The effect of lesions in the locus coeruleus on the physiological responses of the cerebral blood vessels in cats.

The effects of cerebral blood flow (CBF) of lesions placed stereotactically in or near the locus coeruleus were studied in 15 lightly anesthetized cats; 5 control cats in which the electrode was placed but no lesion created, and 10 experimental cats in which a lesion was created. The response of CBF to changes in Paco2 and in mean arterial blood pressure was determined by 133Xe-washout studies 10 days after the stereotactic procedures. The sites of the lesions were studied histologically, and their effects on catecholamine concentrations in the paraventricular hypothalamic nucleus, anterior ventral nucleus of the thalamus, and parietal cortex were determined by radio-chemical assay. Control animals and those with lesions near, but not in, the locus coeruleus had normal Paco2--CBF response curves and normal catecholamine concentrations in the areas of biopsy. Bilateral destruction of the locus coeruleus was confirmed in 3 animals on histological examination and in these animals there were decreased levels of catecholamines in the areas of assay, higher resting CBFs at normocapnia, and significantly abnormal CBF--Paco2 response curves. The autoregulatory response to changes in perfusion pressure was preserved. Thus, noradrenergic neurons originating in the locus coeruleus may contribute to the control of intraparenchymal cerebral vessels and disturbance of this control may be important in the pathology of cerebral ischemia.