7-Nitroindazole, a selective inhibitor of nNOS, increases hippocampal extracellular glutamate concentration in status epilepticus induced by kainic acid in rats

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.

Proconvulsant effects of Nepeta menthoides hydro alcoholic extract in different seizure tests: behavioral and biochemical studies

In Iran, both Nepeta menthoides - the endemic species of Nepeta genus - and Lavandula officinalis are known as Ustukhuddoos and used widely as medicinal herbs. In Iranian traditional medicine, Ustukhuddoos has been recommended for several neuronal diseases including depression and epilepsy. While the antiepileptic effects of Lavandula officinalis have been investigated in a number of studies, no reports are available taking into account the effect of Nepeta menthoides on epilepsy. Since convulsion is an important side effect of some medicinal plants, a thorough study of the effects of Nepeta menthoides on epilepsy seems necessary.

This study was designed to investigate the potential anti- or pro-convulsant activity of Nepeta menthoides and its effects on oxidative stress markers. Since an herbal medicine showed opposite effects in two animal models of epilepsy in our laboratory, authers decided to study Nepeta effects through several seizure tests including the intravenous pentylenetetrazol (i.v. PTZ) infusion, the maximal electroshock (MES), acute PTZ and PTZ-kindling tests. These seizure models are generally used for screening pro- or anti-epileptic drugs. Nepeta menthoides (400 mg/kg) significantly reduced the dose of PTZ necessary for clonus seizure induction. Combining either phenytoin (Phen) or Valproate (Val) with Nepeta decreased their antiepileptic effects. Therefore, Nepeta menthoides not only failed to prevent the seizures but also increased sensitivity to them. Nepeta raised brain NO levels in different seizure tests. It seems there is a relation between NO elevation by Nepeta and increased sensitivity to seizures that should be investigated later.

Evaluation of a Portable Microchip Electrophoresis Fluorescence Detection System for the Analysis of Amino Acid Neurotransmitters in Brain Dialysis Samples

A portable fluorescence detection system for use with microchip electrophoresis was developed and compared to a benchtop system. Using this system, six neuroactive amines commonly found in brain dialysate (arginine, citrulline, taurine, histamine, glutamate, and aspartate) were derivatized offline with naphthalene-2,3-dicarboxaldehyde/cyanide, separated electrophoretically, and detected by fluorescence. The limits of detection for the analytes of interest were 50 - 250 nM for the benchtop system and 250 nM - 1.3 μM for the portable system, both of which were adequate for most analyte detection in brain microdialysis samples. The portable system was then demonstrated for the detection of the same six amines in a rat brain microdialysis sample.

Effects of AT1 receptor antagonism on kainate-induced seizures and concomitant changes in hippocampal extracellular noradrenaline, serotonin, and dopamine levels in Wistar-Kyoto and spontaneously hypertensive rats

In the management of epilepsy, AT1 receptor antagonists have been suggested as an additional treatment strategy. A hyperactive brain angiotensin (Ang) II system and upregulated AT1 receptors are implicated in the cerebrovascular alterations in a genetic form of hypertension. Uncontrolled hypertension could also, in turn, be a risk factor for a seizure threshold decrease and development of epileptogenesis. The present study aimed to assess the effects of the selective AT1 receptor antagonist ZD7155 on kainic acid (KA)-induced status epilepticus (SE) development and accompanying changes in the hippocampal extracellular (EC) neurotransmitter levels of noradrenaline (NAD), serotonin (5-HT), and dopamine (DA) in spontaneously hypertensive rats (SHRs) and their parent strain Wistar-Kyoto (WKY) rats, since monoamines are well-known neurotransmitters involved in mechanisms of both epilepsy and hypertension. Status epilepticus was evoked in freely moving rats by a repetitive intraperitoneal (i.p.) administration of KA in subconvulsant doses. In the treatment group, ZD7155 (5mg/kg i.p.) was coadministered with the first KA injection. Spontaneously hypertensive rats exhibited higher susceptibility to SE than WKY rats, but the AT1 receptor antagonist did not alter the development of SE in SHRs or in WKY rats. In vivo microdialysis demonstrated significant KA-induced increases of the hippocampal NAD and DA levels in SHRs and of NAD, 5-HT, and DA in WKY rats. Although SHRs developed more severe seizures while receiving a lower dose of KA compared to WKY rats, AT1 receptor antagonism completely prevented all KA-induced increases of hippocampal monoamine levels in both rat strains without affecting seizure development per se. These results suggest a lack of direct relationship between KA-induced seizure susceptibility and adaptive changes of hippocampal NAD, 5-HT, and DA levels in the effects of ZD7155 in WKY rats and SHRs.

Propolis ameliorates tumor nerosis factor-α, nitric oxide levels, caspase-3 and nitric oxide synthase activities in kainic acid mediated excitotoxicity in rat brain

BACKGROUND

Increased nitric oxide (NO), neuronal inflammation and apoptosis have been proposed to be involved in excitotoxicity plays a part in many neurodegenerative diseases. To understand the neuro-protective effects of propolis, activities of Nitric oxide synthase (NOS) and caspase-3 along with NO and tumor necrosis factor-α (TNF-α) levels were studied in cerebral cortex (CC), cerebellum (CB) and brain stem (BS) in rats supplemented with propolis prior to excitotoxic injury with kainic acid (KA).

MATERIALS AND METHODS

Male Sprague-Dawley rats were divided into four groups (n=6 rats per group) as Control, KA, Propolis and KA+Propolis. The control group and KA group have received vehicle and saline. Propolis group and propolis + KA group were orally administered with propolis (150 mg/kg body weight), five times every 12 hours. KA group and propolis +KA group were injected subcutaneously with kainic acid (15 mg/kg body weight) and were sacrificed after 2 hrs. CC, CB and BS were separated, homogenized and used for estimation of NOS, caspase-3, NO and TNF-α by commercial kits. Results were analyzed by one way ANOVA, reported as mean + SD (n=6 rats), and p<0.05 was considered statistically significant.

RESULTS

The concentration of NO, TNF-α, NOS and caspase-3 activity were increased significantly (p<0.001) in all the three brain regions tested in KA group compared to the control. Propolis supplementation significantly (p<0.001) prevented the increase in NOS, NO, TNF-α and caspase-3 due to KA.

CONCLUSION

Results of this study clearly demonstrated that the propolis supplementation attenuated the NOS, caspase-3 activities, NO, and TNF-α concentration and in KA mediated excitotoxicity. Hence propolis can be a possible potential protective agent against excitotoxicity and neurodegenerative disorders.

Restoration of glutamine synthetase activity, nitric oxide levels and amelioration of oxidative stress by propolis in kainic acid mediated excitotoxicity

BACKGROUND

Propolis has been proposed to be protective on neurodegenerative disorders. To understand the neuroprotective effects of honeybee propolis, glutamine synthetase (GS) activity, nitric oxide (NO), thiobarbituric acid reactive substances (TBARS) and total antioxidant status (TAS) were studied in different brain regions-cerebral cortex (CC), cerebellum (CB) and brain stem (BS) of rats supplemented with propolis and subjected to kainic acid (KA) mediated excitotoxicity.

MATERIALS AND METHODS

Male Sprague-Dawley rats were divided into four groups; Control group and KA group received vehicle and saline. Propolis group and propolis + KA group were orally administered with propolis (150mg/kg body weight), five times every 12 hours. KA group and propolis + KA group were injected subcutaneously with kainic acid (15mg/kg body weight) and were sacrificed after 2 hrs and CC, CB and BS were separated homogenized and used for estimation of GS activity, NO, TBARS, and TAS concentrations by colorimetric methods. Results were analyzed by one-way ANOVA, reported as mean + SD from 6 animals, and p<0.05 considered statistically significant.

RESULTS

NO was increased (p< 0.001) and GS activity was decreased (p< 0.001) in KA treated group compared to control group as well as propolis + KA treated group. TBARS was decreased and TAS was increased (p< 0.001) in propolis + KA treated group compared KA treated group.

CONCLUSION

This study clearly demonstrated the restoration of GS activity, NO levels and decreased oxidative stress by propolis in kainic acid mediated excitotoxicity. Hence the propolis can be a possible potential candidate (protective agent) against excitotoxicity and neurodegenerative disorders.

Anti-epileptogenic and antioxidant effect of Lavandula officinalis aerial part extract against pentylenetetrazol-induced kindling in male mice

ETHNOPHARMACOLOGICAL RELEVANCE

Repeated application of Lavandula officinalis (L. officinalis) has been recommended for a long time in Iranian traditional medicine for some of nervous disorders like epilepsy and dementia. However, there is no available report for the effect of chronic administration of Lavandula extract in development (acquisition) of epilepsy. Therefore, this study was designed to investigate the anti-epileptogenic and antioxidant activity of repeated administration of Lavandula officinalis extract on pentylenetetrazol (PTZ) kindling seizures in mice model.

MATERIALS AND METHODS

Lavandula officinalis was tested for its ability (i) to suppress the seizure intensity and lethal effects of PTZ in kindled mice (anti-epileptogenic effect), (ii) to attenuate the PTZ-induced oxidative injury in the brain tissue (antioxidant effect) when given as a pretreatment prior to each PTZ injection during kindling development. Valproate (Val), a major antiepileptic drug, was also tested for comparison.

RESULTS

Val and Lavandula officinalis extract showed anti-epileptogenic properties as they reduced seizure score of kindled mice and PTZ-induced mortality. In this regard, Lavandula officinalis was more effective than Val. Both Lavandula officinalis and Val suppressed brain nitric oxide (NO) level of kindled mice in comparison with the control and PTZ group. Meanwhile, Lavandula officinalis suppressed NO level more than Val and Lavandula officinalis also decreased brain MDA level relative to PTZ group.

CONCLUSION

This is the first report to demonstrate NO suppressing and anti-epileptogenic effect of chronic administration of Lavandula officinalis extract on acquisition of epilepsy in PTZ kindling mice model. In this regard, Lavandula officinalis extract was more effective than Val, possibly and in part via brain NO suppression.

Effect of 7-nitroindazoleon superoxide production and MnSOD activity in threat brain following kainate-induced neurotoxicity

We investigated the effect of 7-nitroindazole (7-NI), a selective neuronal nitric oxide synthase inhibitor in vivo, on superoxide concentration as well its influence on mitochondrial MnSOD activity since this activity is associated with the production of reactive oxygen species after kainate-induced neurotoxicity. The time course of in vivo oxidative damage in different brain regions was investigated. Measurements were performed at different times (5 min, 15 min, 2 h, 48 h, and 7 days) in the ipsi- and contralateral hippocampus, forebrain cortex, striatum, and cerebellum homogenates. Our results indicated that 7-NI had no statistically significant influence on superoxide concentrations in the tested brain structures compared to the control values. However, superoxide concentrations after kainate-induced neurotoxicity returned to the control values after pretreatment with 7-NI in all tested brain structures. Regarding the activity of MnSOD, our results demonstrated statistically significant increase 7 days after intrahippocampal KA treatment in all tested brain structures after pretreatment with 7-NI. The obtained 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/ABS150330033E">10.2298/ABS150330033E</a><u></b></font>

Effect of glutamate antagonists on nitric oxide production in rat brain following intrahippocampal injection

Stimulation of glutamate receptors induces neuronal nitric oxide (NO) release, which in turn modulates glutamate transmission. The involvement of ionotropic glutamate NMDA and AMPA/kainate receptors in induction of NO production in the rat brain was examined after injection of kainate, a non-NMDA receptor agonist; kainate plus 6-cyano- 7-nitroquinoxaline-2,3-dione (CNQX), a selective AMPA/kainate receptor antagonist; or kainate plus 2-amino-5-phosphonopentanoic acid (APV), a selective NMDA receptor antagonist. Competitive glutamate receptor antagonists were injected with kainate 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) in hippocampus, forebrain cortex, striatum, and cerebellum homogenates. The used glutamate antagonists APV and CNQX both provided sufficient neuroprotection in the sense of reducing nitrite concentrations, but with different mechanisms and time dynamics. Our findings suggest that NMDA and AMPA/kainate receptors are differentially involved in nitric oxide production. <br><br><font color="red"><b> This article has been retracted. Link to the retraction <u><a href="http://dx.doi.org/10.2298/ABS150319031E">10.2298/ABS150319031E</a><u></b></font>

Differential effects of NMDA and AMPA/kainate receptor antagonists on nitric oxide production in rat brain following intrahippocampal injection

Stimulation of glutamate receptors induces neuronal nitric oxide (NO) release, which in turn modulates glutamate transmission. The involvement of ionotropic glutamate NMDA and alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate (AMPA)/kainite (KA) receptors in the induction of NO production in the rat brain was examined after injection of kainate, non-NMDA receptor agonist, KA+6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), selective AMPA/KA receptor antagonist, or KA+2-amino-5-phosphonopentanoic acid (APV), selective NMDA receptor antagonist. Competitive glutamate receptor antagonists were injected with KA 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) in the ipsi- and contralateral hippocampus, forebrain cortex, striatum and cerebellum homogenates. The detected increase of NO production in distinct brain regions, which are functionally connected via afferents and efferents, suggests that these regions are affected by the injury. The effect of KA on nitrite production was blocked by the glutamate antagonists. Intrahippocampal KA+CNQX injection resulted in decrease of nitrite production, around control levels, in all tested brain structures. Significant decrease in nitrite levels was found only in comparison to KA-treated animals, i.e. the overall effect of selective AMPA/KA receptor antagonist was a decrease of KA-induced excitotoxicity. The accent effect of intrahippocampal KA+APV injection resulted, also, in decrease of nitrite production. However, this effect was detected after 5 min from the injection indicating the existence of an NMDA receptor-mediated component of basal nitrite production in physiological conditions and difference in mechanisms and time dynamics between CNQX and APV. The used antagonists showed same pattern in all tested brain structures. APV and CNQX both expressed sufficient neuroprotection in sense of reducing nitrite concentrations, but with differential effect in mechanisms and time dynamics. Our findings suggest that NMDA and AMPA/KA receptors are differentially involved in NO production.

Sequential changes of nitric oxide levels in the temporal lobes of kainic acid-treated mice following application of nitric oxide synthase inhibitors and phenobarbital

Although studies have indicated a close relationship between nitric oxide (NO) and kainic acid (KA)-induced seizures, the role of NO in seizures is not fully understood. Here, we quantified NO levels in the brain of KA-treated mice using EPR spectrometry to elucidate the role of NO in KA-induced seizures. KA was administered to mice with or without pretreatment with one of the following: N(G)-nitro-l-arginine methyl ester (l-NAME), an NO synthase (NOS) inhibitor that acts on both endothelial NOS (eNOS) and neuronal NOS (nNOS); 7-nitroindazole (7-NI), which acts more selectively on nNOS in vivo; or the anti-epileptic drug, phenobarbital. To accurately assess NO production during seizure activity, we directly measured KA-induced NO levels in the temporal lobe using an electron paramagnetic resonance NO trapping technique. Our results revealed that the both dose- and time-dependent changes of NO levels in the temporal lobe of KA-treated mice were closely related to the development of seizure activity. l-NAME mediated suppression of the KA-induced NO generation led to enhanced severity of KA-induced seizures. In contrast, 7-NI induced only about 50% suppression and had little effect on seizure severity; while phenobarbital markedly reduced both NO production and seizure severity. These results show that KA-induced neuroexcitation leads to profound increases in NO release to the temporal lobe of KA-treated mice and that NO generation from eNOS exerts an anti-convulsant effect.

Role of nitric oxide in cerebral blood flow changes during kainate seizures in mice: genetic and pharmacological approaches

The role of neuronal nitric oxide (NO) in the cerebrovascular response to partial seizures induced by intrahippocampal injection of kainate (KA) was investigated in mice deleted for the neuronal NO synthase gene (nNOS-/-) and in wild-type controls (WT). A second group of WT mice received the nNOS inhibitor, 7-nitroindazole (WT-7NI). Local cerebral blood flow (LCBF) was measured using the quantitative (14)C-iodoantipyrine method. Within the epileptic focus, all three groups of seizing mice (WT, WT-7NI, and nNOS-/-) showed significant 26-88% LCBF increases in ipsilateral hippocampus, compared to saline-injected mice. Contralaterally to the epileptic focus, KA seizures induced a 21-47% LCBF decreases in hippocampus and limbic cortex of WT mice and in most contralateral brain structures of nNOS-/- mice, while WT-7NI mice showed no contralateral CBF change. Neuronal NO appears to be not involved in the cerebrovascular response within the epileptic focus, but may rather have a role in the maintenance of distant LCBF regulation during seizures.

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>

Kainate-induced oxidative stress and neurotoxicity in the rat brain

We investigated superoxide production and MnSOD activity after kainate injection into the CA3 region of the rat hippocampus. The measurements took place at different times in hippocampus, forebrain cortex, striatum, and cerebellum homogenates. Free radicals including superoxide are responsible for post-lesional cytotoxicity. Neuronal cells responded to oxidative stress in kainate-induced neurotoxicity and caused the protective mechanism to increase MnSOD levels. The increase of MnSOD in distinct brain regions functionally connected via afferents and efferent suggests that these regions are affected by the injury. It implies that MnSOD protects the cells in these regions from superoxide-induced damage and therefore may limit the retrograde and anterograde spread of neurotoxicity. <br><br><font color="red"><b> This article has been retracted. Link to the retraction <u><a href="http://dx.doi.org/10.2298/ABS150318027E">10.2298/ABS150318027E</a><u></b></font>

Mitochondrial superoxide production and MnSOD activity following exposure to an agonist and antagonists of ionotropic receptors in rat brain

The involvement of NMDA and AMPA/kainate receptors in the induction of superoxide production in the rat brain was examined after intrahippocampal injection of kainate, a non-NMDA receptor agonist; kainate plus CNQX, a selective AMPA/kainate receptor antagonist; or kainate plus APV, a selective NMDA receptor antagonist. The measurements took place at different times in the ipsi- and contralateral hippocampus, forebrain cortex, striatum, and cerebellum homogenates. The used glutamate antagonists both ensured sufficient neuroprotection in the sense of lowering superoxide production and raising MnSOD levels, but in the mechanisms and time dynamics of their effects were different. Our findings suggest that NMDA and AMPA/kainate receptors are differentially involved in superoxide production. <br><br><font color="red"><b> This article has been retracted. Link to the retraction <u><a href="http://dx.doi.org/10.2298/ABS150318026E">10.2298/ABS150318026E</a><u></b></font>

Involvement of nitric oxide-dependent pathways of dorsolateral periaqueductal gray in the effects of ethanol in rats submitted to the elevated plus-maze test

Our previous study showed the microinjection of drugs that influence the nitric oxide (NO)-mediated neurotransmission in the hippocampus impacts upon the anxiolytic-like effect of ethanol. In this study, we examined whether NO-dependent pathways of the dorsolateral periaqueductal gray (dlPAG) participate in the anxiolytic effect of ethanol in rats submitted to the elevated plus-maze test. We evaluated the impact on ethanol effects of the nitric oxide synthase (NOS) inhibitor 7-nitroindazole, the soluble guanylate cyclase inhibitor 1H-(1,2,4)-oxodiazolo (4,3-a) quinoxalin-1-one (ODQ), the cyclic guanylate monophosphate (cGMP) analogue 8-bromo-cGMP and the NO donor sodium nitroprusside. The results showed that ODQ and 7-nitroindazole increased the percentage of open arm entries and of time spent on open arms in the elevated plus maze in rats injected with ethanol at 1.0g/kg, a dose that did not produce anxiolysis per se. Conversely, 8-bromo-cGMP and sodium nitroprusside blocked the increased exploration of open arms exhibited by rats treated with a higher dose of ethanol (1.2g/kg). Taken together, the results suggest that the inhibition of NO-dependent pathways of the dlPAG enhances the anxiolytic effect of ethanol, whereas the activation of these pathways results in an opposite effect.

Differential effects of NMDA and AMPA/kainate receptor antagonists on superoxide production and MnSOD activity in rat brain following intrahippocampal injection

The involvement of NMDA and AMPA/kainate receptors in the induction of superoxide radical production in the rat brain was examined after injection of kainate, non-NMDA receptor agonist, kainate plus 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), selective AMPA/kainate receptor antagonist, or kainate plus 2-amino-5-phosphonopentanoic acid (APV), selective NMDA receptor antagonist. Competitive glutamate receptor antagonists were injected with kainate unilaterally into the CA3 region of the rat hippocampus. We investigated superoxide production and mitochondrial MnSOD activity after injection. The measurements took place at different times (5, 15 min, 2, 48 h and 7 days) in the ipsi- and contralateral hippocampus, forebrain cortex, striatum, and cerebellum homogenates. Used glutamate antagonists APV and CNQX both expressed sufficient neuroprotection in sense of decreasing superoxide production and increasing MnSOD levels, but with differential effect in mechanisms and time dynamics. Our findings suggest that NMDA and AMPA/kainate receptors are differentially involved in superoxide production. Following intrahippocampal antagonists injection they, also, interpose different neuroprotection effect on the induction of MnSOD activity in distinct brain regions affected by the injury, which are functionally connected via afferents and efferents. It suggests that MnSOD protects the cells in these regions from superoxide-induced damage and therefore may limit the retrograde and anterograde spread of neurotoxicity.

Ability of GDNF to diminish free radical production leads to protection against kainate-induced excitotoxicity in hippocampus

The primary aim of this study is to explore the protective mechanisms of glial-derived neurotrophic factor (GDNF) during excitotoxicity by kainate in the hippocampus. After a 15-min microinjection with kainate, excitotoxicity was induced in the rat hippocampus. The protective effect of GDNF in the hippocampus was evaluated by administering GDNF 14 min after injection of kainate. The resulting hydroxyl free radicals were quantified by microdialysis of the hippocampus. The results show that GDNF can effectively suppress the production of kainate-induced hydroxyl free radical production. In addition, histological observation indicated the ability of GDNF to decrease the damage level of pyramidal neurons in the CA3 and CA4 areas of the hippocampus. Superoxide dismutase (SOD) activity in the hippocampus was elevated significantly at 30 min and 7 days after kainate induction, while glutathione peroxidase (cGPx) activity did not increase significantly until the seventh day. With GDNF treatment, SOD and cGPx activity in the hippocampus was elevated significantly 7 days after kainate induction. We suggest that mechanisms including a decrease in free radical generation and scavenging of free radicals might be involved in GDNF protection against kainate-induced excitotoxicity.

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.

Modulation of cortical nitric oxide synthase, glutamate, and redox state by nifedipine and taurine in PTZ-kindled mice

PURPOSE

Correlation between pentylenetetrazol (PTZ)-induced kindling and the cortical nitric oxide synthase (NOS), intracellular calcium [Ca2+]i, glutamate, and free radicals was studied in mice, as well as the modulatory action of nifedipine and taurine on these parameters.

METHODS

Male Swiss albino mice were used. Mice in one group received a single convulsive dose of PTZ (50 mg/kg, i.p), and were killed 24 h later. To induce kindling, PTZ was injected in a subconvulsive dose (40 mg/kg, i.p.) every other day for 3 weeks. One kindled group was used as control, whereas two other groups were injected 30 min before PTZ with either nifedipine (30 mg/kg, i.p) or taurine (100 mg/kg, i.p). All three kindled groups were killed 24 h after the last injection.

RESULTS

Compared with normal control group, PTZ-kindled mice had significantly higher levels of [Ca2+]i, malonaldehyde (MDA), NOS, and lactate dehydrogenase (LDH) but had lower levels of superoxide dismutase (SOD) and reduced glutathione (GSH). Acute seizures of the same intensity did not induce these alterations, indicating their link to the kindling phenomenon and not to seizure activity. The effect of taurine, known as an antioxidant, was more pronounced than that of the Ca2+-channel blocker, nifedipine. The first drug reversed the PTZ-kindled action on [Ca2+]i, NOS, LDH, GSH, and SOD, whereas nifedipine restored only LDH and GSH levels. However, both drugs did not restore the elevated MDA level.

CONCLUSIONS

This study suggests that free radicals, as well as NOS, are implicated in PTZ-induced kindling, and that antioxidants could play a role in controlling the accompanying changes.

Treatment with 7-nitroindazole enhances kainic acid induced cholinergic neurotoxicity in the rat striatum: a neuroprotective role for neuronal nitric oxide

1. In this study we investigated the effect of 7-nitroindazole (7-NI), a preferential inhibitor of neuronal nitric oxide synthase (nNOS), on kainic acid (KA) induced neurotoxicity in rats. Choline acetyltransferase activity (CAT), a cholinergic marker, and histological changes were employed to assess neurotoxicity. 2. In control rats, the local intrastriatal injection of 0.5 microg of KA reduced CAT from 22.9 +/- 2.2 to 14.7 +/- 2.0 nmol/h/mg tissue ((38 +/- 6)% reduction) (P < 0.001). Greater reductions in CAT were observed with 1 and 2 microg of KA ((70 +/- 6)% and (80 +/- 3)%, respectively). 7-NI aggravated KA-induced cholinergic and histological damage. KA reduced CAT by (68.2 +/- 4)% in 7-NI-treated rats, by (38 +/- 6)% in saline-treated controls, and by (41 +/- 4)% in peanut-oil- (7-NI-vehicle-) treated rats (P = 0.0047). 3. After KA, CAT activity averaged 14.3 +/- 2.0 in peanut-oil-treated rats and 7.9 +/- 1.0 nmol/h/mg tissue in 7-NI- (peanut-oil-) treated rats (P = 0.015). Similarly to changes in CAT, 7-NI treatment aggravated KA-induced histological changes indicative of neuronal damage (acute ischemic neuronal changes, disorganization of myelinated fibers bundle, and vacuolation changes of the neuropil). Treatment with 7-NI was not associated with increased mortality. 4. Our findings suggest that neuronal NO plays a neuroprotective action on excitotoxicity.

Effects of intracerebroventricular administration of 7-nitroindazole on tolerance to ethanol

Previous studies have shown that nitric oxide (NO) is involved in the development of rapid tolerance to the motor incoordination produced by ethanol. In order to further investigate this involvement, three experiments were undertaken using the tilt-plane and the hypothermia tests. The first demonstrated that 7-nitroindazole (7-NI), a preferential neuronal NO synthase (nNOS) inhibitor, injected by intracerebroventricular (i.c.v.) route, blocked the development of rapid tolerance to ethanol-induced motor incoordination. This effect was prevented by i.c.v. injection of L-arginine. The second experiment showed that D-arginine did not influence the blockade of tolerance produced by 7-NI. The third experiment revealed that i.c.v. injection of 7-NI also blocked the development of tolerance to the hypothermic effect of ethanol. These results support the hypothesis that nNOS-derived NO participates in the development of rapid tolerance to ethanol.

Neuronal nitric oxide synthase (NOS) regulates leukocyte-endothelial cell interactions in endothelial NOS deficient mice

1. The present study was designed to examine the possible role of neuronal nitric oxide synthase (nNOS) in regulation of leukocyte - endothelial cell interactions in the absence of endothelial nitric oxide synthase (eNOS), using intravital microscopy of the cremasteric microcirculation of eNOS(-/-) mice. 2. Baseline leukocyte rolling and adhesion revealed no differences between wild-type and eNOS(-/-) mice in either the cremasteric or intestinal microcirculations. 3. Superfusion with L-NAME (100 microM) caused a progressive and significant increase in leukocyte adhesion in both wild-type and eNOS(-/-) mice, without detecting differences between the two strains of mice. 4. Superfusion with 7-nitroindazole (100 microM), a selective inhibitor of nNOS, had no effect on leukocyte adhesion in wild-type animals. However, it increased leukocyte adhesion significantly in eNOS(-/-) mice, which was reversed by systemic L-arginine pre-administration. 5. Stimulation of the microvasculature with H(2)O(2) (100 microM) induced a transient elevation in leukocyte rolling in wild-type mice. Conversely, the effect persisted during the entire 60 min of experimental protocol in eNOS(-/-) mice either with or without 7-nitroindazole. 6. Semi-quantitative analysis by RT - PCR of the mRNA for nNOS levels in eNOS(-/-) and wild-type animals, showed increased expression of nNOS in both brain and skeletal muscle of eNOS(-/-) mice. 7. In conclusion, we have demonstrated that leukocyte-endothelial cell interactions are predominantly modulated by eNOS isoform in postcapillary venules of normal mice, whereas nNOS appears to assume the same role in eNOS(-/-) mice. Interestingly, unlike eNOS there was insufficient NO produced by nNOS to overcome leukocyte recruitment elicited by oxidative stress, suggesting that nNOS cannot completely compensate for eNOS.