Effects of VIIth (facial) nerve degeneration on vasoactive intestinal polypeptide and substance P levels in ocular and orbital tissues of the rabbit

Levels of vasoactive intestinal polypeptide (VIP)- and substance P (SP)-like immunoreactivity were measured in ocular and orbital tissues of albino rabbits. Substantial amounts of VIP were detected in the choroid (22·6±3·6 pmol g −1), and in the lacrimal (13·6±4·4 pmol g −1) and Harderian glands (20·2±4·9 pmol g −1). Somewhat less was found in the anterior uvea (3·6±1·1 pmol g −1), retina (5·4±1·3 pmol g −1) and optic nerve head (4·1 ± 1·1 pmol g −1). Other tissues, including conjunctiva and extraocular muscle showed very little VIP-like immunoreactivity. Seven days after diathermic damage to the region of the pterygopalatine ganglion VIP was virtually eliminated from all these tissues. SP levels were also reduced, notably in the anterior uvea, probably due to concurrent destruction of sensory fibres. Electron microscopy revealed extensive degeneration of unmyelinated axons in the short ciliary nerves and in the choroid. No changes in ocular VIP levels were detected after sympathetic denervation, although a significant rise in SP was observed in the anterior uvea. The decrease in retinal VIP, believed to be confined to the amacrine cells, is considered to be a result of post-operative lid closure, rather than of VIIth nerve degeneration. Nevertheless, with this exception, VIP in ocular and orbital tissues of the rabbit appears to be contained exclusively within parasympathetic fibres of facial nerve origin.