The long term objectives of this proposal are to analyze the mechanisms regulating single cell membrane properties, as expressed by electrical excitability and synaptic interactions, in the vertebrate central nervous system. In all aspects of the work the goldfish Mauthner (M-) cell and its associated inputs will serve as the experimental model and the results of intracellular recordings will be correlated with morphological investigations of single identified neurons, following injections of horseradish peroxidase (HRP). We will first continue to explore basic mechanisms of synaptic transmission by analyzing the statistical properties of fluctuations in unitary inhibitory postsynaptic potentials (IPSPs) using experimental paradigms which alter transmitter release. We wish to determine the consequent alterations in binomial release parameters and to test out findings suggesting that each terminal bouton releases transmitter in an all or none manner. Repetitive stimulations, altered divalent cation concentrations, and competitive inhibition by strychnine of the effect of released transmitter will be used. By correlating the statistical analysis with presynaptic morphology we will also study the bases for variations in synaptic efficacy of different presynaptic interneurons. Then, we propose to apply the same analysis to different excitatory inputs to the M-cell from VIIIth nerve branches. Also, the normal separation between electrically and chemically excitable membranes of the M-cell is altered following transection of its axon. We propose to further analyze the ionic basis and membrane distribution of the somadendritic electrogenesis induced by axotomy, and to study the changes in synaptic responsiveness and connectivity which occur during the same time span. Antibodies to the Na+ channel will be used to determine channel distribution, normal vectorial transport of these proteins, and possible alterations following axotomy. In addition, in order to better understand the role of the cytoskeleton in regulating membrane properties, we will analyze these changes following minimal mechanical damage to the axon (local injury restricted to the M-axon) and the effects of agents known to selectively disrupt cytoskeletal components. These studies are relevant to understanding responses of the nervous system to traumatic and toxic damage, and the bases for neuronal plasticity, both under normal conditions and during slow degenerative processes.