Morphological plasticity of astrocytes

Studies of the central nervous system plasticity have concentrated on synaptic and neuronal changes and often ignored the role that glial cells play in interneuronal communication. Current research has begun to examine one type of glial cell, the astrocyte. Astrocytes are involved in the regulation of the metabolic and ionic microenvironment and may modulate synaptic activity or regulate synapse formation. Two experimental procedures were used to examine the plasticity of astrocytes to begin to determine whether CNS astrocytes may be involved in the processes of information storage. The first experiment exposed rats to complex (EC), social (SC) or individual (IC) environments and the second experiment used in vivo long-term potentiation (LTP) of the rat dentate gyrus. Previous work has indicated that synapses form as a consequence of both of these experimental manipulations. Examinations of anti-GFAP labeled astrocytes were made in the occipital cortex of young adult rats exposed to their environments for 10, 30 or 67 days and in the dentate gyrus of LTP and activity control rats. Both LTP and EC rats (exposed to their environment for at least 30 days) had a greater surface density of astrocytic processes (Sv) than the activity control and SC or IC rats respectively. The greater EC surface density appeared to be due to an increase in the mean size of astrocytes after 30 days of environment exposure but after 67 days of environmental exposure the greater Sv appeared to be due to an increase in the density of astrocytes. No difference in Sv was detectable after only 10 days of environmental exposure. Therefore, astrocytic plasticity appears to develop rather slowly after exposure to a complex environment and may occur in two stages. The first stage is a hypertrophy of astrocytic processes and the second stage may be a proliferation of astrocytes. Since activity dependent controls had a lower Sv than LTP rats, synaptic activity alone does not appear to be responsible for the astrocytic plasticity observed in either the EC or LTP rats, although the effects of brief bursts of high activity or activity-based effects of synapse number changes cannot be ruled out. In contrast to the complex environment results, astrocytes appeared to respond rapidly to the high frequency stimulation of LTP. This suggests that when adequate amounts or patterns of stimulation are used that astrocytic plasticity can be induced rapidly.U of I OnlyETDs are only available to UIUC Users without author permissio