Sex differences and the role of estrogen in animal models of schizophrenia: interaction with BDNF.

Schizophrenia is a severe psychiatric disorder with a complex and variable set of symptoms. Both genetic and environmental mechanisms are involved in the development of the illness and lead to structural and neurochemical abnormalities in the brain. An intriguing facet of schizophrenia is sex differences, which have been described for nearly all features of the illness, including the peak age of onset, symptoms and treatment response. The ovarian hormone, estrogen, may be protective against schizophrenia and evidence is accumulating that estrogen may exert this effect via an interaction with brain-derived neurotrophic factor (BDNF). Both estrogen and BDNF have trophic effects on the developing brain and promote synaptic plasticity and maintain neurons well into adulthood. Major neurotransmitter systems including dopaminergic, serotonergic and glutamatergic pathways are modulated and supported by estrogen and BDNF. Despite their commonalities, estrogen and BDNF have mostly been examined independently but increasing evidence suggests an interaction between the two in brain regions pertinent to schizophrenia. This review will focus on the role of estrogen and BDNF in clinical and animal studies of schizophrenia. We include animal models of neurotransmitter dysfunction and genetic manipulation to show how estrogen may provide a protective effect in schizophrenia, including through mediating BDNF expression and activity. This posited estrogen-BDNF interaction could play a key role in modulating sex-dependent results reported in animal work as well as sex differences in clinical aspects of schizophrenia.