An increase of vasoactive intestinal polypeptide-, but not neuropeptide Y-, substance P- or catecholamine-containing nerves in the iris of the streptozotocin-induced diabetic rat.

The distribution of adrenergic and vasoactive intestinal polypeptide-, neuropeptide Y- and substance P-immunoreactive nerves was studied histochemically and immunohistochemically in the irides of rats 8 weeks after the induction of diabetes with streptozotocin. In the control animals, catecholamine-containing, vasoactive intestinal polypeptide- and substance P-immunoreactive nerve fibres were found in the constrictor pupillae, dilator muscle and the ciliary processes. They also formed perivascular nerve plexuses of blood vessels in the dilator muscle. Neuropeptide Y-immunoreactive nerve fibres were only observed in the dilator muscle and ciliary processes. In the irides from diabetic animals, a considerable increase was observed in the fluorescence intensity and/or density of vasoactive intestinal polypeptide-immunoreactive nerves. Some varicosities of the vasoactive intestinal polypeptide-immunoreactive nerves appeared enlarged. In contrast, no apparent change in the density and/or fluorescence intensity of catecholamine-containing, neuropeptide Y- and substance P-immunoreactive nerve fibres was observed in the irides from diabetic animals when compared with controls. The results are discussed in relation to the symptoms of autonomic neuropathy of the irides in diabetes.