Species differences in choroidal vasodilative innervation: evidence for specific intrinsic nitrergic and VIP-positive neurons in the human eye.

PURPOSE There is evidence that vasodilation of choroidal vessels results from facial nerve stimulation. To obtain more information about the role of this innervation, the authors examined the presence and spatial organization of nitrergic and vasoactive intestinal peptide (VIP) immunoreactive nerves in the human choroid. For comparison, the choroid of rabbit and rat eyes, with different types of retinal vascularization and no fovea, were studied. METHODS Whole mounts of five human, nine rat, and two rabbit choroids were stained for NADPH-diaphorase. In addition, immunocytochemical staining was carried out on tangential frozen sections of two human choroids using antibodies against nitric oxide synthase (NOS), synaptophysin, and VIP. RESULTS In all species, a perivascular network of diaphorase-positive nerve fibers with varicose terminals accompanied the arteries and arterioles of the choroidal stroma. A striking difference to rat and rabbit choroids was the presence of numerous positively stained ganglion cells in human choroids. Positively stained axons connected the neurons with each other and with the perivascular network. Most of the ganglion cells were concentrated in the temporal-central region, adjacent to the fovea. Immunocytochemically, the choroidal ganglion cells were immunoreactive for NOS. Some ganglion cells stained for VIP. Staining for synaptophysin demonstrated varicose terminals innervating the perikarya of the ganglion cells. Many of these terminals stained for NOS and VIP. CONCLUSIONS The presence of an intrinsic nerve cell plexus that is specifically localized in human eyes in the temporal-central portion of the choroid indicates a functional significance of the nitrergic choroidal innervation for the fovea.