Pharmacodynamics of potassium channel openers in cultured neuronal networks

A novel class of drugs - potassium (K(+)) channel openers or activators - has recently been shown to cause anticonvulsive and neuroprotective effects by activating hyperpolarizing K(+) currents, and therefore, may show efficacy for treating tinnitus. This study presents measurements of the modulatory effects of four K(+) channel openers on the spontaneous activity and action potential waveforms of neuronal networks. The networks were derived from mouse embryonic auditory cortices and grown on microelectrode arrays. Pentylenetetrazol was used to create hyperactivity states in the neuronal networks as a first approximation for mimicking tinnitus or tinnitus-like activity. We then compared the pharmacodynamics of the four channel activators, retigabine and flupirtine (voltage-gated K(+) channel KV7 activators), NS1619 and isopimaric acid ("big potassium" BK channel activators). The EC50 of retigabine, flupirtine, NS1619, and isopimaric acid were 8.0, 4.0, 5.8, and 7.8µM, respectively. The reduction of hyperactivity compared to the reference activity was significant. The present results highlight the notion of re-purposing the K(+) channel activators for reducing hyperactivity of spontaneously active auditory networks, serving as a platform for these drugs to show efficacy toward target identification, prevention, as well as treatment of tinnitus.

Acute seizure tests in epilepsy research: electroshock- and chemical-induced convulsions in the mouse

Epilepsy is a common (50 million patients worldwide) neurological disorder characterized by seizures that are caused by episodic abnormal electrical activity in the brain. Animal models play an essential role in epilepsy research including the discovery and development of new antiepileptic drugs. Described in this unit are protocols for traditional acute tests in which seizures are induced by either an electrical stimulation or a convulsant agent in non-epileptic mice. Specifically, protocols for the following acute seizure tests are provided: the maximal electroshock induced test (MES), the maximal electroshock seizure threshold (MEST) test, the 6-Hz seizure test, the subcutaneous pentylenetetrazol (s.c. PTZ) seizure test, and the intravenous pentylenetetrazol (i.v. PTZ) seizure test. These tests can be used to characterize anticonvulsant and/or proconvulsant properties of compounds in mice. The MES, s.c. PTZ, and 6-Hz seizure tests represent the three most widely used animal tests in drug-screening programs. Although the parameters of these tests are optimized for mice, the same tests (except for the 6-Hz seizure test), with some modifications, can be used with rats.

Synthesis, anticonvulsant and neurotoxicity screening of some novel 1,2,4-trisubstituted-1H-imidazole derivatives

A series of 1,2,4-trisubstituted-1H- imidazole derivatives (4a-o) was synthesized by reacting 2,4-disubstituted-1H-imidazoles (3a-o) with chlorobenzene in the presence of triethylamine. Phenylglyoxal (2) was reacted with different aromatic aldehydes in the presence of ammonium acetate and glacial acetic acid to afford the disubstituted imidazoles (3a-o). The structures of the synthesized compounds were confirmed on the basis of their elemental analysis and spectral data results. Anticonvulsant activity was shown by majority of the synthesized compounds in the maximal electroshock (MES) and subcutaneous pentylenetetrazole (scPTZ) screens when given i.p. to mice. In anticonvulsant screening, only one compound 4k showed potent activity comparable to that of standard drugs phenytoin and carbamazepine. Compounds 4a, 4c, 4e, 41 and 4n passed the rotorod test successfully without any sign of neurological deficit.

Effects of gamma-decanolactone on seizures induced by PTZ-kindling in mice

Gamma-decanolactone is a monoterpene compound, and its psychopharmacological evaluation in mice revealed that it has a dose-dependent effect on the central nervous system, with hypnotic, anticonvulsant, and hypothermic activity. The aim of the present study was to investigate the effect of gamma-decanolactone on pentylenetetrazole (PTZ)-kindling in mice. Phenobarbital, an antiepileptic drug, was also tested for the purpose of comparison. After the behavioral procedures had been undertaken, the animals were killed and brain tissue was sampled to evaluate DNA damage in the brain using comet assay. The data reported here suggest that the administration of phenobarbital (10 mg/kg) and gamma-decanolactone at 0.3 g/kg, but not at 0.1 g/kg, impairs both the severity and the progression of seizures in the PTZ-kindling model. DNA damage to brain tissue decreased in gamma-decanolactone-treated kindling animals (similar to phenobarbital) as compared to nontreated animals. The results suggest that gamma-decanolactone has dose-dependent anticonvulsant properties, and may also have antiepileptogenic and neuroprotective effects in the PTZ-kindling model.

Synthesis and CNS depressant activity of some novel 3-[5-substituted 1,3,4-thiadiazole-2-yl]-2-styryl quinazoline-4(3H)-ones

A series of novel 3-[5-substituted phenyl-1,3,4-thiadiazole-2-yl]-2-styryl quinazoline-4(3H)-ones were synthesized and evaluated for anticonvulsant, sedative-hypnotic and CNS depressant activities. After i.p. injection to mice at doses of 30, 100, and 300mg/kg body weight 2-styrylquinazolin-4(3H)-one derivatives were examined in the maximal electroshock induced seizures (MES) and subcutaneous pentylenetetrazole (scPTZ) induced seizure models in mice. The neurotoxicity was assessed using the rotorod method. Out of eighteen compounds only 4a, 4d, 4e, 4j and 4k showed anticonvulsant activity in one or more test models. All except 4e and 4f exhibited significant sedative-hypnotic activity via actophotometer screen. CNS depressant activity screened with the help of the forced swim pool method resulted into some potent compounds. From the experimental observation it can be concluded that synthesized compounds exhibited relatively better sedative-hypnotic and CNS depressant activities.

Synthesis, physicochemical and anticonvulsant properties of new N-phenylamino derivatives of 2-azaspiro[4.4]nonane- and [4.5]decane-1,3-diones: part V

The synthesis, physicochemical and pharmacological properties of new N-phenylamino derivatives of 2-azaspiro[4.4]nonane-1,3-dione (8-10), 2-azaspiro[4.5]decane-1,3-dione (11-18) and 3-cyclohexyl-pyrrolidine-2,5-dione (19, 20) derivatives were described. The anticonvulsant properties of those compounds were examined by a maximal electroshock (MES) and a pentylenetetrazole (scPTZ) tests, and their neurotoxicity was determined using a rota-rod test. The most active was N-[(2,4-dichlorophenyl)-amino]-2-azaspiro[4.4]nonane-1,3-dione (9), which exhibited anti-seizure properties in the MES model at a dose of 100mg/kg in mice and at a dose of 30mg/kg in rats. To explain the possible mechanism of action, for chosen active derivatives N-[(2,4-dichlorophenyl)-amino]-2-azaspiro[4.4]nonane-1,3-dione (9), N-[(4-bromophenyl)-amino]-2-azaspiro[4.4]nonane-1,3-dione (10), N-[(2,4-dichlorophenyl)-amino]-2-azaspiro[4.5]decane-1,3-dione (12) and N-[(4-bromophenyl)-amino]-2-azaspiro[4.5]decane-1,3-dione (13) their influence on GABA(A) receptors were tested in vitro. Moreover, for all compounds obtained the lipophilic properties were determined by use of RP-HPLC method.

Fluoxetine attenuates the effects of pentylenetetrazol on rat freezing behavior and c-Fos expression in the dorsomedial periaqueductal gray

The aim of the study was to investigate the role of the periaqueductal gray (PAG) in anxiolytic-like actions of fluoxetine in animals treated with an anxiogenic drug, pentylenetetrazol (PTZ), and subjected to fear conditioning procedure. The data showed that PTZ given at the dose of 30 mg/kg 15 min before a retention trial significantly decreased freezing reaction (p<0.01), and potently enhanced rat locomotor activity (p<0.01), in comparison to the control group. These effects were reversed by prior (60 min) administration of fluoxetine (20 mg/kg). Simultaneously, PTZ significantly increased c-Fos expression in the dorsomedial periaqueductal gray (DMPAG), examined 2h after the retention trial, in comparison to the control group (p<0.01). Fluoxetine (20 mg/kg) administered 60 min before PTZ reversed this effect. PTZ given at the same dose and time interval in the open field test did not affect rat locomotor behavior. Importantly, fluoxetine pretreatment did not change PTZ concentration in brain tissue. Our experiment based on PTZ-enhanced aversive conditioning revealed that acutely administered fluoxetine antagonized PTZ-induced panic-like behavior, and this phenomenon was accompanied by inhibition of activity of DMPAG.

Effects of tianeptine on onset time of pentylenetetrazole-induced seizures in mice: possible role of adenosine A1 receptors

Depression is a common psychiatric problem in epileptic patients. Thus, it is important that an antidepressant agent has anticonvulsant activity. This study was organized to investigate the effects of tianeptine, an atypical antidepressant, on pentylenetetrazole (PTZ)-induced seizure in mice. A possible contribution of adenosine receptors was also evaluated. Adult male Swiss-Webster mice (25-35 g) were subjects. PTZ (80 mg/kg, i.p.) was injected to mice 30 min after tianeptine (2.5-80 mg/kg, i.p.) or saline administration. The onset times of 'first myoclonic jerk' (FMJ) and 'generalized clonic seizures' (GCS) were recorded. Duration of 600 s was taken as a cutoff time in calculation of the onset time of the seizures. To evaluate the contribution of adenosine receptors in the effect of tianeptine, a nonspecific adenosine receptor antagonist caffeine, a specific A1 receptor antagonist 8-cyclopentyl-1,3-dipropylxanthine (DPCPX), a specific A2A receptor antagonist 8-(3-chlorostyryl) caffeine (CSC) or their vehicles were administered to the mice 15 min before tianeptine (80 mg/kg) or saline treatments. Tianeptine (40 and 80 mg/kg) pretreatment significantly delayed the onset time of FMJ and GCS. Caffeine (10-60 mg/kg, i.p.) dose-dependently blocked the retarding effect of tianeptine (80 mg/kg) on the onset times of FMJ and GCS. DPCPX (20 mg/kg) but not CSC (1-8 mg/kg) blocked the effect of tianeptine (80 mg/kg) on FMJ. Our results suggest that tianeptine delayed the onset time of PTZ-induced seizures via adenosine A1 receptors in mice. Thus, this drug may be a useful choice for epileptic patients with depression.

Nicotine antagonizes caffeine- but not pentylenetetrazole-induced anxiogenic effect in mice

RATIONALE

Nicotine and caffeine are widely consumed licit psychoactive drugs worldwide. Epidemiological studies showed that they were generally used concurrently. Although some studies in experimental animals indicate clear pharmacological interactions between them, no studies have shown a specific interaction on anxiety responses.

OBJECTIVES

The present study investigates the effects of nicotine on anxiety induced by caffeine and another anxiogenic drug, pentylenetetrazole, in mice. The elevated plus-maze (EPM) test was used to evaluate the effects of drugs on anxiety.

METHODS

Adult male Swiss Webster mice (25-32 g) were given nicotine (0.05-0.25 mg/kg s.c.) or saline 10 min before caffeine (70 mg/kg i.p.) or pentylenetetrazole (15 and 30 mg/kg i.p.) injections. After 15 min, mice were evaluated for their open- and closed-arm time and entries on the EPM for a 10-min session. Locomotor activity was recorded for individual groups by using the same treatment protocol with the EPM test.

RESULTS

Nicotine (0.05-0.25 mg/kg) itself did not produce any significant effect in the EPM test, whereas caffeine (70 mg/kg) and pentylenetetrazole (30 mg/kg) produced an anxiogenic effect, apparent with decreases in open-arm time and entry. Nicotine (0.25 mg/kg) pretreatment blocked the caffeine- but not pentylenetetrazole-induced anxiety. Administration of each drug and their combinations did not produce any effect on locomotor activity.

CONCLUSIONS

Our results suggest that the antagonistic effect of nicotine on caffeine-induced anxiety is specific to caffeine, instead of a non-specific anxiolytic effect. Thus, it may extend the current findings on the interaction between nicotine and caffeine.

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.

Synthesis and evaluation of antimicrobial and anticonvulsant activities of some new 3-[2- (5-aryl-1,3,4-oxadiazol-2-yl/4-carbethoxymethylthiazol-2-yl) imino-4-thiazolidinon-5-ylidene]-5-substituted/nonsubstituted 1H-indole-2-ones and investigation of their structure-activity relationships

In the present study, 20 new compounds having 3-[2-(5-aryl-1,3,4-oxadiazol-2-yl) imino-4-thiazolidinon-5-ylidene]-5-substituted/nonsubstituted 1H-indole-2-one (I-XII) and 3-[2-(4-carbethoxymethylthiazol-2-yl)imino-4-thiazoldinon-5-ylidenel-5-substituted/nonsubstituted IH-indole-2-one (XIII-XX) systems were synthesized. The structures were confirmed by spectral methods (UV, IR, 1H-NMR, 13C-NMR, 13C-DEPT (135), electron impact mass spectrometry) and elemental analysis. All compounds were tested for in vitro antimicrobial activity against Staphylococcus aureus ATCC 6538, Staphylococcus epidermidis ATCC 12228, Escherichia coli ATCC 8739, Klebsiella pneumoniae ATCC 4352, Pseudomonas aeruginosa ATCC 1539, Salmonella typhi, Shigella flexneri, Proteus mirabilis ATCC 14153, Candida albicans ATCC 10231, Microsporum gypseum (NCPF-580), Microsporum canis, Trichophyton mentagrophytes and Trichophyton rubrum and some of them were found to be active. Especially, compound I was more active than cefuroxime sodium (CAS 56238-63-2) which was used as a standard, and the activity of compound XII was close to that of cefuroxime sodium against Staphylococcus epidermidis ATCC 12228. Primary screening for antituberculous activity was conducted at 6.25 microg/ml against Mycobacterium tuberculosis H37Rv in BACTEC 12B medium using the BACTEC 460 radiometric system. The anticonvulsant activities of selected prototoype compounds (I, IV-VI, VIII, XI, XIII, XVI-XVIII) administered at doses of 50-200 mg/kg (i.p.) were evaluated using the pentetrazol test (PTZ) in mice.

TPA023 [7-(1,1-dimethylethyl)-6-(2-ethyl-2H-1,2,4-triazol-3-ylmethoxy)-3-(2-fluorophenyl)-1,2,4-triazolo[4,3-b]pyridazine], an agonist selective for alpha2- and alpha3-containing GABAA receptors, is a nonsedating anxiolytic in rodents and primates

7-(1,1-Dimethylethyl)-6-(2-ethyl-2H-1,2,4-triazol-3-ylmethoxy)-3-(2-fluorophenyl)-1,2,4-triazolo[4,3-b]pyridazine (TPA023) is a triazolopyridazine that binds with equivalent high (subnanomolar) affinity to the benzodiazepine binding site of recombinant human GABA(A) receptors containing an alpha1, alpha2, alpha3, or alpha5 subunit but has partial agonist efficacy at the alpha2 and alpha3 subtypes and essentially antagonist efficacy at the alpha1 and alpha5 subtypes. In rats, TPA023 gave time- and dose-dependent occupancy after oral dosing, with 50% occupancy corresponding to a dose of 0.42 mg/kg. It has anxiolytic-like activity in unconditioned (elevated plus maze) and conditioned (fear-potentiated startle and conditioned suppression of drinking) rat models of anxiety with minimum effective doses (MED; 1-3 mg/kg) corresponding to 70 to 88% occupancy. However, there was no appreciable sedation in a response sensitivity (chain-pulling) assay at a dose of 30 mg/kg, resulting in 99% occupancy. Similarly, TPA023 was robustly anxiolytic in the squirrel monkey conditioned emotional response assay, with a MED of 0.3 mg/kg, but did not produce any sedation in a lever-pressing test of sedation even at 10 mg/kg. TPA023 produced no impairment in performance in the mouse Rotarod assay, and there was only a mild interaction with ethanol. In addition to anxiolytic-like efficacy, TPA023 had anticonvulsant activity in a mouse pentylenetetrazole seizure model. Finally, TPA023 did not cause precipitated withdrawal in mice treated for 7 days with the nonselective agonist triazolam, nor did N-methyl-beta-carboline-3-carboxamide (FG 7142) precipitate withdrawal in mice treated for 7 days with TPA023. In summary, the novel alpha2/alpha3-selective efficacy profile of TPA023 translates into a nonsedating anxiolytic profile that is distinct from nonselective agonists.

The novel GABA adamantane derivative (AdGABA): design, synthesis, and activity relationship with gabapentin

A facile preparation of 2-aminomethyl-2-tricyclo[3.3.1.1(1,7)]decaneacetic acid hydrochloride 5 (AdGABA) is described. The synthesis of AdGABA involves the hydrogenation of 2-cyano-2-tricyclo[3.3.1.1(1,7)]decaneacetic acid 11, which was synthesized by two different synthetic routes. AdGABA was found to antagonize the pentylenetetrazole (PTZ) and semicarbazide (SCZ) induced tonic convulsions and exhibits analgesic activity in the hot plate test on mice. Although its mechanism of action is quite similar to that proposed previously for gabapentin (interaction with the alpha2delta subunit of the voltage gated Ca2+ channels), further studies were undertaken in order to clarify the precise mechanism of the anticonvulsant and analgesic effects of AdGABA on a molecular level.

Anticonvulsant effects of 1,25-dihydroxyvitamin D in chemically induced seizures in mice

Here, we study the role of a neurosteroid hormone Vitamin D in epilepsy. To examine this problem, we used 1,25-dihydroxyvitamin D, an active form of Vitamin D, injected subcutaneously to NMRI mice (33 microg/20 microl) 40 min prior to seizures induced by systemic injection of pentylenenetrazole (PTZ, 70 mg/kg). Overall, compared to the vehicle-treated control animals (n=11 in each group), the Vitamin D-treated mice demonstrated reduced severity of PTZ-induced seizures (longer latency, shorter duration and lower mortality). In a separate experiment, we assessed the time-course of antiepileptic effects of 1,25-dihydroxyvitamin D. For this, we injected this compound (33 microg/20 microl) to NMRIx129S1 mice (n=11) 40 min, 3, 6, 12 and 24 h prior to seizures, showing that antiepileptic effects were short-term, almost disappearing 3h after administration. Our findings show that Vitamin D plays a direct anticonvulsant role in the brain and suggest that the Vitamin D endocrine system may represent a new target for the development of anticonvulsant drugs.

Amiloride protects against pentylenetetrazole-induced kindling in mice

This study was performed to investigate whether or not amiloride, a sodium-hydrogen exchanger (NHE) inhibitor, can protect against seizure development of pentylenetetrazole (PTZ)-induced kindling in mice.Kindling was induced by once every 2 days treatment with PTZ (25 mg kg(-1) i.p.) for 5 weeks. Challenge experiments were carried out after 15 or 30 days of last treatment with PTZ. Administration of amiloride (2 h before PTZ, in doses of 0.65 and 1.3 mg kg(-1), p.o.) significantly prolonged the onset of kindling and reduced the incidence and severity of seizures in a dose-dependent manner. The effect of amiloride on the incidence of PTZ-induced seizures was evident even after 15 or 30 days of last treatment. The results indicate a protective role for amiloride against PTZ-induced kindling in mice. The possibility of mediation of such effects by NHE inhibition is discussed.

Pharmacological and behavioral characteristics of interactions between vigabatrin and conventional antiepileptic drugs in pentylenetetrazole-induced seizures in mice: an isobolographic analysis

To characterize the anticonvulsant effects and types of interactions exerted by mixtures of vigabatrin (VGB) and conventional antiepileptic drugs (valproate (VPA), ethosuximide (ESM), phenobarbital (PB), and clonazepam (CZP)) in pentylenetetrazole (PTZ)-induced seizures in mice, the isobolographic analysis for three fixed-ratio combinations of 1 : 3, 1 : 1, and 3 : 1 was used. The adverse-effect profile of the combinations tested, at the doses corresponding to their median effective doses (ED(50)) at the fixed-ratio of 1 : 1 against PTZ-induced seizures, was determined by the chimney (motor performance), step-through passive avoidance (long-term memory), pain threshold (pain sensitivity), and Y-maze (general explorative locomotor activity) tests in mice. Additionally, the observed isobolographic interactions were verified in terms of a pharmacokinetic interaction existence. VGB combined with PB or ESM exerted supra-additive (synergistic) interactions against the clonic phase of PTZ-induced seizures, which was associated with the increment of PB or ESM concentrations in the brains of examined animals. The remaining combinations tested (ie VGB+VPA and VGB+CZP) occurred additive in the PTZ test, which was associated with no significant changes in the brain concentrations of VPA and CZP. None of the examined combinations exerted motor impairment in the chimney test in mice. In the standard variant of passive avoidance task (current of 0.6 mA; 2 s of stimulus duration), the combinations of VGB+CZP and VGB+VPA significantly affected long-term memory in mice. Moreover, VGB in a dose-dependent manner lengthened the latency to the first pain reaction in the pain threshold test in mice. The modified variant of step-through passive avoidance task (current of 0.6 mA; stimulus duration based on the latency from the pain threshold test) revealed no significant changes in the long-term memory of animals for the combinations of VGB+VPA and VGB+CZP; so the observed effects in the standard variant of passive avoidance task were a result of the antinociceptive effects produced by VGB. In the Y-maze test, VGB also, in a dose-dependent manner, increased the general explorative locomotor activity of the animals tested. Similarly, the total number of arm entries in the Y-maze was significantly increased for the combinations of VGB+CZP and VGB+ESM, but not for VGB+PB and VGB+VPA. The application of VGB in combination with PB, ESM, CZP, and VPA suppressed the clonic phase of PTZ-induced seizures, having no harmful or deleterious effects on behavioral functioning of the animals tested, which might be advantageous in further clinical practice.

Anticonvulsant activity of Heracleum persicum seed

The anticonvulsant activity of acetone extract of the seeds of Heracleum persicum (Umbelliferae) was examined against pentylenetetrazole (PTZ) and maximal electroshock (MES)-induced seizures in mice. The extract showed a dose-dependent protective effect in both seizure models. However, the sedative dose of the extract, examined by rotarod test, was close to the anticonvulsant doses. Preliminary phytochemical analysis showed the presence of alkaloids, terpenoids, triterpenes and steroids in the extract. The observed pharmacological effects could be due to alkaloids, terpenoids and triterpenes present in the plant.

General pharmacology of KP-102 (GHRP-2), a potent growth hormone-releasing peptide

The general pharmacological effects of the hexapeptide KP-102 (D-alanyl-3-(2-naphthyl)-D-alanyl-L-alanyl-L-tryptophyl-D-phenylalanyl-L-lysinamide dihydrochloride, growth hormone-releasing peptide-2, GHRP-2, pralmorelin, CAS 158861-67-7), which potently promotes growth hormone (GH) release by acting at both hypothalamic and pituitary sites, were evaluated in various animal experimental models. The administration of KP-102 showed no obvious effect at a pharmacological dose on the central nervous system. KP-102 had no significant effect on the autonomic nervous system and smooth muscle except a slight and transient increase in spontaneous motility of isolated rabbit ileum and contraction of isolated guinea pig ileum at high doses. There was negligible effect on the respiratory and cardiovascular systems, digestive system, renal function and blood system after KP-102 treatment. These results suggest that KP-102 has no serious general pharmacological effects at dose levels showing GH-releasing activity in the experimental animals. Therefore, it is concluded that KP-102 will be a useful drug for the diagnosis of serious GH deficiency and for treatment of short stature.

Kynurenine administered together with probenecid markedly inhibits pentylenetetrazol-induced seizures. An electrophysiological and behavioural study

The kynurenine pathway converts tryptophan into various compounds, including l-kynurenine, which in turn can be converted to the excitatory amino acid receptor antagonist kynurenic acid, which may therefore serve as a protective agent in such neurological disorders as epileptic seizures. Kynurenic acid, however, has a very limited ability to cross the blood-brain barrier, whereas kynurenine passes the barrier easily. In this study, we tested the hypothesis that kynurenine administered systemically together with probenecid, which inhibits kynurenic acid excretion from the cerebrospinal fluid, results in an increased level of kynurenic acid in the brain that is sufficiently high to provide protection against the development of pentylentetrazol-induced epileptic seizures. CA3 stimulation-evoked population spike activity was recorded from the pyramidal layer of area CA1 of the rat hippocampus, and in another series of behavioural experiments, water maze and open-field studies were carried out to test the presumed protective effect of kynurenine + probenecid pre-treatment against pentylenetetrazol-induced seizures. This study has furnished the first electrophysiological proof that systemic kynurenine (300 mg/kg, i.p.) and probenecid (200 mg/kg, i.p.) administration protects against pentylenetetrazol-induced (60 mg/kg, i.p.) epileptic seizures.

Group I metabotropic glutamate receptors interfere in different ways with pentylenetetrazole seizures, kindling, and kindling-related learning deficits

LY 367385 (mGluR1) and MPEP (mGluR5), which are group I metabotropic glutamate receptor (mGluR) antagonists, were used to investigate their effects on pentylenetetrazole (PTZ) seizures, kindling, and kindling-related learning deficits. Both substances showed anticonvulsant efficacy against seizures induced by lower doses of PTZ (40 mg/kg), but they were ineffective in counteracting seizures evoked by higher PTZ doses. When these substances were given in the course of kindling induction, LY significantly depressed the progression of kindled seizure severity. In contrast, MPEP was ineffective in this experiment. Treatment with either LY or MPEP did not modify the reaction to challenge dose of PTZ. Kindling results in a worsening of shuttle-box learning. LY improved shuttle-box learning when administered in the course of kindling development or when given prior to the learning experiment. This suggests protective and restorative effectiveness. In contrast, MPEP was only effective on the learning performance of kindled rats when given prior to the shuttle-box experiment, which demonstrates restorative effectiveness. Kindling is associated with an increase in glutamate binding. LY counteracted this increase whereas MPEP was ineffective. It was concluded that mGluR1 and mGluR5 play a specific role in the convulsive component of kindling. The beneficial action of the antagonists on kindling-induced impairments in shuttle-box learning may be associated with their effect on glutamatergic synaptic activity.

Mécanisme d’action des effets anticonvulsivant et anti-immobilité (nage forcée) de la 3’, 4’-dihydro-N, N-diméthylspiro [9H-fluorène-9, 2’ (5’H)- furane] - 3’-méthanamine (AE37F)

AE37F, a new aminotetrahydrofuranic derivative, exhibited, at 10-30 mg/Kg (po) or 1-10 mg/Kg (ip), antagonism of tonic convulsions, induced by pentetrazole (130 mg/Kg, ip), and of forced swin immobility, in mice. At these doses AE37F induced a considerable (100-250%) increase of serotonin (5-HT) and its main metabolite, 5-hydroxyindolacetic acid (5-HIAA), in the rat nucleus reticularis pontis oralis (NRPO), antagonized by amantadine, which also increased 5-HT and 5-HIAA levels in the NRPO. It is suggested: a) that the anti-immobility effect of AE37F is related to its antimuscarinic properties, b) that the rate of 5-HT release in the NRPO, calculated here by a new approach (from the 5-HT and 5-HIAA brain levels) is increased by AE37F and decreased by amantadine, in the NRPO, c) that the anti-convulsant action, observed with AE37F, could be related to a NMDA-sigma mediated stimulation of serotoninergic, GABAergic and glycinergic brain neurones, antagonized by the NMDA-sigma inhibition induced by amantadine.

[Experimental characteristics of the neurotropic spectrum of some antiepileptic agents]

Investigation of the psychotropic spectrum of phenobarbital, diphenin, milontin, pufemide, sodium valproate (depakine), and diazeparn showed that, besides antagonism with the corazole and electroshock effects, all these drugs prevented to a considerable degree the kindling seizures in rats on a "tonsil swing" (chronic electroencephalographic partial epilepsy) model. The mechanism of this effect probably involves exciting amino acids. All anticonvulsants except for diazepam also restored memory in experimental animals with retrograde electroshock amnesia. The administration of diazepam, diphenin, and sodium valproate to rats with kindling convulsions led to activation of the spontaneous horizontal motions in the open-field test, which can be explained by the presence of antianxiety component in the drug action.

Effects of endogenous histamine on seizure development of pentylenetetrazole-induced kindling in rats

This study was performed to investigate whether or not endogenous histamine can protect seizure development of pentylenetetrazole (PTZ)-induced kindling in rats. An intracerebroventricular (i.c.v.) injection with clobenpropit (5 and 10 microg), a representative H(3)-antagonist, significantly prolonged the onset of kindling and inhibited the seizure stages in a dose-dependent manner. Its action was significantly reversed by both immepip (2 microg, i.c.v.), an H(3)-agonist, and alpha-fluoromethylhistidine (alpha-FMH, 10 microg, i.c.v.), a selective histidine decarboxylase inhibitor. alpha-FMH (20 microg, i.c.v.) and pyrilamine (1 and 5 mg/kg i.p.), a classical H(1)-antagonist, markedly augmented the severity of seizure development of PTZ-induced kindling. Therefore, these results indicate that brain endogenous histamine plays a certain protective role on seizure development of PTZ-induced kindling in rats, and that its protective roles are mediated by H(1)-receptors.

Synthesis and evaluation of anticonvulsant activities of some bis Mannich bases and corresponding piperidinols

Some acetophenone derived bis Mannich bases (B1-B5) and piperidinols (C1, C4), which are the structural isomers of B1 and B4, and also quaternary piperidine derivative C6 were synthesized and studied for anticonvulsant activity. Of the compounds, C6 was reported for the first time. Chemical structures of the compounds were confirmed by UV, IR, 1H-NMR, 13C-NMR, mass spectra and elemental analysis. Their anticonvulsant activities were determined by maximal electroshock (MES), subcutaneous metrazol (scMet) tests and rotarod test for neurological deficits. According to the activity studies, B2, B4, C1 and C4 derivatives were found to be protective against MES at 30 mg/kg and above. B1, B2, B3, B4, C4 and C6 derivatives were found to be protective against scMet. at different dose levels ranging from 30 to 300 mg/kg. Since no neurotoxicity was detected for the compounds B4 and C4, they seem to be candidate compounds for further synthesis and in vivo studies for their potential anticonvulsant activity.

Design and synthesis of 4H-3-(2-phenoxy)phenyl-1,2,4-triazole derivatives as benzodiazepine receptor agonists

A series of new 5-substituted analogues of 4H-3-(2-phenoxy)phenyl-1,2,4-triazole and its chlorinated derivatives was designed and prepared. Conformational analysis and superimposition of energy minima conformers of the compounds on estazolam, a known benzodiazepine receptor agonist, revealed that the main proposed benzodiazepine pharmacophores were well matched. Rotarod and pentylenetetrazole-induced lethal convulsion tests showed that the introduction of an amino group in position 5 of 1,2,4-triazole ring especially in chlorinated derivatives had the best effect which was comparable with diazepam.

Anti-nociceptive and anti-inflammatory effects of methanolic extract of Asparagus pubescens root in rodents

The effect of methanolic extract of Asparagus pubescens was investigated on chemical, thermal-induced pain as well as fresh egg albumin-induced inflammation and pentylenetetrazol (PTZ)-induced convulsion in rodents. The extract dose-dependently (0.25-1.5 g/kg) inhibited acetic acid-induced writhing, formalin-induced pain licking and hot plate-induced pain in mice. The extract significantly inhibited both the fresh egg albumin-induced inflammation in rats as well as PTZ-induced convulsion in mice. These inhibitions were statistically significant (P < 0.02-0.001). It increased the latencies of both clonic and tonic convulsions and delayed their mortalities. Its ability to reduce both neurogenic and non-neurogenic pains may be related to its active constituents such as tannins, saponins, steroid and flavonoids.

Synthesis and biological activity of certain novel derivatives of 1H-pyrrolo[1,2-c][1,3]thiazine

The reaction of 2-(beta-hydroxyethyl)-pyrrolidine with isothiocyanates gave rise to the formation of thiourea derivatives which cyclised on refluxing in hydrobromic acid to yield N-(3,4,4a,5,6,7-hexahydro-1H-pyrrolo[1,2-c][1,3]thiazin-1-ylidene)-aryl(alkyl)amines. The results of preliminary pharmacological screening are presented.

Synthesis and anticonvulsant activity of 3-(6-substituted-benzothiazol-2-yl)-6-phenyl-[1, 3]-xazinane-2-thiones

A new series of 3-(6-substituted-benzothiazol-2-yl)-6-phenyl-[1, 3]-oxazinane-2-thiones (4a-j) has been synthesised using an appropriate synthetic route (Scheme 1) and characterised by elemental analyses and spectral (IR, (1)HNMR, (13)C NMR, and EI MS) data. The anticonvulsant activity of all the title compounds (4a-j) was evaluated against Maximal Electroshock (MES) induced seizures and furthermore the most potent compounds were evaluated against subcutaneous pentylenetetrazole (sc PTZ) induced seizures model in mice. The neurotoxicity was assessed using the rotorod procedure. All the test compounds were administered intraperitoneally at various dose levels ranging from 30-200 mg/kg body wt and the median effective dose (ED(50)), median toxic dose (TD(50)), and protection index (PI) values were determined (Table 2). Among the compounds tested, the 3-(6-dimethylaminobenzothiazol-2-yl)-6-phenyl-[1, 3]-oxazinane-2-thiones (4j) was found to be the most potent (ED(50): 9.85 and 14.8 in MES model and 12 and 17 in scPTZ model at t = 0.5 h and 4 h, respectively, and TD(50) 42.8 and 44 at t = 0.5 h and 4 h, respectively, which has been found to be significant at p < 0.01 with respect to reference standard phenytoin) with protection index (PI) 4.85.

Experimental conditions for the continuous subcutaneous infusion of four central analgesics in rats

For the analysis of pharmacotherapeutic regimens for chronic pain in animals, it is important to establish delivery methods in which analgesics can be administered continuously and at a constant rate for a prolonged period of time. This allows for the assessment of how drug effects may vary over time in the presence of ongoing pain. The present study determined, for four analgesic compounds, the maximal doses that met all of the following criteria: (i) water-soluble, (ii) stable over 14 days at 38 degrees C, and (iii) devoid of undesirable side-effects in normal rats, as assessed by evolution of body weight and temperature after the subcutaneous implantation of an osmotic mini-pump that continuously infused the compounds over a 14-day period. The results showed the maximal doses to be 5 mg/rat/day for morphine hydrochloride, 2.5 mg/rat/day for imipramine hydrochloride, 20 mg/rat/day for ketamine hydrochloride, and 10 mg/rat/day for gabapentin. These doses were further found to be sufficient to express each compound's representative pharmacological activity. The conditions identified here appear appropriate for future studies of these four compounds in rat models of chronic pain and neuropathic allodynia.

Anticonvulsive activity of Butea monosperma flowers in laboratory animals

The bioassay-guided fractionation of dried flowers of Butea monosperma (BM) was carried out to isolate the active principle responsible for its anticonvulsant activity. The petroleum ether extract was fractionated by column chromatography using solvents of varying polarity such as n-hexane, n-hexane:ethyl acetate, ethyl acetate, and methanol. The anticonvulsive principle of B. monosperma was found to be a triterpene (TBM) present in the n-hexane:ethyl acetate (1:1) fraction of the petroleum ether extract. TBM exhibited anticonvulsant activity against seizures induced by maximum electroshock (MES) and its PD(50) was found to be 34.2+/-18.1 mg/kg. TBM also inhibited seizures induced by pentylenetetrazol (PTZ), electrical kindling, and the combination of lithium sulfate and pilocarpine nitrate (Li-Pilo). However, TBM was not effective against seizures induced by strychnine and picrotoxin. TBM exhibited depressant effect on the central nervous system. After repeated use for 7 days, the PD(50) (MES) of TBM increased to 51.5+/-12.1 mg/kg. Similarly, after repeated use of TBM, the duration of sleep induced by pentobarbital was not reduced significantly. Further studies are required to investigate its usefulness in the treatment of epilepsy.

Selectivity of the protective effects of dihydropyridine calcium channel antagonists against the ethanol withdrawal syndrome

Four dihydropyridine calcium channel antagonists were compared for their ability to protect against the hyperexcitability produced in mice by withdrawal from chronic ethanol treatment and to protect against seizures due to bicuculline or pentylenetetrazol. Comparison was also made of their effects on locomotor activity, body temperature and motor co-ordination, and with the corresponding effects of the benzodiazepine, diazepam. Nitrendipine, nimodipine, nicardipine (at 50 and 10 mg/kg) and isradipine (at 10 and 4 mg/kg) decreased the withdrawal hyperexcitability, but showed no anticonvulsant action against either bicuculline or pentylenetetrazol. Diazepam (1.5 and 4 mg/kg) both protected against the withdrawal signs and decreased seizure incidence after bicuculline and pentylenetetrazol, although the latter effects were of shorter duration than those on the withdrawal signs. The four dihydropyridines decreased spontaneous locomotor activity, an effect which lasted up to 6 h. Only isradipine and diazepam had any ataxic actions at the doses tested. All the dihydropyridines had hypothermic actions, considerably shorter in duration than effects on withdrawal hyperexcitability, with little evidence of dose dependence, except for nicardipine, which had a larger, dose-related, hypothermic action. Of the four compounds, isradipine was more potent in terms of dose, but not any more selective for effectiveness against the withdrawal signs, than the other three dihydropyridines, and nicardipine was slightly less effective in protecting against the withdrawal signs. The results indicate that the anticonvulsant effects of the dihydropyridines were selective for ethanol withdrawal hyperexcitability, whereas diazepam showed no such selectivity.

Synthesis and pharmacological activity of 1,4-benzodiazepine derivatives

2-Aminobenzamides (3a-g) were prepared starting with isatoic anhydride. These compounds reacted with chloroacetic acid to give (4a-g), which were cyclized by dicyclohexylcorbodiimide to afford (5a-g). The preliminary pharmacological screening revealed that some of the new 2H-1,4-benzodiazepin-3,5(1H,4H)-dione derivatives (5) exhibited CNS-depressant and anticonvulsant activities.

Anticonvulsant activities of ethanolic extract and aqueous fraction isolated from Delphinium denudatum

Dried roots of Delphinium denudatum Wall. are a popular folk remedy for the treatment of epilepsy in the traditional Unani system of medicine in the sub-continent. We carried out anticonvulsant screening of the ethanolic extract (EE) and aqueous fraction (AF) of this plant utilising the maximal electroshock (MEST) and subcutaneous pentylenetetrazole (scPTZ), bicuculline (scBIC), picrotoxin (scPTX) and strychnine (scSTN) tests for anticonvulsant activity. EE had weak dose-dependent anticonvulsant effects on seizures induced by PTZ and BIC. AF exhibited dose-dependent activity against hind limb tonic extension phase (HLTE) of MEST and comparatively stronger anticonvulsant activity against seizures induced by PTZ and BIC. The results suggest the presence of potent anticonvulsant compounds in AF of D. denudatum and deserve further investigation for isolation of active compounds and elucidation of the mechanism of anticonvulsant action.

Anticonvulsant and neurotoxicity evaluation of 5-(un)-substituted isatinimino derivatives

Various Schiff bases were prepared by reacting 5-(un)-substituted isatin with some heterocyclic compounds, viz., N-[4-(4'-chlorophenyl-thiazol-2-yl] semicarbazide, 3-amino-2-methylmercaptoquinazolin-4-one, 3-(4'-pyridyl)-4-amino-5-mercapto-4(H)-1,2,4-triazole and 4-(4'-chlorophenyl)-6-(4"-methylphenyl)-2-aminopyrimidine. The compounds were evaluated for anticonvulsant and neurotoxic properties. The compound 3-(3',4'-dihydro-2'-methylmercapto-4'-oxoquinazolin-3'-yl) iminoisatin (3) emerged as the most active analogue showing anti-MES and anti-PTZ activities better than valproic acid. All the compounds showed lower neurotoxicity than phenytoin and carbamazepine.

Synthesis and anticonvulsant activity of N,N-phthaloyl derivatives of central nervous system inhibitory amino acids

In order to study the influence of the length of the amino acid chain of N,N-phthaloyl-amino acid amides as analogues of the former anticonvulsant taltrimide on the seizure-antagonizing activity glycine, beta-alanine and gamma-aminobutyric acid (GABA) derivatives were synthesized. The corresponding taurine derivatives were also included. Generally, the glycine-derived amides showed a higher activity than the beta-alanine and GABA derivatives in the maximal electroshock seizure (MES) test in mice upon intraperitoneal administration. The activity was comparable to the respective taurine derivatives. The N,N-phthaloyl-glycine amides were also active in the MES test upon oral administration to rats. No significant activity was noted in the seizure threshold test with subcutaneous pentylene-tetrazole. The ED50 of N,N-phthaloyl-glycine ethyl amide (4b) in the MES test upon intraperitoneal administration to mice was 19.1 mg/kg. On a molar basis this activity is comparable to the activity of phenytoin with little toxicity in the rotorod test. In conclusion, N,N-phthaloyl-glycine amides might represent promising antiepileptic drugs.

Low doses of AMPA exert anticonvulsant effects on pentylenetetrazol-kindled seizures

Excitatory amino acids (EAAs) are critically involved in the initiation and propagation of seizures. N-methyl-D-aspartate (NMDA) and alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA) receptors appear to be of special interest in this regard. Besides receptor binding by antagonists, the function of glutamatergic synapses can be altered via autoreceptor-mediated mechanisms or by receptor desensitisation. Therefore, the effect of AMPA (1, 10 or 100 pmol per animal, intracerebroventricular injection) was tested on acutely induced pentylenetetrazol (PTZ) seizures. The lowest dose exerted clear anticonvulsant effects. Furthermore, 1 and 10 pmol AMPA were tested for their efficacy to suppress PTZ kindling. The lower dose reduced seizure severity significantly but 10 pmol AMPA was ineffective. In reaction to a test dose of PTZ, the kindled groups pretreated with AMPA reached seizure scores similar to saline-pretreated kindled rats, suggesting that the kindled state was reached. In a further experiment, we tested the effect of cyclothiazide (CYC, which blocks AMPA receptor desensitisation) on the 1 pmol AMPA-mediated anticonvulsant effect. The AMPA response was not altered. These results suggest that autoreceptor-mediated mechanisms rather than desensitisation might contribute to the anticonvulsant effect found.

Spatiotemporal analysis of Fos expression associated with cocaine- and PTZ-induced seizures in prenatally cocaine-treated rats

We previously reported that prenatal cocaine exposure (40 mg/kg s.c., E10-E20) increased susceptibility to convulsant-induced seizures later in life, with female rats becoming more sensitive to seizures induced by cocaine and pentylenetetrazol (PTZ), and males more sensitive to PTZ-induced seizures (Snyder-Keller and Keller, 1995, 2000). In order to determine the locus of enhanced seizure susceptibility in the brains of prenatally cocaine-treated rats, we examined the distribution and density of Fos-immunoreactive cells after cocaine- and PTZ-induced seizures in mature rats. Subconvulsive cocaine doses induced c-fos in cortical areas as well as densely dopamine-innervated regions such as striatum and nucleus accumbens. Following cocaine-induced seizures, intense c-fos induction was observed in piriform cortex, amygdala, and hippocampus. Quantification of the number of Fos-immunoreactive cells in the brains of prenatally cocaine-treated versus prenatally saline-treated rats revealed differences in piriform cortex and amygdala that were indicative of a lower threshold in prenatally cocaine-treated female rats. Following PTZ-induced seizures, the same pattern of limbic structures were recruited with increasing seizure severity. Only females exhibited changes in the number of Fos-immunoreactive cells as a result of prenatal cocaine treatment. Pretreatment with the noncompetitive NMDA antagonist MK-801 blocked both cocaine- and PTZ-induced seizures, and Fos expression in limbic areas was also blocked. The dopamine D1 antagonist SCH 23390 blocked cocaine-induced seizures and associated c-fos induction, but not PTZ-induced seizures or Fos. Examination of the pattern of Fos expression at 15-20 min postseizure revealed that the initial site of c-fos induction associated with PTZ-induced seizures appeared to be the piriform cortex, whereas cocaine-induced seizures induced early expression in both piriform cortex and lateral amygdala. These findings suggest that neural alterations residing in the piriform cortex and amygdala are likely to account for the increased seizure susceptibility of prenatally cocaine-treated rats.

[Psychotropic effects of alkaloid lappaconitine and its various derivatives]

The psychotropic activity of (I, base), its N-oxide, and a complex of the base with 18-alpha-H-glycyrrhizic acid (1:2) was studied. It was established that I and its N-oxide exhibit dopaminopositive effect whereas the complex produces a serotoninopositive effect. Toxicities of the lipophilic I is half that of the hydrophilic; toxicity of N-oxide and the complex are 60 and 100 times lower than the activity of lappaconitine (base).

Amino acid derivatives with anticonvulsant activity

A series of benzylamides of N-alkylated, N-acylated or free nine cyclic and one linear amino acids as potential anticonvulsants have been synthesized. The structures of the obtained compounds were designed on the basis of the previously determined structure and physicochemical properties/anticvonvulsant activity relationship of the formerly synthesized compounds of this type. The obtained compounds were evaluated in mice after intraperitoneal (i.p.) administration, by maximal electroshock seizure test (MES test), subcutaneous (s.c.) pentylenetetrazol test (s.c. PTZ test) and by the rotarod neurotoxicity test (Tox test). The results were the basis for their classification into one of three classes of the Anticonvulsant Screening Project (ASP) of the Antiepileptic Drug Development Program (ADDP) of the NIH. Three selected compounds were tested quantitatively in rats after oral administration. The MES ED50, s.c. PTZ ED50, Tox TD50 were determined and their protective index (PI) values were calculated. Anticonvulsant activity of the most promising compound (15) was examined in different seizure models. The respective ED50 and PI values of this compound were as follows: against bicuculline, 73 and 1.4; against PTZ, 47 and 2.2; against strychnine, 73 and 1.4; against pilocarpine 156, and 0.7; against kainic acid (2-carboxy-4-isopropenyl-3-pyrrolidineacetic acid), 39 and 2.6; against AMPA (alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid), 10 and 10.3 and against NMDA (N-methyl-D-Aspartic acid), 114 and 0.9.

Anticonvulsant and sedative effects of some 5-substituted bromopyrazolinic spirobarbiturates

We studied in mice the neuropharmacological effect of some 5-substituted bromopyrazolinic spirobarbiturates. LD50 and CL50 values were estimated for all the investigated compounds. The effect on potentiation of sodium pentobarbital activity and on generalised tonic-clonic seizures produced by PTZ on mice was studied. All the compounds had the same pharmacological profile, they extended sleeping-time induced by sodium pentobarbital and showed protection against PTZ-induced convulsions, decreasing the death rate.

Previous prolonged clonic seizures diminish antiepileptic activity of valproate against pentetrazol-evoked convulsions

Prolonged seizures may alter the brain function in numerous ways. It is conceivable that they might lead to modifications of seizure susceptibility or anticonvulsive drug efficacy, however, only limited data address this issue. Therefore, we have decided to estimate the antiepileptic activity of drugs interfering with GABA-ergic neurotransmission in mice subjected to prolonged clonic seizures 2 weeks before, using pentetrazol test. The activity of valproate, but not diazepam or phenobarbital, was diminished in animals following repetitive clonic seizures. It might be hypothesized that in humans suffering from epilepsy, prolonged seizures in the past might contribute to the lowered efficacy of valproic acid later on.

4-Hydroxybenzaldehyde from Gastrodia elata B1. is active in the antioxidation and GABAergic neuromodulation of the rat brain

Ether fraction of G. elata methanol extract significantly inhibited the recovery time and severity induced by pentylenetetrazole (PTZ) treatment. Pretreatment of ether fraction of G. elata methanol extract successfully prevented diminution of brain GABA level in subconvulsive dose of PTZ-treated rats. 4-Hydroxybenzaldehyde, an analogue of p-hydroxybenzyl alcohol, showed an inhibitory effect on the GABA transaminase, and its inhibitory activity was higher than that of valproic acid, a known anticonvulsant. In the brain of PTZ-treated rats, brain lipid peroxidation was significantly increased, while it recovered to the control level after treatment with 4-hydroxybenzaldehyde. It may be concluded that antioxidation and positive modulation of GABAergic neuromodulation of 4-hydroxybenzaldehyde partially contribute to an antiepileptic and anticonvulsive activity of G. elata B1.

Anticonvulsant activity of essential oils and active principles from chemotypes of Lippia alba (Mill.) N.E. Brown

In the present work we studied the anticonvulsive effects of the essential oils (EOs) from three chemotypes of Lippia alba (Mill.) N.E.Brown (Verbenaceae). Animals (female Swiss mice, 25 g) were treated with the EO and, 30 or 60 min after intraperitoneal (i.p.) or oral (p.o.) administration, respectively, injected with pentylenetetrazole (80 mg/kg, i.p.) and observed for 30 min. The results showed that EO I (200 and 400 mg/kg), EO II (100, 200 and 400 mg/kg), and EO III (400 mg/kg), i.p., produced an increased latency time for the first convulsion as related to controls. Death latency was greater in the groups receiving EO I (50 and 100 mg/kg), EO II (100 and 200 mg/kg), and EO III (200 mg/kg), i.p. Orally, while no effect was demonstrated with EOs at doses of 200 or 400 mg/kg, significant increases in the latency of convulsion and latency of death were observed with EO I at the highest dose (800 mg/kg). Similarly, EO III at this dose was also effective as far as latency of convulsion is concerned. Animals treated with citral (100 mg/kg, i.p.), beta-myrcene or limonene (200 mg/kg, i.p.), EOs chemical constituents, presented significant increases in the latency of convulsion and percentage of survival as compared to controls. After oral administration these effects were observed only with a higher dose (400 mg/kg). The association of EOs with diazepam significantly potentiated their effects, suggesting a similar mechanism of action and indicating that citral, beta-myrcene, and limonene are probably the EOs active compounds.

Does fucose or piracetam modify the effect of hypoxia preconditioning against pentylenetetrazol-induced seizures?

To clarify the question whether the duration of hypoxia exposure has an influence on the point in time or the strength of hypoxic preconditioning, hypoxia exposure of rats lasting 1 and 8 h was tested regarding the modification of susceptibility to acute pentylenetetrazol-induced seizures. Following the short-lasting (1 h) hypoxia, the maximum level of preconditioning action was observed 7 days after hypoxia, whereas the longer-lasting hypoxia (8 h) produced the maximum level of protection 14 days after hypoxia. We investigated the influence of fucose and piracetam on the effect of hypoxia preconditioning by the application of the substances 20 min before the beginning of hypoxia exposure. Fucose did not modify the result of hypoxia preconditioning. But after the treatment with piracetam, the preconditioning effect was prevented following hypoxia lasting 1 and 8 h. We suggest that the radical scavenger properties of piracetam are responsible for the absence of protection against pentylenetetrazol-evoked seizures.

Progesterone and testosterone modulate the convulsant actions of pentylenetetrazol and strychnine in mice

The influence of progesterone and testosterone on the incidence of seizures after administration of intraperitoneal pentylenetetrazol and subcutaneous strychnine was evaluated in mice. Pentylenetetrazol and strychnine were administered in doses that induced seizures in 40-50% of control mice in dioestrus (48 and 0.9 mg/kg, respectively). The percentage of seizures induced by pentylenetetrazol and strychnine was significantly lower in female mice in prooestrus/oestrus, when progesterone levels are high, than in dioestrus, when progesterone levels are low. Pretreatment of pentylenetetrazol-challenged mice with progesterone (250 microg/kg) increased the incidence of seizures in prooestrus/oestrus, without affecting seizures in dioestrus. The same pretreatment in strychnine-challenged mice also increased the incidence of seizures in prooestrus-dioestrus, but significantly reduced the incidence of seizures in dioestrus. In addition, progesterone pretreatment significantly increased the percentage of deaths induced by strychnine in prooestrus-oestrus, reducing deaths in dioestrus. Orchidectomized male mice had a significantly higher incidence of seizures after administration of pentylenetetrazol and strychnine than control mice. Administration of 11 daily doses of 250 microg/kg of testosterone to castrated mice significantly reduced the incidence of seizures induced by pentylenetetrazol. These results confirm the modulatory influence of reproductive steroids on the excitability of the central nervous system and the possible clinical importance of progesterone and testosterone in the management of partial epilepsy.

GABA-level increasing and anticonvulsant effects of three different GABA uptake inhibitors

The present study examines the effect of tiagabine (a selective inhibitor of GABA transporter 1, GAT-1), SNAP-5114 (a semi-selective inhibitor of rat GAT-3/mouse GAT4) and NNC 05-2045 (a non-selective GABA uptake inhibitor) in modulating GABA levels in the hippocampus and thalamus. Anticonvulsant effects of the same compounds were assessed (after intranigral administration) after maximal electroshock (MES) in juvenile rats. Anticonvulsant effects were also tested after intraperitoneal (i.p.) administration against audiogenic seizures in DBA/2 mice and against pentylentetrazole (PTZ)-induced tonic convulsions or MES in NMRI mice. Tiagabine (30 microM, perfused through the microdialysis probe in halothane anaesthetized rats) increased GABA levels to (% basal+/-SEM) 645+/-69 in the hippocampus and 409+/-61 in the thalamus. SNAP-5114 (100 microM) increased GABA levels in the thalamus (% basal+/-SEM) to 247+/-27 but had no effect on hippocampal GABA-levels. NNC 05-2045 (100 microM) increased GABA levels both in the hippocampus (% basal+/-SEM, 251+/-51) and in the thalamus (298+/-27). All compounds protected against tonic hindlimb extension (THE) in juvenile male rats after intranigral administration. Sound induced convulsions in DBA/2 mice were dose-dependently inhibited by all compounds (administered intraperitoneal, i.p.) with ED(50) values of 1, 6 and 110 micromol/kg, for tiagabine, NNC 05-2045 and SNAP-5114, respectively. Tiagabine and NNC 05-2045 but not SNAP-5114 protected against PTZ-induced tonic convulsions whereas only NNC 05-2045 protected against MES-induced tonic convulsions in NMRI mice. However, tiagabine and NNC 05-2045 exerted a synergistic effect in the MES model. These findings substantiate and extend previous findings of different effects of selective versus non-selective GABA uptake inhibitors in animal models of epilepsy.

Acute and chronic effects of the synthetic neuroactive steroid, ganaxolone, against the convulsive and lethal effects of pentylenetetrazol in seizure-kindled mice: comparison with diazepam and valproate

A high-affinity positive modulator of the GABA(A) receptor complex, ganaxolone, is a 3beta-methylated analog of the naturally occurring neuroactive steroid allopregnanolone. In the present study, ganaxolone was tested for its ability to (1) suppress seizures (clonic and tonic) and lethality induced by pentylenetetrazol (PTZ) in PTZ-kindled mice (anticonvulsive effect) and (2) to attenuate the development of sensitization to the convulsive and lethal effects of PTZ in kindled mice (anti-epileptogenic effect) when given as a pretreatment prior to each PTZ injection during kindling acquisition. Two classical antiepileptic drugs, diazepam and valproate, were tested for comparison. All three drugs dose-dependently suppressed tonic seizures and lethality induced by PTZ in kindled mice; only ganaxolone was effective against clonic seizures. Ganaxolone showed anti-epileptogenic properties as it reduced the sensitivity of kindled mice to the convulsive (clonic and tonic seizures) and lethal effects of PTZ. Diazepam showed anti-epileptogenic effects against tonic seizures and lethality, but not clonic seizures; valproate was ineffective in preventing development of any of these effects. Sensitivity to PTZ-induced seizures and lethality was not affected in mice with a history of repeated treatment with ganaxolone, diazepam, or valproate. The drugs had effects on ambulatory activity that ranged from no effect (ganaxolone) through moderate impairment (diazepam) to marked disruption (valproate). Taken together, the results of the present study add to accumulating evidence of the unique anticonvulsive/behavioral profile of neuroactive steroids.

Roles of group II metabotropic glutamate receptors in modulation of seizure activity

Evidence suggests that metabotropic glutamate receptors (mGluR) are involved in mediating seizures and epileptogenesis. In the present experiments, the selective, group II mGluR agonist (+)-2-aminobicyclo-[3.1.0]hexane-2,6-dicarboxylic acid (LY354740, 0.1-1.0 microM) inhibited spontaneous epileptiform discharges which developed in rat cortical slices in Mg2+-free medium. LY354740 (4-16 mg/kg) administered prior to an injection of pentylenetetrazol (80 mg/kg) or picrotoxin (3.2 mg/kg) produced a dose-dependent decrease in the number of mice exhibiting clonic convulsions, but had no effect on N-methyl-D-aspartate (NMDA, 150 mg/kg)-induced convulsions. LY354740 (4-16 mg/kg) did not affect lethality induced in mice by pentylenetetrazol, picrotoxin or NMDA. LY354740 potentiated the anticonvulsant activity of the conventional antiepileptic drug diazepam, significantly decreasing the ED50 for that drug's effect on pentylenetetrazol-induced convulsions by 30%, but had no influence on anticonvulsant activity of ethosuximide and valproic acid. A pharmacokinetic interaction between LY354740 and diazepam, leading to the lowering of the plasma level of free diazepam, was also demonstrated. Our data suggest that the group II mGluR agonist LY354740 possesses anti-seizure activity and may modify the effects of some conventional antiepileptic drugs.

Modification of behavioral effects of drugs in mice by neuroactive steroids

RATIONALE

Neuroactive steroids represent a novel class of potential therapeutic agents (epilepsy, anxiety, migraine, drug dependence) thought to act through positive allosteric modulation of the GABA(A) receptor. A synthetically derived neuroactive steroid, ganaxolone (3alphahydroxy-3beta-methyl-5alpha-pregnan-20-one), is in phase-II clinical trials for epilepsy. Unlike traditional anticonvulsants such as diazepam and phenobarbital, ganaxolone shows equipotent suppression of both the seizure activity and the behavioral effects of pentylenetetrazol (PTZ) administration.

OBJECTIVES

The present study explored possible reversal by ganaxolone and related neuroactive steroids of some behavioral effects of additional pharmacological challenges.

METHODS

Direct behavioral observation and photocell-counted locomotor activity of male, Swiss-Webster mice were made with various compounds alone and in conjunction with ganaxolone.

RESULTS

Ganaxolone both prevented and reversed PTZ-induced locomotor depression in mice. Further, ganaxolone reversed the locomotor depression induced by other convulsant/anxiogenic stimuli: bicuculline, picrotoxin and, to a lesser extent, yohimbine. Ganaxolone failed to reverse the locomotor stimulation induced by cocaine, methamphetamine, dizocilpine, and phencyclidine. In addition to ganaxolone, the endogenous neuroactive steroids allopregnanolone and pregnanolone and the synthetic neuroactive steroid Co 2-1068 also reversed observed behaviors and locomotor depression induced by PTZ.

CONCLUSIONS

The present findings support the unique pharmacological effects of neuroactive steroids as a novel class of positive allosteric modulators of GABA.