Sympathetic postganglionic reinnervation of mesenteric arteries and enteric neurones of the ileum of the rat

The reinnervation by sympathetic postganglionic noradrenergic nerve fibres of a mesenteric artery and the ganglionic plexuses of the mid ileum of young rats has been examined using both physiological and anatomical techniques at various times, up to 6 months, after the interruption of their nerve supply by a freezing technique. Reinnervation of the artery was extremely slow and even 6 months after the operation there were fewer fibres over the surface of the artery than before denervation. The responses to nerve stimulation were smaller than those recorded from control vessels. Two distinct post-junctional membrane potential responses to nerve stimulation were recorded from the arterial smooth muscle cells during the process of reinnervation. These responses were similar to those previously recorded during the development of the sympathetic innervation to mesenteric arteries. The responses within the gut wall to sympathetic postganglionic nerve stimulation reappeared by 3 weeks after the operation. At this time, however, a minority of ganglia had been reinnervated as judged by the histochemical localization of catecholamines. The sympathetic fibres reinnervating both the arteries and the intramural plexuses regenerated from the interrupted axons of the paravascular nerve trunks. There was little or no contribution to the reinnervation pattern as a result of sprouting of existing noradrenergic nerve fibres either on the artery proximal to the point of denervation or within adjacent segments of the gut wall.