Restraint stress-induced brain activation patterns in two strains of mice differing in their anxiety behaviour.

Genetically identical inbred mouse strains are one of the most useful tools in dissecting the genetic basis of complex disorders. C57BL/6 and BALB/c mice differ markedly in emotionality. In particular, BALB/c mice are more stress-sensitive and have been proposed to be a model of pathological anxiety. There is a paucity of studies investigating whether brain activation in response to a stressor is different in these two strains. To this end, having confirmed that the strains differ in anxiety responses in a light-dark box test, we then examined if restraint stress induced increases in c-Fos protein expression in selective regions of the mouse brain. The areas of interest analysed were the paraventricular nucleus (PVN) of the hypothalamus, prefrontal cortex (PFC), the paraventricular thalamic nucleus (PV) and the hippocampus. These areas were chosen due to their known involvement in stress response. Our data demonstrate that BALB/c showed a similar cellular activation pattern to stress, with respect to c-Fos expression, in the PVN, PV and in the hippocampus. On the other hand, BALB/c showed markedly blunted stress-induced brain activation compared with stressed C57BL/6 mice in both the CG1 and CG2 regions of the PFC. The lower levels of stress-induced activity in high anxiety BALB/c mice, possibly indicate a circuit dysregulation at the cortico-limbic level in response to stress.