ABSTRACT
Converging evidence indicates that dysfunctions in glutamatergic neurotransmission and in the glutamate-glutamine cycle play a role in the pathophysiology of schizophrenia. Here, we investigated glutamate and glutamine levels in the blood of patients with recent onset schizophrenia or chronic schizophrenia compared to healthy controls. Compared with healthy controls, patients with recent onset schizophrenia showed increased glutamine/glutamate ratio, while patients with chronic schizophrenia showed decreased glutamine/glutamate ratio. Results indicate that circulating glutamate and glutamine levels exhibit a dual behavior in schizophrenia, with an increase of glutamine/glutamate ratio at the onset of schizophrenia followed by a decrease with progression of the disorder. Further studies are warranted to elucidate the mechanisms and consequences of changes in circulating glutamate and glutamine in schizophrenia.
ABSTRACT
Changes in D-serine availability in the brain may contribute to the hypofunction of NMDA-glutamate receptors in schizophrenia; however, measurements of blood levels of D-serine in individuals with schizophrenia have not been consistent amongst previous studies. Here we studied plasma levels of D-serine and L-serine in 84 Brazilian individuals with schizophrenia and 75 gender- and age-matched controls. Plasma levels of D-serine and the ratio of plasma D-serine to total serine were significantly lower in individuals with schizophrenia as compared to the control group. Levels of D-serine were significantly and negatively correlated to the severity of negative symptoms of schizophrenia. We also observed that plasma levels of D-serine significantly decreased with aging in healthy controls. Our results suggest that the possible role of D-serine in the pathophysiology of schizophrenia should be further investigated, with possible implications for the drug treatment of this disorder.
