Different parts of the body’s internal clock respond differently to melatonin

A single melatonin injection at the light/dark transition significantly increases endogenous pineal melatonin levels for the following two days.

• Melatonin injection affects specific components of the circadian clock.
• Pineal melatonin secretion shows a marked increase after melatonin administration.
• The amplitude of the corticosterone rhythm remains unchanged following melatonin treatment.
• These findings suggest melatonin influences a selective group of neurons related to the pineal pathway.

Simplified