Clinical studies have shown that estrogen (E2) can ameliorate symptoms of mood disorders in women, including severe depression. The presence of symptoms may represent an abnormal response to normal hormonal changes, thereby implicating contextual factors in the brain in the etiology of these symptoms. Some of these factors include second messenger systems that lead to the production of neurotrophic agents, including brain-derived neurotrophic factor (BDNF). Chronic stress results in deleterious effects on neurons and synapses which, in turn, may be related to alterations in affective behavior. Because of its involvement in cellular and synaptic growth and/or function, BDNF may counteract these negative effects and restore the appropriate behavioral responses. The gene transcription factor cyclic AMP response element-binding protein (CREB), has been shown to be a target of antidepressant and E2 action. Activation of CREB can lead to transcription of the BDNF gene. We propose that the Ca2+/calmodulin-dependent protein kinase IV (CaMK IV) pathway, """"""""CaMK IV - CREB - phosphorylated CREB (pCREB) - BDNF,"""""""" mediates some of the effects of long-term E2 treatment on behavior. Long-term E2 treatment results in the persistence of these messengers, even after two weeks. E2 may regulate CaMK IV and BDNF via alterations in their mRNAs; we will perform in situ hybridization to address the hypothesis that E2 regulates levels of CaMK IV mRNA and BDNF mRNA. We will also determine if E2 decreases relevant phosphatases, including protein phosphatase 2A and the calcineurin pathway, negative regulators of CaMK IV and pCREB, respectively. To determine if CaMK IV, CREB and/or BDNF mediate E2 effects in the forced swim test, a test for the efficacy of antidepressants in rodents, antisense oligodeoxynucleotides (ODNs) to CaMK IV, CREB or BDNF will be infused into the amygdala or hippocampus and animals will be subjected to the test conditions. Infusion of these antisense ODNs may interfere with the positive effects of E2 on forced swim. We will also determine if infusions of BDNF protein with the antisense ODNs to CaMK IV and CREB reverse the actions of the ODNs on behavior. These experiments will give insight to the molecular effects of E2 in areas of the brain related to affective processing and will uncover mechanisms that may allow hormonal intervention for the amelioration of female-related mood disorders.
