[Analgesic effect of pentazocine and its action on nociceptive afferent pathway]

Nociceptive stimulus was applied to the skin of adult cats by pinching with a serrated forceps or by radiant heat with Pain meter. This stimulation caused motor or emotional responses such as movements of the head and trunk, vocalization, escape and attack. After the administration of pentazocine, these responses disappeared and the animals behaved normally. Analgesic action appeared approximately 15 min after the administration and lasted more than 90 min. Effects of pentazocine on pain-afferent pathways were studied and the evoked potential was recorded by tibial nerve stimulation. Though pentazocine did not influence the evoked potential recorded from somatic sensory area I and mesencephalic central gray, the evoked potential in pre-central association area, nucleus centralis lateralis, nucleus suprageniculatus-limitans and reticularis pontis caudalis was reduced by pentazocine.