Human brain cortex and platelet serotonin2 receptor binding properties and their regulation by endogenous serotonin.

In patients with affective disorder and suicidality up-regulation of the serotonin2 receptor has been observed in brain and on platelets. Although the pharmacological profiles of the receptor in brain synaptosomes and platelet membranes are similar, it is a matter of debate whether the platelet serotonin2 receptor reflects the characteristics of the receptor in the brain and whether serotonin regulates the receptor activity. To answer these questions we measured in healthy human subjects the platelet serotonin2 receptor activity and blood serotonin concentrations. In an attempt to find whether the serotonin2 receptor activity in brain cortex synaptosomes and on platelets is similarly expressed we investigated the receptor's binding characteristics in neurosurgical patients. The results suggest that in men and women increased platelet serotonin concentrations correlate with a decrease in platelet membrane serotonin2 receptor affinity. The affinities of the brain cortex synaptosomal and platelet membrane serotonin2 receptor correlate intra-individually. These data suggest that the platelet serotonin2 receptor affinity appears to be regulated at the cellular level by blood serotonin and that the binding characteristics of the serotonin2 receptor in brain cortex synaptosomes corresponds to that on platelets. The latter finding supports the hypothesis of the platelet as a model for neuronal function.