The cardiac ganglion of the mudpuppy, Necturus maculosus, is an excellent model system for analysis of synaptic integration within a vertebrate cardiac ganglion. Two neuron types are present: parasympathetic postganglionic neurons and SIF cells. The SIF cells contain a number of neurotransmitters including: catecholamines, 5-HT, a substance P-like peptide and a galanin-like peptide. Further, there is an extensive substance P/GGRP immunoreactive afferent fiber input into the cardiac ganglion which make pericellular complexes around postganglionic neurons and SIF cells. We will establish the mechanism(s) by which the afferent fiber and SIF cell input influence the activity of the postganglionic neurons. The following specific questions will be addressed: a) Determine the function and source of the afferent transmission and on the conductance properties of the postganglionic neurons. Immunocytochemical and tracing studies will be done to establish the central origin (i.e., vagal versus spinal) and the peripheral distribution of the substance P/GGRP-immunoreactive fibers. b) Establish the role of SIf cells in the cardiac ganglion. Sif cells will be stimulated while recording from adjacent postganglionic neurons to test whether SIF cells influence postganglionic neuron activity. We will test whether the SIF cells respond to ACh, substance P and CGRP to establish whether these cells are activated by preganglionic and/or afferent transmitters. The action of other neurotransmitters, present in SIF cells such as 5-HT and dopamine, on the membrane properties of postganglionic neurons and ganglionic transmission will be tested. c) Establish the mechanism(s) by which galanin alters, excitability of the postganglionic neurons. The influence of galanin on membrane currents in isolated postganglionic neurons will be determined using cell attached patch and whole cell voltage clamp techniques. The kinetic properties of the galanin activated potassium conductance will be determined using cell attached patch and whole cell voltage clamp techniques. The kinetic properties of the galanin activated potassium conductance, will be determined from single channel activity. An analysis of galanin induced alteration of calcium and potassium conductances will be performed using whole cell voltage clamp procedures. This project will provide important new information in three areas: a) the mechanism(s) of action of specific neurotransmitters on an identified postsynaptic cell, b) the role(s) of SIF cells in autonomic ganglia, and c) the role of afferent fiber input and type (s) of integration which may occur in vertebrate cardiac ganglia that are important in local reflex control of cardiac function.
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