Upregulated mRNA levels of SERT, NET, MAOB, and BDNF in various brain regions of ovariectomized rats exposed to chronic aversive stimuli.

Estrogen deficiency increases the risk of anxiety and mood disorders, presumably by deranging metabolism of the monoamine neurotransmitters and the expression of their reuptake transporters in the brain. Although estrogen-deficient individuals were also susceptible to stress, little was known regarding the effect of stress on the levels of transcripts related to brain monoamine metabolism. Herein, we used quantitative real-time PCR to quantify the mRNA levels of serotonin reuptake transporter (SERT), norepinephrine transporter (NET), monoamine oxidase-B (MAOB), tryptophan hydroxylase (TPH), and tyrosine hydroxylase (TH) in various brain regions of ovariectomized (OVX) rats which had been exposed for 4 weeks to chronic aversive stimuli (CAS), such as water deprivation, cage tilt, and illumination. We found that CAS induced stress responses in OVX rats as indicated by increases in the adrenal gland weight and sucrose intake. After CAS exposure, mRNA levels of SERT and NET were upregulated in the frontal cortex, hippocampus, amygdala, and periaqueductal gray. In addition, CAS also increased the mRNA levels of MAOB, an enzyme for dopamine degradation, in the same brain regions. However, CAS did not alter the mRNA levels of TPH or TH, both of which are rate-limiting enzymes for the synthesis of serotonin and norepinephrine in the dorsal raphé and locus coeruleus, respectively. Interestingly, mRNA expression of brain-derived neurotrophic factor precursor was upregulated in the hippocampus of CAS-exposed OVX rats, suggesting a compensatory mechanism which might counteract the stress-induced depression. Therefore, the present data have provided evidence to explain how stress affected brain monoamine metabolism in estrogen-deficient stressed patients.