Glutamatergic abnormalities of the thalamus in schizophrenia: a systematic review

The thalamus, a key information processing centre in facilitating sensory discrimination and cognitive processes, has been implicated in schizophrenia due to the increasing evidence showing structural and functional thalamic abnormalities. Glutamatergic abnormalities, in particular, have been examined since glutamate is one of the main neurotransmitters found in the thalamus. We aimed to review the existing literature (1978 till 2007) on post-mortem and in vivo studies of the various components of glutamatergic neurotransmission as well as studies of the glutamate receptor genes within the thalamus in schizophrenia. The literature search was done using multiple databases including Scopus, Web of Science, EBSCO host, Pubmed and ScienceDirect. Keywords used were "glutamate", "thalamus", "schizophrenia", "abnormalities", and "glutamatergic". Further searches were made using the bibliographies in the main journals and related papers were obtained. The extant data suggest that abnormalities of the glutamate receptors as well as other molecules involved in glutamatergic neurotransmission (including glutamate transporters and associated proteins, N-methyl D-aspartate (NMDA) receptor-associated intracellular signaling proteins, and glutamatergic enzymes) are found within the thalamus in schizophrenia. There is a pressing need for more rapid replication of findings from post mortem and genetic studies as well as the promotion of multi-component or multi-modality assessments of glutamatergic anomalies within the thalamus in order to allow a better appreciation of disruptions in these molecular networks in schizophrenia. These and future findings may represent potential novel targets for antipsychotic drugs to ameliorate the symptoms of schizophrenia.