Effects of early experience on c- fos gene expression in the chick forebrain

The expression of c- fos mRNA was studied by blot and in situ hybridisation in the forebrains of young chicks subjected to different types of experience-dependent stimulation. Exposure to one hour of activity in a rich visual environment produced a significant increase in forebrain c- fos mRNA in 1-day or 2-day-old chicks; this increase was most marked in cerebellum and medial forebrain - especially intermediate medial hyperstriatum ventrale (IMHV) regions. Levels of c- fos mRNA were not elevated in birds which had been accommodated to the enriched environment for 2 days, suggesting that the novelty of presented stimuli play a critical role in the c- fos induction. Training chicks on a one-trial passive avoidance task was followed by 2- to 2.5-fold increases in c- fos mRNA in both left and right IMHV and lobus parolfactorius (LPO) 30 min after the learning experience. Occlusion of one eye during training resulted in an asymmetrical expression of c- fos in the hemisphere contralateral to the open eye. Therefore c- fos is induced in the chick forebrain during learning and its activation cannot be attributed to ‘stress’, arousal or intensity of sensory stimulation alone. These observations support the hypothesis that c- fos expression in the brain is related to the acquisition of new experience.