Reinnervation following guanethidine-induced sympathectomy of adult rats.

The reinnervation of various tissues by autonomic neurons has been studied in adult rats which had been sympathectomized by chronic guanethidine treatment (30 or 60 mg/kg/day for 8--15 weeks). In the heart, iris, ileum, mesentery, vas deferens and epididymis, fluorescence histochemistry reveals an almost complete disappearance of adrenergic fibres which is very longlasting. Even after 63 weeks few fluorescent fibres can be seen in these tissues and the density of innervation is not increased by incubation in alpha-methylnoradrenaline. The superior cervical ganglion represents an exception; large numbers of fluorescent fibres but few fluorescent ganglion cells were apparent during recovery. Axon counts carried out by electron microscopy on the vas deferens showed that after recovery for one year the number of axons was similar to that of controls; however, the pattern of innervation was abnormal, small granular vesicles were rarely seen and there was little uptake of 5-hydroxydopamine. On the basis of this evidence and of some pharmacological data it is suggested that there is a limited reinnervation by adrenergic axons accompanied by a great increase in the number of non-adrenergic, possibly cholinergic, axons.