Importance of Nitric Oxide Synthase Inhibition to the Attenuated Vascular Responses Induced by Topical L-Nitroarginine during Vibrissal Stimulation

Abstract

Summary:We assessed the regional cerebral blood flow (rCBF) response to vibrissal stimulation before and after nitric oxide synthase (NOS) inhibitors were topically ap plied through a closed cranial window placed over the cortical barrel fields in anesthetized Sprague-Dawley rats. In the presence of L-nitroarginine (l mM), both the maximum and total responses became reduced, but only in those animals demonstrating >50% inhibition of NOS activity as determined by the conversion of [ 3 H]arginine to eHlcitrulline within homogenates taken from cortical gray matter under the cranial window. The degree of en-The mechanism which couples blood flow and metabolism within the brain is not well understood. Recently, nitric oxide was suggested as a potential mediator because it is formed and released from neurons (Garthwaite et aI., 1988; Knowles et aI., 1989; Bredt et aI., 1990), diffuses readily (e.g., 0.5 fJ.m theoretical distance) (Knowles and Moncada, 1992), crosses cellular membranes freely, and is a potent vasodilator (Palmer et al., 1987). Although certain publications note that nitric oxide synthase (NOS) inhibitors attenuate the blood flow response elicited by somatosensory stimulation (Northington et aI., 1992; Dirnagl et aI., 1993), others have not observed this relation (Adachi et aI., 1993; N gai et aI., 1993).Studies were undertaken to establish a possibleReceived June 18 , 1993; final revision received July 6, 1993; accepted July 6, 1993.Address correspondence and reprint requests to Dr. Michael A. Moskowitz, Massachusetts General Hospital, 32 Fruit Street, Boston, MA 02114, U.S.A.Abbreviations used: CSF, cerebrospinal fluid; EDTA, ethyl enediaminetetra-acetic acid; HEPES, N-2-hydroxyethylpipera zine-N' -2-ethanesulfonic acid; L-NA, NG-nitro-L-arginine; L-NAME, �-nitro-L-arginine methylester; �-NADPH, �-nico tinamide adenine dinucleotide phosphate; NOS, nitric oxide syn thase; rCBF, regional CBF. 45zyme inhibition depended in part, upon duration after topical application of NOS inhibitor. When >50%, en zyme inhibition correlated with the decrease in maximum and total rCBF response (p < 0.01). These findings em phasize the merits of assessing enzyme activity after ad ministering NOS inhibitors, and suggest that NO gener ated from parenchymal NOS activity plays an important role in the cerebrovascular response to physiologic so matosensory stimulation under the stated conditions. Key Words: Nitric oxide-Nitric oxide synthase-L Nitroarginine-Cortical barrel fields-rCBF.role for NO as a coupling mediator for regional CBF (rCBF) and metabolism, and to extend our own pre liminary negative findings examining the effects of topical NOS inhibitors on the rCBF response to vibrissal stimulation 30 min after topical application (Irikura et aI., 1993). Accordingly, NOS activity was determined in vitro based on the conversion of eH]arginine to [3H]citrulline within homogenates taken from subjacent cerebral cortex. Our results support an important role for NO under the condi tions of this assay, and for the need to asse...

Interaction of Mechanisms Involving Epoxyeicosatrienoic Acids, Adenosine Receptors, and Metabotropic Glutamate Receptors in Neurovascular Coupling in Rat Whisker Barrel Cortex

“…With chloralose anesthesia and the use of cranial windows, others reported an average increase in LDF during whisker stimulation in the rat in the range of 15 to 20% (Dirnagl et al, 1994;Irikura et al, 1994;Lindauer et al, 1999). In this study with chloralose anesthesia and subarachnoid superfusion, the average response for each group generally fell into this range, although the LDF response displayed some variability among groups.…”

Investigating the post-stimulus undershoot of the BOLD signal—a simultaneous fMRI and fNIRS study

“…Our study did not measure simultaneously changes in rCBF, which should be done in future experiments. The post-stimulus undershoot of rCBF occurs only in a minority of subjects, is highly variable (Irikura et al, 1994;Ma et al, 1996), task-dependent (Hoge et al, 1999), and can even be explained as an artifact of delayed rCBV changes (Mandeville et al, 1999). Furthermore, the ratio between post-stimulus and stimulus changes of rCBF, as calculated from these studies, reaches only values between approximately 0.15 and 0.3 (Hoge et al 1999;Irikura et al, 1994;Ma et al, 1996).…”

Dependency of Cortical Functional Hyperemia to Forepaw Stimulation on Epoxygenase and Nitric Oxide Synthase Activities in Rats

“…For each animal, time-gated averaging of the LDF response was performed on three trials approximately 3 or 4 minutes apart after 90 minutes of drug superfusion. This exposure duration is sufficient for inhibiting cortical NOS activity and functional hyperemia (Irikura et al, 1994). The average percent change from the 60-second baseline for each animal was used for determining the mean and standard deviation of the group on a second-by-second basis (n ‫ס‬ number of rats).…”

“…One hour after discontinuing isoflurane inhalation, artificial CSF (Peng et al, 2002) was infused through this subdural catheter at a rate of 5 L/min. The superfusion continued with either vehicle or a single drug regimen in six groups of rats: (1) artificial CSF with a 0.5% ethanol used as a vehicle for MS-PPOH and miconazole (n ‫ס‬ 7); (2) 1-mmol/L N -nitro-L-arginine (L-NNA; n ‫ס‬ 6) to inhibit NOS activity (Irikura et al, 1994)…”

“…In experimental models using whisker stimulation, increases in CBF in whisker barrel cortex are attenuated by adenosine antagonists (Dirnagl et al, 1994), nitric oxide synthase (NOS) inhibitors (Dirnagl et al, 1993;Irikura et al, 1994;Ma et al, 1996), soluble guanylyl cyclase inhibition (Lindauer et al, 1999), cyclooxygenase-2 inhibition and gene deletion (Niwa et al, 2000), and antagonists of calciumactivated potassium (K Ca ) channels (Gerrits et al, 2002). Pial arteriolar dilation during sciatic nerve stimulation also is attenuated by an adenosine antagonist (Ko et al, 1990).…”