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.     

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.     

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.     

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.     

Constipation enhances the propensity to seizure in pentylenetetrazole-induced seizure models of mice

Epilepsy is characterized by spontaneous recurrent seizures and represents one of the most frequent neurological diseases, affecting about 60 million people worldwide. The cellular and neurocircuit bases of epilepsy are poorly understood. Constipation is a common gastrointestinal disorder characterized by symptoms such as straining, hard stool, and infrequent defecation. Population-based studies have shown that the prevalence of constipation is up to 30% of the population in developed countries. The causal link between seizure and constipation is a common belief among patients and physicians, but there are no scientific data to support this association. The current investigation evaluated the effects of constipation induced by loperamide (a peripheral μ-opioid receptor agonist without effect on central nervous system receptors) and clidinium (a quaternary amine antimuscarinic agent with reduced central nervous system effects) on two different seizure models of mice: (1) myoclonic, clonic, and generalized tonic seizures and death induced by intraperitoneal administration of pentylenetetrazole and (2) clonic seizure threshold induced by intravenous infusion of pentylenetetrazole. We demonstrated that the measured intestinal transit (%intestinal transit) decreased after loperamide or clidinium treatment for 3 days. Constipation in mice which was induced by loperamide or clonidine caused a decrease in threshold to clonic seizure in the intravenous pentylenetetrazole seizure model. Moreover loperamide- or clidinium-induced constipation decreased latencies to, clonic, and tonic seizures and death in the intraperitoneal pentylenetetrazole model of mice. Serum ammonia levels were slightly elevated in both loperamide- and clidinium-treated mice. In conclusion, loperamide- or clidinium-induced constipated mice are more prone to seizure which might confirm the belief of patients and physicians about constipation as a trigger of seizure.     

The interaction between morphine and propranolol in chemical and electrical seizure models of mice

Objectives: Morphine and propranolol have different effects on seizure. Several studies have shown interaction between adrenergic and opioid systems in different models. In this study, interaction between morphine and propranolol in different seizure models was examined in mice.

Methods: In this study, three seizure models, including intravenous pentylenetetrazole (PTZ), intraperitoneal PTZ and electroshock, were examined in mice. Animals were injected with different doses of morphine or propranolol in the 60th and 45th min, before seizure induction, respectively.

Results: Acute administration of propranolol or lower doses of morphine induced an anticonvulsant effect in intravenous PTZ, intraperitoneal PTZ and electroshock-induced seizure models; on the contrary, higher doses of morphine exert proconvulsant effects in all three models. Also additive anticonvulsant effect of propranolol and lower doses of morphine was observed in all examined models. The additive anti-seizure effect of propranolol and lower doses of morphine was blocked by naltrexone in intraperitoneal PTZ model. Moreover, the anticonvulsant effect of propranolol was inhibited by naltrexone in intraperitoneal PTZ seizure model of mice. Propranolol restrained the proconvulsant effects in higher doses of morphine in clonic seizures of intravenous and intraperitoneal PTZ models.

Discussion: In conclusion, we believe that this is the first study that has indicated the interaction of propranolol and lower doses of morphine in the anticonvulsant effects in three seizure models of intravenous PTZ, intraperitoneal PTZ and electroshock. The involvement of μ-opioid receptor in this interaction was also demonstrated. Simultaneously, we showed the interaction between propranolol and higher doses of morphine in proconvulsant effects.     

The involvement of endogenous opioids and nitricoxidergic pathway in the anticonvulsant effects of foot-shock stress in mice

The involvement of endogenous opioids and nitric oxide (NO) in the anticonvulsant effects of stress against pentylenetetrazole (PTZ)- or electroconvulsive shock-induced seizures was assessed in mice. The prolonged and intermittent foot-shock stress, which induced opioid-mediated analgesia, had significant protective effects against both seizure types which was reversible by naloxone (0.3, 1 or 2 mg/kg), while brief and continuous foot-shock did not alter the seizure susceptibility. Pre-treatment with non-specific nitric oxide synthase (NOS) inhibitor, N(G)-nitro-L-arginine methyl ester (L-NAME, 1, 2, 5, 10 or 30 mg/kg), but not with specific inducible NOS (iNOS) inhibitor, aminoguanidine (50 or 100 mg/kg), blocked the stress-induced anticonvulsant effects. The lower doses of naloxone (0.3 mg/kg) and L-NAME (2 mg/kg) showed additive effects in blocking the stress-induced anticonvulsant properties. L-arginine at a per se non-effective dose of 20 mg/kg potentiated the stress-induced anticonvulsant properties, an effect which was inhibited by L-NAME but not by aminoguanidine. Furthermore, a low dose of morphine (0.5 mg/kg) showed potentiation with stress in increasing PTZ seizure threshold. This potentiation was reversed by either naloxone or L-NAME at low doses but not by aminoguanidine. Taken together, these results show that NO synthesis, through constitutive but not iNOS, is involved in opioid-dependent stress-induced anticonvulsant effects against electrical and PTZ-induced convulsions.     

Role of nitric oxide in pentylenetetrazol-induced seizures: age-dependent effects in the immature rat

PURPOSE: Seizure susceptibility and consequences are highly age dependent. To understand the pathophysiologic mechanisms involved in seizures and their consequences during development, we investigated the role of nitric oxide (NO) in severe pentylenetetrazol (PTZ)-induced seizures in immature rats. METHODS: Four cortical electrodes were implanted in 10-day-old (P10) and 21-day-old (P21) rats, and seizures were induced on the following day by repetitive injections of subconvulsive doses of PTZ. The effects of NG-nitro-l-arginine methyl ester (l-NAME; 10 mg/kg) and 7-nitroindazole (7NI; 40 mg/kg), two NO synthase (NOS) inhibitors, and l-arginine (l-arg; 300 mg/kg), the NOS substrate, were evaluated regarding the mean PTZ dose, seizure type and duration, and mortality rate. RESULTS: At P10, the postseizure mortality rate increased from 18-29% for the rats receiving PTZ only to 100% and 89% for the rats receiving l-NAME and 7NI, respectively; whereas l-arg had no effect. Conversely, at P21, NOS inhibitors did not affect the 82-89% mortality rate induced by PTZ alone, whereas l-arg decreased the mortality rate to 29%. In addition, all NO-related drugs increased the duration of ictal activity at P10, whereas at P21, l-arg and l-NAME affected the first seizure type, producing clonic seizures with l-arg and tonic seizures with l-NAME. CONCLUSIONS: The relative natural protection of very immature rats (P10) against PTZ-induced deaths could be linked to a high availability of l-arg and, hence, endogenous NO. At P21, the modulation of seizure type by NO-related compounds may be related to the maturation of the brain circuitry, in particular the forebrain, which is involved in the expression of clonic seizures.     

Possible involvement of PPAR-gamma receptor and nitric oxide pathway in the anticonvulsant effect of acute pioglitazone on pentylenetetrazole-induced seizures in mice

Besides the receptor-mediated effects of pioglitazone, the involvement of nitric oxide (NO) has been previously demonstrated in some pioglitazone-induced central and peripheral effects. In the present study, the effects of acutely administered pioglitazone on pentylenetetrazole (PTZ)-induced seizures and involvement of NO were evaluated in mice. To determine the threshold for clonic seizures, PTZ was administered intravenously. A single dose of pioglitazone (10, 20, 40 and 80 mg/kg, p.o.) was administered either 2 or 4h prior to induction of seizures. For determination of possible role of peroxisome proliferator activated receptor gamma (PPAR-γ) and nitric oxide pathway in this effect, the effects of a PPAR-γ antagonist, GW9662 (2 mg/kg); a non-specific nitric oxide synthase (NOS) inhibitor, NG-nitro-L-arginine methyl ester (L-NAME; 0.3, 1, 3, and 10 mg/kg); a specific iNOS inhibitor, aminoguanidine (100mg/kg, i.p.) or a nitric oxide precursor, L-arginine (30, 60, 100 and 200mg/kg, i.p.); each administered 15 min prior to pioglitazone, were investigated on the anticonvulsant effect of this drug. Administration of pioglitazone (40 and 80 mg/kg) increased the threshold of PTZ-induced seizure in a dose-dependent, and time-dependent manner. GW9662 reversed the anticonvulsant effect of pioglitazone (40 mg/kg). Acute administration of L-NAME (1, 3 and 10mg/kg) inhibited the anticonvulsant effect of pioglitazone (40 mg/kg), the same result was detected with aminoguanidine (100mg/kg); whereas L-arginine, in the noneffective dose (100mg/kg), potentiated the seizure threshold when co-administered with a subeffective dose of pioglitazone (20mg/kg). CONCLUSION: The present study demonstrates the anticonvulsant effect of acute pioglitazone on PTZ-induced seizures in mice. This effect was reversed by PPAR-γ antagonist, and both a specific- and a non-specific nitric oxide synthase inhibitors, and augmented by nitric oxide precursor, L-arginine. These results support that the anticonvulsant effect of pioglitazone is mediated through PPAR-γ receptor-mediated pathway and also, at least partly, through the nitric oxide pathway.     

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 (10–100 mg/kg) increased the seizure threshold. In addition, the nonselective NOS inhibitor L-NAME (10 mg/kg) and the neural NOS inhibitor, 7-nitroindazole (40 mg/kg), at doses that had no effect on seizure threshold, augmented the anticonvulsant effect of DM (3 mg/kg), while the inducible NOS inhibitor, aminoguanidine (100 mg/kg), did not affect the anticonvulsant effect of DM. Moreover, the NOS substrate l-arginine (60 mg/kg) blunted the anticonvulsant effect of DM (100 mg/kg). Also, NMDA antagonists, ketamine (0.5 mg/kg) and MK-801 (0.05 mg/kg), augmented the anticonvulsant effect of DM (3 mg/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.     

The effect of l-arginine and l-NAME on pentylenetetrazole induced seizures in ovariectomized rats,an in vivo study

The role of ovarian hormones and nitric oxide (NO) on seizure and their interaction have been widely investigated. The present study carried out to evaluate the effect of chronic administration of l-arginine (lA) and l-NAME (lN) on pentylenetetrazole (PTZ) induced epilepsy in ovariectomized (OVX) and naïve female rats.Fourty-eight female rats were randomly divided into six groups (n = 8) as follows: (1) sham, (2) ovarectomized (OVX), (3) sham-lA, (4) sham-lN, (5) OVX-lA, and (6) OVX-lN.The animals of sham-lA and OVX-lA received daily injection of 500 mg/kg l-arginine (i.p.) during 4 weeks. Sham-lN and OVX-lN were treated by 10 mg/kg l-NAME (i.p.) daily for 4 weeks. The animals of sham and OVX groups received 1 ml/kg saline (i.p.) instead of l-arginine and l-NAME. The latencies to minimal clonic seizures (MCS) and generalized tonic–clonic seizures (GTCS) after intraperitoneal injection of penetylenetetrazole (PTZ, 90 mg/kg) was recorded and compared between groups.A significant increase in the GTCS, but not MCS, latency was seen in OVX rats in comparison with sham-operated animals. Pretreatment of animals with l-NAME resulted in a significant increase in the GTCS and MCS latencies in sham group while no significant effects were seen in OVX rats. On the contrary, while pretreatment with l-arginine had no effects on MCS and GTCS latencies in sham group, a significant decrease in GTCS latency was observed in OVX rats.It is concluded that ovarian sex hormones affect seizure thresholds induced by PTZ and NO has a role on seizures susceptibility following PTZ administration. This NO effect might be differing in the presence or absence of ovarian hormones, but further investigations need to be done.     

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.     

l-NAME inhibits pentylenetetrazole and strychnine-induced seizures in mice

Nitric oxide (NO) formation has been shown in many neuronal tissues subserves a variety of functions. N-Methyl-d-aspartate (NMDA) receptor stimulation which releases nitric oxide and raises cGMP levels, mediates epileptiform activity induced by various agents. Disinhibition of inhibitory neurotransmitter γ-aminobutyric acid (GABA) and/or activation of NMDA receptor appears to be factors involved in the initiation and generalization of the pentylenetetrazole (PTZ) induced seizures. In the present study, we examined the effects of N^ω-nitro-l-arginine methylester (l-NAME) which inhibits nitric oxide synthase, on PTZ and strychnine induced seizures in mice. l-NAME (100 mg/kg) significantly prolonged the onset time of tonic generalized extension without affecting myoclonic jerks and tonic-clonic convulsions. l-NAME (200 mg/kg) significantly delayed three characteristic behavioral changes including first myoclonic jerk (FMJ), generalized clonic seizure (GCS) and tonic generalized extension (TGE). The effects of l-NAME were reversed by l-arginine (1000 mg/kg). l-NAME (100 and 200 mg/kg) significantly delayed the onset time of strychnine induced TGE. The effects of both doses of l-NAME were reversed by l-arginine. In conclusion, our results demonstrate that NO synthase inhibition suppresses the onset time of PTZ and strychnine induced seizures. Under the light of our current knowledge NO synthase inhibitors seem far away to be considered as a group of antiepileptic drugs. On the other hand there are some strong evidences about the role of NO in central pathophysiological mechanisms. © 1997 Elsevier Science B.V. All rights reserved.     

Nitric oxide mediates the anticonvulsant effects of thalidomide on pentylenetetrazole-induced clonic seizures in mice

Thalidomide is an old glutamic acid derivative which was initially used as a sedative medication but withdrawn from the market due to the high incidence of teratogenicity. Recently, it has reemerged because of its potential for counteracting number of diseases, including neurodegenerative disorders.Other than the antiemetic and hypnotic aspects, thalidomide exerts some anticonvulsant properties in experimental settings. However, the underlying mechanisms of thalidomide actions are not fully realized yet. Some investigations revealed that thalidomide could elicit immunomodulatory or neuromodulatory properties by affecting different targets, including cytokines (such as TNF α), neurotransmitters, and nitric oxide (NO). In this regard, we used a model of clonic seizure induced by pentylenetetrazole (PTZ) in male NMRI mice to investigate whether the anticonvulsant effect of thalidomide is affected through modulation of the l-arginine–nitric oxide pathway or not.Injection of a single effective dose of thalidomide (10 mg/kg, i.p. or higher) significantly increased the seizure threshold (P < 0.05). On the one hand, pretreatment with low and per se noneffective dose of l-arginine [NO precursor] (10, 30 and 60 mg/kg) prevented the anticonvulsant effect of thalidomide. On the other hand, NOS inhibitors [l-NAME and 7-NI] augmented the anticonvulsant effect of a subeffective dose of thalidomide (1 and 5 mg/kg, i.p.) at relatively low doses. Meanwhile, several doses of aminoguanidine [an inducible NOS inhibitor] (20, 50 and 100 mg/kg) failed to alter the anticonvulsant effect of thalidomide significantly. In summary, our findings demonstrated that the l-arginine–nitric oxide pathway can be involved in the anticonvulsant properties of thalidomide, and the role of constitutive nNOS is prominent in the reported neuroprotective feature.     

Avian brainstem neurogenesis is stimulated during cochlear hair cell regeneration

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.     

Morphine sensitization in the pentylenetetrazole-induced clonic seizure threshold in mice: role of nitric oxide and μ receptors

Behavioral sensitization occurs after repeated administration of μ-opioid receptor agonists following a drug-free period. It seems that the changes in dopaminergic systems induced by μ-opioid receptor agonists play a crucial role in behavioral sensitization to opioids. Nitric oxide also plays a role in some behavioral effects of morphine, including sensitization to the locomotor-stimulating effect. This study investigated whether morphine sensitization appears in seizure threshold and the possible role of μ-opioid receptor and nitric oxide in this sensitization. Sensitization was produced by daily injections of morphine (0.1, 0.5, 1, 5, 15, or 30 mg/kg), followed by a 10-day washout period. Then the challenge test was performed using morphine (0.1, 0.5, 1, 5, 15, or 30 mg/kg) in different groups. To assess clonic seizure threshold, pentylenetetrazole (PTZ) was administered intravenously. Subcutaneous administration of morphine (0.1 and 0.5 mg/kg) induced sensitization in PTZ-induced clonic seizures in mice. Intraperitoneal administration of L-NAME (20 mg/kg), a nonselective inhibitor of nitric oxide synthase, or naltrexone (10 mg/kg), an opioid receptor antagonist, along with morphine inhibited morphine-induced sensitization in PTZ-induced seizure threshold. In conclusion, at low doses, morphine induces sensitization in PTZ-induced clonic seizures in mice probably as a result of the interaction with μ-receptors and nitric oxide.     

Antiepileptic effects of inhibitors of nitric oxide synthase examined in pentylenetetrazol-induced seizures in rats

The effects of intraperitoneal and methyl ester, specific inhibitors of nitric oxide (NO) synthase, were examined on the pentylenetetrazol (PTZ)-induced seizures in rats. The incidence and latency for the onset of myoclonic jerks, clonic seizures, and tonic generalized extension were observed as specific parameters among PTZ-induced seizures. Both drugs preferentially suppressed the tonic generalized extension and prolonged the latency for the onset of each parameter, suggesting NO has a significant effect on the PTZ-induced seizure.     

Anticonvulsant effect of flutamide on seizures induced by pentylenetetrazole: involvement of benzodiazepine receptors

PURPOSE: There is some structural similarity between the androgen receptor antagonist, flutamide (Flut) and benzodiazepines (BZDs). We evaluated the possible anticonvulsant effect and interaction of Flut with BZD receptors in common seizure models. METHODS: (a) Different groups of mice each were pretreated i.p. with Flut, and after 0.5 h, they received chemoconvulsants [pentylenetetrazole (PTZ), bicuculline, aminophylline, strychnine or kainic acid]. Latency and incidence of a clonic seizure were recorded. (b) Mice were pretreated i.p. with Flut, and after 0.5 h, transauricular electroshock was applied. Occurrence of a tonic seizure was observed. (c) Amygdala-kindled rats were pretreated i.p. with Flut, and 0.5, 1, or 2 h later, they were stimulated at afterdischarge threshold. Then the seizure parameters (afterdischarge duration, seizure severity, and stage 5 duration) were recorded. (d) The effect of Flut on clonic seizure threshold was determined by i.v. infusion of bicuculline or PTZ to different groups of Flut-receiving mice. To determine the possible interaction of Flut with BZD receptors, the flumazenil (FMZ)+Flut effect on clonic seizure threshold was compared with the effect of Flut. (e) Neurotoxicity of Flut was evaluated by rotarod test at 30 min after administration. RESULTS: Flut produced a dose-dependent anticonvulsant effect against PTZ-induced seizures [median effective dose (ED50), 67.0 mg/kg]. Moreover, Flut elevated the clonic seizure threshold induced by bicuculline or PTZ. FMZ reversed the effect of Flut on the threshold of PTZ seizures. A median toxic dose (TD50) value of 124.8 mg/kg was obtained for Flut. CONCLUSIONS: Flut both blocks PTZ-induced clonic seizures and elevates the threshold of PTZ or bicuculline-induced clonic seizures, through interaction with BZD receptors.     

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.     

Involvement of the nitric oxide pathway in the anticonvulsant effect of tramadol on pentylenetetrazole-induced seizures in mice

In the present study, the effects of tramadol on pentylenetetrazole (PTZ)-induced seizures and involvement of nitric oxide (NO) were assessed in mice. To determine the threshold for clonic seizures, PTZ was administered intravenously. Tramadol was administered intraperitoneally (0.5-50mg/kg) 30 minutes prior to induction of seizures. The effects of the nitric oxide synthase (NOS) inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME; 0.5, 1, 5, and 10mg/kg), the nitric oxide precursor L-arginine (10, 30, and 60 mg/kg), and the nonspecific opioid receptor antagonist naloxone (0.1, 0.5, 1, and 5mg/kg) on the anticonvulsant effect of tramadol were investigated. Administration of tramadol (1mg/kg) increased the threshold for seizures induced with PTZ in a monophasic, dose-independent, and time-dependent manner. Acute administration of L-NAME (5 and 10mg/kg) inhibited the anticonvulsant effect of tramadol (1mg/kg), whereas L-arginine, in the noneffective dose range (30 and 60 mg/kg), potentiated the seizure threshold when co-administered with a subeffective dose of tramadol (0.5mg/kg). Naloxone partially and dose-independently antagonized the anticonvulsant effect of tramadol (1mg/kg). These results indicate that the anticonvulsant effect of tramadol is mediated by the nitric oxide pathway and also by classic opioid receptors.