Reward components of feeding behavior are preserved during mouse aging.

Mazen R Harb,Nuno Sousa,Joseph Zihl,Osborne F X Almeida

doi:10.3389/fnagi.2014.00242

Abstract

Eating behavior depends on associations between the sensory and energetic properties of foods. Healthful balance of these factors is a challenge for industrialized societies that have an abundance of food, food choices and food-related cues. Here, we were interested in whether appetitive conditioning changes as a function of age. Operant and pavlovian conditioning experiments (rewarding stimulus was a palatable food) in male mice (aged 3, 6, and 15 months) showed that implicit (non-declarative) memory remains intact during aging. Two other essential components of eating behavior, motivation and hedonic preference for rewarding foods, were also found not to be altered in aging mice. Specifically, hedonic responding by satiated mice to isocaloric foods of differing sensory properties (sucrose, milk) was similar in all age groups; importantly, however, this paradigm disclosed that older animals adjust their energy intake according to energetic need. Based on the assumption that the mechanisms that control feeding are conserved across species, it would appear that overeating and obesity in humans reflects a mismatch between ancient physiological mechanisms and today's cue-laden environment. The implication of the present results showing that aging does not impair the ability to learn stimulus-food associations is that the risk of overeating in response to food cues is maintained through to old age.

Highlights

Metabolic status, a reflection of eating habits, is an important determinant of an individual’s physical and mental health trajectory, especially from middle age onwards when the incidence of metabolic syndrome rises steeply (Mathus-Vliegen et al, 2012)
OPERANT CONDITIONED LEARNING IS NOT IMPAIRED DURING AGING Operant or instrumental conditioning involves learning to associate an action with an outcome; the paradigm requires that the subject “works” in order to receive a reward
The main finding of our experiments is that three essential components of feeding behavior—conditioned learning, motivation and, ability to choose foods based on their hedonic properties—remain intact during aging in the mouse

Summary

Introduction

A reflection of eating habits, is an important determinant of an individual’s physical and mental health trajectory, especially from middle age onwards when the incidence of metabolic syndrome rises steeply (Mathus-Vliegen et al, 2012). While hunger provides the primary motivation to eat, food-seeking (wanting/liking) and ingestive behavior may be triggered by associations between the real or anticipated higher reward value of foods in a particular environmental context or because certain foods are imbued with hedonic properties (Berridge and Robinson, 2003; Berridge et al, 2009; Ferriday and Brunstrom, 2011; Ziauddeen et al, 2012). The present study examined whether implicit memory (associative learning), motivation and food preference (triggered by the food’s hedonic qualities) are affected during aging in the mouse. Our results show that old mice do not suffer from impairments in their (i) ability to perceive hedonic stimuli, (ii) motivation to consume rewarding foods, and (iii) capacity to learn stimulus-food associations. Mice maintain their ability to adjust their calorific intake according to their metabolic status

Methods

Results

Conclusion