Dynamics of immediate early gene and neuropeptide gene response to prolonged immobilization stress: evidence against a critical role of the termination of exposure to the stressor.

Stress-induced expression of immediate early genes (IEGs) appears to be transient even if the exposure to the stressor persists. However, there are some exceptions which suggest that particular characteristics of stressors can affect the dynamics of IEG expression. We studied in selected telencephalic, diencephalic and brainstem regions the mRNA levels of two clearly distinct IEGs (c-fos and arc) during prolonged exposure to a severe stressor such as immobilization (IMO) and after releasing the rats from the situation.

Differences in the brain expression of c-fos mRNA after restraint stress in Lewis compared to Sprague-Dawley rats.

In order to study the contribution of genetic factors to the pattern of stress-induced brain activation, we studied the expression of c-fos mRNA, a marker of neuronal activity, in male Sprague-Dawley and Lewis strains, the latter being known to have a deficient responsiveness of the hypothalamic-pituitary-adrenal (HPA) axis. Immobilization (IMO) alone or combined with the immersion into water at 21 degrees C was applied for 15 or 60 min. The expression of c-fos mRNA was quantified by in situ hybridization in those brain areas that represent important parts of neuronal circuits activated by stress: medial prefrontal cortex, medial amygdala, lateral septum ventral part, paraventricular nucleus of the hypothalamus and locus coeruleus.

Effects of two types of restraint stress on the spontaneous behaviour in rats.

Our previous findings suggested the existence of stressor-specific behavioural and cognitive responses in rats. In the present study, restraint stressor (immobilization, IMO) and restraint stressor combined with partial immersion of rats into water (IMO+C) were applied for 1 hour to Wistar male rats and their spontaneous behaviour was examined in the open field test. The classic behavioural parameters were recorded: crossing, rearing, and resting.