Submitted on January 16, 2007
Revised on May 31, 2007
Accepted on June 27, 2007
The components required for amino acid neurotransmitter signaling are present in adipose tissues
Anne Nicolaysen, Runhild Gammelsaeter, Jon Storm-Mathisen, Vidar Gundersen, and Per Ole Iversen
Department of Nutrition, University of Oslo, Oslo 0316
Corresponding Author: poiversen{at}hotmail.com
The adipocyte does not only serve as fuel storage, but produces and secretes compounds with modulating effects on food intake and energy homeostasis. Although there is firm evidence for a centrally-mediated regulation of adipocyte function via the autonomous nervous system, little is known about signaling between adipocytes. Amino acid neurotransmitters are candidates for such paracrine signaling. Here we applied immunohistochemistry to detect components required for amino acid transmitter signaling in rat fat depots. In interscapular brown adipose tissue as well as in interscapular-, mesenteric-, perirenal- and epididymal white adipose tissues, we demonstrate robust immunosignals for the excitatory neurotransmitter glutamate, the inhibitory neurotransmitter gamma-aminobutyric acid (GABA), and the GABA synthesizing enzyme glutamate decarboxylase isoforms (GAD65, GAD67). Moreover, all adipose tissues stained for the vesicular glutamate transporter VGLUT1 and the vesicular GABA transporter VGAT in addition to the vesicle marker synaptophysin. Electron microscopic immunocytochemistry showed that VGLUT1 and VGAT, but not VGLUT2 or -3, are localized in vesicular organelles in adipocytes. The receptors for glutamate (subunits GluR2/3, NR1, but not mGluR2) and for GABA (GABAARa2) were present in the adipocytes. The presence of glutamate, GABA, their vesicular transporters and their receptors, indicates a paracrine signaling role for amino acids in adipose tissues.
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