PARASYMPATHETIC INNERVATION OF THE RAT CORNEA

The mammalian cornea receives a dense sensory innervation and a modest sympathetic innervation. The purpose of the current study was to dete rmine if the rat cornea is also innervated by parasympathetic nerves. In the first set of experiments, unilateral combined sympathetic and s ensory ocular denervations were performed in adult rats by surgical re moval of the superior cervical ganglion and intracranial transection o f the trigeminal ophthalmomaxillary nerve. Completeness of the denerva tion procedure was verified postmortem by a variety of macroscopic and immunohistochemical methods. Five to twelve days later, the corneas w ere serially sectioned tangential to the ocular surface and processed immunohistochemically with antibodies against the pan-neuronal markers , protein gene product 9.5 (PGP-9.5) and peripherin. In every animal a small, but constant, population of corneal and limbal immunoreactive fibers were unaffected by the surgical denervations and were concluded to derive from parasympathetic ganglia. In the second set of experime nts, the origins of the rat corneal innervation were determined by app lying the neuroanatomical tracer, wheat germ agglutinin-horseradish pe roxidase (WGA-HRP) to the central cornea. Two to four days later, the trigeminal, superior cervical, ciliary, accessory ciliary and pterygop alatine ganglia were sectioned and analysed for the presence of HRP-la beled neurons. Examination of the corneal application site and associa ted ocular tissues revealed no evidence of tracer spread into neighbou ring structures, Small numbers (0-6 per animal) of HRP-labeled neurons were observed in the ipsilateral ciliary and accessory ciliary gangli a of most animals. The results of these carefully controlled studies p rovide strong anatomical evidence of a modest parasympathetic innervat ion of the rat cornea. (C) 1998 Academic Press Limited.