Increased neuronal nitric oxide synthase (nNOS) activity triggers picrotoxin-induced seizures in rats and evidence for participation of nNOS mechanism in the action of antiepileptic drugs

The potential role of nitric oxide in the anticonvulsant effects of betulin in pentylenetetrazole (PTZ)-induced seizures in mice

Epilepsy poses a significant challenge, especially for drug-resistant cases, necessitating novel treatment avenues. This study explores the potential interplay between nitric oxide (NO) and the anticonvulsant effects of betulin, a triterpene with promising neuroprotective properties. While betulin exhibits anticonvulsant effects, the specific involvement of NO remains inadequately understood, constituting a pivotal gap in current knowledge. One hundred NMRI mice were randomly assigned to diverse treatment groups, with seizures induced by pentylenetetrazol (PTZ). Parameters such as seizure threshold, nitrite levels, total antioxidant capacity (TAC), malondialdehyde (MDA) levels, and iNOS/nNOS gene expressions were assessed. Betulin significantly increased seizure thresholds and mitigated PTZ-induced NO levels. These findings suggest a potential modulation of NO-related pathways, emphasizing betulin's anti-inflammatory and antioxidant attributes. The study sheds light on betulin's multifaceted impact on oxidative stress, NO regulation, and iNOS/nNOS gene expressions. The ability of betulin to suppress iNOS/nNOS gene expressions, leading to reduce NO production, underscores its potential as an anticonvulsant.

Effect of Gabapentin-Fluoxetine Derivative GBP1F in a Murine Model of Depression, Anxiety and Cognition

Background and Objective

Gabapentin is a commonly prescribed antiepileptic agent for seizures, which is also used for pain and addiction management. Due to growing evidence of its abuse liability, there has been an incentive to synthesise potentially useful gabapentin derivatives devoid of adverse effects. A gabapentin adduct with a fluoxetine moiety, GBP1F, was assessed for any sedative, cognitive, anxiolytic, or antidepressant-like actions in murine behavioral models.

Materials and Methods

Selected groups of mice were used for each behavioral paradigm, and the effect of GBP1F (5, 10, and 15 mg/kg) was assessed using spontaneous locomotor activity, the tail suspension test, elevated plus maze test, and the Y maze test models. Immediately following behavioral experiments, postmortem striatal and hippocampal tissues were evaluated for the effect of GBP1F on concentrations of dopamine, DOPAC, HVA, serotonin, 5-HIAA, vitamin C, and noradrenaline using high performance liquid chromatography with electrochemical detection.

Results

GBP1F induced a mild suppression of locomotor activity, ameliorated anxiety and depression-like behavior, did not alter cognitive behavior, and raised serotonin and 5-HIAA concentrations in the hippocampus and striatum. GBP1F also positively enhanced dopamine and vitamin C tissue levels in the striatum. Thus, GBP1F represents a compound with anxiolytic- and antidepressant-like effects though further studies are warranted at the molecular level to focus on the precise mechanism(s) of action.

Involvement of nNOS, and α1, α2, β1, and β2 Subunits of Soluble Guanylyl Cyclase Genes Expression in Anticonvulsant Effect of Sumatriptan on Pentylenetetrazole-Induced Seizure in Mice

Epileptic seizure is phenomenon of abnormal synchronous neuronal discharge of a set of neurons in brain as a result of neuronal excitation. Evidence shows the nitric oxide (NO) involvement in neuronal excitability. Moreover, the role of cyclic guanosine monophosphate (cGMP) activation in seizure pathogenesis is well-established. Sumatriptan is a selective agonist of 5-Hydroxytryptamine1B/D auto-receptor, has been reassessed for its neuroprotection. This study was aimed to explore the anticonvulsant effect of sumatriptan through possible involvement of NO-cGMP pathway in mice. For this purpose, the protective effect of sumatriptan on PTZ-induced clonic seizure threshold (CST) was measured using NO-cGMP pathway inhibitors including N(G)-nitro-L-arginine (L-NNA, 1, 5, and 10 mg/kg), 7-nitroindazole (7-NI, 30, 45, and 60 mg/kg), aminoguanidine (AG, 30, 50, and 100 mg/kg), methylene blue (MB, 0.1, 0.5, and 1 mg/kg) and sildenafil (5, 10, and 20 mg/kg). The involvement of nitrergic system was further confirmed by measurement of nitrite levels by Griess reaction. The gene expression of neuronal nitric oxide synthase (nNOS) and subunits of soluble guanylyl cyclase (sGC) was studied using qRT-PCR analysis. Acute administration of sumatriptan (1.2 and 0.3 mg/kg) in combination with subeffective doses of NOS, sGC, and phosphodiesterase 5 inhibitors significantly reversed the PTZ-induced CST (P ≤ 0.001). The nitrite level in prefrontal cortex was significantly attenuated by sumatriptan (P ≤ 0.01). Furthermore, sumatriptan downregulated the PTZ-induced mRNA expression of nNOS (P ≤ 0.01), α1 (P ≤ 0.001), α2 (P ≤ 0.05), and β1 (P ≤ 0.05) genes in cerebral cortex of mice. In conclusion, the anticonvulsant activity of sumatriptan at least, in part, is mediated through inhibiting NO-cGMP pathway.

Thalidomide protects against acute pentylenetetrazol and pilocarpine-induced seizures in mice

Thalidomide was originally developed to treat primary neurological and psychiatric diseases. There are reports of anticonvulsant effects of thalidomide in rats and antiepileptic effects in patients. Hence, thalidomide (100, 200 and 400 mg/kg) was herein administered to mice to evaluate possible protection against seizures induced by the systemic administration of neurotoxins: 10 mg/kg of 4-aminopyridine (4-AP), 90 mg/kg of pentylenetetrazol (PTZ), or 380 mg/kg of pilocarpine. The effect of an NO and COX inhibitor (7-NI and ibuprofen, respectively) was also examined. The results show that thalidomide (1) induces the typical sedative effects, (2) has no anticonvulsant effect in mice treated with 4-AP, and (3) has anticonvulsant effect (400 mg/kg) in mice treated with PTZ and pilocarpine. It was found that 7-NI has an anticonvulsant effect in the pilocarpine model and that thalidomide's effect is not enhanced by its presence. However, thalidomide (200 mg/kg) plus 7-NI or ibuprofen tend to have a toxic effect in PTZ model. On the other hand, the combination of thalidomide and 7-NI or ibuprofen protects against pilocarpine-induced seizures. In conclusion, thalidomide did not exert an anticonvulsant effect for clonic-tonic type convulsions (4-AP), but it did so for seizures induced by PTZ and pilocarpine (representing absence seizures and status epilepticus, respectively). NO and prostaglandins were involved in the convulsive process elicited by pilocarpine.

Anticonvulsant effect of minocycline on pentylenetetrazole-induced seizure in mice: involvement of nitric oxide and N-methyl-d-aspartate receptor

Anticonvulsant effects of minocycline have been explored recently. This study was designed to examine the anticonvulsant effect of acute administration of minocycline on pentylenetetrazole-induced seizures in mouse considering the possible role of the nitric oxide/N-methyl-d-aspartate (NMDA) pathway. We induced seizure using intravenous administration of pentylenetetrazole. Our results showed that acute administration of minocycline increased the seizure threshold. Furthermore, co-administration of subeffective doses of the nonselective nitric oxide synthase (NOS) inhibitor NG-l-arginine methyl ester (10 mg/kg) and the neuronal NOS inhibitor 7-nitroindazole (40 mg/kg) enhanced the anticonvulsant effect of subeffective doses of minocycline (40 mg/kg). We found that inducible NOS inhibitor aminoguanidine (100 mg/kg) had no effect on the antiseizure effect of minocycline. Moreover, l-arginine (60 mg/kg), as a NOS substrate, reduced the anticonvulsant effect of minocycline. We also demonstrated that pretreatment with the NMDA receptor antagonists ketamine (0.5 mg/kg) and MK-801 (0.05 mg/kg) increased the anticonvulsant effect of subeffective doses of minocycline. Results showed that minocycline significantly decreased the hippocampal nitrite level. Furthermore, co-administration of a neuronal NOS inhibitor like NMDA receptor antagonists augmented the effect of minocycline on the hippocampal nitrite level. In conclusion, we revealed that anticonvulsant effect of minocycline might be, at least in part, due to a decline in constitutive hippocampal nitric oxide activity as well as inhibition of NMDA receptors.

Pathology of nNOS-Expressing GABAergic Neurons in Mouse Model of Alzheimer's Disease

Alzheimer's disease (AD) is the most common form of dementia that is often accompanied by mood and emotional disturbances and seizures. There is growing body of evidence that neurons expressing γ-aminobutyric acid (GABA) play an important role in regulation of cognition, mood, and emotion as well as seizure susceptibility, but participation of GABAergic neuronal pathology in Alzheimer's disease (AD) is not understood well at present. Here, we report that transgenic mice expressing human amyloid precursor protein Swedish-Dutch-Iowa mutant (APP_SweDI) exhibit early loss of neurons expressing GAD67, a GABA-synthesizing enzyme, in advance of the loss of pyramidal neurons in hippocampal CA1 region. The loss of GAD67⁺ neurons in APP_SweDI mice accompanied with decreased spatial cognition as well as increased anxiety-like behaviors and kainic acid-induced seizure susceptibility at early phase. In the hippocampal CA1 region, GAD67⁺ neurons expressed high basal levels of neuronal nitric oxide synthase (nNOS) and nitrosative stress (nitrotyrosine). Similarly, GAD67⁺ neurons in primary cortical and hippocampal neuron cultures also expressed high basal levels of nNOS and degenerated in response to lower Aβ concentrations due to their high basal levels of nitrosative stress. Given the role of GABAergic neurons in cognitive and neuropsychiatric functions, this study reports the role of nNOS-mediated nitrosative stress in dysfunction of GABAergic neurons and its potential participation in early development of cognitive and neuropsychiatric symptoms in AD.

Possible involvement of ATP-sensitive potassium channels in the antidepressant-like effects of gabapentin in mouse forced swimming test

Gabapentin as an anticonvulsant drug also has beneficial effects in treatment of depression. Previously, we showed that acute administration of gabapentin produced an antidepressant-like effect in the mouse forced swimming test (FST) by a mechanism that involves the inhibition of nitric oxide (NO). Considering the involvement of NO in adenosine triphosphate (ATP)-sensitive potassium channels (KATP), in the present study we investigated the involvement of KATP channels in antidepressant-like effect of gabapentin. Gabapentin at different doses (5–10 mg/kg) and fluoxetine (20 mg/kg) were administrated by intraperitoneal route, 60 and 30 min, respectively, before the test. To clarify the probable involvement of KATP channels, mice were pretreated with KATP channel inhibitor or opener. Gabapentin at dose 10 mg/kg significantly decreased the immobility behavior of mice similar to fluoxetine (20 mg/kg). Co-administration of subeffective dose (1 mg/kg) of glibenclamide (inhibitor of KATP channels) with gabapentin (3 mg/kg) showed a synergistic antidepressant-like effect. Also, subeffective dose of cromakalim (opener of KATP channels, 0.1 mg/kg) inhibited the antidepressant-like effect of gabapentin (10 mg/kg). None of the treatments had any impact on the locomotor movement. Our study, for the first time, revealed that antidepressant-like effect of gabapentin in mice is mediated by blocking the KATP channels.

Comparative studies on the effects of clinically used anticonvulsants on the oxidative stress biomarkers in pentylenetetrazole-induced kindling model of epileptogenesis in mice

BACKGROUND

Oxidative stress plays a key role in the pathogenesis of epilepsy and contributes in underlying epileptogenesis process. Anticonvulsant drugs targeting the oxidative stress domain of epileptogenesis may provide better control of seizure. The present study was carried out to investigate the effect of clinically used anti-epileptic drugs (AEDs) on the course of pentylenetetrazole (PTZ)-induced kindling and oxidative stress markers in mice.

METHODS

Six mechanistically heterogeneous anticonvulsants: phenobarbital, phenytoin, levetiracetam, pregabalin, topiramate, and felbamate were selected and their redox profiles were determined. Diazepam was used as a drug control for comparison. Kindling was induced by repeated injections of a sub-convulsive dose of PTZ (50 mg/kg, s.c.) on alternate days until seizure score 5 was evoked in the control kindled group. Anticonvulsants were administered daily. Following PTZ kindling, oxidative stress biomarkers were assessed in homogenized whole brain samples and estimated for the levels of nitric oxide, peroxide, malondialdehyde, protein carbonyl, reduced glutathione, and activities of nitric oxide synthase and superoxide dismutase.

RESULTS

Biochemical analysis revealed a significant increase in the levels of reactive oxygen species with a parallel decrease in endogenous anti-oxidants in PTZ-kindled control animals. Daily treatment with levetiracetam and felbamate significantly decreased the PTZ-induced seizure score as well as the levels of nitric oxide (p<0.001), nitric oxide synthase activity (p<0.05), peroxide levels (p<0.05), and malondialdehyde (p<0.05). Levetiracetam and felbamate significantly decreased lipid and protein peroxidation whereas topiramate was found to reduce lipid peroxidation only.

CONCLUSIONS

An AED that produces anticonvulsant effect by the diversified mechanism of action such as levetiracetam, felbamate, and topiramate exhibited superior anti-oxidative stress activity in addition to their anticonvulsant activity.

Involvement of NO/cGMP pathway in the antidepressant-like effect of gabapentin in mouse forced swimming test

Based on clinical studies regarding the beneficial effect of gabapentin in depression, we aimed to evaluate the antidepressant-like properties of gabapentin in mice and also the participation of nitric oxide (NO)/cyclic guanosine monophosphate pathway in this effect. The following drugs were used in this study: gabapentin; N(G)-nitro-L-arginine methyl ester (L-NAME), a non-specific NO synthase (NOS) inhibitor; 7-nitroindazole, a specific neuronal NOS inhibitor; aminoguanidine, a specific inducible NOS inhibitor; L-arginine, a NO precursor; and sildenafil, a phosphodiestrase inhibitor. Finally, we studied the behavioral effects through the forced swimming test (FST) and the changes of the hippocampus NO level through nitrite assay. The immobility time was significantly reduced after gabapentin administration. Co-administration of non-effective doses of gabapentin and L-NAME or 7-nitroindazole (7-NI) resulted in antidepressant-like effect in FST, while aminoguanidine did not affect the immobility time of gabapentin-treated mice. Furthermore, the antidepressant-like property of gabapentin was prevented by L-arginine or sildenafil. Also, the hippocampal nitrite level was significantly lower in gabapentin-treated mice relative to saline-injected mice, and co-administration of 7-NI with sub-effective gabapentin caused a significant decrease in hippocampal nitrite levels. Our results indicate that the antidepressant-like effect of gabapentin in the mice FST model is mediated at least in part through nitric oxide/cyclic guanosine monophosphate (cGMP) pathway.

[Effect of anticonvulsants on the nitric oxide system]

The effect of phenobarbital, carbamazepine, valproate sodium, depakine, topiramate and lamotrigine on the content of NO and NO-synthase activity in white rat brain tissues has been studied. It was established that the action of carbamazepine, valproate sodium, topiramate and lamotrigine decreases the activity of NO-synthase and the level of NO in the brain tissues. The amount of NO does not change while NO-synthase activity increases with the introduction of phenobarbital. The involvement of nitric oxide in the mechanism of action of the studied anticonvulsant drugs is discussed.

Effects of pentoxifylline and H-89 on epileptogenic activity of bucladesine in pentylenetetrazol-treated mice

The present study shows interactive effects of pentoxifylline (PTX) as a phosphodiesterase (PDE) inhibitor, H-89 as a protein kinase A (PKA) inhibitor and bucladesine (db-cAMP) as a cAMP agonist on pentylenetetrazol (PTZ)-induced seizure in mice. Different doses of pentoxifylline (25, 50, 100 mg/kg), bucladesine (50, 100, 300 nM/mouse), and H-89 (0.05, 0.1, 0.2 mg/100g) were administered intraperitoneally (i.p.), 30 min before intravenous (i.v.) infusion of PTZ (0.5% w/v). In combination groups, the first and second components were injected 45 and 30 min before PTZ infusion. In all groups, the control animals received an appropriate volume of vehicle. Single administration of PTX had no significant effect on both seizure latency and threshold. Bucladesine significantly decreased seizure latency and threshold only at a high concentration (300 nM/mouse). Intraperitoneal administration of H-89 (0.2 mg/100g) significantly increased seizure latency and threshold in PTZ-treated animals. All applied doses of bucladesine in combination with PTX (50 mg/kg) caused a significant reduction in seizure latency. Pretreatment of animals with PTX (50 and 100 mg/kg) attenuated the anticonvulsant effect of H-89 (0.2 mg/100g) in PTZ-exposed animals. H-89 (0.05, 0.2 mg/100g) prevented the epileptogenic activity of bucladesine (300 nM) with significant increase of seizure latency and seizure threshold. In conclusion, we showed that seizure activities were affected by pentoxifylline, H-89 and bucladesine via interactions with intracellular cAMP and cGMP signaling pathways, cyclic nucleotide-dependent protein kinases, and related neurotransmitters.

The neuroprotective effect of curcumin and Nigella sativa oil against oxidative stress in the pilocarpine model of epilepsy: a comparison with valproate

Oxidative stress has been implicated to play a role in epileptogenesis and pilocarpine-induced seizures. The present study aims to evaluate the antioxidant effects of curcumin, Nigella sativa oil (NSO) and valproate on the levels of malondialdehyde, nitric oxide, reduced glutathione and the activities of catalase, Na⁺, K⁺-ATPase and acetylcholinesterase in the hippocampus of pilocarpine-treated rats. The animal model of epilepsy was induced by pilocarpine and left for 22 days to establish the chronic phase of epilepsy. These animals were then treated with curcumin, NSO or valproate for 21 days. The data revealed evidence of oxidative stress in the hippocampus of pilocarpinized rats as indicated by the increased nitric oxide levels and the decreased glutathione levels and catalase activity. Moreover, a decrease in Na⁺, K⁺-ATPase activity and an increase in acetylcholinesterase activity occurred in the hippocampus after pilocarpine. Treatment with curcumin, NSO or valproate ameliorated most of the changes induced by pilocarpine and restored Na⁺, K⁺-ATPase activity in the hippocampus to control levels. This study reflects the promising anticonvulsant and potent antioxidant effects of curcumin and NSO in reducing oxidative stress, excitability and the induction of seizures in epileptic animals and improving some of the adverse effects of antiepileptic drugs.

Effects of sildenafil on pentylenetetrazol-induced convulsions in mice and amygdala-kindled seizures in rats

Sildenafil is the first marketed phosphodiesterase 5 inhibitor for the treatment of erectile dysfunction and recently, for pulmonary hypertension. While the treatment was found to be highly effective, several adverse effects are associated with this compound. Among numerous central nervous system-related untoward effects, proconvulsant activity was reported. The purpose of this study was to assess the effect of sildenafil on seizure threshold in rodents. Two seizure models/tests were used: the timed intravenous (iv) pentylenetetrazol (PTZ) infusion test in mice and the amygdala-kindling model in rats. Sildenafil was administered intraperitoneally 30 min before induction of seizures. In the iv PTZ paradigm, the first myoclonic twitch, generalized clonus with loss of the righting reflex, and forelimb tonus were recorded. In the amygdala-kindling model in rats, the following parameters were analyzed: threshold for induction of epileptiform discharges in the stimulated amygdala (afterdischarge threshold, ADT), seizure severity, seizure duration, and afterdischarge duration. Sildenafil (dosage range of 5-40 mg/kg) did not significantly affect the threshold for myoclonic twitches in the timed iv PTZ infusion test in mice but significantly decreased the threshold for clonic seizures at a dose of 20 mg/kg. Sildenafil at all doses tested neither significantly influenced the focal seizure threshold in the amygdala-kindling model of epilepsy in rats nor influenced seizure severity. Sildenafil significantly shortened afterdischarge duration and seizure duration recorded at the ADT current, indicative of a weak anticonvulsant activity. Our results show that sildenafil may have both pro- and anticonvulsant activity, which depends on the experimental model of epilepsy, on animal species and the dose of sildenafil. Based on these data and in view of the clinical observations, sildenafil should be used in patients suffering from epilepsy with caution and only based on a careful individual risk/benefit evaluation.

Neuroprotection after status epilepticus by targeting protein interactions with postsynaptic density protein 95

N-methyl-D-aspartate receptors (NMDARs) mediate essential neuronal excitation, but overactivation of NMDARs results in excitotoxic cell death in a variety of pathologic conditions, including status epilepticus (SE). Although NMDAR antagonists attenuate SE-induced brain injury, undesirable side effects have limited their clinical efficacy. Tat-NR2B9c was designed to disrupt protein interactions involving postsynaptic density protein 95 in the NMDAR signaling complex while not interfering with function of the NMDAR ion channel. We examined the ability of Tat-NR2B9c to provide neuroprotection in the hippocampus of rats after 60 minutes of SE induced by the repeated injection of low doses of pilocarpine (10 mg/kg). Tat-NR2B9c was administered 3hours after the termination of SE, and neuronal densities were assessed 14 days later by stereologic analysis of NeuN-positive cells. After SE, pyramidal cell densities were reduced by 70% in CA1, 34% in CA3, 58% in CA4, and 88% in the piriform cortex. In Tat-NR2B9c-treated rats, neuronal densities in CA1, a subregion of CA3, and CA4 were decreased by only 38%, 4%, and 26%, respectively. Tat-NR2B9c did not reduce cell loss in the posterior piriform cortex. The results indicate that targeted disruption of the NMDAR signaling complex represents a potential therapeutic approach for limiting neuronal cell loss after SE.

Endogenous nitric oxide is a key promoting factor for initiation of seizure-like events in hippocampal and entorhinal cortex slices

Nitric oxide (NO) modulates synaptic transmission, and its level is elevated during epileptic activity in animal models of epilepsy. However, the role of NO for development and maintenance of epileptic activity is controversial. We studied this aspect in rat organotypic hippocampal slice cultures and acute hippocampal-entorhinal cortex slices from wild-type and neuronal NO synthase (nNOS) knock-out mice combining electrophysiological and fluorescence imaging techniques. Slice cultures contained nNOS-positive neurons and an elaborated network of nNOS-positive fibers. Lowering of extracellular Mg(2+) concentration led to development of epileptiform activity and increased NO formation as revealed by NO-selective probes, 4-amino-5-methylamino-2',7'-difluorofluorescein and 1,2-diaminoanthraquinone sulfate. NO deprivation by NOS inhibitors and NO scavengers caused depression of both EPSCs and IPSCs and prevented initiation of seizure-like events (SLEs) in 75% of slice cultures and 100% of hippocampal-entorhinal cortex slices. This effect was independent of the guanylyl cyclase/cGMP pathway. Suppression of SLE initiation in acute slices from mice was achieved by both the broad-spectrum NOS inhibitor N-methyl-L-arginine acetate and the nNOS-selective inhibitor 7-nitroindazole, whereas inhibition of inducible NOS by aminoguanidine was ineffective, suggesting that nNOS activity was crucial for SLE initiation. Additional evidence was obtained from knock-out animals because SLEs developed in a significantly lower percentage of slices from nNOS(-/-) mice and showed different characteristics, such as prolongation of onset latency and higher variability of SLE intervals. We conclude that enhancement of synaptic transmission by NO under epileptic conditions represents a positive feedback mechanism for the initiation of seizure-like events.

The interaction of sildenafil with the anticonvulsant effect of diazepam

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

Cerebrospinal fluid Diacron-Reactive Oxygen Metabolite levels in pediatric patients with central nervous system diseases

This study assessed the validity of cerebrospinal fluid oxidative status of pediatric patients with central nervous system diseases, using the Diacron-Reactive Oxygen Metabolites test (d-Roms; Diacron International s.r.l.; Grosseto, Italy). Eighty-seven pediatric patients (8 with bacterial meningitis, 18 with aseptic meningitis, 23 with febrile seizures, 6 with rotavirus gastroenteritis-induced convulsions, 16 with epilepsy, 2 with adrenoleukodystrophy, 2 with multiple sclerosis, and 12 control subjects) were enrolled. An analysis of the infection-associated group (bacterial meningitis, aseptic meningitis, febrile seizures, and rotavirus gastroenteritis-induced convulsions) indicated that cerebrospinal fluid Diacron-Reactive Oxygen Metabolite levels in the bacterial meningitis group were significantly higher than in other infection-associated groups. In the bacterial meningitis group, the cerebrospinal fluid Diacron-Reactive Oxygen Metabolite levels obtained after improvement were significantly decreased compared with pre-improvement values. In the noninfection-associated group (epilepsy, adrenoleukodystrophy, and multiple sclerosis), the cerebrospinal fluid Diacron-Reactive Oxygen Metabolite levels in symptomatic epilepsy patients were higher than in cryptogenic epilepsy patients and control subjects, but not significantly. Progressive patients with adrenoleukodystrophy or multiple sclerosis demonstrated high Diacron-Reactive Oxygen Metabolite levels compared with another early-stage adrenoleukodystrophy patient. Oxidative stress may be associated with the pathogenesis of various pediatric central nervous system diseases. Cerebrospinal fluid Diacron-Reactive Oxygen Metabolite levels may correlate with clinical status in these diseases.

Modulatory effects of nitric oxide-active drugs on the anticonvulsant activity of lamotrigine in an experimental model of partial complex epilepsy in the rat

Background

The effects induced by administering the anticonvulsant lamotrigine, the preferential inhibitor of neuronal nitric oxide synthase 7-nitroindazole and the precursor of NO synthesis L-arginine, alone or in combination, on an experimental model of partial complex seizures (maximal dentate gyrus activation) were studied in urethane anaesthetized rats. The epileptic activity of the dentate gyrus was obtained through the repetitive stimulation of the angular bundle and maximal dentate gyrus activation latency, duration and post-stimulus afterdischarge duration were evaluated.

Results

Either Lamotrigine (10 mg kg^-1) or 7-nitroindazole (75 mg kg^-1) i.p. administration had an anticonvulsant effect, significantly reducing the number of animals responding to angular bundle stimulation. On the contrary, i.p. injection of L-arginine (1 g kg^-1) induced an aggravation of the epileptiform phenomena, demonstrated by the significant augmentation of the duration of both maximal dentate activation and afterdischarge. Furthermore, the injection of lamotrigine and 7-nitroindazole in combination significantly increased the anticonvulsant effects induced by the same drugs separately, either reducing the number of responding animals or decreasing both maximal dentate gyrus activation and afterdischarge durations. On the contrary, the combined treatment with L-arginine and lamotrigine did not modify the maximal dentate gyrus activation parameters suggesting an adversative effect of L-arginine-increased nitric oxide levels on the lamotrigine-induced anticonvulsant action.

Conclusion

The present results indicate that the nitrergic neurotransmission exerts a significant modulatory role in the control of the development of paroxystic phenomena in the maximal dentate gyrus activation model of epilepsy. Finally, our data suggest a functional relationship between the nitric oxide system and the anticonvulsant effect of lamotrigine which could be enhanced by reducing nitric oxide levels and, conversely, dampened by an increased nitrergic activity.

Gabapentin completely attenuated the acute morphine induced c-Fos expression in the rat striatum

The neuro-anatomical sites and molecular mechanism of action of gabapentin (GBP)-morphine interaction to prevent and reverse morphine side effects as well as enhancement of the analgesic effect of morphine is not known. Therefore, we examined the combined effects of GBP-Morphine on acute morphine induced c-Fos expression in rat striatum. The combined effect of GBP-Morphine was examined by means of c-Fos immunohistochemistry. A single intraperitoneal injection (i.p.) of morphine (10 mg/kg), saline (control), co-injection of GBP (150 mg/kg) with morphine (10 mg/kg) was administered under anaesthesia. Ninety minutes after drugs administration the deeply anesthetized rats were perfused transcardially with 4% paraformaldehyde. Serial 40 mum thick sections of brain were cut and processed by immunohistochemistry to locate and quantify the sites and number of neurons with c-Fos immunoreactivity. Detection of c-Fos protein was performed using the peroxidase-antiperoxidase (PAP) detection protocol. Our present study demonstrated that, administration of GBP (150 mg/kg, i.p.) in combination with morphine (10 mg/kg, i.p.) significantly (p < 0.01) attenuated the acute morphine (10 mg/kg, i.p.) induced c-Fos expression in the rat striatum. Present results showed that GBP-morphine combination action prevented the acute morphine induced c-Fos expression in rat striatum. Moreover, this study provides first evidence of neuro-anatomical site and that GBP neutralized the morphine induced activation of rat striatum.

Effects of levetiracetam in lipid peroxidation level, nitrite-nitrate formation and antioxidant enzymatic activity in mice brain after pilocarpine-induced seizures

: Oxidative stress has been implicated in a large number of human degenerative diseases, including epilepsy. Levetiracetam (LEV) is a new antiepileptic agent with broad-spectrum effects on seizures and animal models of epilepsy. Recently, it was demonstrated that the mechanism of LEV differs from that of conventional antiepileptic drugs. Objectifying to investigate if LEV mechanism of action involves antioxidant properties, lipid peroxidation levels, nitrite-nitrate formation, catalase activity, and glutathione (GSH) content were measured in adult mice brain. The neurochemical analyses were carried out in hippocampus of animals pretreated with LEV (200 mg/kg, i.p.) 60 min before pilocarpine-induced seizures (400 mg/kg, s.c.). The administration of alone pilocarpine, 400 mg/kg, s.c. (P400) produced a significant increase of lipid peroxidation level in hippocampus. LEV pretreatment was able to counteract this increase, preserving the lipid peroxidation level in normal value. P400 administration also produced increase in the nitrite-nitrate formation and catalase activity in hippocampus, beyond a decrease in GSH levels. LEV administration before P400 prevented the P400-induced alteration in nitrite-nitrate levels and preserved normal values of catalase activity in hippocampus. Moreover, LEV administration prevented the P400-induced loss of GSH in this cerebral area. The present data suggest that the protective effects of LEV against pilocarpine-induced seizures can be mediated, at least in part, by reduction of lipid peroxidation and hippocampal oxidative stress.

Allopregnanolone reduces immobility in the forced swimming test and increases the firing rate of lateral septal neurons through actions on the GABAA receptor in the rat

Since allopregnanolone reduces the total time of immobility in rats submitted to the forced swimming test, we decided to explore whether this neuroactive steroid shares other antidepressant-like actions, such as increasing the neuronal firing rate in the lateral septal nucleus (LSN). In order to discard the influence of the oestrous cycle on immobility and on the firing rate of LSN neurons, all Wistar rats used in the study underwent ovariectomy before treatments. A group of rats received different doses of allopregnanolone (0.5, 1.0, 2.0 and 3.0 mg/kg, i.p.) 1 hour before being forced to swim in order to identify the minimum effective dose diminishing immobility. None of the tested doses of allopregnanolone produced significant changes in motor activity in the open-field test. The minimum dose of allopregnanolone producing a significant reduction in the total time of immobility (p<0.05) against the vehicle was 1.0 mg/kg, while 2.0 mg/kg and above also increased the latency to the first period of immobility (p<0.05). The minimum effective dose of allopregnanolone reducing immobility in the forced swimming test (1.0 mg/kg) significantly (p <0.05) produced a higher (twofold) neuronal firing rate in LSN neurons, but did not produce any change in septofimbrial nucleus neurons, which fired at a rate similar to that of vehicle-treated rats. The pretreatment with the non-competitive GABAA receptor antagonist, picrotoxin (1.0 mg/kg), blocked the aforementioned actions of allopregnanolone on both immobility and LSN firing rate. In conclusion, allopregnanolone produces an antidepressant-like effect in the forced swimming test, associated with an increase in the LSN neuronal firing rate, seemingly mediated by the GABAA receptor.

Involvement of nitric oxide-soluble guanylyl cyclase pathway in the control of maximal dentate gyrus activation in the rat

Nitric oxide/soluble Guanylyl cyclase (NO/sGC) pathway on the maximal dentate gyrus activation (MDA) was studied in rats. The cerebral NO levels were modified by administrating 7-Nitroindazole (7-NI), a selective inhibitor of neuronal NOS, and L-arginine, a precursor of the synthesis of NO. 1H-[1,2,4]Oxadiazole[4,3-a]quinoxalin-1-one (ODQ), a specific inhibitor of the NO-sGC pathway, was administered to study the involvement of cGMP pathway. The epileptic activity of the dentate gyrus was obtained through the repetitive stimulation of the angular bundle; MDA parameters studied were: onset time, MDA duration and post-stimulus afterdischarge (AD) duration. 7-NI caused an increase of MDA onset time and a decrease of MDA and AD duration. L-arginine, induced an aggravation of the epileptiform phenomena. ODQ induced modifications of MDA parameters as those caused by 7-NI. Our results indicate that the nitrergic neurotransmission exerts a modulatory role in the proneness to the epileptogenic phenomena through the activation of sGC metabolic pathway.

Effects of sodium nitroprusside, a nitric oxide donor, on γ-aminobutyric acid concentration in the brain and on picrotoxin-induced convulsions in combination with phenobarbitone in rats

The concentrations of nitric oxide (NO), the neuronal messenger molecule, and gamma-aminobutyric acid (GABA), the inhibitory neurotransmitter, and the activity of gamma-aminobutyric acid transaminase (GABA-T), the enzyme involved in the degradation of GABA, were measured in the brain of rats treated with graded doses (1.25, 2.5, 5.0 mg/kg) of sodium nitroprusside (SNP), the donor of NO. The effect of SNP was tested alone and in combination with phenobarbitone (PB), the GABA potentiating antiepileptic drug, against picrotoxin (PCT) (5 mg/kg)-induced convulsions in rats. The results of these studies showed that NO released from SNP (2.5 mg/kg) had a potential to inhibit GABA-T activity resulting in an increase in the concentration of GABA in the brain. Thus, SNP (2.5 mg/kg) was able to inhibit PCT-induced convulsions and was able to produce an additive anticonvulsant action with PB. However, a much greater increase in the concentration of NO by 5.0 mg/kg of SNP did not change the activity of GABA-T and the concentration of GABA, and promoted the convulsant action of PCT. These results suggest that a moderate increase in the concentration of NO following the administration of its donor SNP (2.5 mg/kg) results in an enhancement of the concentration of GABA in the brain and in an inhibition of PCT-induced convulsions independently and additively with PB and that a marked increase in NO concentration after the administration of a larger dose of SNP (5.0 mg/kg) results in proconvulsant action.

Gestational and postnatal malnutrition affects sensitivity of young rats to picrotoxin and quinolinic acid and uptake of GABA by cortical and hippocampal slices

It is widely known that a complex interaction between excitatory and inhibitory systems is required to support the adequate functioning of the brain and that significant alterations induced by early protein restriction are complex, involving many systems. Based on such assumptions, we investigated the effects of maternal protein restriction during pregnancy and lactation followed by offspring protein restriction on some GABAergic and glutamatergic parameters, which mediate inhibitory and excitatory transmission, respectively. The sensitivity of young malnourished rats to convulsant actions of the GABA(A) receptor antagonist picrotoxin (PCT; s.c.) and to N-methyl-d-aspartate (NMDA) receptor agonist quinolinic acid (QA; i.c.v) and also gamma-amino-n-butyric acid (GABA) and glutamate uptake by cortical and hippocampal slices were evaluated in P25 old rats. Early protein malnutrition induced higher sensitivity to picrotoxin, which could be associated with the observed higher GABA uptake by cortical, and hippocampal slices in malnourished rats. In contrast, we observed lower sensitivity to quinolinic acid in spite of unaltered glutamate uptake by the same cerebral structures. Picrotoxin enhanced GABA uptake in hippocampus in well- and malnourished rats; however, it did not affect cortical GABA uptake. Our data corroborate our previous report, showing that malnutrition depresses the glutamatergic activity, and point to altered modulation of GABAergic neurotransmission. Such findings allow us to speculate that malnutrition may affect the excitatory and inhibitory interaction.

Seizure-induced oxidative stress in rat brain regions: blockade by nNOS inhibition

Free radicals have been implicated in the pathogenesis of various neurological disorders including epilepsy. Experimental seizures are often accompanied by the generation of free radicals that cause lipid peroxidation (LPO), which may subsequently cause neurodegeneration observed in certain types of human epilepsy. We recently reported a trigger role for nitric oxide (NO) derived by activation of neuronal isoform of nitric oxide synthase (nNOS) and that the action of conventional antiepileptic drugs (AEDs) was potentiated by inhibition of nNOS. In the present study, we extend our observations to understand the significance of blockade of the nNOS pathway on seizure-induced oxidative stress. Increased NO and LPO levels was observed at the time that corresponded to the onset of generalized seizures in rat brain regions following administration of GABA(A) receptor antagonist, picrotoxin (PCT). Treatment with the selective nNOS inhibitor, 7-nitroindazole (7-NI), decreased NO and LPO levels. The AEDs, diazepam and phenobarbitone also prevented seizure-induced increase in NO and LPO levels. Seizures resulted in a significant increase in the activity of antioxidant enzymes, superoxide dismutase in the frontal cortex and hippocampus. On the other hand, the activity of glutathione peroxidase was decreased in the hippocampus and midbrain. Whereas treatment with 7-NI could minimize the effects of PCT, the AEDs per se did not have any significant impact on the activity of the antioxidant enzymes, though co-treatment with 7-NI and AEDs could significantly decrease seizure-induced alterations in antioxidant enzyme activities. These observations suggest that the AEDs may not have a significant role in modulating the activities of antioxidant enzymes and that their ability to decrease LPO is realized more likely by their ability to prevent free radical formation. In conclusion, the present study demonstrates that NO contributes to LPO observed following seizures induced by PCT. The study also provides evidence for the ability of the AEDs to inhibit seizure-induced increase in LPO levels, the effect being enhanced by co-treatment with 7-NI suggesting that 7-NI and the AEDs together could prevent the neurotoxic cascade induced by oxidative stress.

Changes of [3H]Muscimol, [3H]Flunitrazepam and [3H]MK-801 Binding in Rat Brain by Prolonged Ventricular Infusion of 7-Nitroindazole

In the present study, we have investigated the effects of prolonged inhibition of nitric oxide synthase (NOS) by infusion of neuronal NOS (nNOS) inhibitor, 7-nitroindazole (7-NI), to examine modulation of NMDA and GABAA receptor binding in rat brain. The duration of sleeping time was significantly increased by the pre-treatment with 7-NI (100 mg/kg) 30 min before pentobarbital (40 mg/kg) treatment in rats. However, the duration of pentobarbital-induced sleep was shortened by the prolonged infusion of 7-NI into cerebroventricle for 7 days. We have investigated the effect of NOS inhibitor on NMDA and GABAA receptor binding characteristics in discrete areas of brain regions by using autoradiographic techniques. The GABAA receptors were analyzed by quantitative autoradiography using [3H]muscimol and [3H]flunitrazepam binding, and NMDA receptor binding was analyzed by using [3H]MK-801 binding in rat brain slices. Rats were infused with 7-NI (500 pmol/10 microl/h, i.c.v.) for 7 days, through pre-implanted cannula by osmotic minipumps. The levels of [3H]muscimol were markedly elevated in cortex, caudate putamen, and thalamus while the levels of [3H]flunitrazepam binding were only elevated in cerebellum by NOS inhibitor. However, there was no change in the level of [3H]MK-801 binding except decreasing in the thalamus. These results show that the prolonged inhibition of NOS by 7-NI-infusion highly elevates [3H]muscimol binding in a region-specific manner and decreases the pentobarbital-induced sleep.

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.