Medical therapy for intracerebral hematoma with the gamma-aminobutyric acid-A agonist muscimol

Background and Purpose No therapy has been rigorously proven effective for intracerebral hematoma, although surgery is frequently used for some types of lobar hemorrhages. Since intracerebral mass causes significant ischemia in surrounding brain, we reasoned that anti-ischemia therapy might improve outcome after experimental hematoma. Methods We stereotaxically injected varying doses of bacterial collagenase into the caudate nucleus of rats. Four hours later we administered intravenously 2 mg/kg muscimol, a potent agonist of the gamma-aminobutyric acid-A receptor (n=20); 1 mg/kg MK-801, an antagonist of the N-methyl-D-aspartate receptor (n=17); or saline (n=28). Forty-eight hours after collagenase injection we rated each animal using a standard rodent neurological examination. The ratings were compared with the amounts of injected collagenase by the quantal bioassay procedure. Brains were then prepared for histomorphometry and brain volumes estimated. Results We found that the ED(50) for collagenase (amount of enzyme that renders 50% of the subjects abnormal) was 0.77+/-0.09 U in saline-treated subjects. Treatment with muscimol significantly increased the ED(50) to 1.2+/-0.21 U, for a potency ratio of 1.55+/-0.34 (t=1.7, P<.05). MK-801 did not affect outcome. Volume of hematoma was significantly correlated with amount of injected collagenase (n=33, r=.64, P<.001). Volumes of basal ganglia and white matter were significantly reduced by hemorrhage, and muscimol partially ameliorated this. Conclusions We conclude that muscimol significantly improves neurological outcome after intracerebral hematoma.