Decreased Cortical Glucose Utilization after Ibotenate Lesion of the Rat Ventromedial Globus Pallidus

Abstract

Rats received unilateral injections of ibotenic acid (12 μg) or vehicle in the ventromedial globus pallidus to lesion the primary source of cortical cholinergic innervation. At 3 or 28–32 days postinjection, the regional cerebral metabolic rate for glucose (rCMR_glu) was measured by the 2-deoxy-d-[¹⁴C]glucose technique in nine cortical areas, the anterior thalamus, and the dorsal hippocampus. Effects of oxotremorine (0.1 mg/kg i.p.) on rCMR_glu in these areas were assessed in ibotenic acid–lesioned and sham-treated rats. Significant effects of ibotenic acid injections and hemispheric asymmetries in rCMR_glu were observed in all cortical areas (p ≤ 0.05), but not in the anterior thalamus or hippocampus. Cortical rCMR_glu generally was lower in the lesioned hemisphere 3 days after ibotenic acid injections, but not after sham treatments. Hemispheric asymmetries were not apparent 28–32 days after pallidal lesions. Oxotremorine produced significant effects in the frontoparietal cortex and anterior thalamic nuclei. In the frontoparietal cortex, rCMR_glu was 32% lower in the ibotenate-lesioned hemisphere as compared with the contralateral hemisphere. Oxotremorine did not eliminate hemispheric asymmetry, but increased rCMR_glu in the lesioned frontoparietal cortex by 38%. Results support the views that cortical metabolic decrements in Alzheimer's disease are due in part to loss of subcortical cholinergic innervation and that muscarinic agonists may partially reverse these decrements.