THE JOURNAL OF COMPARATIVE NEUROLOGY 350~382-396 (1994) Distribution of P-Endorphin-Like-Immunoreactive Structures in the Chicken and Quail Brain as Demonstrated With a New Homologous Antibody Directed Against a Synthetic Peptide JELLE VAN GILS, PHILIPPE ABSIL, LIEVE MOONS, LUC GRAUWELS, FRANS VANDESANDE, AND JACQUES BALTHAZART zyxw Laboratory of Neuroendocrinology, University of Leuven, Leuven (J.v.G, L.M., L.G., F.V.), and Laboratory of General and Comparative Biochemistry, University of Liege, B-4020 Liege (P.A., J.B.), Belgium ABSTRACT A polyclonal rabbit antibody was raised against a synthetic peptide fragment located at the C-terminal end of turkey P-endorphin (P-END) and used to analyze the distribution of P-END-immunoreactive-like structures in the quail and chicken brain. Three major groups of immunopositive cells were detected in the preoptic area-hypothalamus complex. A thin layer of immunopositive cells was parallel and adjacent to the ventral edge of the brain in the preoptic and anterior hypothalamic region, a more numerous group of immunoreactive perikarya was located along the walls of the third ventricle in these same regions, and, finally, a few scattered cells were found in a more lateral position on both the internal and external sides of the tip of the fasciculus prosencephali lateralis. The periventricular cell population extended in the caudal direction until the posterior hypothalamus. Labelled fibers were always associated with these immunoreactive perikarya, and they were also found in the adjacent hypotha- lamic regions. A dense innervation of the median eminence was also detected. These data are compared with previous studies in mammals and birds that had identified more restricted populations of immunoreactive cells and the possible sources of the observed discrepancy are discussed. The functional significance of the present data is also briefly analyzed. zyxwvutsrq o 1994 Wiley-Liss, Inc. Key words: immunohistochemistry, opioids, neurosecretorysystem, hypothalamus, POMC The neuropeptide p-endorphin (P-END), representing the 31-amino-acid C-terminal end of the 6-lipotropin (P- LPH) molecule (p-LPH61-91), was first isolated from camel pituitary glands in 1976 (Li and Chung, 1976). It was later found to derive from the posttranslational processing of the precursor molecule proopiomelanocortin (POMC), and, therefore, P-END, like P-LPH, was recognized as a member of the POMC-derived peptide family (for review see Cooper et al., 1991). Several studies indicated that this endogenous peptide has the most potent morphine-like activity among the natural opioids, and that it binds to opiate receptors (Dupont et al., 1980). Later, p-END-like peptides were identified in the brain, suggesting that the endorphins probably play an important role at this level (for reviews see Dupont et al., 1980; Siege1 et al., 1989; Cooper et al., 1991; Kandel et al., 1991). Many studies were carried out in an attempt to clarify the central role of f3-END, and some of these were devoted to the problem of drug addiction. These pharmacological experiments demonstrated that opiates, in general, and p-END, in particular, are implicated in the regulation of important physiological and behavioral systems including the processing of pain signals (for reviews see Rossier and Chapouthier, 1.982; Kandel et al., 19911, feeding (Grandi- Accepted June 16,1994. Address reprint requests to Dr. J. Balthazart, Laboratoire de Biochimie, Universite de Liege (Bat. Ll), 17 place Delcour, B-4020 Liege, Belgique. zy Q 1994 WILEY-LISS, INC.