Abstract
Unit discharges of 44 neurons were recorded with microelectrodes from the periaqueductal central gray (PAG, 31 neurons) and the midbrain reticular formation (MRF, 13 neurons) in unanesthetized and the unrestrained rabbits. Those neurons were the selected ones, which did not respond to noxious or external stimuli, to evaluate the efferent neuron activity.
The changes in unit discharges caused by acupuncture stimulation, inversion and morphine (10 mg/kg i.p.) were increase (20%) or decrease (34%) of spontaneous firing rates and those neurons were mostly found in the ventral region of PAG and MRF. The parall changes induced by two of above three procedures were observed in 67% of responded neurons to one of three procedures. Naloxone (1 mg/kg i.p.) completely antagonized the changes induced by three procedures.
These data indicate that 1) the responsive neurons to acupuncture, morphine and inversion might be belonged to descending inhibitory system, since such neurons were mostly found in the ventral PAG around the dorsal raphe; 2) the common mechanism in acupuncture anesthesia and inversion might exist at least in analgesia since naloxone commonly antagonized the neuronal changes induced by acupuncture stimulation and inversion.
