Differential Localization of Melatonin and N-Acetylserotonin in Brain

Until 1974 quantitative and qualitative localization of melatonin (M) had been performed mainly by bioassay (Ralph and Lynch, 1970). As this technique is relatively insensitive, the detection of M outside of the pineal gland was infrequent (Pang et al. 1974). This led to the conclusion that the epiphysis cerebri was the unique source of M and its derivatives (Reiter, 1973). This firm opinion persisted for more than 15 years after the discovery of M in 1958 (Lerner et al. 1958) despite numerous reports of extrapineal detection of hydroxyindole-O-methyl transferase (HIOMT) the enzyme essential for M synthesis (Quay, 1965; Cardinali and Rosner, 1971a; Cardinali and Wurtman, 1972) as well as the demonstration of synthesis of melatonin in the retina (Gern et al. 1978, Pevet et al. 1980).