Histological and immunohistochemical studies of the cornea of some animal species : I. reappraisal of cholinergic innervation

Abstract EN

The corneas of rat, mouse and guinea pig were investigated using light and electron microscopy as well as immunohistochemistry.

We, here, examined the cholinergic structures in the cornea by immunohistochemistry for choline acetyltransferase of the two forms, the alternative splice variant from choline acetyltransferase (ChAT) cDNA preferentially located in peripheral nerves (pChAT) and the common type (cChAT).

Positive staining for cChAT was found only in non-neuronal epithelial cells, while pChAT positive staining occurred exclusively in nerve fibers being distributed throughout the cornea.

Such pChAT positive nerve axons were frequently smooth with few varicosities, except for their terminal swellings.

The distribution pattern of pChAT positive nerves was compared with that of three neuropeptides known to be found in corneal nerves, including protein gene product 9.5 (PGP 9.5), substance P (SP) and calcitonin gene-related peptide (CGRP).

The co-localization of pChAT with either of these neuropeptides has been assumed on the base of their great similarity in distribution pattern and closeness in their routes inside the cornea.

From these results it is concluded that rat, mouse and guinea pig corneas have little morphological differences and have a remarkable non-neuronal cholinergic activity in their epithelium together with what can be suggested to be cholinergic nerves represented in the pChAT positive nerve fibers.

The function of acetyl choline in the corneal epithelium and the possible origin and function of corneal cholinergic nerves has been discussed.