Differential activation of c-Fos and Egr1 during development of the mouse visual cortex

<p>Critical periods (CP) in brain development are associated with profound changes in gene expression cascades. Here we examine the expression of the immediate early genes <i>c-Fos</i> and <i>Egr1</i> at different stages of mouse visual cortex (VC) development. Mice 11, 25, and 50 days of age were maintained under standard light-dark conditions, deprived of light for 5 days, or deprived of light for 5 days and then exposed to light for 90 min. Their brains were analyzed at PND16 (before the onset of the CP), PND30 (during the CP) and PND55 (after the CP) to determine the changes in the number of cells expressing <i>c-Fos</i> and <i>Egr1</i> in the binocular primary visual and primary somatosensory cortices. We found highly specific induction of <i>c-Fos </i>expression in the primary VC in response to light. We also observed transient cross-modal activation of <i>c-Fos</i> in the barrel field of the primary somatosensory cortex in response to light before and during the CP; such activation disappeared after the CP. Expression of <i>Egr1</i> was not induced by light in the VC before the CP, but was evident during and after the CP, although the induction was much less pronounced than that of <i>c-Fos</i>. Dynamic changes in <i>c-Fos</i> and <i>Egr1</i> expression may reflect their contribution to the VC plasticity during the CPs of postnatal brain development.</p>