The neurotensin-related hexapeptide LANT6 is found in retinal ganglion cells and in their central projections in pigeons.

Previous biochemical and immunohistochemical studies have shown that the neurotensin-related hexapeptide LANT6 is widespread and abundant in the avian nervous system. In the present study, immunohistochemical techniques were used to show that LANT6 is present in numerous cells of the retinal ganglion cell layer in pigeons. Consistent with the possibility that these LANT6+ retinal cells might be retinal ganglion cells, it was found that (1) the distribution of LANT6+ fibers and terminals in the central retinal target areas matched the distribution of central retinal projections; (2) the LANT6+ fibers and terminals are eliminated from retinal target areas by transection of the contralateral optic nerve; and (3) LANT6+ retinal cells in the ganglion cell layer can be retrogradely labeled by injections of fluorogold in the tectum. These results suggest that LANT6 may be utilized as a neuroactive substance by the central terminals of numerous retinal ganglion cells in birds. Similar anatomical findings have been previously reported for members of several other vertebrate groups, giving rise to the possibility that LANT6 (or its homologues in nonavians) may be a phylogenetically ubiquitous neuroactive substance used by retinal ganglion cells.