Developmental expression of the immediate early gene EGR-1 mirrors the critical period in cat visual cortex

Immediate early gene (IEG) expression in the central nervous system is thought to play a role in coupling extracellular stimulation with the transcriptional events responsible for long-term functional changes in neurons. The goal of the present study was to determine the postnatal developmental profile of EGR-1 protein (also termed zif268, Krox-24, NGFI-A) expression across the layers of cal visual cortex and relate it to the state of visual cortical development and plasticity. Using a polyclonal antibody, EGR-1 immunoreactivity was studied in animals of various postnatal ages (from 0.5 week to adult). In very young animals (0.5 weeks), EGR-1 positive cells were restricted to deep cortical layers (layer VI/Subplate). With the increasing age, EGR-1 immunoreactivity spread across layers of the visual cortex in an inside-outside manner, and by 5 weeks of age, EGR-1 protein was highly expressed in all layers. EGR-1 expression remained high until approximately 10 weeks of age and then gradually began to decline in layer IV with little change in supra- and infragranular layers. In adult animals, EGR-1 was located predominantly in the layers above and below layer IV. This pattern of EGR-1 expression in developing cat visual cortex has both temporal and laminar similarities with the development of visual cortical connectivity, with the development of orientation selective receptive field properties, and with the level of visual cortical plasticity, suggesting an involvement of EGR-1 expression in these processes.