Catestatin-like immunoreactivity in the rat eye

The aim of the study was to investigate the presence and distribution of the chromogranin A-derived peptide catestatin in the rat eye and trigeminal ganglion by immunofluorescence using an antibody which recognizes not only free catestatin but also larger fragments containing the sequence of catestatin. Western blots were performed in an attempt to characterize the immunoreactivities detected by the catestatin antiserum. Sparse immunoreactive nerve fibers were visualized in the corneal stroma, in the chamber angle, in the sphincter muscle but also in association with the dilator muscle, in the stroma of the ciliary body and processes, but dense in the irideal stroma, around blood vessels at the limbus and in the choroid and in cells of the innermost retina representing amacrine cells as identified by colocalization with substance P. Furthermore, catestatin-immunoreactivity was detected in the trigeminal ganglion in small to medium-sized cells and there were abundant catestatin-positive nerve fibers stained throughout the stroma of the ganglion. Double immunofluorescence of catestatin with substance P revealed colocalization both in cells of the trigeminal ganglion as well as in nerve fibers in the choroid. The immunoreactivities are present obviously as free catestatin and/or small-sized catestatin-containing fragments in the retina and ocular nerves but as large processed fragments as well, weak in the retina and more prominent in remaining ocular tissues, possibly in endothelial cells. This indicates that this peptide is a constituent of sensory neurons innervating the rat eye and the presence in amacrine cells in the retina is typical for neuropeptides. Catestatin is biologically highly active and might be of significance in the pathophysiology of the eye.