The alteration of serotonin binding sites in aged human brain

The $\text{in}$$\text{vitro}$ binding of ³H]serotonin (³H]5-HT) to cerebral cortex from young and old adult humans was studied. With cortex from human males 23–29 years old, the binding of ³H]5-HT was a saturable process, and bound ³H]5-HT could be displaced by unlabeled 5-HT or by lysergic acid diethylamide (LSD). Two separate binding sites were discernible by Scatchard analysis. The dissociation constants were 7 nM (Kd₁) and 52 nM (Kd₂), and the total number of binding sites were 0.65 (n₁) and 2.06 (n₂) pmoles/mg protein, respectively. In cerebral cortex from aged humans (61–70 years old), the dissociation constant for ³H]5-HT binding was 198 nM, and the total number of binding sites were 4.78 pmoles/mg protein. The alteration of serotonin binding sites may be related to cerebral malfunction in old people, particularly to mental depression and sleep disturbances that commonly occur.