The pineal gland and mammalian photoperiodism

The mammalian pineal gland appears to be a major endocrine component in the regulation of photoperiodic responses. The circadian pattern of secretion of the pineal hormone, melatonin, is regulated by the nervous system. Changes in photoperiod, acting via the nervous system, alter the temporal pattern of melatonin secretion. The changes in secretion pattern convey information about daylength from neural components of the circadian system to the reproductive system, and probably to other physiological systems.