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

Abstract

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.

The integrity of the nucleus of the lateral olfactory tract is essential for the normal functioning of the olfactory system

“…The nucleus of the lateral olfactory tract (nLOT) is a small three-layered structure, with a volume of 0.24 mm 3 and 19,000 neurons (Vaz et al 2016 ). It is located in the ventral surface of the brain interposed between the anterior amygdaloid area and the anterior medial amygdala (Ennis et al 2015 ), and is related laterally with the anterior cortical amygdaloid nucleus (de Olmos et al 2004 ).…”

“…Along with its peculiar neurogenic pattern, the nLOT also stands up as a unique region within the group of the cortical pallial nuclei due to some particular aspects of its morphology, neurochemistry and connections. It displays a distinctive three-layered organization (Price 1973 ; McDonald 1983 ; Millhouse and Uemura-Sumi 1985 ; Vaz et al 2016 ) and its layer 2 neurons, which are relatively large and represent over 80% of the total neuronal population of the nLOT (Vaz et al 2016 ), express a type of vesicular glutamate transporter (type 2) that is considerably less abundant, or even non-existent, in other areas of the pallial amygdala (Hur and Zaborszky 2005 ). It has a much higher density of heavy metals (Friedman and Price 1984 ) and stains more intensely for cholinergic markers (Millhouse and Uemura-Sumi 1985 ; Vaz et al 2016 ) than the surrounding structures.…”

“…It displays a distinctive three-layered organization (Price 1973 ; McDonald 1983 ; Millhouse and Uemura-Sumi 1985 ; Vaz et al 2016 ) and its layer 2 neurons, which are relatively large and represent over 80% of the total neuronal population of the nLOT (Vaz et al 2016 ), express a type of vesicular glutamate transporter (type 2) that is considerably less abundant, or even non-existent, in other areas of the pallial amygdala (Hur and Zaborszky 2005 ). It has a much higher density of heavy metals (Friedman and Price 1984 ) and stains more intensely for cholinergic markers (Millhouse and Uemura-Sumi 1985 ; Vaz et al 2016 ) than the surrounding structures. Unlike other components of the olfactory amygdala (Kevetter and Winans 1981 ; Swanson and Petrovich 1998 ; McDonald 2003 ; Gutiérrez-Castellanos et al 2014 ), it does not send direct projections to the extended amygdala or the hypothalamus (Santiago and Shammah-Lagnado 2004 ).…”

Bi-directional encoding of context-based odors and behavioral states by the nucleus of the lateral olfactory tract

“…We also demonstrated that the go-cue and no-go-cue responsive neurons highly contributed to the population dynamics of cue encoding and decoding, for accuracy of the animal's choices (Figure 5), suggesting that these bidirectional response neurons for cue odors effectively provided sufficient information to account for the behavioral choices. These bidirectional cues encoding a small number of neurons with a high level of information may be effective in the NLOT with only a small volume of 0.24 mm 3 and 19,000 neurons (Vaz et al, 2016).…”

Bi-directional encoding of context-based odor signals and behavioral states by the nucleus of the lateral olfactory tract neurons

“…Olfactory information is transmitted into the nLOT with a three-layered structure (layers I, II, and III). The nLOT layer Ⅱ neurons contributing to over 80% of the total neuronal population of the nLOT (17), project to the dwarf cell regions in the OT (6). The OT sends a major projection to the ventral pallidum regulating expected positive and negative valences (21)(22)(23).…”