Double-label analyses of the coexistence of somatostatin with GABA and glycine in amacrine cells of the larval tiger salamander retina.

To investigate the possible GABAergic nature of somatostatin-immunoreactive neurons of the larval tiger salamander retina, somatostatin immunocytochemistry was combined with either gamma-aminobutyric acid (GABA) immunocytochemistry or autoradiography of GABA high-affinity uptake. A total of 1,062 somatostatin cells were visualized in these studies. Double-label immunocytochemistry revealed that 96.3% of somatostatin-immunoreactive cells expressed GABA immunoreactivity. Double-label studies combining somatostatin immunocytochemistry with autoradiography of GABA high-affinity uptake revealed a slightly lower percentage (93%) of colocalization. Double-labelled cells were identified as Type 1, Type 2 and displaced amacrine cells. The small percentage of somatostatin-immunoreactive cells that did not co-label for GABA were identified as Type 1 amacrine cells. An analysis of retinal sections processed for double-label immunocytochemistry revealed that approximately 5% of GABA-immunoreactive cells in the amacrine and ganglion cell layers co-label for somatostatin. Somatostatin immunocytochemistry was combined with autoradiography of glycine high-affinity uptake to examine whether tiger salamander somatostatin-amacrine cells express this glycine marker. A total of 100 somatostatin-immunoreactive amacrine cells were visualized in double-label preparations. None of these cells were observed to exhibit glycine high-affinity uptake.