COMPLEMENTARY AND OVERLAPPING EXPRESSION OF Y1, Y2 AND Y5 RECEPTORS IN THE DEVELOPING AND ADULT MOUSE NERVOUS SYSTEM P. NAVEILHAN,* I. NEVEU,† E. ARENAS* and P. ERNFORS*‡ *Department of Medical Biophysics and Biochemistry, Laboratory of Molecular Neurobiology, Karolinska Institute, S17177 Stockholm, Sweden †INSERM U298, CHR d’Angers, F49033 Angers cedex, France Abstract––Neuropeptide Y, a 36 amino acid peptide, mediates its biological effects by activating the Y1, Y2, Y5 and Y6 receptors, which are also receptors for the structurally related peptide YY. Different classes of receptors have been suggested to be involved in different neuropeptide Y functions. In this report, we have characterized the developmental regulation and compared the cellular localization of these receptors in the developing and in the adult central and peripheral nervous systems of the mouse. RNase protection assays revealed that Y1, Y2 and Y5 messenger RNAs were expressed very early in spinal cord, brain, cerebellum and dorsal root ganglion development and were often down- regulated at times corresponding to their aquirement of the adult function in neurotransmission. In situ hybridization of the adult brain showed that Y1 was widely expressed, Y2 displayed a more restricted pattern, Y5 was expressed at very low levels and only in a few brain nuclei and Y6 was not expressed. Virtually all areas containing neurons positive for Y5 also expressed Y1, whereas many Y1-positive cells clearly did not express Y5. In contrast, Y2 was not expressed by the neurons expressing Y1 or Y5. These findings suggest that neuropeptide Y signaling in the brain could be mediated by simultaneous Y1 and Y5 activation. Similar results were also obtained in peripheral sensory neurons. Furthermore, our results suggest that neuropeptide Y/peptide YY receptors play an important role in nervous system development and that selective receptor combinations are responsible for signaling the differents effects of neuropeptide Y in the peripheral and central nervous systems.  1998 IBRO. Published by Elsevier Science Ltd. Key words: Y1, Y2, Y5 and Y6, development, nervous system, cerebellum. Neuropeptide Y (NPY) is a 36-amino acid peptide which is highly conserved through many species, and together with peptide YY (PYY) and pancreatic polypeptide (PP) forms a family of structurally similar peptides. The abundant and wide-spread ex- pression of NPY in many areas of the brain has been suggested to reflect the multiple roles this peptide plays in the CNS 1,15,51 (for review see R efs 29, 57 and 58). For instance, intracranial administration of NPY produces a striking anxiolytic effect and a phase shift in suprachiasmatic nucleus-generated circadian rhythms. 28 NPY is also a potent physiological stimu- lant of feeding. Intraventricular injection of NPY or neutralizing antiserum leads to increased and pro- longed food intake and ultimately obesity or a reduc- tion in food intake, respectively. 11,38,48,55 Following injections in the spinal cord, this peptide generates an antinociceptive effect 32 and is also a ffecting auto- nomic functions, such as the reduction of arterial blood pressure and heart tone when injected in the nucleus tractus solitarius. 6,53 Pharmacological approaches predicted several NPY receptors by their preference of binding to different fragments of NPY. 23,26,35,45,54 The Y1 and Y2 receptors are shared by NPY and PYY whereas the Y3 receptor only interacts with NPY. 4,31,42,52 A fourth class of NPY receptors was suggested to be involved in food intake. 34,37,49 Most of these different classes of NPY/PYY-receptors have now been cloned and characterized. The first receptor (Y1) was cloned as an orphan receptor in the rat, and later also in other species, 20,30,35 whereas Y2 has so far only been isolated from human. 26,45 Recently, cDNAs encod- ing two new receptors suggested to mediate NPYs effect on food intake, Y5 and Y6, were isolated from the rat and mouse, respectively. 25,56 The putative Y3 receptor has not yet been cloned and another recep- tor, Y4, was shown to be a receptor predominantly for PP. 5 The lack of antagonists specific for subclasses of NPY/PYY receptors has severely hampered the determination of which receptors are implicated ‡To whom correspondence should be addressed. A bbreviations: -MSH, -melanin stimulating hormone; DRG, dorsal root ganglia; E, embryonic day; EDTA, ethylenediaminetetra-acetate; NPY, neuropeptide Y; P, postnatal day; PCR, polymerase chain reaction; PP, pancreatic polypeptide; PYY, peptide YY; Y1, Y2, Y5, Y6, neuropeptide Y receptors 1, 2, 5 and 6; SCG, superior cervical ganglion; SSC, standard saline citrate. Pergamon N euroscience Vol. 87, No. 1, pp. 289–302, 1998 Copyright  1998 IBRO. Published by Elsevier Science Ltd Printed in Great Britain. All rights reserved 0306–4522/98 $19.00+ 0.00 PII: S0306-4522(98)00141-9 289