The Effects of N-Methyl-D-Aspartate Agonists and Antagonists on Isolated Bovine Cerebral Arteries

American Journal of Physiology-Heart and Circulatory Physiology

Perciaccante

Shimizu

et al. 2002

. N-methyl-D-aspartate-induced vasodilation is mediated by endothelium-independent nitric oxide release in piglets. Am J Physiol Heart Circ Physiol 282: H1404-H1409, 2002. First published November 23, 2001 10.1152/ajpheart. 00523.2001.-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 M) elicited virtually identical dose-dependent dilations in paired arterioles (r ϭ 0.94, n ϭ 15). However, NMDA-but not bradykinin (BK)-induced dilations of arteriolar sections over large veins were reduced by 31 Ϯ 1% (means Ϯ SE, P Ͻ 0.05, n ϭ 4) compared with adjacent sections on the cortical surface. Also, 100 M NMDA increased cerebrospinal fluid levels of NO metabolites from 3.7 Ϯ 1.0 to 5.3 Ϯ 1.2 M (P Ͻ 0.05, n ϭ 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 ϳ70% (n ϭ 7). Finally, miconazole (n ϭ 6, 20 M) 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 PREVIOUS STUDIES suggest that stimulation of N-methyl-D-aspartate (NMDA) receptors on cortical neurons results in dose-dependent pial arteriolar dilation via a mechanism involving neuronal nitric oxide (NO) synthase (nNOS) activation and subsequent NO release in newborn pigs (11,29). Because cerebral resistance vessels and cortical astroglia lack NMDA receptors, cerebral vasodilation to NMDA must be initiated by substances released from activated neurons (30,38). Similar involvement of NO in NMDA-induced pial arteriolar vasodilation or increased cerebral blood flow (CBF) have been observed in many other species (14,32,40). Glutamate receptor activation either by nervous or pharmacological stimulation results in increased blood flow in a variety of regions, such as the cerebral cortex (25, 33, 41), striatum (10), hippocampus (18), cerebellum (3), and medulla (16) in rats. In all these regions, NO seems to be involved in the mechanism of CBF increase, and the major glutamate receptor subtype appears to be the NMDA receptor, except in the cerebellum (3, 40). However, many of the details of this relationship between activation of NMDA receptors and cerebrovascular dilation are unclear. Whereas there is agreement that NO is essential for NMDAinduced arteriolar dilation, it is unclear whether parenchymal-derived N...

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confidence: 99%

N-methyl-d-aspartate-induced vasodilation is mediated by endothelium-independent nitric oxide release in piglets

American Journal of Physiology-Heart and Circulatory Physiology

Perciaccante

Shimizu

et al. 2002

“…An advantage of this approach is that we can repeatedly assess neuronal function in a minimally invasive manner in the same animal under different conditions. Because cerebral resistance vessels do not themselves possess NMDA receptors linked to vasomotor responses (6,20,31), pial arteriolar dilation to NMDA requires initial activation of receptors on the surface of neurons with subsequent synthesis, diffusion, and actions of NO. Additionally, recent studies by our laboratory directly document the involvement of neuronally derived NO in the mediation of dilator responses (16).…”

Section: Discussionmentioning

confidence: 99%

Effects of hypothermia on neuronal-vascular function after cerebral ischemia in piglets

Perciaccante

American Journal of Physiology-Regulatory, Integrative and Comp

Puskar

et al. 2002

We determined whether cerebral arteriolar dilation to N-methyl-d-aspartate (NMDA), a response dependent on stimulation of cortical neurons and inhibited by anoxic stress, would be preserved by hypothermia during and following ischemia. Pial arteriolar diameters in anesthetized piglets were determined via intravital microscopy. Arteriolar responses to NMDA (10, 50, and 100 μmol/l) were measured before and 1 h after 10 min of global ischemia. Piglets were exposed to either total body or selective brain cooling (33–34°C). Arteriolar dilation to lower doses or to 100 μmol/l NMDA was not affected by hypothermia alone (51 ± 3 vs. 46 ± 7%, normothermia vs. hypothermia; n = 7) in nonischemic animals. However, arteriolar responses to 100 μmol/l NMDA were clearly attenuated after ischemia despite body cooling during ischemia (53 ± 3 vs. 32 ± 6%; n = 8), hypothermia during ischemia and early reperfusion (49 ± 10 vs. 20 ± 3%; n = 8), or selective brain cooling (48 ± 5 vs. 20 ± 5%; n = 10). In contrast, pretreatment with indomethacin resulted in complete preservation of NMDA-induced vasodilation after ischemia. Thus, hypothermia fails to protect against neuronal dysfunction during ischemia.

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confidence: 93%

“…Indeed, the BBB was found to be intact even after 24-h L-glut infusion in rats (20). Third, L-glut and NMDA dilate cerebral arteries in vivo (3, 30) but not in vitro (37,44), suggesting that CMVECs do not respond directly to L-glut. The present study was designed to study the effect of millimolar concentrations of L-glut and NMDA on CMVEC viability and function in two species.…”

mentioning

confidence: 99%

See 1 more Smart Citation

Cerebromicrovascular endothelial cells are resistant to l-glutamate

American Journal of Physiology-Regulatory, Integrative and Comp

Kis

Gáspár

et al. 2008

Cerebral microvascular endothelial cells (CMVECs) have recently been implicated as targets of excitotoxic injury by L-glutamate (L-glut) or N-methyl-Daspartate (NMDA) in vitro. However, high levels of L-glut do not compromise the function of the blood-brain barrier in vivo. We sought to determine whether primary cultures of rat and piglet CMVECs or cerebral microvascular pericytes (CMVPCs) are indeed sensitive to L-glut or NMDA. Viability was unaffected by 8-h exposure to 1-10 mM L-glut or NMDA in CMVECs or CMVPCs isolated from both species. Furthermore, neither 1 mM L-glut nor NMDA augmented cell death induced by 12-h oxygen-glucose deprivation in rat CMVECs or by 8-h medium withdrawal in CMVPCs. Additionally, transendothelial electrical resistance of rat CMVEC-astrocyte cocultures or piglet CMVEC cultures were not compromised by up to 24-h exposure to 1 mM L-glut or NMDA. The Ca 2ϩ ionophore calcimycin (5 M), but not L-glut (1 mM), increased intracellular Ca 2ϩ levels in rat CMVECs and CMVPCs assessed with fluo-4 AM fluorescence and confocal microscopy. CMVEC-dependent pial arteriolar vasodilation to hypercapnia and bradykinin was unaffected by intracarotid infusion of L-glut in anesthetized piglets by closed cranial window/intravital microscopy. We conclude that cerebral microvascular cells are insensitive and resistant to glutamatergic stimuli in accordance with their in vivo role as regulators of potentially neurotoxic amino acids across the blood-brain barrier.N-methyl-D-aspartate; blood-brain barrier; cerebrovascular reactivity; glutamate excitotoxicity; intracellular calcium L-GLUTAMATE (L-glut) is one of the most important excitatory amino acids in the central nervous system. Apart from its well-known neurotransmitter role, L-glut plays a critical role in ammonia removal from the brain. L-Glut transported from the blood plasma takes up ammonia and leaves as L-glutamine (12). This balanced L-glutamate/L-glutamine countertransport is regulated by cerebral microvascular endothelial cells (CMVECs) forming the blood-brain barrier (BBB). Furthermore, CMVECs can pump L-glut from the brain to the blood, and thus they provide a functional interface for the regulated bidirectional transport of L-glut (18, 39). Human blood plasma L-glut levels range between 20 and 200 M, and they may exceed 700 M after ingestion of high amounts of L-glut under experimental conditions (4, 41). These plasma L-glut concentrations are not neurotoxic in vivo, although these levels are excitotoxic to neurons in vitro, suggesting that CMVECs are resistant to high L-glut levels and prevent the passive transport of L-glut into the brain.Surprisingly, several recent reports have proposed that the L-glut levels that occur during cerebral ischemia can injure or kill CMVECs via excitotoxic mechanisms in vitro. CMVECs have been reported to possess various L-glut receptor subunits or L-glut binding sites in rat, piglet, or human CMVECs (1,5,27,34,36,45). High concentrations of L-glut (1-3 mM), at least in vitro, are claimed to result in N-met...