Development of the extrinsic sympathetic innervation to the enteric neurones of the rat small intestine.

The development of the sympathetic control of motility of the small intestine of the rat has been studied over the early postnatal period. An inhibition of spontaneous motility was recorded in response to stimulation of the mesenteric paravascular nerve bundles as early as 3-4 days postnatal. At this time, the ganglia of the myenteric plexus were well supplied with noradrenergic nerve fibres, while not all of the ganglia of the submucous plexus were contacted by fibres until 6 days postnatal. The sympathetic innervation to the submucous arteries developed even later and at 9 days postnatal was still less dense than in adults. The onset of sympathetic function in the gut preceded that in the mesenteric arteries by several days. These results further support the hypothesis that the sympathetic neurones supplying the enteric ganglia are a subpopulation of cells distinct from those supplying the blood vessels of the mesentery and submucosa.