THE JOURNAL OF COMPARATIVE NEUROLOGY 243~1-12 (1986) Retinal Neurochemistry of Three Elasmobranch Species: zy An Immunohistochemical Approach WILLIAM J. BRUNKEN, PAUL WITKOVSKY, zyxwvu AND HARVEY J. KARTEN zyxw Daniel B. Kirby Eye Institute and the Departments of Ophthalmology and Physiology and Biophysics, New York University Medical Center, New York, New York 10016 W.J.B., P.W.), Departments of Anatomical Sciences (W.J.B.) and Neurobiology and Behavior (H.J.K.) SUNY-Stony Brook, Stony Brook, New York 11794 ABSTRACT We surveyed retinas of zyxwvutsr Raja erinacecr, Mustelus canis, and Squalus acanthias for neurotransmitter substances by using antisera directed against the substances themselves or against their synthesizing enzymes. Both the peroxidase-antiperoxidase (PAP) and indirect fluorescent techniques were employed to visualize the primary antisera. In all three species positive results were obtained with antisera directed against tyrosine hydroxylase CTOH), glutamic acid decarboxylase (GAD), serotonin (5-HT), and leucine enkephalin (Lenk), Antisera directed against glucagon, neurotensin, beta- endorphin, vasoactive intestinal peptide, or bombesin failed to show any specific staining. Immunoreactivity was located in amacrine, interplexiform, and horizon- tal cells as well as in axons of the optic fiber layer. The four antisera labelled different amacrine cell classes, distinguished on the bases of perikaryal morphology and the distribution of cell processes in the inner plexiform layer (IPL). Amacrine cells that labelled with the same marker were seen to have different morphologies in the species studied. Thus, TOH-like immu- noreactivity was distributed in layers 1, 3, and 5 of the IPL in Mustelus but only in layers 1 and 3 in Raja retina. GAD-like immunoreactivity was found diffusely over all layers of the IPL in Raja, but in Mustelus it was confined primarily to layers 1,3, and 5 of the IPL. Lenk- and 5-HT-like immunoreac- tivities showed similar species variations. Two neurochemical classes of interplexiform cell were identified in this study. In Mustelus GAD-like and Lenk-like immunoreactive interplexiform cells were seen whereas in Raja only GAD-positive interplexiform cells were detected. In Squalus no unequivocal demonstration of any interplexiform cell was made with these antisera. The GAD antiserum also labelled a subset of the horizontal cells in the dorsal retina of Raja. TOH and 5-HT-antisera labelled axons in the optic fiber layer of all three species but reactive ganglion cell perikarya were not identified. Key words: retina, GABA, dopamine, serotonin, peptides Putative neurotransmitters have been localized zyxwvu to indi- tion either of transmitter substances or the enzymes in vidual neurons with the aid of three techniques: (1) autora- their synthetic pathways. The vertebrate retina has been diographic demonstration of high-affinity uptake mechanisms for exogenously applied transmitter sub- Accepted August 21,1985. stances or their precursors (Iversen, '71); (2) hiStOflUOreS- cent demonstration of catecholamines and indoleamines (Bjorklund et al., '72); (3) immunohistochemical demonstra- Address reprint requests to Dr. W.J. Brunken, Department of Cell Biology Physiology, Washington University, School of Medi- cine, 660 S. Euclid Ave, St Louis, MO 63110. zyx 0 1986 ALAN R. LISS, INC.