Seizure susceptibility alteration through 5-HT3 receptor: Modulation by nitric oxide

There is some evidence that epileptic seizures could be induced or increased by 5-hydroxytryptamine (5-HT) attenuation, while augmentation of serotonin functions within the brain (e.g. by SSRIs) has been reported to be anticonvulsant. This study was performed to determine the effect of selective 5-HT₃ channel/receptor antagonist granisetron and agonist SR57227 hydrochloride on the pentylenetetrazole (PTZ)-induced seizure threshold in mice. The possible interaction of this effect with nitrergic system was also examined using the nitric oxide (NO) synthase inhibitor N^G-nitro-l-arginine methyl ester (l-NAME) and the NO precursor l-arginine. SR57227 (10 mg/kg, i.p.) significantly increased the seizure threshold compared to control group, while high dose granisetron (10 mg/kg, i.p.) proved proconvulsant. Co-administration of sub-effective doses of the 5-HT₃ agonist with l-NAME (5 and 60 mg/kg, i.p., respectively) exerted a significant anticonvulsive effect, while sub-effective doses of granisetron (3 mg/kg) was observed to have a proconvulsive action with the addition of l-arginine (75 mg/kg, i.p.). Our data demonstrate that enhancement of 5-HT₃ receptor function results in as anticonvulsant effect in the PTZ-induced seizure model, and that selective antagonism at the 5-HT₃ receptor yields proconvulsive effects. Furthermore, the NO system may play a role in 5-HT₃ receptor function.     

Levetiracetam in submaximal subcutaneous pentylentetrazol-induced seizures in rats

Despite anticonvulsant efficacy in animal models of generalized epilepsy, levetiracetam was not effective in the maximal subcutaneous PTZ model in mice and rats.Aim of this study was to assess the efficacy of levetiracetam (LEV) against submaximal, s.c. MET test (PTZ at the dose of 70 mg/kg) acute seizures in Wistar rats, in comparison to valproic acid (VPA).Thirty male Wistar rats (P42) were divided in three drug-treatment groups (10 rats in each group) as follows: valproic acid, levetiracetam, and controls. All animals were tested for seizure threshold at age P50. VPA (110 mg/kg) and LEV (108 mg/kg) were freshly dissolved in saline and injected i.p. in 2–3 ml/kg, 15 and 30 min, respectively, before pentylenetetrazol (PTZ) injection at the dose of 70 mg/kg.The average latency of the seizure type 3 (generalized clonic seizure with loss of righting reflexes) significantly differed between controls and the drug-treated animal groups (p ≤ 0.02). The average duration of the seizure type 2 (threshold seizure) was significantly longer in both groups compared to controls (<0.02).In conclusion, LEV plays a role against seizures triggered by subcutaneous PTZ injection given at submaximal doses in rats, as demonstrated by a significant increase in duration of the seizure type 2 (threshold seizure).     

Two mechanisms underlie the slow noradrenergic depolarization in the rat tail artery in vitro

In rat tail artery, short trains of electrical stimuli evoke both ATP-mediated excitatory junction potentials (EJPs) and a slow noradrenaline (NA)-mediated depolarization (NAD). Here we have investigated the contribution of α₁- and α₂-adrenoceptors to the NAD. The α₁-adrenoceptor antagonist, prazosin (0.1 μM), and the α₂-antagonist, rauwolscine (1 μM), reduced the amplitude of the NAD and in combination these agents virtually abolished the NAD. The K_ATP channel blocker, glibenclamide (10 μM) abolished the α₂-adrenoceptor-mediated component of the NAD, indicating that activation of these receptors produces closure of K_ATP channels. The α₁-adrenoceptor-mediated component of the NAD was increased in amplitude by glibenclamide. Changes in membrane conductance were monitored by measuring the time constant of decay of EJPs (τEJP). The τEJP was increased during α₁-adrenoceptor-mediated depolarization, indicating a decrease in membrane conductance; i.e. closure of K⁺ channels. Broad-spectrum K⁺ channel blockers (tetraethylammonium, 4-aminopyridine, Ba²⁺) and the TASK-1 K⁺ channel blocker, anandamide (10 μM), did not reduce the α₁-adrenoceptor-mediated NAD. The α₁-adrenoceptor-mediated NAD was unaffected by the Cl^? channel blockers, 9-anthracene carboxylic acid (100 μM) and niflumic acid (10 μM) or by the non-selective cation channel blocker, SKF 96365 (10 μM). These findings indicate that the NAD is produced by activation of both α₁-and α₂-adrenoceptors. The α₂-adrenoceptor-mediated component is produced by closure of K_ATP channels whereas the α₁-adrenoceptor-mediated component is most likely mediated by closure of another type of K⁺ channel.     

Mouth breathing increases the pentylenetetrazole-induced seizure threshold in mice: a role for ATP-sensitive potassium channels

Nasal obstruction and consequent mouth breathing have been shown to change the acid–base balance, producing respiratory acidosis. Additionally, there exists a large body of evidence maintaining that acidosis affects the activity of ATP-sensitive potassium (K_ATP) channels, which play a crucial role in the function of the central nervous system (CNS), for example, in modulating seizure threshold. Thus, in the study described here, we examined whether mouth breathing, induced by surgical ligation of nostrils, could affect the seizure threshold induced by pentylenetetrazole in male NMRI mice. Using the selective K_ATP channel opener (diazoxide) and blocker (glibenclamide), we also evaluated the possible role of K_ATP channels in this process. Our data revealed that seizure threshold was increased 6 to 72 hours after nasal obstruction, reaching a peak 48 hours afterward, compared with either control or sham-operated mice (P < 0.01). There was a significant decrease in pH of arterial blood samples and increase in CO₂ partial pressure (PCO₂) during this time. Systemic injection of glibenclamide (1 and 2 mg/kg, ip, daily) significantly prevented the increase in seizure threshold in 48-hour bilaterally nasally obstructed mice, whereas it had no effect on seizure threshold in sham-operated mice. Systemic injection of diazoxide (25 mg/kg, ip, daily) had no effect on seizure threshold in all groups, whereas higher doses (50 and 100 mg/kg, ip, daily) significantly increased seizure threshold in both 48-hour-obstructed and sham-operated mice. The decrease in seizure threshold induced by glibenclamide (2 mg/kg, ip, daily) was prevented by diazoxide (25 mg/kg, ip, daily). These results demonstrate for the first time that mouth breathing, which could result in respiratory acidosis, increases seizure threshold in mice and K_ATP channels may play a role in this effect.     

Probing the role of the sodium/calcium exchanger in pentylenetetrazole-induced generalized seizures in rats

The Na⁺/Ca²⁺ exchanger (NCX) is thought to play an important role in the pathogenesis of pentylenetetrazole (PTZ)-induced tonic flexion in mice. Here, I investigated the expression of PTZ-induced generalized clonic and tonic–clonic seizures in rats, using two potent NCX reverse mode inhibitors, KB-R7943 and SN-6 for NCX subtypes 3 (NCX3) and 1 (NCX1), respectively. Pretreatment with KB-R7943 (3, 10, and 30 mg/kg; p.o.) significantly reduced the expression of PTZ-induced generalized seizures with clonic and tonic–clonic components in 12–62% and 25–62% of the treated animals, respectively. In the remaining animals that exhibited seizures, KB-R7943 (3 mg/kg; p.o.) pretreatment significantly delayed the onset of the first seizure episode and reduced the seizure severity. Following pretreatment with SN-6 (0.3, 1, 3, 10, and 30 mg/kg; p.o.), clonic and tonic–clonic PTZ-induced generalized seizures were reduced in 25–50% and 38–63% of treated animals, respectively. SN-6 (0.3, 1, and 3 mg/kg; p.o.) also significantly reduced PTZ-induced seizure severity scores, but did not alter seizure latencies. KB-R7943 (3 and 30 mg/kg; p.o.) or SN-6 (3 and 30 mg/kg; p.o.) administration potentiated the sub-anticonvulsant dose of diazepam (2.5 mg/kg; i.p.) that suppresses clonic and tonic–clonic PTZ-induced seizures. These findings suggested that Ca²⁺ influx via the NCX in reverse mode contributes to a neuronal hyperexcitability that leads to clonic and tonic–clonic generalized seizures and that the NCX1 and NCX3 isoforms may serve as novel molecular targets for seizure suppression.     

Evidence for the involvement of 5-HT1A receptor in the acute antidepressant-like effect of creatine in mice

Creatine was previously shown to produce an antidepressant-like effect in the tail suspension test through a modulation of the dopaminergic system. In this study, the mechanisms underlying its antidepressant-like effect were further evaluated by investigating the involvement of the serotonergic system in its effect. The anti-immobility effect of creatine (1 mg/kg) was prevented by the pretreatment of mice with p-chlorophenylalanine methyl ester (PCPA; 100 mg/kg, i.p., for 4 consecutive days, an inhibitor of serotonin (5-HT) synthesis). Creatine (0.01 mg/kg, sub-effective dose) in combination with sub-effective doses of WAY100635 (0.1 mg/kg, s.c., a 5-HT_1A receptor antagonist), 8-OH-DPAT (0.1 mg/kg, i.p., a 5-HT_1A receptor agonist) or selective serotonin reuptake inhibitors fluoxetine (5 mg/kg, p.o.), paroxetine (0.1 mg/kg, p.o.), citalopram (0.1 mg/kg, p.o.) and sertraline (3 mg/kg, p.o.) reduced the immobility time in the tail suspension test as compared with either drug alone. These results indicate that the antidepressant-like effect of creatine is likely mediated by an interaction with 5-HT_1A receptors. Of note, the present results also indicate that creatine improves the effectiveness of the selective serotonin reuptake inhibitors, a finding that may have therapeutic implications for the treatment of depressive disorders.     

The antidepressant sertraline prevents the behavioral and EEG changes induced in two animal models of seizures

In order to investigate a potential anticonvulsive action of sertraline (i.p.), its effects on seizures, EEG epileptiform activity and EEG amplitude increases induced by two convulsive agents were evaluated and compared with the effects of carbamazepine. Around 20 min following 4-aminopyridine (4-AP, 2.5 mg/kg, i.p.), tonic-clonic seizures and epileptiform activity were observed in control animals. A single sertraline pre-injection of 2.5 mg/kg, but not of 0.75 mg/kg, prevented these changes to 4-AP. Repeated daily administration of 0.75 mg/kg for one week, however, effectively inhibited the changes induced by 4-AP. The first generalized tonic-clonic seizure and EEG changes in response to pentylenetetrazole (PTZ, 50 mg/kg, i.p.) were observed near the first minute in control animals. Single sertraline doses above 5 mg/kg prevented the PTZ-induced changes. Moreover, a single carbamazepine dose of 25 mg/kg (i.p.), but not of 15 mg/kg, prevented the changes induced by the above convulsive agents. An anti-seizure action of the antidepressant sertraline is strongly suggested by these findings.     

Involvement of ATP-sensitive potassium channels and the opioid system in the anticonvulsive effect of zolpidem in mice

Zolpidem is a hypnotic medication that mainly exerts its function through activating γ-aminobutyric acid (GABA)_A receptors. There is some evidence that zolpidem may have anticonvulsive effects. However, the mechanisms underlying this effect have not been elucidated yet. In the present study, we used the pentylentetrazole (PTZ)-induced generalized seizure model in mice to investigate whether zolpidem can affect seizure threshold. We also further evaluated the roles of ATP-sensitive potassium (K_ATP) channels as well as μ-opioid receptors in the effects of zolpidem on seizure threshold. Our data showed that zolpidem in a dose-dependent manner increased the PTZ-induced seizure threshold. The noneffective (i.e., did not significantly alter the PTZ-induced seizure threshold by itself) doses of K_ATP channel blocker (glibenclamide) and nonselective opioid receptor antagonist (naloxone) were able to inhibit the anticonvulsive effect of zolpidem. Additionally, noneffective doses of either K_ATP channel opener (cromakalim) or nonselective μ-opioid receptor agonist (morphine) in combination with a noneffective dose of zolpidem exerted a significant anticonvulsive effect on PTZ-induced seizures in mice. A combination of noneffective doses of naloxone and glibenclamide, which separately did not affect zolpidem effect on seizure threshold, inhibited the anticonvulsive effects of zolpidem. These results suggest a role for K_ATP channels and the opioid system, alone or in combination, in the anticonvulsive effects of zolpidem.     

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

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

Rosmarinic acid is anticonvulsant against seizures induced by pentylenetetrazol and pilocarpine in mice

Epilepsy is a chronic neurological disease characterized by spontaneous recurrent seizures (SRS). Current anticonvulsant drugs are ineffective in nearly one-third of patients and may cause significant adverse effects. Rosmarinic acid is a naturally occurring substance which displays several biological effects including antioxidant and neuroprotective activity. Since oxidative stress and excitotoxicity play a role in the pathophysiology of seizures, we aimed the present study to test the hypothesis that rosmarinic acid displays anticonvulsant and disease-modifying effects. Female C57BL/6 mice received rosmarinic acid (0, 3, 10, or 30 mg/kg; p.o.) 60 min before the injection of pentylenetetrazol (PTZ, 60 mg/kg; i.p.) or pilocarpine (300 mg/kg, i.p.). Myoclonic and generalized tonic–clonic seizure latencies and generalized seizure duration were analyzed by behavioral and electroencephalographic (EEG) methods. The effect of acute administration of rosmarinic acid on mice behavior in the open-field, object recognition, rotarod, and forced swim tests was also evaluated. In an independent set of experiments, we evaluated the effect of rosmarinic acid (3 or 30 mg/kg, p.o. for 14 days) on the development of SRS and behavioral comorbidities in the pilocarpine post-status epilepticus (SE) model of epilepsy. Rosmarinic acid dose-dependently (peak effect at 30 mg/kg) increased the latency to myoclonic jerks and generalized seizures in the PTZ model and increased the latency to myoclonic jerks induced by pilocarpine. Rosmarinic acid (30 mg/kg) increased the number of crossings, the time at the center of the open field, and the immobility time in the forced swim test. In the chronic epilepsy model, treatment with rosmarinic acid did not prevent the appearance of SRS or behavioral comorbidities. In summary, rosmarinic acid displayed acute anticonvulsant-like activity against seizures induced by PTZ or pilocarpine in mice, but further studies are needed to determine its epilepsy-modifying potential.     

Effects of asenapine,olanzapine, and risperidone on psychotomimetic-induced reversal-learning deficits in the rat

BackgroundAsenapine is a new pharmacological agent for the acute treatment of schizophrenia and bipolar disorder. It has relatively higher affinity for serotonergic and α₂-adrenergic than dopaminergic D₂ receptors. We evaluated the effects of asenapine, risperidone, and olanzapine on acute and subchronic psychotomimetic-induced disruption of cued reversal learning in rats.MethodsAfter operant training, rats were treated acutely with d-amphetamine (0.75 mg/kg intraperitoneally [i.p.]) or phencyclidine (PCP; 1.5 mg/kg i.p.) or subchronically with PCP (2 mg/kg i.p. for 7 days). We assessed the effects of acute coadministration of asenapine, risperidone, or olanzapine on acute d-amphetamine- and PCP-induced deficits and the effects of long-term coadministration of these agents (for 28 additional days) on the deficits induced by subchronic PCP.ResultsDeficits in reversal learning induced by acute d-amphetamine were attenuated by risperidone (0.2 mg/kg i.p.). Acute PCP-induced impairment of reversal learning was attenuated by acute asenapine (0.025 mg/kg subcutaneously [s.c.]), risperidone (0.2 mg/kg i.p.), and olanzapine (1.0 mg/kg i.p.). Subchronic PCP administration induced an enduring deficit that was attenuated by acute asenapine (0.075 mg/kg s.c.) and by olanzapine (1.5 mg/kg i.p.). Asenapine (0.075 mg/kg s.c.), risperidone (0.2 mg/kg i.p.), and olanzapine (1.0 mg/kg i.p.) all showed sustained efficacy with chronic (29 days) treatment to improve subchronic PCP-induced impairments.ConclusionThese data suggest that asenapine may have beneficial effects in the treatment of cognitive symptoms in schizophrenia. However, this remains to be validated by further clinical evaluation.     

Electrical stimulation of left anterior thalamic nucleus with high-frequency and low-intensity currents reduces the rate of pilocarpine-induced epilepsy in rats

PurposeBilateral electrical stimulation of anterior nuclei of thalamus (ANT) has shown promising effects on epileptic seizures. However, bilateral implantation increases the risk of surgical complications and side effects. This study was undertaken to access the effectiveness of a stimulation paradigm involving high frequency and low intensity currents to stimulate the left ANT in rats.MethodsMale Sprague-Dawley rats were implanted with electroencephalogram (EEG) electrodes, and an additional concentric bipolar stimulation electrode into either the left or right ANT. The stimulus was a train of pulses (90 μs duration each) delivered with a frequency of 200 Hz and a current intensity of 50 μA. Thalamic stimuli were started 1 h before the first intraperitoneal pilocarpine injection (i.p., 300 mg/kg), and were applied for 5 h.ResultsEEG documented seizure activity and status epilepticus (SE) developed in 87.5% of rats treated with no ANT stimulation after a single dose of pilocarpine. Left ANT stimulation significantly increased the tolerance threshold for pilocarpine-induced EEG seizure activity; 20% of rats developed their EEG documented seizure activity after receiving the first dose, whereas 50%, 10% and 20% of rats did not develop seizure activity until they had received the 2nd, 3rd and 4th pilocarpine injection at 1-h intervals. Moreover, left thalamic stimulation reduced the occurrences of both EEG documented seizure activity and SE induced by single-dose pilocarpine to 25%. However, our result demonstrated that little effect on the occurrence rate of seizures and SE was found when rats received right ANT stimulation.ConclusionsThese results suggest that continuously 5-h left ANT stimulation with high frequency and low intensity currents, beginning from 1 h before the pilocarpine administration, may successfully reduce the occurrence rate of EEG documented seizure activity and SE development in rats.     

A possible participation of gonadotropin-releasing hormone in the neuroleptic and cataleptic effect of haloperidol

Haloperidol, an antipsychotic agent, stimulates the release of gonadotropin-releasing hormone (GnRH), and this hormone is known to mimic some of the behavioral effects of haloperidol. Hence, the present study was carried out to find out the contribution of GnRH in the behavioral effects of haloperidol. The studies revealed that haloperidol (0.15, 0.25 and 0.5 mg/kg, i.p.) and leuprolide (GnRH agonist; 50, 100, 200 and 400 μg/kg, s.c.) dose-dependently inhibited conditioned avoidance response (CAR) in male Sprague–Dawley rats. In higher doses, haloperidol (0.5, 1 mg/kg, i.p.) and leuprolide (200, 400 μg/kg, s.c.) produced catalepsy in rats. Co-administration of sub-effective dose of leuprolide (50 or 100 μg/kg, s.c.) and haloperidol (0.15 or 0.5 mg/kg, i.p.) similarly inhibited CAR and induced catalepsy. Pre-treatment of rats with antide (GnRH antagonist; 10 μg/rat, s.c.), attenuated the inhibitory effect of both the agents on CAR; blocked leuprolide-induced catalepsy; and attenuated the intensity and reduced the duration of haloperidol-induced catalepsy. In conclusion, the studies suggest a possible role of GnRH in the neuroleptic and cataleptic effect of haloperidol.     

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

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

Effects of agomelatine on pentylenetetrazole-induced kindling,kindling-associated oxidative stress,and behavioral despair in mice and modulation of its actions by luzindole and 1-(m-chlorophenyl) piperazine

In view of well-evidenced antiepileptic effects of melatonin and few reports of anticonvulsant action of agomelatine, the present study investigated whether agomelatine protects against pentylenetetrazole (PTZ)-induced kindling in mice and kindling-associated oxidative stress, depression, and impairment of spatial memory. In order to explore whether effects are mediated by melatonergic or serotonergic mechanisms, 1-(m-chlorophenyl) piperazine (mCPP), selective 5HT2c receptor agonist and luzindole, melatonergic receptor antagonist, were taken as pharmacological tools. In view of few hepatotoxic reports on agomelatine, the study evaluated effects on hepatic enzyme levels. Swiss strain albino mice were injected with PTZ (25 mg/kg, i.p.) once every two days for 5 weeks to induce kindling. The effects of agomelatine (10 mg/kg, p.o.) alone and in combination with luzindole (2.5 mg/kg, i.p.) or mCPP (7 mg/kg, i.p.) on seizure severity during induction and % incidence of animals kindled at the end of 5 weeks were recorded. Modified forced swim test was used for studying depression-like behavior while spontaneous alternation behavior was used for studying effects on spatial memory. Serum AST and ALT concentrations, cortical and hippocampal malondialdehyde, and reduced glutathione were measured. Agomelatine 10 mg/kg, p.o. effectively delayed development of kindling, reduced seizure severity, and decreased % incidence. Luzindole reversed the protective effects of agomelatine while mCPP failed to show such a reversal, indicating melatonergic (and not serotonergic) mechanisms in the observed effects. Agomelatine also showed antioxidant effects that can partially contribute to its anticonvulsant action. In addition, it alleviated PTZ-kindling-associated behavioral despair and favorably modulated liver enzymes. Its effects on improvement of kindling-associated spatial memory could possibly be related to its effects on locomotor activity. Agomelatine, thus, could be explored as an adjunct to antiepileptic drugs for seizure control and for alleviating epilepsy-associated depression.     

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 6 h 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^ω-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.     

Trimetazidine exerts protection against increasing current electroshock seizure test in mice

Trimetazidine, a novel anti-ischemic agent, is used in the therapy of angina, vertigo and chorioretinal diseases. It has also been examined for its effect on nociception, inflammation and neuroprotection in various animal models. The present study was designed to investigate the effect of trimetazidine on electrically induced seizures in mice. Trimetazidine was administered orally in doses of 5, 10 and 20 mg/kg (single dose) to observe its effect on the increasing current electroshock seizure (ICES) test in mice. Trimetazidine in 10 and 20 mg/kg doses significantly raised the seizure-threshold current in the ICES test. Further, co-administration of per se ineffective dose of trimetazidine (5 mg/kg, p.o.) with sub-anticonvulsant dose of nimodipine (10 mg/kg, p.o.) and phenytoin (12.5 mg/kg, p.o.) offered significant protection in the ICES test. These results indicate that trimetazidine possesses significant anticonvulsant activity against electro-convulsions in the mice.     

The neuroprotective effect of diazoxide is mediated by mitochondrial ATP-dependent potassium channels in a rat model of acute subdural hematoma

Acute subdural hematoma (ASDH) results in neuronal death due to mitochondrial dysfunction and a subsequent cascade of apoptotic and necrotic events. We previously demonstrated that mitochondrial ATP-dependent potassium (mitoK_ATP) channels have a major role in cerebral ischemic preconditioning in vivo and in vitro. However, the role of the mitoK_ATP channel has not been investigated in the context of ASDH. Thus, the purpose of this study was to determine whether the mitoK_ATP channel mediates neuroprotection in a rat model of ASDH. Male Wistar rats were subjected to subdural infusion of 400 μL autologous venous blood. The rats were assigned to four experimental groups pretreated intraventricularly 15 minutes before ASDH with (1) vehicle (n = 10); (2) the mitoK_ATP channel agonist diazoxide (n = 9); (3) diazoxide plus the selective mitoK_ATP channel antagonist 5-hydroxydecanoate (5-HD) (n = 6); or (4) 5-HD alone (n = 6). Infarct volume was assessed at 4 days after ASDH. Brain edema formation was also measured. Pretreatment with diazoxide significantly reduced infarct volume and brain edema formation after ASDH. However, the effects of diazoxide were abolished by co-treatment with 5-HD. 5-HD alone increased infarct volume. These data suggest that the mitoK_ATP channel is an important mediator of the neuroprotective effects of cerebral preconditioning in a rat model of ASDH.     

GABAB receptor activation exacerbates spontaneous spike-and-wave discharges in DBA/2J mice

Rich evidence has highlighted that stimulation of γ-amino-butyric acid (GABA)_B receptors increases the occurrence of spike-and-wave discharges (SWDs), the electroencephalographic (EEG) landmark of absence epilepsy (AE). Recent findings suggest that the outcomes of GABA_B activation in vivo are contingent on the chemical characteristics of the agonist. In particular, the endogenous ligand γ-hydroxybutyrate (GHB) and its precursor γ-butyro-lactone (GBL) have been shown to elicit different effects than the prototypical GABA_B agonist baclofen. In view of these premises, the present study was aimed at the characterization of the effects of baclofen (0.5–10 mg/kg, i.p.) and GBL (5–100 mg/kg, i.p.) on the spontaneous SWDs and locomotor activity of DBA/2J mice.While both baclofen and GBL dose-dependently increased SWDs episodes, high doses of the latter (100 mg/kg, i.p.) reduced the occurrence of these phenomena and increased the number of isolated spikes. Interestingly, both compounds elicited a dose-dependent reduction of locomotor activity, in comparison with their vehicle-treated controls. The GABA_B selective antagonist, SCH50911 (50 mg/kg, i.p.), reversed the changes in SWD occurrence and locomotion induced by baclofen and GBL, but failed to elicit intrinsic effects on either paradigm. These results indicate that GABA_B receptor signaling might exert differential effects on SWDs in DBA/2J mice.     

Mechanisms operated by endothelin ETA and ETB receptors in the trigeminal ganglion contribute to orofacial thermal hyperalgesia induced by infraorbital nerve constriction in rats

Endothelins, acting through specific endothelin ET_A and/or ET_B receptors, participate in nociceptive processing in models of cancer, inflammatory and neuropathic pain. The present study investigated which cell types express endothelin receptors in the trigeminal ganglion, and the contribution of mechanisms mediated by endothelin ET_A and ET_B receptors to orofacial heat hyperalgesia induced by unilateral constriction of the infraorbital nerve (CION). Both receptor types were identified by immunohistochemistry in the trigeminal ganglion, ET_A receptors on small-sized non-myelinated and myelinated A-fibers and ET_B receptors on both satellite glial cells and small-sized non-myelinated neuronal cells. CION promoted ipsilateral orofacial heat hyperalgesia which lasted from Day 2 until Day 10 after surgery. Ongoing CION-induced heat hyperalgesia (on Day 4) was reduced transiently, but significantly, by systemic or local treatment with antagonists of endothelin ET_A receptors (atrasentan, 10 mg/kg, i.v.; or BQ-123, 10 nmol/lip), endothelin ET_B receptors (A-192621, 20 mg/kg, i.v.; or BQ-788, 10 nmol/ lip), or of both ET_A/ET_B receptors (bosentan, 10 mg/kg, i.v.; or BQ-123 plus BQ-788, each at 10 nmol/lip). On the other hand, CION-induced heat hyperalgesia was transiently abolished over the first 90 min following i.p. injection of morphine hydrochloride (2.5 mg/kg), but fully resistant to reversal by indomethacin (4 mg/kg, i.p.) or celecoxib (10 mg/kg, i.p.). Thus, heat hyperalgesia induced by CION is maintained, in part, by peripheral signaling mechanisms operated by ET_A and ET_B receptors. Endothelin receptors might represent promising therapeutic targets for the control of trigeminal neuropathic pain.