The effect of locus ceruleus lesion on water, sodium and potassium content of the rat cerebral cortex.

Locus ceruleus lesion decreases the density of ouabain binding sites, and presumably Na+, K+-ATPase, in brain microvessels. To determine if this decrease affects the transport of Na+, K+ or water across the blood-brain barrier, we studied the influence of unilateral locus ceruleus lesion on Na+, K+ and water content of the ipsilateral cerebral cortex. Unilateral locus ceruleus lesion depleted norepinephrine in the ipsilateral cerebral cortex but had no effect on tissue Na+, K+ or water under steady-state conditions. When the Na+/K+ exchange pump of the blood-brain barrier was stressed by hyperkalaemia, K+ content in the ipsilateral cerebral cortex rose to higher levels than in the contralateral cortex, but the difference did not reach statistical significance. Locus ceruleus lesion also did not cause significant differences in the cerebral cortical content of water, Na+ or K+ in hyponatraemia. The results suggest that brain water and ion homeostasis are tightly controlled, probably by multiple mechanisms with biological redundancies, so that even a 50% decrease in the density of ouabain binding sites in brain endothelium does not result in significant alterations in brain water, Na+ or K+ content.