Functional and structural changes in mammalian sympathetic neurones following interruption of their axons
The effects of interrupting the axons of principal neurones in the superior cervical ganglion of adult guinea pigs were studied by means of intracellular recording, and light and electron microscopy. Within 72 hr of axon interruption, the amplitude of exitatory postsynaptic potentials (e.p.s.p.s) recorded in principal neurones in response to maximal preganglionic stimulation declined. E.p.s.p.s were maximally reduced (by more than 70% on average) 4 to 7 days following interruption, and failed to bring many cells to threshold. E.p.s.p.s recorded in nearby neurones whose axons remained intact were unaffected. In ganglia in which axon interruption was achieved by means of nerve crush (thus allowing prompt regeneration) mean e.p.s.p. amplitudes began to increase again after about 1 to 2 wk. 1 Mth after the initial injury many neurones had e.p.s.p.s of normal amplitude, and by 2 mth affected neurones were indistinguishable from control cells. Functional peripheral connections were reestablished during the period of synaptic recovery. The mean number of synapses identified electron microscopically in ganglia in which all the major efferent branches had been crushed decreased by 65 to 70% in parallel with synaptic depression measured by intracellular recording. However, synapse counts did not return to normal levels even after 3 mth.
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