Synaptic activation of Helix ganglion cells by barium ions.

Experiments were carried out on Helix suboesophageal ganglion cells by use of microelectrodes in order to study the effects of barium ions applied in 1-8 mM concentration. The overall effect of barium ions consisted in a marked depolarization, the thresholds of the ganglion cells, however, were quite different. In case of the most sensitive cells, bursting transformation and paroxysmal depolarization shifts occurred. A minor part of the neurons responded to barium ions with interruption of the spike generation which, in most cases, was accompanied by hyperpolarization. For a considerable part of the cells, the application of barium ions resulted in appearance of repetitive EPSP's and, infrequently, IPSP's. This was ascribed to excitatory effects exerted on the presynaptic terminals. It is concluded that barium ions have at least 2 points of attack in the ganglion: 1, on the soma membrane of the neurones, and 2, on the presynaptic terminals controlling them.