Emese Domonkos

Sex differences and sex hormones in anxiety-like behavior of aging rats

Abstract Sex differences in the prevalence of affective disorders might be attributable to different sex hormone milieu. The effects of short‐term sex hormone deficiency on behavior, especially on anxiety have been studied in numerous animal experiments, mainly on young adult rats and mice. However, sex differences in aged animals and the effects of long‐term hypogonadism are understudied. The aim of our study was to analyze sex differences in anxiety‐like behavior in aged rats and to prove whether they can be attributed to endogenous sex hormone production in males. A battery of tests was performed to assess anxiety‐like behavior in aged female, male and gonadectomized male rats castrated before puberty. In addition, the aged gonadectomized male rats were treated with a single injection of estradiol or testosterone or supplemented with estradiol for two‐weeks. Female rats displayed a less anxious behavior than male rats in most of the conducted behavioral tests except the light‐dark box. Long‐term androgen deficiency decreased the sex difference in anxiety either partially (open field, PhenoTyper cage) or completely (elevated plus maze). Neither single injection of sex hormones, nor two‐week supplementation of estradiol in gonadectomized aged male rats significantly affected their anxiety‐like behavior in the elevated plus maze. In conclusion, our results confirm sex differences in anxiety in aged rats likely mediated by endogenous testosterone production in males. Whether long‐term supplementation with exogenous sex hormones could affect anxiety‐like behavior in elderly individuals remains to be elucidated. Graphical abstract Figure. No Caption available. HighlightsAged male rats display higher anxiety‐like behavior than aged female rats.Endogenous androgens seem to be responsible for the sex differences in anxiety.Short‐term exogenous sex hormones do not reverse long‐term effects of hypogonadism.

The sex-dependent effects of letrozole on anxiety in middle-aged rats

Aromatase catalyzes the conversion of testosterone to estradiol and is involved in the physiological effects of sex hormones on brain function. Animal experiments have shown that the aromatase inhibitor, letrozole, can induce anxiety in young ovariectomized females that are used as a model of aging. Whether or not these effects would be similar in intact middle‐aged animals is unknown. The aim of our study was to analyze the effects of letrozole on anxiety in middle‐aged rats of both sexes. Fifteen month old male and female rats were treated daily with either letrozole or vehicle for 2 weeks. The elevated plus maze was used to test anxiety‐like behaviour. Sex differences were found not only in plasma concentrations of testosterone but also in the effects of letrozole treatment on plasma testosterone (P<.05). The interaction between sex and treatment was also proven in locomotor activity (P<.05) and time spent in the open arms of the elevated plus maze (P<.05). Letrozole‐treated male rats spent 95% less time in the open arms of the elevated plus maze than the control rats did (P<.05) suggesting an anxiogenic effect of aromatase inhibition. This difference was not found between letrozole‐treated and vehicle‐treated females. In contrast to previous experiments on young animals, letrozole seems to induce anxiety in male but not in female middle‐aged rats. This sex‐specific effect might be related to sex differences of oestrogen and androgen signalling in aging brains. These results should be taken into account in clinical applications of letrozole, especially in men.

No effect of testosterone on behavior in aged Wistar rats

In men, aging is accompanied by a gradual decline in androgen secretion. Studies suggest beneficial effects of endogenous and exogenous testosterone on affective behavior and cognitive functions. The aim of this study was to describe behavioral and cognitive sex differences and to analyze the effects of long-term androgen deficiency in aged male rats. Thirty-months old rats divided into three groups (males, females and males gonadectomized as young adults) underwent a battery of behavioral tests assessing locomotor activity, anxiety, memory, anhedonia, sociability and depression-like behavior. No major effect of gonadectomy was found in any of the analyzed behavioral measures in male rats. The only consistent sex difference was confirmed in depression-like behavior with longer immobility time observed in males. In an interventional experiment, a single dose of testosterone had no effect on gonadectomized male and female rats in the forced swim test. In contrast to previous studies this comprehensive behavioral phenotyping of aged rats revealed no major role of endogenous testosterone. Based on our results long-term hypogonadism does not alter the behavior of aged male rats, neither does acute testosterone treatment. Whether these findings have any consequences on androgen replacement therapy in aged men remains to be elucidated.

17β-Estradiol treatment reversed left ventricular dysfunction in castrated male rats: an echocardiographic study

No data are available on heart function in chronic testosterone deficiency and on the effect of estrogen treatment. Eighteen 4-week-old male Lewis rats were randomly divided into 3 groups (n = 6): 1 group of sham-operated rats and 2 groups of castrated rats. Sixty-six weeks after surgery, 1 castrated group received a dose of 17β-estradiol (10 μg/kg per day) and the remaining 2 groups received a placebo subcutaneously for 14 days. Left ventricular (LV) systolic and diastolic functions were measured by transthoracic echocardiography. Castration decreased LV ejection fraction (9%) and fractional shortening (15%) and deteriorated LV diastolic function (94%). 17β-Estradiol treatment increased LV ejection fraction (15%) and fractional shortening (31%) and improved LV diastolic function (48%). Plasma testosterone concentrations were decreased in both castrated groups. In conclusion, chronic testosterone deficiency induced LV systolic and diastolic dysfunction; these disorders were reversed by short-term treatment with 17β-estradiol.

Does long-term androgen deficiency lead to metabolic syndrome in middle-aged rats?

ABSTRACT Evidence from clinical observational studies and animal experiments suggests that hypogonadism is associated with the metabolic syndrome. In most of the experiments, androgen deficiency is induced by gonadectomy in the adulthood and relatively short‐term effects of hypogonadism on metabolic parameters are usually observed. The purpose of this study was to evaluate the metabolic effects of long‐term androgen deficiency starting before puberty in middle‐aged male rats. The components of the metabolic syndrome were examined in male, female and gonadectomized male rats at the age of 18 months. Sex differences were observed in plasma testosterone, cholesterol, high‐density lipoproteins and also in body weight and in glycemia dynamics during oral glucose tolerance test. Gonadectomy and long‐term hypogonadism did not affect most of the analyzed metabolic parameters such as blood pressure, glycemia, plasma insulin and uric acid. The only exception was the significantly higher liver enzymes in plasma and triacylglycerol in liver found in gonadectomized males. Except low‐density lipoprotein, neither treatment of middle‐aged males and females with letrozole, nor supplementation of estradiol as the metabolite of testosterone in gonadectomized male rats changed any of the observed metabolic parameters. Our results suggest that long‐term hypogonadism started before puberty does not induce metabolic syndrome in middle‐aged male rats, but may affect the liver. Sex differences in metabolic parameters in middle‐aged rats are not mediated by testosterone. Whether hypogonadism predispose to metabolic syndrome in combination with other risk factors needs further clarification. HighlightsLong‐term hypogonadism leads to partial liver damage in aged rats.Long‐term hypogonadism does not induce metabolic syndrome in aged rats.Sex differences in metabolic parameters are not mediated by testosterone.Short‐term administration of letrozole does not affect the metabolic parameters.Short‐term supplementation of estradiol does not affect the metabolic parameters.

On the Role of Testosterone in Anxiety-Like Behavior Across Life in Experimental Rodents

Testosterone affects brain functions and might explain some of the observed behavioral sex differences. Animal models may help in elucidating the possible involvement of sex hormones in these sex differences. The effects of testosterone have been intensively investigated, especially in anxiety models. Numerous experiments have brought inconsistent results with either anxiolytic or anxiogenic effects. Besides methodological variations, contradictory findings might be explained by the divergent metabolism of testosterone and its recognition by neurons during prenatal and postnatal development. Gonadectomy and subsequent supplementation have been used to study the role of sex hormones. However, the variable duration of hypogonadism might affect the outcomes and the effect of long-term androgen deficiency is understudied. Testosterone can be metabolized to dihydrotestosterone strengthening the androgen signaling, but also to estradiol converting the androgen to estrogen activity. Moreover, some metabolites of testosterone can modulate γ-aminobutyric acid and serotonergic neurotransmission. Here we review the currently available experimental data in experimental rodents on the effects of testosterone on anxiety during development. Based on the experimental results, females are generally less anxious than males from puberty to middle-age. The anxiety-like behavior of females and males is likely influenced by early organizational effects, but might be modified by activational effects of testosterone and its metabolites. The effects of sex hormones leading to anxiogenesis or anxiolysis depend on factors affecting hormonal status including age. The biological and several technical issues make the study of effects of testosterone on anxiety very complex and should be taken into account when interpreting experimental results.