The mechanism of the burst formation in the cardiac ganglion of the lobster (Panulirus japonicus): A re-examination
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Electrical interaction among the ganglion cells in the heart of the lobster (Panulirus japonicus) was studied using intracellular microelectrodes, attention being focused on the identification of the direct driver of the anterior four large cells, i.e. the presynaptic cell responsible for the large EPSPs seen in these cells.
The direct driver was thought to be Cell 5, the most posterior large cell, since (1) spike-like potentials were recorded from Cell 5, just preceding the large EPSPs (Fig.1), (2) intracellular stimulation of Cell 5 caused the large EPSPs (Fig.3), and (3) intracellular stimulation of Cell 6, which was reported to be the direct driver by Friesen (1975b), caused small EPSPs (Fig.4).
Depolarization imposed on an anterior large cell induced a slow potential followed by an after-hyperpolarization in the adjacent large cell. Strong depolarization resulted in the large EPSPs super-imposed on the slow potential (Fig.8), suggesting that the imposed depolarization with the induced slow potential elicited spikes of the direct driver. This result implies a possible feedback from the anterior large cells to their direct driver, Cell 5, through electrotonic spread of slow potential changes.
Simultaneous recordings from the ganglion cells suggested that the small cell was innervated by more posterior cells and by one of the more anterior small cells (Figs. 5 and 6).
Cell 9 showed EPSPs with marked antifacilitation (Fig. 5), resembling the anterior large cells rather than the other small cells.
The large cells did not show any burst activity when the activity of the small pacemaker cell was inhibited by injecting a long hyperpolarizing current into Cell 5 or a small cell (Fig.9), suggesting that the large cells are not the endogenous bursters under the experimental conditions used. Based on these results, the mechanism of the burst formation was considered.
KeywordsGanglion Cell Large Cell Pacemaker Cell Slow Potential Direct Driver
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