ISSN 2320-5407 International Journal of Advanced Research (2014), Volume 2, Issue 7, 42-59 42 Journal homepage: http://www.journalijar.com INTERNATIONAL JOURNAL OF ADVANCED RESEARCH RESEARCH ARTICLE Anatomical localization of SER and certain peptides in the developing gastrointestinal tract of the axolotl Ambystoma mexicanum Gamal M. Badawy  , Faculty of Science Menoufiya University, Shebeen El-Koom, Egypt Manuscript Info Abstract Manuscript History: Received: 12 May 2014 Final Accepted: 25 June 2014 Published Online: July 2014 Key words: Anatomy; Development; SER; Peptides; Immunohistochemistry; Ambystoma mexicanum. List of abbreviations BMSU, Biomedical services unit; BSA, Bovine serum albumin; CGRP, Calcitonin gene-related peptide; EC, Endocrine cells; FITC, Fluorescein- isothiocyanate; GAS/CCK Gastrin/cholecystokinin; GINCS Gastrointestinal neuroendocrine control system; GIT, Gastrointestinal tract; IHC, Immunohistochemical; IN, Intestine; IR, Immunoreactive; LIN, Large intestine; NF, Nerve fibres; NT, Neurotensin; PACAP, Pituitary adenylate cyclase- activating polypeptide; PBS, Phosphate buffer saline; SER, Serotonin; SIN, Small intestine; SP, Substance P; SS, Somatostatin; ST, Stomach; VIP Vasoactive intestinal polypeptide.  Correspondence Gamal M. Badawy Gamalbadawy940@Yahoo.c om The developing gastrointestinal tract (GIT) of the axolotl, Ambystoma mexicanum, was investigated, by the use of standard immunohistochemical techniques, for the localization of immunoreactivity to serotonin (SER) and five regulatory peptides all known to occur in the mammalian GIT. The actual utilized developmental stages started at stage 42 and ended with late juvenile stage. Microwave pre-treatment of the sections was employed to improve the detection of antigens. Entero-endocrine cells reacted specifically with antisera to SER, substance P (SP), somatostatin (SS), gastrin/cholecystokinin (GAS/CCK) and neurotensin (NT). Enteric nerve fibers, on the other hand, reacted specifically with antisera to SER, SP, NT and calcitonin gene-related peptide (CGRP) starting at the first juvenile stage. Based on its nature, the present study represents the second investigation which emerged from the same laboratory and principally yields two new findings. Firstly, neither SER- nor any of the investigated regulatory peptides-immunoreactivity was detected at stages earlier than the pre- hatching stage (42). Secondly, GAS/CCK-immunoreactivity was detected chronologically earlier (at stage 42) and this is consistent with the previously known trophic effect for both hormones during the early development of the GIT. The study provides a description of the qualitative distribution and a semi-quantitative account of the relative abundance of the mentioned neuroendocrine substances within the developing GIT. Copy Right, IJAR, 2014,. All rights reserved INTRODUCTION For survival, the developing gastrointestinal tract (GIT) with its neuroendocrine control system (GINCS) must be functional by the time of external feeding. The distribution and relative frequency of the gastrointestinal endocrine cells and nerve fibres, which constitute the GINCS, vary among different vertebrates but their general frame is quite similar (Holmgren 1989). These neuroendocrine elements characteristically secrete peptides which control different activities of the GIT and are thus known collectively as regulatory peptides. The latter are built of amino acids and show remarkable structural similarity among different vertebrate species with the biologically active part is usually the most conserved (Holmgren and Jensen 2001). As a consequence, it is believed that this similarity is retained by