Antianalgesic action of thiamylal sodium in cats.

The effects of thiamylal on the nociceptor-driven neural activity in the spinal cord were studied in decerebrate, non-anesthetized cats. Noxious stimulation was induced by the injection of bradykinin into the femoral artery and the neutral response in the lateral funiculus was measured by the multi-unit activity technique. The effects of thiamylal on the bradykinin-induced response were compared before and after the spinal cord transection, above the recording site. Thiamylal, 5 mg/kg i.v., potentiated the response significantly before the cord transection and depressed it after the transection. These findings indicate that the antianalgesic action of thiamylal is induced at the spinal cord level: although this anesthetic agent does have a direct intraspinal depressant action, the multisynaptic neural network of the supraspinal pain inhibition system is more susceptible to the actions of anesthetics, and the depression of this descending system by thiamylal results in a release of spinal cord nociceptive neural mechanisms from the supraspinal control.