Bicuculline-induced Convulsions Research Articles

Comparative study of taurine and tauropyrone: GABA receptor binding, mitochondrial processes and behaviour

Taurine, a sulfur-containing amino acid, has high hydrophilicity and is poorly absorbed. Tauropyrone, a taurine-containing 1,4-dihydropyridine derivative, is suggested to have greater activity than taurine owing to improved physicochemical properties that facilitate delivery of the compound to target cells. The aim of this study was to determine whether the 1,4-dihydropyridine moiety in tauropyrone improves the pharmacological efficacy of taurine in vitro and in vivo. The effects of taurine and tauropyrone, as well as of the 1,4-dihydropyridine moiety were compared in in-vitro experiments to determine the binding to GABA receptors and influence on mitochondrial processes (isolated rat liver mitochondria), and in in-vivo tests to assess the influence on behavioural effects caused by the GABA-A receptor ligands, bicuculline, diazepam and ethanol. Unlike taurine, tauropyrone did not display binding activity for the GABA-A receptor, and only taurine (but not tauropyrone) at low doses (0.1, 1.0 and 10 mg/kg) antagonised the bicuculline-induced convulsion effect. Taurine and tauropyrone had no effect on diazepam myorelaxing action, and they both exerted a comparable 'anti-ethanol' effect (shortening of the ethanol-sleeping time). Taurine and tauropyrone did not influence processes of mitochondrial bioenergetics. The action of tauropyrone at the level of the GABA-A receptor differs qualitatively from that of taurine, probably because of its 1,4-dihydropyridine moiety, which may hinder access to the GABA-A receptor GABA site. Tauropyrone does not show improved pharmacological efficacy in in-vitro and in-vivo studies in comparison with taurine.

Anticonvulsant Activity of New GABA Prodrugs

4-(3,4-Dihydro-2,4-dioxo-2H-1,3-benzoxazin-3-yl)-butyric acid (7) and its ethyl (6), two potential y-aminobutyric acid (GABA) prodrugs, were synthesized and studied to determine their stability in aqueous buffer and their susceptibility to undergo enzymatic hydrolysis in vitro (mouse plasma). Both compounds were fairly stable in aqueous media, (t((1/2)) = 68.2 h and 25.7 h, respectively). The 3,4-dihydro-2,4-dioxo-2 H-I,3-benzoxazine ring underwent enzymatic hydrolysis (t((1/2)) =5.8 h) in compound 7, whereas in compound 6 it seemed not to be opened by mouse plasma esterases within the observation lime (3 h). Both compounds were tested for their central nervous system activity by using both anticonvulsive and behavioral tests. The anticonvulsive study was performed using the convulsive agent pentetrazole (PTX) and bicuculline. The anticonvulsive study indicated that compound both compounds 6 and 7 (10, 20 and 40 mg/kg, i.p.), injected 60 min before PTX (75 mg/kg, i.p.) or bicuculline (10 microg/intracerebroventricular (i.c.v.)/mouse) induced a dose-dependent and significant reduction of the convulsive activity of PTZ and bicuculline whereas it was ineffective if injected immediately before the convulsive agent. Both compounds 6 and 7 (10, 20 and 40 mg/kg, i.p.) did not significantly modify animal behavior or the nociceptive threshold of the animals. However, in PTZ- and bicuculline- treated mice, compound 7 showed significant activity, compared to compound 6, because it was active at relatively low doses. The behavior elements considered were locomotor activity, motor coordination, catalepsy, behavior and antinociception. The results of the behavoral study indicate that these new GABA mimetic drugs did not modify the animal behavior. Our data indicate that these new GABA mimetic drug possesses good anticonvulsive activity without altering the animalbehavior and their ability to block bicuculline-induced convulsions suggests that they could be a GABA(A) mimetic drug. Furthermore, since these compounds are able to act after systemic administration, our data suggest that these new GABA mimetic drug cross the blood-brain barrier.

Involvement of NMDA Receptors in Thiopental-Induced Loss of Righting Reflex, Antinociception and Anticonvulsion Effects in Mice

Potentiation of GABA_A receptor-mediated inhibitory neurotransmission contributes to the anesthetic action of thiopental. However, the inhibiting action of general anesthetic on excitatory neurotransmission also purportedly underlies its effects. The aim of the study was to elucidate the role of glutamate receptors (NMDA and AMPA receptors) in thiopental-induced anesthesia. Intracerebroventricular (i.c.v.) NMDA (50 ng) significantly increased the induction time of loss of righting reflex and decreased sleep time induced by intraperitoneal injection (i.p.) of thiopental (50 mg/kg). Furthermore, NMDA at 50 ng i.c.v. increased the 50% effective dose values for thiopental to produce loss of righting reflex and immobility in response to noxious tail clamp by 25% and 21% (p < 0.05), respectively. However, intrathecal (IT) administration of NMDA or both of i.c.v. or IT administration of AMPA did not show such antagonizing effects on thiopental action at subconvulsive dose. Finally, thiopental (25 mg/kg i.p.) inhibited convulsions induced by NMDA (0.4 µg i.c.v.) or bicuculline (0.6 µg i.c.v.). However, i.p. muscimol (1 mg/kg) blocked the convulsions induced by bicuculline, but not those induced by NMDA at 3 mg/kg. Similarly, i.p. MK-801 (0.1 mg/kg) antagonized NMDA-induced convulsions, but not bicuculline-induced convulsions at 0.3 mg/kg. Therefore, we suggest that the effects of the selective GABA_A and NMDA receptors on convulsive behavior are special to their sites of action, and that the inhibitory action of thiopental on NMDA receptors is possibly not mediated by secondary effects of its GABA_A receptors agonism. These results above indicate the involvement of NMDA receptors in thiopental-induced anesthesia in mice.

Imidazenil: An antagonist of the sedative but not the anticonvulsant action of diazepam

Flumazenil (FLU), a specific benzodiazepine (BZ) receptor antagonist has been used in the treatment of acute BZ intoxication or the alleviation of BZ-induced withdrawal syndrome on the basis of its weak partial agonist action at GABA A receptors. However, given to patients, FLU can worsen diazepam-induced withdrawal syndrome by lowering seizure threshold. We therefore investigated whether imidazenil, a selective positive allosteric modulator of GABA action at GABA A receptors containing α 5 subunit, can antagonize diazepam-induced sedative action and suppression of locomotor activity without affecting diazepam anti-bicuculline action. We report here that while FLU (16.5 μmol/kg) showed no effect on locomotor activity and bicuculline-induced convulsion, it completely antagonized diazepam (10.5 μmol/kg) anti-bicuculline action and the suppression of locomotor activity. However, imidazenil (0.76 μmol/kg) elicited anti-bicuculline action and was dose-dependently antagonized by FLU (16.5 and 33 μmol/kg). Furthermore, imidazenil showed no effect on path length traveled but slightly decreased (40%) horizontal activity when compared to diazepam (85%), and maintained the anti-bicuculline action of diazepam to a threshold level similar to that observed with diazepam. Whereas cross-tolerance between BZs has been reported in animals and humans, we previously reported the absence of cross-tolerance between imidazenil and diazepam. Thus, we suggest that imidazenil might be more effective than FLU at alleviating the withdrawal syndrome associated with long-term BZ administration.

Extremely Low Frequency Magnetic Fields Modulate Bicuculline-lnduced-Convulsion in Rats

The effect of extremely low frequency (ELF, 60 Hz) magnetic fields (MFs) on convulsions was investigated in rats. We determined the onset and duration of convulsions induced by bicuculline alone or by co-exposure to MFs and bicuculline. In addition, we measured the GABA concentrations in the rat brains using HPLC-ECD. MFs strengthened the convulsion induced by bicuculline (0.3, 1, and 3 microg, i.c.v.), with a shortening of the onset time, but lengthening of the duration time. Co-exposure to MFs and bicuculline decreased the GABA levels in the cortex, hippocampus and hypothalamus, whereas MFs alone reduced the level of GABA only in the hippocampus. These results suggest that the exposure to MFs may modulate bicuculline-induced convulsions due to GABA neurotransmissions in rat brains.

Cannabinoid suppressed bicuculline-induced convulsion without respiratory depression in the brainstem-spinal cord preparation from newborn rats

Previous studies have suggested that cannabinoid compounds are anticonvulsants and that these compounds depress respiratory activity. However, the anticonvulsant potential of cannabinoids and their depressive effect on respiration have not been evaluated simultaneously. In the present study, we used a brainstem-spinal cord preparation model to investigate changes in inspiratory activity and the anticonvulsant effects of a cannabinoid receptor agonist, WIN 55, 212-2, in bicuculline-induced convulsion. Application of 10 microM WIN 55, 212-2 caused no change in inspiratory activity (6.9+/- 0.89 bursts/min vs. 8.0+/- 1.3 bursts/min, not significant) and decreased bicuculline-induced seizure-like nerve activity (number of seizure-like activities in 10 min, 11+/- 7.4 bursts vs. 1.5+/- 1.6 bursts, P< 0.01; average duration of seizure-like activity, 8.9+/- 4.0 sec vs. 4.7+/- 2.1 sec, P> 0.01). Our results suggest that administration of an appropriate dose of cannabinoid receptor agonist WIN 55,212-2 has an anticonvulsant effect but does not cause respiratory depression.

An anticonvulsant profile of the ketogenic diet in the rat

The present study was designed to evaluate the anticonvulsant effects of a high-fat ketogenic diet (KD) in rats. Animals were maintained on one of four experimental diets: (1) calorie-restricted ketogenic (KCR); (2) calorie-restricted normal (NCR); (3) ad libitum ketogenic (KAL); or (4) ad libitum normal (NAL). The calorie-restricted diets were fed in quantities such that they were calorically equivalent. All animals began diet treatment at age P37 and each was subjected to one of five chemically-induced seizure tests: bicuculline (BIC; s.c.), picrotoxin (PIC; s.c.), kainate (KA, i.p. or s.c.) and γ-butyrolactone (GBL, i.p.), strychnine (s.c.). Bipolar epidural electrodes were implanted under ketamine/xylazine anesthesia to permit recording the spike and wave discharges (SWD) characteristic of electroencephalograms during absence seizures. Ketonemia was assayed by measuring blood levels of β-hydroxybutyrate (BHB) spectrophotometrically prior to induction of seizures in each experiment. Animals fed ketogenic diets (i.e. either calorie restricted or ad libitum) exhibited greater blood levels of BHB compared to control groups. Seizure results show that treatment with a KD: (1) reduced the incidence of bicuculline-induced convulsions; (2) diminished the number of picrotoxin-induced seizures (KCR group only); (3) increased latency to GBL-induced SWD and reduced both the number and duration of SWD; but (4) conferred no protection from strychnine-induced seizures; and (5) made KA-induced seizures more severe. Together these results indicate a spectrum of anticonvulsant action for the KD in rats that includes threshold seizures induced via GABA receptors (BIC, PIC, GBL) but not those induced at glycine (strychnine) or the KA-subclass of glutamate receptors. Uniquely, the KD is the only treatment described that protects against both convulsive and non-convulsive (absence) seizures in rats.

Effect of alkylpyrazine derivatives on the duration of pentobarbital-induced sleep, picrotoxicin-induced convulsion and gamma-aminobutyric acid (GABA) levels in the mouse brain.

The effect of alkylpyrazine derivatives on pentobarbital-induced sleeping time, picrotoxicin-induced convulsion and gamma-aminobutyric acid (GABA) levels in mouse brain were studied. The duration of pentobarbital-induced sleep in mice was dose-dependently increased by 2,5-dimethylpyrazine (DMP). The duration of pentobarbital-induced sleep was also increased by an administration route of intracerebroventricular injection. Sleep duration was also increased by the administration of isomers of DMP, 2-chloro-3,6-dimethylpyrazine (DMP-Cl) and 2-fluoro-3,6-dimethylpyrazine (DMP-F), but 3,6-dimethylpyrazine-2-thiol (DMP-SH) did not affect sleep duration. The interval until the appearance of picrotoxicin-induced convulsion was prolonged by DMP and DMP-Cl. Increased sleep duration was obtained by administering DMP in combination with aminooxyacetic acid (AOAA) and diazepam compared to a single injection. The interval until convulsion due to picrotoxin was also prolonged by the administration of DMP combined with diazepam and valproic acid (VPA). The interval until the appearance of bicuculline-induced convulsion was also prolonged by pretreatment with DMP. The GABA level in mouse brain was increased by the administration of AOAA, VPA, DMP and DMP-Cl. These results suggest that DMP and other derivatives may strengthen the GABAnergic system in the brain.

The targeted disruption of the adenosine A 2A receptor in mice reduces hypokinesia caused by haloperidol or reserpine and catalepsy induced by various drugs

Dihydroergosine (50 and 100 mg/kg) enhanced the incidence of bicuculline (3 mg/kg)-induced convulsions in female rats, while 100 mg/kg of dihydroergosine given to female mice made 45% convulsive dose of bicuculline (2.5 mg/kg) to be subconvulsive. The same dose of dihydroergosine enhanced in mice the latency of bicuculline (4 mg/kg)-induced convulsions. Although, in invitro experiments dihydroergosine showed very weak ability to prevent the binding of 3H-muscimol, the drug was able to diminish and to augment the IC50 of bicuculline and GABA when added to crude synaptosomal pellet of the rat and mouse brain respectively. Lower concentrations of dihydroergosine stimulated and higher inhibited 3H-TBOB binding to the crude synaptosomal pellet of the rat brain. In the preparation of mouse brain dihydroergosine produced only inhibition of 3H-TBOB binding. Only slight quantitative differences were observed in bicuculline-induced stimulation and in GABA- and diazepam-induced inhibition of 3H-TBOB binding between the two species. The results suggest that the opposite species-dependent effects of dihydroergosine on bicuculline-induced convulsions are due to the ability of this drug to modulate species-dependently the benzodiazepine/GABA receptor chloride channel complex.

Effects of differential modulation of μ-, δ- and κ-opioid systems on bicuculline-induced convulsions in the mouse

The present study investigated the effects of μ-, δ- and κ-opioid receptor agonists on seizures produced by blockade of γ-aminobutyric acid (GABA)-mediated synaptic transmission in the mouse. The selective GABA A receptor antagonist bicuculline (1.25–3 mg/kg) given subcutaneously caused dose-dependent clonic–tonic convulsions. These convulsions were potentiated by the prototypic μ-opioid receptor agonist morphine given subcutaneously 20 min prior to a subconvulsive dose of bicuculline. The potentiation by morphine was completely reversed by pretreatment intraventricularly with the selective μ-opioid receptor antagonist β-funaltrexamine (0.5 μg/mouse). Pretreatment intraventricularly with the selective δ-opioid receptor agonists 2-methyl-4aα-(3-hydroxyphenyl)-1,2,3,4,4a,5,12,12aβ-octahydro-quinolino[2,3,3-g]isoquinoline ((−)TAN-67) or [D-Pen 2,5]-enkephalin (DPDPE) showed a dose-dependent increase in the incidence of convulsions. Pretreatment with naltrindole (2 mg/kg, s.c.), a selective δ-opioid receptor antagonist, abolished the enhancement of the bicuculline-induced convulsions by DPDPE. In contrast, pretreatment with the selective κ-opioid receptor agonist U-50,488H (0.6–80 mg/kg, subcutaneously or 25–100 μg/mouse, intraventricularly) produced a dose-dependent suppression of the bicuculline-induced convulsions. The inhibitory effect of U-50,488H was completely blocked by pretreatment subcutaneously with nor-binaltorphimine (5 mg/kg), a selective κ-opioid receptor antagonist. This study demonstrates that activation of both μ- and δ-opioid receptors increases the incidence of convulsions produced by blockade of GABA-mediated synaptic transmission, while stimulation of κ-opioid receptors has an anticonvulsive effect.

Effects of adrenalectomy and gonadectomy on sex and stress-induced differences in bicuculline-induced convulsions.

The effects of adrenalectomy, gonadectomy and combined adrenalectomy plus gonadectomy on the previously described sex-dependent anticonvulsive effect of swim stress were studied in rats. The convulsive signs (myoclonic twitch, generalized convulsions, tonic hindlimb extension) were produced by constant i.v. infusion of gamma-aminobutyric acid(A) (GABA(A)) antagonist bicuculline, which started 15 min after termination of swim stress (10-min swim at 18-19 degrees C). Adrenalectomy decreased the threshold doses of bicuculline producing the first myoclonic twitch and the onset of generalized convulsions only in females. In adrenalectomized females, but not in males, swim stress enhanced the threshold dose of bicuculline producing generalized convulsions, but, unlike in adrenal-intact animals, it failed to enhance the dose of bicuculline producing tonic hindlimb extension. In gonadectomized stressed and unstressed animals all sex differences disappeared, and swim stress enhanced in both sexes only the threshold doses of bicuculline producing tonic hindlimb extension. Adrenalectomized plus gonadectomized animals displayed clear sex differences in doses of bicuculline necessary to produce all the convulsive signs. In the same animals swim stress postponed, especially in females, the onset of the first myoclonic twitch and generalized convulsions, but not the onset of tonic hindlimb extension. In summary, our results suggest that hormones of the adrenal and gonadal glands are only partly responsible for decreased susceptibility, especially of female rats, to the GABA(A) antagonist bicuculline. Moreover, they have demonstrated that stress produces a gender-specific anticonvulsive effect even in the animals completely deprived of steroid hormones of peripheral origin.

Abecarnil enhances recovery from diazepam tolerance

Treatment with diazepam (25 mg/kg; p.o., twice-daily for 17 days) induced tolerance to the anticonvulsant effect of diazepam against bicuculline-induced convulsions in mice. Cross-tolerance was observed to the anticonvulsant action of clonazepam, imidazenil but not abecarnil. While substitution of clonazepam (12 mg/kg; p.o., twice-daily for 15 days) for diazepam did not affect tolerance to diazepam, substitution of imidazenil (17 mg/kg; p.o., twice-daily for 15 days) for diazepam significantly increased sensitivity to the anticonvulsant effect of diazepam, although tolerance was not abolished. Tolerance to diazepam progressively decreased either after suspension of diazepam administration or replacement treatment with abecarnil (20 mg/kg; p.o., twice-daily). Complete recovery of diazepam efficacy was detected after 8 and 15 days of administration of abecarnil and vehicle, respectively. Binding experiments using [ 3H]-flumazenil showed that K d values did not differ among treatment groups. A significant decrease in B max (−42%) was observed in the cortex of diazepam-tolerant mice whether or not also treated with imidazenil and clonazepam. Conversely, chronically diazepam-treated mice, that further received abecarnil for either 8 or 15 days or vehicle for 15 days showed B max values similar to those of vehicle-treated mice never exposed to diazepam. Results suggest that repeated abecarnil administration to diazepam-tolerant mice can facilitate re-adaptation of receptors to the diazepam-free state. It is proposed that replacement therapy with abecarnil after long-term treatment with conventional benzodiazepines (BDZs) may provide a novel approach for reducing tolerance to their anticonvulsant effects.

Sex differences in bicuculline-induced convulsions: interaction with stress and ligands of benzodiazepine binding sites

The response to i.v. administration of bicuculline and its interaction with the benzodiazepine agonist diazepam and antagonist flumazenil were studied in male and female handling stressed and swim stressed rats. Both handling stressed and swim stressed male rats needed less bicuculline to produce myoclonic twitch and running/bouncing (RB) clonus than females. Besides, a lower dose of bicuculine produced tonic hindlimb extensor convulsion (THE) in male than in female swim stressed rats. Flumazenil failed to affect seizure thresholds for bicuculline either in handling stressed or in swim stressed animals. Sex differences remained present after diazepam pre-treatment as well. While diazepam enhanced doses of bicuculline producing all three convulsive signs similarly in both handling and swim stressed rats (141–162%), swim stress had the lowest anticonvulsive effect for the onset of myoclonic twitch (110% in males and 117% in females) and the highest for THE (148% in males and 188% in females). The anticonvulsive effect of diazepam was not sex-dependent, while the anticonvulsive effect of swim stress was greater in female than in male rats. The results suggest that greater sensitivity of male rats to bicuculline and the anticonvulsive effect of swim stress do not result from the release of endogenous modulators of benzodiazepine binding sites.

Anticonvulsive activity of a new GABA mimetic drug

This study examines the pharmacological profile of a new GABA mimetic drug, 4-[(2H)-1,3-benzoxazine-2,4(3H)-dione]-butyric acid (BXDBA), using both a behavioral and an anticonvulsive study. The behavior elements considered were locomotor activity, motor coordination, catalepsy, behavior and antinociception. The anticonvulsive study was performed using the convulsive agent bicuculline. BXDBA [10, 20 and 40 mg/kg, intraperitoneally (i.p.)] did not significantly modify animal behavior or the nociceptive threshold of the animals. The anticonvulsive study indicated that BXDBA (10, 20 and 40 mg/kg, i.p.), injected 60 min before bicuculline (10 μg/intracerebroventricular (i.c.v.)/mouse) induced a dose-dependent and significant reduction of the convulsive activity of bicuculline whereas it was ineffective if injected immediately before the convulsive agent. Our data indicate that this new GABA mimetic drug possesses good anticonvulsive activity and its ability to block bicuculline-induced convulsions suggests that it could be a GABA A mimetic drug. Furthermore, since BXDBA is able to act after systemic administration, our data suggest that this new GABA mimetic drug crosses the blood–brain barrier.

Influence of Gender and Gonadectomy on Bicuculline-Induced Convulsions and on GABAA Receptors

The response to IV administration of GABAA receptor antagonist bicuculline was studied in young (30 days) and in adult gonad-intact or gonadectomized male and female rats. The properties of GABAA receptors, obtained from cortex and cerebellum 30 days following gonadectomy, and the affinity of muscimol and bicuculline for cortical and cerebellar GABA binding sites were also studied. While young rats failed to show sex differences, the threshold doses of bicuculline producing the first myoclonic twitch and running/bouncing clonus (RB clonus) were lower in adult male than female rats. Fifteen days after gonadectomy or sham operation male rats needed less bicuculline to the onset of myoclonic twitch and RB clonus than identically treated females, while orchidectomized rats needed more bicuculline to the onset of tonic hindlimb extension than all other groups examined. All sex differences disappeared 30 days following gonadectomy. At the same time, in males gonadectomy decreased the affinity and enhanced the density of cortical 3H-muscimol binding sites. In female rats, gonadectomy only decreased the affinity of cortical GABAA receptors. Only regional but not sex differences were observed in the affinity of muscimol and bicuculline for GABAA receptors. Sex differences in the threshold doses of bicuculline-producing convulsions do not correlate either with the properties of cortical and cerebellar GABAA receptors or with the affinity of bicuculline for the same binding sites.

Abecarnil, a beta-carboline derivative, does not exhibit anticonvulsant tolerance or withdrawal effects in mice.

Development of tolerance and dependence has been reported to occur upon chronic administration of traditional benzodiazepines (BZDs). We compared the effect of chronic treatment with abecarnil, a beta-carboline derivative with high affinity for central BDZ receptors, and diazepam, the BDZ prototype, in mice. After acute administration, abecarnil was as potent and effective as diazepam in protecting from bicuculline-induced convulsion. The time-course analysis of two peak equieffective doses of abecarnil (1.9 mg/kg p.o.) and diazepam (2.7 mg/kg p.o.) showed a similar duration of action. The anticonvulsant potency of diazepam was reduced in mice given chronic diazepam (25 mg/kg p.o., 2 times a day for 17 days). No tolerance to abecarnil was apparent when the drug was administered for the same period using a comparable dose (20 mg/kg p.o.). Severe symptoms of precipitated withdrawal were observed upon administration of the BDZ partial inverse agonist Ro 15-3505 in mice treated chronically with diazepam but not abecarnil. In mice made tolerant to diazepam, maximum [3H]-flumazenil binding sites were reduced in both cerebral cortex (-50%) and cerebellum (-55.2%). No changes in [3H]-flumazenil binding were measured in chronic abecarnil-treated mice. These data indicate that abecarnil possesses a very low tolerance/dependence liability and does not affect BZD receptor density after chronic administration.

Previous heat shock treatment attenuates bicuculline-induced convulsions in rats

Exposure to elevated temperature provokes a sequence of events (heat shock response) in all living organisms. Through this response, heat shock proteins (HSPs) are induced and protect the cells against subsequent injury. We investigated the effect of heat treatment on bicuculline-induced convulsions, and analyzed a possible role of HSPs. Screw electrodes were implanted in the brain of mature male Wistar rats for electroencephalogram (EEG) recording. Experimental rats were subjected to whole-body hyperthermia at 41-42 degrees C for 15 min. Fifteen hours later, bicuculline was injected intraperitoneally to induce convulsions in both experimental and control groups. The heated rats showed a significant attenuation of the convulsive response, in terms of both spike discharges in EEG and clinical seizures. Further-more, induction of HSP72 was detected in the brain of heat-treated rats by immunoblotting, appearing at 4 h and reaching a maximal level 16-24 h after the heat shock. We conclude that the previous heat treatment stabilized neuronal excitability, most probably through the induction of HSP72.

Interactions of some analogues of the anticonvulsant milacemide with monoamine oxidase

A series of analogues of the anticonvulsant drug milacemide (2-( n-pentylamino)-acetamide; Compound I) has been synthesized: 2-(benzylamino)acetamide (Compound II), 2-(phenethylamino)acetamide (Compound III), 2-(2-indol-3-yl)-ethylamino acetamide (Compound IV), 2-(2-(5-methoxyindol-3-yl)ethylamino)-acetamide (Compound V), 2-(2(4-chlorobenzamido)-ethylamino)acetamide (Compound VI), 2-(2-benzamidoethylamino)-acetamide (Compound VII) and 2-(4-(3-chlorobenzyloxy)phenethylamino)acetamide (Compound VIII). These compounds involve retention of the aminoacetamide portion of milacemide but replacement of the pentyl moiety with aromatic residues present in the structures of substrates and inhibitors of the monoamine oxidases. All the compounds tested were substrates for ox liver monoamine oxidase-B (MAO-B), producing an aldehyde that could act as a substrate for ox liver aldehyde dehydrogenase and H 2O 2 as a result of oxidative cleavage which also released glycinamide, although their Michaelis-Menten parameters differed markedly. None showed detectable activity as substrates for rat liver monoamine oxidase-A (MAO-A). Inhibition of the MAO-B by all the compounds except Compounds VIII and IV showed marked time dependence and was at least partly irreversible. There was no apparent change in the inhibition of MAO-A during enzyme-inhibitor preincubation at 37° for 60 min. Compound VIII was a potent reversible inhibitor of both MAO-A and MAO-B ( K i = 2.8 ± 0.1 and 4.1 ± 0.8 μM), respectively. Comparison of the inhibitory potencies and the specificity constants of the series of compounds as substrates for MAO-B revealed no simple correlations with their anticonvulsant activities, as measured by their ability to prevent bicuculline-induced convulsions and death in the mouse. These results suggest that neither inhibition of MAO nor oxidative cleavage by this enzyme to yield glycinamide plays the major role in the anticonvulsant action of these compounds.

Attenuation of anticonvulsant effects of diazepam after chronic treatment with bicuculline

Changes in the GABAergic system after chronic treatment with bicuculline were examined in two strains of inbred rats, Fischer 344 (F344) and Lewis (LEW). Rats received an IP injection of either bicuculline (2 mg/kg) or vehicle once a day for 12 days. After this chronic treatment, the effects of diazepam (1 mg/kg, IP) and pentobarbital (20 mg/kg, IP) on bicuculline-induced convulsions were measured. Bicuculline was acutely infused into a tail vein at 0.0415 mg/min, and the infusion was terminated when rats showed seizure. Following the chronic bicuculline treatment, the anticonvulsant effect of diazepam, but not of pentobarbital, was significantly reduced as compared to its effect following chronic vehicle treatment in both strains. Both diazepam and pentobarbital showed a significant difference in anticonvulsant effects between strains (F344 > LEW). The hypnotic effects of muscimol, barbital, pentobarbital, and ethanol following chronic bicuculline treatment were examined. There was no significant difference in sleep time induced by these drugs between bicuculline-and vehicle-treated rats. These results suggest that the attenuation of diazepam's anticonvulsant effect after chronic bicuculline treatment may result from functional changes in benzodiazepine receptors and that the anticonvulsant effects of diazepam and pentobarbital may be influenced by genetic factors. Moreover, the hypnotic effects of several drugs tested are apparently not affected by chronic bicuculline treatment.

An ATP-sensitive potassium channel blocker abolishes the potentiating effect of morphine on the bicuculline-induced convulsion in mice.

ICV bicuculline, a selective GABAA antagonist, dose-dependently induced clonic-tonic convulsions in mice. Coadministration of ICV morphine (mu opioid agonist) significantly potentiated ICV bicuculline-induced convulsions, and this effect of morphine was completely blocked by pretreatment with beta-funaltrexamine (beta-FNA), a mu antagonist. ICV glibenclamide, a selective ATP-sensitive potassium (KATP) channel blocker, at a dose which alone did not affect the convulsive threshold of bicuculline, was capable of blocking the exacerbation of ICV bicuculline-induced convulsions by morphine. The present data further suggest that KATP channels may play a tonic regulatory role in the potentiative effect of morphine on ICV bicuculline-induced convulsions.