Convulsant component of a depressant benzodiazepine

The convulsant influence of high doses of diazepam, in the presence of the benzodiazepine receptor antagonist Ro 15-1788, was studied in rats. Animals were implanted with permanent cortical screw electrodes for EEG recording. EEG spiking and accompanying clonic activity was observed in rats receiving greater than or equal to 200 mg/kg diazepam, followed 10 minutes later by Ro 15-1788 (20 mg/kg). Pentylenetetrazole and picrotoxin seizure thresholds, measured during constant rate iv infusion, were significantly lowered by pretreatment with diazepam (250 mg/kg) and Ro 15-1788 (20 mg/kg) administered 30 and 20 minutes, respectively, before seizure threshold measurement. It is proposed that this convulsive activity of diazepam is mediated through the picrotoxinin receptor.     

Antiepileptic effects of amphetamine may require GABA (benzodiazepine) activity

Secondary components of visual evoked potentials (slow negative wave-SNW, and photically-evoked sensory afterdischarge-SAD) are known to be precursors of experimentally activated wave-spike discharges, similar to wave-spikes of petit mal epilepsy. Both SNW and SAD may be potently suppressed wither by amphetamine or GABAergic compounds such as diazepam and sodium valproate. A hypothesis was tested in the present study, that amphetamine-induced suppression of wave-spike discharges may require GABA-benzodiazepine activity for its expression.Electrocortical activity was recorded and averaged in unrestrained albino rats with chronically implanted epicortical electrodes. SNW and SAD obtained in habituated rats in the predrug state were potently suppressed by amphetamine (1 mg/kg, i.p.). Fifteen minutes after amphetamine injection, a challenging drug (metrazol, picrotoxin, convulsant benzodiazepine, Ro 5-3663, or imidazodiazepine, Ro 15-1788) was administered intraperitoneally. Subconvulsive doses of metrazol (10 mg/kg) reversed amphetamine suppression; imidazodiazepine (20 mg/kg) and picrotoxin (1.5 mg/kg) reliably opposed the SNW suppression; convulsant benzodiazepine, Ro 5-3663 (2 mg/kg), showed modest and nonsignificant effect in the same direction. It is proposed that the antiepileptic potency of amphetamine may be associated with its ability, apparently via modulatory effect of norepinephrine, to facilitate the activation of benzodiazepine-GABA receptors.     

Effects of calcium channel blockers on bupivacaine-induced toxicity

The purpose of this study was to investigate the influence of calcium channel blockers on bupivacaine-induced acute toxicity. For each of the three tested calcium channel blockers (diltiazem, verapamil and bepridil) 6 groups of mice were treated by two different doses, i.e. 2 and 10 mg/kg/i.p., or an equal volume of saline for the control group (n=20); 15 minutes later, all the animals were injected with a single 50 mg/kg/i.p. dose of bupivacaine. The convulsant activity, the time of latency to convulse and the mortality rate were assessed in each group. The local anesthetic-induced mortality was significantly increased by the three different calcium channel blockers. The convulsant activity of bupivacaine was not significantly modified but calcium channel blockers decreased the time of latency to obtain bupivacaine-induced convulsions; this effect was less pronounced with bepridil.     

CNS Adenosine A1 Receptors Are Altered After the Administration of Convulsant 3-Mercaptopropionic Acid and Cyclopentyladenosine: An Autoradiographic Study

Rat CNS adenosine A₁ receptors were studied by quantitative autoradiography after the administration of convulsant 3-mercaptopropionic acid (MP) and an adenosine analogue cyclopentyladenosine (CPA), using 2-chloro-N⁶-[cyclopentyl-2,3,4,5-³H adenosine]-([³H]CCPA) as radioactive ligand. Specific binding was quantified in hippocampus, cerebellum, cerebral cortex, thalamic nuclei, superior colliculus and striatum, and the highest densities were found in CA1, CA2, and CA3 hippocampus subareas and the lowest levels in superior colliculus and striatum. MP administration (150 mg/kg, i.p.) produced significant increases in [³H]CCPA binding in CA1 subarea at seizure (15%) and postseizure (21%) and in CA2 at seizure (15%) but a tendency to decrease in dentate gyrus. There was an increase in cerebellum at seizure (18%) but no significant changes in the other studied regions. CPA injection (2 mg/kg, i.p.) enhanced [³H]CCPA binding in CA1 and CA2 areas (17–18%) but not in CA3 area of the hippocampus. When CPA was administered before MP, which delayed seizure onset, an increase in [³H]CCPA binding in CA1 hippocampus subarea (19%) and cerebellum (28%) was also observed. Results showed that the administration of convulsant MP and adenosine analogue CPA exerts differential effects on adenosine A₁ receptors in CNS areas; hippocampus is the most affected area with all treatments, specially CA1 subarea, supporting an essential role in convulsant activity as well as in seizure prevention.     

Anticonvulsant effects of clonazepam on chemically induced convulsions

The anticonvulsant effects of two doses of clonazepam (CZP, Rivotril Roche, 0.1 and 1 mg/kg i.p.) were studied on model motor seizures induced by strychnine, bicuculline, 3-mercaptopropionic acid and metrazol in male laboratory rats (Wistar strain). In the first part the effects of different doses of the convulsants were investigated and for interaction with CZP doses were chosen after which more than 70% of the animals displayed generalized tonic-clonic convulsions (a grand mal seizure). Strychnine induced this type of seizure only: two doses (2 and 3 mg/kg s.c.) were used. CZP reduced the incidence of convulsions only after the larger dose, but plain solvent (propylene glycol, ethanol, water) was equally effective. The other substances first induced a seizure of minimal (mainly clonic) convulsions and only later a grand mal seizure. CZP was highly effective against bicuculline (3 mg/kg s.c.) and metrazol (100 mg/kg s.c.), but was less so against 3-mercaptopropionic acid. The effect on grand mal seizures was more pronounced in every case than on minimal seizures. The decisive role in the anticonvulsant effect of CZP is played by the mechanisms by which the convulsants induce epileptic manifestations. CZP is most effective against substances acting on the supramolecular complex GABA receptor (benzodiazepine receptor) chloride ionophore (bicuculline and probably metrazol).     

Solubilization of convulsant/barbiturate binding activity on the gamma-aminobutyric acid/benzodiazepine receptor complex

Binding activity of the radioactive cage convulsant [35S]t-butylbicyclophosphorothionate was solubilized from rat brain membranes using the zwitterionic detergent 3-[(3-cholamidopropyl)-dimethylammonio] propanesulfonate. Binding (KD = 26 nM, Bmax = 0.4 pmol/mg protein) was inhibited by picrotoxin and related convulsants and by barbiturates and related depressants that interact with gamma-aminobutyric acid and benzodiazepine receptors via the picrotoxinin binding site. The convulsant/barbiturate binding activity chromatographed on gel filtration as a single peak coinciding with the benzodiazepine/gamma-aminobutyric acid receptor protein complex.     

Effects of Modafinil on Clonic Seizure Threshold Induced by Pentylenetetrazole in Mice: Involvement of Glutamate,Nitric oxide,GABA, and Serotonin Pathways

Epilepsy is the third most common chronic brain disorder. Modafinil is an awakening agent approved for narcolepsy. In addition to its clinical uses some reports revealed that modafinil was associated with some alterations in seizure threshold. The purpose of this study was to clarify the effect of acute administration of modafinil in clonic seizure threshold (CST) induced by pentylenetetrazole in mice and the involvement of glutamate, nitric oxide, gamma amino butyric acid (GABA), and serotonin systems in this feature. Modafinil at 80 and 150 mg/kg showed anti- and pro-convulsant effects respectively and expressed maximum anti- and pro-convulsant activities at 30 min after injection. Both modulatory effects were blunted by pretreatment of l-NAME [nonspecific nitric oxide synthase (NOS) inhibitor; 10 mg/kg, i.p.], 7-nitroindazole (a neuronal NOS inhibitor; 40 mg/kg, i.p.), and aminoguanidine (an inducible NOS inhibitor; 50 mg/kg, i.p.). Injection of the NOS precursor l-arginine (60 mg/kg, i.p.) before modafinil did not change the anti-convulsant effect, while thoroughly reversed the pro-convulsant one. Our experiments displayed that administration of diazepam (a GABA_A receptor agonist; 0.02 mg/kg, i.p.) and MK-801 (a NMDA receptor antagonist; 0.05 mg/kg, i.p.) before different doses of modafinil significantly increased CST. Finally, pretreatment of citalopram (a selective serotonin reuptake inhibitor; 0.1 mg/kg, i.p.) did not modify the convulsant activities of modafinil. Therefore, nitric oxide system may mediate anti-convulsant activity, while glutamate, nitric oxide, and GABA pathways may involve in pro-convulsant property. Serotonin receptors have no role on convulsant effects of modafinil.     

Recrystallization from ether causes unusual changes in the convulsant activity of pentylenetetrazol

The convulsant activity of commercial pentylenetetrazol (PTZ) and that of pentylenetetrazol recrystallized from ether (PTZE) were compared in the waking rabbit by means of recording the electrical activity of the brain. In addition, the interaction between the two substances was studied. When given in slow intravenous infusion, PTZE proved only half as effective as PTZ (threshold doses: 23.18 +/- 1.8 mg/kg and 12.40 +/- 0.7 mg/kg, respectively). One single infusion of PTZE 5-10 days prior to the administration of PTZ decreased the latter's convulsant activity to half of the original, while PTZ pretreatment left the activity of PTZE unaltered. Previous physico-chemical investigations suggested that, after recrystallization from ether the molecule might be present in dimer form at the phase-boundaries. Such a process, if taking place also at the cell membrane surface might account for the diminished convulsant activity of the recrystallized molecule.     

D-1 dopamine agonist administration reduces the threshold for convulsions produced by pilocarpine

Focal, limbic seizures were produced by systemically administered pilocarpine (200 mg/kg, i.p.); as previously described this dose produces limbic stereotypies but neither convulsions nor seizure-related brain damage. The pretreatment, 5 minutes prior pilocarpine, with the D-1 agonist SKF 38393 (-ED50 = 1 mg/kg; i.p.) induced convulsions similar to those produced by a higher, convulsant dose of pilocarpine. On the other hand, the pretreatment with the D-2 agonist LY 171555 failed to induce convulsions. The D-1 receptor antagonist SCH 23390 prevented the convulsions induced by SKF 38393 plus pilocarpine (200 mg/kg). This study indicates that D-1, but not D-2, receptor stimulation converts subconvulsant doses of pilocarpine into convulsant ones.     

Modification of the anticonvulsant efficacy of diazepam by Ro-15-1788 in the kindled amygdaloid seizure model

The effects of various doses of diazepam and the new central benzodiazepine antagonist Ro-15-1788 were investigated in fully amygdaloid kindled rats. Diazepam had a pronounced dose-dependent anticonvulsant effect in this model. Ro-15-1788 dose-dependently reduced the behavioral ranks of the elicited kindled seizures to a maximum of 60% of control without consistently modifying the afterdischarge duration. No prestimulation convulsant effects were seen with Ro-15-1788. When 2 mg/kg i.p. of Ro-15-1788 was given after various doses of diazepam, the prestimulation sedation and ataxia anticonvulsant effects of diazepam (0.5-2.0 mg/kg) were attenuated by treatment with 2 mg/kg dose of Ro-15-1788. At the low dose of diazepam (0.25 mg/kg), increased reduction of behavioral rank and after discharge duration was seen after the 2 mg/kg dose of Ro-15-1788. Thus, Ro-15-1788 appears not to have proconvulsant properties in the kindled amygdaloid seizure model. Further, Ro-15-1788 appears to have some anticonvulsant properties of its own. Mixed agonist and antagonist effects were seen with Ro-15-1788 when given after various doses of diazepam in this model.     

Korazol-induced kindling in animals with different sensitivities to the epileptogen]

To select homogeneous groups of sensitive and low-sensitive animals (male Wistar rats) for subsequent kindling experiments the animals's reaction to the threshold dose of pentylenetetrazole (PTZ) (40 mg/kg, i.p.) was defined. Rats showing convulsive response of 1 to 3 scores (seizures were estimated according to a 6-score scale) were assumed to be sensitive animals. Rats when injected with this dose showing no seizures were defined as low-sensitive animals. One week after the test kindling was started by daily administration of a subconvulsive dose of PTZ (30 mg/kg, i.p.). Low-sensitive animals displayed a 3 day delay in the development of kindling seizures and a decrease in the severity of seizures as well as an extended latency period before the first manifestations of seizures after each injection of PTZ. Thus testing by means of the threshold dose of PTZ is a comparatively simple method of preliminary estimation of the animals's sensitivity to this convulsant in order to select groups of relatively sensitive and low-sensitive animals in PTZ kindling experiments. For a more precise selection of animals it is suggested to be useful to repeat the initial test after an interval of 5-7 days. The proposed method seems to be applied in principle to other convulsants as well.     

Cyclosporine lowers seizure threshold in an experimental model of electroshock-induced seizures in Munich-Wistar rats

We have developed a model of cyclosporin A (CsA) central nervous system toxicity in the Munich-Wistar rat in which CsA, 20 mg/kg/day i.p., produces significant EEG abnormalities and mortality. In the present study we used cohorts of Munich-Wistar rats to assess effects of CsA on the threshold for tonic-clonic electroshock-induced seizures. Rat cohorts were begun on cremephore, CsA-10 mg/kg/day, or CsA-20 mg/kg/day. On day 7 and day 14 of the dosing protocol, cohorts of animals were exposed to maximal electroshock (MES) using a minimal staircase method within each cohort. Multiple logistic regression models were used to determine differences between groups on the relative odds of producing a MES-induced seizure while controlling for other variables. Seizure threshold was significantly affected by shock amperage and body weight, but not by SUN, creatinine, bilirubin, sodium, potassium, weight loss or day the shock was delivered. The odds ratios of seizure induction in the CsA-treated groups versus placebo group were 1.91 for CsA-10 mg/kg/day and 3.63 for CsA 20-mg/kg/d, both statistically significant. These results suggest that cyclosporine lowers seizure threshold and probably increases susceptibility to seizures, the etiology of which may be multifactorial clinically.     

The Anxiogenic β-Carboline FG 7142 Selectively Increases Dopamine Release in Rat Prefrontal Cortex as Measured by Microdialysis

The effect of the anxiogenic beta-carboline methyl-beta-carboline-3-carboxyamide (FG 7142) on dopamine release in prefrontal cortex and striatum in the awake freely moving rat was determined using the technique of microdialysis. FG 7142 (25 mg/kg, i.p.) caused a time-dependent increase in dopamine release in prefrontal cortex which was statistically significantly greater than the response to vehicle administration. Dopamine release in striatum was unaltered by FG 7142. Pretreatment of animals with the benzodiazepine antagonist Ro 15-1788 (30 mg/kg, i.p., 15 min prior to FG 7142 administration) completely abolished the increase in dopamine release caused by FG 7142 in prefrontal cortex. These data indicate that the anxiogenic benzodiazepine inverse agonist FG 7142 can selectively increase dopamine release in prefrontal cortex, and that this effect appears to be mediated via the gamma-aminobutyric acid/benzodiazepine receptor complex.     

Reduction of pentylenetetrazol-induced convulsions by the octadecaneuropeptide ODN

Intracerebroventricular injection of the octadecaneuropeptide ODN in mouse, at doses of 12.5-1000 ng, reduced the percentage of convulsing animals and increased the latency of convulsions elicited by pentylenetetrazol (50 mg/kg, intraperitoneal [i.p.]). ODN also reduced the percentage of mortality induced by pentylenetetrazol (100 mg/kg, i.p.). The COOH-terminal octapeptide fragment of ODN was approximately equally effective but acted more rapidly than ODN to reverse the convulsant effect of pentylenetetrazol. ODN (100 ng, intracerebroventricular [i.c.v.]) increased the convulsion latency and reduced the percentage of animals that convulsed after the administration of the inverse agonist of benzodiazepine receptors DMCM (13 mg/kg, i.p.), whereas the benzodiazepine receptor antagonist flumazenil (1 mg/kg, subcutaneously) abrogated the protective effect of ODN (100 ng, i.c.v.) on pentylenetetrazol-induced convulsions. ODN (100 ng, i.c.v.) also reduced the percentage of DBA/2J mice displaying audiogenic convulsions. In contrast, ODN did not reduce the percentage of mice displaying tonic or clonic convulsions when electrical interauricular stimulations were applied. It is concluded that ODN, or more likely a proteolytic fragment derived from ODN, reduces pentylenetetrazol-induced convulsions through activation of central-type benzodiazepine receptors.     

Reduction of pentylenetetrazol-induced convulsions by the octadecaneuropeptide ODN

Intracerebroventricular injection of the octadecaneuropeptide ODN in mouse, at doses of 12.5-1000 ng, reduced the percentage of convulsing animals and increased the latency of convulsions elicited by pentylenetetrazol (50 mg/kg, intraperitoneal [i.p.]). ODN also reduced the percentage of mortality induced by pentylenetetrazol (100 mg/kg, i.p.). The COOH-terminal octapeptide fragment of ODN was approximately equally effective but acted more rapidly than ODN to reverse the convulsant effect of pentylenetetrazol. ODN (100 ng, intracerebroventricular [i.c.v.]) increased the convulsion latency and reduced the percentage of animals that convulsed after the administration of the inverse agonist of benzodiazepine receptors DMCM (13 mg/kg, i.p.), whereas the benzodiazepine receptor antagonist flumazenil (1 mg/kg, subcutaneously) abrogated the protective effect of ODN (100 ng, i.c.v.) on pentylenetetrazol-induced convulsions. ODN (100 ng, i.c.v.) also reduced the percentage of DBA/2J mice displaying audiogenic convulsions. In contrast, ODN did not reduce the percentage of mice displaying tonic or clonic convulsions when electrical interauricular stimulations were applied. It is concluded that ODN, or more likely a proteolytic fragment derived from ODN, reduces pentylenetetrazol-induced convulsions through activation of central-type benzodiazepine receptors.     

Dose-finding study with nicotine as a proconvulsant agent in PTZ-induced seizure model in mice

The present study was conducted to investigate the possible interaction between low doses of nicotine and pentylenetetrazole (PTZ) in vivo and also to evaluate the influence of nicotine on the antiseizure efficacy of topiramate and sodium valproate in the PTZ-induced seizure model in mice. Graded dose–response study with nicotine showed the CD50 value for nicotine at 6.76 mg/kg. i.p. Subtheshold dose of nicotine (4 mg/kg, i.p.) pretreatment significantly decreased the CD50 value for PTZ from 47.86 mg/kg, i.p. (of PTZ per se) to 31.62 mg/kg, i.p. Sodium valproate but not topiramate, significantly inhibited PTZ-induced seizures in mice with an ED50 value of 177.83 mg/kg, i.p. Nonconvulsive dose of nicotine (1 mg/kg, i.p.) significantly antagonized the protective efficacy of sodium valproate against PTZ-induced seizures and increased the ED50 value to 338.84 mg/kg, i.p. PTZ-induced seizures significantly increased the mouse brain levels of MDA and reduced the level of GSH while sodium valproate reversed such changes. Nicotine pretreatment reversed the anti-lipid peroxidative action of sodium valproate in the PTZ-induced seizure model in mice. The study highlighted the convulsant as well as proconvulsant role of nicotine and established dose discrimination for nicotine as a proconvulsant agent and an anti-antiseizure agent. The study bears significant clinical relevance particularly amongst epileptic smokers who may show failure of efficacy of antiepileptic agents and present with breakthrough seizure attacks on exposure to nicotine.     

Benzodiazepine antagonists abolish electrophysiological effects of sodium valproate in the rat

A hypothesis was considered that anti-epileptic potency of sodium valproate (VPA) may be associated with its action via the benzodiazepine system. The ability of anti-petit mal drugs to suppress the slow secondary negative wave (SNW) of the visually evoked potential was used as a sensitive electrophysiological “tag” for comparison of VPA (200 mg/kg, i.p.) and Diazepam (5 mg/kg, i.p.) effects. Both drugs induced a profound inhibition of the SNW. Benzodiazepine antagonists Ro 5-3663 (2 mg/kg, i.p.) and Ro 15-1788 (5 mg/kg, i.p.) caused recovery of the SNW amplitude within several minutes of injection. Both antagonists abolished immobility and sedation produced by VPA and Diazepam. The possibility should be considered that therapeutic effects of VPA are mediated through the benzodiazepine receptor coupled to GABA.     

The non-benzodiazepine anxiolytic buspirone inhibits stress-induced renin secretion and lowers heart rate

The non benzodiazepine drug, buspirone, produces a dose-dependent biphasic effect on plasma renin activity in non-stressed rats. Low doses (0.1 - 2.0 mg/kg i.p.) decrease while high doses (10.0 - 50.0 mg/kg i.p.) increase plasma renin activity. The maximal decrease in plasma renin activity produced by buspirone (1.0 mg/kg i.p.) was observed 30 minutes post-injection. In addition, buspirone (0.5 and 2.0 mg/kg i.p.) blocked the stress-induced rise in plasma renin activity. This effect of buspirone is in contrast to the previously observed failure of the benzodiazepine anxiolytics to alter the effect of stress on plasma renin activity. Administration of buspirone (0.5 mg/kg i.p.) produced a sustained reduction (15%) in heart rate but did not affect mean arterial pressure. The present data support the view that the mechanism of the anxiolytic action of buspirone is different from that of the benzodiazepines.     

海马mu型阿片肽受体介导大鼠癫痫发作敏感性形成

为探讨海马mu型阿片肽受体介导癫痫发作敏感性形成的作用,实验采用微渗透泵技术,观察大鼠腹侧海马注射mu型阿片肽受体激动剂PL017(2.09、2.59、3.29μg/μ1)、拮抗剂β-funaltrexamine hydrochloride(β-FNA、0.88、1.10、1.35μg/μl)对红藻氨酸(kainic acid,KA)诱导癫痫发作的干预作用.PL017能够明显缩短癫痫发作潜伏期、增加癫痫发作级别(P＜0.05),β-FNA则可显著延长癫痫发作潜伏期、降低发作级别(P＜0.01);PL017和β-FNA的干预作用均表现出剂量依赖效应.结果表明,海马mu型阿片肽受体具有促进KA诱导的癫痫发作敏感性形成作用.