Search PubMed⌕ Search

Biomedical subjects

G Yang

Publications and source records attributed to G Yang.

At least 325 records · Page 18Linked to original sources
PubMed1997

[A four-box multi-function testing system of pharmacology reaction].

The organism position matrix method, a new method of testing pharmacology reaction is proposed. On the basis of the method, we have developed a four-box multi-function testing system which can test the spontaneous activity, analgesic effect, and learning and memory ability of 1 to 4 mice in three dimensions respectively. Four quantitative parameters, the total distance, the movement intensity, the vertical number and the jumping number are put forward to describe the spontaneous activity. The starting time of continuous jumping and the jumping number are used to describe the analgesic effect. The time from the electrical shock to escape onto a safety platform and the number of the electrical shock are used to describe the learning and memory ability. The system has the characteristics of good repeatability, high efficiency, quantitative and automatic control.

Animals↗
PubMed1997

[Comparison of effects of two kinds of soluble algae polysaccharide on blood lipid, liver lipid, platelet aggregation and growth in rats].

SD rats were fed with 1% cholesterol and 0.2% cholate for eight weeks. Sodium alginate and carrageenan, two kinds of soluble algae polysaccharide, were added to the fodder for the trial groups and none added for the control one. Results showed that 5% sodium alginate could lower lipid levels in the blood and liver and platelet aggregation (P < 0.05) in rats, but not affect their food intake and growth. Addition with 5% or 10% carrageenan had no obvious effects on lowering blood lipid and liver total cholesterol (P > 0.05), could not lower the ratio of liver weight to body weight, and had no stable (or sure) effect on lowering platelet aggregation. Ten percent of carrageenan could decrease their mean body weight by 12.17% in rats (P > 0.05), but a few rats suffered from slight diarrhea.

Alginates↗
PubMed1996

Perineural invasion of prostate carcinoma cells is associated with reduced apoptotic index.

BACKGROUND: Prostate carcinoma is often associated with perineural (PN) invasion. The common occurrence of this phenomenon has led to speculation regarding the mechanisms of this association, yet to date there have been no studies that clearly define biologic differences between PN and nonperineural (NPN) carcinoma cells. To explore the mechanisms underlying PN invasion by prostate carcinoma cells, the authors investigated the influence of neural components on the growth potential of prostate carcinoma cells. METHODS: Proliferative and apoptotic activities of PN and NPN carcinoma cells were analyzed on whole-mount sections of human prostates using immunohistochemical techniques in conjunction with a polyclonal Ki-67 antiserum, and the terminal deoxynucleotidyl transferase (TdT) mediated dUTP biotin nick end labeling (TUNEL) technique, respectively. RESULTS: The proliferative index (Ki-67 positive cells per 100 carcinoma cells) of PN carcinoma cells (median, 4.10) was higher than that of their intraprostatic, NPN counterparts (median, 3.25), although the difference was not statistically significant (median difference, 0.38; 95% confidence interval [CI] = -0.99 to 1.32; P = 0.52). In contrast, the apoptotic index (AI = apoptotic bodies per 1000 carcinoma cells) in the NPN carcinoma cells was significantly lower (median, 4.10), than the PN carcinoma cells (median, 7.23) with a median difference of -3.45 (95% CI = -5 to -1.39; P = 0.02). The authors also found that AI was lower in the carcinoma cells surrounding nerves with a large diameter (P = 0.0005). CONCLUSIONS: These results suggest that PN invasion by prostate carcinoma cells may not be only a volume effect of growing carcinomas; the neural components may favor the growth of carcinoma cells by inhibiting apoptosis, presumably through a paracrine mechanism, and thereby facilitate the spread of carcinoma cells along nerves. The data also suggest that heterogeneity in growth potential of prostate carcinoma cells may be determined by their local microenvironments, such as an association with neural components.

Adenocarcinoma↗
PubMed1996

Identification of active site residues essential to 4-chlorobenzoyl-coenzyme A dehalogenase catalysis by chemical modification and site directed mutagenesis.

4-Chlorobenzoyl-coenzyme A (4-CBA-CoA) dehalogenase catalyzes the hydrolysis of 4-CBA-CoA to 4-hydroxybenzoyl-coenzyme A (4-HBA-CoA) via a nucleophilic aromatic substitution pathway involving the participation of an active site carboxylate side chain in covalent catalysis. In this paper we report on the identification of conserved aspartate, histidine, and tryptophan residues essential to 4-CBA-CoA catalysis using chemical modification and site-directed mutagenesis techniques. Treatment of the dehalogenase with diethyl pyrocarbonate resulted in complete loss of catalytic activity (Kinact = 0.17 mM-1 min-1 at pH 6.5, 25 degrees C) that was fully regained by subsequent treatment with hydroxylamine. The protection from inactivation afforded by enzyme bound 4-HBA-CoA indicated that the essential histidine residues are located at the active site. Replacement of conserved histidine residues 81, 90, 94, and 208 with glutamine residues resulted in a significant loss of catalytic activity only in the cases of the histidine 81 and 90 mutants. Substrate and product ligand binding studies showed that binding is not significantly inhibited in these mutants. Site directed mutagenesis of a selection of conserved aspartate and glutamate residues, identified aspartate 145 as being essential to dehalogenase catalysis. Ligand binding studies showed that this residue is not required for tight substrate/product binding. Chemical modification of the dehalogenase with N-bromosuccinimide resulted in full loss of catalytic activity that was prevented by saturation of the active site with product ligand, providing evidence favoring an essential active site tryptophan. Phenylalanine replacement of conserved tryptophan residues 179 and 137 reduced catalytic activity only in the latter (Kcat = 0.03% of wild-type dehalogenase). On the basis of these results and the recently determined X-ray crystal structure of the complex of 4-CBA-CoA dehalogenase and 4-HBA-CoA [Benning, M. M., Taylor, K.L., Liu, R.-Q., Yang, G., Xiang, H., Wesenberg, G., Dunaway-Mariano, D., Holden, H.M. (1996) Biochemistry 35,8103-8109] we propose that aspartate 145 functions as the active site nucleophile, that tryptophan 137 serves as a hydrogen bond donor to the aspartate 145 C = O, and that histidine 90 serves to deprotonate the bound H2O molecule.

Amino Acids↗
PubMed1996

Structure of 4-chlorobenzoyl coenzyme A dehalogenase determined to 1.8 A resolution: an enzyme catalyst generated via adaptive mutation.

Here we describe the three-dimensional structure of 4-chlorobenzoyl-CoA dehalogenase from Pseudomonas sp. strain CBS-3. This enzyme catalyzes the hydrolysis of 4-chlorobenzoyl-CoA to 4-hydroxybenzoyl-CoA. The molecular structure of the enzyme/4-hydroxybenzoyl-CoA complex was solved by the techniques of multiple isomorphous replacement, solvent flattening, and molecular averaging. Least-squares refinement of the protein model reduced the crystallographic R factor to 18.8% for all measured X-ray data from 30 to 1.8 A resolution. The crystallographic investigation of this dehalogenase revealed that the enzyme is a trimer. Each subunit of the trimer folds into two distinct motifs. The larger, N-terminal domain is characterized by 10 strands of beta-pleated sheet that form two distinct layers which lie nearly perpendicular to one another. These layers of beta-sheet are flanked on either side by alpha-helices. The C-terminal domain extends away from the body of the molecule and is composed of three amphiphilic alpha-helices. This smaller domain is primarily involved in trimerization. The two domains of the subunit are linked together by a cation, most likely a calcium ion. The 4-hydroxybenzoyl-CoA molecule adopts a curved conformation within the active site such that the 4-hydroxybenzoyl and the adenosine moieties are buried while the pantothenate and pyrophosphate groups of the coenzyme are more solvent exposed. From the three-dimensional structure it is clear that Asp 145 provides the side-chain carboxylate group that adds to form the Meisenheimer intermediate and His 90 serves as the general base in the subsequent hydrolysis step. Many of the structural principles derived from this investigation may be directly applicable to other related enzymes such as crotonase.

Acyl Coenzyme A↗
PubMed1996

The influence of cigarette smoking, alcohol, and green tea consumption on the risk of carcinoma of the cardia and distal stomach in Shanghai, China.

BACKGROUND: The divergent incidence patterns of gastric cardia and distal stomach cancer may suggest different etiologies. This study examined the role of cigarette smoking, alcohol drinking, and green tea consumption as risk factors for carcinoma by anatomic subsite of stomach. METHODS: Newly-diagnosed stomach carcinoma patients (n = 1124) and frequency-matched population controls (n = 1451) were interviewed in person. Adjusted odds ratios (ORs) and 95% confidence intervals (CIs) were estimated using logistic regression models. RESULTS: Excess risks associated with cigarette smoking and alcohol consumption were observed largely among men. The adjusted ORs for all stomach cancer combined were 1.35 (CI: 1.06-1.71) for current smokers, and 1.26 (CI: 0.86-1.84) for ex-smokers. For tumors of the distal stomach, statistically significant positive dose-response trends were found for the number of cigarettes smoked per day, the duration and pack-years of smoking, and inverse trends for years of stopped smoking. For tumors of the gastric cardia, however, a monotonic association was found only for the number of cigarettes smoked per day (P=0.06). Alcohol consumption was not related to the risk of cardia cancer, while a moderate excess risk of distal stomach cancer (OR: 1.55; CI: 1.07-2.26) was observed among heavy alcohol drinkers. Green tea drinking was inversely associated with risk of stomach cancer arising from either subsite, with ORs of 0.77 (CI: 0.52-1.13) among female heavy drinkers, and 0.76 (CI: 0.55-1.27) among male heavy drinkers. CONCLUSIONS: Our findings provide further evidence that cigarette smoking and, possibly, alcohol consumption increase the risk of stomach carcinoma, notably of the distal segment. An inverse association with green tea drinking was also observed.

Adult↗
PubMed1996

Converting an alcohol to an amine in a cationic lipid dramatically alters the co-lipid requirement, cellular transfection activity and the ultrastructure of DNA-cytofectin complexes.

Cytofectins are positively charged lipophilic molecules that readily form complexes with DNA and other anionic polynucleotides. Normally, cytofectins are combined with an activity-augmenting phospholipid such as dioleoylphosphatidylethanolamine (DOPE), and a film of dried, mixed lipid is prepared and hydrated to form cationic liposomes. The liposome solution is then mixed with a plasmid DNA solution to afford cytofectin-DNA complexes which, when presented to living cells, are internalized and the transgene is expressed. One of the most potent cytofectins, dimyristoyl Rosenthal inhibitor ether (DMRIE), is presently being used to deliver transcriptionally active DNA into human tumor tissues. Here we report the remarkable consequences of replacing the alcohol moiety of DMRIE with a primary amine. The resulting cytofectin, called beta-aminoethyl-DMRIE (betaAE-DMRIE), promoted high level transfection over a broad range of DNA and cationic lipid concentrations. A comparison of in vitro transfection activity between DMRIE and betaAE-DMRIE in 10 cell types revealed that betaAE-DMRIE was more active than DMRIE, and that betaAE-DMRIE, unlike DMRIE, was maximally effective in the absence of colipid. The consequences of the alcohol-to-amine conversion on the structure of the cytofectin/DNA complex was also examined by Atomic Force Microscopy. Strikingly dissimilar images were found for plasmid DNA alone and for the plasmid complexes of betaAE-DMRIE and DMRIE/DOPE.

Alcohols↗
PubMed1996

Use of chimeric human immunodeficiency virus types 1 and 2 reverse transcriptases for structure-function analysis and for mapping susceptibility to nonnucleoside inhibitors.

The human immunodeficiency virus type 1 and type 2 (HIV-1 and HIV-2) reverse transcriptases (RTs) are evolutionary related. To study the effect of homologous sequence replacements on polymerase function and to map the determinants of the lack of susceptibility of HIV-2 RT to nonnucleoside drugs, a series of chimeric HIV-1/HIV-2 RTs were constructed. Analysis of the chimeric RTs showed that wild-type levels of RNA-dependent DNA polymerase activity were retained when both finger and palm subdomains were exchanged as a unit between the two parental RTs. Analysis of enzymatically active chimeras for inhibition by the thiobenzimidazolone derivative TIBO R82150 showed that a segment of HIV-2 RT at 212-250, when placed in the HIV-1 RT context, conferred a 40-fold decrease in susceptibility to TIBO R82150. Site-directed mutagenesis of this segment found Tyr227 to be a key residue in this segment for the natural resistance of HIV-2 RT to TIBO R82150.

Amino Acids↗
PubMed1996

Prostate cancer gene therapy: herpes simplex virus thymidine kinase gene transduction followed by ganciclovir in mouse and human prostate cancer models.

Prostate cancer is the most common internal malignancy in men in the United States. Most cancers are diagnosed when they are locally advanced or metastatic and there is no effective treatment. In this study we evaluated the effectiveness of cytotoxic gene therapy in human PC-3 and DU145 prostate cancer cell lines and in a rodent cell line, RM-1, derived from the mouse prostate reconstitution model system. The cell lines were efficiently transduced in vitro by a replicative-defective recombinant adenovirus (ADV) carrying the herpes simplex virus thymidine kinase gene (HSV-tk). A virus titer-dependent sensitivity to ganciclovir (GCV) was observed. To determine a target therapeutic viral dose in vivo, subcutaneous tumors were generated by injection of RM-1 cells in syngeneic male hosts and injected with escalating doses of HSV-tk virus (5 x 10(7) to 1 x 10(9) pfu). The mice received GCV twice daily for 6 days and were sacrificed when tumor volumes exceeded 2.5 cm3 or when they appeared to be in distress. Because the two highest doses were equally as effective, further controlled studies were performed with the lower dose of 5 x 10(8) pfu with ADV/RSV-tk or a control virus containing the beta-galactosidase gene (ADV/RSV-beta-Gal) and treated with GCV or saline (PBS). The mean tumor volume in the treated animals was 16% that of control animals at 13 days. Histologically, treated tumors demonstrated necrosis and had a significantly higher apoptotic index. Survival data indicated that the treatment animals lived 7 days (21 in total) longer than the control animals, with 1 treatment animal being totally free of tumor. These results demonstrate that HSV-tk + GCV cytotoxic gene therapy can inhibit the growth of mouse and human prostate cancer cells in vitro and interrupt tumor growth of an aggressive mouse prostate cancer cell line in vivo.

Adenoviridae↗
PubMed1996

Extracellular matrix is a source of mitogenically active platelet-derived growth factor.

Platelet-derived growth factor (PDGF) is a chemotactic and mitogenic agent for fibroblasts and smooth muscle cells and plays a key role in the development of atherosclerotic lesions. PDGF is produced by a number of normal and transformed cell types and occurs as homo- or heterodimers of A and B polypeptide chains. Using Chinese hamster ovary (CHO) cells transfected with various forms of PDGF, we have previously shown that PDGF A(s) (short splice version) is secreted, PDGF A(l) (long splice version) predominantly extracellular matrix-associated, and PDGF B divided between medium, cells, and matrix. In the present study we have demonstrated the mitogenic activity of matrix-localized PDGF in artificial and more physiologically relevant models by culturing Balb/c-3T3 cells (3T3), human foreskin fibroblasts (HFF), and rabbit aortic smooth muscle cells (SMC) on extracellular matrix (ECM) laid down by PDGF-expressing CHO cells and human umbilical vein endothelial cells (HUVEC). These cells responded to the local growth stimulus of PDGF-containing CHO ECM and HUVEC ECM. We showed that 3T3 cells required proteolytic activity to utilize matrix-localized PDGF, as aprotinin and epsilon-ACA inhibited growth and 3T3 cells were shown to possess plasminogen activator activity. HFF and SMC did not appear to require proteolytic activity (including metalloproteinase and serine protease activity) as a prerequisite for mitogenesis but were able to access immobilized PDGF by contact with the matrix. An understanding of the mechanisms whereby the utilization of stored PDGF is controlled in situations of excessive cellular proliferation will aid in the development of therapy for these conditions.

3T3 Cells↗
PubMed1996

Apoptosis in renal cell carcinoma: detection by in situ end-labeling of fragmented DNA and correlation with other prognostic factors.

Because stage and grade of renal cell carcinoma (RCC) sometimes fail to predict the patient's outcome, additional prognostic predictors are needed. Apoptosis is a process of programmed cell death seen in both normal and neoplastic tissues, which has been shown to have prognostic significance in some tumor types. Forty-seven RCCs were studied for size, grade, stage, apoptosis, and proliferation. Fragmented DNA, a hallmark of apoptosis, was detected in situ by a process in which the fragmented DNA was labeled with a biotinylated nucleotide, which, in turn, was detected by an avidin-biotin-peroxidase labeling system. The proliferating tumor cells were detected by immunostaining with the MIB-1 antibody. The apoptotic index and proliferation index of each RCC were expressed as the number of tumor cells undergoing apoptosis and proliferation per 1,000 tumor cells. For grade I to IV RCCs, the median proliferative index was 13, 41, 119, and 143; the median apoptotic index was 8, 12, 39, and 73. For stage I to IV RCCs, the median proliferative index was 21, 34, 70, and 144; the median apoptotic index was 8, 9, 20, and 69. There was a statistically significant correlation of tumor grade, stage, and size with both proliferative index and apoptotic index. There was a statistically significant correlation between proliferation index and apoptotic index. In conclusion, apoptosis can be easily and reliably recognized by the in situ end labeling of fragmented DNA and may help predict the outcome of RCC.

Antibodies, Monoclonal↗
PubMed1996

Cell apoptosis and proliferation in experimental chronic obstructive uropathy.

Cell proliferation and apoptosis in kidneys with chronic obstructive uropathy (COU) have not been adequately studied. Whether these fundamental cellular processes play any role in the pathogenesis and evolution of COU remains undetermined. Sprague-Dawley rats with COU induced by unilateral ureteral ligation were sacrificed at postoperative days 1, 6, 9, 15, 34, 43, 60, 75, and 90, and were compared with control, sham-operated rats sacrificed at days 0, 15, 43, and 90. The kidneys with ureteral ligation, the contralateral kidneys, and the control kidneys were submitted to in situ end-labeling of fragmented DNAs for the detection of apoptotic cells, and to immunostaining with many monoclonal antibodies directed against the nuclear antigens associated with cell proliferation for the detection of proliferating cells. Additional rats with COU were also submitted to BrdU labeling to detect proliferating cells. The tubular, interstitial, and glomerular cells showing either apoptosis or proliferation were separately quantitated and the obtained data were correlated with dry kidney weight, tubular diameter, glomerular surface area and interstitial volume. Apoptotic tubular cells in kidney with COU increased rapidly, reaching 30-fold that of control at day 25, which was followed by an equally rapid decrease to the control level. During the same period, both the dry kidney weight and the mean tubular diameter decreased markedly. These data suggest that apoptosis may play a significant role in tubular atrophy and renal weight loss. The rapid increase in tubular cell apoptosis was immediately preceded by a 37% gain in the dry kidney weight over the control; just before that increase, there was also an approximate 60-fold increase in the proliferation rate of tubular cells detected by immunostaining for proliferating nuclear antigen or by BrdU labeling. The significance of this intriguing temporal relationship of tubular cell apoptosis and proliferation remains to be elucidated, but it may have pathogenetic implications. In contrast to the rise and fall of the frequency of tubular cell apoptosis and proliferation, the frequency of interstitial cell apoptosis and proliferation displayed continuous increase toward the end of the experiment, with a roughly parallel increase in the interstitial damage. Apoptosis and proliferation of glomerular cells in kidneys with COU did not show any significant changes throughout the experiment. In conclusion, the obtained data suggest that tubular cell apoptosis may be pathogenetically related to the tubular atrophy and renal tissue loss in COU, and that proliferation and apoptosis of interstitial cells may play a role in the observed interstitial changes in this model. This study should provide the impetus for further exploration of the mechanisms of cell death and cell proliferation as a novel venue for understanding the pathogenesis of COU.

Animals↗
PubMed1996

Human cytomegalovirus is not implicated in benign prostatic hyperplasia: a study using immunohistochemistry and the polymerase chain reaction.

PURPOSE: To evaluate whether human cytomegalovirus (CMV) may play a role in the pathogenesis of benign prostatic hyperplasia. MATERIALS AND METHODS: We used immunohistochemistry and the polymerase chain reaction (PCR) to evaluate the presence of CMV in normal prostatic tissue (n = 12) and BPH tissue (n = 21). RESULTS: Immunostaining for CMV in prostatic tissue was negative; however, staining was evident in mononuclear cells seen in the tissues of both groups. With nested PCR, CMV genomic material was demonstrated in 1 tissue specimen from each group (p > 0.1). CONCLUSIONS: These data suggest that CMV is unlikely to be a significant factor in the pathogenesis of BPH.

Base Sequence↗
PubMed1996

Unusual sequence relationships between two isolates of citrus tristeza virus.

The complete, 19,226 nt sequence of the RNA genome from VT, a seedling yellows strain of citrus tristeza virus (CTV), was determined and found to have a genome organization identical with that of the previously determined CTV-T36 isolate, except that ORF 1 of CTV-VT was 70 nt shorter due to two widely separated 18 nt deletions. Sequence comparison of CTV-VT and CTV-T36 revealed approximately 89% identity throughout the ten 3' ORFs, but only 60-70% identity throughout ORF 1. The 5' nontranslated regions were only 60% identical whereas the 3' nontranslated regions were 97% identical. The transition between regions of similarity and deviation was gradual, suggesting that the sequence similarities and differences compared to CTV-T36 were unlikely to have arisen from a recent recombination event between a close T36 relative and a distantly related CTV isolate. This is the first attempt to compare in detail the variation between the genomes of two strains of a member of the closterovirus group. The observed deviation between the large RNA genomes of the two CTV strains is greater than that among different viruses of most other groups, raising the question of how to define the taxonomy of these viruses.

Base Sequence↗
PubMed1996

A polyketide synthase is required for fungal virulence and production of the polyketide T-toxin.

Race T of the fungal pathogen Cochliobolus heterostrophus is highly virulent toward Texas male sterile (T) maize and differs from its relative, race O, at a locus (Tox1) that is responsible for the production of T-toxin, a family of linear long-chain (C35 to E41) polyketides. In a previous study, the restriction enzyme-mediated integration procedure was used to mutagenize and tag Tox1. Here, we report that the DNA recovered from the insertion site of one mutant encodes a 7.6-kb open reading frame (2530 amino acids) that identifies a multifunctional polyketide synthase (PKS)-encoding gene (PKS1) with six catalytic domains arranged in the following order, starting at the N terminus: beta-ketoacyl synthase, acyltransferase, dehydratase, enoyl reductase, beta-ketoacyl reductase, and acyl carrier protein. PKS1 is interrupted by four apparent introns (74, 57, 49, and 41 bp) and exists in the genome as a single copy surrounded by highly repetitive, A + T-rich DNA. When PKS1 in race T was inactivated by targeted gene disruption, T-toxin production and high virulence were eliminated, indicating that this PKS is required for fungal virulence. Race O strains, which do not produce T-toxin, lack a detectable homolog of PKS1, suggesting that race T may have acquired PKS1 by horizontal transfer of DNA rather than by vertical inheritance from an ancestral strain.

Amino Acid Sequence↗
PubMed1996

Effect of E2 envelope glycoprotein cytoplasmic domain mutations on Sindbis virus pathogenesis.

The cytoplasmic domain of the E2 envelope glycoprotein is important in Sindbis virus assembly, but little is known about its role in the pathogenesis of Sindbis virus encephalitis. To investigate its role in viral pathogenesis, we constructed six recombinant viruses containing site mutations in the E2 cytoplasmic domain, using the neurovirulent background strain, TE12. Our findings demonstrate that the E2 cytoplasmic domain is a determinant of Sindbis virus growth and neurovirulence in suckling mice as well as persistent infection in weanling scid mice. They also suggest that the tyrosine, serine, or threonine residues are not essential for replication in mouse brain or anti-E2 monoclonal antibody-mediated restriction of Sindbis virus replication.

Alphavirus Infections↗
PubMed1996

7-Nitroindazole attenuates vasodilation from cerebellar parallel fiber stimulation but not acetylcholine.

We used the relatively selective inhibitor of neuronal nitric oxide synthase 7-nitroindazole (7-NI) to test the hypothesis that the increases in local cerebellar blood flow (BFcrb) elicited by activation of the cerebellar parallel fibers (PF) are mediated by neuronal production of nitric oxide. In halothane-anesthetized rats, the cerebellar cortex was exposed and superfused with Ringer solution (37 degrees C; pH 7.3-7.4). The PF were stimulated electrically (100 microA, 30 Hz, 40 s), while BFcrb was monitored at the site of stimulation by a laser-Doppler flow probe. In vehicle-treated rats (n = 5), PF stimulation increased BFcrb by 61 +/- 5% (P < 0.05; analysis of variance and Tukey's test). 7-NI attenuated the increase in BFcrb dose dependently (10-100 mg/kg i.p.; n = 5 animals/dose) and by 55 +/- 7% at 100 mg/kg (P < 0.05). The attenuation of the response to PF stimulation was correlated with the degree of inhibition of calcium-dependent brain nitric oxide synthase activity, measured ex vivo by the citrulline assay (n = 21). 7-NI also attenuated the cerebrovasodilation elicited by hypercapnia (PCO2 = 50-60 mmHg) but did not affect the vasodilation evoked by acetylcholine (10 microM; n = 4; P > 0.05; t-test), a response mediated by endothelial nitric oxide synthase. 7-NI did not attenuate the BFcrb increase evoked by the nitric oxide donor S-nitroso-N-acetylpenicillamine (1 mM; n = 5; P > 0.05; t-test). Similarly, 7-NI did not affect resting systemic arterial pressure. These observations suggest that selective inhibition of neuronal nitric oxide synthase by 7-NI attenuates the increases in BFcrb evoked by PF stimulation. The findings provide additional support to the hypothesis that the increase in BFcrb evoked by PF stimulation is mediated, in part, by glutamate-induced activation of neuronal nitric oxide synthase.

Acetylcholine↗