DISTRIBUTION OF PUTATIVE AMINO-ACID TRANSMITTERS, CHOLINE-ACETYLTRANSFERASE AND GLUTAMATE-DECARBOXYLASE IN THE INFERIOR COLLICULUS

Levels of glutamic acid, aspartic acid, glycine, taurine, alanine, choline acetyltransferase, and glutamate decarboxylase were measured in ten regions of the inferior colliculus in the cat. None of these substances were uniformity distributed in the colliculus. The highest concentrations of asparate occurred in central regions, whereas those of glycine were in ventral central regions. The distributions of glutamic acid and glutamate decarboxylase were highly correlated, with both being generally high in dorsal regions. There was also a high correlation in the distributions of taurine and alanine, with these substances having their highest concentrations in the posterior region and lowest concentrations in the anterior region. The concentration of choline acetyltransferase was highest in the anterior region. No consistent changes in any of the substances were seen following elimination of inputs ascending to the colliculus via the dorsal and intermediate acoustic striae. Small decreases in glutamic acid were seen in two extracentral regions following removal of the auditory cortex. The nonuniform distribution of the substances that were analyzed suggest that there may be previously undescribed differences in the structure and function of the inferior colliculus. The lack of change in the content of choline acetyltransferase and glutamate decarboxylase after lesion of inputs from the cortex or cochlear nucleus makes it unlikely that acetylcholine or α-aminobutyrate are transmitters in these pathways. © 1979.