Nicotinic acetylcholine receptors (nAChRs) were identified in a subpopulation of cultured adult rat trigeminal ganglia (TG) neurons by whole-cell patch-clamp recordings. Dimethylphenylpiperazinium (DMPP), a nAChR agonist, induced inward currents in 21/68 of TG neurons having soma diameters greater than 28 microns. These currents were inhibited by hexamethonium, mecamylamine and atropine, indicating the presence of neuronal ganglionic-type nAChRs. This interpretation is consistent with the finding that the nicotine- or DMPP-induced currents were not inhibited by alpha-bungarotoxin (alpha-Bng) in 5 of the 9 cells tested with this compound. However, in 2 of the 9 cells tested, the DMPP-induced currents were completely inhibited by alpha-Bng, and in the remaining two cells tested, the currents were partially inhibited by alpha-Bng. About 22% of the cells having diameters > or = 28 microns were specifically labeled with FITC-labeled alpha-Bng, whereas only 2% of the cells with soma diameters < 28 microns were labeled. These data taken together suggest that more than one subtype of nAChR is present in TG.