Noval mechanism for neural control of muscle in crustacean heart : analysis of graded neuromuscular transmission

神经突触和神经肌肉接头中的信号传递是通过全或无神经冲动实现的。然而，最近，分级突触传递已被发现在中枢神经系统的信号传递中发挥重要作用。即使在神经肌肉接头中，也有实验证明，运动神经元的突触前神经末梢依赖于膜电位的变化释放递质，并在肌肉的突触后膜上产生分级的接头电位。然而，运动神经元通常远离靶肌肉，神经肌肉接头中的分级传递尚未报道。许多甲壳类动物的心脏是神经源性的，心跳是由心神经节发起的。等足类Ligia的心神经节由六个具有起搏和运动功能的神经元组成，这些神经元通过电连接同步放电。在心脏神经节中产生的神经冲动的周期性爆发诱导心肌的动作电位并引起心跳。在Ligia心脏中，心肌也具有起搏器特性，而心神经节作为主要起搏器，通过神经肌肉接头将肌肉节律带入神经节节律。在本研究中，进一步研究了心神经节和心肌之间的神经肌肉传递。结果表明，心神经节对心脏粘液的调控不仅通过脉冲传递，而且通过分级传递。这是首次报道神经肌肉突触传递的功能分级。包括这些结果的论文已经发表。

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.