The effect of conditioning and pseudoconditioning on RNA metabolism of rat hippocampus and neocortex

Abstract

After a 25-min session of conditioned avoidance in a shuttle-box, there was an increase of rat hippocampal and neocortical RNA concentration, together with an increase of uridine incorporation into cold- and hot-phenol-extractable hippocampal RNA, and with a slight increase of alkaline ribonuclease activity in the neocortex. Shorter, 15-min conditioning sessions had no appreciable effect on any of these variables. After either 15 or 25 min of pseudoconditioning there was a fall of hippocampal RNA concentration together with an increase of hippocampal acid ribonuclease activity. In rats pseudoconditioned for 25 min there was, in addition, an increase of uridine uptake by both hippocampal and neocortical cold- and hot-phenol-extractable RNA, and an enhancement of neocortical acid ribonuclease activity. These results show that changes in brain RNA metabolism caused by both behavioral variables are clearly different. Whereas conditioning seems to stimulate precursor incorporation into hippocampal RNA primarily, pseudoconditioning appears to stimulate first acid ribonuclease activity, and RNA labeling only secondarily as a “rebound” effect both in hippocampus and neocortex.