mg/kg naloxone. Unilke ARN-SPA, HVA-SPA was not influenced by intraperitoneal 2mg/kg pimozide, dopamine antagonist. The HVM-SPA was partially blocked by electrical lesion of the ventral part of the periaqueductal central gray (V-PAG) or by intraperitoneal 2mg/kg methysergide, serotonergic antagonist. Evoked potential was produced in the V-PAG by stimulation of the HVM. It was concluded from these results that the HVM was the part of the DPIS between the ARN and V-PAG which is the origin of the serotonergic DPIS. The neurotransmitter of the HVM neuron to the V-PAG and the relation between HVM and noradrenergic DPIS were still obscure.
