Novelty suppressed feeding in rats bred for divergent intrinsic aerobic capacity maintained on high fat diet
Dykhuis KE, Burghardt PR, Krolewski DM, Koch LG, Britton SL, Watson SJ, Akil H
Society for Neuroscience. 2011.
Selection for intrinsic treadmill running capacity in rats has produced two lines with high or low capacity for running (HCR and LCR, respectively). LCR rats exhibit the hallmarks of metabolic syndrome while HCRs display a healthy phenotype. Behaviorally, LCRs employ a less cautious or vigilant approach to environmental novelty and exhibit passive coping strategies in the forced swim test, while HCRs are more vigilant in response to novelty and show more active coping strategies. Previous work has shown that HCR and LCR rats respond in a situation with conflicting motivational factors like the novelty suppressed feeding (NSF) paradigm (Dykhuis et al, SFN Abstracts 2010). Given the metabolic and behavioral phenotype of these animals we sought to examine how a high fat diet (HFD) might influence behavioral responding in the NSF paradigm in HCR and LCR rats. Male HCR and LCR rats (n=16/group) were maintained on standard a high fat diet (Science Diet, D12492) for 6 weeks prior to testing. At the start of the experiment, access to food was restricted for either 24 or 48 hours. Following food restriction rats were placed in an open field (100 x 100 x 50cm) with 8 pieces of chow located in the center of the arena. Animals were allowed to explore the open field for up to 15 minutes and latency to begin eating the chow in the center of the open field was recorded. Following NSF latency to start eating as well as the amount of chow consumed in the home cage was measured. Following 24-hours of food restriction, HCR rats showed a longer latency to begin eating chow in the center of the open field compared to LCR rats. After 48-hours of fasting, HCR and LCRs did not differ in their latency to begin eating in the open field. Latency to eat in the home cage was similar in LCR and HCR rats following 24- and 48-hours of fasting. Taken together these studies suggest that when there is conflict between environmental novelty and hunger, HCR rats are more cautious following 24-hours of fasting. However, following extended fasting of up to 48 hours, the increased hunger drive becomes dominant and HCR rats become less cautious and are no longer different from the LCR rats. These studies indicate that the metabolic phenotype, diet, and feeding status of an individual influence their behavioral repertoire for coping with environmental novelty, and may have impact how individuals with metabolic syndrome cope with mild stress. Given these behavioral differences we have also examined gene expression in homeostatic and hedonic brain circuitry following 24-hours of fasting, and these results are described by Burghardt et al, (SfN Abstracts, 2011).