Galanin receptor over-expression within the amygdala in early Alzheimer's disease:: An in vitro autoradiographic analysis

Abstract

Galanin receptor (GALR) expression is increased in various areas of the limbic system in end stage Alzheimer's disease (AD). The amygdaloid complex is a key component of the limbic circuit, is involved in homeostatic and cognitive functions, is impacted in AD and contains the peptide and receptor for galanin. Although GALR expression occurs in the amygdala in end stage AD, it remains to be determined whether a plasticity response occurs early or late in the disease. Therefore, we analyzed the distribution and associated changes in GALR binding in the amygdala during the progression of AD using an in vitro receptor autoradiographic method. Human galanin ([ 125I]hGAL) receptor binding was performed on brain sections from early and late AD cases, as well as normal age-matched control subjects. In aged controls, densities of [ 125I]hGAL binding sites were found in the central and the corticomedial nuclei. Relative to controls, possible/early AD cases displayed significantly greater numbers of [ 125I]hGAL binding sites in the central nucleus and cortico-amygdaloid transition area. In contrast, we found a decrease in the number of binding sites for [ 125I]hGAL in late as compared to early AD cases. The over-expression of GALRs in subfields of the amygdaloid early in AD suggests that galaninergic systems play a key role in limbic related behavioral changes during the disease process.