Age effects on the nucleus of the lateral olfactory tract of the rat

The olfactory deficits that occur during aging influence the quality of life and have been regarded as a risk factor for malnutrition in the elderly. The nucleus of the lateral olfactory tract (nLOT) is a cortical nucleus of the pallial amygdala that has been implicated in feeding behavior. Here we present quantitative data on the anatomy of the nLOT in the adult rat and on the effects of age on its structure and neurochemistry. Total neuron numbers, neuronal volumes, and volumes of layers 1-3 of the nLOT were estimated in adult and old male rats using stereological techniques. We also estimated the total number of interneurons expressing neuropeptide Y (NPY) and vasoactive intestinal polypeptide (VIP), and the numerical density of the nLOT cholinergic varicosities. Our data show that aging is associated with a reduction of the total neuron numbers in the nLOT, due to cell loss in layers 2 and 3. There were no age-related variations in neuronal volumes. Similarly, the volume of the nLOT was unchanged in aged rats, except in layer 3 where it was reduced. The numerical density of cholinergic varicosities was also unchanged in aged rats. Conversely, the total numbers of NPY- and VIP-immunoreactive neurons were reduced by 55% and 30%, respectively, in aged rats. These findings include the nLOT in the list of cortical olfactory structures susceptible to aging and raise the possibility that the age-related changes that occur in the nLOT might contribute for the decline in olfactory functions reported in normal aging.