Release of Endogenous Amino Acids from Superior Colliculus of the Rabbit: In Vitro Studies After Retinal Ablation

Abstract
Tissue slices from the superior colliculi (SC) of the rabbit were superfused and investigated 1 wk after unilateral eye removal. Amino acid levels were determined both in the tissue slices and in the medium after chemical depolarization (56 mM K). The amino acid determinations were done fluorimetrically by precolumn derivation and HPLC [high performance liquid chromatography] separation. Colliculi contralateral to the enucleation exhibited a 16% reduction in glutamate compared with the ipsilateral colliculi. The Ca-dependent release of glutamate or other amino acids tested was not appreciably affected by enucleation. Both the total and the Ca-independent release of glutamate was lower from contralateral SC slices compared with the ipsilateral slices. The results do not favor glutamate as the major optic nerve transmitter in the rabbit, but do not rule out glutamate as a transmitter in a minor population of retinal fibers.