Ischaemia of the insular cortex increases the vagal contribution to the baroreceptor reflex in the rat.

Abstract

Neurones in the insular cortex have been shown to innervate medullary autonomic nuclei. Occlusion of the stem of the left proximal middle cerebral artery in rats caused a lesion in the insular and adjacent lateral frontoparietal cortices. Nine and 10 days after lesioning or sham operation, we examined the relationship between mean blood pressure and the heart rate in conscious rats, using the steady-state method. Individual contributions to blood pressure from the cardiac vagus and sympathetic nerves were determined after the administration of atenolol and methylatropine, respectively. Lesioning the insular cortex did not affect mean blood pressure or the heart rate. However, the lesion selectively enhanced the reflex vagal bradycardia that occurred when blood pressure was artificially elevated. There was no effect on the sympathetic heart rate range. These observations suggest that the unilateral cortical lesion chronically affected the baroreceptor control of the heart rate through mechanisms affecting the vagus.