Stress-induced expressionc-fos in the rat brain: A comparison of averaging and typological analysis

Abstract

The effect of acute stress (5 sec footshock, 2.5 mA) on brain levels of c-Fos protein expression was studied in the adult male Wistar rats. Expression of c-Fos was evaluated by immunohistochemistry 2 hours after the footshock. Two types of analysis were employed in the study. First the data on Fos-like immunoreactivity (FLI) for each of the analyzed brain structures were pooled together from all the stressed rats. These averaged values were compared with corresponding data from the control unstressed animals. Second, the same data were analyzed separately for the two groups of rats that differed in their behavior in the open-field test and were characterized as “stress-resistant” and “stress-predisposed” types according to our previous studies. Though the averaged data showed a significant increase in the number of FLI cells in the brains of stressed rats over the control animals, a dramatic difference was also observed between stress-induced FLI in “stress-predisposed” versus “stress-resistant” rats. While “stress-predisposed” rats had large number of FLI cells in the areas of the frontal cortex, cingulate cortex, ventromedial and paraventricular nuclei of hypothalamus and ventral tegmental area, the rats from the “stress-resistant” group had very weak c-Fos staining in these structures and displayed significantly lower number of FLI cells in most of the other brain areas. It is concluded that stress-induced activation of c-Fos expression has large individual variability depending on the typological behavioral profile of the rats and that these transcriptional variations might play a significant role in the individual differences of animal's long-term responses to the same stressors.