Pineal gland & melatonin in ewes: a review in understanding and optimizing their reproductivity

Abstract

Melatonin is produced in the pinealocytes, granulosa cells, the oocytes, and the cumulus oophorus. The secretion of this hormone by the pineal gland is modulated by both intrinsic and extrinsic pathways, respectively centered on the pineal synaptic ribbons (SRs) and on environmental photic stimuli perception. As the cellular development of a mammalian embryo advances, the intrinsic pineal SRs behaving at first like direct photoreceptors progressively develop into cellular organelles enabling neighboring pineal cells – or pinealocytes – to modulate their functions in a paracrine manner. Aside from this intrinsic modulation, the pineal cells are under extrinsic control originating from the retinal photic stimuli perception, as well as being under the circadian clock’s influence.