Effects of aging and nerve growth factor on the neuropeptide expression and cholinergic innervation of the rat basolateral amygdala

Abstract

The basolateral amygdala (BLA) contains interneurons that express neuropeptide Y (NPY) and vasoactive intestinal polypeptide (VIP), both of which are involved in the regulation of functions and behaviors that undergoes deterioration with aging. In this study, we sought to determine if aging alters the densities of NPY- and VIP-positive neurons and cholinergic varicosities in the BLA and, in the affirmative, if those changes might rely on insufficient neurotrophic support provided by nerve growth factor (NGF). The number of NPY-positive neurons was significantly reduced in aged rats, whereas the number of VIP-immunoreactive neurons was unaltered. The decreased NPY expression was fully reversed by infusion of NGF in the lateral ventricle. No statistically significant difference in the density of vesicular acetylcholine transporter (VAChT)-immunoreactive varicosities was found between groups. Our results indicate a dissimilar resistance of different populations of BLA interneurons to aging. Furthermore, the present data also show that the BLA cholinergic innervation is particularly resistant to aging effects. Finally, our results also show that the reduced NPY expression in the BLA of aged rats can be related to changes in NGF neurotrophic support.