Changes in astroglial GLT-1 expression after neural transplantation or stab wounds

Uncontrolled release of glutamate from damaged brain initiates events that result in excitotoxic neuronal death. Glutamate uptake by specialized astroglial transporters is essential for control of extracellular glutamate levels. Many studies have demonstrated a reduction in astrocytic GLT-1 expression after different forms of injury. Because extensive neuronal death does not occur after direct cortical stab wounds and viable developing neurons populate fetal CNS grafts, we hypothesized that reactive astroglia associated with these procedures might maintain or up-regulate GLT-1. We examined the temporal and spatial distribution of GLT-1, GFAP and nestin proteins by confocal double-label immunohistochemistry combined with a new methodology in which precise brain areas are microdissected and analyzed for protein content by immunoaffinity chromatography. In stab wounds, GLT-1 protein content did not change compared to normal cortex, as determined by direct protein measurements; GLT-1 colocalized with nestin- and GFAP(+) astroglia adjacent to the lesion. In contrast, host reactive astroglia adjacent to grafts significantly upregulated GLT-1 by 3 days postoperative. The GFAP protein analysis suggests that increased GLT-1 is not the result of greater numbers of activated astroglia around grafts, but that developing graft tissue influences adjacent host astroglia to upregulate GLT-1. GLT-1 protein within grafts was rapidly accelerated to mature levels by just three days, and was expressed by the nestin(+) cell population. These data, which demonstrate immunoexpression of GLT-1 protein combined with a new method for protein measurement in situ indicate that, in contrast to other injury models, astroglial GLT-1 is upregulated or maintained following invasive CNS procedures. (c)2002 Elsevier Science (USA).