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BioMed Research International
Volume 2013 (2013), Article ID 546516, 8 pages
http://dx.doi.org/10.1155/2013/546516
Research Article

Leptin Modulates Norepinephrine-Mediated Melatonin Synthesis in Cultured Rat Pineal Gland

Department of Physiology and Biophysics, Institute of Biomedical Sciences, University of São Paulo, Avenue Professor Lineu Prestes 1524, Room 118, 05508-900 São Paulo, SP, Brazil

Received 23 April 2013; Revised 10 June 2013; Accepted 13 June 2013

Academic Editor: Christian-Heinz Anderwald

Copyright © 2013 Rodrigo Antonio Peliciari-Garcia et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Pineal melatonin synthesis can be modulated by many peptides, including insulin. Because melatonin appears to alter leptin synthesis, in this work we aimed to investigate whether leptin would have a role on norepinephrine- (NE-)mediated melatonin synthesis in cultured rat pineal glands. According to our data, cultured rat pineal glands express leptin receptor isoform b (Ob-Rb). Pineal expression of Ob-Rb mRNA was also observed in vivo. Administration of leptin (1 nM) associated with NE (1 µM) reduced melatonin content as well as arylalkylamine-N-acetyl transferase (AANAT) activity and expression in cultured pineal glands. Leptin treatment per se induced the expression of STAT3 in cultured pineal glands, but STAT3 does not participate in the leptin modulation of NE-mediated pineal melatonin synthesis. In addition, the expression of inducible cAMP early repressor (ICER) was further induced by leptin challenge when associated with NE. In conclusion, leptin inhibition of pineal melatonin synthesis appears to be mediated by a reduction in AANAT activity and expression as well as by increased expression of Icer mRNA. Peptidergic signaling within the pineal gland appears to be one of the most important signals which modulates melatonin synthesis; leptin, as a member of this system, is not an exception.