Characteristics of Calcium 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 (rNST). We used whole cell recording to study the characteristics of the Ca2+ channels in isolated Fluorogold-labeled GG neurons that innervate different peripheral receptive fields. PA neurons were significantly larger than CT and GSP neurons, and CT neurons could be further subdivided based on soma diameter. Although all GG neurons possess both low voltage–activated (LVA) “T-type” and high voltage–activated (HVA) Ca2+ currents, CT, GSP, and PA neurons have distinctly different Ca2+ current expression patterns. Of GG neurons that express T-type currents, the CT and GSP neurons had moderate and PA neurons had larger amplitude T-type currents. HVA Ca2+ currents in the GG neurons were separated into several groups using specific Ca2+ channel blockers. Sequential applications of L, N, and P/Q-type channel antagonists inhibited portions of Ca2+ current in all CT, GSP, and PA neurons to a different extent in each neuron group. No difference was observed in the percentage of L- and N-type Ca2+ currents reduced by the antagonists in CT, GSP, and PA neurons. Action potentials in GG neurons are followed by a Ca2+ current initiated afterdepolarization (ADP) that may influence intrinsic firing patterns. These results show that based on Ca2+ channel expression the GG contains a heterogeneous population of sensory neurons possibly related to the type of sensory information they relay to the rNST.