Not only does the suprachiasmatic nucleus (SCN) play an important role in the ci

Question

Not only does the suprachiasmatic nucleus (SCN) play an important role in the circadian regulation of endocrine systems, but the hormones being regulated by this neural nucleus have been shown to, in turn, provide feedback to the SCN and regulate its activity. Studies indicate that the steroid hormones estradiol and testosterone each influence SCN activity. In your answer, describe the regulatory effect(s) that each of these hormones exerts on the SCN. Also, as part of your answer, compare and contrast the efficacy that each hormone possesses when regulating SCN activity.

Explanation / Answer

Ans. Sex hormones estradiol and testosterone affects many aspects of circadian responses but the mechanism whereby they affect the circadian function are less well known.

Testosterone regulatory effect

The SCN of the hypothalamus is the locus of circadian clock that controls physiological and behavioural rhythms, including rhythmic secretion of gonadal hormones. One of the study found that gonadectomy results in alternation of circadian behaviour, includes lengthening of free running periods, decreased precision of daily onset of running. But they found that androgen(testosterone) replacement restores these responses. They examined that steroid receptors are localized to the specific compartment of the brain clock and the androgen receptor is concentrated in the SCN core.

Estradiol regulatory effect

Hormonal changes during the menstrual cycle cause by the increase or decrease level of estradiol hormones and other hormones alter the body temperature, there is an increase of 0.3 to 0.4°C in CBT(Core body temperature) level as well as they also reduce the amplitude of circadian variation by CBT.

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