Pharmacologic implications of neurobiological models of schizophrenia

Glutamatergic dysbalance and oxidative stress in in vivo and in vitro models of psychosis based on chronic NMDA receptor antagonism

Background

The psychotomimetic effects of N-methyl-D-aspartate (NMDA) receptor antagonists in healthy humans and their tendency to aggravate psychotic symptoms in schizophrenic patients have promoted the notion of altered glutamatergic neurotransmission in the pathogenesis of schizophrenia.

Methods

The NMDA-receptor antagonist MK-801 was chronically administered to rats (0.02 mg/kg intraperitoneally for 14 days). In one subgroup the antipsychotic haloperidol (1 mg/kg) was employed as a rescue therapy. Glutamate distribution and 3-NT (3-nitrotyrosine) as a marker of oxidative stress were assessed by immunohistochemistry in tissue sections. In parallel, the effects of MK-801 and haloperidol were investigated in primary embryonal hippocampal cell cultures from rats.

Results

Chronic NMDA-R antagonism led to a marked increase of intracellular glutamate in the hippocampus (126.1 +/− 10.4% S.E.M of control; p = 0.037), while 3-NT staining intensity remained unaltered. No differences were observed in extrahippocampal brain regions. Essentially these findings could be reproduced in vitro.

Conclusion

The combined in vivo and in vitro strategy allowed us to assess the implications of disturbed glutamate metabolism for the occurrence of oxidative stress and to investigate the effects of antipsychotics. Our data suggest that oxidative stress plays a minor role in this model than previously suggested. The same applies to apoptosis. Moreover, the effect of haloperidol seems to be mediated through yet unidentified mechanisms, unrelated to D2-antagonism. These convergent lines of evidence indicate that further research should be focused on the glutamatergic system and that our animal model may provide a tool to explore the biology of schizophrenia.

The treatment of cognitive impairment in schizophrenia

Cognitive deficits are major contributors to disability in schizophrenia. Many pharmacologic targets have been identified for cognitive enhancing agents, including receptors involved in dopaminergic, glutamatergic, GABAergic, serotonergic and cholinergic neurotransmission. In addition, new approaches to drug development have been directed towards neuroprotection and the facilitation of neuroplasticity. While several pharmacologic agents and cognitive remediation have shown promise in early trials, no treatment has yet demonstrated efficacy in large replication trials. The experience with different pharmacologic targets is reviewed and methodologic issues are discussed with recommendations for future research.

Inflammation and schizophrenia

Previous research has demonstrated that prenatal infections with bacterial or viral agents during pregnancy are associated with an increased risk of schizophrenia in the offspring during adulthood. Furthermore, there has been evidence linking obstetric complications to schizophrenia. In parallel, there is a separate body of evidence relating subclinical chronic inflammation and schizophrenia in individuals, usually in their adulthood, who have already developed schizophrenia. On the other hand, unequivocal experimental, epidemiological and clinical evidence has emerged during the past decade linking inflammation to the development of insulin resistance and metabolic disturbances, which are common in the schizophrenic population. Inflammation might be an important common pathophysiological process related to both schizophrenia psychopathology and metabolic disturbances seen in patients with schizophrenia. Future studies targeting proinflammatory cytokines and their molecular signaling pathways may lead to novel pharmacological intervention strategies treating both psychopathology and medical comorbidity in patients with this devastating mental illness.

The schizophrenic faces of PICK1

Schizophrenia is a grave psychiatric disorder with psychotic symptoms and an enigmatic etiology. Family studies have strongly indicated that genetic risk factors have a role in this disease. Recent findings, together with previously established evidence, highlight the PDZ-domain-containing protein interacting with C-kinase 1 (PICK1) as a promising candidate for a schizophrenia susceptibility gene. Here, we outline possible molecular mechanisms, discuss clinical case-studies that indicate an unexpected role of PICK1 in schizophrenia and discuss potential avenues for pharmacological manipulation of PICK1.