[Convergence of preganglionic fibers on neurons of the rabbit superior cervical ganglion].

Responses of neurons of the rabbit superior cervical ganglion to stimulation of the fascicles of preganglionic fibres and tonic activity of these neurons were recorded with intracellular electrodes in vitro and in situ, respectively. Marked convergence of preganglionic fibres onto ganglion cells was found: 8.5 +/- 1.2 fibres, on the average, converged on each cell. It was found that each ganglionic neuron received two preganglionic inputs: single and multiple. The single input was formed by a single preganglionic fibre which evoked EPSP strong enough to trigger a postsynaptic spike. The multiple input was formed by two or more converging preganglionic fibres which could trigger a postsynaptic spike only through summation of the EPSPs they evoked. The interspike intervals for these two preganglionic inputs in tonic activity of neurons were described by distributions of different types: Gaussian and Poisonian ones. Those two distributions were typical of single and multiple inputs, respectively.