EFFECT OF LEARNING AND OF DRUGS ON RIBONUCLEIC ACID CONCENTRATION OF BRAIN STRUCTURES OF RAT

Hippocampal RNA concentration of rats was increased by: (a) One intraperitoneal injection of saline solution; (b) ten daily intraperitoneal injections of saline solution; (c) one intraperitoneal injection of amphetamine or nicotine; (d) one session of 25-min duration, of avoidance conditioning; (e) six daily sessions of 15 min each, of avoidance conditioning. The increases observed upon single amphetamine or nicotine injections were significant when values were compared to those of rats receiving one saline injection, taken as controls. The acute conditioning procedure led, in addition, to an increase in neocortical RNA. An acute pseudoconditioning procedure was without effect on hippocampal and neocortical RNA. The injection of saline solution was considered to involve a sequence of stimuli characteristic of a conditioning procedure, and the results obtained upon such injections were correspondingly interpreted. Animals which received ten daily injections of strychnine or amphetamine had a lower hippocampal RNA content than those which received ten daily saline injections. The chronic treatment with nicotine or strychnine raised cerebellar RNA levels. The results suggest: (a) A link between the learning process and the action of drugs known to favor learning, on one hand, and hippocampal RNA synthesis, on the other; (b) the possibility of a cerebellar site of action for nicotine and strychniine. © 1969.