Differential blood-brain barrier breakdown and leucocyte recruitment following excitotoxic lesions in juvenile and adult rats.

Acute neuronal degeneration can be induced by intracerebral injections of the glutamate receptor agonists kainic acid (KA) and NMDA (N-methyl-D-aspartate). It is accompanied by an inflammatory response that has not yet been fully investigated. We have previously demonstrated that the juvenile rat brain is more susceptible to an inflammatory challenge when compared to adult rat brain. This study set out to investigate whether this also applied to the inflammatory response associated with acute neuronal degeneration. NMDA and kainic acid were injected into the rat striatum and lesion size, leucocyte recruitment, and blood-brain barrier (BBB) breakdown were assessed after 4, 8, 12, 24, 72, and 168 h. Both NMDA and KA induced lesions of similar volume at either age and apoptotic and necrotic nuclei could be detected. NMDA induced cellular loss by 4 h, whereas KA-injected rats did not show signs of neuronal loss until 8-12 h. The inflammatory response was characterized by an infiltration of neutrophils followed by macrophages. Juvenile rats showed a greater susceptibility to leucocyte recruitment compared to adult rats. BBB breakdown in response to NMDA injection occurred in the absence of cellular recruitment at 4 h in juveniles and was significantly greater in juvenile compared to adult rats at 8 h. BBB breakdown was minimal in KA-injected animals while at 7 days an influx of serum IgG coincided with a loss of astrocytic GFAP staining within the lesion.