Rat strains with different metabolic statuses differ in food olfactory-driven behavior

In most species, food intake is influenced by olfactory cues and metabolic status can affect the olfactory function of animals and regulate feeding-related behaviors. We investigated whether modulation of the endocrine system that regulates or modifies energy balance affected the olfactory system by examining four rat strains, obese Zucker and obesity-resistant Lou/C rats and their counterparts. Such models were chosen because they differ largely in their energy status and in their insulin and leptin blood levels, two hormones known to impact olfactory behaviors. After evaluation of the main metabolic parameters, we analyzed the food-driven olfactory behaviors of the four strains by measuring general activity time and sniffing time in response to food cues together with food reward localization performances in fed and fasted states. In fed conditions, obese Zucker and Wistar rats exhibited a great interest for food odor, which was not enhanced by fasting, in contrast to Lou/C and Zucker lean rats. All strains, except Lou/C, showed decreased latencies to find a hidden food reward with time, whereas a 24-h fasting was necessary to improve food search performances in Lou/C. These metabolic and behavioral changes were partly associated with variations in the transcription profiles of leptin, insulin and orexin and their receptors in the hypothalamus and olfactory system. The results show that variations in metabolic-related genes expression along the olfactory pathways comes with obesity in influencing food odors-driven behaviors. Our data indicate that food-olfactory driven behaviors are clearly affected by the long-term metabolic status.