Paradoxical facilitation of pilocarpine-induced seizures in the mouse by MK-801 and the nitric oxide synthesis inhibitor L-NAME

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.

N(Omega)-nitro-l-arginine methyl ester potentiates lidocaine analgesic and anaesthetic effect in rats

OBJECTIVES

The purpose of the experiment was to study the effect of L-NAME (N(Omega)-nitro-L-arginine methyl ester) and its cotreatment with lidocaine on the spinal block and infiltrative cutaneous analgesia.

METHODS

The quality of cutaneous analgesia was examined by the block of the cutaneous trunci muscle reflexes following needle stimuli in the rat. Spinal anaesthetic potency was assessed by measuring three neurobehavioral examinations of nociceptive, proprioceptive and motor function following intrathecal injection in the rat.

KEY FINDINGS

L-NAME (0.6, 6 and 60 nmol) when cotreatment with lidocaine (ED50) produced dose-related cutaneous analgesia. Coadministration of L-NAME (0.6 μmol) with lidocaine intensified (P < 0.01) and prolonged (P < 0.001) cutaneous analgesia, whereas subcutaneous L-NAME (0.6 μmol) and saline did not provoke cutaneous analgesic effects. Adding L-NAME (2.5 μmol) to lidocaine intrathecally prolonged spinal sensory and motor block (P < 0.01), while intrathecal L-NAME (2.5 μmol) or 5% dextrose (vehicle) produced no spinal block.

CONCLUSIONS

L-NAME at 60 nmol (the minimum effective dose) increases and prolongs the effect of cutaneous analgesia of lidocaine. L-NANE at an ineffective dose potentiates lidocaine analgesic and anaesthetic effects.

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.

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.

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

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

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

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.

PDI Knockdown Inhibits Seizure Activity in Acute Seizure and Chronic Epilepsy Rat Models via S-Nitrosylation-Independent Thiolation on NMDA Receptor

Redox modulation and S-nitrosylation of cysteine residues are the post-translational modifications of N-methyl-D-aspartate receptor (NMDAR) to regulate its functionality. Recently, we have reported that protein disulfide isomerase (PDI) reduces disulfide bond (S-S) to free thiol (-SH) on NMDAR. Since PDI is a modulator of S-nitrosylation on various proteins, it is noteworthy whether PDI affects S-nitrosylation of NMDAR in acute seizure and chronic epilepsy models. In the present study, we found that acute seizures in response to pilocarpine and spontaneous seizures in chronic epilepsy rats led to the reduction in S-nitrosylated thiol (SNO-thiol)-to-total thiol ratio on NMDAR, while they elevated nitric oxide (NO) level and S-nitrosylation on NMDAR. N-nitro-L-arginine methyl ester (L-NAME, a non-selective NOS inhibitor) did not affect seizure activities in both models, although it decreased SNO-thiol levels on NMDAR. However, PDI knockdown effectively inhibited pilocarpine-induced acute seizures and spontaneous seizures in chronic epilepsy rats, accompanied by increasing the SNO-thiol-to-total thiol ratio on NMDAR due to diminishing the amounts of total thiols on GluN1 and GluN2A. Therefore, these findings indicate that PDI may not be a NO donor or a denitrosylase for NMDAR, and that PDI knockdown may inhibit seizure activity by the S-nitrosylation-independent thiolation on NMDAR.

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.

Nitric oxide synthase inhibition reverts muscarinic receptor down-regulation induced by pilocarpine- and kainic acid-evoked seizures in rat fronto-parietal cortex

We investigated how nitric oxide (NO) synthase inhibitor modulates muscarinic receptor expression in epileptic rats. We found that subchronic treatment (4 days) with Nω-nitro-l-arginine reduced the down-regulation of muscarinic receptors induced by pilocarpine and kainic acid in rat fronto-parietal cortex, notwithstanding the dramatic potentiation of seizures induced by both convulsants. Furthermore, functional experiments in fronto-parietal cortex slices, showed that Nω-nitro-l-arginine reduces the down-regulating effect of pilocarpine on carbachol-induced phosphoinositol hydrolysis. Finally, Nω-nitro-l-arginine greatly potentiated the induction of basic fibroblast growth factor (FGF2) by pilocarpine. These data suggest a potential role of NO in a regulatory feedback loop to control muscarinic receptor signal during seizures. The dramatic potentiation of convulsions by NO synthase inhibitors in some animal models of seizures could derive from preventing this feedback loop.

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

ETHNOPHARMACOLOGICAL RELEVANCE

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

MATERIALS AND METHODS

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

RESULTS

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

CONCLUSION

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

5-HT(3) receptor mediates the dose-dependent effects of citalopram on pentylenetetrazole-induced clonic seizure in mice: involvement of nitric oxide

Citalopram is a selective serotonin reuptake inhibitor (SSRI), widely used in the treatment of depressive disorders. It has been shown that citalopram affects seizure susceptibility. Although the exact mechanism of these effects are not yet fully understood, recent data suggest that 5HT(3) receptors and nitric oxide (NO) might participate in the central effects of SSRIs. In this study in a mouse model of clonic seizure induced by pentylenetetrazole we investigated whether 5-HT(3) receptors are involved in the effects of citalopram on seizure threshold. In our experiments, citalopram at lower doses (0.5 and 1mg/kg, i.p) significantly increased the seizure threshold and at higher doses (≥25mg/kg) showed proconvulsive effects. Moreover, mCPBG (a 5-HT(3) receptor agonist) at low and non-effective doses augmented while non-effective doses of tropisetron prevented the anticonvulsive properties of citalopram. On the other hand, Low doses of nitric oxide synthase inhibitors l-NAME and 7-NI alone or in combination with lower doses of 5-HT(3) receptor agonist enhanced the anticonvulsive property of citalopram, while l-arginine (NO precursor) alone or in combination with tropisetron blocked the protective effect of citalopram. In summary, our findings demonstrate that 5-HT(3) receptor mediates the anticonvulsant properties of low doses of citalopram, whereas it seems that the proconvulsive effect is mostly mediated through the NO pathway and can be totally blocked by NOS inhibitors. This could propose a new approach toward finding the mechanism of citalopram activity, curtailing the adverse effects of citalopram and perhaps managing the convulsions as a vicious consequence of citalopram overdose.

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.

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.

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.

Kainic Acid-induced Neuronal Death is Attenuated by Aminoguanidine but Aggravated by L-NAME in Mouse Hippocampus

Nitric oxide (NO) has both neuroprotective and neurotoxic effects depending on its concentration and the experimental model. We tested the effects of NG-nitro-L-arginine methyl ester (L-NAME), a nonselective nitric oxide synthase (NOS) inhibitor, and aminoguanidine, a selective inducible NOS (iNOS) inhibitor, on kainic acid (KA)-induced seizures and hippocampal CA3 neuronal death. L-NAME (50 mg/kg, i.p.) and/or aminoguanidine (200 mg/kg, i.p.) were administered 1 h prior to the intracerebroventricular (i.c.v.) injection of KA. Pretreatment with L-NAME significantly increased KA-induced CA3 neuronal death, iNOS expression, and activation of microglia. However, pretreatment with aminoguanidine significantly suppressed both the KA-induced and L-NAME-aggravated hippocampal CA3 neuronal death with concomitant decreases in iNOS expression and microglial activation. The protective effect of aminoguanidine was maintained for up to 2 weeks. Furthermore, iNOS knockout mice (iNOS(-/-)) were resistant to KA-induced neuronal death. The present study demonstrates that aminoguanidine attenuates KA-induced neuronal death, whereas L-NAME aggravates neuronal death, in the CA3 region of the hippocampus, suggesting that NOS isoforms play different roles in KA-induced excitotoxicity.

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.

The pilocarpine model of temporal lobe epilepsy

Understanding the pathophysiogenesis of temporal lobe epilepsy (TLE) largely rests on the use of models of status epilepticus (SE), as in the case of the pilocarpine model. The main features of TLE are: (i) epileptic foci in the limbic system; (ii) an “initial precipitating injury”; (iii) the so-called “latent period”; and (iv) the presence of hippocampal sclerosis leading to reorganization of neuronal networks. Many of these characteristics can be reproduced in rodents by systemic injection of pilocarpine; in this animal model, SE is followed by a latent period and later by the appearance of spontaneous recurrent seizures (SRSs). These processes are, however, influenced by experimental conditions such as rodent species, strain, gender, age, doses and routes of pilocarpine administration, as well as combinations with other drugs administered before and/or after SE. In the attempt to limit these sources of variability, we evaluated the methodological procedures used by several investigators in the pilocarpine model; in particular, we have focused on the behavioural, electrophysiological and histopathological findings obtained with different protocols. We addressed the various experimental approaches published to date, by comparing mortality rates, onset of SRSs, neuronal damage, and network reorganization. Based on the evidence reviewed here, we propose that the pilocarpine model can be a valuable tool to investigate the mechanisms involved in TLE, and even more so when standardized to reduce mortality at the time of pilocarpine injection, differences in latent period duration, variability in the lesion extent, and SRS frequency.

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 lack of effects of zinc and nitric oxide in initial state of pilocarpine-induced seizures

In this study we investigated whether intracerebroventricular (i.c.v.) injection of L-NAME (a nitric oxide synthase inhibitor) or CaEDTA (an extracellular zinc chelator) or the combination of the two could affect the initial phase of pilocarpine induced (2 h) seizures. Two groups of rats were used. Animals from both groups were given with i.c.v. injections of either saline (10 microl), L-NAME (150 microg/10 microl), CaEDTA (100 mM/10 microl) or L-NAME and CaEDTA. One group received pilocarpine HCl (380 mg/kg i.p.) the other served as control. Pilocarpine HCl was injected intraperitoneally 10 min later. The behavior of the animals was observed for 2h and the intensity of their seizures was scored. The rats were then sacrificed and their brains were removed and analyzed for zinc ions by using the immersion autometallography and the TSQ fluorescence staining. All the animals which received pilocarpine HCl developed seizures. Despite treatment with L-NAME and/or CaEDTA we found that the latency and the intensity of seizures were similar in both groups investigated. The distribution of stainable zinc ions and the intensity of staining in hippocampus were not affected by pilocarpine and found unchanged after L-NAME and/or CaEDTA injections in both the control animals and the pilocarpine treated animals. The data suggest that the nitric oxide system and zinc ions do not affect pilocarpine-induced seizures in their initial state.

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.

Long-term l-NAME treatment potentiates the blood–brain barrier disruption during pentylenetetrazole-induced seizures in rats

We investigated whether the severity of blood-brain barrier disruption caused by pentylenetetrazole-induced seizures is modified by long-term nitric oxide synthase inhibition in rats. Rats were given N-omega-nitro-L-arginine methyl ester (L-NAME), a nitric oxide synthase inhibitor, in drinking water for 4 weeks, and then treated with pentylenetetrazole to induce seizures. Damage to the blood-brain barrier was investigated using Evans blue dye extravasation. Serum nitric oxide concentration was decreased in L-NAME-treated rats (P<0.01). L-NAME and/or pentylenetetrazole treatments elevated systolic blood pressure of animals (P<0.01). L-NAME caused an increase in the mortality rate after pentylenetetrazole injection leading to the death of animals at about 15 min after the onset of the seizure. Pentylenetetrazole-induced seizures in rats treated with L-NAME caused a significant increase in Evans blue dye extravasation into cerebral cortex, diencephalon and cerebellum, as compared with seizures evoked by pentylenetetrazole injection to L-NAME-untreated rats (P<0.01). Data presented here suggest that the degree of blood-brain barrier disruption induced by seizures is more pronounced in long-term nitric oxide deficiency.

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.

Increased nitric oxide caused by the ketogenic diet reduces the onset time of kainic acid-induced seizures in ICR mice

Although the antiepileptic effects of the ketogenic diet (KD) are well documented, the mechanisms underlying this action remain obscure. Nitric oxide (NO) has long been thought to play a role in regulating seizures. However, the effects of the KD on endogenous NO production have not been characterized. Therefore, the present study was designed to examine the effect of the KD on endogenous NO production, as well as the precise role of NO in kainic acid (KA)-induced seizures, in male ICR mice. We first found that preadministration of the KD for 4 weeks increased endogenous NO generation in the hippocampus. We also demonstrated that the increase in NO induced by the KD resulted from increased neuronal NO synthase (nNOS) activity and exerted an antiepileptic effect on KA-induced seizures, based on the results of experiments using NOS-knockout mice and two NOS inhibitors, N-omega-nitro-L-arginine methyl ester (L-NAME) and 7-nitroindazole (7-NI). These data suggest that the antiepileptic effects of the KD might be mediated, at least in part, by increased NO levels in the hippocampus.

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.

Involvement of NO in the convulsive behavior and oxidative damage induced by the intrastriatal injection of methylmalonate

Acute intrastriatal administration of methylmalonic acid (MMA) induces convulsions through NMDA receptor-mediated mechanisms and increases production of end products of oxidative damage. Although it has been demonstrated that nitric oxide (NO) production increases with NMDA receptor stimulation and contributes to the oxidative damage observed in several neurodegenerative disorders, the role of NO in MMA-induced convulsions has not been investigated to date. In the present study we investigated the effects of the intrastriatal injection of N(omega)-nitro-L-arginine methyl ester (L-NAME: 10(-4) to 10(0) nmol/0.5 microl) on the convulsions and striatal protein carbonylation induced by the intrastriatal injection of MMA (4.5 micromol/1.5 microl). l-NAME (10(-3) to 10(-1)nmol) protected against MMA-induced convulsions and protein carbonylation ex vivo. These results suggest the involvement of NO in the convulsive behavior and protein carbonylation elicited by MMA.

Lithium ion "cyclotron resonance" magnetic fields decrease seizure onset times in lithium-pilocarpine seized rats

The cyclotron resonance equation predicts that the frequency of an applied magnetic field that might optimally interact with a single ion species may be computed as a function of the charge-to-mass ratio of the ion and the strength of the background static magnetic field. The present study was undertaken to discern the applicability of this equation for optimizing lithium ion utilization in the rat, as inferred by the predicted magnetic "ion resonance "field-induced shift of lithium's dose-dependent curve for seizure onset times (SOTs) when combined with the cholinergic agent pilocarpine. Groups of rats were administered 1.5 thru 3 mEq/kg lithium chloride (in 0.5 mEq/kg increments) and exposed to reference conditions or to one of three intensities (70 nanoTesla, 0.8 microTesla, or 25 microTesla) of a 85 Hz magnetic field calculated to resonate with lithium ions given the background static geomagnetic field of approximately 38,000 nanoTesla (0.38 Gauss). A statistically significant quadratic relationship for SOT as a function of magnetic field intensity (irrespective of lithium dose) was noted: this U-shaped function was characterized by equal SOTs for the reference and 25 microTesla groups, with a trend toward shorter SOTs for the 70 nanoTesla and 0.8 microTesla groups. Although not predicted by the equations, this report extends other findings suggestive of discrete intensity windows for which magnetic field frequencies derived from the cyclotron ion resonance equation may affect ion activity.

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.

Intestinal inflammation alters the susceptibility to pentylenetetrazole-induced seizure in mice

BACKGROUND

Inflammatory bowel disorders are associated with increased incidence of seizures. Alteration in the endogenous opioid system and overproduction of nitric oxide have been implicated in colitis. The possible contribution of opioid receptors and nitric oxide to increased seizure susceptibility was examined in a putative model of intestinal inflammation.

METHODS

The alterations in clonic seizure threshold, induced by pentylenetetrazole, following the induction of intestinal inflammation by the administration of two consecutive daily oral doses of croton oil, was evaluated in mice. This model was used to evaluate the effects of pretreatment with opioid receptor antagonist naltrexone (10 mg/kg, once daily for 4 days or a single dose on the test day), non-specific nitric oxide synthase inhibitor NG-nitro-L-arginine methyl ester (10 mg/kg, once daily), and specific inducible nitric oxide synthase inhibitor aminoguanidine (100 mg/kg, once daily) on seizure threshold in intestinal inflammation.

RESULTS

A significant decrease in clonic seizure threshold was observed in mice with intestinal inflammation compared to the control group. Chronic pretreatment with naltrexone per se did not cause any significant change in seizure threshold, but it significantly restored the threshold in croton oil-treated mice to that of the control animals. However, acute naltrexone pretreatment (on the test day) could not restore the decreased seizure threshold to control level. Chronic pretreatment with neither NG-nitro-L-arginine methyl ester nor aminoguanidine altered the seizure threshold in the control animals and in mice treated with croton oil.

CONCLUSIONS

Experimental croton oil-induced intestinal inflammation leads to a proconvulsant effect, which may have clinical relevance. Chronic alterations mediated by endogenous opioids may be involved in this process, though a direct opioid-receptor-mediated effect is unlikely. Nitric oxide synthesis, via constitutive or inducible pathways, is not involved in this increased susceptibility.

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

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

Involvement of nitric oxide in kainic acid-induced excitotoxicity in rat brain

The involvement of nitric oxide (NO) in kainic acid (KA)-induced excitotoxicity was studied in rat brain. With the onset of KA (15 mg kg(-1), s.c.)-induced seizures (convulsions) 30 min after injection, increases in NO, as measured by the formation of citrulline, were seen in cortex (302%), amygdala (171%) and hippocampus (203%). The highest increases were determined 90 min after onset of seizures (120 min after KA injection) with 633%, 314% and 365%, respectively. These changes in NO preceded significant decreases in ATP and phosphocreatine (PCr) ranging from 44 to 53% for ATP and from 40 to 52% for PCr in the respective brain areas. With the exception of the cortex, normal citrulline values were restored within 24 h. Pretreatment with the spin trapping agent N-tert-butyl-alpha-phenylnitrone (PBN, 200 mg kg(-1), i.p.) or the antioxidant vitamin E (Vit-E, 100 mg kg(-1) per day for 3 days) prevented the increase in citrulline and significantly attenuated the loss in ATP and PCr without affecting seizure activity. It is concluded that seizures induced by KA produced a marked increase in the free radical NO, causing oxidative stress and leading to depletion of energy stores. The prevention of the increase in NO and preservation of ATP and PCr levels by PBN and Vit-E suggests the involvement of NO and other related free radicals, such as peroxynitrite (ONOO(-)). The lack of effect of PBN and Vit-E on seizure activity, suggests that NO is not involved in mechanisms regulating KA seizure generation and propagation. PBN and Vit-E or similar compounds may be important protective agents against status epilepticus-induced neuronal degeneration.

Phosphinothricin induces epileptic activity via nitric oxide production through NMDA receptor activation in adult mice

Phosphinothricin (PPT), the active component of a widely used herbicide, induces convulsions in rodents and humans. PPT shares structural analogy with glutamate, which could explain its powerful inhibitory effect on glutamine synthetase and its probable binding to glutamate receptors. To characterize the epileptogenic effect of PPT, electrographic and behavioural studies were carried out on PPT-treated adult mice. We investigated the role of N-methyl-D-aspartate (NMDA) receptor activation and nitric oxide (NO) production in induction of seizures triggered by PPT, by using specific NMDA antagonist and nitric oxide synthase (NOS) inhibitor. The inhibitory effect of PPT on glutamine synthetase of mouse brain was assessed after in vitro and in vivo treatments. The results obtained show that PPT induces tonic-clonic seizures and generalized convulsions in mice. They suggest that these seizures are mediated through an NMDA receptor activation and NO production, without involvement of inhibition of glutamine synthetase.

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 synthase expression in the cerebral cortex of patients with epilepsy

PURPOSE

Nitric oxide (NO), a short-lived radical synthesized from L-arginine by activation of the enzyme nitric oxide synthase (NOS), has been implicated in the pathophysiology of epilepsy by some investigators. However, the current data about NO and NOS in epilepsy are controversial and are derived only from animal models of epilepsy. In this study we investigated possible changes in NOS expression in the cerebral cortex of patients with epilepsy.

METHODS

Qualitative and quantitative parameters of the immunolabeling pattern of the neuronal, endothelial, and inducible isoforms of NOS were analyzed in biopsy material obtained from patients with short and long seizure history and from patients without epilepsy.

RESULTS

The comparative study showed that in the cerebral cortex of patients with epilepsy, particularly in those with a long seizure history, the number and labeling intensity of NOS-positive neurons increased, and that a subpopulation of nonpyramidal GABAergic neurons (type II NOS neurons) was responsible for this phenomenon.

CONCLUSIONS

The fact that NOS upregulation is more evident in patients with a long seizure history suggests that this is a consequence of seizures, acting probably as an adaptative response to the sustained release of excitatory amino acids.

7-nitroindazole differentially affects the anticonvulsant activity of antiepileptic drugs against amygdala-kindled seizures in rats

PURPOSE

The objective of this study was to evaluate the interaction of the preferential brain nitric oxide synthase (NOS) inhibitor, 7-nitroindazole (7-NI), with conventional antiepileptic drugs (AEDs) against amygdala-kindled seizures in rats.

METHODS

Experiments were performed on fully kindled rats. Adverse effects were evaluated with the rotorod test, which assesses motor coordination, and the passive-avoidance task, which assesses memory. Plasma levels of AEDs were measured by immunofluorescence.

RESULTS

7-NI (up to 100 mg/kg) failed to modify seizure parameters. However, it reduced the severity and duration of kindled seizures when coadministered with otherwise ineffective doses of carbamazepine (CBZ) (10-20 mg/kg) or phenobarbital (PB) (20 mg/kg). Combinations of 7-NI with valproate (VPA), diphenylhydantoin (DPH), or clonazepam (CLO) were not protective. L-Arginine (500 mg/kg) did not reverse the seizure-suppressing interactions between 7-NI and the conventional AEDs. The combinations of 7-NI and CBZ or PB did not impair performance in the rotorod test. Coadministration of 7-NI with CBZ did not affect long-term memory, and 7-NI given with PB didn't affect the mnemonic effect of PB. Finally, 7-NI did not affect the free plasma levels of CBZ or PB.

CONCLUSIONS

Pharmacokinetic interactions do not seem to account for the anticonvulsant effects of 7-NI combined with CBZ or PB. Central nitric oxide (NO) is possibly not involved in the synergism between 7-NI and these AEDs.