Sarinee Kalandakanond-Thongsong

Anxiolytic property of estrogen related to the changes of the monoamine levels in various brain regions of ovariectomized rats.

Anxiety is a symptom reflecting the dysregulation of monoaminergic neurotransmitters which may be modulated by estrogen. In our current study, we investigated the effects of chronic estrogen administration (10 microg/kg, s.c. for 4 weeks) on anxiety-like behavior using the elevated plus-maze with the corresponding changes of monoamines in the brain regions contributing to anxiety. The behavioral test revealed that estrogen-treated rats (Ovx+E(2)) spent more time in the open arm of the maze as well as a higher time/entry ratio in open arms than ovariectomized (Ovx) rats, indicating an anxiolytic property of estrogen. The increase in open arm time corresponded to an increase in uterine weight, indicated a correlation between the function of estrogen and its anxiolytic effect. Measurements of brain monoamines following estrogen treatment revealed decreases in norepinephrine, dopamine and serotonin in all of the brain regions studied, which also lead to an increase in turnover rates. The concentrations of norepinephrine in caudate putamen, of dopamine in nucleus accumbens, of serotonin in frontal cortex, hippocampus, caudate putamen, nucleus accumbens, and substantia nigra and of the serotonin metabolite, the 5-hydroxyindolacetic acid in substantia nigra of Ovx+E(2) rats were significantly lower than those of Ovx rats. Interestingly, the uterine weight was negatively correlated with the changes of dopamine and serotonin (with the exception of the hippocampus), suggesting a regulatory role of estrogen on these systems. From these data, we concluded that, in fact, there is a relationship between estrogen and monoamines (i.e. serotonin, dopamine) in modulating the anxiety-like behaviors in female rats.

Differential effects of exogenous and endogenous estrogen on anxiety as measured by elevated T-maze in relation to the serotonergic system.

The effects of estrogen on anxiety-like behaviors have been widely studied but the mechanisms responsible are still inconclusive. The purpose of the current study was to compare the effects of transient high levels of endogenous estrogen and chronic exogenous estrogen treatment on the anxiety-like behaviors using the elevated T-maze (ETM) test. In addition, serotonin (5-HT) and its metabolite (5-HIAA), serotonin reuptake transporter (SERT) and tryptophan hydroxylase enzyme (TPH) were measured at the end of the study and correlated to the task performances. Female sham-operated rats in proestrous phase (Sham-Pro) and ovariectomized rats treated with or without 17beta-estradiol (10 microg/kg, s.c.; Ovx+E(2) or Ovx) for 4 weeks were used. In the ETM test, the Ovx+E(2) group had reduced inhibitory avoidance responses compared to others, suggesting that exogenous E(2) replacement is anxiolytic, while escape latency was prolonged in the Sham-Pro group suggesting endogenous E(2) is panicolytic. Further, the serotonin turnover rate (5-HIAA/5-HT ratio) in the hippocampus and nucleus accumbens was highest in the Ovx+E(2) group. While the TPH protein in the midbrain of Ovx rats was significantly higher than others, the SERT levels were not significantly different among groups in all measured brain areas. In conclusion, Ovx rats with chronic estrogen administration and Sham-Pro rats with naturally high levels of estrogen, demonstrated anxiolytic behavior by exhibiting different forms of anxiety that related to the changes in the function of serotonergic system.

Effect of the acute and chronic estrogen on anxiety in the elevated T-maze

Despite the extensive studies on the influences of estrogen (E(2)) on anxiety-like behaviors, there is still conflicting evidence regarding the specific effects of E(2) on anxiety. These discrepancies may be a result of different replacement regimens. The goals of this study were to evaluate anxiety-like behavior in ovariectomized rats (Ovx) using the elevated T-maze (ETM) test for the following variables: (1) the effects of acute versus chronic E(2) dosing, (2) the effects of chronic E(2) at different doses and, (3) the effects of Tamoxifen (Tam) co-administered with E(2). Rats in the acute E(2) dosing group (aE(2)) showed reduced inhibitory avoidance responses with prolong escape latencies compared to Ovx; while rats in the chronic E(2) dosing group (cE(2)) showed reduced inhibitory avoidance responses only. These results suggest that E(2) contains anxiolytic effects when given once or repeatedly. Moreover, when various doses of E(2) (1-100 μg/kg) were chronically given to the Ovx rats, all doses produced impaired inhibitory avoidance responses compared to Ovx, suggesting that chronic replacement of E(2) had no dose-dependent effect on anxiety-like behavior. Interestingly, in the 3-week delay replacement regimen, the low dose E(2) (1 μg/kg, s.c.) group displayed no anxiolytic effects as their inhibitory avoidance responses in the ETM were not different from their Ovx counterparts. On the contrary, the Ovx group that received Tam+E(2) (Tam 1 mg/kg, PO and E(2) 1 μg/kg, s.c.) had reduced inhibitory avoidance responses compared to other groups. These findings indicate that when Tam is co-administered with chronic low dose estrogen, it can act as an estrogen receptor agonist and result in anti-anxiety effects. Therefore, it is likely that the anxiolytic-like behavior relative to generalized anxiety disorder can be conserved when estrogen is given acutely or chronically; while the anxiolytic-like behavior relative to panic disorder can be conserved only when estrogen is given acutely.

Effects of time of estrogen deprivation on anxiety-like behavior and GABAA receptor plasticity in ovariectomized rats

Ovariectomized animals have frequently been used to study the effects of estrogen deficiency on mood disorders, particularly anxiety disorder. However, a range of results including anxiolytic, anxiogenic, and no behavioral effects have been reported. One discrepancy was the different in behavioral testing time following ovariectomized; therefore, the aim of this study was to examine the effects of time of estrogen deprivation on anxiety-like behavior and on GABAA receptor subunit gene expressions in ovariectomized rats. The GABAA receptor was of special interest as it had been shown to be influenced by estrogen. In this study, adult female Wistar rats were ovariectomized and randomly assigned into 2 groups: ovariectomized-rat (Ovx) and ovariectomized-rat treated with estrogen (E2) at the dosage of 1μg/kg BW. At 7, 14, 21 and 28 days after ovariectomy, the rats were tested with elevated T-maze (ETM) and open field. We found that after ovariectomy, the Ovx showed signs of anxiety as demonstrated by the increased in inhibitory avoidance latency in the ETM with significant effect at day 21 and even higher at day 28. On the other hand, the escape latency was not differed between each time point. These behavioral data implied that the anxiety in term of generalized anxiety disorder as interpreted from impaired inhibitory avoidance in the ETM was affected by estrogen depletion; while, the anxiety disorder in term of panic disorder as shown by escape latency was unaffected. For gene expression analysis, the GABAA receptor α2-, α3- and α4-subunits in Ovx groups were significantly increased in the midbrain compared to E2 groups; whereas, in the amygdala, the gene expressions were not different between Ovx and E2 groups. In conclusion, these results indicated that ovariectomized as early as 21 day can induce anxiety and the altered GABAA receptor subunit may be partially responsible for anxiety following estrogen deprivation.

Transmural dispersion of repolarization and cardiac remodeling in ventricles of rabbit with right ventricular hypertrophy.

INTRODUCTION Recent publications demonstrated that rabbits with right ventricular hypertrophy (RVH) possess high sensitivity and specificity for drug-induced arrhythmias. However, the underlying mechanism has not been elucidated. This study aimed to evaluate RVH induced changes in cardiac remodeling especially the transmural dispersion of repolarization (TDR), epicardial monophasic action potentials (MAP), and hERG mRNA expression in rabbits. METHODS New Zealand White rabbits (n=13) were divided into 2 groups: sham operated (SHAM, n=6) and pulmonary artery banding (PAB, n=7). PAB was induced by narrowing the pulmonary artery. Twenty weeks after surgery, hemodynamic, cardiac function, electrocardiograms, and MAP were obtained from PAB compared with SHAM. After measurement, rabbits were sacrificed to collect ventricular myocardium for histopathological analysis and measurement of hERG mRNA expression by real time PCR. RESULTS After 20weeks, the % HW to BW ratio of whole heart and right ventricle (RV) and left and right ventricular free wall thickness was significantly increased in PAB when compared with those in SHAM. PAB has a significant electrical remodeling as demonstrated by lengthening of QT, QTc intervals, and increased Tp-Te duration. PAB also has a significant functional remodeling verified by decreased contractility index of RV and lengthened time constant of relaxation of LV. MAP of RV epicardium was significantly shortened in PAB consistently with increased hERG mRNA expression at the epicardium of RV. DISCUSSION The rabbit with PAB demonstrates cardiac remodeling diastolic and systolic dysfunctions. These rabbits also demonstrate increased TDR and electrical remodeling related to the change of hERG mRNA expression which may be prone to develop arrhythmias.