Multiple innervation of normal and re‐innervated parasympathetic neurones in the frog cardiac ganglion.

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Abstract
Multiple innervation of parasympathetic neurons was examined in normal and re-innervated frog cardiac ganglia. The number of synaptic inputs impinging on individual ganglion cells was determined by recording intracellularly and stimulating the vagosympathetic nerves. In unoperated cardiac ganglia most neurons (93%) received a large, suprathreshold synaptic input. Some ganglion cells received additional, small synaptic inputs. Roughly equal numbers of cells encountered were singly and doubly innervated, and only 8% received more than 2 inputs. Re-innervation of cardiac ganglion cells began 3 wk after bilateral crush of the vagosympathetic nerves. By 7 wk more than 90% of the ganglion cells were re-innervated. At this stage the pattern of multiple innervation was significantly different than normal: doubly innervated neurons outnumbered singly innervated ones, and 31% of the cells encountered received more than 2 inputs. This pattern was stable for at least 1 yr. Apparently, polyneuronal innervation of cardiac ganglion cells is more widespread after re-innervation than it is normally and that synapse elimination does not occur during re-innervation of these cells.