The role of nitric oxide in modulating brain activity and blood flow during seizure

Neuroprotective effects of coenzyme Q10 on neurological diseases: a review article

Neurological disorders affect the nervous system. Biochemical, structural, or electrical abnormalities in the spinal cord, brain, or other nerves lead to different symptoms, including muscle weakness, paralysis, poor coordination, seizures, loss of sensation, and pain. There are many recognized neurological diseases, like epilepsy, Alzheimer's disease (AD), Parkinson's disease (PD), multiple sclerosis (MS), stroke, autosomal recessive cerebellar ataxia 2 (ARCA2), Leber's hereditary optic neuropathy (LHON), and spinocerebellar ataxia autosomal recessive 9 (SCAR9). Different agents, such as coenzyme Q10 (CoQ10), exert neuroprotective effects against neuronal damage. Online databases, such as Scopus, Google Scholar, Web of Science, and PubMed/MEDLINE were systematically searched until December 2020 using keywords, including review, neurological disorders, and CoQ10. CoQ10 is endogenously produced in the body and also can be found in supplements or foods. CoQ10 has antioxidant and anti-inflammatory effects and plays a role in energy production and mitochondria stabilization, which are mechanisms, by which CoQ10 exerts its neuroprotective effects. Thus, in this review, we discussed the association between CoQ10 and neurological diseases, including AD, depression, MS, epilepsy, PD, LHON, ARCA2, SCAR9, and stroke. In addition, new therapeutic targets were introduced for the next drug discoveries.

Possible mechanisms involved in the neuroprotective effect of Trans,trans-farnesol on pilocarpine-induced seizures in mice

This study aimed to investigate, through in vivo and in vitro methodologies, the effect of acute trans,trans-farnesol (12.5, 25, 50 or 100 mg/kg, p.o.) administration on behavioral and neurochemical parameters associated with pilocarpine-induced epileptic seizure (300 mg/kg, i.p.) in mice. The initial results showed that the compound in question presents no anxiolytic-like or myorelaxant effects, despite reducing locomotor activity in the animals at all doses tested. In addition, the lowest dose increased the latency to onset of the first epileptic seizure, and the time to death. In addition to decreasing the mortality percentage in mice submitted to the pilocarpine model. In this same model, pretreatment with the lowest dose of the compound decreased the hippocampal concentrations of thiobarbituric acid and nitrite, and partially restored striatal concentrations of noradrenaline, dopamine, and serotonin. Taken together, the results suggest that trans,trans-farnesol presents a central depressant effect which contributes to its antiepileptic action which, in turn, seems to be mediated by the antagonism of muscarinic cholinergic receptors, reduction of oxidative stress. and modulation of noradrenaline, dopamine and serotonin concentrations in the central nervous system.

Modafinil exerts anticonvulsive effects against lithium-pilocarpine-induced status epilepticus in rats: A role for tumor necrosis factor-α and nitric oxide signaling

BACKGROUND

Status epilepticus (SE) is a continuous episode of seizures which leads to hippocampal neurodegeneration, severe systemic inflammation, and extreme damage to the brain. Modafinil, a psychostimulant and wake-promoting agent, has exerted neuroprotective and anti-inflammatory effects in previous preclinical studies. The aim of this study was to assess effects of modafinil on the lithium-pilocarpine-induced SE rat model and to explore possible involvement of tumor necrosis factor-α (TNF-α) and nitric oxide (NO) pathways in this regard.

METHODS

Status epilepticus was provoked by injection of lithium chloride (127 mg/kg, intraperitoneally [i.p]) and pilocarpine (60 mg/kg, i.p.) in rats. Animals received different modafinil doses (50, 75, 100, and 150 mg/kg, i.p.) and SE scores were documented over 3 hours of duration. Moreover, the role of the nitrergic pathway in the effects of modafinil was evaluated by injection of the non-selective NO synthase (NOS) inhibitor L-N^G-Nitro arginine methyl ester (L-NAME, 10 mg/kg, i.p.), the selective neuronal NOS inhibitor 7-nitroindazole (30 mg/kg, i.p.), and the selective inducible NOS inhibitor aminoguanidine (100 mg/kg, i.p.) 15 min before saline/vehicle or modafinil. The ELISA method was used to quantify TNF-α and NO metabolite levels in the isolated hippocampus.

RESULTS

Modafinil at 100 mg/kg significantly decreased SE scores (P < 0.01). Pre-treatment with L-NAME, 7-nitroindazole, and aminoguanidine significantly reversed the anticonvulsive effects of modafinil. Status epilepticus-induced animals showed significantly higher NO metabolite and TNF-α levels in their hippocampal tissues, an effect that was reversed by modafinil (100 mg/kg, i.p.) treatment. Administration of NOS inhibitors resulted in excessive NO level reduction but an escalation of TNF-α level in modafinil-treated SE-animals.

CONCLUSION

Our study revealed anticonvulsive effects of modafinil in the lithium-pilocarpine-induced SE rat model via possible involvement of TNF-α and nitrergic pathways.

The Possible Role of Nitric Oxide signaling and NMDA Receptors in Allopurinol effect on Maximal Electroshock- and Pentylenetetrazol-Induced Seizures in Mice

Allopurinol, a uric-acid-lowering medication, has shown its efficacy in several studies suggesting that allopurinol can be prescribed as adjunctive cure meant for intractable epilepsy. The exact mechanism of allopurinol is still unknown. This study evaluates allopurinol's effect on seizure threshold, seizure incidence, and mortality rate in mice models. Moreover, the possible involvement of nitric oxide (NO) pathway and N-methyl-D-aspartate (NMDA) receptors are investigated. To evaluate the effect of allopurinol on seizure, we used the pentylenetetrazole (PTZ)-induced seizure along with maximal electroshock (MES)-induced seizure. To assess the underlying mechanism behind the allopurinol activity, we used nitric oxide synthase (NOS) substrate (L-arginine), NOS inhibitors (L-NAME, aminoguanidine, 7-nitroindazole), and NMDA receptor antagonist (MK-801). Intraperitoneal allopurinol administration at a dose of 50 mg/kg in mice showed a significant (p<0.001) anti-convulsant activity in the PTZ-induced seizure. Even though pre-treatment with L-Arginine (60 mg/kg) potentiates allopurinol's anti-convulsant effect in the PTZ-induced seizure, pre-treatment with L-NAME (10 mg/kg), aminoguanidine (100 mg/kg), and 7-nitroindazole (30 mg/kg) reversed the anti-convulsant effect of allopurinol in the PTZ-induced seizure. In addition, pre-treatment with MK-801 also decreased the anti-convulsant effect of allopurinol in the PTZ-induced seizure. While allopurinol at a dose of 50 mg/kg and 100 mg/kg did not induce protection against seizure incidence in the MES-induced seizure, it revealed a remarkable effect in reducing the mortality rate in the MES-induced seizure. Allopurinol increases the seizure threshold in PTZ-induced seizure and enhances the survival rate in MES-induced seizure. Allopurinol exerts its anti-convulsant effect, possibly through targeting NO pathway and NMDA receptors.

Effect of Lenalidomide on Pentylenetetrazole-Induced Clonic Seizure Threshold in Mice: A Role for N-Methyl-D-Aspartic Acid Receptor/Nitric Oxide Pathway

Background and Purpose

Accumulating evidence suggest that lenalidomide, a structural analog of thalidomide, has neuro-modulatory and neuroprotective properties. In the present study, we investigated effects of acute administration of lenalidomide on clonic seizure threshold in mice induced by pentylenetetrazole (PTZ) and possible role of N-methyl-D-aspartic acid receptor (NMDAR) and nitric oxide (NO) pathway.

Methods

We have utilized a clonic model of seizure in NMRI mice induced by PTZ to evaluate the potential effect of lenalidomide on seizure threshold. Different doses of lenalidomide (5, 10, 20, and 50 mg/kg, intraperitoneal [i.p.]) were administered 1 hour before PTZ. To evaluate probable role of NMDAR/NO signaling, the non-selective NO synthase inhibitor L-N^G-nitroarginine methyl ester (L-NAME; 10 mg/kg, i.p.), neuronal NOS (nNOS) inhibitor 7-nitroindazole (7-NI; 30 mg/kg, i.p.), selective inducible NOS inhibitor aminoguanidine (AG; 100 mg/kg, i.p.), selective NMDAR antagonist MK-801 (0.01 mg/kg, i.p.), and selective NMDAR agonist D-serine (30 mg/kg, i.p.) were injected 15 minutes before lenalidomide.

Results

Lenalidomide at 10 and 20 mg/kg significantly elevated the PTZ-induced seizure thresholds. Interestingly, L-NAME (10 mg/kg, i.p), 7-NI (30 mg/kg, i.p), and AG (100 mg/kg, i.p) reversed the anticonvulsive effect of lenalidomide (10 mg/kg). Moreover, treatment with the NMDAR agonist D-serine (30 mg/kg, i.p.) did not alter the anticonvulsive properties of lenalidomide (10 mg/kg, i.p). However, the NMDAR antagonist MK-801 (0.01 mg/kg, i.p) significantly reversed the anticonvulsive effects of lenalidomide (10 mg/kg).

Conclusions

Our study demonstrated a role for the NMDAR/NO pathway in the anticonvulsive effects of lenalidomide on the PTZ-induced clonic seizures in mice.

Interaction of morphine tolerance with pentylenetetrazole-induced seizure threshold in mice: The role of NMDA-receptor/NO pathway

N-methyl-d-aspartate receptor (NMDA-R)/nitric oxide (NO) pathway is involved in the intensification of the analgesic effect of opioids and the reduction of the intensity of opioids tolerance and dependence. In the current study, we investigated the involvement of NMDA-R/NO pathway in chronic morphine-treated mice in both the development of tolerance to the analgesic effect of morphine and in pentylenetetrazole (PTZ)-induced seizure threshold. Chronic treatment with morphine (30 mg/kg) exhibited increased seizure resistance in morphine-induced tolerant mice. The development of morphine tolerance was withdrawn when used concomitantly with NOS inhibitors and NMDA-R antagonist, suggesting that the development of tolerance to the anticonvulsant effect of morphine (30 mg/kg) is mediated through the NMDA-R/NO pathway. A dose-dependent biphasic seizure modulation of morphine was demonstrated in the acute treatment with morphine; acute treatment at a dose of 0.5 mg/kg shows the anticonvulsant effect and at a dose of 30 mg/kg shows proconvulsant effect. However, a different pattern was observed in the mice treated chronically with morphine: they demonstrated tolerance in the tail-flick test; five consecutive days of chronic treatment with a high dose of morphine (30 mg/kg) showed anticonvulsant effect while a low dose of morphine (0.5 mg/kg) showed a proconvulsant effect. The anticonvulsant effect of morphine was inhibited completely by the concomitant administration of NO synthase (NOS) inhibitors including nonspecific NOS inhibitor (L-NAME, 10 mg/kg), inducible NOS inhibitor (aminoguanidine, 50 mg/kg), and neuronal NOS inhibitor (7-nitroindazole (7-NI), 15 mg/kg) for five consecutive days. Besides, five days injection of NMDA-R antagonist (MK-801, 0.05 mg/kg) significantly inhibited the anticonvulsant effect of morphine on the PTZ-induced clonic seizures. The results revealed that chronic treatment with morphine leads to the development of tolerance in mice, which in turn may cause an anticonvulsant effect in a high dose of morphine via the NMDA-R/NO pathway.

Effect of Curcuma zedoaria hydro-alcoholic extract on learning, memory deficits and oxidative damage of brain tissue following seizures induced by pentylenetetrazole in rat

BACKGROUND

Previous studies have shown that seizures can cause cognitive disorders. On the other hand, the Curcuma zedoaria (CZ) has beneficial effects on the nervous system. However, there is little information on the possible effects of the CZ extract on seizures. The aim of this study was to investigate the possible effects of CZ extract on cognitive impairment and oxidative stress induced by epilepsy in rats.

METHODS

Rats were randomly divided into different groups. In all rats (except the sham group), kindling was performed by intraperitoneal injection of pentylenetetrazol (PTZ) at a dose of 35 mg/kg every 48 h for 14 days. Positive group received 2 mg/kg diazepam + PTZ; treatment groups received 100, 200 or 400 mg/kg CZ extract + PTZ; and one group received 0.5 mg/kg flumazenil and CZ extract + PTZ. Shuttle box and Morris Water Maze tests were used to measure memory and learning. On the last day of treatments PTZ injection was at dose of 60 mg/kg, tonic seizure threshold and mortality rate were recorded in each group. After deep anesthesia, blood was drawn from the rats' hearts and the hippocampus of all rats was removed.

RESULTS

Statistical analysis of the data showed that the CZ extract significantly increased the tonic seizure threshold and reduced the pentylenetetrazol-induced mortality and the extract dose of 400 mg/kg was selected as the most effective dose compared to the other doses. It was also found that flumazenil (a GABA_A receptor antagonist) reduced the tonic seizure threshold compared to the effective dose of the extract. The results of shuttle box and Morris water maze behavioral tests showed that memory and learning decreased in the negative control group and the CZ extract treatment improved memory and learning in rats. The CZ extract also increased antioxidant capacity, decreased MDA and NO in the brain and serum of pre-treated groups in compared to the negative control group.

CONCLUSION

It is concluded that the CZ extract has beneficial effects on learning and memory impairment in PTZ-induced epilepsy model, which has been associated with antioxidant effects in the brain or possibly exerts its effects through the GABAergic system.

Oxidative Stress in Patients with Drug Resistant Partial Complex Seizure

Oxidative stress (OS) has been implicated as a pathophysiological mechanism of drug-resistant epilepsy, but little is known about the relationship between OS markers and clinical parameters, such as the number of drugs, age onset of seizure and frequency of seizures per month. The current study’s aim was to evaluate several oxidative stress markers and antioxidants in 18 drug-resistant partial complex seizure (DRPCS) patients compared to a control group (age and sex matched), and the results were related to clinical variables. We examined malondialdehyde (MDA), advanced oxidation protein products (AOPP), advanced glycation end products (AGEs), nitric oxide (NO), uric acid, superoxide dismutase (SOD), glutathione, vitamin C, 4-hydroxy-2-nonenal (4-HNE) and nitrotyrosine (3-NT). All markers except 4-HNE and 3-NT were studied by spectrophotometry. The expressions of 4-HNE and 3-NT were evaluated by Western blot analysis. MDA levels in patients were significantly increased (p ≤ 0.0001) while AOPP levels were similar to the control group. AGEs, NO and uric acid concentrations were significantly decreased (p ≤ 0.004, p ≤ 0.005, p ≤ 0.0001, respectively). Expressions of 3-NT and 4-HNE were increased (p ≤ 0.005) similarly to SOD activity (p = 0.0001), whereas vitamin C was considerably diminished (p = 0.0001). Glutathione levels were similar to the control group. There was a positive correlation between NO and MDA with the number of drugs. The expression of 3-NT was positively related with the frequency of seizures per month. There was a negative relationship between MDA and age at onset of seizures, as well as vitamin C with seizure frequency/month. We detected an imbalance in the redox state in patients with DRCPS, supporting oxidative stress as a relevant mechanism in this pathology. Thus, it is apparent that some oxidant and antioxidant parameters are closely linked with clinical variables.

Modulation of the anticonvulsant effect of swim stress by agmatine

Agmatine is an endogenous l-arginine metabolite with neuroprotective effects in the stress-response system. It exerts anticonvulsant effects against several seizure paradigms. Swim stress induces an anticonvulsant effect by activation of endogenous antiseizure mechanisms. In this study, we investigated the interaction of agmatine with the anticonvulsant effect of swim stress in mice on pentylenetetrazole (PTZ)-induced seizure threshold. Then we studied the involvement of nitric oxide (NO) pathway and endogenous opioid system in that interaction. Swim stress induced an anticonvulsant effect on PTZ seizures which was opioid-independent in shorter than 1-min swim durations and opioid-dependent with longer swims, as it was completely reversed by pretreatment with naltrexone (NTX) (10mg/kg), an opioid receptor antagonist. Agmatine significantly enhanced the anticonvulsant effect of opioid-independent shorter swim stress, in which a combination of subthreshold swim stress duration (45s) and subeffective dose of agmatine (1mg/kg) revealed a significantly higher seizure threshold compared with either one. This effect was significantly reversed by NO synthase inhibitor N^G-nitro-l-arginine (L-NAME (Nω-Nitro-L-arginine methyl ester), 5mg/kg), suggesting an NO-dependent mechanism, and was unaffected by NTX (10mg/kg), proving little role for endogenous opioids in the interaction. Our data suggest that pretreatment of animals with agmatine acts additively with short swim stress to exert anticonvulsant responses, possibly by mediating NO pathway.

The role of nitric oxide in anticonvulsant effect of nanocurcumine on pentylenetetrazole-induced seizure in mice

A plant alkaloid obtained from Curcuma longa, curcumin possesses anti-oxidant and anti-inflammatory effects. Nanoformulations have been developed for preclinical studies which demonstrate enhanced therapeutic efficacy. Effect of acute intraperitoneal (i.p.) administration of curcumin C3 complex nanoparticles [1,5, 10, 20, 40, 80mg/kg, (i.p.)] 75min prior to PTZ, on clonic seizure thresholds induced by intravenous infusion of pentylenetetrazole (PTZ) 0.5% was investigated in comparison with curcumin (40 and 80mg/kg, i.p.) in male mice. Moreover, to clarify the probable role of NO in the anticonvulsant property of nanocurcumin, non-effective doses of l-arginine (l-Arg), a NO donor; 7-nitroindazole, 7-NI, a preferential neuronal NO synthase inhibitor; L-NAME, a non-selective NO synthase inhibitor and aminoguanidine (AG), a selective inducible NO synthase inhibitor (iNOS), in combination with nanocurcumin (80mg/kg, i.p.), 15-30min before it were employed.

RESULTS

While curcumin did not show any anticonvulsant effect, nanocurcumin revealed dose-dependent anticonvulsant property at the doses 20, 40 and 80mg/kg, P<0.01, P<0.01 and P<0.001, respectively. l-Arg (30 and 60mg/kg) dose-dependently reversed the anticonvulsant effect of the most effective nanocurcumin dose (80mg/kg), P<0.01 and P<0.001, respectively. On the other hand, L-NAME (3 and 10mg/kg, i.p.) markedly potentiated the sub effective dose of nanocurcumin (10mg/kg), P<0.01 and P<0.001, respectively. Similarly, AG (50 and 100mg/kg, i.p.) profoundly augmented the seizure thresholds of nanocurcumin (10mg/kg), P<0.01 and P<0.001, respectively. In addition, 7-NI (10, 30 and 60mg/kg, i.p.) failed to influence the responses.

CONCLUSION

These data may support excess of NO production following PTZ infusion probably resulting from iNOS source. Consequently, nanocurcumin probably down regulated NO. To conclude, nanocurcumin showed anticonvulsant effect. Furthermore, this effect was reversed following l-arginine as an external NO precursor. However, both the non-selective NOS inhibitor and selective iNOS inhibitor increased the thresholds. It is evident that nanocurcumin may influence the seizure thresholds at least in part through a decrease in NO.

Anticonvulsant effect of dextrometrophan on pentylenetetrazole-induced seizures in mice: Involvement of nitric oxide and N-methyl-d-aspartate receptors

Dextrometrophan (DM), widely used as an antitussive, has recently generated interest as an anticonvulsant drug. Some effects of dextrometrophan are associated with alterations in several pathways, such as inhibition of nitric oxide synthase (NOS) enzyme and N-methyl d-aspartate (NMDA) receptors. In this study, we aimed to investigate the anticonvulsant effect of acute administration of dextrometrophan on pentylenetetrazole (PTZ)-induced seizures and the probable involvement of the nitric oxide (NO) pathway and NMDA receptors in this effect. For this purpose, seizures were induced by intravenous PTZ infusion. All drugs were administrated by intraperitoneal (i.p.) route before PTZ injection. Our results demonstrate that acute DM treatment (10-100mg/kg) increased the seizure threshold. In addition, the nonselective NOS inhibitor L-NAME (10mg/kg) and the neural NOS inhibitor, 7-nitroindazole (40mg/kg), at doses that had no effect on seizure threshold, augmented the anticonvulsant effect of DM (3mg/kg), while the inducible NOS inhibitor, aminoguanidine (100mg/kg), did not affect the anticonvulsant effect of DM. Moreover, the NOS substrate l-arginine (60mg/kg) blunted the anticonvulsant effect of DM (100mg/kg). Also, NMDA antagonists, ketamine (0.5mg/kg) and MK-801 (0.05mg/kg), augmented the anticonvulsant effect of DM (3mg/kg). In conclusion, we demonstrated that the anticonvulsant effect of DM is mediated by a decline in neural nitric oxide activity and inhibition of NMDA receptors.

An Abnormal Nitric Oxide Metabolism Contributes to Brain Oxidative Stress in the Mouse Model for the Fragile X Syndrome, a Possible Role in Intellectual Disability

BACKGROUND

Fragile X syndrome is the most common genetic cause of mental disability. Although many research has been performed, the mechanism underlying the pathogenesis is unclear and needs further investigation. Oxidative stress played major roles in the syndrome. The aim was to investigate the nitric oxide metabolism, protein nitration level, the expression of NOS isoforms, and furthermore the activation of the nuclear factor NF-κB-p65 subunit in different brain areas on the fragile X mouse model.

METHODS

This study involved adult male Fmr1-knockout and wild-type mice as controls. We detected nitric oxide metabolism and the activation of the nuclear factor NF-κBp65 subunit, comparing the mRNA expression and protein content of the three NOS isoforms in different brain areas.

RESULTS

Fmr1-KO mice showed an abnormal nitric oxide metabolism and increased levels of protein tyrosine nitrosylation. Besides that, nuclear factor NF-κB-p65 and inducible nitric oxide synthase appeared significantly increased in the Fmr1-knockout mice. mRNA and protein levels of the neuronal nitric oxide synthase appeared significantly decreased in the knockout mice. However, the epithelial nitric oxide synthase isoform displayed no significant changes.

CONCLUSIONS

These data suggest the potential involvement of an abnormal nitric oxide metabolism in the pathogenesis of the fragile X syndrome.

Effects of D-penicillamine on pentylenetetrazole-induced seizures in mice: involvement of nitric oxide/NMDA pathways

Besides the clinical applications of penicillamine, some reports show that use of D-penicillamine (D-pen) has been associated with adverse effects such as seizures. So, the purpose of this study was to evaluate the effects of D-pen on pentylenetetrazole (PTZ)-induced seizures in male NMRI mice. It also examined whether N-methyl-D-aspartate (NMDA) receptor/nitrergic system blockage was able to alter the probable effects of D-pen. Different doses of D-pen (0.1, 0.5, 1, 10, 100, 150, and 250 mg/kg) were administered intraperitoneally (i.p.) 90 min prior to induction of seizures. D-Penicillamine at a low dose (0.5 mg/kg, i.p.) had anticonvulsant effects, whereas at a high dose (250 mg/kg, i.p.), it was proconvulsant. Both anti- and proconvulsant effects of D-pen were blocked by a single dose of a nonspecific inhibitor of nitric oxide synthase (NOS), L-NAME (10 mg/kg, i.p.), and a single dose of a specific inhibitor of neuronal nitric oxide synthase (nNOS), 7-nitroindazole (30 mg/kg, i.p.). A selective inhibitor of iNOS, aminoguanidine (100 mg/kg, i.p.), had no effect on these activities. An NMDA receptor antagonist, MK-801 (0.05 mg/kg, i.p.), alters the anti- and proconvulsant effects of D-pen. The results of the present study showed that the nitric oxide system and NMDA receptors may contribute to the biphasic effects of D-pen, which remain to be clarified further.

The effects of coenzyme Q10 on seizures in mice: the involvement of nitric oxide

Coenzyme Q10 is a potent antioxidant in both mitochondria and lipid membranes. It has also been recognized to have an effect on gene expression. This study was designed to investigate whether acute or subchronic treatment with coenzyme Q10 altered the seizures induced by pentylenetetrazole or electroshock in mice. We also evaluated the involvement of nitric oxide in the effects of coenzyme Q10 in pentylenetetrazole-induced seizure models. Acute oral treatment with different doses of coenzyme Q10 did not affect the seizure in intraperitoneal pentylenetetrazole, intravenous pentylenetetrazole, and electroshock models in mice. Subchronic oral administration of coenzyme Q10 (100 mg/kg or more) increased time latencies to the onset of myoclonic jerks and clonic seizures induced by intraperitoneal pentylenetetrazole and at the doses of 25 mg/kg or more increased the seizure threshold induced by intravenous infusion of pentylenetetrazole. Subchronic doses of coenzyme Q10 (50 mg/kg or more) also decreased the incidence of tonic seizures in the electroshock-induced seizure model. Moreover, acute treatment with the precursor of nitric oxide synthesis, L-arginine (60 mg/kg), led to a significant potentiation of the antiseizure effects of subchronic administration of coenzyme Q10 (400 mg/kg in intraperitoneal and 6.25 mg/kg in intravenous pentylenetetrazole tests). Acute treatment with l-NAME (5 mg/kg), a nonspecific nitric oxide synthase inhibitor, significantly attenuated the antiseizure effects of subchronic doses of coenzyme Q10 in both seizure models induced by pentylenetetrazole. On the other hand, acute administration of aminoguanidine (100 mg/kg), a specific inducible nitric oxide synthase inhibitor, did not affect the seizures in mice treated with subchronic doses of coenzyme Q10 in both intraperitoneal and intravenous pentylenetetrazole tests. In conclusion, only subchronic and not acute administration of coenzyme Q10 attenuated seizures induced by pentylenetetrazole or electroshock. We also demonstrated, for the first time, the interaction between nitric oxide and coenzyme Q10 in antiseizure activity probably through the induction of constitutive nitric oxide synthase.

Chronic administration of atorvastatin induced anti-convulsant effects in mice: the role of nitric oxide

Atorvastatin has neuroprotective effects, and there is some evidence that nitric oxide is involved in atorvastatin effects. In this study, we evaluated whether the nitrergic system is involved in the anticonvulsant effects of chronic atorvastatin administration. Intravenous and intraperitoneal pentylenetetrazol were used to induce seizures in mice. Chronic atorvastatin treatment significantly increased the seizure threshold which is induced by both intravenous and intraperitoneal pentylenetetrazol. Intraperitoneal pentylenetetrazol also decreased the incidence of tonic seizure and death in atorvastatin-treated groups. Chronic co-administration of a non-selective nitric oxide synthase inhibitor, l-NAME, or a selective inducible nitric oxide synthase inhibitor, aminoguanidine, with atorvastatin inhibited atorvastatin-induced anticonvulsant effects in intravenous model of pentylenetetrazol. Acute injection of l-NAME or aminoguanidine inhibited the anticonvulsant effects of atorvastatin in both models of intravenous- and intraperitoneal-pentylenetetrazol-induced seizures. In conclusion, we demonstrated that nitric oxide signaling probably through inducible nitric oxide synthase could be involved in the anticonvulsant effects of atorvastatin.

Sub-chronic treatment with pioglitazone exerts anti-convulsant effects in pentylenetetrazole-induced seizures of mice: The role of nitric oxide

OBJECTIVES

Pioglitazone delayed the development of seizure responses and shortened the duration of convulsion of genetically epileptic EL mice. The anti-epileptic effect of pioglitazone was attributed partly through the reduction of inflammatory responses and preventing apoptosis. There are also some reports showing that some pioglitazone effects mediate through nitric oxide. In this study we evaluated sub-chronic pioglitazone effects in two models of intravenous and intraperitoneal pentylenetetrazole-induced clonic seizures in mice.

MATERIALS AND METHODS

Different doses of pioglitazone were administered orally for 10 days in different groups of male mice. L-NAME, a non selective inhibitor of nitric oxide synthase, aminoguanidine, a selective inhibitor of inducible nitric oxide synthase, or L-arginine, a nitric oxide donor, was administered acutely or sub-chronically to evaluate the role of nitric oxide in pioglitazone anti-seizure effects.

RESULTS

We demonstrated that sub-chronic administration of pioglitazone exerted anti-convulsant effects in both models of intravenous and intraperitoneal pentylenetetrazole. Acute and sub-chronic pre-administration of L-NAME prevented the anti-convulsant effect of pioglitazone in both models of intravenous and intraperitoneal pentylenetetrazole. Aminoguanidine did not alter the anti-convulsant effect of pioglitazone in two models of intravenous and intraperitoneal pentylenetetrazole. Both acute and sub-chronic pre-treatment of mice with L-arginine exerted anti-convulsant effect when administered with a non effective dose of pioglitazone in intraperitoneal method. In intravenous method, acute administration of L-arginine with a non-effective dose of pioglitazone enhanced the seizure clonic latency.

CONCLUSION

Taken together, sub-chronic pioglitazone treatment exerts anti-convulsant effects in intravenous and intraperitoneal pentylenetetrazole-induced seizures of mice probably through induction of constitutive nitric oxide synthase.

Agmatine enhances the anticonvulsant effect of lithium chloride on pentylenetetrazole-induced seizures in mice: Involvement of L-arginine/nitric oxide pathway

After nearly 60years, lithium is still the mainstay in the treatment of mood disorders. In addition to its antimanic and antidepressant effects, lithium also has anticonvulsant properties. Similar to lithium, agmatine plays a protective role in the central nervous system against seizures and has been reported to enhance the effect of different antiepileptic agents. Moreover, both agmatine and lithium have modulatory effects on the L-arginine/nitric oxide pathway. This study was designed to investigate: (1) whether agmatine and lithium exert a synergistic effect against clonic seizures induced by pentylenetetrazole and (2) whether or not this synergistic effect is mediated through inhibition of the L-arginine/nitric oxide pathway. In our study, acute administration of a single potent dose of lithium chloride (30mg/kg ip) increased seizure threshold, whereas pretreatment with a low and independently noneffective dose of agmatine (3mg/kg) potentiated a subeffective dose of lithium (10mg/kg). N(G)-L-arginine methyl ester (L-NAME, nonspecific nitric oxide synthase inhibitor) at 1 and 5mg/kg and 7-nitroindazole (7-NI, preferential neuronal nitric oxide synthase inhibitor) at 15 and 30mg/kg augmented the anticonvulsant effect of the noneffective combination of lithium (10mg/kg ip) and agmatine (1mg/kg), whereas several doses (20 and 40mg/kg) of aminoguanidine (inducible nitric oxide synthase inhibitor) failed to alter the seizure threshold of the same combination. Furthermore, pretreatment with independently noneffective doses (30 and 60mg/kg) of L-arginine (substrate for nitric oxide synthase) inhibited the potentiating effect of agmatine (3mg/kg) on lithium (10mg/kg). Our findings demonstrate that agmatine and lithium chloride have synergistic anticonvulsant properties that may be mediated through the L-arginine/nitric oxide pathway. In addition, the role of constitutive nitric oxide synthase versus inducible nitric oxide synthase is prominent in this phenomenon.

Involvement of nitric oxide-cGMP pathway in the anticonvulsant effects of lithium chloride on PTZ-induced seizure in mice

Lithium is still the mainstay in the treatment of affective disorders as a mood stabilizer. Lithium also shows some anticonvulsant properties. While the underlying mechanisms of action of lithium are not yet exactly understood, we used a model of clonic seizure induced by pentylenetetrazole (PTZ) in male NMRI mice to investigate whether the anticonvulsant effect of lithium is mediated via NO-cGMP pathway. Injection of a single effective dose of lithium chloride (25 mg/kg) intraperitoneally (i.p.) increased significantly the seizure threshold (P<0.01). The anticonvulsant properties of the effective dose of lithium were prevented by pre-treatment with the per se non-effective doses of L-ARG [the substrate for nitric oxide synthase; NOS] (30 and 50 mg/kg) or sildenafil [a phosphodiesterase 5 inhibitor] (10 and 20 mg/kg). L-NAME [a non-specific NOS inhibitor] (5, 15 and 30 mg/kg), 7-NI [a specific neural NOS inhibitor] (30 and 60 mg/kg) or MB [a guanylyl cyclase inhibitor] (0.5 and 1 mg/kg) augmented the anticonvulsant effect of a sub-effective dose of lithium (10 mg/kg, i.p.). Whereas several doses of aminoguanidine [an inducible NOS inhibitor] (20, 50 and 100 mg/kg) failed to alter the anticonvulsant effect of lithium. Our findings demonstrated that nitric oxide-cyclic GMP pathway could be involved in the anticonvulsant properties of the lithium chloride. In addition, the role of constitutive NOS versus inducible NOS is prominent in this phenomenon.

Oxidative stress mediates hippocampal neuron death in rats after lithium-pilocarpine-induced status epilepticus

Oxidative stress, which is defined as the over-production of free radicals, can dramatically alter neuronal function and has been linked to status epilepticus (SE). The pathological process and underlying mechanisms involved in the oxidative stress during SE are still not fully clear. In the current study, SE was induced in rats by lithium-pilocarpine administration. Our data show that hippocampal neuron death occurs at 6h and is sustained for 7 days after SE. The production of nitric oxide (NO) started to increase at 30 min and was evident at 6h and 7 days after SE, which coincided with increased expression of neuronal nitric oxide synthase (nNOS), inducible nitric oxide synthase (iNOS) and malondialdehyde (MDA) after SE, whereas, activated caspase-3 prominently appeared at 7 days after SE. Further, FK506, an immunosuppressant, partially rescued the neuron death and attenuated the expression of NO, nNOS, iNOS, MDA and activated caspase-3. Taken together, our study indicates that oxidative stress mediated hippocampal neuron death occurs prior to caspase-3 activation and that FK506 plays an important role in protecting hippocampal neurons during status epilepticus.

Seizure susceptibility alteration through 5-HT(3) receptor: modulation by nitric oxide

There is some evidence that epileptic seizures could be induced or increased by 5-hydroxytryptamine (5-HT) attenuation, while augmentation of serotonin functions within the brain (e.g. by SSRIs) has been reported to be anticonvulsant. This study was performed to determine the effect of selective 5-HT(3) channel/receptor antagonist granisetron and agonist SR57227 hydrochloride on the pentylenetetrazole (PTZ)-induced seizure threshold in mice. The possible interaction of this effect with nitrergic system was also examined using the nitric oxide (NO) synthase inhibitor N(G)-nitro-l-arginine methyl ester (l-NAME) and the NO precursor l-arginine. SR57227 (10mg/kg, i.p.) significantly increased the seizure threshold compared to control group, while high dose granisetron (10mg/kg, i.p.) proved proconvulsant. Co-administration of sub-effective doses of the 5-HT(3) agonist with l-NAME (5 and 60mg/kg, i.p., respectively) exerted a significant anticonvulsive effect, while sub-effective doses of granisetron (3mg/kg) was observed to have a proconvulsive action with the addition of l-arginine (75mg/kg, i.p.). Our data demonstrate that enhancement of 5-HT(3) receptor function results in as anticonvulsant effect in the PTZ-induced seizure model, and that selective antagonism at the 5-HT(3) receptor yields proconvulsive effects. Furthermore, the NO system may play a role in 5-HT(3) receptor function.

The interaction of sildenafil with the anticonvulsant effect of diazepam

In order to assess the role of nitric oxide/cyclicGMP signaling pathway in the anticonvulsant effect of benzodiazepines, we studied the potential interaction of a phosphodiesterase type 5 inhibitor, sildenafil with the effect of diazepam on a mouse model of clonic seizures induced by intravenous infusion of GABA antagonist, pentylenetetrazole (PTZ). Administration of sildenafil (10 mg/kg; per se effective on seizure threshold) could abolish the anticonvulsive effect of diazepam, and a subeffective dose (5 mg/kg), when added to NO precursor L-arginine (50 mg/kg) could cause the same effect. Conversely, subeffective doses of diazepam (0.02 mg/kg) and NO synthase inhibitor N(omega)-nitro-L-arginine methyl ester (L-NAME, 5 mg/kg), administered together, reversed the proconvulsive effect of sildenafil. Our findings indicate that the enhancement of NO/cGMP signaling pathway by sildenafil attenuates the anticonvulsant effect of the benzodiazepine prototype, diazepam. This suggests that the effects of facilitating GABA(A)-mediated inhibition and modulating NO pathways are additive and there might be a role for NO pathway in benzodiazepine effect against PTZ-induced seizures in mice.

Role of nitric oxide in the anticonvulsive effect of progesterone

Described here is an investigation of the potential interaction of the nitric oxide signaling pathway with the anticonvulsant effects of progesterone. In ovariectomized Swiss mice, the threshold for seizures induced by intravenous infusion of pentylenetetrazole was determined after treatment with progesterone (25, 50, or 75 mg/kg, given subcutaneously 6h before seizure testing) or vehicle. Progesterone induced significant anticonvulsive activity at moderate (50 mg/kg) and high (75 mg/kg) doses. This effect of progesterone was abolished by the NO precursor compound L-arginine (200 mg/kg). Moreover, when subeffective doses of progesterone (25 mg/kg) and the NO synthase inhibitor N(omega)-nitro-L-arginine methyl ester (10 mg/kg) were injected, a strong anticonvulsant effect was observed. These findings suggest a potential role for NO signaling as an anticonvulsant target in females.

Melatonin enhances the anticonvulsant and proconvulsant effects of morphine in mice: Role for nitric oxide signaling pathway

Melatonin has different interactions with opioids including enhancing their analgesic effect and reversal of opioid tolerance and dependence. Opioids are known to exert dose-dependent anti- and proconvulsant effects in different experimental seizure paradigms. This study investigated the effect of melatonin on biphasic modulation of seizure susceptibility by morphine, in mouse model of pentylenetetrazole (PTZ)-induced clonic seizures. We further investigated the involvement of the nitric oxidergic pathway in this interaction, using a nitric oxide synthase inhibitor, NG-nitro-L-arginine-methyl-ester (L-NAME). Melatonin exerted anticonvulsant effect with doses as high as 40-80 mg/kg, but with a dose far bellow that amount (10 mg/kg), it potentiated both the anticonvulsant and proconvulsant effects of morphine on the PTZ-induced clonic seizures. Possible pharmacokinetic interaction of melatonin and morphine cannot be ruled out in the enhancement of two opposing effects of morphine on seizure threshold. L-NAME (1 mg/kg) reversed the anticonvulsant property of the combination of melatonin (10 mg/kg) plus morphine (0.5 mg/kg). Moreover, L-NAME (5 mg/kg) blocked the enhancing effect of melatonin (10 mg/kg) on proconvulsant activity of morphine (60 mg/kg). Our results indicate that co-administration of melatonin enhances both anti- and proconvulsant effects of morphine via a mechanism that may involve the nitric oxidergic pathway.

The involvement of nitric oxide in the anticonvulsant effects of α-tocopherol on penicillin-induced epileptiform activity in rats

A variety of animal seizure models exist which help to document the effects of alpha-tocopherol (Vitamin E) and specify its action. In the present study, we provide further evidence for the functional involvement of NO in the anticonvulsant effects of alpha-tocopherol on penicillin-induced epileptiform electrocorticographical (ECoG) activity in rats. The epileptiform ECoG activity was induced by microinjection of penicillin into the left sensorimotor cortex. Thirty minutes after penicillin injection, the most effective dose of alpha-tocopherol (500 mg/kg) was administrated intramuscularly (i.m.). Alpha-tocopherol decreased the frequency of penicillin-induced epileptiform ECoG activity without changing the amplitude. The effect of systemic administration of nitric oxide synthase (NOS) inhibitor, NG-nitro-L-arginine methyl ester (L-NAME) and NO substrates, L-arginine and sodium nitro prusside (SNP) on anticonvulsive effects of alpha-tocopherol was investigated. The administration of L-NAME (60 mg/kg, i.p.) did not influence the frequency of epileptiform ECoG activity while administration of L-arginine (500 mg/kg, i.p.) and SNP (6 mg/kg, i.p.) significantly decreased in the penicillin-treated group. The administration of L-NAME (60 mg/kg, i.p.) 10 min after alpha-tocopherol (500 mg/kg, i.m.) application reversed the anticonvulsant effects of alpha-tocopherol. The administration of L-arginine (500 mg/kg, i.p.) and SNP (6 mg/kg, i.p.) did not affect the frequency of epileptiform ECoG activity in alpha-tocopherol supplemented group. L-arginine and SNP did not provide an additional anticonvulsant effect in alpha-tocopherol supplemented group. These results support the involvement of the nitric oxide pathway in the anticonvulsant effect of alpha-tocopherol on the penicillin-induced epileptiform ECoG activity.

The proconvulsant effect of sildenafil in mice: role of nitric oxide-cGMP pathway

Recent evidence indicates that sildenafil may exert some central effects through enhancement of nitric oxide (NO)-mediated effects. NO is known to have modulatory effects on seizure threshold, raising the possibility that sildenafil may alter seizure susceptibility through NO-mediated mechanisms. This study was performed to examine whether sildenafil influences the threshold of clonic and/or generalized tonic seizures through modulation of nitric oxide (NO)-cGMP pathway. The effect of sildenafil (1-40 mg kg(-1)) was investigated on clonic seizures induced by intravenous administration of GABA antagonists pentylenetetrazole (PTZ) and bicuculine and on generalized tonic seizures induced by intraperitoneal administration of high dose PTZ in male Swiss mice. The interaction of sildenafil-induced effects with NO-cGMP pathway was examined using nitric oxide synthase (NOS) inhibitor, N(G)-nitro-L-arginine methyl ester (L-NAME), NOS substrate L-arginine, NO donor, sodium nitroprusside (SNP) and guanylyl cyclase inhibitor methylene blue (MB). Sildenafil induced a dose-dependent proconvulsant effect in both models of clonic, but not generalized tonic type of seizures. Pretreatment with either MB or L-NAME inhibited the proconvulsant effect of sildenafil, indicating the mediation of this effect by NO-cGMP pathway. In addition, a subeffective dose of sildenafil induced an additive proconvulsant effect when combined with either L-arginine or SNP. Sildenafil induces a proconvulsant effect on clonic seizure threshold that interacts with both exogenously and endogenously released NO and may be linked to activation of NO-cGMP pathway.

Amino acid levels in some brain areas of inducible nitric oxide synthase knock out mouse (iNOS−/−) before and after pentylenetetrazole kindling

Inducible nitric oxide synthase knock-out (iNOS(-/-)) mice are valid models of investigation for the role of iNOS in patho-physiological conditions. There are no available data concerning neuroactive amino acid levels of iNOS(-/-) mice and their behaviour in response to pentylenetetrazole (PTZ). We found no significant differences in the convulsive dose 50 (CD(50)) between iNOS(-/-) and control (iNOS(+/+)) mice, however, iNOS(-/-) mice reach the kindled status more slowly than control, suggesting that in basal condition the GABA-benzodiazepine inhibitory inputs are unaltered by iNOS mutation. Clear differences between iNOS(+/+) and iNOS(-/-) mice amino acid concentrations were evident both in basal conditions and after kindling. Our results show that aspartate was significantly lower in all brain areas studied except the brain stem whereas glutamate and glutamine were significantly higher in the cortex, hippocampus and brain stem. GABA was slightly and not significantly higher in the cortex, hippocampus and brain stem, whereas taurine was significantly higher in all areas except diencephalon and glycine was significantly lower in the diencephalon and cerebellum. In this context, the inability of iNOS(-/-) mice to increase the NO levels following PTZ administrations indicate that NO might play a pro-epileptogenic role in the genesis and development of some types of epilepsy. Since there is no correlation between neurotransmitter levels and the development of kindling, it is possible to exclude that the difference between the two strains is due to an imbalance between the considered neurotransmitters, and it is then possible that this difference is due to the presence of iNOS, which might be involved in long term plasticity of the brain.

Involvement of nitric oxide pathway in the acute anticonvulsant effect of melatonin in mice

Melatonin, the major hormone produced by the pineal gland, is shown to have anticonvulsant effects. Nitric oxide (NO) is a known mediator in seizure susceptibility modulation. In the present study, the involvement of NO pathway in the anticonvulsant effect of melatonin in pentylenetetrazole (PTZ)-induced clonic seizures was investigated in mice. Acute intraperitoneal administration of melatonin (40 and 80 mg/kg) significantly increased the clonic seizure threshold induced by intravenous administration of PTZ. This effect was observed as soon as 1 min after injection and lasted for 30 min with a peak effect at 3 min after melatonin administration. Combination of per se non-effective doses of melatonin (10 and 20 mg/kg) and nitric oxide synthase (NOS) substrate L-arginine (30, 60 mg/kg) showed a significant anticonvulsant activity. This effect was reversed by NOS inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME, 30 mg/kg), implying an NO-dependent mechanism for melatonin effect. Pretreatment with L-NAME (30 mg/kg) and N(G)-nitro-L-arginine (L-NNA, 10 mg/kg) inhibited the anticonvulsant property of melatonin (40 and 80 mg/kg) and melatonin 40 mg/kg, respectively. Specific inducible NOS (iNOS) inhibitor aminoguanidine (100 and 300 mg/kg) did not affect the anticonvulsant effect of melatonin, excluding the role of iNOS in this phenomenon, while pretreatment of with 7-NI (50 mg/kg), a preferential neuronal NOS inhibitor, reversed this effect. The present data show an anticonvulsant effect for melatonin in i.v. PTZ seizure paradigm, which may be mediated via NO/L-arginine pathway by constitutively expressed NOS.

Defective lysosomal arginine transport in juvenile Batten disease

Mutations in the CLN3 gene, which encodes a lysosomal membrane protein, are responsible for the neurodegenerative disorder juvenile Batten disease. A previous study on the yeast homolog to CLN3, designated Btn1p, revealed a potential role for CLN3 in the transport of arginine into the yeast vacuole, the equivalent organelle to the mammalian lysosome. Lysosomes isolated from lymphoblast cell lines, established from individuals with juvenile Batten disease-bearing mutations in CLN3, but not age-matched controls, demonstrate defective transport of arginine. Furthermore, we show that there is a depletion of arginine in cells derived from individuals with juvenile Batten disease. We have, therefore, characterized lysosomal arginine transport in normal lysosomes and show that it is ATP-, v-ATPase- and cationic-dependent. This and previous studies have shown that both arginine and lysine are transported by the same transport system, designated system c. However, we report that lysosomes isolated from juvenile Batten disease lymphoblasts are only defective for arginine transport. These results suggest that the CLN3 defect in juvenile Batten disease may affect how intracellular levels of arginine are regulated or distributed throughout the cell. This assertion is supported by two other experimental approaches. First, an antibody to CLN3 can block lysosomal arginine transport and second, expression of CLN3 in JNCL cells using a lentiviral vector can restore lysosomal arginine transport. CLN3 may have a role in regulating intracellular levels of arginine possibly through control of the transport of this amino acid into lysosomes.

Lithium inhibits the modulatory effects of morphine on susceptibility to pentylenetetrazole-induced clonic seizure in mice: involvement of a nitric oxide pathway

Lithium has been reported to inhibit opioid-induced properties. The present study examined the effect of acute and chronic administration of lithium chloride (LiCl) on morphine's biphasic modulation of susceptibility to pentylenetetrazole (PTZ)-induced clonic seizure in mice. We also examined the possible involvement of nitric oxide (NO) pathway in lithium effect. Both acute (0.1 and 1 mg/kg) and chronic (same doses, 21 consecutive days) administration of LiCl completely inhibited the anticonvulsant and proconvulsant effects of morphine (at doses 1 and 30 mg/kg, respectively). A very low and per se noneffective dose of LiCl (0.05 mg/kg) significantly inhibited both phases of morphine effect when administered concomitant with a noneffective low dose of naloxone (0.1 mg/kg). The NO synthase inhibitor N(G)-nitro-l-arginine methyl ester (L-NAME) at a per se noneffective dose of 0.3 mg/kg potentiated the inhibitory effects of low doses of LiCl (0.01 and 0.05 mg/kg) on both phases of morphine effect. l-arginine, a NO synthase substrate, at a per se noneffective dose of 30 mg/kg reversed the inhibitory effects of lithium (1 mg/kg). Lithium is capable of antagonizing both modulatory effects of morphine on seizure susceptibility even at relatively low doses. These inhibitory effects of lithium may also involve NO synthesis.

Hypothermia during kainic acid-induced seizures reduces hippocampal lesions and cerebral nitric oxide production in immature rabbits

We investigated (1) whether cerebral hypothermia during kainic acid (KA)-induced seizures was neuroprotective; and (2) whether nitric oxide (NO) production in the brain during seizures was altered by cerebral hypothermia in immature rabbits. Twelve female rabbits, aged 2 weeks, were anesthetized, paralyzed and mechanically ventilated. We continuously measured NO production in the brain by NO-selective electrode, cortical electroencephalogram (EEG), regional cerebral blood flow (rCBF) by laser Doppler flowmetry, rectal and cerebral temperatures and mean arterial blood pressure (MABP) during KA (12 mg/kg, i.v.)-induced seizures in the hypothermic group (n = 6; rectal temperature, 33 degrees C), and in the normothermic group (n = 6; rectal temperature, 37 degrees C). The normothermic group showed a gradual increase in NO generation in the brain, which was significantly inhibited in the hypothermic group. There were no significant differences in the increases in rCBF, MABP, arterial blood gases, blood glucose, or EEG abnormalities between the two groups. Neuronal damages in the hippocampus (CA3) were significantly lower in hypothermia than in normothermia. These results suggest that hypothermia attenuates NO production during drug-induced seizures and decreases hippocampal brain lesions in the immature rabbit brain. These results may help to explain the neuroprotective effects of hypothermia.

Endogenous heme oxygenase prevents impairment of cerebral vascular functions caused by seizures

In newborn pigs, the mechanism of seizure-induced cerebral hyperemia involves carbon monoxide (CO), the vasodilator product of heme catabolism by heme oxygenase (HO). We hypothesized that seizures cause cerebral vascular dysfunction when HO activity is inhibited. With the use of cranial window techniques, we examined cerebral vascular responses to endothelium-dependent (hypercapnia and bradykinin) and endothelium-independent (isoproterenol and sodium nitroprusside) dilators during the recovery from bicuculline-induced seizures in saline controls and in animals pretreated with a HO inhibitor, tin protoporphyrin (SnPP). SnPP (3 mg/kg iv) blocked dilation to heme and reduced the CO level in cortical periarachnoid cerebrospinal fluid, indicating HO inhibition in the cerebral microcirculation. In saline control piglets, seizures increased the CO level, which correlated with the time-dependent cerebral vasodilation; during the recovery (2 h after seizure induction), responses to all vasodilators were preserved. In SnPP-treated animals, cerebral vasodilation and the CO responses to seizures were greatly reduced, and cerebral vascular reactivity was severely impaired during the recovery. These findings suggest that HO in the cerebral microcirculation is rapidly activated during seizures and provides endogenous protection against seizure-induced vascular injury.

Anticonvulsant effects of cyclosporin A on pentylenetetrazole-induced seizure and kindling: modulation by nitricoxidergic system

Cyclosporin A (CsA) is known to decrease nitric oxide (NO) release in the nervous system. The present study was aimed at investigating the effects of acute administration of CsA on pentylenetetrazole (PTZ)-induced seizure threshold and latency and probable modulation of these effects by NO synthesis substrate L-arginine, and NO synthesis inhibitors N(G)-nitro-L-arginine methyl ester (L-NAME) or aminoguanidine. Moreover, the effect of CsA per se or concomitant with L-arginine on the development of PTZ-induced kindling was assessed. CsA (0.05, 1, 5, 10 and 20 mg/kg, s.c.) dose-dependently increased PTZ-induced clonic seizure threshold and the latency for onset of myoclonic jerks, clonic seizures and clonic-tonic generalized seizures following PTZ administration. L-NAME (10 and 30 mg/kg, i.p.) but not aminoguanidine (50 and 100 mg/kg, i.p.) potentiated the anticonvulsant effects of CsA (1 and 10 mg/kg). L-arginine (60, 100 and 200 mg/kg, i.p.) inhibited the anticonvulsant effects of CsA (20 mg/kg) in a dose-related manner. The inhibitory effect of L-arginine on CsA-induced alterations of seizure threshold and latency was blocked by L-NAME but not with aminoguanidine. CsA (20 mg/kg) significantly inhibited the development of PTZ kindling and decreased the seizure intensity as tested by a challenge dose of PTZ. Pretreatment with L-arginine (60 mg/kg) reversed the inhibitory effects of CsA on kindling development. It was concluded that CsA exerts some anticonvulsant properties that may be due to its inhibition of nitric oxide synthesis.

The role of nitric oxide in anticonvulsant and proconvulsant effects of morphine in mice

Acute subcutaneous administration of lower doses of morphine (0.5, 1 and 3 mg/kg) increase the threshold of seizures induced by pentylenetetrazole (PTZ) in mice, whereas higher doses of morphine (15, 30 and 60 mg/kg) have proconvulsant effects. The effect of systemic administration of nitric oxide synthase (NOS) inhibitors N(G)-nitro-L-arginine methyl ester (L-NAME) and N(G)-nitro-L-arginine (L-NNA) and nitric oxide synthase (NOS) L-arginine on biphasic effect of morphine was investigated. Acute administration of both L-NAME (1, 3 and 10 mg/kg) and L-NNA (1 and 10 mg/kg) as well as chronic pretreatment with L-NAME (1 and 10 mg/kg, 4 days) dose-dependently inhibited both the anticonvulsant and proconvulsant effects of morphine (1 and 30 mg/kg, respectively). The inhibition was complete for anticonvulsant effect while partial for proconvulsant effect. L-arginine at doses that did not affect seizure threshold per se (acute, 30 and 60 mg/kg; chronic, 60 mg/kg) potentiated both anticonvulsant and proconvulsant properties of less potent doses of morphine (0.5 and 15 mg/kg, respectively). The L-arginine induced potentiation of both phases of morphine effect was blocked by L-NAME (0.5-30 mg/kg). Moreover, low and per se non-effective doses of naloxone (0.1 mg/kg) and L-NAME (0.3, 0.5 or 1 mg/kg) showed additive effects in inhibiting both phases of morphine effects. These results support the involvement of L-arginine/nitric oxide pathway in the modulation of seizure threshold by morphine.

Different effects between 7-nitroindazole and L-NAME on cerebral hemodynamics and hippocampal lesions during kainic acid-induced seizures in newborn rabbits

We examined the effects of 7-nitroindazole (7-NI) and N-omega-nitro-L-arginine methyl ester (L-NAME) on the endogenous nitric oxide (NO) production in vivo, cerebral hemodynamics, and hippocampal lesions to investigate the different roles between endothelial NOS (eNOS) and neuronal NOS (nNOS) during kainic acid (KA)-induced seizures in newborn rabbits. After a pre-treatment with 7-NI (50 mg/kg, i.p.), L-NAME (20 mg/kg, i.v.) or saline (1 ml, i.v.), KA (12 mg/kg, i.v.) was administered. NO production in the brain, regional cerebral blood flow (rCBF), cerebral oxygenation (concentrations of oxyhemoglobin (HbO2), deoxyhemoglobin (HbR), and total hemoglobin (tHb) in the brain tissue), and electroencephalography (EEG) were continuously monitored throughout the experiment lasting at least 60 min after the KA administration. There was a significant increase in NO generation in the brain during KA-induced seizures, which was inhibited by a pre-treatment with 7-NI or L-NAME. KA-induced seizures also increased rCBF significantly, which was inhibited not by 7-NI but by L-NAME. L-NAME pre-treatment caused a significant decrease in HbO2 and a significant increase in HbR during KA-induced seizures, compared with 7-NI and saline pre-treatment. EEG abnormalities and Neuronal damages in the hippocampus were significantly lower in 7-NI- and L-NAME-treated animals respectively, than in saline-treated animals. The present data demonstrated that the selective nNOS inhibitor, 7-NI, attenuated neither rCBF nor cerebral oxygenation during the seizures, while the non-selective NOS (nNOS and eNOS) inhibitor, L-NAME, attenuated both. These findings suggest that NO, probably originating from eNOS, may play an important role in the cerebral circulation. Both 7-NI and L-NAME inhibited the NO production and EEG abnormalities during the seizures that led to less damage to the hippocampus.

Nitric oxide metabolites, nitrates and nitrites in the cerebrospinal fluid in children with west syndrome

Nitric oxide (NO) has been implicated in the mediation of the neuronal excitotoxic cascade. In order to estimate brain NO production, cerebrospinal fluid (CSF) levels of NO metabolites, nitrates and nitrites (NN(x)) were measured in 31 children with west syndrome (WS) and in 12 controls. There was no age-related change in the NN(x) levels during the first year of life. The mean of the NN(x) levels was significantly higher in patients with WS than in controls (8.43 vs. 5.27 microM; P=0.01). Analysis of the etiological subgroups showed that the patients with a symptomatic etiology of WS had significantly higher NN(x) levels than controls (P<0.005) or than the patients with a cryptogenic etiology. The cryptogenic cases, in turn, did not differ from the controls (P=0.48). Levels of NN(x) were also significantly higher in children with focal brain abnormalities (infarction, atrophy or previous infection) than in those with other abnormalities or with normal neuroradiological findings (P<0.005). No correlation was found between the NN(x) levels and the duration of the symptoms, while paired samples obtained from eight children with WS showed that the NN(x) levels rose significantly (P=0.02) within the first 40 days of symptoms. The levels of NN(x) did not correlate with the CSF levels of neuronal growth factor or with the later decline in mental performance. This study demonstrates that the production of NO can be measured in human epileptic conditions and supports the idea gained from experimental studies that NO is involved in the pathophysiology of epilepsy. However, normal levels of NN(x) in patients with cryptogenic infantile spasms suggest that an increase in NO production be due to the concomitant neuronal damage rather than seizure activity per se. The findings suggest that there are no age-related changes in the NN(x) levels during the first year of life, and that children with symptomatic WS have elevated levels of NN(x), which rise during the first 40 days of symptoms. Although the NN(x) levels cannot be used to estimate the duration of symptoms or to predict the prognosis of mental development, they may support the differentiation of symptomatic from cryptogenic etiologies of WS.

Changes in nitric oxide synthesis and epileptic activity in the contralateral hippocampus of rats following intrahippocampal kainate injection

PURPOSE

To investigate the effects of nitric oxide (NO) on seizure activity observed in brain areas that are remote from a primary epileptic focus.

METHODS

Following an injection of kainate (concentration 1 mg/ml, volume 1 microl) in the rat hippocampus, we measured NO synthesis in the contralateral hippocampus and epileptic activity by electroencephalogram (EEG). The NO end products, nitrite and nitrate, were measured by in vivo microdialysis combined with an automated NO end-product analyzer and then used as indices of NO synthesis. We also assessed the effect of a specific inhibitor of neuronal NO synthase (NOS) on both the epileptic activity and NO synthesis in the contralateral hippocampus. For this assessment, we administered 7-nitroindazole (7-NI) (50 mg/kg) intraperitoneally 30 min before the kainate injection.

RESULTS

Epileptic discharges in the contralateral hippocampus were frequently observed 90 min after unilateral hippocampus kainate injection. The duration of these discharges gradually increased until 240 min after the kainate injection. The NO end-product levels increased immediately after kainate injection and continued to increase gradually throughout the experiments, to a maximum of 213% of the base level. This elevation of NO end products was followed by epileptic discharges. Both the seizure activity and the elevation of contralateral hippocampus NO end-product levels were markedly attenuated in the animals that received 7-NI.

CONCLUSIONS

The results suggest that remote seizure activity caused by the transneuronal spread of kainate-induced discharges may be related to NO derived from neuronal NOS.

Nitric oxide modulation affects the tissue distribution and toxicity of bupivacaine

We have previously demonstrated that inhibition of nitric oxide synthase (NOS) alters the toxicity of local anesthetics including bupivacaine. Because significant changes in blood distribution are associated with the use of nonselective NOS inhibitors, the purpose of this study was to determine whether modification of bupivacaine toxicity by nonselective NOS inhibition is due to alteration in tissue disposition of bupivacaine. Rats were anesthetized with halothane and pretreated with either: 1) a nonselective NOS inhibitor, N(omega)-nitro-L-arginine methyl ester (L-NAME, 2 mg/kg/min, IV for 30 min); 2) a neuronal NOS inhibitor, 7-nitroindazole (7-NI, 30 mg/kg, IP); or 3) vehicle (control). Thirty minutes later, bupivacaine 2 mg/kg/min IV was infused until onset of seizures, arrhythmias, or asystole. L-NAME caused a rapid increase in plasma bupivacaine concentrations (3-4 times faster than in the other groups), which was associated with markedly lower bupivacaine doses (mg/kg) required to produce arrhythmias in L-NAME (4.2 +/- 0.5) vs. control (26 +/- 3, p < 0.01) and 7-NI groups (17 +/- 3, p < 0.01). Myocardial bupivacaine concentrations at arrhythmia onset were slightly lower in the L-NAME group. Bupivacaine seizure doses in 7-NI and L-NAME pretreated animals were similar to control but significantly different from each other. Brain bupivacaine concentrations at seizure onset were similar among the groups. There were no significant differences between 7-NI and control groups in any parameter observed. We conclude that enhanced cardiotoxicity of bupivacaine by nonselective NOS inhibition is primarily due to rapid increases in plasma and myocardial distribution of bupivacaine.

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.

Effects of nitric oxide synthase inhibition on the cerebral circulation and brain damage during kainic acid-induced seizures in newborn rabbits

The nitric oxide (NO) synthase inhibitor, N-omega-nitro-L-arginine methyl ester (L-NAME), was used to investigate the effect of endogenous NO on the cerebral circulation and brain damage during kainic acid (KA)-induced seizures in newborn rabbits. The cerebral blood flow (CBF), by laser doppler flowmetry, cerebral oxygenation (concentrations of oxy-(HbO2), deoxy-(HbR) and total hemoglobin (tHb) in brain tissue), by near-infrared spectroscopy (NIRS), mean arterial blood pressure (MABP), electroencephalography (EEG), and hippocampal neuronal damage were evaluated. Pretreatment with L-NAME caused significant decreases in CBF, HbO2, and tHb, and a significant increase in HbR during KA-induced seizures, compared with pretreatment with saline (P < 0.05), without a significant difference in MABP. Our study also demonstrated that pretreatment with L-NAME reduced the seizure activity and neuronal cell death in the hippocampus elicited by the systemic administration of KA in the neonatal brain. These results suggest that NO is of major importance in the neurodestructive process in spite of its roles in maintaining both the CBF and cerebral oxygenation during KA-induced seizures in the neonatal brain.

Changes in NADPH-diaphorase positivity induced by status epilepticus in allocortical structures of the immature rat brain

The distribution and time course of changes of nicotinamide adenine dinucleotide phosphate diaphorase (NADPH-d) positivity were studied in immature rats (12 and 25 days old) surviving motor status epilepticus (SE) induced by a high dose of pilocarpine. Motor SE characterized by continuous convulsions was interrupted after 2 h by an injection of clonazepam (0.5 mg/kg or 1 mg/kg in 12- and 25-day-old rats, respectively) in order to reduce mortality. Correlation between electroencephalographic and behavioral seizure activity was confirmed using animals with electrodes implanted bilaterally in the hippocampus and sensorimotor cortex. Brains were examined 2, 6, 13, and 21 days after motor SE using NADPH-diaphorase histochemistry. Two types of changes were found in both age groups: (a) decrease of NADPH-d positivity occurred in both neuropil and cell bodies in piriform, periamygdalar, and entorhinal cortices; and (b) NADPH-d positivity was induced in the cell bodies in the hippocampal fields CA1/2, CA3, and dentate gyrus. These changes were more intense in animals surviving SE at postnatal day 25 than in younger age group, and they peaked 2 days after SE. The changes observed after SE disappeared quickly in 12-day-old rat pups, where only moderate changes could be observed in piriform, periamygdalar, and entorhinal cortices 6 days after SE, whereas the changes in the histochemical positivity persisted in older animals even 21 days after SE.

Kainic acid may enhance hippocampal NO generation of awake rats in a seizure stage-related fashion

Temporal changes in kainate-induced seizure activity and hippocampal NO generation were evaluated simultaneously in conscious rats by using in vivo microdialysis and by determining the concentrations of nitrite and nitrate in perfusates. Intraperitoneal injection of kainic acid produced 'wet dog shake', focal seizure of the limbs and neck, hypersalivation, or generalized convulsion. These behavioral changes peaked at 120 min after the drug challenge and lasted for about 100 min. In contrast, the concentrations of NO metabolites, nitrite and nitrate, in the hippocampal perfusates increased rapidly and reached a plateau level at 40 min after the injection, and the level remained high for over 220 min. The increase was more marked in animals presenting severe seizures than those presenting mild ones. Pre-treatment with 25 mg/kg N(G)-nitro-L-arginine methyl ester promoted the severity of kainate-induced seizures, but it suppressed the increase in NO metabolites. These results suggest that kainic acid enhances hippocampal NO generation in a severity-related manner of the induced seizures. The enhanced NO generation upon kainate challenge appears mainly to be involved in seizure suppression.