Voltage and synaptically activated channels in brainstem preganglionic parasympathetic cardiac neurons

This report briefly describes the voltage gated and synaptically gated currents in parasympathetic cardiac neurons that originate in the medulla and project to the heart. Fluorescent tracers are used to identify these neurons within an in-vitro slice and patch clamp electrophysiological techniques allow us to control intracellular voltage and characterize the electrophysiology and pharmacology of voltage dependent and post-synaptic ligand gated channels. Depolarization of these neurons to voltages more positive than -50 mV activate tetrodotoxin (TTX) sensitive inward sodium currents, in addition to two types of outward potassium currents. The potassium currents are the I(A) and I(DR) type of potassium channels which are blocked by 4- aminopyridine (4AP) and tetraethylammonium (TEA), respectively. Stimulation of another nucleus, the nucleus tractus solitarius (NTS), which receives cardiovascular sensory information, activates a monosynaptic pathway to these neurons. Glutamate is synaptically released from these NTS neurons which activates both long lasting (>200 ms) N-methyl-D-Aspartate (NMDA) and transient non-NMDA postsynaptic currents in parasympathetic cardiac neurons