The Topographical Distribution of Alanine, Aspartate, γ‐Aminobutyric Acid, Glutamate, Glutamine, and Glycine in the Pigeon Optic Tectum and the Effect of Retinal Ablation

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Abstract
The concentrations of alanine, aspartate, GABA, glutamine, glutamate and glycine were measured in the pigeon optic nerve and in the individual tectal layers. Characteristic topographical distribution patterns were observed for the different amino acids. After unilateral retinal ablation, the concentration of aspartate and glutamate was decreased in the nerve and contralateral tectum. The reduction was restricted to the superficial part of the tectum, which receives a direct retinal input. The maximal loss was measured in the first 2 layers, where aspartate was reduced by 51% and glutamate by 75% in comparison with the ipsilateral side 4 wk after ablation. A special role for aspartate and glutamate as putative transmitters in pigeon retino-tectal afferents is favored.