GLYCINE IN THE LIZARD RETINA - COMPARISON TO THE GABA SYSTEM

Neurons likely to utilize glycine (GLY) as a neurotransmitter were ide ntified immunocytochemically in the ''all-cone'' lizard retina and the basic anatomical organization of the retinal GLY and gamma-aminobutyr ic acid (GABA) systems was compared. Four types of GLY-immunoreactive (GLY-IR) neurons were identified. Most GLY-IR cells were amacrine cell s, which comprised at least two types. GLY-IR interplexiform cells and ganglion cells also were identified. The first GLY-IR amacrine cell t ype was characterized by a small pyriform soma, located distal to the border of the inner plexiform layer (IPL), and fine dendrites. Most GL Y-IR amacrine cells were of this type and several subtypes may exist w ithin this group. The second amacrine cell type was characterized by a large, distally located soma and a large descending process. This ama crine cell type showed colocalization of GLY-IR and GABA-IR and compri sed about 4% of the total GLY-IR amacrine cell population. Comparison of GLY-IR and GABA-IR on serial sections showed that GLY and GABA were present in largely separate neuronal populations. Generally, GLY-IR a macrine cells were smaller, more distally located in the inner nuclear layer and had finer dendrites than GABA-IR amacrine cells. Distributi on of GLY-IR and GABA-IR in the outer plexiform layer and the inner pl exiform layer differed considerably. Based on the segregated distribut ion of GLY-IR and GABA-IR in the synaptic layers of the lizard retina, GLY and GABA may have fundamentally different roles in retinal proces sing.