Injection of endothelin-1 (ET-1, 9 pmol) into a lateral cerebral ventricle (LCV) of rats produces barrel-rolling and other convulsive signs that resemble those of generalized seizures in some types of epilepsy. Using the quantitative autoradiographic [14C]deoxyglucose technique, we documented that the neuroanatomical metabolic correlates of the ET-1-induced convulsions in rats are high rates of glucose utilization by structures near the site of LCV injection and throughout a diverse circuit of anatomically related brain regions. We speculate that this circuitry connects the caudate nucleus (putative site of initial stimulation in the forebrain) to the paramedian lobule and vermis of the caudal cerebellar cortex in the hindbrain. We evaluated the behavioral, physiological, and hypermetabolic responses to central ET-1 in the presence of three agents with anticonvulsant properties, providing clues about the cellular mechanisms of this convulsive and hypermetabolic state. Intraventricular MK-801 [a noncompetitive antagonist of glutamic acid N-methyl-D-aspartate (NMDA) receptors], nimodipine (an antagonist of dihydropyridine-sensitive, voltage-gated calcium L-channels), or methylene blue (an inhibitor of guanylate cyclase, the enzyme on which nitric oxide acts) each produced significant attenuation of the behavioral and cerebral metabolic activation. The results introduce several quantitative parameters for an experimental model of employing intraventricular ET-1 in rats to study mechanisms of peptidergic convulsive disorders and the efficacies of promising anticonvulsant compounds in the treatment of epilepsy.
Animals Autoradiography