The effect of l-arginine and l-NAME on pentylenetetrazole induced seizures in ovariectomized rats,an in vivo study

The role of ovarian hormones and nitric oxide (NO) on seizure and their interaction have been widely investigated. The present study carried out to evaluate the effect of chronic administration of l-arginine (lA) and l-NAME (lN) on pentylenetetrazole (PTZ) induced epilepsy in ovariectomized (OVX) and naïve female rats.Fourty-eight female rats were randomly divided into six groups (n = 8) as follows: (1) sham, (2) ovarectomized (OVX), (3) sham-lA, (4) sham-lN, (5) OVX-lA, and (6) OVX-lN.The animals of sham-lA and OVX-lA received daily injection of 500 mg/kg l-arginine (i.p.) during 4 weeks. Sham-lN and OVX-lN were treated by 10 mg/kg l-NAME (i.p.) daily for 4 weeks. The animals of sham and OVX groups received 1 ml/kg saline (i.p.) instead of l-arginine and l-NAME. The latencies to minimal clonic seizures (MCS) and generalized tonic–clonic seizures (GTCS) after intraperitoneal injection of penetylenetetrazole (PTZ, 90 mg/kg) was recorded and compared between groups.A significant increase in the GTCS, but not MCS, latency was seen in OVX rats in comparison with sham-operated animals. Pretreatment of animals with l-NAME resulted in a significant increase in the GTCS and MCS latencies in sham group while no significant effects were seen in OVX rats. On the contrary, while pretreatment with l-arginine had no effects on MCS and GTCS latencies in sham group, a significant decrease in GTCS latency was observed in OVX rats.It is concluded that ovarian sex hormones affect seizure thresholds induced by PTZ and NO has a role on seizures susceptibility following PTZ administration. This NO effect might be differing in the presence or absence of ovarian hormones, but further investigations need to be done.     

Mapping of neuronal networks underlying generalized seizures induced by increasing doses of pentylenetetrazol in the immature and adult rat: a c‐Fos immunohistochemical study

Previous studies from our group have shown that pentylenetetrazol (PTZ)-induced status epilepticus (SE) leads to age-dependent acute and long-term metabolic and circulatory changes in immature rats. In order to define the neural substrates involved in PTZ seizures according to age, the purpose of the present study was to map the areas of cellular activation during seizures of increasing severity in 10-day-old (P10), 21-day-old (P21) and adult rats. Seizures were induced by repetitive injections of subconvulsive doses of PTZ. The total dose received by the animals ranged from 4 to 125 mg/kg. These doses induced a variety of seizure profiles including absence-like, clonic seizures and SE. The cellular activation was measured as the density of c-Fos immunoreactive cells in animals at 2 h after the onset of the seizures. In P10 rats receiving a behaviourally non-active dose of PTZ, c-Fos immunoreactivity appeared only in the amygdala. The dose of 40 mg/kg that induced absence-like seizures led to a weak c-Fos expression in the medial thalamus, some cortical areas and globus pallidus. Clonic seizures reinforced labelling in the previous areas and induced a spread of c-Fos immunoreactivity to other cortical areas, thalamus, hypothalamus and some brainstem nuclei. At that age, only SE led to a widespread and stronger expression of c-Fos which was, however, totally lacking in the midbrain, and remained incomplete in the brainstem and forebrain limbic system, including the hippocampus. In P21 and adult rats, the inactive dose of PTZ induced c-Fos immunoreactivity in thalamus and hypothalamus. With absence-like seizures, c-Fos labelling spread to the cerebral cortex, amygdala, septum and some brainstem regions. With clonic seizures, immunoreactivity was reinforced in all areas already activated by absence-like seizures, and appeared in the striatum, accumbens, brainstem and hippocampus, except in CA1. After SE, c-Fos was strongly expressed in all brain areas. The intensity of c-Fos labelling was higher in most regions of P21 compared to adult rats. These data are in agreement with the immaturity of cellular and synaptic connectivity in P10 rats, the known greater sensitivity of rats to various kinds of seizures during the third week of life and the nature of the neural substrates involved in PTZ seizures.     

l-NAME inhibits pentylenetetrazole and strychnine-induced seizures in mice

Nitric oxide (NO) formation has been shown in many neuronal tissues subserves a variety of functions. N-Methyl-d-aspartate (NMDA) receptor stimulation which releases nitric oxide and raises cGMP levels, mediates epileptiform activity induced by various agents. Disinhibition of inhibitory neurotransmitter γ-aminobutyric acid (GABA) and/or activation of NMDA receptor appears to be factors involved in the initiation and generalization of the pentylenetetrazole (PTZ) induced seizures. In the present study, we examined the effects of N^ω-nitro-l-arginine methylester (l-NAME) which inhibits nitric oxide synthase, on PTZ and strychnine induced seizures in mice. l-NAME (100 mg/kg) significantly prolonged the onset time of tonic generalized extension without affecting myoclonic jerks and tonic-clonic convulsions. l-NAME (200 mg/kg) significantly delayed three characteristic behavioral changes including first myoclonic jerk (FMJ), generalized clonic seizure (GCS) and tonic generalized extension (TGE). The effects of l-NAME were reversed by l-arginine (1000 mg/kg). l-NAME (100 and 200 mg/kg) significantly delayed the onset time of strychnine induced TGE. The effects of both doses of l-NAME were reversed by l-arginine. In conclusion, our results demonstrate that NO synthase inhibition suppresses the onset time of PTZ and strychnine induced seizures. Under the light of our current knowledge NO synthase inhibitors seem far away to be considered as a group of antiepileptic drugs. On the other hand there are some strong evidences about the role of NO in central pathophysiological mechanisms. © 1997 Elsevier Science B.V. All rights reserved.     

Postnatal caffeine treatment affects differently two pentylenetetrazol seizure models in rats

Effects of repeated postnatal administration of caffeine (10 and 20 mg/kg s.c. daily from P7 to P11) were studied in two models of epileptic seizures characterized by spike-and-wave EEG rhythm in 18- and 25-day-old rats. Rhythmic metrazol activity (RMA, model of human absences) was induced by low dose of pentylenetetrazol (PTZ, 20 mg/kg or 40 mg/kg, i.p.) and minimal clonic seizures (model of human myoclonic seizures) by two successive doses of PTZ (20 and 40 mg/kg i.p.). Early postnatal caffeine treatment resulted in significant changes of RMA only in 18-day-old rats. Anticonvulsant effects were observed in RMA episodes elicited by the 20-mg/kg dose of PTZ in both caffeine groups whereas latency of RMA episodes induced by the 40-mg/kg dose was shortened and their duration was prolonged. No changes were found in 25-day-old animals. Incidence, EEG and motor pattern of minimal clonic seizures were not changed. Some animals in both control age groups exhibited transition to generalized tonic–clonic seizures. This type of seizures never appeared in caffeine-treated 25-day-old animals. Mixed effects of postnatal caffeine exposure were demonstrated; these predominantly anticonvulsant effects are age- and model-specific.     

The effect of acute aripiprazole treatment on chemically and electrically induced seizures in mice: The role of nitric oxide

Aripiprazole is an antipsychotic drug which acts through dopamine and serotonin receptors. Aripiprazole was noted to have antiseizure effects in a study on mice, while it induced seizures in a few human case reports. Dopaminergic and serotonergic systems relate to nitric oxide, and aripiprazole also has effects on dopamine and serotonin receptors. This study investigated the effects of aripiprazole on seizures and the potential role of nitric oxide in the process. The following three models were examined to explore the role of aripiprazole on seizures in mice: 1 — pentylenetetrazole administered intravenously, 2 — pentylenetetrazole administered intraperitoneally, and 3 — electroshock. Aripiprazole administration delayed clonic seizure in intravenous and intraperitoneal pentylenetetrazole models. In the electroshock-induced seizure model, tonic seizure and mortality protection percent were increased after aripiprazole administration. In intraperitoneal administration of pentylenetetrazole, aripiprazole effects on clonic seizure latency were significantly decreased when l-NAME — a nonselective nitric oxide synthase (NOS) inhibitor, 7-nitroindazole — a selective neuronal NOS (nNOS) inhibitor, or aminoguanidine — a selective inducible NOS (iNOS) inhibitor was injected before aripiprazole administration. In the intravenous pentylenetetrazole method, administration of l-NAME or aminoguanidine inhibited aripiprazole effects on clonic seizure threshold. Aminoguanidine or l-NAME administration decreased aripiprazole-induced protection against tonic seizures and death in the electroshock model. In both intravenous and intraperitoneal seizure models, aripiprazole and l-arginine coadministration delayed the onset of clonic seizures. Moreover, it increased protection against tonic seizures and death in intraperitoneal pentylenetetrazole and electroshock models. In conclusion, the release of nitric oxide via iNOS or nNOS may be involved in anticonvulsant properties of aripiprazole.     

Nitric oxide involvement in seizures elicited by pentylentetrazol and sex dependence

It has been known that susceptibility to some types of epilepsy is affected by sex. In addition, the role of NO in epileptogenesis is still unclear; NO has been suggested to be either an anticonvulsive or a proconvulsive agent. In an attempt to elucidate both the role of NO and sex differences in sensitivity to seizures, male and female Wistar rats were treated intraperitoneally (i.p.) by pentylentetrazol (PTZ)(80 mg/kg) and by a nitric oxide synthase(NOS) inhibitor N-omega-nitro-L-arginine-mthylester(L-NAME)(50mg/kg) and a NO precursor sodium-nitroprusside(SNP)(2.5mg/kg)- applied 15 min. before PTZ injection. Latency, frequency, severity, and duration of generalized clonic and clonic-tonic convulsions were recorded. Furthermore, alterations in severity, latency, frequency, and duration of convulsions were observed to correlate with NO. Both sexes, injected with PTZ, showed repetitive seizure patterns. Seizures were found to be more severe in females. L-NAME and SNP pretreatment produced paradoxical effects on PTZ-induced seizures in both sexes. L-NAME completely prevented PTZ-induced seizures in male rats, whereas increased severity, frequency, duration, and significantly shortened the latency in female rats. Unexpectedly, SNP increased convulsion severity, frequency, duration, and shortened latencies in male, whereas it decreased convulsion severity, frequency, and duration and prolonged latency in females. These results indicate that endogenous NO is involved in the regulation of convulsive action suggesting a role depending on sex.     

NITRIC OXIDE INVOLVEMENT IN SEIZURES ELICITED BY PENTYLENTETRAZOL AND SEX DEPENDENCE

It has been known that susceptibility to some types of epilepsy is affected by sex. In addition, the role of NO in epileptogenesis is still unclear; NO has been suggested to be either an anticonvulsive or a proconvulsive agent. In an attempt to elucidate both the role of NO and sex differences in sensitivity to seizures, male and female Wistar rats were treated intraperitoneally (i.p.) by pentylentetrazol (PTZ)(80 mg/kg) and by a nitric oxide synthase(NOS) inhibitor N-omega-nitro-L-arginine-mthylester(L-NAME)(50mg/kg) and a NO precursor sodium-nitroprusside(SNP)(2.5mg/kg)- applied 15 min. before PTZ injection. Latency, frequency, severity, and duration of generalized clonic and clonic-tonic convulsions were recorded. Furthermore, alterations in severity, latency, frequency, and duration of convulsions were observed to correlate with NO. Both sexes, injected with PTZ, showed repetitive seizure patterns. Seizures were found to be more severe in females. L-NAME and SNP pretreatment produced paradoxical effects on PTZ-induced seizures in both sexes. L-NAME completely prevented PTZ-induced seizures in male rats, whereas increased severity, frequency, duration, and significantly shortened the latency in female rats. Unexpectedly, SNP increased convulsion severity, frequency, duration, and shortened latencies in male, whereas it decreased convulsion severity, frequency, and duration and prolonged latency in females. These results indicate that endogenous NO is involved in the regulation of convulsive action suggesting a role depending on sex.     

Involvement of nitric oxide pathway in the acute anticonvulsant effect of melatonin in mice

Melatonin, the major hormone produced by the pineal gland, is shown to have anticonvulsant effects. Nitric oxide (NO) is a known mediator in seizure susceptibility modulation. In the present study, the involvement of NO pathway in the anticonvulsant effect of melatonin in pentylenetetrazole (PTZ)-induced clonic seizures was investigated in mice. Acute intraperitoneal administration of melatonin (40 and 80 mg/kg) significantly increased the clonic seizure threshold induced by intravenous administration of PTZ. This effect was observed as soon as 1 min after injection and lasted for 30 min with a peak effect at 3 min after melatonin administration. Combination of per se non-effective doses of melatonin (10 and 20 mg/kg) and nitric oxide synthase (NOS) substrate L-arginine (30, 60 mg/kg) showed a significant anticonvulsant activity. This effect was reversed by NOS inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME, 30 mg/kg), implying an NO-dependent mechanism for melatonin effect. Pretreatment with L-NAME (30 mg/kg) and N(G)-nitro-L-arginine (L-NNA, 10 mg/kg) inhibited the anticonvulsant property of melatonin (40 and 80 mg/kg) and melatonin 40 mg/kg, respectively. Specific inducible NOS (iNOS) inhibitor aminoguanidine (100 and 300 mg/kg) did not affect the anticonvulsant effect of melatonin, excluding the role of iNOS in this phenomenon, while pretreatment of with 7-NI (50 mg/kg), a preferential neuronal NOS inhibitor, reversed this effect. The present data show an anticonvulsant effect for melatonin in i.v. PTZ seizure paradigm, which may be mediated via NO/L-arginine pathway by constitutively expressed NOS.     

Two different anticonvulsant actions of tiagabine in developing rats

PURPOSE: Our goal was to study the anticonvulsant action of tiagabine (TGB) at different levels of brain maturation in rats. METHODS: Wistar rats in five age groups (7, 12, 18, 25, and 90 days old) were injected intraperitoneally with TGB at doses of 0.5-32 mg/kg. Thirty minutes later, motor seizures were induced by the subcutaneous adminstration of pentylenetetrazol (PTZ) in a dose of 100 mg/kg for all of the groups except the 18-day-old rat pups, which received a 90-mg/kg dose. The incidence and latency of two types of motor seizures, minimal clonic and generalized tonic-clonic seizures (GTCSs), were evaluated, and the seizure severity was scored. The time profile of TGB action at the 8-mg/kg dose was studied in the 12-and 25-day-old rats. RESULTS: Minimal clonic seizures were reliably induced in rats 18 days old or older, and the seizures were suppressed by TGB in all of these age groups. Although TGB was very effective against this type of seizure in the 18-day-old rats, the efficacy of the drug decreased with the age of the animal. GTCSs were suppressed by TGB in the adult and 25-day-old rats, and a U-shaped dose-response curve was outlined in these two groups. The 18-and 12-day-old rat pups exhibited a selective suppression of the tonic phase of GTCSs. A mixture of these two effects was observed in the youngest group. TGB demonstrated a markedly longer action in the 12-day-old rats than in the 25-day-old rats. CONCLUSIONS: TGB exhibits anticonvulsant action against both minimal seizures and GTCSs. Ontogenetic development of these two actions is markedly different.     

Avian brainstem neurogenesis is stimulated during cochlear hair cell regeneration

Cyclosporin A (CsA) is known to decrease nitric oxide (NO) release in the nervous system. The present study was aimed at investigating the effects of acute administration of CsA on pentylenetetrazole (PTZ)-induced seizure threshold and latency and probable modulation of these effects by NO synthesis substrate L-arginine, and NO synthesis inhibitors N(G)-nitro-L-arginine methyl ester (L-NAME) or aminoguanidine. Moreover, the effect of CsA per se or concomitant with L-arginine on the development of PTZ-induced kindling was assessed. CsA (0.05, 1, 5, 10 and 20 mg/kg, s.c.) dose-dependently increased PTZ-induced clonic seizure threshold and the latency for onset of myoclonic jerks, clonic seizures and clonic-tonic generalized seizures following PTZ administration. L-NAME (10 and 30 mg/kg, i.p.) but not aminoguanidine (50 and 100 mg/kg, i.p.) potentiated the anticonvulsant effects of CsA (1 and 10 mg/kg). L-arginine (60, 100 and 200 mg/kg, i.p.) inhibited the anticonvulsant effects of CsA (20 mg/kg) in a dose-related manner. The inhibitory effect of L-arginine on CsA-induced alterations of seizure threshold and latency was blocked by L-NAME but not with aminoguanidine. CsA (20 mg/kg) significantly inhibited the development of PTZ kindling and decreased the seizure intensity as tested by a challenge dose of PTZ. Pretreatment with L-arginine (60 mg/kg) reversed the inhibitory effects of CsA on kindling development. It was concluded that CsA exerts some anticonvulsant properties that may be due to its inhibition of nitric oxide synthesis.     

Involvement of the nitric oxide pathway in the anticonvulsant effect of tramadol on pentylenetetrazole-induced seizures in mice

In the present study, the effects of tramadol on pentylenetetrazole (PTZ)-induced seizures and involvement of nitric oxide (NO) were assessed in mice. To determine the threshold for clonic seizures, PTZ was administered intravenously. Tramadol was administered intraperitoneally (0.5-50mg/kg) 30 minutes prior to induction of seizures. The effects of the nitric oxide synthase (NOS) inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME; 0.5, 1, 5, and 10mg/kg), the nitric oxide precursor L-arginine (10, 30, and 60 mg/kg), and the nonspecific opioid receptor antagonist naloxone (0.1, 0.5, 1, and 5mg/kg) on the anticonvulsant effect of tramadol were investigated. Administration of tramadol (1mg/kg) increased the threshold for seizures induced with PTZ in a monophasic, dose-independent, and time-dependent manner. Acute administration of L-NAME (5 and 10mg/kg) inhibited the anticonvulsant effect of tramadol (1mg/kg), whereas L-arginine, in the noneffective dose range (30 and 60 mg/kg), potentiated the seizure threshold when co-administered with a subeffective dose of tramadol (0.5mg/kg). Naloxone partially and dose-independently antagonized the anticonvulsant effect of tramadol (1mg/kg). These results indicate that the anticonvulsant effect of tramadol is mediated by the nitric oxide pathway and also by classic opioid receptors.     

Hyperthermic seizures and hyperthermia in immature rats modify the subsequent pentylenetetrazole-induced seizures

It has been described that febrile seizures during infancy increase risk of subsequent non-febrile seizures during the adulthood. However, latency period between febrile seizure and the onset of the first spontaneous seizure has not been evaluated. The present study was designed to investigate the susceptibility to subsequent seizures in immature rats that had experienced early-life hyperthermic seizures and before they achieved the adult age. The results were compared with those induced by hyperthermia alone. Pentylenetetrazol (PTZ) was applied 24 h or 20 days after hyperthermic seizures or hyperthermia were induced in 10-day-old rats by a regulated stream of moderately heated air. One day after hyperthermic seizures or hyperthermia, animals demonstrated enhanced latency to the PTZ-induced myoclonic (88% and 53%, respectively), clonic (60% and 60%, respectively) and tonic seizures (233% and 659%, respectively). The incidence of myoclonic and clonic seizures was similar to that in control group (100%). However, hyperthermic seizures reduced (50%) the incidence of tonic seizures. Twenty days after hyperthermic seizures there was an augmented latency to tonic seizures (123%) and reduced incidence for all the PTZ-induced seizures (71% myoclonic; 71% clonic seizures; 57% tonic seizures) when compared with control group (100%). In contrast, hyperthermia enhanced only the latency to myoclonic (133%) and clonic seizures (659%). Our data indicate that hyperthermic seizures or hyperthermia induces a protective effect against PTZ-induced seizures during a latency period. A possible involvement of γ-aminobutyric acid (GABA) system is discussed.     

Anticonvulsant Effects of Bretazenil (Ro 16-6028) During Ontogenesis

Anticonvulsant action of a new benzodiaze-pine, bretazenil (Ro 16–6028), was studied in 240 rats in five age groups: age 7, 12, 18, 25 and 90 days. Motor seizures induced by metrazol (pentamethylenetetrazol, PTZ, 100 mg/kg subcutaneously (s.c.) except for 18-day-old rats which received a dose of 90 mg/kg) served as a model. Animals were pretreated with Ro 16–6028 in doses of 0.001–0.1 mg/kg intraperitoneally (i.p.) 10 min before metrazol. Both types of metrazol-induced seizures, minimal (mMS, predominantly clonic with preserved righting ability) and major (MMS, generalized tonic-clonic), were suppressed by Ro 16–6028 in a dose-dependent manner. Major seizures were always more sensitive to Ro 16–6028 than were minimal seizures. The youngest rats exhibited maximal effects of Ro 16–6028 against major seizures. On the other hand, this drug increased the incidence of minimal seizures in 7- and 12-day-old rats, i.e., in age groups in which this type of seizure is rare under control conditions.     

Nitric oxide content measured by ESR-spectroscopy in the rat brain is increased during pentylenetetrazole-induced seizures

Nitric oxide (NO) content in rat cerebral cortex was measured using Electron Spin Resonance (ESR) spectroscopy. A nearly fivefold elevation in NO content was found at the peak time of pentylenetetrazole (PTZ)-induced seizures. The administration of N-nitro-l-arginine (L-NNA), a competitive inhibitor of NO-synthase, at the dose of 250 mg/kg, completely prevented the NO increase induced by PTZ, although clonic convulsions in the animals have been observed. L-NNA (10 mg/kg) was shown to delay the onset of clonic seizures as well as to shorten the latency of the first convulsive twitch. The level of lipid peroxidation secondary products measured as the content of thiobarbituric acid reactive species (TBARS) was increased in the cerebral cortex of PTZ-treated rats. L-NNA (250 mg/kg) failed to prevent the increased TBARS level produced by PTZ. The results support the notion that NO may play a trigger role in the pathophysiology of convulsive seizures.     

Anticonvulsant effect of flutamide on seizures induced by pentylenetetrazole: involvement of benzodiazepine receptors

PURPOSE: There is some structural similarity between the androgen receptor antagonist, flutamide (Flut) and benzodiazepines (BZDs). We evaluated the possible anticonvulsant effect and interaction of Flut with BZD receptors in common seizure models. METHODS: (a) Different groups of mice each were pretreated i.p. with Flut, and after 0.5 h, they received chemoconvulsants [pentylenetetrazole (PTZ), bicuculline, aminophylline, strychnine or kainic acid]. Latency and incidence of a clonic seizure were recorded. (b) Mice were pretreated i.p. with Flut, and after 0.5 h, transauricular electroshock was applied. Occurrence of a tonic seizure was observed. (c) Amygdala-kindled rats were pretreated i.p. with Flut, and 0.5, 1, or 2 h later, they were stimulated at afterdischarge threshold. Then the seizure parameters (afterdischarge duration, seizure severity, and stage 5 duration) were recorded. (d) The effect of Flut on clonic seizure threshold was determined by i.v. infusion of bicuculline or PTZ to different groups of Flut-receiving mice. To determine the possible interaction of Flut with BZD receptors, the flumazenil (FMZ)+Flut effect on clonic seizure threshold was compared with the effect of Flut. (e) Neurotoxicity of Flut was evaluated by rotarod test at 30 min after administration. RESULTS: Flut produced a dose-dependent anticonvulsant effect against PTZ-induced seizures [median effective dose (ED50), 67.0 mg/kg]. Moreover, Flut elevated the clonic seizure threshold induced by bicuculline or PTZ. FMZ reversed the effect of Flut on the threshold of PTZ seizures. A median toxic dose (TD50) value of 124.8 mg/kg was obtained for Flut. CONCLUSIONS: Flut both blocks PTZ-induced clonic seizures and elevates the threshold of PTZ or bicuculline-induced clonic seizures, through interaction with BZD receptors.     

Antiepileptic effects of inhibitors of nitric oxide synthase examined in pentylenetetrazol-induced seizures in rats

The effects of intraperitoneal and methyl ester, specific inhibitors of nitric oxide (NO) synthase, were examined on the pentylenetetrazol (PTZ)-induced seizures in rats. The incidence and latency for the onset of myoclonic jerks, clonic seizures, and tonic generalized extension were observed as specific parameters among PTZ-induced seizures. Both drugs preferentially suppressed the tonic generalized extension and prolonged the latency for the onset of each parameter, suggesting NO has a significant effect on the PTZ-induced seizure.     

Sequential changes of nitric oxide levels in the temporal lobes of kainic acid-treated mice following application of nitric oxide synthase inhibitors and phenobarbital

Although studies have indicated a close relationship between nitric oxide (NO) and kainic acid (KA)-induced seizures, the role of NO in seizures is not fully understood. Here, we quantified NO levels in the brain of KA-treated mice using EPR spectrometry to elucidate the role of NO in KA-induced seizures. KA was administered to mice with or without pretreatment with one of the following: N(G)-nitro-l-arginine methyl ester (l-NAME), an NO synthase (NOS) inhibitor that acts on both endothelial NOS (eNOS) and neuronal NOS (nNOS); 7-nitroindazole (7-NI), which acts more selectively on nNOS in vivo; or the anti-epileptic drug, phenobarbital. To accurately assess NO production during seizure activity, we directly measured KA-induced NO levels in the temporal lobe using an electron paramagnetic resonance NO trapping technique. Our results revealed that the both dose- and time-dependent changes of NO levels in the temporal lobe of KA-treated mice were closely related to the development of seizure activity. l-NAME mediated suppression of the KA-induced NO generation led to enhanced severity of KA-induced seizures. In contrast, 7-NI induced only about 50% suppression and had little effect on seizure severity; while phenobarbital markedly reduced both NO production and seizure severity. These results show that KA-induced neuroexcitation leads to profound increases in NO release to the temporal lobe of KA-treated mice and that NO generation from eNOS exerts an anti-convulsant 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.     

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).     

Calorie-restricted ketogenic diet increases thresholds to all patterns of pentylenetetrazol-induced seizures: critical importance of electroclinical assessment

PURPOSE: Thresholds to pentylenetetrazol (PTZ) seizures were usually based only on clinical symptoms. Our purpose was to use electroclinical patterns to assess the efficacy of a ketogenic and/or calorie-restricted diet on PTZ-induced seizures. METHODS: Forty 50-day-old rats were divided in four weight-matched groups and fed controlled diets: normocalorie carbohydrate (NC), hypocalorie carbohydrate (HC), normocalorie ketogenic (NK), and hypocalorie ketogenic (HK). After 21 days, blood glucose and beta-hydroxybutyrate levels were determined and seizures were induced by continuous infusion of PTZ. The clinical and EEG thresholds to each seizure pattern were compared between the different groups. RESULTS: The electroclinical course of PTZ-induced seizures was similar in all groups. The HK group exhibited higher thresholds than the other ones for most clinical features: absence (p = 0.003), first overt myoclonia (p = 0.028), clonic seizure (p = 0.006), and for EEG features: first spike (p = 0.036), first spike-and-wave discharge (p = 0.014), subcontinuous spike-and-wave discharges (p = 0.005). NK, HC, and NC groups were not significantly different from each other. Blood glucose and beta-hydroxybutyrate levels were not correlated with electroclinical seizure thresholds. After the clonic seizure, despite stopping PTZ infusion, a tonic seizure occurred in some animals, without significant difference regarding the diet. CONCLUSION: This approach permitted a precise study of the electroclinical course of PTZ-induced seizures. In addition to the usually studied first overt myoclonia, we clearly demonstrated the efficiency of a calorie restricted KD in elevating thresholds to most electroclinical seizure patterns. We confirmed the lack of efficiency of the KD to reduce seizure severity once the seizure has started.