Individual differences in novelty-seeking behavior in rats: a c-fos study.

Novelty-seeking personality traits have been implicated in substance abuse and psychiatric disorders in humans. Novelty-seeking behaviors are also observed in rats, and individual rats exhibit substantial differences in expression of these behaviors. Thus, some rats exhibit low reactivity to novelty and high anxiety-like behavior and are termed low responders, while others are hyperresponsive to novelty and exhibit low anxiety-like behavior and are termed high responders. While we and others had shown differences in patterns of gene expression in high and low responding animals at rest, no studies have described their brain activation following an anxiety test. We report here that a 5-min exposure to an anxiogenic stressor induced distinct patterns of c-fos expression in the brains of high and low responding rats. When compared to low responders, high responding rats showed low expression of c-fos mRNA in the CA1 area of the hippocampus, but high c-fos mRNA levels in the olfactory area, the orbital cortex, the cingulate cortex, the dorsal striatum and the paraventricular nucleus of the hypothalamus. Given that c-fos is a trans-acting factor, we suggest that the short- and long-term consequences of the exposure to the anxiogenic stressor may also be quantitatively and anatomically different in these two groups of animals. Thus, these c-fos results demonstrate how experience may further exaggerate individual differences. Animals that differ in emotional reactivity not only exhibit basal differences in gene expression, but also react to novelty with different molecular responses, further increasing the neuronal differences between them.