Peptide-like immunoreactivity in anuran optic nerve fibers

Abstract

Unilateral section, crush, or ligation of the optic nerve was performed in Rana pipiens. Following optic nerve disruption, Substance P (SP)-, leucine-enkephalin (LENK)-, cholecystokinin octapeptide (CCK8)-, and bombesin (BOM)-like immunoreactivities were analyzed in the retinae and optic nerves. Peptide-like immunoreactivity developed in the retinal stump of disrupted optic nerves within 1 hour after surgery and was retained until at least 30 days. Peptide-positive staining in the retinal stump of the optic nerves was abolished by preabsorption of each of the antibodies/antisera with the corresponding synthetic substances. No massive peptide-like immunoreactivity was observed in the cerebral stump of the ligated side, nor in the contralateral, nonoperated, optic nerve. No change in the pattern of peptide-like immunoreactivity was apparent in the retina ipsilateral or contralateral to the experimental procedure. The optic tectum contralateral to the surgical procedure displayed those changes in peptide-like immunoreactivity described previously following retinal deafferentation (Kuljis and Karten, '82a, '83a). Peptide-like immunoreactivity in the stump retinad to the surgical procedure occurred in the form of beaded and fibrillar elements often ending in an irregular expansion near the lesion site. Fluorescent double-label antibody methods demonstrated that SP-like immunoreactivity is present in different processes than those containing LENK, CCK8, or BOM. Electron microscopical immunocytochemistry revealed that peptide-like immunoreactivity is contained within unmyelinated and possibly also within myelinated axons in the stump retinad to the traumatic procedure. Radioimmunoassay studies of SP demonstrated a four- to sixfold increase in SP-like content in the retinal stump of ligated nerves, compared with both the cerebral stump and with the contralateral nonoperated optic nerves. These findings demonstrate the presence of peptide-like immunoreactivity in retinal ganglion cell processes, which is compatible with either a posttraumatic expression of previously repressed peptide-like phenotypes, or, most likely, with the existence of various classes of peptide-containing retinal ganglion cells. The latter prospect strongly suggests that peptide-specific subsets of retinal ganglion cells terminate in highly specific laminae in the optic tectum (Kuljis and Karten, '81, '82a-83a) and presumably differ in their physiological role in vision. Thus, these observations provide direct anatomo-chemical evidence in support of Lettvin et al. ('59) and Maturana et al. ('60), regarding the differential laminar termination of physiologically diverse classes of retinal ganglion cells in the tectum.