This research exploits the cardiac ganglion of crabs and lobsters as a model in which to seek basic knowledge of endogenous neuronal properties, their biophysical bases, the mechanisms by which they are modified and controlled by synaptic interactions, both electrotonically and chemically mediated, mechanisms of integration, and the mode of action on an intergrating neural system of a peptide neurohormone. The ganglion exhibits spontaneity, stable rhythmicity and burst impulse firing. With 9 neurons, it is the smallest neural system that can be isolated functionally intact which exhibits major features of central nervous system functioning. Electrophysiological techniques employing several intracellular and extracellular electrodes simultaneously will be used. They permit monitoring of all impulse traffic, evaluation of synaptic interactions and recording of endogenously generated potential changes such as pacemaker (PMP) and burst forming or 'driver' potentials (DP). The characterization of DPs, recently found to persist in the absense of other responses in tetrodotoxin, will be refined and extended. Functional isolation and biophysical characterization of PMPs will be undertaken. The observations will be extended with intracellular recording from the small cells, recently found to be possible in the local crab, Portunus sanguinolentus. Functional and electronmicroscopical (EM) localization of the sites of PMP and DP generation will be made with extracellular microelectrodes. To analyze endogenous potentials and the modfication by them by neural interactions, chemically mediated synaptic transmission will be pharmacologically blocked. A technique will be sought to 'decouple' the electrotonic junctions; effects will be correlated with EM observable changes. Success in decoupling would open the possibility of utilizing voltage clamping techniques. The cardioactive peptide hormones(s) of crab pericardial organs will be separated and their mode of action in enhancing burst rate, duration and coordination analyzed. Knowledge gained from study of this model system may be expected to contribute and have general relevance to basic understanding of CNS functioning.