Neurochemical heterogeneity of retinal bipolar cells

Retinal bipolar cells show neurochemical changes in response to retinal insult, which could have profound effects on retinal function or recovery after insult however, the neurochemistry of bipolar cells is incompletely understood. METHODS The distribution of the amino acid neurotransmitters glutamate, gamma-aminobutyric acid (GABA), and glycine, and the metabolic amino acids, aspartate and glutamine, was examined immunocytochemically in the retina of the tiger salamander, a major model for the study of retinal anatomy and function.

Each amino acid showed a unique distribution among retinal bipolar cells. All bipolar cells appear to contain glutamate and, under appropriate conditions, may also contain aspartate. GABA and glycine were restricted to a subset of conventionally placed bipolar cells located in the inner nuclear layer, but were not present in displaced bipolar cells located in the outer nuclear layer. In contrast, high levels of glutamine were almost exclusively restricted to displaced bipolar cells. Analysis of co-localization patterns revealed several different amino acid signatures within the bipolar cell population.

The striking neurochemical heterogeneity among bipolar cells suggests important differences in signaling and metabolism that could affect cell survival, plasticity, and functional recovery from retinal insult in a cell-type-specific manner.