EVIDENCE FOR THE EXISTENCE OF SUBSTANCE-P AUTORECEPTOR IN THE MEMBRANE OF RAT DORSAL-ROOT GANGLION NEURONS

Substance P, a putative peptide neurotransmitter contained in primary sensory neurons, is suggested to play a major role in nociceptive tran smission. In the present study, the existence of substance P autorecep tor in dorsal root ganglion neurons was identified with a method we de veloped recently and substance P-activated inward current in the dorsa l root ganglion neurons and its ionic mechanism were also explored pre liminarily. The majority of the cells examined (68/76, 89.5%) were sen sitive to external application of substance P (0.01-10 mu M) with a co ncentration-dependent inward current. This current was found to result from the opening of nonselective ion channel, preferring the Na+ chan nel. The substance P-activated current can be supressed by Cd2+ (0.05 mu M), which suggested Ca2+ may also be involved. Soon after the neuro ns had been identified to be endowed with substance P receptor with wh ole-cell patch-clamp technique, 17 cells were chosen for immunocytoche mical staining to detect substance P-immunoreactivity. Seven neurons w hich were classified into small and intermediate size were found to re veal substance P-immunoreactivity. Using this method we have identifie d the existence of substance P autoreceptor in rat DRG neurons. (C) 19 97 IBRO.