Differential effects of locus coeruleus lesions upon metabolic activity in CNS nuclei involved in cardiovascular regulation.

The alterations of local cerebral glucose utilization in 5 medullary and 6 supramedullary regions involved in cardiovascular regulation, which result from unilateral electrolytic lesions of the locus coeruleus, have been examined in conscious rats, using the quantitative autoradiographic [14C]2-deoxyglucose technique. Unilateral lesions of the locus coeruleus (72 h prior to study) did not result in any significant alteration in glucose utilization in any of medullary (e.g. nucleus of the tractus solitarius, dorsal motor nucleus of the vagus) or diencephalic (e.g. periventricular and paraventricular hypothalamic nuclei, lateral habenular nucleus) regions which were examined. However, the increased glucose utilization which occurred in some medullary nuclei (e.g. nucleus of the solitary tract, dorsal motor nucleus of the vagus) following administration of the alpha-receptor antagonist, phenoxybenzamine (30 mg/kg, i.v.), was significantly attenuated by lesions of the locus coeruleus, whereas the increased glucose utilization elicited in hypothalamic nuclei by the drug was unaffected by locus coeruleus lesions. In contrast, glucose utilization in the lateral habenular nucleus was elevated significantly following phenoxybenzamine only in animals bearing unilateral locus coeruleus lesion; the drug being without effect in this region in sham-lesioned rats. These differential consequences of locus coeruleus lesions upon glucose utilization in nuclei involved in cardiovascular regulation emphasize the complex nature of the influence of the locus coeruleus upon blood pressure control.