Nitric oxide signaling pathway in the anti-convulsant effect of adenosine against pentylenetetrazol-induced seizure threshold in mice

Implication of nitrergic system in the anticonvulsant effects of ferulic acid in pentylenetetrazole-induced seizures in male mice

OBJECTIVES

Seizures are abnormal discharge of neurons in the brain. Ferulic acid (FA) is a phenolic compound with antioxidant and neuroprotective effects. The present study aimed to investigate the role of the nitrergic system in the anticonvulsant effect of FA in pentylenetetrazol (PTZ)-induced seizures in male mice.

METHODS

64 male Naval Medical Research Institute (NMRI) mice weighing 25-29 g were randomly divided into eight experimental groups (n=8). FA at doses 5, 10, and 40 mg/kg alone and in combination with L-nitro-arginine methyl ester (L-NAME) (nitric oxide synthase inhibitor) or L-arginine (L-arg) (nitric oxide [NO] precursor) was administrated (intraperitoneal). PTZ was injected (i.v. route) 30 min after drugs administration (1 mL/min). Seizure onset time was recorded and the nitrite levels of prefrontal cortex and serum were determined by the Griess method.

RESULTS

FA at doses of 10 and 40 mg/kg significantly increased the seizure threshold as well as reduced the serum and brain NO levels in comparison to the saline-received group. Co-administration of the effective dose of FA (10 mg/kg) plus L-arg significantly decreased the seizure threshold in comparison to the effective dose of FA alone. Co-injection of the sub-effective dose of FA (5 mg/kg) with L-NAME significantly increased the seizure threshold as well as significantly decreased the brain NO level in comparison to the sub-effective dose of FA alone.

CONCLUSIONS

We showed that the nitrergic system, partially at least, mediated the anticonvulsant effect of FA in PTZ-induced seizures in mice. We concluded that L-NAME potentiated while L-arg attenuated the anticonvulsant effect of FA.

Anticonvulsant Activity of Essential Oil From Leaves of Zhumeria majdae (Rech.) in Mice: The Role of GABAA Neurotransmission and the Nitric Oxide Pathway

The essential oil from the leaves of Zhumeria majdae Rech. (ZMEO) has been shown to have several beneficial effects in the clinic. In this work we examined the anticonvulsant activities of ZMEO in an experimental mouse model of seizure and aimed to identify any possible underlying mechanisms. ZMEO (5, 10, 20, and 40 mg/kg intraperitoneally (i.p.)) or diazepam, as the reference anticonvulsant drug (25, 50 and 100 µg/kg i.p.), were administered 60 minutes prior to pentylenetetrazol (PTZ) injection (intravenously (i.v.) or i.p.) and changes in threshold, latency, and frequency of clonic seizure were examined. The PTZ i.p.-induced model of seizure was also applied for examining the protective effects of ZMEO pretreatment against PTZ-induced mortality. In some studies, the anticonvulsant effect of the combination of diazepam and ZMEO was also studied. The protective effects of ZMEO against hindlimb tonic extensions (HLTEs) were also examined by maximal electroshock (MES) seizure testing. The γ-aminobutyric acid (GABA)ergic mechanism and nitric oxide (NO) pathway involvement in anticonvulsant activity of ZMEO were assessed by pretreating animals with flumazenil, Nω -nitro-L-arginine methyl ester (L-NAME), aminoguanidine, and L-arginine in a PTZ-induced model of seizure. Administration of 20 mg/kg ZMEO significantly increased chronic seizure threshold and latency while reducing frequency of convulsions and mortality in the PTZ-induced model. In the doses studied, ZMEO could not protect mice from HLTE and mortality induced by MES. Pretreatment with L-arginine and diazepam potentiated the anticonvulsant effects of ZMEO, whereas pretreatment with L-NAME, aminoguanidine, and flumazenil reversed anticonvulsant activity. The anticonvulsant activity of ZMEO may be mediated in part through a GABAergic mechanism and the NO signaling pathway.

Posible involvement of nitric oxide in anticonvulsant effects of citicoline on pentylenetetrazole and electroshock induced seizures in mice

Cerebroneurovascular trauma is recognized as an important risk factor in the development of seizure and epilepsy. Administration of citicoline in these situations is a conventional therapeutic strategy, which combines neurovascular protection and repair effects. The aim of the present study is clarifying the effect of acute and sub-chronic citicoline administration on pentylenetetrazole (PTZ) and electroshock induced seizures in mice. Besides we examined the probable role of NO and its interaction with citicoline in seizure experiments.

Male mice were received acute and sub-chronic regimens of different doses of citicoline (62.5, 125, 250 and 500 mg/kg) before the intravenous or intraperitoneal PTZ-induced seizures or electroshock. To clarify the probable role of NO, 7-nitroindazole (7-NI) (60 mg/kg) or aminoguanidine (AG) (100 mg/kg) were injected 5 min before citicoline in separate groups.

The results revealed that neither acute nor sub-chronic treatment with citicoline could affect the seizures induced by intravenous or intraperitoneal PTZ, but in electroshock model, citicoline showed anti-epileptic properties. Co-administration of citicoline and selective nitric oxide synthase (NOS) inhibitors amplified the anticonvulsant effect of citicoline.

The current results indicated that citicoline has anticonvulsant effects probably through the inhibition of NO.

Effect of Interaction between Adenosine and Nitric Oxide on Central Nervous System Oxygen Toxicity

The metabolism of adenosine (ADO) and nitric oxide (NO) in brain tissues is closely associated with the change of oxygen content. They have contrary effects in the onset of hyperbaric oxygen (HBO)-induced central nervous system oxygen toxicity (CNS OT): ADO can suppress the onset, while NO promotes it. We adopted the ADO-augmenting measure and NO-inhibiting measure in this study and found the combined use had a far superior preventive and therapeutic effect in protecting against CNS OT compared with the use of either measure alone. So we hypothesized that there is an interaction between ADO and NO which has an important impact on the onset of CNS OT. On this basis, we administered ADO-augmenting or ADO-inhibiting drugs to rats. After exposure to HBO, the onset of CNS OT was evaluated, followed by the measurement of NO content in brain tissues. In another experiment, rats were administered NO-augmenting or NO-inhibiting drugs. After exposure to HBO, the onset of CNS OT was evaluated, followed by measurement of the activities of ADO metabolism-related enzymes in brain tissues. The results showed that, following ADO augmentation, the content of NO and its metabolite was significantly reduced, and the onset of CNS OT significantly improved. After ADO inhibition, just the opposite was observed. NO promotion resulted in a decrease in the activity of ADO-producing enzyme, an increase in the activity of ADO-decomposing enzyme, and an aggravation in CNS OT. The above results were all reversed after an inhibition in NO content. Studies have shown that exposure to HBO has a significant impact on the content of ADO and NO in brain tissues as well as their biological effects, and ADO and NO might have an intense interaction, which might generate an important effect on the onset of CNS OT. The prophylaxis and treatment effects of CNS OT can be greatly enhanced by augmenting ADO and inhibiting NO.

Effect of acute caffeine administration on PTZ-induced seizure threshold in mice: Involvement of adenosine receptors and NO-cGMP signaling pathway

PURPOSE

Caffeine is a non-selective antagonist of A₁ and A_2A adenosine receptors (ARs). In this regard, nitric oxide (NO) is partly involved in the central effects of caffeine. In this study, we examined the effect of acute caffeine administration on pentylenetetrazole (PTZ)-induced seizure threshold by focusing on A₁Rs, A_2ARs, and NO-cGMP signaling pathway.

METHODS

NMRI male mice (25-30 g) received caffeine (5, 50, and 100 mg/kg) alone, whereas 8-CPT (1 and 5 mg/kg, a selective A₁Rs antagonist), SCH-442416 (5 and 10 mg/kg, a selective A_2ARs antagonist) or sildenafil (5 and 10 mg/kg, a phosphodiesterase 5 inhibitor) were administrated alone or as pre-treatment before caffeine. Seizure threshold was assessed by intravenous infusion of PTZ. Nitric oxide metabolites (NOx) were measured with the Griess method.

RESULTS

When administrated alone, caffeine (5 and 50 mg/kg) and 8-CPT (1 and 5 mg/kg) significantly decreased seizure threshold, while 100 mg/kg of caffeine, SCH-442416 or sildenafil did not change it. Only pre-treatment with SCH-442416 (5 and 10 mg/kg) or sildenafil (5 and 10 mg/kg) before 100 mg/kg of caffeine significantly decreased seizure threshold. Moreover, NOx levels significantly decreased following alone administration of caffeine (100 mg/kg) or 8-CPT (5 mg/kg).

CONCLUSION

The results of present study showed that 5 and 50 mg/kg of caffeine had a proconvulsant effect but caffeine at a dose of 100 mg/kg had no effect on seizure threshold. In addition, it seems that the effect caffeine on seizure threshold is partly mediated through ARs or modulation of the NO-cGMP signaling pathway.

Maerua angolensis DC. (Capparaceae) Stem Bark Extract Protects against Pentylenetetrazole-Induced Oxidative Stress and Seizures in Rats

Introduction

The stem bark of Maerua angolensis DC. (Capparaceae) is traditionally used for management of epilepsy. Our aim was to evaluate the antiseizure potential and identify possible mechanisms by which the effects are registered.

Methods

The petroleum ether/ethyl acetate extract (100–1000 mg kg⁻¹) was administered per os to male Sprague-Dawley rats after pretreatment with flumazenil (0.3 mg kg⁻¹) or L-arginine (150 mg kg⁻¹) or sildenafil (5 mg kg⁻¹) and they subsequently received a subcutaneous injection of pentylenetetrazole (65 mg kg⁻¹). Rats were observed for latency to and duration of myoclonic seizures and additionally the level of protection against oxidant markers and products was assessed in vitro and in vivo.

Results

The extract (300 and 1000 mg kg⁻¹, p.o.) significantly delayed the onset and decreased the duration and frequency of PTZ-induced convulsions. The anticonvulsant effect of MAE (300 mg kg⁻¹, p.o.) was reversed by pretreatment with flumazenil, L-arginine, or sildenafil. Also, MAE (300 mg kg⁻¹) treatment reversed significantly PTZ-induced oxidative stress in rat brain tissue.

Conclusion

The petroleum ether/ethyl acetate fraction exhibits antiseizure activity by affecting GABAergic and nitric oxide-cGMP pathways. In addition, the extract protects against the generation of free radicals and the oxidative products of the PTZ-induced seizures.

Anticonvulsant activity of Pseudospondias microcarpa (A. Rich) Engl. hydroethanolic leaf extract in mice: The role of excitatory/inhibitory neurotransmission and nitric oxide pathway

ETHNOPHARMACOLOGICAL RELEVANCE

Pseudospondias microcarpa (A. Rich) Engl. is a plant used for managing various diseases including central nervous system disorders.

AIM OF THE STUDY

This study explored the anticonvulsant activity of P. microcarpa hydroethanolic leaf extract (PME) as well as possible mechanism(s) of action in animal models.

METHODS

Effects of PME was assessed in electroconvulsive (the maximal electroshock and 6-Hz seizures) and chemoconvulsive (pentylenetetrazole-, picrotoxin-, isoniazid-, 4-aminopyridine-, and strychnine-induced seizures) models of epilepsy. In addition, effect of the extract on the nitric oxide pathway and GABA_A receptor complex was evaluated.

RESULTS

The extract (30, 100 and 300mgkg^-1, p.o.) significantly delayed the onset as well as decreased the duration and frequency of pentylenetetrazole-, picrotoxin- and strychnine-induced seizures. In addition, PME pre-treatment significantly improved survival in the 4-aminopyridine- and isoniazid-induced seizure tests. Furthermore, the extract protected against 6-Hz psychomotor seizures but had no effect in the maximal electroshock test. The anticonvulsant effect of PME (100mgkg^-1, p.o.) was also reversed by pre-treatment with flumazenil, L-arginine or sildenafil. However, L-NAME or methylene blue (MB) augmented its effect.

CONCLUSION

Results show that PME has anticonvulsant activity and may probably be affecting GABAergic, glycinergic, NMDA, K⁺ channels and nitric oxide-cGMP pathways to exert its effect.

Resveratrol lacks protective activity against acute seizures in mouse models

Resveratrol (3,4',5-stilbenetriol) is a natural product having diverse anti-inflammatory and antioxidant properties. The compound has a wide spectrum of pharmacological and metabolic activity, including cardioprotective, neuroprotective, anticarcinogenic and anti-aging effects reported in numerous studies. Some reports also suggest potential anticonvulsant properties of resveratrol. In the present study, we used in mice three different seizure models which are routinely applied in preclinical drug discovery. The protective effects of resveratrol were evaluated in the pentylenetetrazole (PTZ), maximal electroshock (MES) and 6-Hz electrical seizure models. Resveratrol (up to 300mg/kg) administered ip (5-60min pre-treatment time) remained without any protective activity against seizures induced in these models. There was only a trend towards a delay in seizure latency, which reached statistical significance after treatment with resveratrol (100mg/kg; 15min) in case of tonic convulsions induced by PTZ. Phenobarbital (PHB, ip, 45min), used as a reference compound, displayed a clear-cut and dose-dependent protection against seizures in all the models. The ED50 values obtained with PHB were as follows: 7.3mg/kg (PTZ model), 13.3mg/kg (MES model) and 29.7mg/kg (6-Hz model). The present data demonstrate that an acute treatment with resveratrol does not provide any significant protection in three seizure models which collectively are able to detect anticonvulsants with diverse mechanisms of action. However, it cannot be excluded that chronic treatment with resveratrol may offer some protection in these or other seizure models.

Seizure protection by intrapulmonary delivery of midazolam in mice

The lung provides a portal of entry that could be used to rapidly deliver anticonvulsant substances to the brain to treat seizures. In the present study, we demonstrate that midazolam, a water-soluble anticonvulsant benzodiazepine, confers potent seizure protection when administered via the intrapulmonary route. High dose (100 mg/kg) intraperitoneal midazolam induced loss-of-righting reflex in mice. Lower doses of midazolam (100-1000 μg/kg) when administered intraperitoneally did not induce loss-of-righting reflex but protected animals against pentylenetetrazol (PTZ)-induced seizures. Intrapulmonary administration of midazolam via a tracheal cannula protected against intraperitoneal PTZ seizures at lower doses. The minimal intraperitoneal and intravenous doses of midazolam required to elevate the threshold for seizure signs induced by intravenous PTZ were 500 and 100 μg/kg, respectively, whereas the minimal intrapulmonary midazolam dose was 12.5 μg/kg. Intratracheal midazolam caused a large increase in intravenous PTZ threshold 5 min after administration but the effect declined rapidly over 60 min and no antiseizure activity was evident at 120 min. The minimal intraperitoneal doses of midazolam required to elevate the threshold for seizure signs induced by intravenous picrotoxin and kainic acid were 100 and 2000 μg/kg, respectively; the corresponding values for intratracheal midazolam were 25 and 100 μg/kg, respectively. We conclude that midazolam is a highly effective anticonvulsant when administered by the intrapulmonary route. Midazolam is substantially more potent when delivered into the lung than when administered intraperitoneally or intravenously. Inhalation could be an alternative to other routes of administration for the delivery of midazolam to rapidly abort acute seizures.

Influence of sildenafil on the anticonvulsant action of selected antiepileptic drugs against pentylenetetrazole-induced clonic seizures in mice

The aim of the present study was to investigate the effect of sildenafil, a selective phosphodiesterase 5 (PDE5) inhibitor, on threshold for clonic seizures in mice. In addition, the effects of sildenafil on the anticonvulsant activity of selected antiepileptic drugs (AEDs), i.e., clonazepam (CZP), valproate (VPA), phenobarbital (PB), ethosuximide (ETS) and tiagabine (TGB), were also evaluated. The subcutaneous pentylenetetrazole (PTZ) test was used to determine the effects of sildenafil on convulsive susceptibility and the anticonvulsant activity of the studied AEDs in mice, while the acute side effects of sildenafil and its combinations with the studied AEDs were evaluated in the chimney test, step-through passive-avoidance task and grip-strength test in mice. Total brain concentrations of AEDs were also determined. Sildenafil (5–40 mg/kg) did not influence the threshold for PTZ-induced clonic seizures in mice, but increased the anticonvulsant activity of ETS in this test without any significant changes in the total brain concentration. The activity of the remaining AEDs was not significantly changed by sildenafil. Neither sildenafil alone nor its combinations with the studied AEDs produced any changes in the motor coordination, long-term memory and muscular strength in mice. Co-administration of sildenafil with ETS in male epileptic patients with co-existing erectile dysfunctions might lead to the pharmacodynamic interactions that may be beneficial for the patients. Combinations of sildenafil with CZP, VPA, PB and TGB appear to be neutral in terms of their influence on seizures.

Influence of sildenafil on the antidepressant activity of bupropion and venlafaxine in the forced swim test in mice

Recent studies highlight the involvement of the nitrergic system in the mechanism of action of antidepressant drugs. Sildenafil, a selective PDE5 inhibitor, was shown to abolish the anti-immobility effects of bupropion, venlafaxine and s-citalopram in mice. In this study we assessed the effects of sildenafil on the activity of bupropion and venlafaxine in the forced swim test in mice. Swim trials were conducted by placing mice in glass cylinders filled with water for 6min and the duration of the behavioral immobility during the last 4min of the test was evaluated. Locomotor activity was evaluated with photoresistor actimeters. Brain and serum concentrations of the studied antidepressants were determined by HPLC method. Sildenafil at a dose of 20mg/kg, but not 5 and 10mg/kg, significantly increased the anti-immobility action of bupropion (20mg/kg). The antidepressant activity of venlafaxine (2mg/kg) was potentiated by joint administration with sildenafil at doses of 10 and 20mg/kg. Since the combined treatments did not increase the locomotor activity, the antidepressant-like effects were not related to non-specific behavioral activation. Data from pharmacokinetic studies revealed that sildenafil increased bupropion and venlafaxine levels in serum without affecting their concentrations in the brain. The present study demonstrates the enhancement of anti-immobility action of bupropion and venlafaxine by sildenafil co-administration. The observed changes might have been partly due to pharmacokinetic interactions. However, mechanisms underlying the effects of sildenafil on the antidepressant activity of bupropion and venlafaxine should be carefully evaluated in further studies.

Novel protective mechanisms of antidepressants against 3-nitropropionic acid induced Huntington's-like symptoms: a comparative study

Huntington's disease (HD) is characterized by progressive degeneration of neurons in the striatum, cortex and other parts of the brain, causing motor and cognitive dysfunction. 3-Nitropropionic acid (3-NP) is a well-known mycotoxin that significantly induces motor dysfunction in animals. Studies suggested the involvement of oxidative stress and nitric oxide mechanisms in HD pathogenesis. Clinical reports have also indicated the neuroprotective potential of antidepressants. Therefore, the present study has been designed to elucidate and compare the mechanistic role of different antidepressants (sertraline, venlafaxine, imipramine and trazodone) and their interaction with nitric oxide modulators if any, against 3-NP-induced neurotoxicity. Systemic 3-NP (10 mg/kg) administration for 14 days significantly reduced locomotor activity, body weight, motor coordination, oxidative defense and impaired mitochondrial complex enzyme activities in the striatum. Sertraline, venlafaxine, imipramine and trazodone treatments significantly improved behavioral, oxidative defense and mitochondrial complex enzyme activities as compared with the 3-NP-treated group. Systemic L-arginine (50 mg/kg) pretreatment with sub-effective dose of sertraline (10 mg/kg), venlafaxine (10 mg/kg), imipramine (10 mg/kg) and trazodone (10 mg/kg) for 14 days significantly attenuated their protective effect. Similarly, L-nitro-arginine methyl ester (L-NAME) (10 mg/kg) pretreatment with sub-effective dose of sertraline (10 mg/kg), venlafaxine (10 mg/kg), imipramine (10 mg/kg) and trazodone (10 mg/kg) for 14 days significantly potentiated their protective effects which were significant as compared with their effect alone, respectively. The results of the present study suggest that a nitric oxide mechanism might be involved in their protective effect against 3-NP-induced neurotoxicity.

Status epilepticus stimulates peroxisome proliferator-activated receptor γ coactivator 1-α/mitochondrial antioxidant system pathway by a nitric oxide-dependent mechanism

Peroxisome proliferator-activated receptor (PPAR) γ coactivator 1-α (PGC-1α) is a transcriptional coactivator identified as an upstream regulator of lipid catabolism, mitochondrial number and function. PGC-1α protects neurons against oxidative damage by inducing several members of the mitochondrial antioxidant system such as superoxide dismutase 2 (SOD2) and uncoupling protein 2 (UCP2). Its role in seizure-induced oxidative stress has not been studied. Here we showed that pilocarpine-induced status epilepticus (SE) stimulates the PGC-1α/mitochondrial antioxidant system signaling pathway in the rat hippocampus. Because nitric oxide (NO) is the key factor of mitochondrial biogenesis through the transcriptional induction of PGC-1α, we investigated whether NO is involved in activation of the PGC-1α/mitochondrial antioxidant system after SE. Treatment with the NO synthase (NOS) inhibitor N(G)-nitro-l-argininemethyl ester (l-NAME) attenuated the increased expression of the PGC-1α/mitochondrial antioxidant system after SE and enhanced oxidative stress. These results suggest that SE can induce the PGC-1α/mitochondrial antioxidant system signaling pathway, which may represent a protective mechanism against SE-induced oxidative stress. Furthermore, NO may positively regulate the mitochondrial antioxidant system by inducing PGC-1α in pilocarpine-induced SE.

Roles of adenosine and serotonin receptors on the antinociception of sildenafil in the spinal cord of rats

PURPOSE

The phosphodiesterase 5 inhibitor sildenafil has antinociceptive effects, mediated by an increase in cGMP. This study examined the role of spinal adenosine and serotonin receptors played in the antinociceptive effects of intrathecal sildenafil.

MATERIALS AND METHODS

Intrathecal catheters were inserted into the subarachnoid space of Sprague-Dawley male rats as a drug delivery device. Pain was induced by injecting formalin into the plantar surface of rats and observing nociceptive behavior (flinching response) for 60 minutes. Then, the effects of intrathecal adenosine and serotonin receptor antagonists on the antinociceptive activity of intrathecal sildenafil were examined.

RESULTS

Intrathecal sildenafil suppressed the flinching response in a dose-dependent manner during phases 1 and 2 in the formalin test. Both CGS 15943 and dihydroergocristine decreased the antinociceptive effects of sildenafil during phases 1 and 2 in the formalin test.

CONCLUSION

Intrathecal sildenafil effectively attenuated the pain evoked by formalin injection. Both adenosine and serotonin receptors may be involved in the antinociceptive action of sildenafil at the spinal level.

Spermidine influence on the nitric oxide synthase and arginase activity relationship during experimentally induced seizures

Nitric oxide (NO), a potential candidate for a modulator of convulsive activity, is a mediator in several pathological events in the central nervous system. The polyamines, spermidine (Spd) and spermine, are neuromodulators influencing the metabolism of L-arginine and NO production. Here we examined the effects of Spd on NO production and arginase activity during convulsions induced by pentylenetetrazol (PTZ). Male Wistar rats were allocated into four experimental groups of 8 animals each and received the following treatments: I (control)--saline, intraperitoneally (i.p.); II (PTZ)--seizures induced by pentylenetetrazol (100mg/kg bw i.p); III (Spd)--Spd (1 mg/kg bw i.p.) 50 min before PTZ application; IV (Mid)--antiepileptic Midazolam (100 mg/kg bw) 45 min before PTZ. In brain cortex, striatum, hippocampus, cerebellum, and brainstem homogenates, nitrite + nitrate levels and arginase activity were determined. Spermidine showed proepileptic effects. shortening seizure latency and inducing a more profound increase of NO production than PTZ in all brain structures. PTZ reduced arginase activity, whereas Spd pretreatment increased enzyme activity, with the most profound effects in cerebellum and brainstem. The results point out the importance of polyamine and arginine metabolism in the brain during seizures, suggesting a regulatory role for polyamines and arginase in NO production.

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.

Seizure protection by intrapulmonary delivery of propofol hemisuccinate

The lung provides a portal of entry for drug delivery that could be used to administer anticonvulsant substances to prevent or abort seizures. Here, we demonstrate that intrapulmonary propofol hemisuccinate (PHS) rapidly confers seizure protection in various rodent chemoconvulsant models. Propofol is a powerful anticonvulsant substance at subanesthetic doses, but it is a viscous, water-immiscible oil that is not suitable for intrapulmonary administration. We found that PHS can be formulated as an aqueous solution that is well tolerated when instilled into the lung. High-dose intraperitoneally administered PHS induced loss-of-righting reflex in rats and mice. The onset of action of PHS was delayed in comparison with propofol, suggesting that conversion to propofol is required for activity. A lower dose of PHS (40 mg/kg i.p.) did not cause general anesthesia but protected against pentylenetetrazol (PTZ)-induced seizures in rats. Intrapulmonary administration of an aqueous PHS solution via a tracheal cannula at lower doses (5 and 10 mg/kg) conferred equivalent seizure protection without acute motor toxicity. In mice, intraperitoneal PHS (60-80 mg/kg) was associated with an elevation in PTZ, bicuculline, picrotoxin, and kainic acid seizure thresholds. Intratracheal PHS was markedly more potent, producing seizure threshold elevations at doses of 10 to 15 mg/kg. In the PTZ threshold model in mice, PHS was active at 5 min, maximally active at 10 min, and no longer active at 20 min. Intratracheal PHS also prolonged the onset of 4-aminopyridine-induced convulsions but did not affect the threshold for N-methyl-D-aspartate-induced convulsions. We conclude that intratracheal administration of an aqueous solution of PHS, a putative propofol prodrug, provides potent seizure protection of rapid onset and brief duration. Intrapulmonary PHS may be useful for preventing the spread of seizures or aborting seizure clusters without causing prolonged sedation.

Nitric oxide mechanism in the protective effect of antidepressants against 3-nitropropionic acid-induced cognitive deficit, glutathione and mitochondrial alterations in animal model of Huntington's disease

Huntington's disease (HD), a basal ganglia disorder, is characterized not only by a spectrum of motor deficits, but also by emotional, cognitive and psychiatric manifestations. Cognitive impairment is one of the serious manifestations of this disease in the later stage of life. Although there is currently no cure for HD, there has been a surge of clinical trials involving patients with HD over the past 5 years. However, cognitive measures have generally been lacking from these trials. The beneficial effect of antidepressants in HD has been suggested in recent clinical trials. However, their mechanism of action is still not clear. Therefore, this study was designed to elucidate and compare the mechanistic role of different classes of antidepressants (sertraline, venlafaxine, imipramine and trazodone) against 3-nitropropionic acid (3-NP)-induced cognitive impairment, oxidative stress (glutathione) and mitochondrial dysfunction in rat hippocampus. Systemic treatment with 3-NP (10 mg/kg for 14 days) significantly impaired memory performance (both in the Morris water maze and elevated plus maze escape retention test), oxidative defence (glutathione redox status) and mitochondrial enzyme complex activities in rat hippocampus. Sertraline, venlafaxine, imipramine and trazodone treatments significantly improved performance in both cognitive tasks and glutathione redox status, and restored mitochondrial enzyme complex activities, as compared with the 3-NP treated group. L-arginine (50 mg/kg) pretreatment for 14 days together with a subeffective dose of sertraline (10 mg/kg), venlafaxine (10 mg/kg), imipramine (10 mg/kg) or trazodone (10 mg/kg) partially attenuated their protective effects. Further, G-nitro-L-Arginine-Methyl Ester (10 mg/kg) pretreatment together with subeffective dose of sertraline (10 mg/kg), venlafaxine (10 mg/kg), imipramine (10 mg/kg) and trazodone (10 mg/kg) significantly enhanced their efficacy. The results of this study suggest that nitric oxide modulation is involved in their protective effect of antidepressants against 3-NP induced cognitive dysfunction in rats.

Endothelial nitric oxide synthase activity involves in the protective effect of ascorbic acid against penicillin-induced epileptiform activity

Ascorbic acid and nitric oxide are known to play important roles in epilepsy. The aim of present study was to identify the involvement of nitric oxide (NO) in the anticonvulsant effects of ascorbic acid on penicillin-induced epileptiform activity in rats. Intracortical injection of penicillin (500, International Units (IU)) into the left sensorimotor cortex induced epileptiform activity within 2-5 min. Thirty minutes after penicillin injection, nitric oxide synthase (NOS) inhibitor, N(G)-nitro-l-arginine methyl ester (l-NAME, 100mg/kg), neuronal nitric oxide synthase (nNOS) inhibitor 7-nitroindazole (7-NI, 40 mg/kg), NO substrate, l-arginine (500 mg/kg) were administered with the most effective dose of ascorbic acid (100 mg/kg) intraperitoneally (i.p.). The administration of l-arginine significantly decreased the frequency of epileptiform activity while administration of l-NAME did not influence the mean frequency of epileptiform activity. Injection of 7-NI decreased the mean frequency of epileptiform activity but did not influence amplitude. Ascorbic acid decreased both the mean frequency and amplitude of penicillin-induced epileptiform activity in rats. The application of l-NAME partially and temporarily reversed the anticonvulsant effects of ascorbic acid. The results support the hypothesis of neuro-protective role for NO and ascorbic acid. The protective effect of ascorbic acid against epileptiform activity was partially and temporarily reversed by nonspecific nitric oxide synthase inhibitor l-NAME, but not selective neuronal nitric oxide synthase inhibitor 7-NI, indicating that ascorbic acid needs endothelial-NOS/NO route to decrease penicillin-induced epileptiform activity.

Effect of sildenafil on the anticonvulsant action of classical and second-generation antiepileptic drugs in maximal electroshock-induced seizures in mice

PURPOSE

The goal of the present study was to evaluate the effects of sildenafil on the threshold for electrically induced seizures in mice. In addition, interactions between sildenafil and classical and second-generation antiepileptic drugs (AEDs), that is, carbamazepine (CBZ), phenobarbital (PB), phenytoin (PHT), valproate (VPA), lamotrigine (LTG), topiramate (TPM), and oxcarbazepine (OXC) were evaluated.

METHODS

Two electroconvulsive tests were used: maximal electroshock seizure threshold (MEST) and maximal electroshock seizure (MES) tests in mice. Acute adverse effects of the studied combinations were investigated in the chimney test, step-through passive avoidance task, and grip-strength test. Total brain and free plasma concentrations of AEDs were also determined.

RESULTS

Sildenafil raised the threshold for electroconvulsions in a dose-dependent manner. It also increased the anticonvulsant activity of CBZ, VPA, and TPM in the MES test, whereas the activity of the remaining AEDs was not significantly changed. Sildenafil increased total brain and free (protein unbound) plasma CBZ concentrations and total brain VPA concentration. Neither sildenafil nor its coadministration with the studied AEDs affected motor coordination and long-term memory in mice. Interestingly, sildenafil dose-dependently enhanced the skeletal muscle strength in mice, although combinations of sildenafil with AEDs were ineffective in this respect.

CONCLUSIONS

Sildenafil significantly raised the threshold for electroconvulsions in mice without any impairment of motor performance and long-term memory, but it enhanced muscle strength. Treatment of patients on CBZ or VPA with sildenafil may not be recommended due to pharmacokinetic interactions. Coadministration of sildenafil with other AEDs, especially with TPM, seems to be a reasonable choice.

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.

Lycopene modulates nitric oxide pathways against 3-nitropropionic acid-induced neurotoxicity

AIM

The present study has been designed to investigate the involvement of the nitric oxide mechanism in the protective effect of lycopene against 3-nitropropionic acid-induced Huntington's disease-like symptoms in rats.

MAIN METHODS

The present experimental protocol design includes systemic 3-nitropropionic acid (10mg/kg i.p) treatment for 14 days. Lycopene (2.5, 5 and 10mg/kg) was given orally, once a day, 1h before 3-nitropropionic acid treatment for 14 days. Body weight and behavioral parameters (locomotor and rotarod activity) were assessed on 1st, 5th, 10th and 15th day post-3-nitropropionic acid administration. Malondialdehyde, nitrite concentration, superoxide dismutase and catalase levels were measured on the 15th day in the striatum, cortex and hippocampus. Mitochondrial enzyme complexes were also assessed in these brain areas. Systemic 3-nitropropionic acid treatment significantly reduced body weight, locomotor activity and oxidative defense. The mitochondrial enzyme activities were also significantly impaired in the examined brain regions in 3-nitropropionic acid-treated animals.

KEY FINDINGS

Lycopene (2.5, 5 and 10mg/kg) treatment significantly attenuated the impairment in behavioral, biochemical and mitochondrial enzyme activities as compared to the 3-nitropropionic acid-treated group. l-arginine (50mg/kg) pretreatment with a sub-effective dose of lycopene (5mg/kg) significantly attenuated the protective effect of lycopene. Furthermore, L-NAME (10mg/kg) pretreatment with a sub-effective dose of lycopene (5mg/kg) for 14 days significantly potentiated the protective effect.

SIGNIFICANCE

The results of the present study suggest that the nitric oxide modulation is involved in the protective effect of lycopene against 3-NP-induced behavioral, biochemical and cellular alterations in rats.

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.

Effect of lycopene and epigallocatechin-3-gallate against 3-nitropropionic acid induced cognitive dysfunction and glutathione depletion in rat: a novel nitric oxide mechanism

Huntington's disease is a neurodegenerative disorder characterized by symptoms like chorea and dementia. There is no exact therapeutic agent available to manage and cure this disease. 3-Nitropropionic acid, a neurotoxin causes gait and memory impairment which leads to oxidative damage and upsets glutathione defense in animals. 3-NP model is a useful tool to develop suitable therapeutic agent in the treatment of Huntington's disease. Present study compares the effects of lycopene and epigallocatechin-3-gallate (EGCG) on memory impairment and disturbs glutathione system against 3-NP treatment. 3-NP treatment significantly impaired memory as assessed in Morris water maze and elevated plus maze tasks. On the 15 day, the levels of reduced glutathione, total glutathione and glutathione-S-transferase were also significantly decreased in the striatum, hippocampus and cortex areas of the brain. The treatment with lycopene (2.5, 5 and 10mg/kg) and EGCG (10, 20 and 40 mg/kg) significantly improved memory and restored glutathione system functioning. Further, L-arginine and L-NAME pretreatment with the sub effective dose of lycopene (5mg/kg) and EGCG (20mg/kg) reversed and potentiate their protective effects respectively. In conclusion, lycopene and EGCG could be used to mange 3-NP induced behavioral and biochemical alterations by involving nitric oxide pathways.