Capsaicin preferentially affects small-diameter acutely isolated rat dorsal root ganglion cell bodies

The effects of capsaicin were tested on 221 acutely isolated dorsal root ganglion neurons of the rat, which ranged in diameter from 15 to 55 microns. In a sub-population of these cells, ranging in diameter from 17.5 to 33 microns (n = 117), capsaicin (1 microM) produced an inward shift in holding current that was associated with an increase in membrane conductance in most cells (114 of 117). These effects of capsaicin were reversible upon washout of the drug. Other cells ranging in diameter from 15 to 52.5 microns (n = 104) were unaffected in this manner by the 1 micron concentration of capsaicin. Capsaicin-sensitive cells had, on average, significantly longer duration action potentials and expressed significantly less IH than capsaicin-insensitive cells. The relatively long duration action potentials and/or small cell body diameter and paucity of IH observed in most of the capsaicin-sensitive cells is consistent with their representing C- or A delta-type sensory neurons.