Cafeteria diet increases approach behavior and appetitive ultrasonic vocalizations triggered by a food-related cue in male rats

Abstract

The omnipresence of highly palatable food and its related cues constitutes an important risk factor for overeating and body weight gain in today's obesogenic environment. This study examined the metabolic, behavioral, and neurobiological effects of a cafeteria (CAF) diet (kcal composition: 42 % carbs, 13 % protein, 45 % fat) against two control grain-based diets: C1 (kcal composition: 63 % carbs, 23 % protein, 14 % fat) and C2 (kcal composition: 58 % carbs, 29 % protein, 13 % fat) in male Wistar rats (n = 27) at postnatal day 38. After a 9-week feeding period, open-field activity and ultrasonic vocalizations (USVs) were assessed using the animals' empty food container to evaluate attribution of incentive salience to food cues. Additionally, we measured biochemical serum profiles, neurotransmitter levels, and mRNA for BDNF, TrkB, CREB, Dnmt3A, and CRF in reward-related brain regions. Results showed that the CAF diet increased food intake, body weight, and adiposity. CAF-fed rats significantly explored the empty food container more and emitted higher rates of 50-kHz frequency-modulated USVs –markers of incentive motivation and positive affect. The CAF diet also upregulated hippocampal BDNF, TrkB, and CREB, while downregulated TrkB, CREB, and Dnmt3A mRNA in the nucleus accumbens. Although both control diets were suitable for studying CAF effects, the C1 and C2 groups differed in some parameters (e.g., mRNA, cholesterol, and glutamate levels), highlighting the need for appropriate control diets. Our findings reveal that the CAF diet enhances behavioral reactivity to food cues and induces distinct neurobiological alterations, shedding light on the mechanisms linking palatable foods, reward processing, and obesity vulnerability.