The Role of the mt1 Melatonin Receptor in Reproduction
Syed, Samina T.
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Reproductive physiology is a process influenced by numerous factors, such as the light-dark cycle, the pineal gland, and more specifically, the hormone melatonin. Melatonin functions via three known sub-types of melatonin receptors: mt1, MT2, and MT3, which are found in various organisms. The mt1 melatonin receptors make up the majority of melatonin receptors in the suprachiasmatic nucleus, the master biological clock of mammals. Melatonin plays a key role in communicating the time of day and year because it is regulated by an endogenous rhythm that is in synchrony with the Iight-dark cycle. Although it is established that melatonin plays a role in reproduction, the sites of melatonin action on the reproductive system remain unclear. To investigate the specific role of the mt1 melatonin receptor at the ovulatory level in reproduction, C57 wild-type mice and mt1 knockout mice were monitored for their ovulatory (estrous) cycle patterns. These patterns were assessed over the course of many estrous cycles with vaginal smears that determined cell morphology, voltmeter measurements of vaginal wall resistance, and running wheel activity measurements. Running wheel activity and cell morphology were also assessed for both strains with and without melatonin in the drinking water. Both groups with and without melatonin in the water continued to have regular estrous cycles, with no difference between the C57 wild-type and mt1 knockout mice. The current observations suggest that the mt1 melatonin receptors do not carry out any inhibitory effects on the estrous cycle, and that the dose of melatonin used in the drinking water did not affect the estrous cycling pattern. These results may suggest that other receptors could play a role in regulating the estrous cycle, either along with the mt1 receptor or independent of it.