K. Koketsu

Characteristics of the slow inhibitory postsynaptic potential of bullfrog symphathetic ganglion cells

Abstract PREGANGLIONIC volleys evoke in the curarized superior cervical ganglion of turtles and rabbits (1,2) a positive wave (P potential) which is followed by a late occurring negative wave (LN potential). Tetanic stimulation enhances the P potential as well as the LN potential, whereas atropine completely abolishes both of them (2,3,4). Inasmuch as dibenamine depresses the P potential preferentially over the LN potential (4), and reserpine selectively depresses the P potential (5), it has been suggested that the P potential is produced by adrenaline which is released from the chromaffin cells in the sympathetic ganglion (4,5,6). A long lasting hyperpolarization, which corresponds to the P potential, has been recorded intracellularly from the postsynaptic neurons of sympathetic ganglia of rabbits, frogs and bullfrogs (7,8,9). The P potential can be considered to be an inhibitory postsynaptic potential (IPSP) by reason of its trans-synaptic occurrence and its polarity (cf. 4), although there is no experimental evidence that it actually inhibits ganglionic transmission. Moreover, there is a report contrary to the idea that catecholamines act as the mediator of the P potential (10). Nevertheless, it was considered worthwhile to study the mechanism of the P potential, regardless of the kind of transmitter involved, in comparison with the IPSP of other cells in general. The present communication deals with the inhibition of postganglionic discharges caused by the P potential, and with the nature of the P potential which differs in characteristics from that of other cells so far studied.

A functional connection between postganglionic neurons in a bullfrog sympathetic ganglion

Abstract A tetanic antidromic stimulation of a group of ganglion cells in a nicotinized bullfrog sympathetic ganglion induced a slow and small hyperpolarization in the unstimulated, adjacent group of ganglion cells. Except for its enhancement by atropine, the hyperpolarization had a property essentially similar to that of the slow IPSP. In addition, the afterdischarge of the adjacent ganglion cells, which was elicited by preganglionic stimulation, in the presence of nicotine and atropine was suppressed at the time the hyperpolarization was generated in these neurons. The results indicate that the antidromic postganglionic volleys cause the liberation of a noncholinergic transmitter substance from the activated ganglion cells or possibly from some interneurons, and that the transmitter brings about in the unstimulated, neighboring ganglion cells a slow hyperpolarization which inhibits the generation of the after-discharge. Thus it is evident that a functional interrelation exists among the ganglion cells in a sympathetic ganglion.

The presynaptic potential produced by postsynaptic activation in bullfrog sympathetic ganglia.

Abstract In amphibian sympathetic ganglia, a transient membrane depolarization was produced at the intraganglionic portion of preganglionic nerve fibers when ganglion cells were activated antidromically. Such a depolarization was produced by the action of a chemical transmitter which was not acetylcholine but an unidentified substance released from some cellular elements in the ganglion. These results suggested that the preganglionic nerve terminals possess some noncholinergic receptors in addition to the cholinergic presynaptic receptors.