Journal of Endocrinology and Reproduction

Sweta Arora ¹, Poonam Singh ¹, Priyoneel Basu ², Chandana Haldar ³

Affiliations
1 Mahila Mahavidyalaya, Banaras Hindu University, Varanasi 221005, IN
2 Behavioural Neuroscience Unit, Department of Psychology, University of Calgary, Calgary, Alberta, CA
3 Pineal Research Laboratory, Department of Zoology - Centre of Advanced Study, Banaras Hindu University, Varanasi 221005, IN

Abstract

Different thresholds of gonadal steroids exert stimulatory or inhibitory effects on GnRH and gonadotropin release. During the reproductively active phase (RAP), the concentration of endogenous gonadal steroids remains high while, during reproductively inactive phase (RIP), it remains low. During RIP the HPG axis is sensitive to gonadal steroids but the circulatory levels of testosterone and estradiol remain low. During this phase one can observe conveniently the effects of gonadal steroids on the HPG axis in male or female rodents. Therefore, the aim of the present study was to find the effects of testosterone and estradiol on the reproductive functions of male and female Indian pygmy field mouse, Mus terricolor, during RIP. The male mice were injected aquaviron (commercially available testosterone, 1mg/100g body weight) while the female mice received estradiol-benzoate (25μg/100g body weight) for 15 consecutive days during the RIP. After completion of the treatment, a significant increase in the weights of gonads and accessory sex organs was noted in both the sexes. The biochemical constituents of accessory sex organs such as epididymal sialic acid, seminal vesicular fructose and uterine protein content reflected significant elevation accompanied by increased levels of plasma testosterone, estradiol and progesterone. Histologically, the gonads and accessory sex organs exhibited increased cellular activity. However, the gonadal cholesterol was significantly decreased in both the sexes. Over all, administration of gonadal steroids to both male and female mice accelerated the gonadal recrudescence but did not inhibit the reproductive functions when administered during the RIP. Therefore, it can be inferred from the present study that during the RIP the HPG axis is sensitive to gonadal steroids and, hence, exogenous gonadal steroids induce gonadal activity.

Keywords

Gonadal Steroids, Mus terricolor, Reproduction, Tropical Rodent, Seasonal Breeder.

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Sweta Arora ¹, Poonam Singh ¹, Chandana Haldar ²

Affiliations
1 Mahila Mahavidyalaya, Banaras Hindu University, Varanasi – 221005, IN
2 Pineal Research Laboratory, Department of Zoology, Centre of Advanced Study, Banaras Hindu University, Varanasi – 221005, IN

Abstract

Inhibitory effects of glucocorticoids have been reported in a number of species ranging from rodents to humans. No report till date exists demonstrating the effect of stress on reproduction in Mus terricolor, a tropical, wild, nocturnal, short day breeder. To replicate stress-like situation under experimental condition, dexamethasone (60μg/ 100g body weight) treatment was given to female M. terricolor during the reproductively active phase (RAP) of its breeding cycle. Suppressive effect of dexamethasone on reproductive functions of this tropical nocturnal rodent was inferred. There was a significant reduction in ovarian and uterine weight, which was accompanied by a significant reduction in uterine protein and plasma estradiol and progesterone levels while there was a significant increase in ovarian cholesterol. Histological observations revealed an inhibitory effect of dexamethasone on the reproductive tissues. The presence of glucocorticoid receptor in the ovary and uterus suggests that glucocorticoid might be directly involved in modulating reproductive functions of this rodent. Thus, exogenous glucocorticoid suppressed the reproductive function of this mouse suggesting a stressful condition.

Keywords

Glucocorticoid, M. terricolor, Reproduction, Stress, Tropical Rodent.

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Sweta Arora ¹, Poonam Singh ², Chandana Haldar ¹

Affiliations
1 Pineal Research Laboratory, Department of Zoology, Centre of Advanced Study, Banaras Hindu University, Varanasi – 221005, Uttar Pradesh, IN
2 Mahila Mahavidyalaya, Banaras Hindu University, Varanasi – 221005, Uttar Pradesh, IN

Abstract

The Indian pygmy field mouse, Mus terricolor, a wild rodent has to face many stressors in the environment such as unpredictable harsh weather, non-static habitats, food shortage, water scarcity, social pressure, risk of predators and parasites, etc. Glucocorticoids are known to suppress reproductive functions during the stressful situations in many rodents. No report till date exists demonstrating the effects of stress on the reproduction in male M. terricolor, a tropical, wild, nocturnal, short day breeder. To replicate stress-like situation under experimental condition, dexamethasone (60μg/100g body weight) treatment was given to this tiny rodent during the Reproductively Active Phase (RAP) of its breeding cycle. Administration of dexamethasone led to significant reductions in the weights of gonad and accessory sex organs, which were accompanied by significant reductions in the biochemical constituents viz epididymal sialic acid and seminal vesicular fructose. The levels of plasma testosterone also decreased significantly while there was a significant increase in the gonadal cholesterol after the treatment. Histological observations revealed inhibitory effects of dexamethasone on the reproductive tissues. It is therefore, suggested that the stressful condition due to exogenous administration of glucocorticoid suppressed the reproductive functions of M. terricolor.

Keywords

Glucocorticoid, M. terricolor, Reproduction, Stress, Tropical Rodent.

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Sweta Arora ¹, Poonam Singh ¹, Priyoneel Basu ², Chandana Haldar ³

Affiliations
1 Mahila Mahavidyalaya, Banaras Hindu University, Varanasi – 221005, Uttar Pradesh, IN
2 Behavioural Neuroscience Unit, Department of Psychology, Banaras Hindu University, Varanasi – 221005, Uttar Pradesh, IN
3 Pineal Research Laboratory, Department of Zoology – Centre of Advanced Study, Banaras Hindu University, Varanasi – 221005, Uttar Pradesh, IN

Abstract

Testosterone, melatonin and glucocorticoids are known to mediate their actions through their respective receptors, i.e., Androgen Receptor (AR), Melatonin Receptor (MT1) and Glucocorticoid Receptor (GR), endowed on the target tissues. The gonads of M. terricolor responded positively to administration of these hormones, suggesting the possibility of a direct action of these hormones on the gonads through their respective receptors. The present study was, therefore, undertaken to localize the Androgen (AR), Melatonin (MT1) and Glucocorticoid (GR) receptors in the testis of this rodent adopting immunohistochemistry as the tool. The result indicated that AR is expressed in the Leydig cells and germ cells of the testis of M. terricolor. MT1 receptor is localized in the Leydig cells, peritubular myoid cells, and endothelial lining of blood vessels, all in the interstitial zone. The GR was localized in the nuclei of Leydig cells, macrophages and fibroblasts, and endothelial cells lining the blood vessels, all in the interstitium. The immunohistochemical localization of AR, MT1 and GR receptors in the testes of M. terricolor support the previous understanding that testis could be a target for the above-mentioned hormones in this rodent.

Keywords

Immunohistochemistry, Mus terricolor, Receptors, Seasonal Reproduction

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Sweta Arora ¹, Poonam Singh ¹, Chandana Haldar ², Priyoneel Basu ³

Affiliations
1 Mahila Mahavidyalaya, Banaras Hindu University, Varanasi - 221005, Uttar Pradesh, IN
2 Pineal Research Laboratory, Department of Zoology - Centre of Advanced Study, Banaras Hindu University, Varanasi - 221005, Uttar Pradesh, IN
3 Kalinga Institute of Social Sciences Deemed to be University, Bhubaneswar - 751024, Odisha, IN

Abstract

Besides being potent regulators of energy balance, thyroid hormones are necessary for the maintenance of seasonal reproductive changes in many species of mammals and birds. The thyroid gland is known to be crucial for the seasonal transition in seasonal breeders from breeding to non-breeding. Many workers have reported that thyroid ablation prevents the animal from entering the non-breeding state in both males and females of different species of animals and, in such a situation, the breeding state is sustained indefinitely. No report exists to date about the involvement of the thyroid gland in the reproduction of the pygmy field mouse Mus terricolor. L-thyroxine was administered subcutaneously to both male and female mice for 15 consecutive days during the reproductively active phase. L-thyroxine treatment led to a significant reduction in the weights of gonads and accessory sex organs along with biochemical constituents like epididymal sialic acid, seminal vesicular fructose and uterine protein. Regressive changes in the histology of the gonads and accessory sex organs were observed which can be attributed to the reduced levels of plasma testosterone in males and plasma estradiol and progesterone in females of the L-thyroxine-treated mice. However, there was a significant increase in the levels of plasma T3, T4, and gonadal cholesterol in both sexes following L-thyroxine treatment. Both hypo- and hyper-thyroidism can influence gonadal activity. The observations in the present study suggest that hyperthyroidism leads to the transition of reproductively active gonads to inactivity substantiating the hypothesis that high levels of thyroxine can accelerate the reproductive inactivity in this rodent.

Keywords

Mus terricolor, Seasonal reproduction, Thyroid, Reproduction, Tropical rodent.

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