Reduction of GFAP induced by long dark rearing is not restricted to visual cortex.

A key component of the astrocyte cytoskeleton is the glial fibrillary acidic protein (GFAP), which plays an essential role in neuron/astrocyte interactions. Environmental conditioning, such as visual experience manipulation, can affect neuronal and/or glial plasticity in specific brain areas. Previous work from our laboratory showed that short light deprivation throughout the period of GFAP maturation does not influence the expression profile of GFAP in mouse visual cortex; however, it was strong enough to affect neuronal phenotype. It was suggested that visual experience controls the maturation of the neuronal circuitry in this brain area. Therefore, to see whether the modifications of neuronal activity induced by light deprivation affect the maintenance of normal astrocytic phenotype, the dark rearing protocol was extended until the adult life. GFAP-immunoreactive cells were dramatically affected, showing an 80% decrease in number. In addition, GFAP protein level exhibited a 50% reduction, while its mRNA remained unaffected. Besides the visual cortex, two other areas of the brain not directly involved in vision, the hippocampus and the motor cortex, were chosen as internal controls. Unexpectedly, also in these areas, astrocytes were affected by light deprivation. The present results show that lack of visual experience for long periods of time deeply affects glial phenotype not only in visual areas but also in brain regions not directly involved in sensory processing.