PHYSIOLOGY OF MUSCARINIC SYNAPSES IN SYMPATHETIC GANGLIA

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Sympathetic ganglia convey commands that implement reactions to bodily stress. The long-term goals of this project are to understand how three slow synaptic potentials contribute to the normal integrative function of bullfrog sympathetic ganglia and to identify factors that regulate the expression of muscarinic synapses in ganglia. The working hypotheses for this proposal are that 1) ganglia contain physiologically specialized and antomically separate functional channels that modulate different classes of peripheral end organs, 2) slow potentials enable ganglion cells to generate characteristic patterns of activity to drive optimally their specific targets and 3) the synaptic connections of ganglion cells regulate their expression of muscarinic synapses. Isolated preparations containing the ninth and tenth paravertebral ganglia will be used to study the muscarinic excitatory postsynaptic potential (epsp), the muscarinic inhibitory post synaptic potential (ipsp) and a peptidergic epsp mediated by leuteinizing hormone releasing hormone (LHRH). Three physiologically identifiable types of neurons (fast B, slow B, C) within these ganglia innvervate viscera in the lower abdomen (e.g. bladder) and other targets in the hindlimbs (e.g. exocrine glands, vasculature, sensory receptor). However, the relation between these cell types and the hypothesized functional channels is uncertain. A combination of electrophysiological and anatomical methods will be used to provide a detailed description of ganglionic synapses, the morphology of identified sympathetic neurons and the projections of identified cells into cutaneous, motor and visceral branches or peripheral nerves. Next, reports that muscarinic epsps are variable in their voltage-sensitivity will be pursued to determine how heterogeneity in muscarinic excitation is related to the subclasses of B cells and how muscarinic epsps differ in their effects upon repetitive firing. Then muscarinic inhibition of repetitive firing will be analyzed by voltage clamping C cells. After the full range of muscarinic modulation of repetitive firing has been characterized, the influence of specific connections between the ganglia, cord and periphery upon the differential expression of muscarinic responses in ganglion cell types will be studied during axotomy, denervation and re-innervation.