125I-Melatonin was used to localize and characterize the melatonin receptor sites in the rat hypothalamus. Autoradiography revealed that displaceable 125I-melatonin binding occurred in suprachiasmatic nuclei and median eminence only. Further studies performed on crude membrane fractions from median eminences revealed high affinity (Kd = 21 pM) melatonin binding sites (Bmax = 8.5 fmol/mg protein). The order of potency of various indole amines to inhibit 125I-melatonin binding was melatonin much greater than N-acetyl-5-hydroxytryptamine greater than 5-methoxytryptamine greater than 5-hydroxytryptamine.

Institute of Physiology Czechoslovak Academy of Sciences Prague

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From the Pineal Gland to the Central Clock in the Brain: Beginning of Studies of the Mammalian Biological Rhythms in the Institute of Physiology of the Czech Academy of Sciences

Melatonin accelerates reentrainment of the circadian rhythm of its own production after an 8-h advance of the light-dark cycle