Brain Melatonin Research Articles

Fate of intracisternally injected melatonin in the rat brain.

The turnover of 3H-melatonin in rat brain was studied at selected times after a single intracisternal injection. 3H-Melatonin disappeared very rapidly from the brain and its decay exhibited at least 2 components, i.e., an early phase lasting 20 min, and a second, slower single-exponential component with a half-life of about 40 min. Only 6% of the administered dose was present in brain as unchanged melatonin 5 min after injection, and only 0.8% remained after 20 min. Unmetabolized 3H-melatonin accounted for 29–83% of the total radioactivity present in brain, depending on the time allowed to elapse after its injection. The concentration of melatonin in the hypothalamus was 3.8–5.1 times that in the rest of the brain at all intervals studied; however, the curve describing the disappearance of 3H-melatonin from the hypothalamus generally resembled the curve for whole brain. Nonradioactive melatonin, administered intracisternally 10 min before the injection of 3H-melatonin, caused significant decreases in the amounts of unmetabolized 3H-melatonin recovered from the hypothalamus or the rest of the brain 60 min later. Exposure of rats for 6 days to either constant light or constant darkness significantly accelerated the rate of 3H-melatonin disappearance from the brain.

Demonstration of melatonin in amphibia

The presence of melatonin in the amphibian epiphysis has been ascertained earlier by several indirect methods, demonstrating the synthesizing enzyme or precursors of the compound. This communication describes the presence of melatonin in amphibian brain in a direct way, using dextran gel chromatography as a separation method.