Effect of excess intracranial amino acids on memory: a behavioural survey

Nineteen naturally occurring amino acids were administered intracranially to day-old chicks at various times before and after a single trial passive avoidance learning task. The results suggest a consistent and simple difference between essential and non-essential amino acids. Except for arginine, phenylalanine, tryptophan and tyrosine, the essential amino acids had no effect on memory formation when administered 5 min before or immediately after learning. However, arginine, phenylalanine and tryptophan yielded amnesia after 60 min following learning, when given between 5 min before and 2.5 min after learning. In the case of tryptophan, amnesia was only temporary, lasting from 60 min to 240 min post-learning. All non-essential amino acids, when administered between 5 min before and 5 min after learning yielded amnesia by 60 min post-learning, with no evidence of recovery by 24 hr post-learning. Alanine-, asparagine-, cysteine- and glutamate-treated chicks, however, showed signs of generalized avoidance shortly after administration. The retention time courses after injection of glutamine, proline, serine and taurine were similar to that obtained with the non-metabolizable amino acid alpha-amino-isobutyric acid, and amnesia arising from administration of these amino acids was counteracted by diphenylhydantoin, as was amnesia induced by phenylalanine and tyrosine. The retention function obtained with tryptophan was similar to that obtained with 5-hydroxytryptamine, and DPH had no effect on the action of tryptophan or the actions of arginine, alanine or asparagine. The findings were interpreted in the context of a three-stage model of memory formation.(ABSTRACT TRUNCATED AT 250 WORDS)