Interaction of central and peripheral benzodiazepine sites in benzodiazepine tolerance and discontinuation.

1. Chronic administration of benzodiazepines is associated with the development of tolerance and discontinuation effects in humans and in a mouse model. 2. Co-administration of compounds active at the "peripheral" benzodiazepine site may alter chronic benzodiazepine effects. 3. During chronic lorazepam administration, addition of the peripheral site antagonist PK11195 attenuates behavioral tolerance and receptor downregulation. 4. In mice treated with both lorazepam and PK11195, discontinuation effects were also attenuated compared to lorazepam alone. 5. Specificity of the action of PK11195 was confirmed by antagonism of its action by the peripheral-site agonist Ro5-4864.