Effects of essential amino acids on central neurons

Effects of eleven essential amino acids ejected by means of electrophoresis through five barrel glass microelectrodes on the frequency of extracellularly recorded action potentials of brain cells were determined. Data were collected on 129 cells from four different parts of the brains of 22 female hooded rats anesthetized with a mixture of chloralose and urethan. Eleven cells were tested in the cerebral cortex, 57 in the thalamus, 33 in the zona incerta, and 28 in the lateral hypothalamus. Of the eleven amino acids tested, cells of the zona incerta and lateral hypothalamus appear to be the most responsive and increases in discharge frequency were observed for all the amino acids except lysine and cystine. Cystine seems to be unusual in that it is the only amino acid tested which produces a decrease in the spontaneous discharge frequency. Cells of the cerebral cortex were not considered responsive in terms of the criteria of this study and displayed relatively high thresholds to all the essential amino acids. These results indicate some differential sensitivity of certain cells of the brain to essential amino acids which might be related to the centrally mediated anorexia which develops when rats are fed disproportionate amounts of these same amino acids in the diet.