Participation of noradrenergic neurotransmission in the suppression by substance P of alpha 2-adrenoceptors at the nucleus reticularis gigantocellularis involved in central cardiovascular regulation in the rat
Abstract
We applied reverse microdialysis and HPLC analysis to quantify the participation of noradrenergic neurotransmission in the modulation by substance P of alpha 2-adrenoceptors at the nucleus reticularis gigantocellularis involved in cardiovascular regulation, using Sprague-Dawley rats anesthetized with pentobarbital sodium. The efficacy of circulatory suppression of a centrally acting alpha 2-adrenoceptor agonist, guanabenz, was used as the experimental index. Continuous infusion of substance P (600 or 1200 pmol/microliters/min) into the nucleus reticularis gigantocellularis through a stereotaxically positioned microdialysis probe (active exchange length: 500 microns, diameter: 220 microns) for 80 min elicited a reduction in the hypotensive and bradycardiac actions of guanabenz (100 micrograms/kg, i.v.). This implied suppression of alpha 2-adrenoceptor activity correlated positively with the time-course of increase in the estimated extracellular concentration of the undecapeptide and norepinephrine in the nucleus reticularis gigantocellularis. Experimentally elevating the concentration of norepinephrine at this reticular nucleus via microinfusion by reverse microdialysis also decreased the efficacy of the cardiovascular suppressi...Continue Reading
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