Pineal gland
Pineal gland is also called as epiphysis cerebri. It situated slightly flattened cone-shaped appendage of the brain. Its base is slightly constricted to form hollow peduncle by which it is attached to the roof of the third ventricle. Narrow prolongation of ventricle called pineal recess.
Pineal gland contains the highest content of serotonin and the enzyme hydroxyl-indol-o-methyl-transferase (N-methyl transferase) which converts serotonin to melatonin (N-acetyl 5-methoxy tryptamine).
Physiological functions of Pineal gland
- Lightening of skin colour in amphibia- May be also in mammals.
- Inhibits gonadal activity in long day breeders- Hamsters, Horse.
- Stimulates onset of breeding season in short day breeders- Sheep.
- Long daily periods of elevated melatonin secretion- induce ovarian cycles in ewes.
- Continuous administration of melatonin induces cyclicity in acyclic ewes- Inhibit ovarian cycles in mares.
- Removal of pineal / cutting nerve connections to pineal leads to removal of seasonality in seasonal breeders.