Carrageenan-induced brain inflammation. Characterization of the model.

Administration of the mucopolysaccharide, carrageenan (CAR), into the hind paw of the rat or mouse induces a local inflammation characterized by increased arachidonic acid metabolism, increased vascular permeability, edema, and neutrophil extravasation. Carrageenan-induced hind-paw inflammation is inhibited by prostaglandin synthesis inhibitors, and this assay predicts the clinical success of anti-inflammatory agents in reducing peripheral inflammation. The purpose of this study was to determine if intraventricular injection of CAR would induce brain inflammation similar to that evoked by CAR in peripheral tissues. The present study demonstrates that CAR injection into the ventricles of the mouse brain does in fact induce an inflammatory response very similar to that caused by injection of CAR into the peripheral tissues. The brain response to CAR was dose-dependent, with the maximum increase in cerebrovascular permeability to iodine-125-labeled human serum albumin and percent brain water occurring after injection of 50 micrograms CAR. As is seen in CAR-induced inflammation of the hind paw, the maximum increase in brain vascular permeability occurred 4 hours after CAR injection. Histological analysis of brains 4 hours after CAR administration showed global neutrophil extravasation into the subarachnoid space and evidence of focal neuronal swelling. Methotrexate-induced neutropenia, however, failed to diminish the permeability response to CAR. Gas chromatographic and mass spectrometric measurements of brain prostaglandins 4 hours after CAR injection revealed a significantly increased level of 6-keto-prostaglandin F1 alpha. These results indicate that a significant increase in prostacyclin, the pro-inflammatory arachidonic acid metabolite, during CAR-induced brain inflammation is likely. These studies suggest that CAR-induced brain inflammation may be a useful model on which to test the efficacy of anti-inflammatory agents in the brain, as well as providing information concerning the mediators and mechanisms by which the brain may sustain inflammatory injury.