Characteristics of c-fos gene expression in the brains of rats with different investigative and defensive behaviors.

Differences were found in the expression of the c-fos gene in brain structures of rats with "active" and "passive" types of behavior in the open field, hole exploration, and step-down tests. The most marked and intense expression of the c-fos gene was seen in "passive" rats. After electrocutaneous stimulation in the step-down test, these animals showed maximum expression of the c-fos gene in most areas of the cerebral cortex, the amygdala, in olfactory structures, the hypothalamus, and the brainstem. In "active" rats in the same conditions, expression of the c-fos gene was seen only in the infralimbic cortex and olfactory nuclei. These results, along with existing data on neurological mapping of the c-fos gene, demonstrate a relationship between the level and topography of c-fos expression, and with typological and, perhaps, individual characteristics of rats.