Elevated AP-1 transcription factor DNA binding activity at the onset of functional plasticity during development of rat sensory cortical areas.

The patterns of three transcription factor DNA binding activities, namely AP-1, Octamer and CREB, were examined in barrel and visual cortices of rat brain during early postnatal development, when activity-dependent plasticity of neuronal responses and connectivity was described. Main peak levels of AP-1 DNA binding activity have been observed at 21 days postnatally in both cortical areas. In addition, slightly elevated AP-1 levels were detected at 3-7 postnatal days in the barrel and in the visual cortex. In contrast, Octamer DNA binding activities were at the highest levels in both areas at 7 days postnatally, and CREB DNA binding activities were not appreciably modulated throughout the development. The AP-1 protein complex at 21 days postnatally was composed of JunD, JunB, Fra-2, FosB and to much lesser extent of c-Fos in both cortical areas. Treatment of 21 day old rats with MK-801, an NMDA receptor antagonist, provoked a dramatic decrease in AP-1 DNA binding activities in the barrel cortex, but not in the visual cortex. Elevated AP-1 DNA binding activity can be taken as a good correlate of an onset of functional plasticity in the rat sensory cortex, although in the two primary sensory cortices examined it seems to be regulated in different ways.