Picrotoxin-induced Convulsions Research Articles

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

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

Picrotoxin-induced convulsions and lysosomal function in the rat brain

The effect of picrotoxin-induced convulsions on lysosomal function in rat brain were evaluated by measuring the free as well as total acid phosphatase, cathepsin D, acid ribonuclease (RNAse II) and acid deoxyribonuclease (DNAse II) activities. Following picrotoxin treatment the free RNAse II activity increased whereas the total activities of practically all the other enzymes decreased. Paradoxically, the cathepsin D activity, free as well the total was completely abolished. In case of all the enzymes the ratio of Total activity/Free activity decreased indicating increased lysosomal membrane fragility which could lead to process of neurodegeneration in the epileptic animals.

Demonstrating the dose- and time-related effects of 7-nitroindazole on picrotoxin-induced convulsions, memory formation, brain nitric oxide synthase activity, and nitric oxide concentration in rats

In this study, the dose (50, 100, 150, and 200 mg/kg)- and time (30 and 60 min)- related effects of 7-nitroindazole (7-NI), a neuronal specific inhibitor of nitric oxide synthase (NOS) were tested on picrotoxin (5 mg/kg)-induced convulsions and memory formation in rats. The changes produced by these doses of 7-NI were determined on NOS activity and nitric oxide (NO) concentration in the brain. The effects of 7-NI were tested in animals pretreated (30 min) with l-arginine (500 and 1000 mg/kg). 7-NI, at 50 and 100 mg/kg, did not produce significant changes in NOS activity and NO concentration in the brain and memory formation. However, the convulsant action of picrotoxin was inhibited in a dose-dependent manner in these animals. A time-dependent decrease in the activity of NOS and the concentration of NO, a promotion of picrotoxin-induced convulsions, and an impairment of memory were found in animals treated with 150 and 200 mg/kg of 7-NI. The larger and not the smaller dose of l-arginine raised the concentration of NO, inhibited picrotoxin-induced convulsions and promoted memory process. Either dose of l-arginine failed to prevent 50 and 100 mg/kg of 7-NI from inhibiting convulsions. The effects of the larger doses of 7-NI (150 and 200 mg/kg) were effectively prevented by the increase of NO and not the ineffective dose of l-arginine. These results suggest that 7-NI (50 and 100 mg/kg) decreases convulsions by a nonspecific mechanism and that an inhibition of NOS by the larger doses of it (150 and 200 mg/kg) results in proconvulsant action and memory impairment. The data further show that the margin between the protective and proconvulsant doses of 7-NI is relatively narrow. These results have been taken together with the earlier reports that 7-NI produces learning impairment and fails to increase the anticonvulsant effect of traditional antiepileptic agents on experimentally induced convulsions to conclude that 7-NI can never emerge as an anticonvulsant agent for clinical use.

Developmental characteristics of picrotoxin-induced convulsions in rats with genetic absence epilepsy

Adult rats with genetic absence epilepsy (GAERS) were shown to be hyperresponsive to convulsions induced by picrotoxin compared to nonepileptic controls (NERs). In contrast, young GAERS aged 22–26 days were less responsive than NERs to picrotoxin-induced convulsions. Around 30 days of age, when spontaneous spike-wave discharges develop in GAERS, the sensitivity of both strains did no longer differ. After 40 days of age, GAERS appeared definitely more prone than NERs to convulse in response to picrotoxin injection. A developmental imbalance in excitation/inhibition may parallel the occurrence of SWDs.

The effect of N-nitro- l-arginine methyl ester posttreatment on the anticonvulsant effect of phenobarbitone and diazepam on picrotoxin-induced convulsions in rats

The present study has investigated the effect of posttreatment of the nonspecific inhibitor of nitric oxide (NO) synthase (NOS), N-nitro- l-arginine methyl ester ( l-NAME), on the anticonvulsant effect of phenobarbitone and diazepam on picrotoxin-induced convulsions in rats. Phenobarbitone, which is known to inhibit convulsions by potentiating γ-aminobutyric acid (GABA) activity in the brain, did not inhibit the convulsive action of picrotoxin in l-NAME-posttreated animals. l-NAME produced no such interaction with diazepam, which inhibits convulsions through GABA potentiation as well as by a GABA-independent mechanism. l-arginine, the precursor of NO, increased the protective effect of both phenobarbitone and diazepam. These results suggest that a decreased synthesis of NO in the brain by the nonspecific inhibitors of NOS is likely to result in an impairment of the anticonvulsant effect of antiepileptics that inhibit convulsions solely by potentiating GABA activity in the brain.

Evidence for the involvement of l-citrulline but not nitric oxide in the proconvulsant action of the precursor l-arginine on picrotoxin-induced convulsions in rats

To determine the role of the metabolites of l-arginine in its actions on picrotoxin-induced convulsions in rats, the concentrations of nitric oxide (NO) and l-citrulline were measured in the brain 30 and 60 min after the administration of l-arginine (1000 and 2000 mg/kg) or of N-nitro- l-arginine methyl ester ( l-NAME, 30 mg/kg), an inhibitor of NO synthase. Animals treated similarly were challenged 30 and 60 min later with picrotoxin (5 mg/kg), and the time of onset of myoclonus and clonic convulsions and the frequency of convulsions were determined. These parameters were also determined 30 and 60 min after administering l-arginine in l-NAME-pretreated (30 min) animals. Thirty minutes after the administration of l-arginine, the concentrations of both NO and l-citrulline were raised, the onset of myoclonus and clonic convulsions was delayed, and the frequency of convulsions was decreased, indicating the anticonvulsant property of l-arginine. A 60-min treatment of l-arginine produced a further increase in the concentration of l-citrulline but not that of NO and promoted the frequency of picrotoxin-induced convulsions. Pretreatment with l-NAME prevented l-arginine from raising the concentrations of both NO and l-citrulline; it also promoted the anticonvulsant actions and prevented the proconvulsant actions of l-arginine. These results lead to the conclusion that NO has no involvement in the time-dependent anti and proconvulsant actions of l-arginine on the picrotoxin convulsion model, and that l-citrulline seems to have a role in the proconvulsant action of l-arginine.

Evidence for an involvement of nitric oxide and gamma aminobutyric acid in the anticonvulsant action of l-arginine on picrotoxin-induced convulsions in rats

Five, 30, and 60 min pretreatment of 1000 mg/kg and not 500 mg/kg of l-arginine inhibited convulsions induced by picrotoxin. The concentrations of nitric oxide (NO) and gamma aminobutyric acid (GABA) were increased in the brain 5, 30, and 60 min after administration of 1000 mg/kg and not 500 mg/kg of l-arginine. A much higher dose of l-arginine (2000 mg/kg), 30 min after administration, produced a lesser anticonvulsant and NO and GABA increasing actions as compared to that produced by 1000 mg/kg of l-arginine. The same dose of l-arginine, 60 min after administration, decreased the concentrations of both NO and GABA and increased the convulsion frequency of picrotoxin. An NO decreasing dose of nitric oxide synthase (NOS) inhibitor, N-nitro- l-arginine methyl ester ( l-NAME) decreased brain GABA concentration and increased the convulsant action of picrotoxin. Further, l-NAME pretreatment prevented l-arginine (1000 mg/kg) from producing anticonvulsant and NO and GABA increasing effects. An interpretation of these results suggests that NO synthesized from systemically administered l-arginine inhibits convulsions by increasing the concentration of GABA in the brain. However, the effects of l-arginine are reversible, if it is administered at a higher dose (2000 mg/kg) 60 min prior to the test. It is concluded that l-arginine produces anticonvulsant or proconvulsant action depending upon the dose and time of its administration-related changes in the concentrations of NO and GABA in the brain.

Evidence for an involvement of the ammonia-decreasing action of L-arginine in suppressing picrotoxin-induced convulsions in rats and its additive action with diazepam

The effects of pre- (30 min before challenge) and post-treatment (5 min after challenge) of L-arginine (840 mg kg-1) were tested on picrotoxin-induced increase in ammonia concentrations in brain regions (cerebral cortex, brain stem and cerebellum) and the accompanying convulsive responses in adult male rats. The effect of pre- and post-treatment of L-arginine was tested on the action of diazepam against picrotoxin-induced convulsions. Picrotoxin-induced increase in ammonia concentrations in the brain regions was reverted partially by L-arginine pre-treatment. However, L-arginine pre-treatment failed to inhibit convulsions independently and concurrently with diazepam. On the other hand, L-arginine posttreatment reverted ammonia to control level in all brain regions. A partial but significant inhibition of convulsions was found in these animals. The effect produced concurrently by L-arginine and diazepam post-treatment was much greater than that produced by these agents independently. These results suggest that brain ammonia has a partial but significant participation in the convulsant action of picrotoxin. L-arginine has produced a partial protection of picrotoxin-induced convulsions by reverting brain ammonia to control level. The data further suggest that the duration of action of L-arginine is considerably short and that L-arginine has an additive anticonvulsant action with diazepam. [Neurol Res 2001; 23: 622-626]

Effects of linalool on [(3)H]MK801 and [(3)H] muscimol binding in mouse cortical membranes.

Linalool is a monoterpene compound reported to be a major component of essential oils of several aromatic species. Several linalool-producing species are used in traditional medical systems for sedative purposes, including the interruption and prevention of seizures. Previous studies in mice revealed that linalool modulates glutamatergic (competitive antagonism of L-[(3)H]glutamate binding, delayed intraperitoneal NMDA-induced convulsions and blockade of intracerebroventricular Quin-induced convulsions) and GABAergic transmission (protection against pentylenetetrazol and picrotoxin-induced convulsions). To further clarify the anticonvulsive mechanisms of linalool, we studied the effects of linalool on binding of [(3)H]MK801 (NMDA antagonist) and [(3)H]muscimol (GABA(A) agonist) to mouse cortical membranes. Linalool showed a dose dependent non-competitive inhibition of [(3)H]MK801 binding (IC(50) = 2.97 mM) but no effect on [(3)H]muscimol binding. The data suggest that the anticonvulsant mode of action of linalool includes a direct interaction with the NMDA receptor complex. The data do not, however, support a direct interaction of linalool with GABA(A) receptors, although changes in GABA-mediated neuronal inhibition or effects on GABA release and uptake cannot be ruled out.

Swim stress alters the behavioural response of mice to GABA-related and some GABA-unrelated convulsants

To elucidate the relationship between stress and seizures, the effect of a single swim stress on the convulsive signs and death produced by several GABA-related and GABA-unrelated convulsants, and the effect of repeated swim stress on picrotoxin-induced convulsions was studied. Mice were subjected to swim stress (10 min swimming at 18–19°C), and the i.v. infusion of convulsants started 15 min thereafter. The latency to the onset of several convulsant signs and death was measured, and the doses of convulsants producing convulsions and death were calculated. Additional experiments included mice swimming at room temperature, and those which were stressed repeatedly (twice a day for four consecutive days, plus one stressful procedure on the fifth day). Swim stress increased the dose needed to produce convulsant signs and death after bicuculline, picrotoxin, pentylenetetrazole, strychnine and 4-aminopyridine, while kainic acid-induced convulsions were not affected. Using picrotoxin infusion, the effect of swimming in room temperature water was less than the effect of swimming in 18–19°C water. In addition, the effect of repeated stress was less than the effect of acute stress on picrotoxin-induced convulsions. The results demonstrate that acute swim stress lowers the convulsive potency of GABA-related and some GABA-unrelated convulsants. Repeatedly stressed animals develop tolerance to anticonvulsive effect of swim stress.

Anticonvulsive Effect of Swim Stress in Mice

PERIČIĆ, D., D. ŠVOB, M. JAZVINŠĆAK AND K. MIRKOVIĆ. Anticonvulsive effect of swim stress in mice. PHARMACOL BIOCHEM BEHAV 66(4) 879–886, 2000. —To explore the possible involvement of glucocorticoids in the previously observed anticonvulsive effect of swim stress, mice were, prior to administration of convulsants, subjected to treatments that diminish or enhance plasma corticosterone levels. Aminoglutethimide, the inhibitor of steroid synthesis, failed to modify convulsant doses of picrotoxin, but enhanced threshold doses of pentylenetetrazole producing myoclonus and death, both in unstressed and stressed animals. The same drug prevented the effect of stress on pentylenetetrazole-induced running bouncing clonus (RB clonus) and abolished the appearance of tonic hindlimb extension (THE). Doses of kainic acid producing convulsions and death were not affected by stress, but they were enhanced by aminoglutethimide. Corticosterone administration could not imitate the effect of swim stress. Finasteride, a 5α-reductase inhibitor, did not interfere with the effect of stress on picrotoxin-induced convulsions. Swim stress failed to modify the binding of the convulsant t[ 3H]-butylbicycloorthobenzoate [ 3H]TBOB, to washed mouse forebrain membranes. The results confirmed an anticonvulsant effect of swim stress against convulsions produced by GABA-related convulsants, but they do not support the hypothesis suggesting the involvement of glucocorticoids or neurosteroids in this effect.

Pharmacological profile of apigenin, a flavonoid isolated from Matricaria chamomilla

Dried flowers of Matricaria chamomilla L. are largely used to provide sedative as well as spasmolytic effects. In the present study, we examined in particular the pharmacological property of a fraction isolated from a methanolic extract of M. chamomilla, which was identified by HPLC–MS–MS analysis as apigenin. By radioreceptor binding assays, we demonstrated the ability of the flavone to displace a specific radioligand, [ 3H]Ro 15-1788, from the central benzodiazepine binding site. Electrophysiological studies performed on cultured cerebellar granule cells showed that apigenin reduced GABA (gamma-aminobutyric acid)-activated Cl − currents in a dose-dependent fashion. The effect was blocked by co-application of Ro 15-1788, a specific benzodiazepine receptor antagonist. Accordingly, apigenin reduced the latency in the onset of picrotoxin-induced convulsions. Moreover, apigenin injected i.p. in rats reduced locomotor activity, but did not demonstrate anxiolytic, myorelaxant, or anticonvulsant activities. The present results seem to suggest that the inhibitory activity of apigenin on locomotor behaviour in rats cannot be ascribed to an interaction with GABA A–benzodiazepine receptor but to other neurotransmission systems, since it is not blocked by Ro 15-1788.

Increased Mortality of Kainic Acid by Pretreatment with Nicardipine, a Calcium Channel Blocker in Rats.

Ca2+ channel blockers from two different chemical classes, nifedipine and varapamil, were compared in rats for their ability to inhibit the wet-dog shakes behavior and limbic seizures induced by kainic acid which binds to a subtype of glutamate receptors in the brain. Pretreatment for 30 minutes with nicardipine or verapamil suppressed slightly kainic acid-induced wet-dog shakes independent of the dose 1-4mg/kg. In the rats treated with 5mg/kg of nicardipine or verapamil, however, the frequency of wet-dog shakes decreased to 50-60% of controls. In contrast, nicardipine accelerated the onset time and frequency of limbic seizures, resulting in increased mortality by kainic acid in the dose-dependent manner. Occurrence of limbic seizures in verapamil-treated rats was similar to that in the controls and the mortality in this group was smaller than in the nicardipine-treated group. Pretreatment with diazepam alone prevented the kainic acid-induced limbic seizures. However, in the rats pretreated with diazepam and nicardipine simultaneously, anticonvulsive effect of diazepam was not shown and the mortality in this group was the similar to that in the nicardipine pretreated group. Both nicardipine and verapamil did not enhance the picrotoxin-induced convulsions. The mechanism of the apparent enhancement of the mortality of kainic acid by even low doses of nicardipine is not clear. This might be, at least in part, correlated with their different mechanism of channel blocking action.

Gonadal hormones and picrotoxin-induced convulsions in male and female rats

Gonadal hormones and picrotoxin-induced convulsions in male and female rats

Gonadal hormones and picrotoxin-induced convulsions in male and female rats

The sensitivity to the GABA-blocking agent picrotoxin was studied in young and adult male and female rats, in rats treated with gonadal hormones and in gonadectomized male and female rats. Picrotoxin was equipotent in producing convulsions in male and female 20-day-old rats. Adult females tended to be more, while adult males were considerably less sensitive to picrotoxin than young rats. Picrotoxin was equipotent in displacing t-[ 3H]butylbicycloorthobenzoate ( 3H]TBOB) binding to crude cortical and cerebellar membranes from male and female rat brain. Chronic treatment of male rats, beginning with 30 days of age, with estradiol benzoate enhanced their sensitivity to picrotoxin, while an analogous treatment of female rats with testosterone propionate was ineffective. Thirty days following castration adult male rats had shorter latencies to the appearance of picrotoxin-induced convulsions and a higher incidence of death. Ovariectomy in females failed to modify the sensitivity to picrotoxin. The results suggest that gonadal hormones have a crucial role in the development of sex related differences in the response of rats to picrotoxin and presumably to other GABA-related drugs. When developed, the male type of reactivity appears to depend more, and the female type less on the presence of circulating hormones in the blood.

The effect of chronic cyclodiene insecticide treatment on some pharmacological actions of diazepam in rats

The sedative and hypnotic effects of diazepam were tested in rats following chronic treatment with subconvulsive doses of the cyclodiene insecticides, endosulfan and aldrin. The anticonvulsant effect of diazepam was determined on picrotoxin-induced convulsions in insecticide-treated and control animals. Both endosulfan and aldrin promoted the convulsant action of picrotoxin indicating that the insecticides were able to show proconvulsant action following chronic administration. Interestingly, the protective effect of diazepam against picrotoxin-induced convulsions was greater in endosulfan- and aldrin-treated animals than in control animals. The sedative and hypnotic effects of diazepam were also increased in insecticide-treated animals. The mechanisms involved in the interaction were discussed with the support of the findings reported by the present and other investigators on the central and hepatic effects of chronic endosulfan and aldrin treatment.

Distribution of Fos-positive neurons in cortical and subcortical structures after picrotoxin-induced convulsions varies with seizure type

The distribution of Fos protein was mapped in rat brain following a single non-focal convulsive seizure. Single seizures were induced with intravenous picrotoxin in unhandled animals housed in isolation. Different convulsive behaviours occurred unpredictably. The least severe seizures were predominantly localised to the face, head and forelimbs, without loss of posture control (restricted seizures). The most extensive seizures affected all limbs and trunk, sometimes with falling (generalised seizures). There was a correlation between seizure behaviour and distribution of Fos induction. After restricted seizures, Fos was induced at highest levels in neocortex and piriform cortex and was prominent in entorhinal cortex, caudal-ventral caudate-putamen and amygdala. Regions of thalamus were consistently and lightly labelled, but Fos induction did not occur in hippocampus. After generalised seizures, there was Fos induction in cortex but less than after restricted seizures and, in three of four animals, also in dentate gyrus, hippocampus and subiculum. There was occasional or variable labelling of thalamus, basolateral amygdala and caudate-putamen. One animal with generalised seizures showed no hippocampal Fos induction. The findings indicate that picrotoxin induces seizures with at least two different patterns of neuronal involvement. The cortex, part of the caudate-putamen, amygdala and thalamus are involved in restricted seizures while the hippocampus, cortex and thalamus are involved in generalised seizures. The results do not support the view that generalised seizures are a progression from restricted forms. Cortical Fos involvement is entirely consistent with the participation of cortex in non-focal epilepsy. In these non-focal seizures, the dentate-hippocampus may be a source of excitation to cortex in the generalised group while the cortex appears to be the predominant site of excitation in the restricted group.

Seizure-protecting effects of kyotorphin and related peptides in an animal model of epilepsy

Administration of peptides kyotorphin (KT), neokyotorphin (NKT), and d-ser-2-NKT into the lateral brain ventricle (10 nmol increased the latency and attenuated the severity of picrotoxin-induced convulsions in rats. Anticonvulsive effects of the peptides were also observed after their administration into the CA1 hippocampi (2.5, 5, 10 nmol, with the order of potency d-ser-2-NKT → NKT → KT. When injected into the substantia nigra reticulata, the 10 nmol dose of NKT and d-ser-2-NKT displayed equal seizure-protecting effect, which was higher than that for KT. It is concluded that kyotorphin and its analogs provide structure-dependent, dose-dependent, and target site-dependent antiepileptic effect.

Role of peptide factors in formation of epileptiform manifestations during picrotoxin-induced kindling in rats

A peptide-containing fraction was extracted from the ventral parts of the rat mesencephalon; donor animals had been subjected to kindling by repeated picrotoxin injections (1.0–1.2 mg/kg). Intraventricular administration of the extract (20 µg in 10 µl isotonic NaCl solution per animal) increased the manifestation of picrotoxin-induced (2.0 mg/kg) convulsions in the intact recipient rats; at the same time, injection of a hippocampal extract in the same doses did not produce such an effect. Proepileptic effects of the injected extract from the ventral mesencephalic region (VMR) tissue were removed by naloxone (1.0 mg/kg) injection. A decrease of β-endorphin, met-enkephalin, and δ-sleep-inducing peptide content in the VMR tissue and the hippocampus has been found in kindling-subjected animals.

Effects of somatostatin and anti-somatostatin serum on picrotoxin-kindled seizures

The effects of somatostatin, administered into different areas of the brain were studied in preliminary picrotoxin-kindled rats. The injection of somatostatin into the lateral ventrical of the brain (i.c.v.) (1.8 nmol), the hippocampus (0.6 nmol) or the amygdala (0.6 nmol), resulted in a decrease in the severity of the picrotoxin-induced convulsions. Application of the peptide into the caudate-putamen or the substantia nigra reticulata did not alter the behavioural manifestations of the kindled Seizures. The local injection of anti-somatostatin serum (1:5) into the hippocampus increased the severity of the kindled convulsions and blocked the anticonvulsive effect of somatostatin, given intraventricularly. Local administration of anti-somatostatin serum into the amygdala did not alter the kindled Scizures and did not abolish the anticonvulsive action of somatostatin given intraventricularly. It is concluded that somatostatin could take part in endogenous control of Scizures through a suppressant influence on limbic structures; the hippocampus could be a specific site for the antiepileptic action of somatostatin.