FMRFamide-immunoreactive retinopetal fibers in the frog, Rana pipiens: demonstration by lesion and immunocytochemical techniques.

Retinopetal fibers, immunoreactive to a molluscan cardioexcitatory-like peptide (FMRFamide-ir), were examined in Rana pipiens with the use of immunocytochemical and lesion techniques. In intact frogs, FMRFamide-ir retinopetal fibers were found in the optic nerve, optic nerve head, and nerve fiber, ganglion cell and inner plexiform layers of the retina. Presumptive monostratified amacrine cells were also labeled. As observed in flat-mounted retinas, the retinopetal fibers radiated from the optic disc toward the peripheral retina, branched many times along their course and were more prevalent in the dorsal retina. Crushing the optic nerve eliminated retinopetal fibers from all regions except the cerebral stump of the optic nerve, indicating that this projection was of central origin. Bilateral prechiasmatic lesions completely eliminated retinopetal fibers from both retinas, indicating that the fibers arose from the rostral forebrain. Within the rostral brain, FMRFamide-ir perikarya were found in olfactory bulb, diagonal band, medial septum, anterior commissure area, and two regions of the posterior preoptic area. Olfactory bulbectomy and midforebrain lesions equally reduced the numbers of these fibers in the retina, implicating the nervus terminalis as a possible source for some of the retinopetal projection. These data will serve as a foundation for future studies on the function of retinopetal fibers in the frog retina.