Tonic Hindlimb Extension Research Articles

Anticonvulsant, analgesic and antipyretic activities of Taxus wallichiana Zucc.

Taxus wallichiana Zucc. (Himalayan Yew) is often used in northern areas of Pakistan for the treatment of pyrexia, acute pains and epilepsy. We have investigated certain pharmacological activities of the methanol leaf extract against convulsion, nociception and pyrexia induced in rodents. The aim was to justify and explore its folk uses in these pathological conditions, on scientific basis. The studies were carried out using acetic acid-induced nociception and pentylenetetrazole-induced convulsions in mice, while formalin test and yeast-induced pyrexia in rats. Significant analgesic (67.77 and 74.29%) effect was found in acetic acid-induced model at doses of 100 and 200 mg/kg, i.p. respectively. Crude extract exhibited significant ( P < 0.05) inhibition of the formalin noxious stimulation on both early and late phases of pain by the extracts (100 and 200 mg/kg doses). In case of yeast-induced pyrexia model, 200 mg/kg dose showed very significant ( P < 0.01) inhibition while 50 and 100 mg/kg dose caused a significant ( P < 0.05) inhibition. Plant extract has controlled the pentylenetetrazole-induced convulsions in mice. 100 and 200 mg/kg i.p doses of the extract significantly ( P < 0.05) inhibited the mioclonus and clonus while inhibition of tonus and hind limb tonic extension (HLTE) was highly significant ( P < 0.01). The anticonvulsant activity of this plant has been reported for the first time throughout the whole genus. The observed pharmacological activities provide the scientific basis for the folkloric use of the plant in treating epilepsy, pyrexia and acute pain.

Anti-Convulsant Activity of Roots and Barks of Calotropis gigantea Linn.

Objective: Calotropis gigantea Linn. (Asclepiadaceae) a widely growing plant has been traditionally used for all kinds of fits, epilepsy, convulsions in children and paralysis complaints. The present study has been undertaken to evaluate scientifically the anti-convulsant effects of roots and barks of Calotropis gigantea Linn. using maximal electroshock seizures (MES) and Pentylenetetrazole (PTZ) induced seizure models. Methods: The effect of different extracts of roots and barks of Calotropis gigantea Linn. were evaluated for their anti-convulsant profile in MES test and PTZ test using albino Wistar rats of either sex. The ED 50 dose of Phenytoin (25 mg/kg) and Diazepam (4 mg/ kg) was used for comparison. Results: The methanolic extract at 400 mg/kg (Root) and 200 mg/kg (Bark) significantly (P<0.001) inhibited the hind limb tonic extension (HLTE) induced by MES and onset of clonic convulsion induced by PTZ respectively. Conclusions: The results show that the methanolic extract of the roots and barks of Calotropis gigantea Linn. produce better anti-convulsant activity compared to other extracts. So, on the basis of the present findings it can be observed that, the methanolic extracts of barks of C. gigantea possess potential anti-convulsant activity than methanolic extracts of roots of C. Gigantea.

Guanosine possesses specific modulatory effects on NMDA receptor-mediated neurotransmission in intact mice

Guanosine, a purine nucleotide, promotes the reuptake of l-glutamate by astrocytes; astrocytic reuptake of glutamate is a major mechanism of its synaptic inactivation. The current experiments showed that guanosine reduced the ability of MK-801 (dizocilpine), a noncompetitive NMDA receptor “open-channel” blocker, to raise the threshold voltage for electrically-precipitated tonic hindlimb extension in unstressed intact mice. This modulatory effect may be due to guanosine's removal of glutamate from the synaptic cleft, resulting in a reduced proportion of NMDA receptor-associated ion channels in the open configuration. The modulatory effect of guanosine on MK-801's ability to disrupt rotorod performance in unstressed mice or antagonize electrically-precipitated seizures in stressed mice was not seen. The inability to demonstrate modulation in the rotorod paradigm may reflect the sensitivity of this measure of motor incoordination to MK-801's disruptive effects. Whereas failure to see this effect in our incremental electroconvulsive shock paradigm in stressed mice may be due to the fact that stress and guanosine act in the same direction to reduce MK-801's antiseizure efficacy. Given the phencyclidine model of schizophrenia and its pharmacological actions as a noncompetitive NMDA receptor “open-channel” blocker and guanosine's antagonistic effect on MK-801's antiseizure efficacy in unstressed mice, the current data support development of guanine-based purines for the treatment of at least some aspects of schizophrenia.

Mirtazapine does not affect pentylenetetrazole- and maximal electroconvulsive shock-induced seizures in mice

Mirtazapine is an antidepressant exhibiting both noradrenergic and serotonergic activity. We have investigated the effects of mirtazapine on pentylenetetrazole (PTZ)- and maximal electroconvulsive shock (MES)-induced seizures in mice. Mirtazapine (1.25–20 mg/kg) or saline was administered, and locomotor activity was evaluated for 30 min. One hour after administration of mirtazapine (1.25–5 mg/kg) or saline, PTZ (80 mg/kg) was injected intraperitoneally into the mice. Immediately afterward, times of onset of the first myoclonic jerk (FMJ), generalized clonic seizures (GCS), and tonic extension (TE) were recorded. In the MES groups, we used the MES protocol to induce convulsions characterized by tonic hindlimb extension. Similarly, 1 h after mirtazapine or saline administration, an electroshock was evoked by ear-clip electrodes to induce convulsion. Mirtazapine, at 10 and 20 mg/kg, depressed locomotor activity. Doses of 1.25–5 mg/kg had no significant effect on the time of onset of FMJ, GCS, or TE induced by PTZ; on the duration of GCS and TE; or on the latency to reinstatement of the righting reflex after MES administration. Our results suggest that mirtazapine neither aggravates nor alleviates PTZ- or MES-induced seizures in mice.

Protection against generalised seizured by &lt;i&gt;Dalbergia saxatilis (Hook, F.) &lt;/i&gt; in the pentylenetetrazole and electroconvulsive models

The aqueous root decoction of Dalbergia saxatilis (DS) is used to manage convulsive disorders in African herbal medicine practice. We had previously reported the anticonvulsant effects of the aqueous root extract of DS against strychnine and picrotoxin seizures. In this study, DS was tested against pentylenetetrazole (PTZ) seizures, and electrically- induced threshold tonic extension (TTE) and kindling seizures in mice. In the PTZ model, DS (50-200 mg/kg) was administered orally to groups of mice, 30 min. before 75 mg/kg PTZ and onset to seizures noted. In the TTE test, foot shock was delivered through an electrode before treatment and 1h post- treatment. Electrical kindling was produced twice daily at 48h interval in groups of mice. Onset to tonic hind-limb extension (THE) was determined, in the kindling experiment. DS produced a dose-dependent protection against PTZ and elevated the TTE. In the electrical kindling, DS retarded the development and progression of THE, but did not produce a significant delay to THE in kindled mice. These results indicate that DS might provide protection against generalized absence and partial seizures, which further justifies its use in the management of epilepsies and convulsions in traditional African medicine. Keywords: Dalbergia saxatilis, generalized seizure, pentylenetetrazole, kindling, electro- foot shock. West African Joural of Pharmacology and Drug Research Vol. 21 (1&2) 2005: pp. 43-47

The role of 5-HT 7 receptors in the control of seizures

Serotonin exerts its effects via at least 14 different receptor subtypes, but the role of only a few of them has been studied in relation to the control of seizures. A negative role of 5-HT 7 receptors has recently been proposed. To evaluate further in unstressed and stressed animals the possible role of this receptor subtype in the control of brain excitability, we treated mice with antagonists and agonists of these receptors prior to exposure to swim stress and the intravenous infusion of picrotoxin, a non-competitive GABA A receptor antagonist. In accordance with the previous studies, swim stress increased the doses of picrotoxin producing two convulsant signs (running/bouncing clonus, tonic hindlimb extension) and death, i.e., swim stress increased the seizure threshold for picrotoxin. SB-269970 (10–30 mg/kg ip), a selective antagonist of 5-HT 7 receptors, and ritanserin (1 mg/kg ip), a nonselective 5-HT 2/7 antagonist, failed to affect, while 5-carboxamidotryptamine (5-CT), a potent 5-HT 1/7 receptor agonist, increased in unstressed and swim-stressed mice the doses of picrotoxin producing convulsions and death. The anticonvulsant effect obtained with 5-CT 0.5 mg/kg was not greater than that obtained with 0.1 mg/kg. The 5-CT (0.1 mg/kg ip)-induced increase of the seizure threshold for picrotoxin in stressed mice was abolished with SB-269970 (10 mg/kg), but not with WAY-100635 (0.3 mg/kg), a selective antagonist of 5-HT 1A receptors, suggesting that the anticonvulsant effect of 5-CT against convulsions produced by picrotoxin was achieved via 5-HT 7 receptors. The results suggest a positive role of 5-HT 7 receptors in the control of seizures.

Compensation by reduced L‐α‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazolepropionic acid receptor responses in a mouse model with reduced γ‐aminobutyric acid type A receptor‐mediated synaptic inhibition

L-alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor antagonists increase the threshold for electroshock-induced convulsions. Here, we show that a transgenic mouse line overexpressing cerebellum-restricted gamma-aminobutyric acid type A (GABA(A)) receptor alpha6 subunit in the hippocampal CA1 pyramidal cells (Thy1alpha6 mouse line) exhibits about a 20% increase in the electroshock current intensity inducing tonic hindlimb extension convulsion in 50% of the mice compared with that of their wild-type controls. AMPA receptor-mediated miniature excitatory postsynaptic currents (mEPSCs) in patch clamp recordings of CA1 pyramidal neurons in hippocampal slices had decreased amplitudes (8.4 +/- 2.2 pA) in the transgenics compared with the wild types (10.3 +/- 2.5 pA) but showed no change in current decay or frequency. Our results suggest that decreased AMPA-mediated neurotransmission might explain the increased threshold for electroconvulsions and warrant further studies on the regulation between various components of inhibition and excitation in neurons.

Ang II and Ang III modulate PTZ seizure threshold in non-stressed and stressed mice: Possible involvement of noradrenergic mechanism

The present study evaluated the effects of Angiotensin (Ang) Ang II and Ang III on pentylenetrazol (PTZ) seizure threshold in non-stressed and stressed mice as well as the possible participation of noradrenergic (NA) mechanism in their effects. While intracerebroventricular (i.c.v.) administered Ang II and Ang III increased the PTZ threshold for myoclonic twitch (MTW), generalized clonus (GNCL) and tonic hindlimb extension (THE) in non-stressed mice, they attenuated the anticonvulsant effects of acute restraint stress. The selective AT(1) receptor antagonist losartan rather than the selective AT(2) receptor antagonist PD 123319 antagonized the effects of Ang II in both non-stressed and stressed animals. Losartan also reversed the effects of Ang III on the thresholds for MTW and GNCL in stressed mice. Concurrent administration of desipramine (NA-uptake inhibitor) and either Ang II or Ang III produced a greater effect on MTW and GNCL in non-stressed mice. However, desipramine reversed the peptide-induced attenuation on PTZ seizure threshold in stressed mice. Prazosin (alpha(1)-adrenoreceptor (AR) antagonist) blocked the effects of Ang II on PTZ seizure threshold for the three convulsive phases in both non-stressed and stressed mice. Prazosin potentiated the anti-seizure effect of Ang III against MTW, GNCL, and THE in non-stressed mice while it reversed the seizure threshold-decreasing effect of this heptapeptide on MTW and GNCL in stressed mice. Yohimbine (alpha(2)-AR antagonist) blocked only the effects exerted by Ang II on the PTZ seizure threshold in non-stressed mice. Our findings suggest that the responses of Ang II and Ang III on PTZ seizure threshold can be mediated by AT(1) receptors in non-stressed and even more in stressed mice. We also hypothesize that the NA-dependent mechanism plays a major role in the effects of Ang peptides in both non-stressed and stressed mice.

Experimental manipulations of the subthalamic nucleus fail to suppress tonic seizures in the electroshock model of epilepsy

Recently, it has been shown that the subthalamic nucleus (STN) has anticonvulsant effects on epileptic seizures originating from the forebrain. The aim of the present study was to determine whether the anticonvulsant properties of the STN extend to the suppression of tonic seizures originating from the brainstem elicited by electroshock in rats. Three different procedures were used to manipulate activity in the STN and in each case the duration of tonic hindlimb extension elicited by electroshock was used as a measure of seizure-severity. Under general anesthesia, two groups of rats received chronic implants of either bilateral stainless steel guide cannulae or bilateral bipolar stimulating electrodes stereotaxically implanted and aimed at the STN. After 3 days of recovery, each rat in the first group was tested with electroshock on three consecutive days after having received 220 nl bilateral microinjections into the STN of either 200 or 400 pmol of muscimol (a GABA agonist) dissolved in saline or the same volume of normal saline. In the second group the electroshock test was conducted, again on three consecutive days, immediately following high frequency electrical stimulation (HFS) of the STN at 130 or 260 Hz or a no current control condition. In the third group, rats were tested with electroshock before and after bilateral excitotoxic lesions of the STN with either kainic or ibotenic acids. None of these manipulations produced significant suppression of the tonic hind limb extension elicited by electroshock compared with the relevant control conditions. This suggests that, within the limitations of the current procedures, the anticonvulsant properties of the STN appear to be ineffective against tonic seizures originating in the brainstem.

Activity of common anticonvulsant drugs on spinal seizure-induced by sudden cooling

Although some of the clinical signs associated with epilepsy have their origin in supraspinal structures, it is the spinal cord in the end, which is responsible for generating the typical pattern of tonic–clonic contractions associated with a convulsion. Indeed, the spinal cord isolated from influence of the brain is capable of convulsive and paroxysmal activity that exhibits the same stereotyped motor pattern seen in the intact animal. This motor pattern can be reproduced experimentally by cooling the isolated spinal cord of amphibians. The isolated spinal cord–hindleg preparation of toad was used. Convulsive activity was induced by placing the isolated spinal cord into a Ringer's bath kept at 7 °C. The characteristic phases of the convulsion and their intensity were assessed by recording tonic–clonic contractions of hindleg muscles. Two main endpoints were used to assess the anticonvulsive activity of the drugs tested: first, their ability to block only the tonic hind-limb extension (THE) and second, their ability to block all tonic–clonic activity. The ED50 values and its 95% confidence interval estimated for abolition of THE for each drugs was (mg/kg): carbamazepine 8.6 (6.8–10.8), phenytoin 13 (7.1–23.6), diazepam 0.007 (0.004–0.01), MK-801 3.4 (2.0–5.7), valproate 120 (40–400), phenobarbital 17.1 (12.2–23.9), pentobarbital 10 (6–16.4), mephenesin 2–5 and acetazolamide > 500. The ability of some of these drugs to inhibit this kind of seizure activity at doses within therapeutic range suggests a potential use of this isolated preparation as a model in the study and testing of new anticonvulsive drugs.

Modulatory effects of d-serine and sarcosine on NMDA receptor-mediated neurotransmission are apparent after stress in the genetically inbred BALB/c mouse strain

Abnormalities of NMDA receptor-mediated neurotransmission are involved in the pathophysiology of schizophrenia, Alzheimer's disease, substance abuse and seizure disorders. The NMDA receptor is implicated in schizophrenia because phencyclidine (PCP), a noncompetitive NMDA receptor antagonist, binds to a hydrophobic domain within the channel, precipitating a schizophreniform psychosis in susceptible persons. Pharmacological, environmental, and genetic variables alter NMDA receptor-mediated neurotransmission. Inbred mouse strains differ in their sensitivity to some of the behavioral effects of MK-801 (dizocilpine), a PCP analogue. The NMDA receptor complex in the BALB/c strain could reflect a unique stoichiometric combination of receptor subunits resulting in a higher proportion of the channels in the open configuration, a higher affinity of MK-801 for its hydrophobic channel domain, and/or a combination of the above. The BALB/c mouse strain, “stressed” mice, and behavioral consequences of MK-801 administration represent models of altered glutamatergic neural transmission. We were interested in examining the effect of stress on the modulatory properties of d-serine and sarcosine. d-Serine is a naturally occurring glycine agonist that modulates the ability of l-glutamate to influence the opening of the NMDA receptor-associated ionophore, and sarcosine is a naturally occurring glycine reuptake inhibitor. The data suggest that 24 h after stress, d-serine and sarcosine interact synergistically to reduce MK-801's ability to antagonize electrically precipitated tonic hindlimb extension. Under conditions of stress, modulatory effects of d-serine and sarcosine on the antiseizure effect of MK-801 are observed that are not apparent in the nonstress condition. The results could be relevant to the development of glycinergic interventions for the treatment of neuropsychiatric disorders.

Isobolographic analysis of interactions between losigamone and conventional antiepileptic drugs in the mouse maximal electroshock model

The aim of this study was the isobolographic evaluation of interactions between losigamone (LSG), valproate (VPA), carbamazepine (CBZ), phenytoin (PHT), and phenobarbital (PB) in the maximal electroshock (MES) test in mice. Electroconvulsions were produced by means of an alternating current (ear-clip electrodes, 0.2-s stimulus duration, and tonic hindlimb extension taken as the endpoint). Adverse effects were evaluated in the chimney test (motor coordination) and the passive avoidance task (long-term memory). Brain concentrations of antiepileptic drugs (AEDs) were measured by immunofluorescence or high-performance liquid chromatography. Isobolographic analysis indicated synergistic interactions between LSG and VPA. For example, in the proportion of 1:1 the theoretically calculated 50% effective dose for additivity (ED 50add) was 138 mg/kg, while the experimentally derived ED 50 for the mixture (ED 50mix) was 85.2 mg/kg. The difference was significant at p < 0.001. LSG combined with CBZ or PHT showed additivity, whereas the combinations of LSG with PB were either additive, for the fixed ratios of 1:3 and 1:1, or antagonistic for the ratio of 3:1 (ED 50add = 18.4 mg/kg versus ED 50mix = 26.7 mg/kg, p < 0.05). Impairment of long-term memory was noted only in the case of VPA given at its ED 50, however this AED did not affect motor performance. LSG, CBZ, PHT and PB (applied at their ED 50 values) and co-administration of LSG with conventional AEDs (including VPA) impaired neither motor performance nor long-term memory. LSG did not affect the brain concentration of VPA or PB, but significantly elevated the brain concentrations of CBZ and PHT. In contrast, VPA, CBZ and PHT significantly increased the brain concentration of LSG, indicating a pharmacokinetic contribution to the observed pharmacodynamic interactions. Although LSG exhibited some favorable pharmacodynamic interactions with various AEDs, these were complicated by pharmacokinetic interactions and emphasize the importance of measuring AED concentrations in studies designed to identify desirable AED combinations.

Exogenously administered d-serine failed to potentiate the ability of MK-801 to antagonize electrically precipitated seizures in nonhandled control and stressed mice

NMDA receptor hypofunction (NRH) has been implicated in the pathophysiology of schizophrenia because of the ability of phencyclidine (PCP), a noncompetitive NMDA receptor antagonist, to precipitate a schizophreniform psychosis. The possible role that NRH plays in the pathophysiology of schizophrenia stimulated characterization of behaviors elicited by PCP and its analogues. For example, MK-801 (dizocilpine), a noncompetitive NMDA receptor antagonist that binds with higher affinity to the same hydrophobic channel domain as PCP, raises the threshold voltage required for the electrical precipitation of tonic hindlimb extension in mice. This ability of MK-801 is significantly reduced following stress. We showed that an exogenously administered glycine prodrug (i.e., milacemide) was able to potentiate MK-801's antiseizure efficacy in unstressed mice and restore MK-801's antiseizure efficacy in stressed animals. d-Serine may serve as an endogenous agonist for the obligatory glycine co-agonist site on the NMDA receptor complex. Orally administered d-serine has been studied clinically as an adjuvant therapeutic intervention in schizophrenia. Thus, we were surprised at its inability to potentiate MK-801's antiseizure efficacy in either control or stressed animals. These data do not support the development of d-serine as a viable therapeutic intervention for schizophrenia and, possibly, other disorders.

Evidence Supporting a Role of Serotonin in Modulation of Sudden Death Induced by Seizures in DBA/2 Mice

Sudden unexpected death in epilepsy (SUDEP) is a serious concern for epilepsy patients. DBA/2 mice are proposed as a SUDEP model, because these mice exhibit respiratory arrest (RA) after audiogenic seizures (AGSs), and RA is also implicated in human SUDEP. Respiratory mechanisms are modulated, in part, by serotonin. Therefore we evaluated the effects of serotoninergic agents on RA incidence in DBA/2 mice. DBA/2 mice (75%) exhibited AGS and RA, and approximately 99% of animals could be resuscitated. The mice exhibiting RA were given a selective serotonin reuptake inhibitor, fluoxetine, 24 h after the initial AGS, and RA susceptibility was evaluated 30 min later. Ten percent of DBA/2 mice exhibited tonic hindlimb extension (TE) without RA, and a serotonin antagonist (cyproheptadine) was administered to these mice. Fluoxetine (15-25 mg/kg, i.p.) significantly reduced the incidence of RA in DBA/2 mice after AGSs, and this effect was reversible by 72 h. Only the 25-mg/kg dose reduced AGS severity. In mice exhibiting TE without RA, the incidence of RA was significantly increased 30 min after cyproheptadine (1-2 mg/kg i.p.). Most of these mice exhibited AGSs without RA again by 72 h. These findings indicate that fluoxetine reduced RA in DBA/2 mice at doses that did not reduce seizure severity. Because DBA/2 mice are a proposed model for human SUDEP, these data support evaluation of fluoxetine for SUDEP prevention in the patient population most susceptible to SUDEP. The data raise concern about the use of serotonin antagonists in this patient population.

Stimulation of 5-HT 1A receptors increases the seizure threshold for picrotoxin in mice

To evaluate the possible role of 5-HT 1A and 5-HT 2A receptors in the anticonvulsant effect of swim stress, mice were pre-treated with agonists and antagonists of these receptors prior to exposure to stress and the intravenous infusion of picrotoxin. 8-OH-DPAT ((±)-8-hydroxy-2-(di- n-propylamino) tetralin) and WAY-100635 (a selective agonist and antagonist of 5-HT 1A receptors), DOI (1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane) and ketanserin (a 5-HT 2A/2C receptor agonist and antagonist) were used. Results demonstrated that 1 and 3 mg/kg of 8-OH-DPAT increased the doses of picrotoxin producing running/bouncing clonus, tonic hindlimb extension and death in stressed and unstressed mice, respectively. Pre-treatment with WAY (0.3 mg/kg) prevented the effect of 8-OH-DPAT (3 mg/kg). DOI (2.5 mg/kg) and ketanserin (1 mg/kg) failed to affect the seizure threshold for picrotoxin. The results show that stimulation of 5-HT 1A receptors exerts anticonvulsant actions in stressed and unstressed mice, while stimulation of 5-HT 2A/2C receptors does not interfere with the effect of stress on picrotoxin-induced convulsions.

Effect of acute versus chronic theophylline administration on acute restraint stress-induced increase of pentylenetetrazol seizure threshold in mice

Various stressful paradigms were found to induce anticonvulsant effects in different seizure models. Methylxanthines, such as theophylline might contribute to the reduction of restraint-induced stress. Therefore, in this study the influence of acute restraint stress on pentylenetetrazol (PTZ) seizure thresholds as well as the effect of acute and chronic theophylline pretreatment on stress-induced modulation of the seizure threshold were assessed in mice. The onset of the three consecutive seizure phases: myoclonic twitch (MTW), generalized clonus (GNCL) and tonic hind limb extension (THE) was delayed after exposure to a 2 h restraint stress by 34%, 23% and 24%, respectively. In nonstressed mice, acute theophylline injection (100 mg/kg, i.p.) decreased the threshold only for THE. However, in stressed animals, the pretreatment with the methylxanthine significantly enhanced the dose of the convulsant producing the same seizure phase. In nonstressed mice, long-term theophylline treatment (50 mg/kg, twice daily for 14 days) increased PTZ threshold for all three seizure phases. In contrast, in chronically treated with theophylline mice exposed to restraint stress, significant decrease in the PTZ threshold for all seizure phases compared to control stressed animals have been observed. These results suggest that, depending on the treatment regimen (acute versus chronic), theophylline specifically and differentially modulates the anticonvulsant effect of restraint stress in mice.

P.4.026 The anticonflict and antidepressant-like effects of proproten are serotonin dependent

Two novel nipecotic acid derivatives, 1-(3-(9H-Carbazol-9-yl)-1-propyl)-4-(4-methoxyphenyl)-4-piperidinol (NNC 05-2045) and 1-(3-(9H-Carbazol-9-yl)-1-propyl)-4-(2-methoxyphenyl)-4-piperidinol (NNC 05-2090) have been tested for inhibition of γ-amino butyric acid (GABA) transporters in synaptosomal preparations of rat cerebral cortex and inferior colliculus and found to differ markedly from gabitril® (tiagabine), a selective GAT-1 inhibitor. IC50 values for inhibition of [3H]GABA uptake into synaptosomes from cerebral cortex for NNC 05-2045 and NNC 05-2090 were 12±2 and 4.4±0.8 μM, respectively. In synaptosomes from inferior colliculus in the presence of 1 μM 1-(2-(((diphenylmethylene)amino)oxy)ethyl)-1,2,5,6-tetrahydro-3-pyridinecarboxylic acid (NNC 05-0711), a highly potent and selective GAT-1 inhibitor, IC50 values for inhibition of [3H]GABA uptake were 1.0±0.1 and 2.5±0.7 μM, respectively. A receptor profile showed that NNC 05-2045 has binding affinities to sigma-, α1- and D2-receptors of 113, 550 and 122 nM, respectively. NNC 05-2090 displayed α1- and D2-receptor affinity of 266 and 1632 nM, respectively. The anticonvulsant action of both compounds was tested in four rodent models after intra peritoneal (i.p.) injection. Both NNC 05-2045 and NNC 05-2090 dose-dependently inhibited sound-induced tonic and clonic convulsions in DBA/2 mice with ED50 values of 6 and 19 μmol/kg, respectively. NNC 05-2045 also antagonized sound-induced seizures in genetic epilepsy prone rats (GEP rats) with ED50 values against wild running, clonic and tonic convulsions of 33, 39 and 39 μmol/kg, respectively (NNC 05-2090 was not tested in GEP rats). Both NNC 05-2045 and NNC 05-2090 dose-dependently antagonized tonic hindlimb extension in the maximal electroshock (MES) test with ED50 values of 29 and 73 μmol/kg, respectively. In amygdala kindled rats NNC 05-2045 and NNC 05-2090 significantly (P<0.05) reduced generalized seizure severity (seizure grade 3–5) at highest doses (72–242 μmol/kg) and NNC 05-2090 also significantly reduced afterdischarge duration at these doses (P<0.05). These data show that inhibition of GABA uptake through non-GAT-1 transporters has different anticonvulsant effects than selective GAT-1 inhibitors (e.g. tiagabine) in that enhanced efficacy against MES and reduced efficacy against kindled seizures is observed. Although a contribution of adrenergic agonistic effects cannot be entirely ruled out, it is proposed that inhibition of GAT-3 (mouse GAT4) is primarily responsible for the anticonvulsant action of these two nipecotic acid derivatives in MES, amygdala kindled rats and in sound-induced seizures in GEP-rats and DBA/2 mice.

Anticonvulsant effects of acute and repeated fluoxetine treatment in unstressed and stressed mice

Comorbidity of epilepsy and depression is not rare. Stress can affect both depression and seizures. Therefore, it is important to know whether an antidepressant drug has pro- or anticonvulsant properties and whether these properties will be modified by stress. We tested the effects of the antidepressant drug fluoxetine on the seizure threshold for picrotoxin in unstressed and swim-stressed mice. The mice were, prior to exposure to swim stress and the intravenous infusion of picrotoxin (a non-competitive GABA A receptor antagonist), pretreated with fluoxetine (a selective serotonin reuptake inhibitor), either acutely or repeatedly (5 days), and the latency to the onset of two convulsant signs and death was registered. The convulsant signs were running/bouncing clonus and tonic hindlimb extension. As expected, swim stress enhanced the seizure threshold for picrotoxin. Fluoxetine (20 mg/kg ip) given acutely increased in unstressed and swim-stressed mice the dose of picrotoxin producing tonic hindlimb extension and in unstressed mice the dose of picrotoxin producing death. Neither 10 nor 20 mg/kg of fluoxetine affected doses of picrotoxin needed to produce running bouncing/clonus. Repeated treatment with fluoxetine (20 mg/kg ip) enhanced significantly in unstressed and swim-stressed mice doses of picrotoxin needed to produce tonic hindlimb extension and death, and in stressed mice also the dose of picrotoxin producing running/bouncing clonus. The results demonstrate that the antidepressant drug fluoxetine, given acutely or repeatedly, shows anticonvulsant properties against convulsions induced in unstressed and swim-stressed mice by antagonist of GABA A receptors, picrotoxin. Swim stress failed to modify the anticonvulsant properties of fluoxetine.

Mice carrying the szt1 mutation exhibit increased seizure susceptibility and altered sensitivity to compounds acting at the m-channel.

Mutations in the genes that encode subunits of the M-type K+ channel (KCNQ2/KCNQ3) and nicotinic acetylcholine receptor (CHRNA4) cause epilepsy in humans. The purpose of this study was to examine the effects of the Szt1 mutation, which not only deletes most of the C-terminus of mouse Kcnq2, but also renders the Chnra4 and Arfgap-1 genes hemizygous, on seizure susceptibility and sensitivity to drugs that target the M-type K+ channel. The proconvulsant effects of the M-channel blocker linopirdine (LPD) and anticonvulsant effects of the M-channel enhancer retigabine (RGB) were assessed by electroconvulsive threshold (ECT) testing in C57BL/6J-Szt1/+ (Szt1) and littermate control C57BL/6J+/+ (B6) mice. The effects of the Szt1 mutation on minimal clonic, minimal tonic hindlimb extension, and partial psychomotor seizures were evaluated by varying stimulation intensity and frequency. Szt1 mouse seizure thresholds were significantly reduced relative to B6 littermates in the minimal clonic, minimal tonic hindlimb extension, and partial psychomotor seizure models. Mice were injected with LPD and RGB and subjected to ECT testing. In the minimal clonic seizure model, Szt1 mice were significantly more sensitive to LPD than were B6 mice [median effective dose (ED50) = 3.4 +/- 1.1 mg/kg and 7.6 +/- 1.0 mg/kg, respectively]; in the partial psychomotor seizure model, Szt1 mice were significantly less sensitive to RGB than were B6 mice (ED50 = 11.6 +/- 1.4 mg/kg and 3.4 +/- 1.3 mg/kg, respectively). These results suggest that the Szt1 mutation alters baseline seizure susceptibility and pharmacosensitivity in a naturally occurring mouse model.

Anticonvulsive effect of agmatine in mice

The present study was designed to examine the effect of agmatine, the decarboxylated product of l-arginine by l-arginine decarboxylase, on convulsion in the mouse maximal electroshock (MES) test and mouse glutamate-induced convulsant test. MES convulsion and glutamate convulsion were respectively induced by an electrical stimulation (110 V, 0.3 s, 8 Hz) and by intracerebroventricular injection of glutamate (0.5 M, pH 7.4, 5μl). The results were expressed as the tonic and clonic time of convulsion in MES or percentage of mice with tonic hind-limb extension in glutamate-induced convulsant assay. Agmatine given intracerebroventricularly (2–16 mg/kg) or subcutaneously (10–160 mg/kg) significantly shortened the tonic and clonic times of convulsion in a dose-dependent manner in the mouse MES test. Glutamate (0.5 M, 5μl icv per mouse) induced an obvious convulsive response indicated by tonic hind-limb extension in mice, and agmatine (2–16 mg/kg icv) decreased the rate of mice with tonic hind-limb extension like NMDA receptor antagonist MK-801. The anticonvulsive effect of agmatine (80 mg/kg sc) on both the tonic and clonic times of convulsion lasted for more than 4 h after administration in the mouse MES test, which was twice that of barbital. Taken together, the results implicate that agmatine has obvious anticonvulsive effects, and its possible mechanism might be related to the antagonism of the function of NMDA receptors.