Animal experiment:

Mice[1] Two-month-old TrkB F616A mice are pretreated with 1NMPP1 in drinking water (50 μM) 1 day before the experiment, followed by administration of N-Acetyl-5-hydroxytryptamine (20 mg/kg, i.p.) or Melatonin (1 mg/kg, i.p.). Mice are killed at 1 h. The brain homogenates are analyzed by immunoblotting with anti-p-TrkB. Two- to three-month-old BDNF forebrain conditional knockout mice are injected i.p. with N-Acetyl-5-hydroxytryptamine or Melatonin. Mice are killed at 0, 0.5, 1, or 2 h following drug administration. Brain lysates are prepared and analyzed by immunoblotting with anti-phospho-TrkB Y816[1].

N-Acetylserotonin is an agonist at the melatonin receptors MT1, MT2, and MT3.

A melatonin receptor is a G protein-coupled receptor binding melatonin. Three types of melatonin receptor have been identified. The MT1 and MT2 receptor subtypes are in humans and other mammals, whereas an additional melatonin receptor subtype MT3 has been identified in amphibia and birds.

In vitro: N-Acetylserotonin, a precursor of melatonin, was acetylated from serotonin by arylalkylamine Nacetyltransferase (AANAT). N-Acetylserotonin was found to be able to swiftly activate TrkB in a circadian manner. N-Acetylserotonin also exhibited antidepressant effect in a TrkB-dependent manner. In additioin, N-acetylserotonin could rapidly activate TrkB, but not TrkA or TrkC, in a neurotrophin- and MT3 receptor-independent manner. Moreover, N-acetylserotonin, but not melatonin, showed a robust antidepressant-like behavioral effect in a TrkB-dependent way [1].

In vivo: Animal study found that in BDNF knockout mice the administration of N-acetylserotonin could activate TrkB. Moreover, the endogenous TrkB was activated in wild-type C3H/f+/+ mice but not in AANAT-mutated C57BL/6J mice, in a circadian rhythm. In addition, TrkB activation was found to be high at night in the dark and low during the day [1].

Clinical trial: So far, no clinical study has been conducted.

Reference:
[1] Jang, S. W.,Liu, X.,Pradoldej, S., et al. N-acetylserotonin activates TrkB receptor in a circadian rhythm. Proceedings of the National Academy of Sciences of the United States of America 107(8), 3876-3881 (2010).