Galanin receptors in the brain of a teleost: Autoradiographic distribution of binding sites in the Atlantic Salmon

• Published in: The Journal of Comparative Neurology
• Main Authors: Holmqvist, Bo I., Carlberg, Mats
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 1992
• Subjects: Atlantic salmon
• Online Access: http://dx.doi.org/10.1002/cne.903260105; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1002%2Fcne.903260105; https://onlinelibrary.wiley.com/doi/pdf/10.1002/cne.903260105

Abstract The distribution of galanin (GAL) binding sites in the brain of the Atlantic salmon (Salmosalar) was investigated by means of radioligand binding in conjunction with autoradiography by using high‐performance liquid chromatography (HPLC) characterized radio‐iodinated porcine galanin ([ 125 I]GAL). On slide‐mounted sections of frozen salmon brain homogenate, [ 125 I]GAL(4 nM) bound rapidly and reversibly to a single population of sites with a K d of 1.0 ± 0.08 nM (n = 3) and B max of 2.380 ± 0.19 fmol/mg wet tissue. Specific [ 125 I]GAL binding was found in cellular regions, in fiber tracts, and in neuropil areas throughout the brain, except for in the olfactory bulb, pineal organ, and cerebellum. Autoradiographic microdensitometric measurements revealed high total [ 125 I]GAL binding in the ventral hypothalamus (inferior lobes; around 7–12 fmol/mg tissue), the dorsal spinal cord (between 6 and 12 fmol/mg tissue), sublayers of the optic tectum (around 8 fmol/mg), torus semicircularis (around 7 fmol/mg), and glomerular complex (around 6 fmol/mg). Intermediate densities of [ 125 I]GAL binding (3–5 fmol/mg tissue) were found in the pituitary, telencephalon, dorsolateral thalamic nucleus, and raphe nuclei and in association with the forebrain bundles. Except for in the optic tectum, there is a good concordance of [ 125 I]GAL binding sites and GAL‐immunoreactive fiber projections in most brain areas of the salmon. The wide distribution of GAL binding sites provides further evidence that a GAL‐like substance might be involved in a diversity of brain functions of teleosts. The topographic distribution of target sites in the hypothalamo‐hypophyseal axis indicates that GAL‐like substances may have both direct and indirect effect on pituitary functions while in extrahypothalamic areas, functional implications by GAL may include involvement in somatosensory, central gustatory, olfactory, and visual functions. This study provides evidence for the presence of a specific GAL receptor in the brain of the Atlantic ...