EFFECTS OF POSTGANGLIONIC NERVE-SECTION ON SYNAPTIC TRANSMISSION IN THE SUPERIOR CERVICAL-GANGLION OF THE GUINEA-PIG

In sympathetic neurons, axotomy induces a marked depression in synapti c transmission. We asked whether the decrease in synaptic efficacy obs erved in a given axotomized cell is more severe if most of the postsyn aptic neurons are also injured. Accordingly, we studied if the synapti c depression induced by axotomy in neurons with axons running in a pos tganglionic nerve is influenced by section of other postganglionic ner ves. The excitatory postsynaptic potentials evoked by preganglionic st imulation were recorded intracellularly in an in vitro preparation of the superior cervical ganglion. Eight days after cutting the inferior postganglionic nerve, postsynaptic potentials recorded from neurons pr ojecting through this nerve were smaller (median = 6 mV, n = 62) than the controls (median = 34 mV, n = 89), but were similar to those found after sectioning the inferior nerve plus most postganglionic nerves ( median = 5 mV, n = 70). If the inferior nerve was left intact, but mos t postganglionic branches were cut, the synaptic potentials recorded f rom inferior nerve neurons were normal (median = 33 mV, n = 77). It is concluded that the synaptic depression induced by axotomy in a sympat hetic neuron is not affected by axotomy of nearby ganglion cells, even if they share part of their presynaptic axons. This suggests that the effect of axotomy is restricted to the synaptic terminals on the inju red neuron.