Severe
psychiatric disorders such as
schizophrenia are related to cognitive and negative symptoms, which often are resistant to current treatment approaches. The glutamatergic system has been implicated in the pathophysiology of
schizophrenia and
affective disorders. A key component is the dysfunction of the glutamatergic
N-methyl-D-aspartate (
NMDA) receptor. Substances regulating activation/inhibition of the
NMDA receptor have been investigated in
schizophrenia and major depression and are promising in therapeutic approaches of negative symptoms, cognition, and mood. In
schizophrenia, add-on treatments with
glycine, D-
serine, D-
alanine, D-
cycloserine,
D-amino acid oxidase inhibitors,
glycine transporter-1 (GlyT-1) inhibitors (e.g.,
sarcosine,
bitopertin) and agonists (e.g.,
LY2140023) or positive allosteric modulator (e.g.,
ADX71149) of group II
metabotropic glutamate receptors (mGluRs) have been studied. In major depression, the
NMDA receptor antagonists (e.g.,
ketamine,
AZD6765), GluN2B subtype antagonists (e.g.,
traxoprodil, MK-0657), and partial agonists (e.g., D-cycloserine, GLYX-13) at the
glycine site of the
NMDA receptor have been proven to be effective in animal studies and first clinical trials. In addition, clinical studies of
mGluR2/3 antagonist
BCI-838 (a
prodrug of
BCI-632 (
MGS0039)),
mGluR2/3-negative allosteric modulators (NMAs) (e.g., RO499819, RO4432717), and mGluR5 NAMs (e.g.,
AZD2066,
RO4917523) are in progress. Future investigations should include effects on brain structure and activation to elucidate neural mechanisms underlying efficacy of these drugs.