ABSTRACT
After synaptic release, glutamate is taken up by the nerve terminal via a plasma membrane-associated protein termed excitatory amino acid transporter 3 (EAAT3). Following entry into the nerve terminal, glutamate is pumped into synaptic vesicles by a vesicular transport system. Three different vesicular glutamate transporter proteins (VGLUT1-3) representing unique markers for glutamatergic neurons were recently characterized. The presence of EAAT3, glutaminase and VGLUT1-3 was examined in mouse, rat and rabbit species at mRNA and protein levels in hypothalamic neurons which are involved in the regulation of body weight using in situ hybridization and immunohistochemistry. EAAT3 and glutaminase mRNAs were demonstrated in all parts of the arcuate nucleus in the dorsomedial and ventromedial hypothalamic nuclei and lateral hypothalamic area. VGLUT1 mRNA was present in the magnocellular lateral hypothalamic nucleus. VGLUT2 mRNA was demonstrated in a subpopulation of neurons in the arcuate nucleus and in the ventromedial and dorsomedial hypothalamic nuclei and lateral hypothalamic area. Few VGLUT3 mRNA expressing neurons were scattered throughout the medial and lateral hypothalamus. EAAT3-like immunoreactivity (-li) was demonstrated in glutamate, neuropeptide Y (NPY), agouti-related peptide (AGRP), pro-opiomelanocortin (POMC), cocaine and amphetamine-regulated transcript (CART), melanin-concentrating hormone and orexin-immunoreactive (-ir) neurons. VGLUT2-li could only be demonstrated in POMC- and CART-ir neurons of the ventrolateral arcuate nucleus. The results show that key neurons involved in regulation of energy balance are glutamatergic and/or densely innervated by glutamatergic nerve terminals. Whereas orexigenic NPY/AGRP neurons situated in the ventromedial part of the arcuate nucleus are mainly GABAergic, it is shown that several anorexigenic POMC/CART neurons of the ventromedial arcuate nucleus are most likely glutamatergic [corrected].
Subject(s)
Amino Acid Transport System X-AG/metabolism , Cell Membrane/metabolism , Hypothalamus/cytology , Intracellular Signaling Peptides and Proteins , Membrane Transport Proteins , Neurons/metabolism , Synaptic Vesicles/metabolism , Vesicular Transport Proteins , Agouti-Related Protein , Amino Acid Transport System X-AG/classification , Amino Acid Transport System X-AG/genetics , Amino Acid Transport Systems, Acidic/metabolism , Animals , Body Weight/physiology , Carrier Proteins/metabolism , Cyclohexanes/metabolism , DNA-Binding Proteins/metabolism , Excitatory Amino Acid Transporter 3 , Glutamate Plasma Membrane Transport Proteins , Glutaminase/metabolism , Immunohistochemistry/instrumentation , Immunohistochemistry/methods , In Situ Hybridization/mortality , Intercellular Signaling Peptides and Proteins , Male , Mice , Mice, Inbred C57BL , Nerve Tissue Proteins/metabolism , Neurons/cytology , Neuropeptide Y/metabolism , Neuropeptides/metabolism , Orexins , Pro-Opiomelanocortin/metabolism , Proteins/metabolism , RNA, Messenger/metabolism , Rabbits , Rats , Rats, Sprague-Dawley , STAT3 Transcription Factor , Species Specificity , Symporters/metabolism , Trans-Activators/metabolism , Vesicular Glutamate Transport Protein 1 , Vesicular Glutamate Transport Protein 2 , Vesicular Glutamate Transport ProteinsABSTRACT
Serotonin (5-hydroxytryptamine; 5-HT) is a regulator of feeding behavior. The effect of serotonin on food intake is believed to be primarily mediated via 5-HT(1A) and 5-HT(2C) receptors, which both are expressed in hypothalamic regions implicated in regulation of feeding behavior. Using an antiserum to the 5-HT(1A) receptor, immunoreactive neurons were observed in the rat supraoptic, paraventricular, arcuate and ventromedial nuclei and lateral hypothalamic area. 5-HT(1A) receptor immunoreactivity was demonstrated in neuropeptide Y-, agouti-related peptide-, proopiomelanocortin- and cocaine- and amphetamine-regulated transcript-containing neurons of the arcuate nucleus. In the lateral hypothalamus, 5-HT(1A) receptor immunoreactivity was observed in melanin-concentrating hormone- and orexin-containing neurons. The results suggest that serotonin via postsynaptic 5-HT(1A) receptors affects the release of peptides regulating food intake.
