Environmental manipulation differentially alters c-Fos expression in amygdaloid nuclei following aversive conditioning.

This study analyzes the impact of environmental complexity in adult rats on their emotional behavior and c-Fos expression (a transcription factor protein implicated in neuronal plasticity) in various subdivisions of amygdala, as well as selected parts of the thalamus and hypothalamus. The animals were housed for 60 days in either enriched or impoverished conditions and then one group of rats was tested in an open field test, and a second group of rats was treated to footshock-motivated aversive training. Two and 24 h later, the animals from the second group, along with the appropriate controls, were sacrificed and their brains were used for the immunocytochemical analysis of c-Fos levels. We found that this long-term environmental manipulation exerts significant effects on animals' emotionality and this behavioral difference is accompanied by the differential c-Fos activation (at 2 h after the aversive training) in the amygdala, a brain structure believed to subserve emotional reactions. On the other hand, no difference was found in c-Fos expression between both groups of animals in the thalamus and hypothalamus. At 24 h after the training, c-Fos levels were down to the values observed in naive rats that did not differentiate between enriched versus impoverished breeding conditions. These results may help to explain differential emotional aspects of behavior that arise following differential housing conditions of adult animals.