Autoradiographic quantitation and anatomical mapping of GTP sensitive-galanin receptors in the guinea pig central nervous system |
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Authors: | Isabelle Dutriez Isabelle Lagny-Pourmir Jacques Epelbaum Jean-Claude Beauvillain |
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Institution: | aUnité 422 INSERM, 1 Place de Verdun, 59045 Lille Cedex, France;bUnité 159 INSERM, Centre Paul Broca, 2 ter rue d'Alésia, 75014 Paris, France |
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Abstract: | Galanin is a 29-amino acid peptide widely distributed in the mammalian central nervous system. Galanin receptors in the guinea pig brain were visualized using 125I]galanin by in vitro receptor quantitative autoradiography. Scatchard analysis of 125I]galanin binding to slide-mounted sections revealed saturable binding to a single class of high affinity receptors with a KD of approximately 1 nM. Specific 125I]galanin binding sites were detected in a large number of brain areas (concentration range: from non detectable to 99.32 fmol/mg of tissular proteins). The anatomical mapping revealed high densities essentially in the telencephalon (e.g. lateral septal nuclei, amygdala, hippocampal dentate gyrus) and the diencephalon (e.g. the anterodorsal and medial habenular thalamic nuclei, the paraventricular, dorsomedian and median mammillary hypothalamic nuclei, the posterior lobe of the pituitary). Addition of Mg2+ and GTP increased binding in some areas such as the zona incerta, the median eminence and the arcuate nucleus, and decreased it in other areas such as the amygdala, the hippocampus and the mammillary nuclei. This regional heterogeneity in the effect of Mg2+ and GTP can be interpreted as: (1) different rates of galanin receptor occupancy by endogenous peptide; (2) a differential coupling of GTP binding proteins to galanin receptors in the brain structures; and (3) a different nature of receptors. At any rate, this study provides evidence for a specific GTP-sensitive galanin receptor in guinea pig brain with an extensive distribution suggesting various physiological implications. Comparison with studies performed in several mammals shows that the overall distribution of galanin receptors is well preserved among species. These data suggest that galanin may posses similar functional properties in the different species tested so far. Nevertheless, very distinct differences were found in some areas like the cortex, the hippocampus and the pituitary. |
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Keywords: | Autoradiography Galanin Guinea pig |
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