Abstract
Previous studies have shown that rats fed a high calorie diet rich in saturated fat for 12weeks exhibit peripheral insulin resistance and impairments of behavioural flexibility when switched from an operant delayed matching to place (DMTP) schedule to a delayed non-matching to place (DNMTP) schedule. However, the metabolic changes evoked by feeding a high fat (HF) diet can be observed within two weeks of commencing the diet. The current study has confirmed that 4weeks exposure to an HF diet resulted in increased body weight, peripheral insulin resistance and plasma leptin. Studies performed during weeks 3 and 4 on the HF diet revealed suppressed lever pressing rates and impaired behavioural flexibility in the operant DMTP/DNMTP task. When animals fed the HF diet were then returned to a standard chow (SC) diet for 5weeks their weight and blood biochemistry no longer differed from those measured in animals that had never been exposed to the HF diet. The animals restored to the SC diet exhibited a clear ability to acquire the DNMTP schedule of reinforcement although these animals continued to lever press at a lower rate when compared with animals that received the SC diet throughout. The data suggest that exposure to an HF diet diminishes the motivation to respond for a reward and, thus, the capacity to adapt behavioural performance. This deficit was ameliorated, but not totally reversed, by the dietary intervention. If also true for humans, the results suggest that deficits in behavioural flexibility develop after only a short period on a high calorie diet but may be largely reversible through simple dietary intervention, at least in the early stages of deficit development. However, the putative effects of short-term exposure to an HF diet on behavioural motivation may persist for some time after switching to a healthier low fat diet and remain a problem for those seeking to adopt a healthier diet.
Highlights
IntroductionThere is compelling evidence that the consumption of high calorie western diets that are rich in sugar and saturated fat can have
There is compelling evidence that the consumption of high calorie western diets that are rich in sugar and saturated fat can have⁎ Corresponding author at: Division of Molecular and Cellular Medicine, School of Medicine, University of Dundee, Ninewells Hospital and Medical School, Dundee DD1 9SY, UK.A.D
The principal finding of the current study is that feeding rats an high fat (HF) diet for only 2 to 3 weeks elicited impairments in operant behaviour in a delayed matching to place (DMTP)/delayed non-matching to place (DNMTP) operant task that resemble those seen in rats treated with the diet for a longer period of time
Summary
There is compelling evidence that the consumption of high calorie western diets that are rich in sugar and saturated fat can have. A.D. McNeilly et al / Physiology & Behavior 167 (2016) 100–109 calorie-rich diet is associated with cognitive impairment but they do not provide definitive insights into the possible roles of insulin resistance or the other metabolic and hormonal changes evoked by exposure to diets of this type [4,5,6]. Some studies have provided support for a link between changes in insulin signalling and diet-induced behavioural deficits while others have not [2,3,7]. Previous studies in our laboratory have shown that rats fed a high calorie diet, rich in saturated fat, evoked a specific effect in behavioural responding in animals trained to lever press in an operant variable delay non-matching to position (DNMTP) task [8]. The behavioural deficits measured in HF fed rats tested in the operant task correlated negatively with the plasma insulin concentration and the fasting insulin resistance index (FIRI) a subsequent study suggested that this might not represent a causative relationship [9]
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