Development of sympathetic innervation to proximal and distal arteries of the rat mesentery.

The changes which occur during the post-natal development of sympathetic innervation to proximal and distal arteries of the rat mesentery have been examined using intracellular recording and histochemical techniques. In the youngest animals examined, single perivascular stimuli initiated slow depolarizing potentials which were not calcium-dependent. After day 4, single stimuli failed to initiate membrane potential changes in a proportion of preparations. This stage coincided with the period of extensive ramification of sympathetic nerve fibres over the surface of the arterioles. From day 9 onwards, membrane potential changes were again initiated by single stimuli in the distal arteries. These responses were distinct from those recorded from the younger animals and in many ways resembled excitatory junction potentials recorded from the arteries of mature animals. There was a gradient in the development of the innervation to the arteries of the rat mesentery, with that to the distal vessels maturing earlier than that to the more proximal vessels.