Decreased levels of plasma glutamate in patients with first-episode schizophrenia and bipolar disorder.

A variety of studies have suggested that glutamatergic neurotransmission is altered in schizophrenia and bipolar disorder. Here, we tested if plasma glutamate levels are altered in 56 patients diagnosed with schizophrenia, bipolar disorder or non-specified psychosis at the first psychotic episode and at various stages during one-year follow-up. A decrease in the levels of plasma glutamate was observed in all groups of patients at the first psychotic episode. Furthermore, plasma glutamate levels were restored after treatment in all instances. Decreased plasma glutamate levels at first psychotic episodes may reflect impaired glutamate signaling during the initial stages of schizophrenia and bipolar disorder.