Forebrain astroglial plasticity is induced following withdrawal from repeated cocaine administration

Abstract

Astrocytes actively participate in synaptic plasticity and respond to insult or metabotropic glutamate receptor activation with increased expression of the intermediate filament glial fibrillary acidic protein (GFAP). Extended withdrawal from repeated cocaine administration induces many forms of neuroplasticity. The present study with rats utilized a 3-week withdrawal period from daily cocaine administration (i.p.; 7 days) to investigate whether astrocytes participate in cocaine-mediated plasticity observed in brain nuclei associated with addiction. Following the 3-week withdrawal period, immunoblotting revealed increased GFAP expression in the prefrontal cortex (PFC) and in the shell and core compartments of the nucleus accumbens (NAshell and NAcore). Upregulation of GFAP did not occur in the striatum or in any brain region tested following shorter withdrawal times from repeated cocaine (24 h or 1 week) or following 2-h withdrawal from an acute cocaine injection (30 mg/kg i.p.). However, GFAP expression increased following a 3-week withdrawal from a single cocaine injection selectively in the NAshell. Cell counts revealed that astrocyte cell number increased only in the NAcore while immunoblots of a marker for immature or reactive astrocytes, vimentin, showed an increase only in the PFC following the 3-week withdrawal. Taken together, these results suggest that altered intermediate filament expression within forebrain astrocytes may be a significant part of the plasticity occurring during withdrawal from repeated cocaine. Furthermore, the increase in GFAP may arise from regionally distinct mechanisms, with the NAcore relying more on cell proliferation while the PFC relies on a larger reactive astrocyte population.