[Inhibitory effect of cysteamine on nociceptive responses of dorsal horn neurons in spinal cord of cats].

The effect of somatostatin depletor cysteamine on the nociceptive responses of neurons in laminae IV-VI of spinal cord was studied in 16 pentobarbitone anesthetized and spinal cord transected (at L1) cats. Intravenous injection of cysteamine (50 mg/kg) markedly inhibited responses of the neurons produced by noxious heating (50 C) of glabrous skin of the plantar region, but not C fibre responses induced by electrical stimulation of unmyelinated fibers of the tibial nerve. However, C responses in 8/13 neurons tested were significantly inhibited by large dose cysteamine (100 mg/kg). Following micropressure ejection of cysteamine (20 psig) into the substantia gelatinosa where somatostatin-containing fibers terminate, heating responses were significantly inhibited in all laminae IV-VI neurons whereas C responses was only weakly inhibited in 7/13 neurons. The results suggest that depletion of spinal somatostatin may be involved in cysteamine-induced inhibition of spinal nociception. The possible mechanism underlying the stronger cysteamine-induced inhibition of heating response was discussed.