NEUROENDOCRINE CONTROL OF SEASONAL REPRODUCTION IN THE EWE

In temperate latitudes, ewes exhibit great seasonal variation in repro ductive activity. Changes in daylength are responsible for the seasona lity of reproduction. The photoperiodic control of ovarian cyclicity i nvolves the regulation of pulsatile luteinizing hormone (LH) secretion . The annual variations of daylength are encoded by the pineal gland i nto a circadian secretion of melatonin which in turn drives the activi ty of the hypothalamohypophyseal axis. Among the neuronal systems invo lved in the seasonal control of LH secretion, the dopaminergic A15 nuc leus appears as an essential link in the cascade of events leading to the inhibition of LH secretion during anoestrus.