Influence of electrical stimulation of locus coeruleus on the rat blood-brain barrier permeability to sodium fluorescein.

The role of central adrenergic innervation of the brain capillaries is still a matter of discussion. The hypothesis that these nerves control the blood-brain barrier permeability was tested by electrically stimulating the locus coeruleus, the major central adrenergic nucleus, in the anaesthetized rat. Frequencies of 5, 15, and 30 Hz were used. A frequency dependent increase in blood-brain barrier permeability to sodium fluorescein was verified. Prior administration of the alpha-adrenoceptor antagonist phenoxybenzamine (10 mg/kg i.p., 24 h before electrical stimulation) totally blocked the effect of 15 Hz stimulation. The same dose of pindolol (a beta-adrenoceptor antagonist) given 1 h before electrical stimulation potentiated the effect of 5 Hz stimulation. Thus, blood-brain barrier permeability is increased, in a frequency dependent manner, by electrical stimulation of the locus coeruleus. The results obtained with phenoxybenzamine and pindolol suggest an opposite effect of alpha and beta-adrenoceptors on the control of sodium fluorescein transport through the blood-brain barrier.