Anticonvulsant effects of nimodipine and two novel dihydropyridines (PCA 50922 and PCA 50941) against seizures elicited by pentylenetetrazole and electroconvulsive shock in mice

Effects of Pregabalin, Nimodipine, and Their Combination in the Inhibition of Status Epilepticus and the Prevention of Death in Mice

Objectives

The current study aims to evaluate the combined antiepileptic effects of pregabalin (PGB) and nimodipine (NMD) in an acute seizure model of epilepsy in mice.

Materials and Methods

This study assessed the combined antiepileptic effects of PGB with NMD on death protection in mice. Pentylenetetrazole was used to induce seizures. Both drugs were used singly and in combination to judge anticonvulsant effects on an acute seizure model of epilepsy in mice. Diazepam (DZ) and valproate (VPT) were used as standard antiepileptic drugs.

Results

The death protection in mice by both these drugs was observed in percentage and deliberated as marked change when the outcome of the tested drug was equal to ED₅₀ of PGB and measured highly marked when the result was more than ED₅₀ for PGB. Treatment with pregabalin and nimodipine combination revealed substantial mortality protection at 30+2.5 mg/kg dose and highly marked at doses from 35+5 mg/kg to 55+15 mg/kg, these effects were superior to individual effects of PGB, showing synergism, however lesser then classic drugs valproate and diazepam.

Conclusion

NMD showed synergistic anticonvulsant effect with PGB. However, clinical studies are required to establish the effectiveness of this combination in humans.

The effects of dairy products on seizure tendency in mice

Epilepsy is a common neurological disorder which occurs as a result of a spontaneous electrical discharge in the brain. According to recent studies there might be a relationship between specific diet and seizure occurrence. Casein is an important protein of milk which often causes hypersensitivity. It seems the release of inflammatory cytokines during the process of immune system response alter the blood-brain-barrier (BBB) integrity and lead to neuronal inflammation which could constitute on epileptogenic focus. On the other hand, several studies represent full-fat milk or higher fat dairy products as an effective anti-inflammatory factor which elevate seizure threshold. The aim of present study was investigation of acute and chronic effects of dairy products including dough (a yogurt-based beverage), cheese, low and high fat yogurt and milk on pentylenetetrazole (PTZ)-induced seizures or electroshock in mice. The results of study indicated that lower fat dairy products reduced seizure threshold in intravenous PTZ-induced seizure as well as reduction in myoclonic and clonic jerk latencies in intraperitoneal PTZ-induced seizure. High fat products or cheese reduced seizure activity in both PTZ-induced models. Meanwhile both acute and chronic administration of dairy products had no effect on an electroshock-induced seizure. Therefore, diet-related seizures may depend upon the method which seizures are provoked.

Synergistic anticonvulsant effects of pregabalin and amlodipine on acute seizure model of epilepsy in mice

Status epilepticus is a life threatening neurological medical emergency. It may cause serious damage to the brain and even death in many cases if not treated properly. There is limited choice of drugs for the short term and long term management of status epilepticus and the dugs recommended for status epilepticus possess various side effects. The present study was designed to investigate synergistic anticonvulsant effects of pregabalin with amlodipine on acute seizure model of epilepsy in mice. Pentylenetetrazole was used to induce acute seizures which mimic status epilepticus. Pregabalin and amlodipine were used in combination to evaluate synergistic anti-seizure effects on acute seizure model of epilepsy in mice. Diazepam and valproate were used as reference dugs. The acute anti-convulsive activity of pregabalin with amlodipine was evaluated in vivo by the chemical induced seizures and their anti-seizure effects were compared with pentylenetetrazole, reference drugs and to their individual effects. The anti-seizure effects of tested drugs were recorded in seconds on seizure characteristics such as latency of onset of threshold seizures, rearing and fallings and Hind limbs tonic extensions. The seizure protection and mortality to the animals exhibited by the drugs were recorded in percentage. Combination regimen of pregabalin with amlodipine exhibited dose dependent significant synergistic anticonvulsant effects on acute seizures which were superior to their individual effects and equivalent to reference drugs.

Combining nanoscale magnetic nimodipine liposomes with magnetic resonance image for Parkinson's disease targeting therapy

AIM

To enhance drug targeting and blood-brain barrier penetration for Parkinson's disease (PD), a novel nanoscale magnetic nimodipine (NMD) delivery system was designed and prepared.

MATERIALS & METHODS

The PD rats were established and treated with free NMD or Fe₃O₄-modified NMD liposomes (Fe₃O₄-NMD-lips). Then, factional anisotropy values were measured by MRI to evaluate therapy efficacy.

RESULTS

Fe₃O₄-NMD-lips showed the best neuroprotective effect, and the NMD concentration of lesions was 2.5-fold higher in Fe₃O₄-NMD-lips group than that of free NMD group.

CONCLUSION

These results demonstrated that the magnetic drug system had a great potential to cross the blood-brain barrier and provided a noninvasive and effective therapeutic strategy for PD.

Evaluation of effects of T and N type calcium channel blockers on the electroencephalogram recordings in Wistar Albino Glaxo/Rij rats, an absence epilepsy model

OBJECTIVES

It is suggested that excessive calcium entry into neurons is the main triggering event in the initiation of epileptic discharges. We aimed to investigate the role of T and N type calcium channels in absence epilepsy experimental model.

MATERIALS AND METHODS

Wistar Albino Glaxo/Rij (WAG/Rij) rats (12-16 weeks old) were randomly allocated into four groups; sham, mibefradil (T type calcium channel blocker), w-Conotoxin MVIIA (N type calcium channel blocker), and mibefradil + w-Conotoxin MVIIA. Beta, alpha, theta, and delta wave ratios of EEG recordings and frequency and duration of spike wave discharges (SWDs) were analyzed and compared between groups.

RESULTS

Beta and delta recording ratios in 1 μM/5 μl mibefradil group was significantly different from basal and other dose-injected groups. Beta, alpha, and theta recordings in 0.2 μM/5 μl w-Conotoxin MVIIA group was significantly different from basal and other dose-injected groups. In w-Conotoxin MVIIA after mibefradil group, beta, alpha, and theta recording ratios were significantly different from basal and mibefradil group. Mibefradil and w-Conotoxin MVIIA significantly decreased the frequency and duration of SWDs. The decrease of frequency and duration of SWDs in mibefradil group was significantly different from w-Conotoxin MVIIA group. The frequency and duration of SWDs significantly decreased in w-Conotoxin MVIIA after mibefradil group compared with basal, mibefradil, and w-Conotoxin MVIIA groups.

CONCLUSIONS

We concluded that both T and L type calcium channels play activator roles in SWDs and have positive effects on frequency and duration of these discharges. These results are related with their central effects more than peripheral effects.

Frequency of non-convulsive seizures and non-convulsive status epilepticus in subarachnoid hemorrhage patients in need of controlled ventilation and sedation

BACKGROUND

Non-convulsive seizures (NCSZ) can be more prevalent than previously recognized among comatose neuro-intensive care patients. The aim of this study was to evaluate the frequency of NCSZ and non-convulsive status epilepticus (NCSE) in sedated and ventilated subarachnoid hemorrhage (SAH) patients.

METHODS

Retrospective study at a university hospital neuro-intensive care unit, from January 2008 until June 2010. Patients were treated according to a local protocol, and were initially sedated with midazolam or propofol or combinations of these sedative agents. Thiopental was added for treatment of intracranial hypertension. No wake-up tests were performed. Using NicoletOne(®) equipment (VIASYS Healthcare Inc., USA), continuous EEG recordings based on four electrodes and a reference electrode was inspected at full length both in a two electrode bipolar and a four-channel referential montage.

RESULTS

Approximately 5,500 h of continuous EEG were registered in 28 SAH patients (33 % of the patients eligible for inclusion). The median Glasgow Coma scale was 8 (range 3-14) and the median Hunt and Hess score was 4 (range 1-4). During EEG registration, no clinical seizures were observed. In none of the patients inter ictal epileptiform activity was seen. EEG seizures were recorded only in 2/28 (7 %) patients. One of the patients experienced 4 min of an NCSZ and one had a 5 h episode of an NCSE.

CONCLUSION

Continuous EEG monitoring is important in detecting NCSZ in sedated patients. Continuous sedation, without wake-up tests, was associated with a low frequency of subclinical seizures in SAH patients in need of controlled ventilation.

Behavioural and histological effects of preconditioning with lipopolysaccharide in epileptic rats

Sublethal stress stimuli such as systemic endotoxin treatment can induce tolerance of the brain to subsequent ischemic stress, which results in a decreased infarct size. Based on this evidence, we hypothesized that lipopolysaccharide (LPS)-induced preconditioning could protect hippocampal neurons in epileptic rats. To test this hypothesis, the anticonvulsant effect of a low dose of LPS against seizures elicited by pilocarpine hydrochloride was measured. Using the pilocarpine model of temporal lobe epilepsy and LPS-preconditioning, we also investigated hippocampal pathology in the rat brain. Based on the behavioural observations conducted, it can be assumed that the preconditioning procedure used may decrease seizure excitability in epileptic rats. However, determination of the seizure excitability threshold needs to be elaborated. Qualitative and quantitative analyses of histological brain sections in the LPS-preconditioned rats showed markedly decreased intensity of neurodegenerative changes in the CA1, CA3 and DG hippocampal fields. The tendency was observed in all the periods of the pilocarpine model of epilepsy. We suggest that preconditioning with LPS may have neuroprotective effects in the CA1, CA3 and DG hippocampal sectors; however, it has no influence on the course of the seizures in rats in the pilocarpine model of epilepsy.

Norfluoxetine and fluoxetine have similar anticonvulsant and Ca2+ channel blocking potencies

Norfluoxetine is the most important active metabolite of the widely used antidepressant fluoxetine but little is known about its pharmacological actions. In this study the anticonvulsant actions of norfluoxetine and fluoxetine were studied and compared to those of phenytoin and clonazepam in pentylenetetrazol-induced mouse epilepsy models. Pretreatment with fluoxetine or norfluoxetine (20mg/kg s.c.), as well as phenytoin (30 mg/kg s.c.) and clonazepam (0.1mg/kg s.c.) significantly increased both the rate and duration of survival, demonstrating a significant protective effect against pentylenetetrazol-induced epilepsy. These effects of norfluoxetine were similar to those of fluoxetine. According to the calculated combined protection scores, both norfluoxetine and fluoxetine were effective from the concentration of 10mg/kg, while the highest protective action was observed with clonazepam. Effects of norfluoxetine and fluoxetine on voltage-gated Ca2+ channels were evaluated by measuring peak Ba2+ current flowing through the Ca2+ channels upon depolarization using whole cell voltage clamp in enzymatically isolated rat cochlear neurons. The current was reduced equally in a concentration-dependent manner by norfluoxetine (EC50=20.4+/-2.7 microM, Hill coefficient=0.86+/-0.1) and fluoxetine (EC50=22.3+/-3.6 microM, Hill coefficient=0.87+/-0.1). It was concluded that the efficacy of the two compounds in neuronal tissues was equal, either in preventing seizure activity or in blocking the neuronal Ca2+ channels.

Antioxidant effect of nimodipine in young rats after pilocarpine-induced seizures

Nimodipine (ND) is a centrally active calcium antagonist that blocks the voltage-dependent L-type channels. Its antiepileptic properties have been proved in various animal models, including pilocarpine-induced seizures in adult rats. In order to investigate protective effects of the ND (10 (ND10) and 30 mg/kg (ND30), i.p.), young male rats (21-day-old) received ND injections before pilocarpine administration (400 mg/kg, s.c., pilocarpine group (P400)). The pretreatment with ND10 and ND30 prolonged the latencies of seizures and death on this seizure model. ND pretreatment in two doses decreased the levels of lipid peroxidation when compared to pilocarpine group. The P400 administration increased the striatal catalase activity. However, the administration of ND, in dose of 30 mg/kg, 30 min before pilocarpine, preserved catalase activity in normal levels. On the other hand, no change was detected in the animals treated with the dose of 10 mg/kg. Our results confirm the neuroprotective effect of ND on the seizures in young rats, suggesting that this drug acts positively on lipid peroxidation. Our observations shows that nimodipine cannot induces these effects via blockade of Ca(2+)-channel.

Nifedipine affects the anticonvulsant activity of topiramate in various animal models of epilepsy

Topiramate (TPM), a new generation antiepileptic drug was investigated for its anticonvulsant effects in various models of genetically determined and chemically induced epilepsy in rodents. In addition, based on recent electrophysiological data suggesting that TPM may interact with L-type Ca(2+) channels, we evaluated the effects of a concomitant administration of L-type Ca(2+) channel modulators on TPM's antiepileptic properties. TPM, dose-dependently, protected against audiogenic seizures in DBA/2 mice. Concomitant treatment with TPM and a low dose of L-type Ca(2+) channel antagonists nifedipine or verapamil or with the L-type Ca(2+) channel agonist, S(-)-1,4-dihydro-2,6-dimethyl-5-nitro-4-[2-(trifluoromethyl)phenyl]-3-pyridinecarboxylic acid methyl ester (Bay k 8644) was able to increase the ED(50) for this drug. TPM also protected against seizures induced by alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA), 4-aminopyridine (4-AP) and pentylenetetrazole (PTZ), but this activity was not significantly modified by nifedipine. TPM, dose-dependently, reduced the number and duration of epileptic spike-wave discharges (SWDs) both in WAG/Rij rats and lethargic (lh/lh) mice, two genetic models of absence epilepsy. Nifedipine decreased TPM's activity in WAG/Rij rats but paradoxically enhanced it in lh/lh mice, whereas Bay k 8644 displayed opposite effects in both absence models. These results confirm TPM's broad spectrum of anticonvulsant activity and support the proposal that a modulation of neuronal L-type Ca(2+) channel activity plays an important role in its antiepileptic activity.

Dihydropiridines mechanism of action in striatal isolated nerve endings: comparison with omega-agatoxin IVA

The relative contribution of Ca2+ and Na+ channels to the mechanism underlying the action of the dihydropiridines (DHPs), nimodipine, nitrendipine and nifedipine was investigated in rat striatum synaptosomes. The rise in internal Ca2+ (Ca(i), as determined with fura-2) induced by high K+ was unchanged by the DHPs, which like tetrodotoxin (TTX) inhibited both the rise in internal Na+ (Na(i), as determined with the Na+ selective indicator dye, SBFI) and the rise in Ca(i) induced by veratridine. Nimodipine and nitrendipine were much more potent than nifedipine. Oppositely to TTX and to the DHPs, the P/Q type Ca2+ channel blocker, omega-agatoxin IVA did not inhibit the rise in Ca(i) induced by veratridine, but inhibited the rise in Ca(i) induced by high K+. Veratridine-evoked release of dopamine, GABA, Glu, and Asp (detected by HPLC) was inhibited by nimodipine, nitrendipine, and TTX, while high K+-evoked release was unchanged by the DHPs or TTX. It is concluded that the reduction in presynaptic Na+ channel permeability might contribute to the cerebral effects of DHPs.

Effects of nimodipine on the behavioral sequalae of experimental status epilepticus in prepubescent rats

OBJECTIVE

The goal of this study was to investigate the potential protective effects of nimodipine (ND), a calcium channel blocker, on the acute manifestations and long-term behavioral sequalae of experimental status epilepticus (SE).

METHODS

Three groups of Postnatal Day (P) 35 rats undergoing kainic acid (KA)-induced SE were injected with phenobarbital (PB) and/or ND, and were subsequently compared with rats injected with KA alone and normal control rats. Behavioral parameters were assessed by the Morris water maze, open field, and handling tests at P125-P135. Acute seizures and spontaneous recurrent seizures (SRS) were assessed by videotape techniques.

RESULTS

PB reduced the severity of SE acutely, and protected completely against subsequent long-term SRS, memory impairment, and hyperactivity, and partially against aggressivity. ND alone had no effect on acute seizure activity, but did protect against subsequent SRS and memory impairment, and partially against aggressivity. When administered together, PB and ND had effects similar to those seen with PB alone. However, in addition, and unlike the PB- and ND-alone groups, the PB-ND group was completely protected against KA-induced increased aggressivity.

CONCLUSIONS

Activation of L-type calcium channels contributes to the long-term behavioral sequalae of KA-induced SE, but is not essential for the development and maintenance of SE. ND has protective effects in SE when given alone or in conjunction with a traditional antiepileptic drug. Calcium channel blockers should be further investigated as add-on protective agents in models of SE and possibly in clinical trials.

Differential effects of dihydropyridine calcium channel blockers in kainic acid-induced experimental seizures in rats

The anticonvulsant effects of the dihydropyridine calcium channel blockers nifedipine, nicardipine and nimodipine were studied on experimental seizures induced by intra-hippocampal injection of kainic acid (KA) in chloralhydrate anesthetized Wistar rats. The rats were anesthetized and placed in a stereotaxic apparatus. After midline incision four screw electrodes were placed over the left and right frontal and parietal cortex and KA was injected into left dorsal hippocampus via 5-microliter Hamilton microsyringe. The changes in electroencephalograph (EEG) activity and EEG power spectra were recorded in basal conditions and 5, 10, 15, 30 and 60 min following KA injection. KA-induced excitatory changes in the surface EEG activity were associated with the marked increase in EEG power spectra in the frequency range from 14.5-22 Hz. Pretreatment with nifedipine, nicardipine and nimodipine revealed that they exerted certain differences in their anticonvulsant properties. Nimodipine significantly delayed the onset of seizures and prevented the KA-induced changes in EEG and in EEG power spectra in all recorded channels and in a dose dependent manner. Nifedipine exerted significant anticonvulsant effect only in channel four, while nicardipine was ineffective. Our results suggest that anticonvulsant action of some dihydropyridine calcium channel blockers, especially nimodipine may be in part independent of its antagonism on L-type voltage-gated calcium (Ca(2+)) channels.

Selectivity of the protective effects of dihydropyridine calcium channel antagonists against the ethanol withdrawal syndrome

Four dihydropyridine calcium channel antagonists were compared for their ability to protect against the hyperexcitability produced in mice by withdrawal from chronic ethanol treatment and to protect against seizures due to bicuculline or pentylenetetrazol. Comparison was also made of their effects on locomotor activity, body temperature and motor co-ordination, and with the corresponding effects of the benzodiazepine, diazepam. Nitrendipine, nimodipine, nicardipine (at 50 and 10 mg/kg) and isradipine (at 10 and 4 mg/kg) decreased the withdrawal hyperexcitability, but showed no anticonvulsant action against either bicuculline or pentylenetetrazol. Diazepam (1.5 and 4 mg/kg) both protected against the withdrawal signs and decreased seizure incidence after bicuculline and pentylenetetrazol, although the latter effects were of shorter duration than those on the withdrawal signs. The four dihydropyridines decreased spontaneous locomotor activity, an effect which lasted up to 6 h. Only isradipine and diazepam had any ataxic actions at the doses tested. All the dihydropyridines had hypothermic actions, considerably shorter in duration than effects on withdrawal hyperexcitability, with little evidence of dose dependence, except for nicardipine, which had a larger, dose-related, hypothermic action. Of the four compounds, isradipine was more potent in terms of dose, but not any more selective for effectiveness against the withdrawal signs, than the other three dihydropyridines, and nicardipine was slightly less effective in protecting against the withdrawal signs. The results indicate that the anticonvulsant effects of the dihydropyridines were selective for ethanol withdrawal hyperexcitability, whereas diazepam showed no such selectivity.

Effects of calcium channel blockers on pentylenetetrazol drug discrimination in rats

The effects of the dihydropyridine L-type calcium channel blockers nitrendipine and nimodipine on the pentylenetetrazol (PTZ) drug discrimination, an operant model of anxiety, were investigated. Male Long-Evans rats were trained to discriminate PTZ (16 mg/kg, i.p.) from saline. Both nitrendipine (5.0-25 mg/kg, i.p.) and nimodipine (5.0-25 mg/kg, i.p.) partially substituted for the PTZ discriminative stimulus. However, pretreatment with nitrendipine (25 mg/kg, i.p.) or nimodipine (25 mg/kg, i.p.) produced no change in the PTZ dose-effect function. Rats were given a nutritionally balanced liquid diet containing 6.5% ethanol for 10 days. Rats selected the PTZ drug lever during withdrawal. Subchronic coadministration of nitrendipine (1.25-5.0 mg/kg, i.p., b.i.d.) with ethanol failed to dose-dependently reduce PTZ-lever responding, but it did reverse withdrawal signs. Acute administration of nitrendipine (5, 10, and 20 mg/kg, i.p.) produced marked suppression of lever responding, but it failed to significantly reduce levels of PTZ-lever responding. Although calcium channel blockers reduce signs of ethanol withdrawal, they also markedly reduce rates of behavior and produce no clear effects on anxiety-like behaviors induced by ethanol withdrawal.

Opposite effects of T- and L-type Ca(2+) channels blockers in generalized absence epilepsy

The role of the T-type Ca(2+) channel blocker, ethosuximide, the L-type Ca(2+) channel blocker, nimodipine and L-type Ca(2+) channel opener, BAY K8644 (1,4 Dihydro-2, 6-dimethyl-5-nitro-4-[trifluoromethyl)-phenyl]-3-pyridine carboxylic acid methyl ester), was investigated on spike-wave discharges in WAG/Rij rats. This strain is considered as a genetic model for generalized absence epilepsy. A dose-dependent decrease in the number of spike-wave discharges was found after i.c.v. ethosuximide, an increase after i.p. nimodipine and a decrease after i.c.v. BAY K8644. BAY K8644 was also able to antagonise the effects of nimodipine. Preliminary data were obtained with two conotoxins, MVIIC and GVIA, which block P/Q-type and N-type Ca(2+) channels, respectively. Only after i.c.v. administration of omega-conotoxin GVIA were the number and duration of spike-wave discharges reduced, but animals showed knock-out lying. The latter suggests behavioural or toxic effects and that the decrease in spike-wave activity cannot unequivocally be attributed to blockade of N-type Ca(2+) channels. It can be concluded that T- and L-type Ca(2+) channel blockers show opposite effects on spike-wave discharges. Furthermore, these effects are difficult to explain in terms of a model for spindle burst activity in thalamic relay cells proposed by McCormick and Bal [Sleep and arousal: thalamocortical mechanisms.

A ketogenic diet has different effects upon seizures induced by maximal electroshock and by pentylenetetrazole infusion

The purpose of these experiments was to determine whether a ketogenic diet previously shown to elevate seizure threshold also reduced seizure severity. Seizure threshold was tested by intravenous infusion of pentylenetetrazole (PTZ) whereas seizure severity was determined from measuring the hindlimb extension to flexion (E/F) ratio after seizures were evoked by maximal electroshock stimulation (MES). Surprisingly, seizures evoked by MES were more severe in animals fed a calorie-restricted ketogenic diet. Controls fed an isocaloric, calorie-restricted normal diet also exhibited more severe seizures than did animals fed the same diet ad libitum. When seizure threshold was evaluated in the same animals, those animals fed a calorie-restricted ketogenic diet exhibited a significant increase in seizure resistance compared to animals fed a ketogenic diet ad libitum, a calorie-restricted normal diet or a normal diet ad libitum. These findings suggest that both the amount and type of food affect seizures in rats and show that diet-related seizure protection depends upon the method by which seizures are provoked.