A serotonergic component of [3H] N-acetylserotonin binding in mammalian brain

1. Evidence that the putative pineal hormone, N-acetylserotonin (NAS) and its synthesizing enzyme, N-acetyltransferase (NAT) are present in various brain areas, prompted a study of its binding characteristics in CNS tissue. 2. In fresh rat brain membranes, tritiated N-acetylserotonin ([3H]NAS) appeared to bind to a single population of high affinity sites with an equilibrium dissociation constant (Kd) of 3-5nM, whereas in frozen tissues from rat, calf and human brain high and low affinity binding site classes were present. 3. Inhibition experiments indicated that NAS and serotonin (5-HT) were the most potent inhibitors of [3H]NAS binding in the rat frontal cortex and cerebellum. The 5-HT agonist, quipazine, and various 5-HT antagonists, including the 5-HT2 antagonist, ketanserine, also inhibited binding with moderate affinity in the frontal cortex. 4. These findings suggest that [3H]NAS labels both 5-HT1 and 5-HT2 sites in the rat Brain.