Stimulus-dependent expression of immediate-early genes in rat somatosensory cortex

Using in situ hybridization histochemistry, we investigated the effects of whisker stimulation in freely moving rats on the expression of the immediate-early genes zif 268 and c-fos in the barrel cortex. Whiskers equipped with metal filaments were stimulated for 5-15 minutes with a pulsating magnetic field. Such whisker stimulation resulted in increased zif 268 and c-fos expression that was largely restricted to radial columns across the barrels representing the stimulated whiskers. In these columns, gene expression was elevated, to a variable degree, across the entire cortical thickness, with a distinct maximum in layer IV. The magnitude of gene expression in a barrel was proportional to the intensity of stimulation. Cellular analysis confirmed that whisker stimulation induced c-fos expression mostly in stellate cells of layer IV and in some pyramidal cells in other layers. However, even after the strongest stimulation, only subsets of neurons were labeled in all layers, suggesting that subpopulations of neurons with a differential genomic response to sensory input exist. These results indicate that the expression of these immediate-early genes is regulated by normal neuronal activity under physiological conditions, and suggest that such gene regulation is an integral part of neuronal function.