Increased platelet membrane [3H]-LSD binding in patients on chronic neuroleptic treatment

Using a [3H]-lysergic acid diethylamide [( 3H]-LSD) binding technique, platelet 5-hydroxytryptamine (5-HT) receptor number and affinity were compared in schizophrenics treated with depot thioxanthenes and phenothiazines and controls. There was an approximately 30% increase in platelet receptor number (Bmax) in the patient group. There was a decrease in affinity (increase in Kd) of about 30% in the patient group. This was probably due to the persistence of the neuroleptic in the platelet membrane preparation. There was a weak positive correlation between receptor number and total neuroleptic dosage. The increased number of 5-HT receptors is consistent with the previously reported enhancement of 5-HT-induced platelet aggregation in patients treated with long-term phenothiazines and thioxanthenes. Our findings are compatible with 5-HT up-regulation in human platelets produced by depot neuroleptic therapy. It is not known whether parallel changes may be occurring in brain 5-HT receptors.