Excitatory amino acid antagonists and pentylenetetrazol-induced seizures during ontogenesis: III. The action of kynurenic acid and glutamic acid diethylester

Antiepileptic effects of antioxidant potent extract from Urtica dioica Linn. root on pentylenetetrazole and maximal electroshock induced seizure models

Urtica dioica Linn. (Urticaceae) is a medicinal plant that has shown various therapeutic utilities in folklore medicine along with its use in the treatment of epilepsy. The entire plant has a sensible reservoir of nutritional elements and micronutrients. The purpose of the present study was to investigate the antiepileptic effect of antioxidant potent extract of Urtica dioica root on animal models. Antioxidant activity of various solvent extracts i.e. Petroleum ether extract (PEE), Ethyl acetate extract (EAE), Chloroform extract (CE) and Ethanolic extract (EE) were screened by DPPH radical scavenging assay using Ascorbic acid as the standard. Further the most potent antioxidant extract was subjected to antiepileptic activity against MES and PTZ model. The IC₅₀ values of different Urtica dioica extracts (PEE, CE, EAE, and EE) in antioxidant assay were found to be 167.54 ± 1.97, 134.41 ± 0.82, 88.15 ± 1.39 and 186.38 ± 1.91 μg/ml in DPPH radical scavenging assay, respectively. The EAE has showed the potent antioxidant activity. In experimental study the EAE (100 and 200 mg/kg, p.o) has found to be effective and significant against MES and PTZ induced seizures. The present study also suggested that antioxidant potent extract (EAE) of Urtica dioica root has antiepileptic effect against MES and PTZ induced seizures. However, further research studies will investigate the active component(s) of Urtica dioica responsible for the observed anticonvulsant effects.

Anticonvulsant effect of the hydroethanolic leaf extract of Psydrax subcordata (DC.) Bridson in murine models

ETHNOPHARMACOLOGICAL RELEVANCE

Psydrax subcordata (DC.) Bridson is a tropical medicinal plant used traditionally for the management of epilepsy. However, there is little scientific evidence to support its use.

AIM OF STUDY

The current study investigated the anticonvulsant properties of the hydroethanolic leaf extract of Psydrax subcordata (PSE) in animal models.

MATERIALS AND METHODS

The anticonvulsant effects were evaluated in mouse models of acute seizures (pentylenetetrazole-, picrotoxin-, 4-aminopyridine-, strychnine- and maximal electroshock-induced seizure tests) and status epilepticus (Lithium/pilocarpine-induced SE). The role of GABAergic mechanisms in the actions of the extract was also examined by pre-treatment of animals with flumazenil in the pentylenetetrazole test.

RESULTS

The extract (30, 100 and 300mg/kg, p.o.) significantly delayed the onset and decreased the duration and frequency of pentylenetetrazole- and picrotoxin-convulsions. PSE also reduced the duration of tonic hind limb extensions in the maximal electroshock-induced seizure test. Furthermore, PSE pre-treatment significantly delayed the onset of seizures and improved survival in the 4-aminopyridine-induced seizure test. In the strychnine-induced seizure test, PSE treatment did not significantly affect the latency to convulsions and time until death when compared to controls. PSE exhibited anticonvulsant effects in the lithium/pilocarpine test by delaying the onset of seizures and status epilepticus as well as reducing the severity of seizures and mortality of mice. Again, the anticonvulsant effect of PSE (100mg/kg, p.o.) was blocked by pre-treatment with flumazenil in the PTZ test.

CONCLUSION

PSE has anticonvulsant activity in animal models, and this effect may be mediated, at least partly, through GABAergic mechanisms.

MK-801, but not naloxone, attenuates high-dose dextromethorphan-induced convulsive behavior: Possible involvement of the GluN2B receptor

Dextromethorphan (DM) is a dextrorotatory isomer of levorphanol, a typical morphine-like opioid. When administered at supra-antitussive doses, DM produces psychotoxic and neurotoxic effects in humans. Although DM abuse has been well-documented, few studies have examined the effects of high-dose DM. The present study aimed to explore the effects of a single high dose of DM on mortality and seizure occurrence. After intraperitoneal administration with a high dose of DM (80mg/kg), Sprague-Dawley rats showed increased seizure occurrence and intensity. Hippocampal expression levels of N-methyl-d-aspartate (NMDA) receptor subunits (GluN1<GluN2A<GluN2B), c-Fos and pro-apoptotic factors (Bax and cleaved caspase-3) were upregulated by DM treatment; while levels of anti-apoptotic factors (Bcl-2 and Bcl-xL) were downregulated. Consistently, DM also induced ultrastructural degeneration in the hippocampus. A non-competitive NMDA receptor antagonist, MK-801, attenuated these effects of high-dose DM, whereas an opioid antagonist, naloxone, did not affect DM-induced neurotoxicity. Moreover, pretreatment with a highly specific GluN2B subunit inhibitor, traxoprodil, was selectively effective in preventing DM-induced c-Fos expression and apoptotic changes. These results suggest that high-dose DM produces convulsive behaviors by activating GluN2B/NMDA signaling that leads to pro-apoptotic changes.

Assessment of seizure susceptibility in pilocarpine epileptic and nonepileptic Wistar rats and of seizure reinduction with pentylenetetrazole and electroshock models

PURPOSE

Pentylenetetrazole (PTZ) and maximal electroshock (MES) models are often used to induce seizures in nonepileptic control animals or naive animals. Despite being widely used to screen antiepileptic drugs (AEDs), both models have so far failed to detect potentially useful AEDs for treating drug-resistant epilepsies. Here we investigated whether the acute induction of MES and PTZ seizures in epileptic rats might yield a distinct screening profile for AEDs.

METHODS

Status epilepticus (SE) was induced in adult male Wistar rats by intraperitoneal pilocarpine injection (Pilo, 320 mg/kg, i.p.). One month later, controls or naive animals (Cont) that did not develop SE postpilocarpine (N-Epi) and pilocarpine-epileptic rats (Epi) received one of the following: phenobarbital (PB, 40 mg/kg), phenytoin (PHT, 50 mg/kg), or valproic acid (VPA, 400 mg/kg). Thirty min later the animals were challenged with either subcutaneous MES or PTZ (50 mg/kg, s.c.).

RESULTS

VPA, PB, and PHT were able to prevent MES in all groups tested (Cont, N-Epi, and Epi groups), whereas for the PTZ model, only the Cont group (naive animals) had seizure control with the same AEDs. In addition, Epi and N-Epi groups when challenged with PTZ exhibited a higher incidence of severe seizures (scores IV-IX) and SE (p < 0.05, Fisher's exact test).

CONCLUSIONS

Our findings suggest that the induction of acute seizures with PTZ, but not with MES, in animals pretreated with pilocarpine (regardless of SE induction) might constitute an effective and valuable method to screen AEDs and to study mechanisms involved in pharmacoresistant temporal lobe epilepsy (TLE).

Perinatal hypothyroidism increases the susceptibility to lidocaine-kindling in adult rats

The present study was developed to ascertain whether or not susceptibility to lidocaine-kindling persists into adulthood in perinatal hypothyroid rats. Pregnant Wistar rats were randomly divided into two groups: the first one, a control group, that drank tap water; and a second one, a hypothyroid group, were treated with 0.02% propylthiouracil in their drinking water from the 14th gestational day to the 10th postpartum day. The pups of both groups were maintained with food and tap water ad libitum until the experiment was over. The pups of each group were divided to test the susceptibility to lidocaine-kindling at 30 and 100 days old, for this, lidocaine (50 mg/kg, i.p.) was administered daily. The seizures were usually present in the form of tonic attacks of fore and hind limbs, followed by intermittent clonic movements. An animal was considered kindled when it showed clonic movements for two consecutive days. We observed that the number of stimuli necessary to produce lidocaine-kindling seizures in hypothyroid rats was significantly lower than in the control group for both ages. Also, the percentage of kindled rats aged 30 days (73% and 89%) was greater than aged of 100 days (26% and 59%) in both control and hypothyroid groups, respectively. In conclusion, the perinatal hypothyroidism increases the susceptibility to lidocaine-kindling in adult rats.

Modulation of cortical nitric oxide synthase, glutamate, and redox state by nifedipine and taurine in PTZ-kindled mice

PURPOSE

Correlation between pentylenetetrazol (PTZ)-induced kindling and the cortical nitric oxide synthase (NOS), intracellular calcium [Ca2+]i, glutamate, and free radicals was studied in mice, as well as the modulatory action of nifedipine and taurine on these parameters.

METHODS

Male Swiss albino mice were used. Mice in one group received a single convulsive dose of PTZ (50 mg/kg, i.p), and were killed 24 h later. To induce kindling, PTZ was injected in a subconvulsive dose (40 mg/kg, i.p.) every other day for 3 weeks. One kindled group was used as control, whereas two other groups were injected 30 min before PTZ with either nifedipine (30 mg/kg, i.p) or taurine (100 mg/kg, i.p). All three kindled groups were killed 24 h after the last injection.

RESULTS

Compared with normal control group, PTZ-kindled mice had significantly higher levels of [Ca2+]i, malonaldehyde (MDA), NOS, and lactate dehydrogenase (LDH) but had lower levels of superoxide dismutase (SOD) and reduced glutathione (GSH). Acute seizures of the same intensity did not induce these alterations, indicating their link to the kindling phenomenon and not to seizure activity. The effect of taurine, known as an antioxidant, was more pronounced than that of the Ca2+-channel blocker, nifedipine. The first drug reversed the PTZ-kindled action on [Ca2+]i, NOS, LDH, GSH, and SOD, whereas nifedipine restored only LDH and GSH levels. However, both drugs did not restore the elevated MDA level.

CONCLUSIONS

This study suggests that free radicals, as well as NOS, are implicated in PTZ-induced kindling, and that antioxidants could play a role in controlling the accompanying changes.

Dynamic variations of local cerebral blood flow in maximal electroshock seizures in the rat

PURPOSE

Measurement of cerebral blood flow is routinely used to locate the areas involved in generation and spread of seizures in epilepsy patients. Because the nature of the hyperperfused regions varies with the timing of injection of tracer, in this study, we used a rat model of maximal electroshock seizures to follow up the time-dependent changes in the distribution of seizure-induced cerebral blood flow (CBF) changes.

METHODS

CBF was measured by the quantitative autoradiographic [14C]iodoantipyrine technique over a 30-s duration. The tracer was injected either at 15 s before seizure induction, simultaneous with the application of the electroshock (tonic phase), at the onset of the clonic phase, or at 3 and 6 min after the seizure (postictal phase).

RESULTS

Rates of CBF underwent dynamic changes during the different phases of seizure activity and largely increased over control levels (< or =400%) in the 45 regions studied during all phases of the seizure (first 3 times). CBF remained higher than control levels in 35 and 15 areas at 3 and 6 min after the seizure, respectively.

CONCLUSIONS

The distribution of maximal CBF increases showed a good correlation with their known involvement in the circuits underlying the clinical expression of the different types of seizure activity, tonic versus clonic.

Behavioural effects of tetrachloroethylene exposure in rats: acute and subchronic studies

This study was carried out to compare the neurobehavioural profile of acute and subchronic tetrachloroethylene (perchloroethylene, PCE) exposure in rats. In the acute study, a single bolus of 50 and 500 mg/kg of PCE in corn oil was administered by gavage. In the subchronic experiments, rats were exposed to PCE at a dosage of 5 and 50 mg/kg in corn oil, 5 days per week for 8 weeks. Nociception, locomotion and seizure susceptibility was tested using open-field, tail immersion and hot plate and pentylenetetrazol-induced seizures, respectively. Subchronic PCE exposure exhibited higher antinociceptive effect and lower motor activity in comparison with acute exposure. Pentylenetetrazol-induced convulsion thresholds were elevated following acute PCE exposure. In contrast, subchronic PCE exposure only increased thresholds for myoclonic twitch and face and forelimb clonus without altering the thresholds for running and bouncing clonus and tonic hindlimb extension. These findings suggest that subchronic PCE exposure results in progressively greater toxic effects on nociception and locomotor activity. The differential effects on seizure susceptibility between acute and subchronic exposure may represent different alterations on neural circuits involved in seizure generation.

Anticonvulsant action of topiramate against motor seizures in developing rats

PURPOSE

To study the anticonvulsant action of topiramate (TPM) in developing rats.

METHODS

Motor seizures were elicited by administering pentylenetetrazol (100 mg/kg subcutaneously) in five age groups of Wistar rats (7, 12, 18, 25, and 90 days old). TPM was administered intraperitoneally in doses from 10 to 640 mg/kg 2 hours before pentylenetetrazol. The time course of TPM action was studied in 12- and 25-day-old rats up to 24 hours after the 160-mg/kg dose, and the incidence and pattern of seizures were evaluated.

RESULTS

TPM did not influence minimal seizures (clonus of forelimb and head muscles with preserved righting ability). Generalized tonic-clonic seizures, however, were reliably changed at all developmental stages studied. The tonic phase was suppressed so that the majority of animals exhibited generalized clonic seizures (with a loss of righting reflexes). In addition, the incidence of generalized seizures was decreased after the 20-, 40-, and 80-mg/kg doses in the 7-day-old rat pups. The specific suppression of the tonic phase of generalized seizures was observed up to 12 hours in the 12-day-old rat pups. The same result was obtained over 6 hours after TPM administration in the 25-day-old animals, and with longer intervals the incidence of generalized seizures decreased in this age group.

CONCLUSIONS

TPM exhibits stable anticonvulsant action against the tonic phase of generalized tonic-clonic seizures throughout development. In addition, it suppresses all phases of generalized seizures in 7-day-old rats. The anticonvulsant action of TPM lasted longer in 25-day-old than in 12-day-old rats. The two actions of TPM might be ascribed to two different mechanisms of action.

Anticonvulsant action of a NMDA receptor antagonist CGP 40116 varies only quantitatively during ontogeny in rats

Anticonvulsant action of CGP 40116, a competitive antagonist of N-methyl-D-aspartate type of excitatory amino acid receptors, was studied in rats during development (7, 12, 18, 25 and 90 days old). Two types of motor seizures were elicited by a subcutaneous injection of pentylenetetrazol. Pretreatment with CGP 40116 did not influence minimal, predominantly clonic seizures in any age group. Generalized tonic-clonic seizures were at first modified--their tonic phase was restricted to forelimbs, then selectively suppressed--and with increasing dosage the clonic phase was blocked too. This effect exhibited only minor quantitative changes during development.

Co-variation of free amino acids in brain interstitial fluid during pentylenetetrazole-induced convulsive status epilepticus

Effects of pentylenetetrazole (PTZ)-induced convulsive status epilepticus on free amino acids changes in venous blood, CSF and interstitial fluid (IF) of the brain were examined in dogs. A volume of brain IF sufficient for analysis was obtained by chronically implanted tissue cages. The onset of PTZ-induced convulsive seizures seemed mainly related to a marked increase of glutamate, aspartate, taurine, glycine and phosphoserine while, the maintenance and frequency of seizures seemed related to a marked increase of serine and glycine, in combination with a moderate rise of glutamate. L-alpha-Aminoadipate was recovered in moderate amount in epileptic brain IF, while, in controls, this compound was present in minimal amount. The observed complex temporal variation of the amino acidic pattern may play a role in PTZ-induced seizures and, possibly, in pharmacological kindling and brain structural alterations induced by PTZ.