Light- and electron-microscopic studies of the somatostatin-immunoreactive plexus in the cat retina.

Two monoclonal antibodies directed against somatostatin 14 were used to study immunoreactive neurons, their processes and their synapses in the cat retina. In retinal whole-mounts, a sparse population of wide-field displaced amacrine cells was observed predominantly in the ventral retina and near the retinal margin. Processes of these cells ramified mainly in two distinct strata within the inner plexiform layer: one near the inner nuclear layer (INL), and the other near the ganglion cell layer (GCL). The length of immunoreactive fibres within each plexus was measured: 232 +/- 32 mm/mm2 near the INL and 230 +/- 74 mm/mm2 near the GCL in all retinal regions. The immunoreactive processes were studied using electron-microscopic techniques; conventional and some ribbon-containing synapses ("dyads") were found. Immunolabelled processes received input synapses from other amacrine cell processes. These investigations provide further evidence that this cell population has a diffuse, regulatory or modulatory role for visual-information processing in the inner plexiform layer.