Effect of a substance P antagonist on capsaicin-induced nociceptive reflex in the isolated spinal cord-tail preparation of the rat.

An isolated spinal cord-tail preparation of the newborn rat was developed and used for studying the effects of various drugs. The cord and the tail were separately perfused with oxygenated artificial cerebrospinal fluid. Application of capsaicin in a small amount to the tail induced a depolarizing response of the lumbar ventral root (L3-L5) lasting for about 30 sec. The stimulating action of capsaicin was potentiated by previous perfusion of the tail with a medium containing prostaglandin E1 or E2. The capsaicin-induced nociceptive reflex was depressed by application to the spinal cord of morphine, Met-enkephalin, dynorphin (1-13), somatostatin, adenosine, GABA and a substance P (SP) antagonist [D-Arg1, D-Pro2, D-Trp7,9, Leu11]SP, and potentiated by bicuculline. The present preparation will be useful for the future studies on pain and analgesic drugs.