Rearrangement of synapses on guinea-pig sympathetic ganglion cells after partial interruption of the preganglionic nerve.

The rearrangement of synaptic connexions maintained by the intact preganglionic axons was examined with intracellular recording after partial denervation of the guinea-pig superior cervical ganglion. After sprouting, the number of superior cervical ganglion cells innervated by each residual preganglionic axon was increased by a factor of about three. These new synaptic connexions were stable in the absence of reinnervation of the ganglion by the injured axons. The intact preganglionic axons that sprouted in the superior cervical ganglion abandoned most of the synaptic connexions they normally maintain with neurones in the stellate ganglion. Several months after the partial denervation some of the injured preganglionic axons had usually re-established synaptic connexions with neurones in the superior cervical ganglion. However, both the rate and final degree of reinnervation were poor compared to reinnervation after complete denervation. During reinnervation of the superior cervical ganglion by the injured axons, there was a reduction in the degree of innervation of this ganglion by the sprouting axons. These results support the idea of an ongoing competition between preganglionic axons, and indicate some of the factors that probably determine the synaptic balance under normal and experimental conditions.