ELSEVIER Neuroscience Letters 179 (1994) 6064 The adult human cerebellum is a target of the neuroendocrine system involved in the circadian timing Jan-Dirk Fauteck ~, Alexander Lerchl b, Markus Bergmann ~, Morten Moller d, Franco Fraschini ~, Werner WittkowskP, Bojidar Stankov e'* "Institute of Anatomy, Westfiilische V~ilhelms- Universitiit, Vesaliusweg 2 4, 48149 Miinstel; Germany t'lnstitute o['Reproductive Medieine, Westfiilische Wilhelms-Universitiit, Steinfurterstrafle 107, 48149 Miinste~; Germal O, "Institute of Neuropathology, Westfiilische Wilhelms-Universitiit, Domagkstrafle 5, 48149 Miiustep; Germany alnstitute of Medical Anatomy, The Panum Institute, Blegdamsvej 3, 2200 Copenhagen, Denmark "Department of Pharmacology, Chair q[" Chemotherapy. University of Milan, via Vanvitelli 32. 20129 Mihmo, Italy Received 17 April 1994; Revised version received 2 July 1994: Accepted 13 July 1994 Abstract In an investigation aimed at comprehensive mapping of the adult human brain with respect to receptor sites lbr the pineal hormone melatonin, we consistently observed specific binding in the cerebellum. Autoradiography and in vitro binding analysis with ~25I-labeled melatonin were used to examine the location and the properties of these binding sites. In all cerebellar lobes, highest- density specific binding was localized to the external zone of the molecular layer. The binding was rapid, saturable, displaceable, specific and of high affinity. Physiological concentrations of NaCI decreased the affinity, while presence of calcium ions promoted it. The non-hydrolyzable GTP analog, GTPrS, inhibited binding in a dose-dependent manner and provoked a shift towards low affinity. The results strongly suggest that these binding sites may be functional melatonin receptors, and indicate that the adult human cerebellum is a target of melatonin, the pineal hormone involved in the control of the circadian timing. Key words: Human cerebellum; Melatonin; Melatonin receptor; Receptor autoradiography In the last decade, the fundamental concept of the cerebellum as a 'neuronal machine' [7] has dramatically evolved [10,11,14]. Still, the adult human cerebellum is not considered among the principal targets of the endo- crine system, and a limited number of hormones and/or their receptors have been identified [19]. In an investiga- tion aimed at a comprehensive mapping of the adult human brain with respect to receptor sites for the pineal hormone melatonin, we consistently observed specific binding in the cerebellum. In vitro autoradiography with 2-[125I]iodomelatonin has uncovered the hypothalamic suprachiasmatic nuclei (SCN) and the pars tuberalis of the pituitary gland as primary melatonin targets in most mammals, including humans [21,25]. Apart from its effects on the human biological (cir- *Corresponding author. Fax: (39) (2) 718687. 0304-3940/94/$7.00 © 1994 Elsevier Science Ireland Ltd. All rights reserved SSD1 0304-3940(94)00593-1 cadian) clock [1,13], where the pineal hormone interacts with presumably functional receptors [21], exogenous melatonin has been shown to influence certain be- havioral parameters [5,15]. Neither the sites nor the mechanism of action are known. We report here the characteristics of a 2-[~zsI]iodomelatonin-labeled binding site indicative for a functional melatonin receptor, local- ized in the human cerebellar cortex. Adult human brains were obtained at autopsy from 8 to 20 h (16 + 0.85 h, mean + S.E.M.) postmor- tem. Cerebellar specimens were selected from subjects (eight males and five females) at routine autopsy from Institute of Neuropathology, Westfftlische Wilhelms- Universit&it, Miinster, Germany. The (mean + S.E.M.) age at death was 57 + 4.4 years, with range from 39 to 100 years. The general data are reported in Table 1. The brain was dissected and different cerebellar areas identi- fied (for nomenclature, see Ref. 9), separated and frozen by immersion in cold 2-methylbutane at -30°C. Sections