Elsevier

Neuroscience

Volume 113, Issue 3, 2 September 2002, Pages 653-662
Neuroscience

Distribution of apelin-synthesizing neurons in the adult rat brain

https://doi.org/10.1016/S0306-4522(02)00192-6Get rights and content

Abstract

The peptide apelin originating from a larger precursor preproapelin molecule has been recently isolated and identified as the endogenous ligand of the human orphan G protein-coupled receptor, APJ (putative receptor protein related to the angiotensin receptor AT1). We have shown recently that apelin and apelin receptor mRNA are expressed in brain and that the centrally injected apelin fragment K17F (Lys1-Phe-Arg-Arg-Gln-Arg-Pro-Arg-Leu-Ser-His-Lys-Gly-Pro-Met-Pro-Phe17) decreased vasopressin release and altered drinking behavior. Using a specific polyclonal antiserum against K17F for immunohistochemistry, the aim of the present study was to establish the precise topographical distribution of apelin immunoreactivity in colchicine-treated adult rat brain. Immunoreactivity was essentially detected in neuronal cell bodies and fibers throughout the entire neuroaxis in different densities. Cells bodies have been visualized in the preoptic region, the hypothalamic supraoptic and paraventricular nuclei and in the highest density, in the arcuate nucleus. Apelin immunoreactive cell bodies were also seen in the pons and the medulla oblongata. Apelin nerve fibers appear more widely distributed than neuronal apelin cell bodies. The hypothalamus represented, by far, the major site of apelin-positive nerve fibers which were found in the suprachiasmatic, periventricular, dorsomedial, ventromedial nuclei and in the retrochiasmatic area, with the highest density in the internal layer of the median eminence. Fibers were also found innervating other circumventricular organs such as the vascular organ of the lamina terminalis, the subfornical and the subcommissural organs and the area postrema. Apelin was also detected in the septum and the amygdala and in high density in the paraventricular thalamic nucleus, the periaqueductal central gray matter and dorsal raphe nucleus, the parabrachial and Barrington nuclei in the pons and in the nucleus of the solitary tract, lateral reticular, prepositus hypoglossal and spinal trigeminal nuclei.

The topographical distribution of apelinergic neurons in the brain suggests multiple roles for apelin especially in the central control of ingestive behaviors, pituitary hormone release and circadian rhythms.

Section snippets

Animals

Adult male Wistar Kyoto rats weighing 250–300 g were obtained from Iffa Credo (L’Arbresle, France) and kept under artificial light (12 h light/12 h dark cycle) with a normal standard diet (Usine alimentation Rationnelle, Epinay-sur-Orge, France) and water given ad libitum. All of the steps of the experimental procedures were conducted in agreement with the guiding principles for the care and use of experimental animals approved by the Society for Neuroscience.

Chemical synthesis of apelin peptides and production of antiserum against apelin 17

K17F (Lys1

Results

Under the conditions used here for immunohistochemistry, we assumed that the primary antiserum directed to apelin labels specifically neurons that contain the K17F fragment of the preproapelin precursor since we previously reported that the antibody has a high affinity for K17F, no signal was detected in sections after incubation with the preimmune serum or without the primary antibody and that preabsorption of the apelin antiserum with K17F completely blocked the apelin-like immunoreactivity

Discussion

Using a specific polyclonal antiserum directed to the apelin fragment K17F for immunohistochemistry, we established for the first time a detailed distribution of apelinergic neurons in the adult rat brain. The detection of apelin-containing neuronal perikarya and/or fibers was enhanced in this study by several technical improvements including the use of i.c.v. colchicine pretreatment, free-floating sections, DAB revelation and the subsequent light microscopic analysis. The high affinity of the

Acknowledgements

The authors thank J. Helfferich (Laboratory of Neuromorphology, Budapest, Hungary) for skillful technical assistance. This work was supported by grants from the ‘Institut National de la Santé et de la Recherche Médicale (INSERM)’ (APEX No. 4X011E to C.L.-C.) and from a French–Hungarian cooperation (Balaton) managed by the OMFB and CIES (Balaton No. 00831YE to C.L.-C. and M.P.). A.R. received a fellowship from Société Française d’Hypertension Arterielle (2000–2001).

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