Melatonin and the seasonal control of reproduction

Abstract

-Many mammalian species from temperate latitudes exhibit seasonal variations in breeding activity which are controlled by the annual photoperiodic cycle. Photoperiodic information is conveyed through several neural relays from the retina to the pineal gland where the light signal is translated into a daily cycle of melatonin secretion: high at night, low in the day. The length of the nocturnal secretion of melatonin reflects the duration of the night and it regulates the pulsatile secretion of gonadotropin-releasing hormone (GnRH)

Melatonin secretion in a strictly subterranean mammal, the Damaraland mole‐rat (Cryptomys damarensis)

“…E-mail: ncbennett@zoology.up.ac.za variation. For instance, in almost all mammals, secretion of the hormone melatonin is far greater at night, when animals are in the dark, than during the day, when animals are exposed to light (Reiter, 1991;Malpaux, Thiery & Chemineau, 1999). Melatonin secretion thus has a diurnal rhythm, the phase of which is determined by the length of day (Reiter, 1988).…”

“…Melatonin secretion thus has a diurnal rhythm, the phase of which is determined by the length of day (Reiter, 1988). As annual changes in day length are predictable, the phase of the melatonin rhythm can be used as a neurochemical index of season, facilitating the use of photoperiod as a zeitgeber (Reiter, 1991(Reiter, , 1993Malpaux, Viguie et al, 1997;Chemineau & Malpaux, 1998;Malpaux et al, 1999). To effectively reflect different day lengths, the phase of the melatonin rhythm needs to be regulated at a resolution that is equal to, or greater than, the average magnitude of change in photoperiod (Reiter, 1987a,b;Malpaux, Thiery et al, 1998.…”

Melatonin Receptor Activation Regulates GnRH Gene Expression and Secretion in GT1–7 GnRH Neurons

“…Some evidence suggests that melatonin regulates reproduction by exerting inhibitory effects on the reproductive axis at the level of the hypothalamus (15)(16)(17). As such, melatonin uptake and binding have been demonstrated in rat and hamster hypothalamus (1,18,19).…”

Synchronization of ovulation in goats using prostaglandin F2α based protocols during the breeding season

“…The annual variation of the daily luminosity duration is perceived by the retina of these animals and a neurohormonal pathway involving suprachiasmatic nucleus, sympathetic neurons, and the pineal gland was responsible for production of melatonin, a key hormone, during short days/darkness periods [1][2][3]. Consequently, melatonin stimulates a neuronal network which modulates the hypothalamic secretion of gonadotropinreleasing hormone (GnRH) [3], and the hypothalamic-pituitarygonadal axis is stimulated.…”