CAPSAICIN AND NICOTINE BOTH ACTIVATE A SUBSET OF RAT TRIGEMINAL GANGLION NEURONS

Nicotine and capsaicin produce many similar physiological responses th at include pain, irritation, and vasodilation. To determine whether ne uronal nicotine acetylcholine receptors (nAChR) are present on capsaic in-sensitive neurons, whole cell patch-clamp recordings were performed on rat trigeminal ganglion cells. It was found that similar to 20% of the total number of neurons tested was activated by both 100 mu M nic otine and 1 mu M capsaicin. Other subsets of neurons were activated by only one of these compounds, whereas a fourth subset was not activate d by either compound. At -60 mV, the magnitude of the capsaicin-activa ted currents was about three times larger than the magnitude of the ni cotine-activated currents. The current-voltage relationship of the nAC hR exhibited marked rectification, such that for voltages greater than or equal to 0 mV the current was essentially zero. In contrast, the c urrent-voltage relationship of the capsaicin-activated current was ohm ic from +/-60 mV. These data indicate the existence of subsets of caps aicin-sensitive afferent neurons.