Short communicationDiazepam-stimulated increases in the synaptosomal uptake of 45ca2+: Reversal by dihydropyridine calcium channel antagonists
Abstract
Pharmacologically relevant concentrations of benzodiazepines have previously been reported to increase 45Ca2+ uptake into synaptosomes. This observation, coupled with the recent report that nifedipine may block the hypnotic effect of flurazepam, led us to study the effects of nifedipine and nitrendipine on 45Ca2+ uptake into synaptosomes. Diazepam (1 μM) significantly increased the uptake of 45Ca2+ to a crude synaptosomal fraction (P2) prepared from rat cerebral corted and depolarized with 55 mM K+. Nifedipine (1 μM) did not alter the uptake of Ca2+, while nitrendipine (1 μM) reduced uptake by 37%. Both nifedipine and nitrendipine completely antagonized the ability of diazepam to increase 45Ca2+ uptake following K+ depolarization. These observations support the notion that the pharmacologic actions of benzodiazepines may be mediated through effects on a calcium channel.
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RH-3421 action and toxicokinetics in the trout: Reduced brain involvement versus mammals
2001, Environmental Toxicology and PharmacologyThe action and distribution of the insecticidal dihydropyrazole RH-3421 was examined in the trout and mouse. RH-3421 antagonized the depolarizing effect of the Na+ channel activator veratridine and inhibited K+-stimulated uptake of 45Ca++ through voltage-sensitive calcium channels in trout brain synaptosomes. RH-3421 was a weaker inhibitor of these cellular targets in fish brain compared to mammalian brain. [14C]RH-3421 distributed rapidly following systemic administration to trout. Trunk kidney, muscle, liver and fat are important sites of accumulation, however, accumulation of [14C]RH-3421 in trout brain was low and polar metabolites were only found in bile. Mice administered an equivalent dose accumulated [14C]RH-3421 more efficiently into brain, and overall metabolism was more extensive. In trout, the brain is unlikely to be a major site of action of dihydropyrazoles. Our data indicate that perturbation of neuronal sites outside of brain cannot be excluded as contributing to the comparatively high acute toxicity of dihydropyrazoles in fish.
Cocaine: Evidence for NMDA-, β-carboline- and dopaminergic-mediated seizures in mice
1998, Brain ResearchThe present study was undertaken to examine the role of the benzodiazepine/GABA and N-methyl-d-aspartate (NMDA) systems in the convulsive effect of cocaine in mice. When cocaine (3.5 mg/ml) solution was infused into the tail vein at a rate of 0.3 ml/min, mice showed clonic and tonic convulsions. These seizures were not affected by low doses of bicuculline or picrotoxin, a GABAA receptor antagonist and a Cl ion channel blocker, respectively. Aminooxyacetic acid (AOAA), a GABA deaminase inhibitor, and phenobarbital, a Cl ion channel activator, and baclofen, a GABAB receptor agonist, also had no effect on these convulsions. Benzodiazepine inverse agonist β-DMCM, at a dose which by itself had no convulsive effect lowered the convulsive threshold of cocaine. This lowered convulsive threshold was reversed by flumazenil, a benzodiazepine inverse antagonist, and diazepam, a benzodiazepine full agonist, which by themselves did not inhibit cocaine seizure. It is likely that cocaine seizure involves a benzodiazepine (β-carboline) recognition site other than the benzodiazepine/GABAA receptor–Cl ionophore complex system. CPP and MK-801, competitive and noncompetitive NMDA receptor antagonists, respectively, inhibited cocaine seizures. The inhibitory effects of CPP on cocaine convulsion were reversed by a low dose of NMDA, which by itself did not induce seizure. A dopamine D1 receptor agonist SKF38393 enhanced both clonic and tonic convulsions, while a dopamine D2 receptor agonist bromocriptine inhibited these convulsions. These stimulatory and inhibitory effects were reversed by the D1 and D2 receptor antagonists, SCH23390 and haloperidol, respectively. These results suggest that the cocaine-induced convulsion may involve an activation of the NMDA–Ca ionophore complex system, which is mediated by the dopaminergic system, and a β-carboline recognition site other than the benzodiazepine/GABAA receptor–Cl ionophore complex system.
Anticonvulsant activity of azirino [1,2-d] [1,4]benzodiazepines and related 1,4-benzodiazepines in mice
1997, Pharmacology Biochemistry and BehaviorDE SARRO, G. B., A. CHIMIRRI, R. MCKERNAN, K. QUIRK, P. GIUSTI AND A. DE SARRO. Anticonvulsant activity of azirino[1,2-d][1,4]benzodiazepines and related 1,4-benzodiazepines in mice. PHARMACOL BIOCHEM BEHAV 58[1]281–289, 1997.—The anticonvulsant properties of several 1,4-benzodiazepine and azirino[1,2-d][1,4]benzodiazepine (ABDZ) derivatives were studied after intraperitoneal (IP) administration in DBA/2 mice (a strain genetically susceptible to sound-induced seizures) and in Swiss mice. The anticonvulsant effects were evaluated on seizures evoked by means of auditory stimulation (109 dB, 12–16 kHz) in animals placed singly under a hemispheric Perspex dome or on seizures induced by administration of pentylenetetrazole. The 1,4-benzodiazepines were generally more potent than the related ABDZ derivatives. The rank order of potency for anticonvulsant activity was flunitrazepam > diazepam > pinazepam > ABDZ5 > ABDZ4 > prazepam > halazepam > ABDZ1 > ABDZ3 > camazepam > ABDZ6 > ABDZ2. The impairment of locomotor performance following IP administration of these derivatives was also evaluated by means of the rotarod test. The rank order of potency for impairment of coordinated motor movements was pinazepam > flunitrazepam > diazepam > ABDZ5 > prazepam > halazepam > ABDZ4 > ABDZ3 > ABDZ1 > camazepam > ABDZ2 = ABDZ6. The potency of various 1,4-benzodiazepines and ABDZs as inhibitors of specific [3H]flumazenil binding to membranes from cerebellum or cortex was evaluated. In general, ABDZs were active as anticonvulsants and inhibited [3H]flumazenil binding in the micromolar range. Radioligand binding studies carried out in stable cell lines demonstrated that none of the ABDZs tested showed a particular subtype specificity. The pharmacological actions of ABDZ4 and ABDZ5, which appeared to be the most potent ABDZs as anticonvulsants, were significantly reduced by treatment with flumazenil (8.24 μmol/kg IP), suggesting a clear involvement of benzodiazepine mechanisms in the anticonvulsant activity of these compounds or their metabolites. The anticonvulsant activity of ABDZ4 and ABDZ5 was also evaluated against seizures induced in DBA/2 mice by two β-carbolines: methyl-β-carboline-3-carboxylate (β-CCM) and methyl-6,6-dimethoxy-4-ethyl-β-carboline-3-carboxylate (DMCM). Both ABDZ4 and ABDZ5 give better protection against seizures induced by β-CCM than DMCM, suggesting a preferential action on the benzodiazepine receptor subtype BDZ1.
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1996, Life SciencesIn a previous study we have shown that microinjection of the benzodiazepine hypnotic triazolam into the medial preoptic area increases sleep in rats. In order to determine whether this effect is specific to benzodiazepines, or whether it occurs with hypnotic medications from other pharmacologic classes, we have microinjected pentobarbital (1 and 100 ug) and vehicle in random sequence into rats and performed two hour sleep studies in the daytime with the lights on. Both doses significantly decreased sleep latency and increased nonREM and total sleep. The amount of REM sleep, REM latency, and intermittent waking time were not significantly altered. These data are consistent with the hypothesis that the medial preoptic area may be involved in sleep induction by both benzodiazepine and barbiturate hypnotic medications.
Azirinol[1,2-d][1,4]benzodiazepine derivatives and related 1,4-benzodiazepines as anticonvulsant agents in DBA/2 mice
1996, General Pharmacology- 1.
1. The behavioral and anticonvulsant effects of several 1,4-benzodiazepine (BDZ) and azirino[1,2-d] [1, 4]benzodiazepine (ABDZ) derivatives were studied after intraperitoneal administration in DBA/2 mice, a strain genetically susceptible to sound-induced seizures.
- 2.
2. The anticonvulsant effects were evaluated on seizures evoked by means of auditory stimulation (109 dB, 12–16 kHz) in animals placed singly under a Perspex dome.
- 3.
3. The 1,4-benzodiazepines were generally more potent than the related azirino[1,2-d][1,4]benzodiazepine derivatives which, however, showed a remarkable anticonvulsant activity. The rank order of potency for anticonvulsant activity was flunitrazepam > diazepam > pinazepam > ABDZ5 > ABDZ4 > prazepam > halazepam > ABDZ1 > ABDZ3 > camazepam > ABDZ6 > ABDZ2.
- 4.
4. The impairment of locomotor performance following intraperitoneal (IP) administration of the aforementioned derivatives was also evaluated by means of rotarod test. The rank order of potency for impairment of coordinated motor movements was pinazepam > flunitrazepam > diazepam > ABDZ5 > prazepam > halazepam > ABDZ4 > ABDZ3 > ABDZ1 > camazepam > ABDZ2 = ABDZ6.
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7. The azirino[1,2-d] [1,4]benzodiazepine derivatives are more lipophilic than the related benzodiazepines, but the different degree of anticonvulsant activity and impairment of coordinated motor movements cannot be directly related to the lipophilicity of the compounds studied.
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8. The pharmacologic actions of ABDZ4 and ABDZ5, which appeared as the most potent anticonvulsants of the azirino[1,2-d] [1,4]benzodiazepine derivatives, were significantly reduced by treatment with flumazenil (8.24μmol/kg IP) suggesting a clear involvement of benzodiazepine mechanisms in the anticonvulsant activity of these compounds or their metabolites.
- 9.
9. The anticonvulsant activity of ABDZ4 and ABDZ5 was also evaluated against seizures induced by the two β-carbolines, methylβ-carboline-3-carboxylate (β-CCM) and methyl6,7-dimethoxy-4-ethyl-β-carboline-3-carboxylate (DMCM), in DBA/2 mice. Both ABDZ4 and ABDZ5 gave better protection against the seizures induced by β-CCM than DMCM, suggesting a preferential action on BDZ1 receptors.
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2. Nerve stimulation was followed immediately by a transient increase in short-circuit current (SCC) and in the potential difference (PD), which consisted of a rapid and then a slow component.
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3. Diazepam concentrations from 5.0 × 10−5M to 5.1 × 10−4M caused a dose-dependent block of both components to a 30% of their control values and also reduced the stimulatory responses to noradrenaline in this preparation.
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4. Diazepam antagonized the potassium blocking effect of barium.
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5. These results, based on electrophysiological and pharmacological evidence, are consistent with a calcium and sodium blocking effect of diazepam on the nerve skin junction of C. caudiverbera.
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