Pharmacokinetics and pharmacodynamics of 7-nitroindazole, a selective nitric oxide synthase inhibitor, in the rat hippocampus

Effects of extended-release 7-nitroindazole gel formulation treatment on the behavior of Shank3 mouse model of autism

Autism spectrum disorder (ASD) is a neurodevelopmental disorder characterized by behavioral deficits such as abnormalities in communication, social interaction, anxiety, and repetitive behavior. We have recently shown that the Shank3 mutation in mice representing a model of ASD causes excessive nitric oxide (NO) levels and aberrant protein S-nitrosylation. Further, 10-day daily injections of 7-NI, a neuronal nitric oxide synthase inhibitor, into Shank3Δ4-22 and Cntnap2(-/-) mutant mice (models of ASD) at a dose of 80 mg/kg reversed the manifestations of ASD phenotype. In this study, we proposed an extended release of 7-NI using a novel drug system. Importantly, unlike the intraperitoneal injections, our new preparation of poly (sebacic acid-co-ricinoleic acid) (PSARA) gel containing 7-NI was injected subcutaneously into the mutant mice only once. The animals underwent behavioral testing starting from day 3 post-injection. It should be noted that the developed PSARA gel formulation allowed a slow release of 7-NI maintaining the plasma level of the drug at ∼45 μg/ml/day. Further, we observed improved memory and social interaction and reduced anxiety-like behavior in Shank3 mutant mice. This was accompanied by a reduction in 3-nitrotyrosine levels (an indicator of nitrative/nitrosative stress) in plasma. Overall, we suggest that our single-dose formulation of PSARA gel is very efficient in rendering a therapeutic effect of 7-NI for at least 10 days. This approach may provide in the future a rational design of an effective ASD treatment using 7-NI and its clinical translation.

Human Nitric Oxide Synthase-Its Functions, Polymorphisms, and Inhibitors in the Context of Inflammation, Diabetes and Cardiovascular Diseases

In various diseases, there is an increased production of the free radicals needed to carry out certain physiological processes but their excessive amounts can cause oxidative stress and cell damage. Enzymes play a major role in the transformations associated with free radicals. One of them is nitric oxide synthase (NOS), which catalyzes the formation of nitric oxide (NO). This enzyme exists in three forms (NOS1, NOS2, NOS3), each encoded by a different gene. The following work presents the most important information on the NOS isoforms and their role in the human body, including NO synthesis in various tissues and cells, intercellular signaling and activities supporting the immune system and regulating blood vessel functions. The role of NOS in pathological conditions such as obesity, diabetes and heart disease is considered. Attention is also paid to the influence of the polymorphisms of these genes, encoding particular isoforms, on the development of these pathologies and the role of NOS inhibitors in the treatment of patients.

Repeated treatment with nitric oxide synthase inhibitor attenuates learned helplessness development in rats and increases hippocampal BDNF expression

BACKGROUND

Nitric oxide synthase (NOS) inhibitors induce antidepressant-like effects in animal models sensitive to acute drug treatment such as the forced swimming test. However, it is not yet clear if repeated treatment with these drugs is required to induce antidepressant-like effects in preclinical models.

OBJECTIVE

The aim of this study was to test the effect induced by acute or repeated (7 days) treatment with 7-nitroindazole (7-NI), a preferential inhibitor of neuronal NOS, in rats submitted to the learned helplessness (LH) model. In addition, we aimed at investigating if 7-NI treatment would increase brain-derived neurotrophic factor (BDNF) protein levels in the hippocampus, similarly to the effect of prototype antidepressants.

METHODS

Animals were submitted to a pre-test (PT) session with inescapable footshocks or habituation (no shocks) to the experimental shuttle box. Six days later they were exposed to a test with escapable footshocks. Independent groups received acute (a single injection after PT or before test) or repeated (once a day for 7 days) treatment with vehicle or 7-NI (30 mg/kg).

RESULTS

Repeated, but not acute, treatment with 7-NI attenuated LH development. The effect was similar to repeated imipramine treatment. Moreover, in an independent experimental group, only repeated treatment with 7-NI and imipramine increased BDNF protein levels in the hippocampus.

CONCLUSION

The results suggest the nitrergic system could be a target for the treatment of depressive-like conditions. They also indicate that, similar to the positive control imipramine, the antidepressant-like effects of NOS inhibition could involve an increase in hippocampal BDNF levels.

Inhibition of neuronal nitric oxide synthase and soluble guanylate cyclase prevents depression-like behaviour in rats exposed to chronic unpredictable mild stress

Depression is the most common psychiatric disorder. It is well established that endogenous nitric oxide (NO) contributes to chronic unpredictable mild stress (CUMS)-induced depression. The aim of this study was to investigate brain-derived neurotropic factor (BDNF) expression in CUMS-induced depression-like behaviour in rats. Rats were exposed to CUMS for 5 weeks. A specific and selective nNOS inhibitor, 3-bromo-7-nitroindazole (3-Br-7-NI; 20 mg/kg/day, i.p.), and a specific soluble guanylate cyclase (sGC) inhibitor, 1H-(1,2,4)oxadiazolo(4,3-a)quinoxalin-1-one (ODQ; 10 mg/kg/day, i.p.), were administered during CUMS. The forced swimming test (FST) was used to assess despair and sucrose consumption, and sucrose preference test was used to assess anhedonia that are the main symptoms of the depression. We show that both 3-Br-7-NI and ODQ administration during CUMS suppressed CUMS-induced, depression-like behavioural changes, including reduced sucrose preference, body-weight and locomotor activity as well as increased immobility time in the FST. CUMS also significantly decreased BDNF protein levels in the CA1 and CA3 regions of the hippocampus, which was reversed by 3-Br-7-NI and ODQ administration. Our findings suggest a novel role for nNOS and sGC-cGMP in the development of the CUMS model of depression.

Antidepressant-like effect of 1-(7-methoxy-2-methyl-1,2,3,4-tetrahydro-isoquinolin-4-YL)-cyclohexanol, a putative trace amine receptor ligand involves l-arginine-nitric oxide-cyclic guanosine monophosphate pathway

1-(7-methoxy-2-methyl-1,2,3,4-tetrahydro-isoquinolin-4-YL)-cyclohexanol is a novel putative trace amine receptor modulator hypothesized to be useful for treatment-resistant depression. In our previous study, we have demonstrated the antidepressant-like effect of this molecule in mouse forced swim and tail suspension tests and shown to act via modulating the levels of norepinephrine, serotonin and dopamine. The present study attempts to explore the involvement of l-arginine-nitric oxide-cyclic guanosine monophosphate pathway in the antidepressant-like effect of 1-(7-methoxy-2-methyl-1,2,3,4-tetrahydro-isoquinolin-4-YL)-cyclohexanol in the mouse forced swim test. The antidepressant-like action of 1-(7-methoxy-2-methyl-1,2,3,4-tetrahydro-isoquinolin-4-YL)-cyclohexanol (8 mg/kg, i.p) was reversed by pretreatment with L-arginine (750 mg/kg, i.p.), a nitric oxide precursor. In contrast, pretreatment with methylene blue (a soluble guanlyate cyclase inhibitor and nitric oxide synthase (NOS) inhibitor) or 7-nitroindazole (a specific neuronal NOS inhibitor) potentiated the antidepressant-like effect of sub-effective dose of 1-(7-methoxy-2-methyl-1,2,3,4-tetrahydro-isoquinolin-4-YL)-cyclohexanol (2mg/kg, i.p.) in this test model. Furthermore, the antidepressant-like effect of this molecule (8 mg/kg, i.p.) was reversed by sildenafil (5mg/kg, i.p.), a phosphodiesterase inhibitor. In conclusion, the antidepressant-like action of 1-(7-methoxy-2-methyl-1,2,3,4-tetrahydro-isoquinolin-4-YL)-cyclohexanol involved L-arginine-nitric oxide-cyclic guanosine monophospate signaling pathway.

Nitric oxide- and cGMP-active compounds affect the discharge of substantia nigra pars reticulata neurons: in vivo evidences in the rat

The nitric oxide (NO)-active drugs influence on the bioelectric activity of neurons of the pars reticulata of the substantia nigra was studied in urethane-anesthetized rats. A first group of animals was treated with 7-nitro-indazole (7-NI), a preferential inhibitor of neuronal NO synthase. In a second group of rats, electrophysiological recordings were coupled with microiontophoretic administration of Nomega-nitro-L-arginine methyl ester (L-NAME, a NO synthase inhibitor), 3-morpholino-sydnonimin-hydrocloride (SIN-1, a NO donor) and 8-Br-cGMP (a cell-permeable analogue of cGMP, the main second-messenger of NO neurotransmission). 7-NI and L-NAME caused a statistically significant decrease in the firing rate of most of the responsive cells, while application of SIN-1 and 8-Br-CGMP induced statistically significant excitatory effects. The results suggest a NO mediated excitatory modulation of the SNr neurons activity with a possible involvement of the cGMP pathway.

Neuronal nitric oxide synthase-deficient mice have impaired renin release but normal blood pressure

BACKGROUND

Nitric oxide deficiency is involved in the development of hypertension, but the mechanisms are currently unclear. This study was conducted to further elucidate the role of neuronal nitric oxide synthase (nNOS) in blood pressure regulation and renin release in relation to different sodium loads.

METHODS

Blood pressure and heart rate were measured telemetrically and assessed during periods of physical activity and inactivity. Urinary solute excretion was measured by metabolism cages and plasma renin concentration (PRC) was determined by radioimmunoassay; all in nNOS knockout (nNOS(-/-)) and wild-type (nNOS(+/+)) mice after 10 days of low (0.01% NaCl) and high (4% NaCl) sodium diets.

RESULTS

The resting heart rate was reduced in nNOS(-/-) mice, but the two genotypes had similar blood pressure during the low (nNOS(+/+) 104 +/- 2 mm Hg; nNOS(-/-) 103 +/- 2 mm Hg) and high (nNOS(+/+) 107 +/- 3 mm Hg; nNOS(-/-) 108 +/- 2 mm Hg) sodium diets. During the high sodium diet, PRC did not differ between the genotypes (nNOS(+/+) 743 +/- 115 10(-5) Goldblatt units; nNOS(-/-) 822 +/- 63 10(-5) Goldblatt units), but during the low sodium diet, nNOS(-/-) mice failed to increase PRC (nNOS(+/+) 2164 +/- 220 10(-5) Goldblatt units; nNOS(-/-) 907 +/- 101 10(-5) Goldblatt units) and renal renin mRNA. On the low sodium diet, nNOS(-/-) mice also showed increased urine flow rate and osmolar excretion, observations not made during a high sodium diet.

CONCLUSIONS

Our results show that nNOS is necessary for stimulation of renin in response to sodium restriction. Furthermore, nNOS(-/-) mice are normotensive, and their blood pressure responds normally to an increased dietary sodium intake, indicating that nNOS deficiency does not cause salt-sensitive hypertension.

Inhibition of neuronal nitric oxide synthase in the rat hippocampus induces antidepressant-like effects

RATIONALE

Systemic inhibition of neuronal nitric oxide synthase (nNOS) induces antidepressant-like effects in rodents. The mechanisms and brain regions mediating this effect are still unknown. The hippocampus is a brain region proposed to mediate adaptation to stress and antidepressant behavioral effects. Therefore, it could be involved in the antidepressant effects of NOS inhibitors.

OBJECTIVES

To test the hypothesis that nNOS inhibition in the dorsal hippocampus will induce antidepressant-like effects in the forced swimming test (FST) in rats.

METHODS

Rats implanted with cannulas aimed at the dorsal hippocampus were submitted to 15 min of forced swimming (pretest). Immediately before or after pretest they received bilateral microinjections of the nNOS inhibitor 7-nitroindazole (7-NI; 50, 100, or 200 nmol/0.5 microl) or vehicle, alone or combined with L-arginine. Additional groups received SIN-1 (125 or 250 nmol/0.5 microl), a NO donor, either before or after the pretest. Twenty-four hours later, immobility time was registered for 5 min in the FST.

RESULTS

7-NI (100 nmol) significantly decreased immobility time when administered either before or after pretest. Pretreatment with L-arginine (100 nmol/0.5 microl) prevented these effects but produced no significant effects per se. SIN-1 did not induce any significant effect.

CONCLUSION

These data suggest that the reduction of NO levels within the hippocampus can induce antidepressant-like effects; thus implicating endogenous hippocampal NO in the neurobiology of stress and depression.

Combined treatment of ascorbic acid or alpha-tocopherol with dopamine receptor antagonist or nitric oxide synthase inhibitor potentiates cataleptic effect in mice

RATIONALE

Drugs like haloperidol (Hal) that decrease dopamine (DA) neurotransmission in the striatum induce catalepsy in rodents and Parkinson disease-like symptoms in humans. Nitric oxide synthase (NOS) inhibitors interfere with motor activity, disrupting rodent exploratory behavior and inducing catalepsy. Catalepsy induced by NOS inhibitors probably involves striatal DA-mediated neurotransmission. Antioxidants such as ascorbic acid (vitamin C) and alpha-tocopherol (vitamin E) have also been shown to interfere with movement modulation and the DA system.

OBJECTIVE

The objective of the study is to investigate if the antioxidants vitamins C and E would influence the catalepsy produced by Hal and NOS inhibitors.

METHODS

The effects of the following treatments on catalepsy were examined using the hanging-bar test on male Swiss mice (25-30 g): (1) vitamin C (30-1,000 mg/kg)xHal (1 mg/kg); (2) vitamin C (90-1,000 mg/kg)xN (G)-nitro-L: -arginine (LNOARG, 10 and 40 mg/kg); (3) vitamin C (300 mg/kg)xN (G)-nitro-L: -arginine methylester (LNAME, 20-80 mg/kg); (4) vitamin C (300 mg/kg) x 7-nitroindazole (7NI, 3-50 mg/kg); (5) vitamin C (90 mg/kg i.p.) x LNOARG [40 mg/kg twice a day during 4 days (subchronic treatment)]; (7) vitamin E (3-100 mg/kg) x Hal (1 mg/kg); and (6) vitamin E (3-100 mg/kg) x LNOARG (40 mg/kg).

RESULTS

Vitamin C enhanced the catalepsy produced by NOS inhibitors and Hal. Treatment with vitamin C did not affect tolerance to LNOARG cataleptic effect induced by subchronic treatment. Vitamin E potentiated the catalepsy induced by LNOARG at all doses tested; in contrast, catalepsy induced by Hal was enhanced only by the dose of 100 mg/kg.

CONCLUSIONS

Results support an involvement of dopaminergic and nitrergic systems in motor behavior control and provide compelling evidence that combined administration of the antioxidants vitamins C and E with either Hal or NOS inhibitors exacerbates extrapyramidal effects. Further studies are needed to assess possible clinical implications of these findings.

Unexpected effects of nitric oxide synthase inhibitors on extracellular nitrite levels in the hippocampus in vivo

The aim of this study was to determine whether extracellular nitric oxide levels in the hippocampus of freely moving animals were reduced by the administration of nitric oxide synthase (NOS) inhibitors via a microdialysis probe. Our results show that extracellular nitrite levels were increased following the infusion of N-nitro-L-arginine methyl ester (L-NAME) and 7-nitroindazole (7-NI), in the case of the latter, the response was biphasic. In contrast, infusion of both inhibitors together resulted in a substantial reduction in nitrite when compared to control. More predictably, the infusion of NMDA elicited an increase in extracellular nitrite levels. This effect was biphasic, the second phase occurring some 3 h after the drug infusion period had ended. When NMDA was infused in the presence of L-NAME, no agonist-induced increase in nitrite production was recorded, in fact nitrite levels were found to decline to below control values. There was no immediate increase in nitrite levels when NMDA was infused in the presence of 7-NI, although this may have been partially obscured by the biphasic effect of the inhibitor. It did appear, however, that the second phase of the NMDA-induced response was attenuated by 7-NI. No NMDA-evoked increase in nitrite was evident when the agonist was infused in the presence of a combination of both inhibitors. We have no clear explanation for the data presented here but suggest that up-regulated activity of particular NOS isoforms might compensate for the inhibition of the other by a mechanism yet to be elucidated. In addition, we propose that caution be exercised when interpreting results from in vivo microdialysis studies where NOS inhibitors are administered directly into the brain via a probe.

7-nitroindazole, a selective neuronal nitric oxide synthase inhibitore in vivo, prevents kainate-induced intrahippocampal neurotoxicity

We investigated the effects of 7-nitroindazole (7-NI), a selective neuronal nitric oxide synthase inhibitor in vivo, on nitrite concentration after kainic acid injection unilaterally into the CA3 region of the rat hippocampus. The accumulation of nitrite, the stable metabolite of NO, was measured by the Griess reaction at different times in hippocampus, forebrain cortex, striatum, and cerebellum homogenates. 7-nitroindazole can effectively inhibit NO synthesis in rat brain after kainate-induced neurotoxicity and suppressed nitrite accumulation. The present results suggest that neuronal NO synthase inhibitors may be useful in the treatment of neurological diseases in which excitotoxic mechanisms play a role. <br><br><font color="red"><b> This article has been retracted. Link to the retraction <u><a href="http://dx.doi.org/10.2298/ABS160412036E">10.2298/ABS160412036E</a><u></b></font>

Effect of neuronal nitric oxide synthase inhibition on CA2+/calmodulin kinase kinase and CA2+/calmodulin kinase IV activity during hypoxia in cortical nuclei of newborn piglets

The present study tests the hypothesis that cerebral tissue hypoxia results in increased Ca(2+)/calmodulin (CaM) kinase kinase activity and that the administration of nitric oxide synthase inhibitors (N-nitro-l-arginine [NNLA], or 7-nitroindazole sodium [7-NINA]) prior to the onset of hypoxia will prevent the hypoxia-induced increase in the enzyme activity. To test this hypothesis, CaM kinase kinase and CaM kinase IV activities were determined in normoxic, hypoxic, NNLA-treated hypoxic, and 7-NINA-treated hypoxic piglets. Hypoxia was induced (FiO(2)=0.05-0.08x1 h) and confirmed biochemically by tissue levels of ATP and phosphocreatine. CaM kinase kinase activity was determined in a medium containing protein kinase and phosphatase inhibitors, calmodulin, and a specifically designed CaM kinase kinase target peptide. CaM kinase IV activity was determined by (33)P-incorporation into syntide-2 in a buffer containing protein kinase and phosphatase inhibitors. Compared with normoxic animals, ATP and phosphocreatine levels were significantly lower in all hypoxic piglets whether or not pretreated with nitric oxide synthase inhibitors. There was a significant difference among CaM kinase kinase activity (pmol/mg protein/min) in normoxic (76.84+/-14.1), hypoxic (138.86+/-18.2, P<0.05 vs normoxia), NNLA-pretreated hypoxic (91.34+/-19.3; P=NS vs normoxia, P<0.05 vs hypoxia) and 7-NINA-pretreated hypoxic animals (100.12+/-23.3; P=NS vs normoxia, P<0.05 vs hypoxia). There was a significant difference among CaM kinase IV activity (pmol/mg protein/min) in normoxia (1270.80+/-126.1), hypoxia (2680.80+/-136.7; P<0.05 vs normoxia), NNLA-pretreated hypoxia (1666.00+/-154.8; P<0.05 vs normoxia, P<0.05 vs hypoxia), and 7-NINA-pretreated hypoxic (1712.9+/-231.5; P=NS vs normoxia, P<0.05 vs hypoxia). We conclude that the hypoxia-induced increase in CaM kinase kinase and CaM kinase IV activity is mediated by neuronal NOS-derived NO.

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.

Demonstrating the dose- and time-related effects of 7-nitroindazole on picrotoxin-induced convulsions, memory formation, brain nitric oxide synthase activity, and nitric oxide concentration in rats

In this study, the dose (50, 100, 150, and 200 mg/kg)- and time (30 and 60 min)- related effects of 7-nitroindazole (7-NI), a neuronal specific inhibitor of nitric oxide synthase (NOS) were tested on picrotoxin (5 mg/kg)-induced convulsions and memory formation in rats. The changes produced by these doses of 7-NI were determined on NOS activity and nitric oxide (NO) concentration in the brain. The effects of 7-NI were tested in animals pretreated (30 min) with L-arginine (500 and 1000 mg/kg). 7-NI, at 50 and 100 mg/kg, did not produce significant changes in NOS activity and NO concentration in the brain and memory formation. However, the convulsant action of picrotoxin was inhibited in a dose-dependent manner in these animals. A time-dependent decrease in the activity of NOS and the concentration of NO, a promotion of picrotoxin-induced convulsions, and an impairment of memory were found in animals treated with 150 and 200 mg/kg of 7-NI. The larger and not the smaller dose of L-arginine raised the concentration of NO, inhibited picrotoxin-induced convulsions and promoted memory process. Either dose of L-arginine failed to prevent 50 and 100 mg/kg of 7-NI from inhibiting convulsions. The effects of the larger doses of 7-NI (150 and 200 mg/kg) were effectively prevented by the increase of NO and not the ineffective dose of L-arginine. These results suggest that 7-NI (50 and 100 mg/kg) decreases convulsions by a nonspecific mechanism and that an inhibition of NOS by the larger doses of it (150 and 200 mg/kg) results in proconvulsant action and memory impairment. The data further show that the margin between the protective and proconvulsant doses of 7-NI is relatively narrow. These results have been taken together with the earlier reports that 7-NI produces learning impairment and fails to increase the anticonvulsant effect of traditional antiepileptic agents on experimentally induced convulsions to conclude that 7-NI can never emerge as an anticonvulsant agent for clinical use.

Pharmacokinetics and pharmacodynamics of L-arginine in rats: a model of stimulated neuronal nitric oxide synthesis

Nitric oxide (NO) is believed to be involved in a variety of central nervous system (CNS) functions, including opioid responsivity. Elucidation of the role of NO in the CNS requires the ability to elevate systematically neuronal NO concentrations in vivo. This study was conducted to assess the pharmacokinetics of L-arginine, a NO precursor, and to relate the disposition of this amino acid to the pharmacodynamic endpoint of neuronal NO production. L-Arginine (250-, 500-, or 1000-mg/kg/h) or saline was infused intravenously for 6 h to rats. L-Arginine was quantified in brain and blood (after in vivo microdialysis) with high-performance liquid chromatography. NO was quantified simultaneously with a sensitive and specific amperometric sensor placed in the hippocampus. The data were fit with a comprehensive pharmacokinetic-pharmacodynamic (PK/PD) model to obtain parameters governing the systemic disposition of L-arginine, the uptake of L-arginine into the brain, and subsequent NO production. Exogenous administration of L-arginine resulted in incremental elevations in hippocampal NO, with a approximately 33, 48, and approximately 50% increase from control for the 250-, 500-, and 1000-mg/kg/h L-arginine treated rats, respectively. The PK/PD model, which incorporated known characteristics of the system (saturable uptake of L-arginine into brain; NO production governed by circadian changes in enzyme activity) was capable of describing accurately the observed data. The model developed herein will be invaluable in characterizing the numerous roles of NO in the CNS.

7-nitroindazole reduces nitrite concentration in rat brain after intrahippocampal kainate-induced seizure

Kainic acid is an endogenous excitotoxin acting on glutamate receptors, that leads to neurotoxic damage resembling the alterations observed in some neurological disorders. Stimulation of glutamate receptors induces neuronal nitric oxide (NO) release, which in turn modulates glutamate transmission. NO may be a key mediator of excitotoxic neuronal injury in the central nervous system. We investigated the effects of 7-nitroindazole, a selective neuronal nitric oxide synthase inhibitor in vivo, on nitrite concentration after kainic acid injection (0.6 mg/ml, pH 7.2) unilaterally into the CA3 region of the rat hippocampus. The accumulation of nitrite, the stable metabolite of NO, was measured by the Griess reaction at different times (5 min, 15 min, 2 h, 48 h and 7 days) following kainate injection in the ipsilateral and contralateral hippocampus, forebrain cortex, striatum and cerebellum homogenates. 7-Nitroindazole (100 microM) can effectively inhibit NO synthesis in rat brain after kainate-induced intrahippocampal neurotoxicity and suppressed nitrite accumulation. The present results suggest that neuronal NO synthase inhibitors may be useful in the treatment of neurological diseases where excitotoxic mechanisms play a role.

CCK-nitric oxide interaction in rat cortex, striatum and pallidum

We have chosen to study the effects of both nitric oxide (NO) and cholecystokinin neuromodulatory systems in some motor structures that are frequently involved in excitotoxic phenomena. In particular, 7-nitroindazole, a selective inhibitor of neuronal NO synthase, was administered in control and sulfated cholecystokinin octapeptide-treated rats. Cortical surface, striatal and pallidal depth bioelectric activities were examined through Fast Fourier Transform analysis. Cortical and pallidal recordings revealed an increase of rapid standard rhythms after the inhibition of neuronal NO synthase; in contrast, striatal depth recordings showed a marked increase of slow standard rhythms. All these effects were completely abolished by chronic pre-treatment with sulfated cholecystokinin octapeptide. The results suggest a functional co-operation between cholecystokinin and NO systems in the modulation of the bioelectric activity of all the motor structures examined, and the possibility of preventing excitotoxic damages induced by an anomalous balance between excitatory and inhibitory neurotransmitters in these areas.

Brain inducible nitric oxide synthase is involved in interleukin-1beta-induced activation of the central sympathetic outflow in rats

Nitric oxide (NO) has been recognized as a neurotransmitter or a neuromodulator in the central nervous system. Brain NO is mainly generated either by neuronal NO synthase (NOS) or by inducible NOS. Previously we reported that central NO is involved in the elevation of plasma noradrenaline levels induced by intracerebroventricularly (i.c.v.) administered interleukin-1beta in rats [Eur. J. Phamacol. 317 (1996) 61]. In the present study, therefore, we tried to characterize which type of NOS isoforms is involved in the cytokine-induced responses using selective inhibitors of each NOS isoform in urethane-anesthetized rats. I.c.v. administered interleukin-1beta (100 ng/animal) elevated plasma levels of noradrenaline but not adrenaline. The cytokine-induced elevation of plasma noradrenaline levels was attenuated by cycloheximide, an inhibitor of protein synthesis, in a dose-dependent manner (10 and 20 microg/animal, i.c.v.). S-ethylisothiourea (0.1 and 0.5 microg/animal, i.c.v.), an inhibitor of inducible NOS, dose-dependently reduced the cytokine-induced elevation of plasma noradrenaline levels, while 7-nitroindazole (5 and 10 microg/animal, i.c.v.), an inhibitor of neuronal NOS, had no effect. These results suggest the involvement of brain inducible NOS in the interleukin-1beta-induced activation of the central sympathetic outflow in rats.