Impulse Activity and Pattern of Large and Small Neurones in the Cardiac Ganglion of the Lobster, Panulirus Japonicus

The cardiac ganglion of the lobster, which contains five large and four small cells (Alexandrowicz, 1932), produces integrated patterns of burst discharges. Maynard (1955, 1966) described how this ganglion may be compared to a miniature central nervous system, and pointed out that integrative processes occurring within the ganglion are of great interest because analyses of a simple nervous system may be an approach to the study of integration in complex nervous systems. Electrophysiological investigations of these ganglion cells have been reviewed by Hagiwara (1961). Intra-cellular studies have been made in detail on large cells of The conclusion concerning their activity is as follows: large cells (followers) are innervated by common presynaptic nerve fibres from small cells (pacemakers), and potential changes during the burst are several kinds of synaptic potentials and spikes. This conclusion is not, however, valid for the Homarus ganglion. Cooke (1966) and Connor (1969) have studied the intracellular activity of its large cells. Connor (1969) has concluded that potential deflexions are due toendogenous activity of the respective neurones and not to synaptic potentials. In Panulirus evidence was provided that two small cells of different types in the repetitive discharge pattern innervate large cells, controlling their activities; one of the two (primary pacemaker neurone) induces small synaptic potentials, and the other (secondary pacemaker neurone) induces large synaptic potentials (Tazaki, 19716). Fig. 1 illustrates a typical pattern of burst in a large-cell soma. The burst was mainly composed of large and small synaptic potentials with small-sized spikes (Fig. 1 A). This was readily shown by the experiment of current injection. Separation of large and small synaptic potentials was performed by applying hyperpolarizing current pulses with varying intensity during the burst discharge. Large synaptic potentials remained with a weak current pulse (Fig. 1B), but they were completely eliminated with a strong current pulse (Fig. 1C). On the other hand, small synaptic potentials usually remained during the applied hyperpolarization, and their amplitude increased. This phenomenon has been interpreted as follows: there is electrotonic interaction between large follower and small pacemaker neurones (Watanabe & Bullock, i960). Apparently, the electrotonic spread was almost negligible between followers and primary pacemaker, while it was rather effective between followers and secondary