Autoradiographic localization of cocaine binding sites by [3H]CFT ([3H]WIN 35,428) in the monkey brain

Abstract

The cocaine analog [3H]2 beta-carbomethoxy-3 beta-(4-fluorophenyl)tropane ([3H]CFT or [3H]WIN 35,428 binds with high affinity and selectivity to cocaine receptors in the monkey caudate-putamen. [3H]CFT was used to map the regional distribution of cocaine binding sites in slide-mounted sections of monkey brains using autoradiographic techniques. Hemicoronal brain sections were incubated with [3H]CFT (3 nM) alone or in the presence of excess (-)-cocaine (30 microM) to mask the binding sites. High densities of [3H]CFT binding sites were detected in the caudate nucleus, putamen, and nucleus accumbens. In all three regions, binding was markedly reduced by coincubation with unlabeled (-)-cocaine, indicating low levels of nonspecific binding. Little or no binding was observed in the cortex, thalamus, globus pallidus, or white matter tracts at the levels studied. In order to characterize binding sites for [3H]CFT in tissue sections, competition experiments were conducted using a fixed concentration of [3H]CFT (3 nM) and a range of concentrations of (-)-cocaine, (+)-cocaine, CFT, Lu 19-005, GBR 12909, bupropion, and citalopram. The IC50 values for the drugs in tissue sections corresponded closely with their reported IC50 values in monkey caudate-putamen membranes (r = 0.99, p less than 0.001), suggesting that [3H]CFT binding is similar in the two preparations. These findings support the view that cocaine receptors labeled by [3H]CFT are localized predominantly in dopamine-rich brain regions implicated in the behavioral effects and abuse of cocaine.