Binding of [ 3 H]Neurotensin in Human Brain: Properties and Distribution

The binding of [ 3 H]neurotensin to membranes from human brain at 0°C was specific, saturable, and reversible. In the frontal cortex, the equilibrium dissociation constant (K D ) for [ 3 H]neurotensin determined from the ratio of rate constants (k ‐1 /k 1 ), saturation isotherms, and inhibition binding experiments was 0.80, 2.0, and 2.0 nM, respectively, and the maximum number of binding sites (B max ) from the saturation isotherms and the competitive binding experiments was 2.4 and 2.2 pmol/g of tissue, respectively. Hill coefficients for binding were equal to 1, indicating the presence of single, noncooper‐ative binding sites. Inhibition of specific binding of [ 3 H]neurotensin by several analogs of neurotensin showed that [Gln 4 ]neurotensin and neurotensin(8–13) had the highest affinities for these binding sites in human frontal cortex, with each analog being ∼13‐fold more potent than neurotensin. In addition, these data showed that the carboxy‐terminal portion of neurotensin played an important part in the binding of this neuropeptide in human brain, a result described for other species. Regional distribution of binding sites was different from that reported for animal brains. Of the 33 different regions investigated, the uncus and substantia nigra showed the highest specific binding of [ 3 H]neurotensin, whereas such areas as the pineal body, medulla, and corpus callosum had few binding sites.