| Research Abstract |
Signal transmission in neural synaps and neuromuscular junctions is achieved by all-or-none nerve impulses. Recently, however, graded synaptic transmission has been found to play an important role for signal transmission in the central nervous systems. Even in the neuromuscular junction, it has been demonstrated experimentally that, the presynaptic nerve terminal of the motoneuron release transmitter depending on changes in the membrane potential and produce graded junctional potentials in the post synaptic membrane of the muscle. Howener, the motoneuron is generally distant from the target muscle and graded transmission in the neuromuscular junction has not been reported. The heart of many crustaceans is neurogenic and the heartbeat is initiated by the cardiac ganglion. The cardiac ganglion of the isopod Ligia is composed of six neurons with pacemaker and motor functions and these neurons fire synchronously through electrical connections. Periodic bursts of nerve impulses generated in the cardiac ganglion induce action potentials of the cardiac muscle and cause heartbeats. In the heart of Ligia, the cardiac muscle also has pacemaker propertied, while the cardiac ganglion acts as a primary pacemaker entraining the mucle rhythm into the ganglion rhythm through the neuromuscular junctions. In the present study, neuromuscular transmission between the cardiac ganglion and cardiac muscle was further examined. The results showed that the cardiac ganglion control the cardiac mucel through not only impulse-mediated transmission but also graded transmission. This is the first report of functional graded synaptic transmission in the neuromuscle juction. The paper including these results has been published.
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