SEROTONIN INHIBITS HIGH-THRESHOLD CA2-SENSITIVE ACUTELY ISOLATED ADULT-RAT DRG NEURONS( CHANNEL CURRENTS IN CAPSAICIN)

1. The effect of serotonin (5HT) was studied on high-threshold Ca2+ ch annel currents in a subpopulation of acutely isolated rat dorsal root ganglion cell bodies that had long-duration action potentials, lacked I-H current, were capsaicin-sensitive, and thus resembled C-type nocic eptors. 2. In these neurons, 10 mu M 5HT inhibited peak high-threshold Ca2+ channel currents by 61.5 +/- 6.9% (mean +/- SE), (n = 7). The ef fects of 5HT were mimicked by 1 mu M (+)8-hydroxy-2-(di-n-propylamino) -tetralin HBr [(+)8-OH-DPAT] in five neurons tested, and the effects o f 1 mu M (+)8-OH-DPAT were antagonized by 100 nM thoxyphenyl)-4-[4-(2- phthalimmido)butyl]piperazine HBr (NAN-190) in six neurons tested. 3. The above data leads us to hypothesize that 5HT, released into the spi nal cord by descending systems, may produce antinociception by inhibit ing Ca2+ entry into afferent terminals of nociceptors via activation o f 5HT(1A) receptors.