Yohimbine increases the binding potential for [11C]flumazenil in the monkey brain

We evaluated the impact of yohimbine administration on benzodiazepine (BDZ) receptor binding in the central nervous system of non-human primates (rhesus monkeys). Estimates of the binding potential (B(max)/K(d)) of BDZ receptors were made following intravenous administration of yohimbine, an alpha (2)-adrenoceptor antagonist. Positron emission tomography was used in conjunction with [(11)C]flumazenil (Ro 15-1788), a tracer for central BDZ receptor binding activity. The effects of yohimbine were compared with a control condition in which saline was administered. Yohimbine significantly increased the binding potential in the hippocampus, as assessed using a Student's t-test with Bonferroni correction. The result that the administration of yohimbine readily induces an increase in the binding potential for BDZ receptors in the primate brain suggests that the presence of an anxiety state potentiates the effect of anxiolytics.