title: Characteristics of sodium currents in rat geniculate ganglion neurons.
abstract: Geniculate ganglion (GG) cell bodies of chorda tympani (CT), greater superficial petrosal (GSP), and posterior auricular (PA) nerves transmit orofacial sensory information to the rostral nucleus of the solitary tract. We have used whole cell recording to investigate the characteristics of the Na(+) channels in isolated Fluorogold-labeled GG neurons that innervate different peripheral receptive fields. GG neurons expressed two classes of Na(+) channels, TTX sensitive (TTX-S) and TTX resistant (TTX-R). The majority of GG neurons expressed TTX-R currents of different amplitudes. TTX-R currents were relatively small in 60% of the neurons but were large in 12% of the sampled population. In a further 28% of the neurons, TTX completely abolished all Na(+) currents. Application of TTX completely inhibited action potential generation in all CT and PA neurons but had little effect on the generation of action potentials in 40% of GSP neurons. Most CT, GSP, and PA neurons stained positively with IB(4), and 27% of the GSP neurons were capsaicin sensitive. The majority of IB(4)-positive GSP neurons with large TTX-R Na(+) currents responded to capsaicin, whereas IB(4)-positive GSP neurons with small TTX-R Na(+) currents were capsaicin insensitive. These data demonstrate the heterogeneity of GG neurons and indicate the existence of a subset of GSP neurons sensitive to capsaicin, usually associated with nociceptors. Since there are no reports of nociceptors in the GSP receptive field, the role of these capsaicin-sensitive neurons is not clear.
authors.affiliation: Department of Biologic and Materials Sciences, School of Dentistry, University of Michigan, Ann Arbor, MI 48109-1078, USA.
authors.forename: Shiro
authors.initials: S
authors.lastname: Nakamura
authors.forename: Robert M
authors.initials: RM
authors.lastname: Bradley
mesh_terms: D000200:Action Potentials / Q000187:drug effects / Q000502:physiology*; D000704:Analysis of Variance; D000818:Animals; D000831:Animals, Newborn; D001703:Biophysics; D002211:Capsaicin / Q000494:pharmacology; D004558:Electric Stimulation; D005830:Geniculate Ganglion / Q000166:cytology*; D037102:Lectins / Q000378:metabolism; D008297:Male; D009474:Neurons / Q000145:classification / Q000187:drug effects / Q000502:physiology*; D018408:Patch-Clamp Techniques; D051381:Rats; D017207:Rats, Sprague-Dawley; D018689:Sensory System Agents / Q000494:pharmacology; D026941:Sodium Channel Blockers / Q000494:pharmacology; D015222:Sodium Channels / Q000378:metabolism*; D013779:Tetrodotoxin / Q000494:pharmacology
chemical_list: D037102:Lectins; D018689:Sensory System Agents; D026941:Sodium Channel Blockers; D015222:Sodium Channels; D013779:Tetrodotoxin; D002211:Capsaicin