Immunocytochemical detection of leptin in non-mammalian vertebrate stomach Francisco J. Muruz abal, a Gema Fr€ uhbeck, b Javier G omez-Ambrosi, b Marta Archanco, a and Mar  ıa A. Burrell a, * a Department of Histology and Pathology, University of Navarra, Pamplona, Spain b Metabolic Research Laboratory, Cl  ınica Universitaria de Navarra, Pamplona, Spain Accepted 1 July 2002 Abstract Leptinisahormoneproducedandsecretedmainlybyadipocytes,butalsobyothertissuessuchasplacenta,brain,mammary,and pituitaryglands.Thegastricepitheliumhasalsobeenreportedasasourceofleptininmammals.Inthisstudyweexaminedthepresence of leptin in the stomach of non-mammalian vertebrates (trout, frog, lizard, and snake). Immunolabeling for leptin was found in the oxyntic-peptic cells of the frog and the two reptilian species studied, but not in the trout. In the trout and the lizard leptin immu- noreactivitywasalsodetectedinscatteredcellspresentingthetypicalfeaturesofendocrinecells.Inthetrout,thefrogandthesnake,in addition to the epithelium, leptin immunostain was found in elements of the enteric nervous system that were also positive for VIP. Ó 2002 Elsevier Science (USA). All rights reserved. Keywords: Leptin; Stomach; Non-mammalian vertebrates; Oxyntic-peptic cells; Endocrine cells; Enteric nervous system; Immunohistochemistry 1. Introduction Leptin is a hormone, product of the ob gene, which is involved in the regulation of food intake and body weight homeostasis (Zhang et al., 1994) but also in very different functions such as reproduction, immune re- sponse, and haematopoiesis (Cioffi et al., 1996; Loffreda etal.,1998).Leptinwasoriginallythoughttobesecreted only by adipocytes. However, more recently, leptin production has also been demonstrated in a variety of tissues, including placenta (Masuzaki et al., 1997), mammary glands (Smith-Kirwin et al., 1998), brain and pituitary (Morash et al., 1999). In the stomach the first description of leptin (mRNA and protein) was per- formed in rat (Bado et al., 1998). Recently, several re- ports have focused on the detection of leptin in the human stomach. Immunoreactivity for leptin was found inthesecretorygranulesofchiefcellsandaespecialtype of endocrine cell (Cinti et al., 2000). Very recently two different research groups have detected both leptin and the leptin receptor in the human stomach (Mix et al., 2000; Sobhani et al., 2000). Regarding the species studied, leptin was initially discovered in mice and subsequently detected in other mammalian species (human, rat, cow and pig, among others).Zhangetal.(1994)reportedahighconservation in the coding sequence of the ob gene in several mam- malian and non-mammalian vertebrate species and suggested that its function is highly conserved. The first report of the cloning of leptin in non-mammalian ver- tebrates was the characterization of leptin cDNA from chicken liver and adipose tissue (Taouis et al., 1998). The deduced amino acid sequence is close to that of mouse leptin. The sequence of the chicken leptin cDNA as well as the expression of this gene in liver has been confirmed by another laboratory (Ashwell et al., 1999). In these studies, leptin mRNA was also found to be present in chicken embryonic yolk sac. However, other authors have been unable to identify and sequence a chicken leptin gene (Friedman-Einat et al., 1999). Very recently, Johnson et al. (2000) reported the presence of General and Comparative Endocrinology 128 (2002) 149–152 www.academicpress.com GENERAL AND COMPARATIVE ENDOCRINOLOGY * Corresponding author. Fax: +34-948-425-649. E-mail address: mburrell@unav.es (M.A. Burrell). 0016-6480/02/$ - see front matter Ó 2002 Elsevier Science (USA). All rights reserved. PII:S0016-6480(02)00072-2