Plasticity of GFAP-immunoreactive astrocyte size and number in visual cortex of rats reared in complex environments.

Previous studies have indicated effects of postweaning rearing environment complexity on astrocyte nuclei. This study examined the effects of rearing for 10, 30 or 67 days in a complex (EC), social (SC) or individual cage (IC) environment upon glial fibrillary acidic protein (GFAP) immunoreactive astrocytes of the occipital cortex. EC rats exposed to their environment for 30 days or longer had a greater surface density of astrocytic processes (Sv) than SC or IC rats. The greater surface density of EC cortical astrocytes appeared to be due to an increase in the mean size of astrocytes after 30 days of differential environmental exposure. After 67 days of environmental exposure, however, the greater Sv appeared to be due to an increase in the number of astrocytes. Astrocytic plasticity appears to develop rather slowly during exposure to a complex environment and appears to involve two stages. The first stage is a hypertrophy of existing astrocytes and the second stage involves proliferation or retarded death of astrocytes. These changes may be related to brain information processing since astrocytes are known modulators of synaptic activity and may possibly serve as regulators of synaptic density.