AP-1 activity rises by stimulation-dependent c-Fos expression in auditory neurons.

Acoustical or intracochlear stimulation may induce expression of the immediate early gene product c-Fos in neurons throughout the auditory brainstem. Attempting to estimate its consequences, we sought to determine if c-Fos expression occurs in neurons that also contain c-Jun p39 with which it could form the heterodimeric transcription factor AP-1 to activate a large number of genes, among them several involved in neuroplastic remodeling. Following intracochlear stimulation, c-Fos and c-Jun were found to be colocalized in nuclei of many neurons at all levels of the subcortical auditory system. We conclude that stimulation triggers Fos-Jun dimerization, causing cascades of gene expression that potentially culminate in structural changes of neurons affected by the specific pattern of activity imposed on the neuronal system.

The developmental dynamics of the brain is reflected by a regionally specific rise and fall of molecular complexity.

Tissue samples of inferior colliculus and cerebellar cortex were obtained from rat brains at various postnatal developmental stages. Samples were analysed by two-dimensional SDS gel electrophoresis. Spots of proteins and their variants were visualized with automated silver staining, the number of spots was determined with a computer-based image analysis system, and age groups were statistically compared. Judging from the waxing and waning of protein spot numbers, colliculus and cerebellum take distinctly different routes through postnatal development. Whereas molecular complexity in the colliculus was initially high, it decreased soon after the onset of hearing and settled on a significantly lower adult level. By contrast, the cerebellum initially showed low molecular complexity, rose sharply in complexity to reach highest values at late juvenile stages corresponding to peak scores of explorative behaviour, and fell off again to an adult level that remained, however, significantly higher than that of the colliculus. We conclude that the changing diversity of proteins may be used to identify landmarks in brain development.