LOCALIZATION OF NEUROPEPTIDE-IMMUNOREACTIVE NEURONS IN THE HUMAN RETINA

Light microscopic immunocytochemistry was utilized to localize populations of neurons in the human retina immunoreactive for the following neuroactive peptides: substance P (SP), vasoactive intestinal polypeptide (VIP), somatostatin (SOM) and LANT-6-(H-Lys-Asn-Pro-Tyr-Ile-Leu-OH), a hexapeptide which is identical to the C-terminal half of neurotensin except for the amino acid substitutions Lys/Arg and Asn/Arg. The majority of SP immunoreactive cells were amacrine cells whose pear-shaped or oval cell bodies (about 8 μm in diameter) were situated in the proximal parts of the inner nuclear layer. A small number of SP-stained somas (about 10-15 μm in diameter) were located in the ganglion cell layer and were designated as those of displaced amacrine cells. The SP-immunoreactive processes were distributed in sublamina 1, 3 and 5 with the most dense plexus being found in sublamina 3 of the inner plexiform layer. VIP-positive cell bodies (8-9 μm) were oval or pear-shaped and were situated in the innermost cell rows of inner nuclear layer. The majority of fine VIP-immunoreactive processes extended to sublamina 3 with only a few branches distributing in sublamina 1 of the inner plexiform layer. The SOM-stained cell bodies (10-11 μm) were round and were situated in the innermost cell rows of inner nuclear layer. SOM-positive processes were observed in sublamina 1 and 2 of the inner plexiform layer. The LANT-6 immunoreactive cell bodies (12-22 μm) were either oval-, round- or pyriform-shaped and were situated in ganglion cell layer. The labeled cell bodies occasionally gave rise to dendrites which entered the inner plexiform layer and apparent processes that emanated from the proximal pole of LANT-6 cells and entered the optic fiber layer. The observations reported here provide the first evidence for the presence of LANT-6-immunoreactive neurons in the human retina and extend previous studies of the localization in humans of SP-, VIP- and SOM-immunoreactive retinal neurons. © 1990.