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1 Department of Physiology and Pharmacology, Wake Forest University School of Medicine, Winston Salem, North Carolina 27157-1010; and 2 Department of Physiology, Faculty of Medicine, University of Szeged, Szeged H-6720, Hungary
N-methyl-D-aspartate (NMDA) elicits pial arteriolar dilation that has been associated with neuronal nitric oxide (NO) production. However, endothelial factors or glial P-450 epoxygenase products may play a role. We tested whether NMDA-induced pial vasodilation 1) primarily involves NO diffusion from the parenchyma to the surface arterioles, 2) involves intact endothelial function, and 3) involves a miconazole-sensitive component. Arteriolar diameters were determined using closed cranial window-intravital microscopy in anesthetized piglets. NMDA (10-100 µM) elicited virtually identical dose-dependent dilations in paired arterioles (r = 0.94, n = 15). However, NMDA- but not bradykinin (BK)-induced dilations of arteriolar sections over large veins were reduced by 31 ± 1% (means ± SE, P < 0.05, n = 4) compared with adjacent sections on the cortical surface. Also, 100 µM NMDA increased cerebrospinal fluid levels of NO metabolites from 3.7 ± 1.0 to 5.3 ± 1.2 µM (P < 0.05, n = 6). Endothelial stunning by intracarotid injection of phorbol 12,13-dibutyrate did not affect NMDA-induced vasodilation but attenuated vascular responses to hypercapnia and BK by ~70% (n = 7). Finally, miconazole (n = 6, 20 µM) pretreatment and coapplication with NMDA did not alter vascular responses to NMDA. In conclusion, NMDA appears to dilate pial arterioles exclusively through release and diffusion of NO from neurons to the pial surface in piglets.
cerebral circulation; miconazole; pial arterioles; bradykinin
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