Early and sharp nitric oxide production and anoxic depolarization in the rat hippocampus during transient forebrain ischemia

This study was designed to characterize nitric oxide (NO) production and anoxic depolarization in the rat hippocampus during transient forebrain ischemia using two NO synthase (NOS) inhibitors, L-N(5)-(1-iminoethyl)ornithine (L-NIO), a relatively selective endothelial NOS (eNOS) inhibitor, and 7-nitroindazole, a relatively selective neuronal NOS (nNOS) inhibitor, and an NO scavenger, [2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide] (carboxy-PTIO). We measured the mean arterial blood pressure, hippocampal blood flow, NO concentration and direct current potential before, during and after transient forebrain ischemia, which was induced by 4-vessel occlusion for 10 min. Saline, L-NIO (20 mg/kg), 7-nitroindazole (25 mg/kg), L-NIO (20 mg/kg)+7-nitroindazole (25 mg/kg) or carboxy-PTIO (1 mg/kg) was administered intraperitoneally 20 min before the onset of ischemia. We observed early and sharp NO production in the hippocampus during ischemia in the saline group. This NO increase during ischemia was significantly reduced by L-NIO (20 mg/kg)+7-nitroindazole (25 mg/kg) or carboxy-PTIO (1 mg/kg), but not L-NIO (20 mg/kg) or 7-nitroindazole (25 mg/kg). On the other hand, NO production after ischemia was significantly reduced by 7-nitroindazole (25 mg/kg), L-NIO (20 mg/kg)+7-nitroindazole (25 mg/kg) or carboxy-PTIO (1 mg/kg), but not L-NIO (20 mg/kg). The peak latency of NO production during ischemia always preceded the onset latency of anoxic depolarization in both the saline group and the carboxy-PTIO group. In the carboxy-PTIO group, the onset latency of anoxic depolarization was significantly longer than that in the saline group. Moreover, carboxy-PTIO significantly reduced the anoxic depolarization amplitude, compared with that of the saline group. These results suggest that both NOS-dependent and-independent NO formation contributes to early and sharp NO production during ischemia, and that this NO increase is, at least in part, related to the triggering of anoxic depolarization.     

7—硝基吲唑对在体大鼠海马l—黄皮酰胺和高频电刺激诱发长时程增强 …

AIM: To study the antagonistic effect of selective neuronal nitric-oxide synthase (nNOS) inhibitor 7-nitroindazole on the long-term potentiation (LTP) induced by l-clausenamide (Cla) in rat hippocampus in vivo. METHODS: Population spike (PS) of evoked potentials was determined by extracellular recording technique in the hippocampal dentate gyrus (DG) of anesthetized rats. RESULTS: 7-Nitroindazole 2 nmol icv blocked the induction of LTP elicited by high-frequency (100 Hz) stimulation or Cla 5 nmol icv (P < 0.01), and L-arginine 225 mg.kg-1 i.p. prevented the action of 7-nitroindazole (P < 0.01). CONCLUSION: Nitric oxide produced by nNOS plays a role in the induction of Cla-induced LTP in hippocampus.     

Protective effect of vinpocetine against brain damage caused by ischemia

The effects of vinpocetine against hippocampal neuronal damage and on local cerebral blood flow (LCBF) were examined in a rat model of forebrain ischemia (10-min occlusion of the carotid arteries and hypotension). Histological evaluation of neuronal loss in the hippocampus was performed 7 days after ischemia. LCBF was measured before ischemia as well as after 2 min and 1 hr of recirculation. Vinpocetine (10 mg/kg) administered pre- or post-ischemically reduced the hippocampal neuronal necrosis, while pre-ischemic administration of 2 or 20 mg/kg vinpocetine was ineffective. Since vinpocetine increased the LCBF after 1 hr of recirculation, it cannot be excluded that blood flow improvements contribute to its neuroprotective activity. On the other hand, there is no clear evidence that an elevation of post-ischemic hypoperfusion could protect neurons against ischemic damage. It is, therefore, suggested that vinpocetine acts directly on brain cells.     

7-Nitroindazole potentiates the antiseizure activity of some anticonvulsants in DBA/2 mice

7-Nitroindazole, a selective neuronal nitric oxide synthase inhibitor (25-200 mg kg(-1), intraperitoneally (i.p.)) antagonized audiogenic seizures in DBA/2 mice in a dose-dependent manner. We investigated the effects of 7-nitroindazole at a dose of 25 mg kg(-1) i.p., which per se did not show anticonvulsant activity against audiogenic seizures in DBA/2 mice, on the antiseizure activity of some conventional antiepileptic drugs. 7-Nitroindazole sometimes potentiated the anticonvulsant activity of carbamazepine, diazepam, lamotrigine, phenytoin, phenobarbital and valproate against audiogenic seizures in DBA/2 mice. The degree of potentiation by 7-nitroindazole was greatest for phenobarbital and diazepam, less for valproate and least for carbamazepine, lamotrigine and phenytoin. The increase in anticonvulsant activity was associated with a comparable increase in motor impairment. However, the therapeutic index of combined treatment with diazepam+7-nitroindazole, phenobarbital+7-nitroindazole or valproate+7-nitroindazole was more favourable than that of the diazepam+vehicle, phenobarbital+vehicle or valproate+vehicle treatment. The results indicate that 7-nitroindazole is able to increase the protective activity of some conventional antiepileptics and this effect appears not to result only from the impaired synthesis of nitric oxide. In fact, mice receiving 7-nitroindazole (25 mg kg(-1), i.p.) and L-arginine (30 microg/mouse, intracerebroventricularly (i.c.v.) did not show significant changes of ED(50) values in comparison to those of related groups of animals treated with 7-nitroindazole and anticonvulsants. 7-Nitroindazole was able to increase the brain levels of dopamine and noradrenaline and its anticonvulsant effects and changes in catecholamine content were antagonized by pretreatment with alpha-methyl-paratyrosine, an agent inhibiting the synthesis of catecholamines. The fact that alpha-methyl-paratyrosine reverses concomitantly both the increase in brain levels of dopamine and noradrenaline and the anticonvulsant properties of 7-nitroindazole strongly suggests an important role of catecholamines in the antiseizure activity of 7-nitroindazole. Since 7-nitroindazole did not significantly influence the total and free plasma levels of the anticonvulsant drugs studied, we suggest that pharmacokinetic interactions, in terms of total or free plasma levels, are not probable. 7-Nitroindazole did not significantly affect the hypothermic effects of the anticonvulsant compounds studied. 7-Nitroindazole showed an additive effect when administered in combination with some classical anticonvulsants, most notably diazepam, phenobarbital and valproate and its activity could be, in part, due to an increase of monoamine levels.     

Neuroprotective effects of 7-nitroindazole in the gerbil model of global cerebral ischaemia

To evaluate the role played by nitric oxide in global cerebral ischaemia we examined the effects of 7-nitroindazole and a sodium salt of 7-nitroindazole (inhibitors of neuronal nitric oxide (NO) synthase) and N^G-nitro- -arginine methyl ester (a more general inhibitor of NO synthase) in the gerbil model of cerebral ischaemia. Four experiments were carried out. In the first experiment, animals were either sham-operated, subjected to 5 min bilateral carotid occlusion (BCAO) or administered 7-nitroindazole orN^G -nitro- -arginine methyl ester immediately after occlusion followed by three further doses at 3, 6 and 24 h post-occlusion. In the second experiment, we examined the effects of a sodium salt of 7-nitroindazole, which is more soluble than 7-nitroindazole, using the same protocol. In the third experiment, the effects of the sodium salt of 7-nitroindazole administered at 10 mg/kg at 0, 3, 6, 24, 27, 30, 33, 52, 55, 72, 75 and 78 h post-occlusion or at 0.05 mg/h for 72 h via mini-pumps were evaluated. In separate experiments, we examined the effects of three reference compounds dizocilpine (MK-801), 2,3-dihydroxy-6-nitro-7-sulphamoyl-benz(F)-quinoxaline (NBQX) and eliprodil using the same model. Extensive neuronal death was observed in the CA1 layer of the hippocampus in 5 min bilateral carotid occluded animals 5 days after surgery. Both 7-nitroindazole and N^G-nitro- -arginine methyl ester provided significant neuroprotection (P < 0.01) against this neuronal death. The sodium salt of 7-nitroindazole showed no protection when administered up to 12 times post-occlusion, but did provide significant (P < 0.01) neuroprotection when administered via mini-pump. The neuroprotection was similar to that provided by MK-801 and eliprodil, but not as good as that observed with NBQX. These results indicate that nitric oxide plays a role in ischaemic cell death and that selective neuronal nitric oxide synthase inhibitors can protect against ischaemic brain damage.     

Acute inhibition of glutathione biosynthesis alters endothelial function and blood pressure in rats

The present study investigated the role of nitric oxide (NO) in the rewarding effects of D-methamphetamine using 7-nitroindazole, a potent inhibitor of neuronal nitric oxide synthase (nNOS), as determined by the conditioned place preference paradigm. Male Sprague-Dawley rats treated with D-methamphetamine (1 mg/kg) or saline every other day for 8 days (four drug and four saline sessions) developed marked place preference for the drug-paired side. The administration of 7-nitroindazole (12.5-50 mg/kg) 30 min prior to the exposure to D-methamphetamine dose-dependently attenuated the acquisition of D-methamphetamine-induced conditioned place preference. In addition, when it was acutely administered 30 min prior to the testing session of an already established D-methamphetamine-induced conditioned place preference, 7-nitroindazole (12.5-50 mg/kg) attenuated the expression of this conditioned response in a dose-dependent manner, while 7-nitroindazole (25 and 50 mg/kg) alone showed no place preference effects. These findings indicate that nitric oxide (NO) is involved in the rewarding properties of methamphetamine and suggest that selective nNOS inhibitors maybe useful in the management of methamphetamine abuse.     

Neuroprotective Effects of Kangen-karyu on Spatial Memory Impairment in an 8-Arm Radial Maze and Neuronal Death in the Hippocampal CA1 Region Induced by Repeated Cerebral Ischemia in Rats

In the present study, we investigated the neuroprotective effects of Kangen-karyu (KGK) in a repeated cerebral ischemia model (2 × 10 min, 1-h interval). A 21-day pre- and postischemic treatment with KGK (10 – 300 mg/kg) and aspirin (5 mg/kg) improved the spatial memory impairment and neuronal death in the hippocampal CA1 region induced by repeated cerebral ischemia. However, a 7-day post-ischemic treatment with KGK did not attenuate the spatial memory impairment and neuronal death in this model. To determine the mechanism of action of KGK, we investigated the effects of a 14-day pre-ischemic treatment with KGK on cerebral blood flow in the hippocampal area of the repeated cerebral ischemia model using laser Doppler flowmetry. The 14-day pre-ischemic treatment with KGK increased the cerebral blood flow during reperfusion. These results suggest that a 21-day pre- and post-ischemic treatment with KGK can protect against brain damage caused by cerebral ischemia by increasing the cerebral blood flow in the hippocampal area.     

A neuronal nitric oxide synthase inhibitor 7-nitroindazole reduces the 5-HT1A receptor against 8-OH-DPAT-elicited hyperphagia in rats.

The effects of the neuronal nitric oxide (NO) synthase inhibitor 7-nitroindazole on 8-hydroxy-2-di-n-(propylamino)tetralin (8-OH-DPAT)-induced hyperphagia, which is mediated by the 5-HT1A autoreceptor, were investigated in rats. 7-Nitroindazole suppressed 8-OH-DPAT-elicited increases in food intake. The inhibitory effects of 7-nitroindazole on 8-OH-DPAT-induced feeding were prevented by the NO precursor L-arginine. Although 8-OH-DPAT decreases 5-hydroxytryptamine (5-HT) synthesis, 7-nitroindazole did not reverse the 8-OH-DPAT-elicited decrease in 5-HT synthesis. Therefore, these results indicate that NO formed in the brain is involved in 8-OH-DPAT-induced hyperphagia and that the hypophagic effects of 7-nitroindazole are not dependent on 5-HT synthesis.     

Use of an electrochemical nitric oxide sensor to detect neuronal nitric oxide production in conscious, unrestrained rats

INTRODUCTION: Amperometric sensors that directly measure nitric oxide (NO) are readily employed in pharmacologic research. While several of these sensors have been developed, none has been investigated for use in conscious, freely moving animals. An approach was developed and validated for real-time quantitation of neuronal NO production in rats without restricting locomotor activity or other potentially useful behavioral endpoints. METHODS: Male Sprague-Dawley rats were equipped with a femoral vein or intraperitoneal cannula. A guide cannula and an amperometric NO sensor were placed in the left and right hippocampus, respectively. Following recovery, rats received a 6-h intravenous infusion of saline, L-arginine (an NO precursor; 250 or 500 mg/kg/h), or incremental intraperitoneal 7-nitroindazole (an NO synthase inhibitor; 200-mg/kg loading dose and 100 mg/kg every 2 h). The sensor recorded NO production continuously and microdialysis samples were collected incrementally throughout the experiment. Griess assay analysis of microdialysate samples was compared to sensor readings in vivo. In vitro degradation of an NO donor also was used to validate sensor performance. RESULTS: Exogenous administration of L-arginine resulted in incremental increases in the neuronal NO signal. A reduction in NO production was observed during administration of 7-nitroindazole, a selective neuronal NO synthase inhibitor. A significant correlation was observed in vitro between the Griess assay analysis, an indirect analytical approach, and the NO sensor readings. The lack of a strong correlation between these measures in vivo is consistent with the indirect nature of the Griess assay. DISCUSSION: The current approach allows real-time determination of neuronal NO production in unrestrained rats. This model will be invaluable in evaluating pharmacologic issues regarding brain tissue NO synthesis, assessing brain NO synthase as a molecular target, and establishing the effects of pharmacologic agents on neuronal NO production.     

Effect of staurosporine, a protein kinase C inhibitor, on impairment of working memory in rats exposed to cerebral ischemia.

A 5-min period of cerebral ischemia induced in rats by the four-vessel occlusion method increased the number of errors (attempts to pass through two incorrect panels of the three panel-gates at four choice points) assessed by a working memory procedure applied in a three-panel runway task. The protein kinase C (PKC) inhibitor, staurosporine 0.03 and 0.1 mg/kg, administered immediately after blood flow reperfusion, significantly reduced the increase in errors expected to occur 24 h after 5 min of ischemia. However, administration of staurosporine 0.1 mg/kg 6 h after ischemia had no effect on the increase in errors. The protective effect of staurosporine suggests that the enhanced PKC activity during the early reperfusion phase plays a crucial role in the post-ischemic impairment of working memory.     

Inhibition of nitric oxide synthesis accelerates the recovery of polysynapitc reflex potentials after transient spinal cord ischemia in cats

Nitric Oxide (NO) has been implicated as a mediator of neuronal injury in vascular stroke. On the other hand, NO is suggested to play a neuroprotective role by increasing blood flow during cerebral ischemia. In order to evaluate the role of NO in the spinal cord ischemia, effects of nitric oxide synthase (NOS) inhibition on the recovery of reflex potentials after a transient spinal cord ischemia were examined in urethane-chloralose anesthetized spinal cats. Spinal cord ischemia was produced by occlusion of the thoracic aorta and the both internal mammary arteries for 10min. Regional blood flow (RBF) in the spinal cord was continuously measured with a laser-Doppler flow meter. The monosynaptic (MSR) and polysynaptic reflex (PSR) potentials elicited by electrical stimulation of the tibial nerve, were recorded from the L7 or S1 ventral root. The recovery process of spinal reflex potentials was reproducible when the oclusion was repeated twice at an interval of 120min. Pretreatment with N ^G-monomethyl-l-arginine (l-NMMA, 10mg/kg), a NOS inhibitor significantly accelerated the recovery of PSR potentials after spinal cord ischemia. The accelerating effect of l-NMMA on the recovery of PSR potentials was abolished by co-administration of l-arginine (1mg/kg/min) but not by that of d-arginine (1mg/kg/min). l-NMMA failed to improve RBF in the spinal cord during ischemia and reperfusion. Nitroprusside (10μg/kg/min), a NO donor, retarded the recovery of PSR potentials after spinal cord ischemia. These results suggest that NO production has a significant influence on the functional recovery after transient spinal cord ischemia. Received: 16 September 1996/Accepted: 2 January 1997     

Differential effects of nitric oxide synthase inhibitor, 7-nitroindazole, on discriminative stimulus and somatic effects of naloxone in morphine-dependent rats.

Our previous report suggested that antagonists acting at NMDA receptors attenuate discriminative stimulus effects of naloxone in morphine dependent rats. Nitric oxide (NO) is a putative second messenger which mediates NMDA receptor activation. The present study evaluated behavioral effects of NO synthase inhibitor, 7-nitroindazole in morphine-dependent rats trained to discriminate 0.1 mg/kg naloxone from saline. 7-Nitroindazole did not significantly affect naloxone's discriminative stimulus effects but decreased naloxone-induced weight loss and abolished expression of several withdrawal signs--diarrhea, scream on touch, tremor and 'wet dog'-like shaking suggesting different mechanisms for subjective and somatic components of opioid withdrawal.     

Regulatory role of nitric oxide over hippocampal 5-HT release in vivo

Previous work has shown that N-methyl-D-aspartate (NMDA) receptor activation decreases 5-hydroxytryptamine (5-HT) release in the hippocampus of freely moving rats. Given the association between NMDA receptor function and nitric oxide (NO) production with the regulation of 5-HT release in other brain regions, we have studied this in rat hippocampus. NMDA (100 microM) decreased hippocampal 5-HT release by approximately 70% and this was reversed by the NMDA receptor antagonist 2-amino-5-phosphonopentanoic acid (AP5; 10 microM). The NO donor S-nitroso-N-acetylpenicillamine (SNAP) had an inverse concentration-dependent effect on 5-HT release. At 500 microM, SNAP elevated dialysate 5-HT by 55% over basal, while at 5 mM a 70% decrease was seen. The non-selective nitric oxide synthase (NOS) inhibitor N-nitro-L-arginine methyl ester (L-NAME) at 1 mM increased extracellular 5-HT, although a return to basal levels occurred despite the continued presence of the drug. At 1 mM L-NAME prevented the decrease in 5-HT elicited by NMDA (100 microM) infusion. 7-Nitroindazole (7-NI), a relatively selective neuronal NOS (nNOS) inhibitor, decreased extracellular 5-HT at 100 microM and 1 mM. When 100 microM 7-NI was infused for 60 min prior to NMDA, 5-HT levels were transiently increased above basal before returning to control levels. Following combined application of the two drugs, no decrease in dialysate 5-HT was seen. Our data support a role for NO in modulating both basal and NMDA-evoked changes in 5-HT release in the hippocampus, however, the association appears to be complex. It may be that the recorded changes in 5-HT release are secondary to changes in the release of amino acid transmitters which we have previously found to be dependent on the prevailing extracellular NO concentration.     

Inhibitory effects of pre-ischemic and post-ischemic treatment with FR 168888, a Na+/H+ exchange inhibitor, on reperfusion-induced ventricular arrhythmias in anesthetized rat

Effects of pre-ischemic and post-ischemic treatment with FR 168888 (5-hydroxymethyl-3-(pyrrol-1-yl) benzoylguanidine methanesulfonate), a Na+/H+ exchange inhibitor, on reperfusion-induced ventricular arrhythmias were examined in an ischemia/reperfusion model of anesthetized rat. FR 168888 (0.3 mg/kg) significantly reduced the incidence of ventricular fibrillation (VF) and mortality induced by reperfusion following 5-min coronary occlusion, when it was intravenously administered 5 min before coronary artery occlusion. Post-ischemic treatment with FR 168888 (0.3-10 mg/kg), i.e. given 3 min after the start of occlusion, reduced the incidence of VF and mortality. In order to examine the optimal time of administration, FR 168888 (3 mg/kg) was administered 1 or 3 min after the start of occlusion or immediately before reperfusion. There was no significant difference in the reduction of VF and mortality among the three post-ischemic treatment groups. FR 168888 (3 and 10 mg/kg) significantly increased the blood pressure during ischemia without affecting the heart rate. These results indicate that FR 168888 has antiarrhythmic effects on reperfusion-induced arrhythmias even administered after coronary occlusion.     

Involvement of nitric oxide in the modulation of dural arterial blood flow in the rat

1. Nitric oxide (NO) has been proposed to be a key molecule in the pathogenesis of migraine pain and other headaches that are linked to vascular disorders. Several lines of evidence indicate that the meningeal vascularization is crucially involved in the generation of these headaches. In an experimental model in the rat a dominating role of calcitonin gene-related peptide (CGRP) in causing neurogenic vasodilatation and increased blood flow has been shown. The aim of the present study was to clarify the role of NO in this model with regard to the meningeal blood flow. 2. The blood flow in and around the medial meningeal artery (dural arterial flow) was recorded in the exposed parietal dura mater encephali of barbiturate anaesthetized rats using laser Doppler flowmetry. Local electrical stimulation of the dura mater (pulses of 0.5 ms delivered at 7.5 - 17.5 V and 5 or 10 Hz for 30 s) caused temporary increases in dural arterial flow for about 1 min that reached peaks of 1.6 - 2.6 times the basal flow. The effects of NO synthase (NOS) inhibitors on the basal flow and the electrically evoked increases in flow were examined. 3. Systemic (i. v.) administration of N(omega)-nitro-L-arginine methyl ester (L-NAME) at cumulative doses of 10 and 50 mg kg(-1) lowered the basal flow to 87 and 72%, respectively, of the control and reduced the evoked increases in blood flow to 82 and 44% on an average. Both these effects could partly be reversed by 300 mg kg(-1) L-arginine. The systemic arterial pressure was increased by L-NAME at both doses. Injection of the stereoisomer D-NAME at same doses did not change basal flow and evoked increases in flow. 4. 4. Topical application of L-NAME (10(-4) - 10(-2) M) was effective only at the highest concentration, which caused lowering of the basal blood flow to 78% of the control; the evoked increases in flow were not changed. Topical application of 2-amino-5,6-dihydro-6-methyl-4H-1,3-thiazine (AMT), a specific inhibitor of the inducible NOS, at concentrations of 10(-4) - 10(-2) M lowered the basal flow to 89, 87.5 and 85%, respectively, but did not significantly change the evoked flow increases. Same concentrations of 7-nitroindazole monosodium salt (7-NINA), a specific inhibitor of the neuronal NOS, had no significant effects on basal flow and evoked increases in flow. 5. It is concluded that NO is involved in the maintenance of the basal level of dural arterial blood flow as well as in the electrically evoked flow increases, which have been shown to be mainly mediated by CGRP released from dural afferent fibres. The most important source of NO is probably the endothelium of dural arterial vessels. The synergistic effect of NO and CGRP on the stimulated blood flow may be in part due to a NO mediated facilitation of the CGRP release.     

Biphasic modulation by nitric oxide of caspase activation due to malonate injection in rat striatum

The present study examined caspase activation and its modulation by nitric oxide (NO) in a model of oxidative stress induced by injection of malonate (3 micromol), a mitochondrial toxin, into rat striatum. Caspase-3-like enzymatic activity was maximal 6 h after malonate while NO production evaluated by its metabolites nitrites and nitrates was increased at 3 h. The neuronal NO-synthase inhibitor 7-nitroindazole reduced malonate induced-NO production by 50% at 25 mg/kg and enhanced by 32% caspase activation. This result suggests that a moderate production of NO potentiates caspase activation, an effect counterbalanced by NO itself at higher concentrations. Accordingly, complete inhibition of NO production by 7-nitroindazole at 50 mg/kg did not modify malonate-induced caspase activity. Thus NO production by the neuronal isoform of NO-synthase is not the major event leading to caspase activation due to malonate. However, NO seems to have pro- and anti-caspase effects that neutralize each other.     

Role of nitric oxide in maintenance of basal oral tissue blood flow in anesthetized cats.

Experiments were undertaken to determine if nitric oxide (NO) plays a role in regulation of basal blood flow in the oral cavity of pentobarbital anesthetized cats and, if so, to quantify this effect using dose-response relationships. Blood flow was continuously measured from the surface of the tongue and mandibular gingiva (laser-Doppler flowmetry) and from the lingual artery (ultrasonic flowmetry). Cardiovascular parameters also were recorded. Administration of the nonselective inhibitor of nitric oxide synthase (NOS), L-NAME (0.08-20 mg/kg i.v.), produced a dose-related increase of blood pressure associated with decreases of blood flow at all three measurement sites. Maximal blood flow depression of 50-60% was seen 30-60 min after administration of 1.25 mg/kg of L-NAME. D-NAME (1.25 mg/kg i.v.) was inactive at all sites. Subsequent administration of L-arginine partially reversed effects of L-NAME in the lingual artery and tongue, but not in the gingival circulation. The neuronally selective NOS inhibitor, 7-nitroindazole (7-NI, 30 mg/kg i.p.), was devoid of effect on any of the measured parameters. These results suggest that endothelial (but not neuronally derived) NO plays an important role in control of basal blood flow in oral tissues of the cat.     

Inhibition of neuronal nitric oxide synthase causes attenuation of cerebrovascular dysfunction in experimental heatstroke

The present study was performed to assess the prophylactic effect of 7-nitroindazole (7-NI), an inhibitor of neuronal nitric oxide synthase (nNOS), in an animal model of heatstroke. Anesthetized rats, immediately before the start of heat stress, were divided into two major groups and given the following: vehicle solution (1 mL per kg body weight) or 7-NI (5-20mg/mL per kg body weight) intraperitoneally. They were exposed to ambient temperature of 43 degrees C to induce heatstroke. Another group of rats were exposed to room temperature (24 degrees C) and used as normothermic controls. Their physiologic and biochemical parameters were continuously monitored. When the vehicle-pretreated rats underwent heat stress, their survival time values were found to be 21-25 min. Pretreatment with intraperitoneal doses of 7-NI significantly improved survival during heatstroke (55-164 min). As compared to those of normothermic controls, all vehicle-pretreated heatstroke animals displayed higher levels of core temperature, intracranial pressure, nitric oxide metabolite (NO(2)(-)), glutamate, glycerol, lactate/pyruvate ratio, neuronal damage score and nNOS expression in the hypothalamus, and tumor necrosis factor-alpha (TNF-alpha) in the serum. In contrast, all vehicle-pretreated heatstroke animals had lower levels of mean arterial pressure, cerebral perfusion pressure, cerebral blood flow, and brain PO(2). Administration of 7-NI before the start of heat exposure significantly reduced the hyperthermia, intracranial hypertension, nNOS-dependent NO(2)(-), glutamate, glycerol, lactate/pyruvate ratio, and neuronal damage score in the hypothalamus, as well as overproduction of TNF-alpha in the serum that occurred during heatstroke. The data show that reduction of nNOS-dependent NO(2)(-) with 7-NI causes attenuation of cerebrovascular dysfunction, hyperthermia, and TNF-alpha overproduction during heatstroke in the rat.     

Nitric oxide synthase mediates delta opioid receptor-induced hypothermia in rats

The role of nitric oxide (NO) production in delta opioid receptor-induced hypothermia has not been reported. The present study investigated the effect of nitric oxide synthase (NOS) inhibitors on the hypothermic effect of (+)-4-[(aR)-a-((2S,5R)-4-allyl-2,5-dimethyl-1-piperazinyl)-3-methoxybenzyl]-N,N-diethylbenzamide (SNC-80), a nonpeptide delta opioid agonist. SNC-80 (35 mg/kg, i.p.) administered to rats caused a significant hypothermia. N-nitro-L-arginine methyl ester (L-NAME) (10, 25 and 50 mg/kg, i.p.), a NOS inhibitor, and 7-nitroindazole (7-NI) (5 and 10 mg/kg, i.p.), a neuronal NOS inhibitor, were ineffective. For combined administration, L-NAME (50 mg/kg, i.p.) or 7-NI (10 mg/kg, i.p.) attenuated SNC-80-evoked hypothermia. To determine the involvement of central NOS, L-NAME (0.25, 0.5 and 1 mg/rat) was administered i.c.v. 30 min prior to SNC-80 (35 mg/kg, i.p.). Experiments revealed that L-NAME (1 mg/rat, i.c.v.) attenuated SNC-80-induced hypothermia. The present data demonstrate that central NO production is necessary for delta opioid receptor-induced hypothermia.