Figure 2.

The different levels and shapes of melatonin circadian rhythms in the CSF of the third ventricle and in the peripheral blood. The nightly melatonin levels in CSF of the third ventricle are more robust than those in the peripheral plasma and also exhibit sharp rises and falls (square wave). The pattern of the melatonin circadian rhythm in CSF of the third ventricle is similar to that of the pineal gland rather than in the plasma (see the insert part which illustrates the melatonin synthetic pattern in pineal gland of rat). The data was obtained from the long term (5 days) pineal gland dialysis in a free running rat. Extrapineal-generated melatonin and the diet-derived melatonin may increase peripheral plasma melatonin levels; however, they do not mimic the pattern and reach the high level of the melatonin circadian rhythm in the CSF of the third ventricle to impact the function of bio-clock. From Tan et al. [63].