In the nervous system, neurons communicate mostly by chemical synapses, where signals are transmitted by transmitter molecules which generate synaptic potentials in the postsynaptic neuron. In addition to the familiar type of fast synaptic potentials which last for tens of milliseconds, there synaptic potentials of much slower time course (lasting for seconds or minutes). These slow potentials may influence the way a neuron integrates its synaptic inputs. Yet, very little is known about the physiological function and underlying mechanism of these responses. The autonomic ganglia are chosen as a model system in this study because, in comparison to the central nervous system, they are much simpler in structure, consisting of only a few neuron types, and much more accessible to experimental manipulations (such as chronic application of drugs, denervation, or iontophoresis and intracellular recording). Furthermore cells in autonomic ganglia receive a rich variety of slow as well as fast synaptic inputs, rather than a single type of fast synaptic potentials as in the vertebrate neuromuscular junction. The last slow excitatory postsynaptic potential, lasting for 5-10 minutes, in the sympathetic ganglia of the bullfrog will be the focus of our attention, because we have evidence suggesting that a luteinizing hormone-releasing hormone (LHRH)-like peptide may mediate this response. We propose to do more experiments to critically test the hypothesis of a peptidergic synapse. We will also investigate the physiological function and the underlying mechanism of this slow synaptic potential.
