Learning-induced Increase of Immediate Early Gene Messenger RNA in the Chick Forebrain

The immediate early genes c-fos and c-jun are activated rapidly in nerve cells in response to in vivo and in vitro stimulation. Because of their involvement in transcriptional regulation, the products of these genes have been proposed as nuclear signals for consolidation of long-term memory. However, no specific changes of immediate early gene expression in relation to learning have yet been reported. Compared with quiet controls, training young chicks to discriminate food grains from inedible pebbles results in a 4.8-fold elevation of c-fos and a 3.7-fold elevation of c-jun mRNA in the forebrain 30 min after an 8-min training session. Compared to chicks that had learned the discrimination and were merely repeating already learned behaviour, the increase in c-jun mRNA in the learning group was 64% (P < 0.03) but a 24% increase in c-fos mRNA was not significant. Because the increased expression is higher in birds that are learning the task than in those that are repeating already learned behaviour, and is not proportional to behavioural activity per se, we conclude that learning a new task is itself responsible for enhanced expression of the genes.