Excessive consumption of highly palatable foods rich in sugar and fat, often referred to as “junk” or “fast” foods, plays a central role in the development of obesity. The highly palatable characteristics of these foods activate hedonic and motivational mechanisms to promote food-seeking behavior and overeating, which is largely regulated by the brain reward system. Excessive junk food consumption can alter the functioning of this reward system, but exact mechanisms of these changes are still largely unknown. This study investigated whether long-term junk food consumption, in the form of Cafeteria (CAF) diet, can alter the reward system in adult, female Long-Evans rats, and whether different regimes of CAF diet influence the extent of these changes. To this end, rats were exposed to a 6-week diet with either standard chow, or ad libitum daily access to CAF diet, 30% restricted but daily access to CAF diet, or one-day-a-week (intermittent) ad libitum access to CAF diet, after which c-Fos expression in the Nucleus Accumbens (NAc), Prefrontal Cortex (PFC), and Ventral Tegmental Area (VTA) following consumption of a CAF reward of choice was examined. We found that all CAF diet regimes decreased c-Fos expression in the NAc-shell when presented with a CAF reward, while no changes in c-Fos expression upon the different diet regimes were found in the PFC, and possibly the VTA. Our data suggests that long-term junk food exposure can affect the brain reward system, resulting in an attenuated activity of the NAc-shell.

Supplementation with natural bioactive compounds has been proposed to be a complementary tool to the calorie-restricted diets and physical exercise programs used to tackle human overweight, obesity and Metabolic syndrome. Herein, we evaluated the effects of 14 weeks of calorie-restricted cafeteria diet either alone or combined with oral administration of the polyphenol oleuropein in obese adult male rats, compared with a control group fed standard chow and a group fed cafeteria diet. Animals were sacrificed at the age of 26 weeks and several tissues of interest were removed. The results showed that both dietary interventions reduced the adiposity index (p < 0.05 and p < 0.01, respectively), and specifically the abdominal fat depots (mesenteric: p < 0.01 and p < 0.01, respectively; and epididymal: both diets p < 0.001) and restored the decreased soleus skeletal muscle mass. Both interventions decreased leptin mRNA expression in mesenteric white adipose tissue (p < 0.05) and normalized hypothalamic Agrp mRNA expression compared to cafeteria-fed obese rats (p < 0.05). However, only the calorie-restricted cafeteria diet supplemented with oleuropein induced additional lower retroperitoneal adipose accretion (p < 0.05) and increased hypothalamic leptin receptor mRNA levels (p < 0.05). Experiments with female animals, at different doses and longer intervention periods, are needed to better determine the potential benefits of this dietary treatment.

The aim of this study was to evaluate, in male Long-Evans rats, whether a restricted-cafeteria diet (CAFR), based on a 30% calorie restriction vs continuous ad libitum cafeteria (CAF) fed animals, administered alone or in combination with moderate treadmill exercise (12 m/min, 35 min, 5 days/week for 8 weeks), was able to ameliorate obesity and the associated risk factors induced by CAF feeding for 18 weeks and to examine the changes in circadian locomotor activity, hypothalamic–pituitary–adrenal (HPA) axis functionality, and stress response elicited by this dietary pattern. In addition to the expected increase in body weight and adiposity, and the development of metabolic dysregulations compatible with Metabolic Syndrome, CAF intake resulted in a sedentary profile assessed by the home-cage activity test, reduced baseline HPA axis activity through decreased corticosterone levels, and boosted exploratory behavior. Both CAFR alone and in combination with exercise reduced abdominal adiposity and hypercholesterolemia compared to CAF. Exercise increased baseline locomotor activity in the home-cage in all dietary groups, boosted exploratory behavior in STD and CAF, partially decreased anxiety-like behavior in CAF and CAFR, but did not affect HPA axis-related parameters.

The goal of the present study was to evaluate the sweet taste function in obese rats fed with a 30% calorie-restricted cafeteria diet (CAFR) and/or subjected to moderate treadmill exercise (12–17 m/min, 35 min, 5 days per week) for 9 weeks. A two-bottle preference test, a taste reactivity test, and a brief-access licking test were carried out when animals were aged 21 weeks; biometric and metabolic parameters were also measured along the interventions. Two separate experiments for females and males were performed. Behaviorally, CAF diet decreased sucrose intake and preference, as well as perceived palatability, in both sexes and decreased hedonic responses in males. Compared to the CAF diet, CAFR exerted a corrective effect on sweet taste variables in females by increasing sucrose intake in the preference test and licking responses, while exercise decreased sucrose intake in both sexes and licking responses in females. As expected, CAF diet increased body weight and Lee index and worsened the metabolic profile in both sexes, whereas CAFR diet ameliorated these effects mainly in females. Exercise had no noticeable effects on these parameters. We conclude that CAF diet might diminish appetitive behavior toward sucrose in both sexes, and that this effect could be partially reverted by CAFR diet in females only, while exercise might exert protective effects against overconsumption of sucrose in both sexes.

Diet-induced obesity models are widely used to investigate dietary interventions for treating obesity. This study was aimed to test whether a dietary intervention based on a calorie-restricted cafeteria diet (CAF-R) and a polyphenolic compound (Oleuropein, OLE) supplementation modified sucrose intake, preference, and taste reactivity in cafeteria diet (CAF)-induced obese rats. CAF diet consists of high-energy, highly palatable human foods. Male rats fed standard chow (STD) or CAF diet were compared with obese rats fed CAF-R diet, alone or supplemented with an olive tree leaves extract (25 mg/kg*day) containing a 20.1% of OLE (CAF-RO). Biometric, food consumption, and serum parameters were measured. CAF diet increased body weight, food and energy consumption and obesity-associated metabolic parameters. CAF-R and CAF-RO diets significantly attenuated body weight gain and BMI, diminished food and energy intake and improved biochemical parameters such as triacylglycerides and insulin resistance which did not differ between CAF-RO and STD groups. The three cafeteria groups diminished sucrose intake and preference compared to STD group. CAF-RO also diminished the hedonic responses for the high sucrose concentrations compared with the other groups. These results indicate that CAF-R diet may be an efficient strategy to restore obesity-associated alterations, whilst OLE supplementation seems to have an additional beneficial effect on sweet taste function.

It has been suggested that the orexin system modulates learning and memory-related processes. However, the possible influence that training could have on the effect of the blockade of orexin-A selective receptor (OX1R) on a spatial memory task has not been explored. Therefore, the present study attempts to compare the effects of OX1R antagonist SB-334867 infusion on spatial memory in two different conditions in the Morris Water Maze (MWM). This experiment evaluated the animals' performance in weak training (2 trials per session) vs strong training (6 trials per session) protocols in a spatial version of the MWM. We found that in the 2-trial condition the post-training SB-334867 infusion had a negative effect on consolidation as well as on the retention and reversal learning of the task 72 h later. This effect was not apparent in the 6-trial condition. In addition, while the strong training groups showed a general increase in c-Fos expression in several brain areas of the hippocampalthalamic-cortical circuit, SB-334867 administration had the opposite effect in areas that have been previously reported to have a high density of OX1R. Specifically, the SB-infused group in the 2-trial condition showed a decrease in c-Fos immunoreactivity in the dentate gyrus, granular retrosplenial and prelimbic cortices, and centrolateral thalamic nucleus. This was not observed for subjects in the 6-trial condition. The activation of these areas could constitute a neuroanatomical substrate involved in the compensatory mechanisms of training upon SB-334867 impairing effects on a MWM spatial task.