AUTORADIOGRAPHIC QUANTITATION AND ANATOMICAL MAPPING OF GTP SENSITIVE-GALANIN RECEPTORS IN THE GUINEA-PIG CENTRAL-NERVOUS-SYSTEM

Galanin is a 29-amino acid peptide widely distributed in the mammalian central nervous system. Galanin receptors in the guinea pig brain wer e visualized using [I-125]galanin by in vitro receptor quantitative au toradiography. Scatchard analysis of [I-125]galanin binding to slide-m ounted sections revealed saturable binding to a single class of high a ffinity receptors with a K-D of approximately 1 nM. Specific [I-125]ga lanin binding sites were detected in a large number of brain areas (co ncentration range: from non detectable to 99.32 fmol/mg of tissular pr oteins). 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 decreas ed it in other areas such as the amygdala, the hippocampus and the mam millary nuclei. This regional heterogeneity in the effect of Mg2+ and GTP can be interpreted as: (1) different rates of galanin receptor occ upancy by endogenous peptide; (2) a differential coupling of GTP bindi ng proteins to galanin receptors in the brain structures; and (3) a di fferent nature of receptors. At any rate, this study provides evidence for a specific GTP-sensitive galanin receptor in guinea pig brain wit h an extensive distribution suggesting various physiological implicati ons. Comparison with studies performed in several mammals shows that t he overall distribution of galanin receptors is well preserved among s pecies. These data suggest that galanin may possess similar functional properties in the different species tested so far. Nevertheless, very distinct differences were found in some areas like the cortex, the hi ppocampus and the pituitary. Copyright (C) 1996 Elsevier Science B.V.