GABAergic and glycinergic pathways to goldfish retinal ganglion cells: An ultrastructural double label study

An ultrastructural double label has been employed to compare GABAergic and glycinergic systems in the inner plexiform layer (IPL) of the goldfish retina. Electron microscope autoradiography of $\sp3$H-GABA and $\sp3$H-glycine uptake was combined with retrograde HRP-labeling of ganglion cells. When surveyed for distribution, GABAergic and glycinergic synapses were found onto labeled ganglion cells throughout the IPL. This reinforces previous physiological work that described GABAergic and glycinergic influences on a variety of ganglion cells in goldfish and carp: These physiological effects often reflect direct inputs. This dissertation presents the following findings regarding GABAergic amacrine cells: (1) Double-labeled synapses are presented as evidence of input by type Ab amacrine cells to on-center ganglion cells. (2) At least one population of GABAergic type Aa sustained-off amacrine cell is proposed, based on profuse GABAergic inputs onto bipolar cells in sublamina a; similar GABA-labeled profiles are shown to synapse onto HRP-labeled probable off-center ganglion cells. Synapses between proposed type Aa amacrine cells are also reported. Apparently, GABAergic amacrine cells not only contribute the predominant feedback to on- and off-center bipolar cells, but feed-forward inputs to on- and off-center ganglion cells as well. (3) Ultrastructural evidence presented supports a bistratified, GABAergic transient amacrine cell, previously described by intracellular recording and dye-injection. Gap junctions are evident between them, as well as GABAergic synapses onto HRP-labeled ganglion cell profiles, in both dendritic strata. Two morphologies of glycinergic amacrine cell are proposed, based on light microscope autoradiography, (1) the previously described small pyriform cell and (2) a multipolar cell. Their dendritic statification and connectivity are as yet indistinguishable. No interaction between glycinergic profiles has been observed. In notable contrast to GABAergic amacrine cells in goldfish, glycinergic interactions with bipolar cells are extremely rare