Substance P-like immunoreactive amacrine cells in the cat retina

Substance P-like immunoreactivity was localized by immunocytochemical techniques to two subpopulations of amacrine cells in the cat retina. One cell was a unistratified amacrine with processes ramifying within stratum 4 of the inner plexiform layer. The other cell type was a bistratified cell with processes in both stratum 1 (s1) and stratum 4 (s4). Both cell types were seen with their somas displaced to the ganglion cell layer as well as in the conventional amacrine location in the inner nuclear layer. Substance P cells were present in the greatest density within the area centralis and decreased in number toward the periphery. The ratio of amacrine to displaced amacrine cells also decreased peripherally. However, the coverage by immunoreactive fibers in s4 remained three times that seen in s1. Computer-assisted analysis confirmed the location of substance P-containing processes at 5-15% (s1) and 50-70% (s4) depth levels in the inner plexiform layer. A comparison of substance P-like immunoreactivity in light- and dark-adapted cat retinas showed no apparent differences in the distribution of immunoreactivity due to lighting conditions.