03: Pineal Gland

Primary hormone released from the pineal gland

Melatonin

What stimulates the release of melatonin

Dark

What inhibits the release of melatonin

Light

Nutritional precursor for melatonin

Tryptophan

How does darkness stimulate melatonin release

Causes norepinephrine to be released from neurons, which activates the enzymes that synthesize melatonin

Receptor that NE binds to on a pinealocyte

α and βAR

What type of receptor is α and βAR

G_sPCR

Result of NE binding to α and βAR

cAMP production

Types of melatonin receptors in the pineal gland

MT1, 2, and 3

MT1/2/3 receptor structure

G_iPCR

Action of melatonin on the pinealocytes

Inhibits cAMP production to stop melatonin synthesis

Additional role of melatonin in reptiles

Part of thermoregulation

Special cells around the third eyelid in reptiles for the recognition of light

Parietal eye cells

Additional role of melatonin in birds

Migration

Effect of melatonin on sheep reproduction

Melatonin in sheep increases the amount of FSH and LH that is secreted, which induces ovulation and is optimal for breeding

What time of year do sheep normally breed

Short days (fall and winter)

Effect of melatonin on human reproduction

Melatonin causes the release of GnIH, which inhibits the release of GnRH