Characterization of Sodium‐Dependent [³H]GBR‐12935 Binding in Brain: A Radioligand for Selective Labelling of the Dopamine Transport Complex

Abstract: High‐affinity and saturable binding sites for the diphenyl‐substituted piperazine derivative [³H]GBR‐12935 have been characterized in crude synaptosomal membranes prepared from rat brain. The specific binding of [³H]GBR‐12935 is sodium‐dependent and is unevenly distributed among various brain regions, with the highest concentration of binding sites being found in the corpus striatum and nucleus accumbens. Sodium‐dependent [³H]GBR‐12935 binding in all other brain areas was 10% or less of the binding found in the striatum. The affinity of [³H]GBR‐12935 for binding sites in the striatum is increased in the presence of Na⁺ but other cations, including K⁺, Ca²⁺, or Mg²⁺, inhibit specific binding. There is an excellent correlation (r= 0.96, p < 0.01) between the potencies of a series of drugs in inhibiting [³H]GBR‐12935 binding to striatal membranes and their potencies in inhibiting [³H]3,4‐dihydroxyphenylethylamine ([³H]dopamine) uptake in synaptosomes. Agonists and antagonists of other neurotransmitter receptor or drug recognition sites have little or no effect on specific [³H]GBR‐12935 binding to striatal membranes. In addition, prior intracerebroventricular administration of 6‐hydroxydopamine results in a decrease in the number of specific [³H]GBR‐12935 binding sites in the striatum. These data indicate that [³H]GBR‐12935 is a selective radioligand of the presynaptic dopamine transport complex in brain.