INDUCTION OF C-FOS MESSENGER-RNA IN THE BRAIN AND ANTERIOR-PITUITARY GLAND BY A NOVEL ENVIRONMENT

To determine the cell groups which are activated by novelty stress, we examined the induction of c-fos mRNA in brain tissues following intro duction of male rats to a novel open field. Male Fischer 344 rats were placed in a brightly lit open field and allowed to roam free for 20 m in. Control animals were sacrificed upon removal from their home cage. Northern blot analysis revealed a 2.2 kb hybridization signal which i ncreased in density following novelty. In situ hybridization analysis showed that c-fos mRNA was induced in a specific pattern consistent wi th the behavior. The regions of induction included the medial prefront al and orbital cortex, cingulate and parietal cortex, hippocampal CA1 and CA3 pyramidal cell regions, dorsal and ventral anterior thalamic n . and paraventricular n. of the hypothalamus. C-fos mRNA also increase d in the anterior pituitary gland and this increase correlated with th e secretion of ACTH. These data demonstrate the brain areas undergoing genomic activation following complex behavior paradigms such as intro duction to a novel environment.