Anticonvulsant tolerance to clonazepam in amygdala kindled rats: clonazepam concentrations and benzodiazepine receptor binding

The relationship between anticonvulsant tolerance to clonazepam and benzodiazepine receptor changes was studied in amygdala kindled rats. Fully kindled rats were given 1 mg/kg clonazepam (clonazepam treated) or vehicle (kindled control) orally three times per day for 4 weeks. During chronic treatment, amygdala stimulation was given twice per week, 30 min after a single protective dose of clonazepam (0.5 mg/kg, i.p.) was injected to both groups of rats. As measured by seizure stage, clonazepam treated rats showed a greater degree of tolerance than kindled control rats; contingent tolerance to the anticonvulsant effects of clonazepam developed in kindled control rats, while clonazepam treated rats shows contingent plus pharmacologic tolerance. There were no significant differences between clonazepam treated and kindled control rats in "peak" plasma clonazepam concentrations 40 min after clonazepam injections. Benzodiazepine receptor assays showed no significant difference in maximal binding capacity (Bmax), dissociation constant (Kd) or gamma-aminobutyric acid (100 microM) enhancement of benzodiazepine receptor binding between clonazepam treated and kindled control rats. These data suggest that pharmacologic tolerance to anticonvulsant action of clonazepam is not related to either plasma clonazepam concentrations or benzodiazepine receptor changes.