Sensory regulation of immediate-early gene expression in mammalian visual cortex: implications for functional mapping and neural plasticity.

The expression of immediate-early genes that code for transcription factors has been extensively studied in the brain with regard to imaging functional activity. The components of the AP-1 transcription factor--in particular, c-Fos--and Zif268 have been widely used for this purpose. However, the precise details by which they are induced after synaptic stimulation remain unknown. Furthermore, the roles of these two proteins in neurons remains speculative and include such varied functions as short-term maintenance of cellular homeostasis to long-term changes that guide cortical plasticity. Current efforts at elucidating the physiological roles of AP-1 and Zif268 rely on assessing their expression in response to different conditions of sensory and pharmacological stimulation. In this review, we have examined the expression patterns of these transcription factors in the mammalian visual cortex under different conditions, with particular emphasis on the constitutive levels and how they change after visual deprivation and stimulation. A synthesis of this information offers further insight into their likely functions and the extent to which transcription factors may represent patterns of neural activity as a possible prelude to plastic events.