Autoradiographic quantitation and anatomical mapping of 125I-galanin binding sites in the rat central nervous system

The distribution of 125I-galanin binding sites in the rat central nervous system was studied by the use of autoradiography, and the amount of peptide bound was determined by the use of microdensitometry. The amount of 125I-galanin bound in various CNS regions ranged from non detectable to 0.40 pmol per gramme tissue at a concentration of 1.5 nM 125I-galanin. The anatomical mapping revealed high density of binding sites in the telencephalon, where labelling was seen in the entorhinal, perirhinal and piriform cortices, in most septal nuclei, in the amygdala and in the hippocampal formation. In the diencephalon binding sites were densely accumulated in the hypothalamus, including the median eminence and periventricular nucleus as well as in the dorsal and medial thalamic nuclei. In the mesencephalon binding sites were seen in many nuclei including the dorsal raphe nucleus, the periaqueductal central grey and pars compacta of the substantia nigra. The pons/medulla revealed high density of binding sites in the locus coeruleus, parabrachial nuclei and in the dorsal vagal complex, while binding in the spinal cord was seen in laminae I, II and X as well as in the intermediolateral horn. The distribution of 125I-galanin binding sites corresponded well to the localization of the peptide as revealed in several earlier immunohistochemical and radioimmunoassay studies, as well as to several previously reported effects of galanin on central autonomic functions.