Frontiers in Endocrinology (Oct 2012)

On the existence and function of galanin receptor heteromers in the Central Nervous System

  • Kjell eFuxe,
  • Dasiel Oscar Borroto-Escuela,
  • Wilber eRomero-Fernandez,
  • Alexander O Tarakanov,
  • Feliciano eCalvo,
  • Pere eGarriga,
  • Mercé eTena,
  • Manuel eNarvaez,
  • Carmelo eMillón,
  • Concepción eParrado,
  • Francisco eCiruela,
  • Luigi Francesco Agnati,
  • José Angel Narvaéz,
  • Zaida eDiaz Cabiale

DOI
https://doi.org/10.3389/fendo.2012.00127
Journal volume & issue
Vol. 3

Abstract

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Galanin receptor (GalR) subtypes1-3 linked to central galanin neurons may form heteromers with each other and other types of G protein coupled receptors (GPCRs) in the Central Nervous System (CNS). These heteromers may be one molecular mechanism for galanin peptides and their N-terminal fragments (gal 1-15) to modulate the function of different types of glia-neuronal networks in the CNS, especially the emotional and the cardiovascular networks. GalR-5-HT1A heteromers likely exist with antagonistic GalR-5-HT1A receptor-receptor interactions in the ascending midbrain raphe 5-HT neuron systems and their target regions. They represent a novel target for antidepressant drugs. Evidence is given for the existence of GalR1-5-HT1A heteromers in cellular models with transinhibition of the protomer signaling. A GalR1-GalR2 heteromer is proposed to be a galanin N-terminal fragment preferring receptor (1-15) in the CNS. Furthermore, a GalR1-GalR2-5-HT1A heterotrimer is postulated to explain why only galanin (1-15) but not galanin (1-29) can antagonistically modulate the 5-HT1A receptors in the dorsal hippocampus rich in gal fragment binding sites. The results underline a putative role of different types of GalR-5-HT1A heteroreceptor complexes in depression. GalR antagonists may also have therapeutic actions in depression by blocking the antagonistic GalR-NPYY1 receptor interactions in putative GalR-NPYY1 receptor heteromers in the CNS resulting in increases in NPYY1 transmission and antidepressant effects. In contrast the galanin fragment receptor (a postulated GalR1-GalR2 heteromer) appears to be linked to the NPYY2 receptor enhancing the affinity of the NPYY2 binding sites in a putative GalR1-GalR2-NPYY2 heterotrimer. Finally, putative GalR-α2-adrenoreceptor heteromers with antagonistic receptor-receptor interactions may be a widespread mechanism in the CNS for integration of galanin and noradrenaline signals also of likely relevance for depression.

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