CAPSAICIN PREFERENTIALLY AFFECTS SMALL-DIAMETER ACUTELY ISOLATED RAT DORSAL-ROOT GANGLION-CELL BODIES

The effects of capsaicin were tested on 221 acutely isolated dorsal ro ot ganglion neurons of the rat, which ranged in diameter from 15 to 55 mu m In a subpopulation of these cells, ranging in diameter from 17.5 to 33 mu m (n=117), capsaicin (1 mu M) produced an inward shift in ho lding current that was associated with an increase in membrane conduct ance in most cells (114 of 117). These effects of capsaicin were rever sible upon washout of the drug. Other cells ranging in diameter from 1 5 to 52.5 mu m (n=104) were unaffected in this manner by the 1 mu m co ncentration of capsaicin. Capsaicin-sensitive cells had, on average, s ignificantly longer duration action potentials and expressed significa ntly less I-H than capsaicin-insensitive cells. The relatively long du ration action potentials and/or small cell body diameter and paucity o f I-H observed in most of the capsaicin-sensitive cell is consistent w ith their representing C- or A delta-type sensory neurons.