Changes in [(3)H]-glutamate uptake into platelets from patients with bipolar I disorder

Glutamate is the most abundant excitatory neurotransmitter in the mammalian brain, and it is increasingly being implicated in the pathophysiology of mental illness. In fact, changes in glutamate neurotransmission seem to be involved in the etiology of schizophrenia, major depression and bipolar disorders. Furthermore, the alterations in platelet sensitivity in major depression are distinct from those of bipolar disorders. The aim of the present investigation was to determine whether patients with bipolar disorders exhibited differences in [(3)H]-glutamate uptake of platelets. [(3)H]-Glutamate uptake of platelets from controls (n=14), patients with bipolar disorders under lithium treatment (600-1800 mg/day for 6 months) (n=7) and patients with bipolar disorders with psychotic features (n=8) were carried out. Analysis of blood platelets from the three groups of subjects revealed significant differences in [(3)H]-glutamate uptake between the control and psychotic patients. The specific glutamate uptake for the control and psychotic groups was 20.5+/-8.4 and 37.5+/-18.1 pmol glutamate/mg protein/10 min, respectively (mean+/-SD). These results indicate that peripheral glutamate metabolism of platelets is modified in bipolar disorders and that more detailed studies must be carried out to determine whether these peripheral modifications correlate with central modifications in humans and in animal models of the disease.