Excitatory and inhibitory synaptic transmission is differentially influenced by two ortho-substituted polychlorinated biphenyls in the hippocampal slice preparation.

Exposure to polychlorinated biphenyls impairs cognition and behavior in children. Two environmental PCBs 2,2',3,3',4,4',5-heptachlorobiphenyl (PCB170) and 2,2',3,5',6-pentachlorobiphenyl (PCB95) were examined in vitro for influences on synaptic transmission in rat hippocampal slices. Field excitatory postsynaptic potentials (fEPSPs) were recorded in the CA1 region using a multi-electrode array. Perfusion with PCB170 (10 nM) had no effect on fEPSP slope relative to baseline period, whereas (100 nM) initially enhanced then depressed fEPSP slope. Perfusion of PCB95 (10 or 100 nM) persistently enhanced fEPSP slope >200%, an effect that could be inhibited by dantrolene, a drug that attenuates ryanodine receptor signaling. Perfusion with picrotoxin (PTX) to block GABA neurotransmission resulted in a modest increase in fEPSP slope, whereas PTX+PCB170 (1-100 nM) persistently enhanced fEPSP slope in a dose dependent manner. fEPSP slope reached >250% of baseline period in the presence of PTX+100 nM PCB170, conditions that evoked marked epileptiform after-potential discharges. PCB95 and PCB170 were found to differentially influence the Ca(2+)-dependence of [(3)H]ryanodine-binding to hippocampal ryanodine receptors. Non-coplanar PCB congeners can differentially alter neurotransmission in a manner suggesting they can elicit imbalances between inhibitory and excitatory circuits within the hippocampus. Differential sensitization of ryanodine receptors by Ca(2+) appears to mediate, at least in part, hippocampal excitotoxicity by non-coplanar PCBs.

Avaliação dos efeitos do tratamento pós-natal com dantrolene no desenvolvimento físico, reflexológico e comportamental de ratos / Evaluation of the effects of the postnatal treatment with dantrolene on physical, reflexologic and behavioral development of rats

O dantrolene é um inibidor da liberação de cálcio intracelular, utilizado no tratamento da hipertermia maligna do recém nascido e no adulto e na síndrome neuroléptica maligna. Estudos anteriores mostraram que o dantrolene pode atenuar danos causados ao hipocampo de ratos, devido a estímulos excitotóxicos, mas pode também levar a morte celular nesta área. Baseando-se nestes dados, buscamos investigar se a administração de dantrolene a ratos recém nascidos pode acarretar alterações no desenvolvimento físico, reflexológico, comportamental e na integridade celular do sistema nervoso central na fase pós-natal e na idade adulta. Foram utilizados um grupo controle (salina 0,9%) e três experimentais tratados com dantrolene nas doses de 5,0; 10,0 ou 15,0 mg/Kg, injetados no 2º dia de vida por via intraperitonial. Os filhotes foram avaliados quanto ao desenvolvimento físico, refexológico e comportamental. Alguns ratos foram sacrificados no PN 7 e no PN 90 e seus cérebros foram processados para análise histológica. Na fase pós-natal foi observado no desenvolvimento físico: aumento de peso em machos e fêmeas no PN 14 e PN 20; adiantamento da abertura de olhos; adiantamento ou atraso no desdobramento de orelhas de machos e fêmeas dependendo da dose; adiantamento ou atraso na abertura do canal vaginal de fêmeas dependendo da dose. No desenvolvimento reflexológico foi observado: diminuição no tempo de preensão palmar no PN 4 (fêmeas); aumento do tempo de reflexo postural no PN 4 e PN 6 (machos); diminuição do tempo de geotaxia negativa no PN 8 (machos e fêmeas); e no comportamento: aumento das atividades locomotora e geral total de fêmeas no PN 22 e de machos no PN 18. Na fase adulta foi observado: diminuição do tempo para parar de nadar na natação forçada de machos; aumento do número de entradas nos braços não aversivo e abertos, na seção de treino em machos; aumento do número de entradas e do tempo de permanência nos braços abertos, na seção de teste de machos. Podemos co...

Avaliação dos efeitos do tratamento pós-natal com dantrolene no desenvolvimento físico, reflexológico e comportamental de ratos

O dantrolene é um inibidor da liberação de cálcio intracelular, utilizado no tratamento da hipertermia maligna do recém nascido e no adulto e na síndrome neuroléptica maligna. Estudos anteriores mostraram que o dantrolene pode atenuar danos causados ao hipocampo de ratos, devido a estímulos excitotóxicos, mas pode também levar a morte celular nesta área. Baseando-se nestes dados, buscamos investigar se a administração de dantrolene a ratos recém nascidos pode acarretar alterações no desenvolvimento físico, reflexológico, comportamental e na integridade celular do sistema nervoso central na fase pós-natal e na idade adulta. Foram utilizados um grupo controle (salina 0,9%) e três experimentais tratados com dantrolene nas doses de 5,0; 10,0 ou 15,0 mg/Kg, injetados no 2º dia de vida por via intraperitonial. Os filhotes foram avaliados quanto ao desenvolvimento físico, refexológico e comportamental. Alguns ratos foram sacrificados no PN 7 e no PN 90 e seus cérebros foram processados para análise histológica. Na fase pós-natal foi observado no desenvolvimento físico: aumento de peso em machos e fêmeas no PN 14 e PN 20; adiantamento da abertura de olhos; adiantamento ou atraso no desdobramento de orelhas de machos e fêmeas dependendo da dose; adiantamento ou atraso na abertura do canal vaginal de fêmeas dependendo da dose. No desenvolvimento reflexológico foi observado: diminuição no tempo de preensão palmar no PN 4 (fêmeas); aumento do tempo de reflexo postural no PN 4 e PN 6 (machos); diminuição do tempo de geotaxia negativa no PN 8 (machos e fêmeas); e no comportamento: aumento das atividades locomotora e geral total de fêmeas no PN 22 e de machos no PN 18. Na fase adulta foi observado: diminuição do tempo para parar de nadar na natação forçada de machos; aumento do número de entradas nos braços não aversivo e abertos, na seção de treino em machos; aumento do número de entradas e do tempo de permanência nos braços abertos, na seção de teste ...

Influence of isradipine, niguldipine and dantrolene on the anticonvulsive action of conventional antiepileptics in mice.

We report the effects of two new dihydropyridine derivatives, isradipine (4-(4'-benzofurazanyl)-1,4-dihydro-2,6-dimethyl-3,5-pyridinedic arboxylic acid methylisopropylester) and niguldipine (1,4-dihydro-2,6-dimethyl-4-(3-nitrophenyl)-3,5-pyridinecarboxylic acid 3-(4,4-diphenyl-1-piperidinyl)-propyl methyl ester hydrochloride), and of dantrolene (1-[(5-[p-nitrophenyl]furfurylidene)-amino]hydantoin sodium, an inhibitor of Ca2+ release from intracellular stores) on the protective efficacy of antiepileptic drugs against maximal electroshock-induced seizures. It was shown that dantrolene (5-20 mg/kg), isradipine (5-10 mg/kg) and niguldipine (up to 2.5 mg/kg) did not influence the electroconvulsive threshold in mice, although a higher dose of niguldipine (5 mg/kg) significantly elevated it. Dantrolene (10-20 mg/kg) and isradipine (1 mg/kg) did not affect the anticonvulsive activity of conventional antiepileptic drugs. In contrast, niguldipine (2.5-5 mg/kg) impaired the protective action of carbamazepine and phenobarbital. No effect of niguldipine (2.5-5 mg/kg) was observed upon the anticonvulsive efficacy of diphenylhydantoin and valproate. BAY k-8644 (methyl-1,4-dihydro-2,6-dimethyl-5-nitro-4- [(2-trifluoromethyl)-phenyl]-pyridine-5-carboxylate, an L-type Ca2+ channel agonist) did not reverse the action of niguldipine alone or the niguldipine-induced impairment of the anticonvulsive action of carbamazepine and phenobarbital. Niguldipine did not influence the free plasma levels of carbamazepine and phenobarbital, so a pharmacokinetic interaction is not probable. The results suggest that in contrast to the anticonvulsive activity of niguldipine against electroconvulsions, this Ca2+ channel inhibitor significantly weakened the protective action of both carbamazepine and phenobarbital. These effects do not seem to result from the blockade of voltage-dependent Ca2+ channels. Isradipine and dantrolene did not have a modulatory action on the threshold for electroconvulsions or on the anticonvulsive activity of antiepileptic drugs. It may be concluded that the use of niguldipine, isradipine, and dantrolene in epileptic patients seems questionable.

Hyperkalemia after dantrolene and verapamil-dantrolene administration in dogs.

The concurrent administration of dantrolene and verapamil has the theoretical advantage of being more efficacious than dantrolene alone in the treatment of malignant hyperthermia. However, the combination has been reported to cause fatal hyperkalemia in pigs. The present study evaluated the serum concentrations of cations, serum osmolarity, and cardiovascular responses in 20 mongrel dogs after dantrolene with and without the concurrent administration of verapamil. The dogs were randomly classified into four groups of five dogs each: group 1 received neither dantrolene nor verapamil; group 2 received three successive intravenous doses of dantrolene (1, 3, and 6 mg/kg) at 30-minute intervals; group 3 received verapamil 0.1 mg/kg IV bolus, followed by a continuous infusion of 5 micrograms.kg-1.hr-1; and group 4 received verapamil as in group 3, followed by dantrolene as in group 2. Measurements were made at 15-minute intervals for 2 1/2 hours. Progressive and similar statistically significant increases in mean serum potassium occurred after 105 minutes in dogs given dantrolene (group 2, mean peak serum potassium levels 5.4 +/- 0.5 mmol/L) and after 90 minutes in dogs given verapamil-dantrolene (group 4, 5.2 +/- 1.6 mmol/L). A statistically significant decrease in serum sodium levels was also found in groups 2 and 4. One dog in group 4 developed intermittent second-degree heart block after the final dose of dantrolene. Serum calcium levels (ionized and total) tended to decrease in groups 2 and 4. There were no statistically significant differences in osmolarities, cardiac outputs, or mean arterial blood pressures among groups. In summary, significant elevations of serum potassium were observed in this dog model given dantrolene with and without verapamil.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of dantrolene sodium on the discharge of alpha and gamma motoneurones to the soleus muscle in the decerebrate rat.

1. The effects of intravenous infusion of the direct acting muscle relaxant, dantrolene sodium (5 mg kg-1), on tension, integrated EMG, soleus muscle motor unit discharge frequency and gamma nerve fibre discharge were measured in the decerebrate rat. 2. Dantrolene sodium did not have any detectable direct effect upon the discharge of the gamma nerve fibres. 3. The soleus muscle of the decerebrate preparations exhibited spontaneous tension and reflex responses. 4. With the muscle held at constant length, dantrolene sodium caused an increase in the integrated EMG in 15 out of 18 experiments and a decrease in muscle tension in 15 out of 17. The results from these experiments showed great variability. 5. Dantrolene sodium caused a slight reduction in the tension response to tonic stretch; this was accompanied by an increase in the integrated EMG. 6. Dantrolene sodium also caused a shift in the relationship between tension and integrated EMG during the phasic component of the stretch reflex, with a greater integrated EMG being associated with a reduced tension. 7. Motor unit discharge frequencies were found to increase but not sufficiently to overcome the action of dantrolene sodium. It is concluded that motor unit recruitment must play an important role in the compensation for the muscle weakening action of dantrolene sodium.

Comparison of dantrolene sodium with erythromycin estolate using primary cultures of rat hepatocytes.

Using primary cultures of parenchymal hepatocytes as a model system, the cytotoxic potential of dantrolene sodium (DS) was compared with that of erythromycin estolate (EE)--a known hepatotoxin. Parallel morphological and functional comparisons were made, following 4-, 8-, or 24-h exposures of hepatocyte cultures, using phase contrast microscopy and lactate dehydrogenase (LDH) leakage, respectively. Four-hour exposures of cultures to rather low concentrations of EE (i.e. 50 microM) resulted in cellular necrosis and significantly elevated LDH release. As the concentration of this hepatotoxin was increased, the changes were more pronounced. However, even 4- or 8-h exposures of cultures to a maximum of 100 microM DS did not affect LDH leakage or morphological integrity, although marginally detectable morphological changes did not occur at the highest concentration after 24-h. The value of using primary parenchymal hepatocyte cultures as a model system for the assessment of xenobiotic-induced hepatotoxicity was confirmed.

Hepatotoxicological evaluation of dantrolene sodium.

The clinical use of dantrolene has been associated with hepatotoxicity, thus the toxicity of dantrolene in Swiss-Webster mice was characterized. Animals were treated orally (po) with single or multiple doses of up to 400 mg/kg of D without any increases in SGPT or alterations in hepato-cellular architecture. To possibly enhance the hepatotoxicity of dantrolene, its biotransformation was altered by inhibiting acetylation, depleting glutathione, inducing biotransformation, and promoting reductive metabolism. None of the metabolic alterations elicited any toxicity of dantrolene. Hepatic microsomal incubations were used to detect the possible bioactivation and covalent binding of 14C-dantrolene. Analysis for covalent adducts found only 20-30 pmol bound/mg microsomal protein. Thus the suspected hepatotoxicity of dantrolene does not appear to be linked to its biotransformation or bioactivation. Additional studies will be necessary to clarify if other parameters are necessary for dantrolene to be a hepatotoxin.

Synthesis and skeletal muscle relaxant activity of 3-(aminoacyl)-1-[[[5-(substituted phenyl)-2-furanyl]methylene]amino] -2,4-imidazolidinediones.

A series of 3-(aminoacyl)-1-[[[5-(substituted phenyl)-2-furanyl] methylene]amino]-2,4-imidazolidinediones was synthesized and evaluated for skeletal muscle relaxant activity. All compounds were active by the intravenous route, and nine of 11 were active orally. One compound was very active when evaluated by the mouse Straub tail and rotarod tests; its efficacy index (ED50 rotarod/ED50 Straub tail) was 2.0, while its therapeutic index (LD50/ED50 Straub tail) was > 225.

Dantrolene sodium: a review of its pharmacological properties and therapeutic efficacy in spasticity.

Dantrolene sodium or dantrolene1 is 1([5-(nitrophenyl)furfurylidend] amino) hydantoin sodium hydrate. It is indicated for use in chronic disorders characterised by skeletal muscle spasticity, such as spinal cord injury, stroke, cerebral palsy and multiple sclerosis. Dantrolene is believed to act directly on the contractile mechanism of skeletal muscle to decrease the force of contraction in the absence of any demonstrated effects on neural pathways, on the neuromuscular junction, or on the excitable properties of the muscle fibre membranes. Controlled trials have demonstrated that dantrolene is superior to placebo in adults or children with spasticity from various causes, as evidenced by clinical assessments of disability and daily activities, and by muscle and reflex responses to mechanical and electrical stimulation. It is somewhat less effective in patients with multiple sclerosis than in those with spasticity from other causes. There has been a general clinical impression in controlled trials that dantrolene caused less sedation than would have been expected from therapeutically comparable doses of diazepam. In 2 controlled trials, there was no significant difference between dantrolene and diazepam in terms of reductions in spasticity, clonus, and hyperreflexia, but side-effects such as drowsiness and inco-ordination occurred significantly more frequently on diazepam. Long-term studies have indicated continuing benefit for patients taking dantrolene, though the incidence of side-effects has often been high and there has been a suggestion of exacerbation of seizures in children with cerebral palsy. Dantrolene may be of value in the medical treatment of spasm of the external urethral sphincter due to neurological and non-neurological disease, and animal studies suggest a potential use in the management of malignant hyperpyrexia. Chemical evidence of liver dysfunction may occur in 0.7 to 1% of patients on long-term treatment with dantrolene, with symptomatic hepatitis in 0.35 to 0.5% and fatal hepatitis in 0.1 to 0.2%. The drug commonly causes transient drowsiness, dizziness, weakness, general malaise, fatigue and diarrhoea at the start of therapy. Muscle weakness may be the principal limiting side-effect in ambulant patients, particularly in those with multiple sclerosis, and therapy could be hazardous in patients with pre-existing bulbar or respiratory weakness. The dosage of dantrolene has been fixed in most controlled trials, though long-term studies have indicated the need for individualisation of dosage. The initial dose is usually 25mg once daily, increasing to 25mg two, three or four times daily, and then by increments of 25mg up to as high as 100mg two, three or four times daily. The lowest dose compatible with optimal response is recommended.

Positional isomer of the muscle relaxant dantrolene.

3-[[5-(P-Nitrophenyl) furfurylidene]amino]hydantoin, a position isomer of dantrolene, was synthesized and evaluated for skeletal muscle relaxant activity.