[The influences of morphine microinjected into preoptic area on electric activities of pain response neurons in parafascicular nucleus of thalamus in rat].

We have observed the influences of opioid-like substances in preoptic area (POA) on the electric activities of pain response neurons in parafascicular nucleus of thalamus (Pf). The results were as follows: 1. Morphine 10 micrograms/microliters or 1 micrograms/microliters microinjected into POA could remarkably inhibit the pain discharges of most (20/26, 19/23 respectively) pain excitatory neurons (PEN) in Pf. The frequency of evoked discharges was decreased nd the duration was shortened. After injecting 10 micrograms/microliters morphine, three neurons showed inhibitory responses to noxious stimuli. 2. Morphine of the two doses could shorten the complete inhibitory period of pain inhibitory neurons (PIN, 23/33). These results suggest that the opioid-like substances in POA might have an inhibitory effects on pain response neurons in Pf.