Enkephalins and dorsal horn neurones of the cat: effects on responses to noxious and innocuous skin stimuli

Abstract

1. In spinal cats anaesthetized with alpha-chloralose, a study was made of the effects of methionine enkephalin and methionine enkephalin amide on the responses of neurones of spinal laminae IV and V to noxious and innocuous skin stimuli. The enkephalins were ejected from micropipettes either in the region of cell bodies or in the substantia gelatinosa. 2. Administered near cell bodies the enkephalins reduced spontaneous firing and cell responses to both types of skin stimuli. These effects were antagonized by naloxone when administered near cell bodies but not when given intravenously in doses (0.3-0.6 mg/kg) more than adequate to antagonize analgesic doses of morphine. 3. Administered in the substantia gelatinosa the enkephalins were more selective in their action. The predominant effect was a reduction in nociceptive responses with little effect on non-nociceptive responses although spontaneous firing was commonly reduced. Naloxone administered either in the substantia gelatinosa or intravenously (0.1-0.3 mg/kg) reversed these effects of the enkephalins.