LANT-6 is a hexapeptide (
H-Lys-Asn-Pro-Tyr-Ile-Leu-OH) isolated from chicken small intestine, which resembles the COOH-terminal half of
neurotensin, except for the amino acid substitutions Lys/Arg and Asn/Arg. The present report concerns the immunocytochemical staining of vertebrate retinas using an antiserum directed against
LANT-6. In the retinas from goldfish, bird and turtle, cells in both the inner nuclear and
ganglion cell layers were labeled, but in the frog no cells were labeled specifically and in the rat only cells in the
ganglion cell layer were labeled. Labeled cell bodies in the inner nuclear layer gave rise to processes which were seen primarily within the following laminas of the inner plexiform layer (IPL): in the goldfish, lamina 3; chicken, laminae 1, 3 and 4; and turtle, laminae 3, 4 and 5. The cell bodies of the labeled neurons in the
ganglion cell layer gave rise to dendrites which entered the IPL and axons which descended to the optic fiber layer. The cells with LANT-6-like immunoreactivity were distributed in both the central and peripheral parts of the retina in all the species examined except frog. Measured by radioimmunoassays, the levels of LANT-6-like-immunoreactivity in extracts of turtle, chicken, and goldfish retinas were 5-30 times those for
neurotensin-like immunoreactivity, however no LANT-6-like immunoreactivity was detected in frog. Multiple chromatographic analyses indicated that while the LANT-6-like immunoreactivity in chicken retina was indistinguishable from synthetic
LANT-6, LANT-6-like immunoreactivity in turtle and goldfish retinas was primarily associated with large molecular forms. Treatment of turtle LANT-6-like immunoreactivity with
pepsin, an
enzyme known to mimic processing for
neurotensin precursors, yielded 3 major
peptides, one of which co-chromatographed with synthetic
LANT-6. The present immunocytochemical localization of LLI within cells in the inner nuclear and
ganglion cell layers, coupled with the biochemical characterization of
LANT-6 in the vertebrate retinas and brains, suggests that
neuropeptides such as
LANT-6 may play a role in visual processing both within the retina and within the visual pathways to the brain.