Central and peripheral benzodiazepine receptors in rat brain and platelets: effects of treatment with diazepam and clobazam.

Tolerance to the effects of benzodiazepines (BZ) may be mediated by changes in benzodiazepine receptors (BZRs). Peripheral BZRs (in brain and platelets) and central BZRs (in brain) were measured in rats following intraperitoneal administration of diazepam and clobazam each for 4 and 12 days. BZRs were measured by binding assays using [3H] PK 11195 (peripheral) and [3H] flunitrazepam (central) as radioligands. Diazepam, but not clobazam, increased peripheral BZR numbers in platelets (both P < 0.005), but not in brain, after 4 and 12 days' treatment compared with appropriate controls. Neither drug altered central BZR affinities or numbers in rat brain. BZ effects on peripheral BZRs in platelets cannot be extrapolated to predict changes in brain receptors, either peripheral or central.