Diazepam dependence prevented by glutamate antagonists.

Long-term treatment leads to tolerance to and dependence on benzodiazepines. Abrupt termination of benzodiazepine administration triggers the expression of signs of dependence. Mice withdrawn from chronic treatment with diazepam showed a time-related evolution of anxiety, muscle rigidity, and seizures between days 4 and 21 after treatment discontinuation. A period between withdrawal days 1 and 3 was symptom-free. Surprisingly, during this "silent phase" the susceptibility of mice to alpha-amino-3-hydroxy-5-tert-butyl-4-isoxazolepropionate (ATPA) and kainate seizures and the magnitude of monosynaptic reflexes mediated by non-N-methyl-D-aspartate (NMDA) mechanisms were enhanced. In apparent contrast, the "active phase", between withdrawal days 4 and 21, was characterized by increased susceptibility to NMDA seizures and enhanced magnitude of polysynaptic reflexes, which are NMDA dependent. Treatment of mice with alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) antagonists 1-(4-aminophenyl)-4-methyl-7,8-methylenedioxy-5H-2,3-benzodiazepine (GYKI 52466) or 2,3-dihydroxy-6-nitro-7-sulfamoylbenzo(f)quinoxaline but not with the NMDA antagonist 3-[(+/-)-2-carboxypiperazin-4-yl]-propyl-1-phosphonate (CPP) during the silent phase prevented signs of dependence. In contrast, treatment with CPP but not with GYKI 52466 during the active phase prevented the symptoms. The development of tolerance to and dependence on diazepam was prevented by concurrent treatment of mice with CPP but was not prevented by GYKI 52466. These data indicate that NMDA-dependent mechanisms contribute to the development of tolerance to diazepam and to the expression of signs of dependence in mice after termination of long-term treatment with diazepam. Nevertheless, the non-NMDA-mediated silent phase is essential for triggering the symptoms. Therefore, AMPA antagonists may offer a therapeutic approach for preventing dependence on benzodiazepines that is an alternative to NMDA antagonism.

Modulation of the seizure threshold for excitatory amino acids in mice by antiepileptic drugs and chemoconvulsants.

A novel method for the assessment of the threshold for clonic seizures induced by excitatory amino acids based on continuous infusion of the glutamate agonists [alpha-amino-3-hydroxy-5-terbutyl-4-isoxazolepropionate (ATPA), kainate or N-methyl-D-aspartate (NMDA)] into the lateral brain ventricle of unrestrained mice is reported. Using this novel method of seizure threshold determination, it was found that systemically administered diphenylhydantoin and carbamazepine elevated the threshold for ATPA and had negligible effects on the threshold for kainate and NMDA. Phenobarbital and trimethadione elevated the threshold for all excitatory amino acids tested, whereas valproate elevated the threshold for ATPA and kainate seizures. Ethosuximide elevated the threshold for ATPA and kainate and decreased the threshold for NMDA seizures. The quisqualate antagonists [2,3-dihydroxy-6-nitro-7-sulfamoyl-benzo(F)quinoxaline and 1-(4-aminophenyl)-4-methyl-7,8-methylenedioxy-5H-2,3-benzodiazepine] elevated the threshold for ATPA and less so for kainate seizures, whereas the NMDA antagonist 3-((+-)2-carboxypiperazine-4-yl)-propyl-1-phosphonate elevated the threshold for NMDA seizures. 1-(4-Aminophenyl)4-methyl-7,8-methylenedioxy-5H-2,3-benzodiazepine in higher doses was also active against NMDA seizures, whereas 3-((+-)2-carboxypiperazine-4-yl)-propyl-1-phosphonate did so with kainate seizures. Among seven different convulsants, pentylenetetrazol, picrotoxin and the beta-carboline methyl 6,7-dimethoxy-4-ethyl-beta-carboline-3-carboxylate lowered the threshold for seizures induced by excitatory amino acids. Pentylenetetrazol and picrotoxin did so with kainate seizures, whereas methyl 6,7-dimethoxy-4-ethyl-beta-carboline-3-carboxylate lowered ATPA thresholds. Bicuculline, 3-mercaptopropionate, strychnine and pilocarpine were inactive.(ABSTRACT TRUNCATED AT 250 WORDS)

Long-term treatment with abecarnil does not induce diazepam-like dependence in mice.

Abecarnil (isopropyl-6-benzyloxy-4-methoxymethyl-beta-carboline-3-carboxylate) is a metabolically stable anxiolytic and anticonvulsant beta-carboline derivative with few sedative and muscle relaxant effects in rodents. Abecamil binds with high affinity to benzodiazepine receptors. Because long-term treatment with benzodiazepines leads to development of dependence, we evaluated in mice whether abecarnil also possesses a potential for producing dependence, using electroencephalographic and electromyographic monitoring, and behavioral assessment of anxiety to detect withdrawal responses after chronic treatment. Diazepam was used as a reference. Mice withdrawn from chronic treatment with diazepam (15 mg/kg/day for 12 days) showed a time-related evolution of anxiety, muscle rigidity and seizures between days 4 and 21 after discontinuation of the treatment. A period between withdrawal days 1 and 3 was symptom free. Mice withdrawn from chronic administration of abecarnil (6 mg/kg/day for 12 days) showed no anxiety and no changes in seizure susceptibility and muscle tone. The doses of diazepam and abecarnil used for chronic treatment were equivalent in terms of kinetics and binding to benzodiazepine receptors. These data indicate that long-term treatment with abecarnil does not induce benzodiazepine-like dependence in mice. Thus, it may be predicted that chronic treatment with abecarnil in humans may offer an important alternative to benzodiazepines in the treatment of anxiety.