Vulnerability to diet-induced obesity is associated with greater food priming-induced reinstatement of palatable food seeking

Dopamine D1-like receptors in prelimbic, but not infralimbic, medial prefrontal cortex contribute to chronic stress-induced increases in cue-induced relapse to palatable food seeking during forced abstinence

Chronic stress exposure causes increased vulnerability to future relapse-like behavior in male, but not female, rats with a history of palatable food self-administration. These effects are mediated by dopamine D1-like receptors, but the anatomical location of chronic stress' dopaminergic mechanism is not known. Thus, male rats were trained to respond for palatable food pellets in daily sessions. During subsequent forced abstinence from food self-administration, stress was manipulated (0 or 3 h restraint/day for 7 days). Rats also received bilateral microinjections of the D1-like receptor antagonist SCH-23390 (0.25 μg/0.5 μl/side) or vehicle (0.5 μl/side) delivered to either prelimbic or infralimbic medial prefrontal cortex prior to daily treatments. Relapse tests in the presence of food-associated cues were conducted 7 days after the last treatment. Stress caused an increase and a decrease in responding during relapse tests in rats that received prelimbic vehicle and SCH-23390 infusions, respectively, relative to unstressed rats. In rats receiving IL infusions, however, stress caused an increase in responding regardless of whether the infusion was vehicle or SCH-23390. These results establish a specific role for prelimbic D1-like receptors in chronic stress-potentiated relapse.

From Obesity to Hippocampal Neurodegeneration: Pathogenesis and Non-Pharmacological Interventions

High-caloric diet and physical inactivity predispose individuals to obesity and diabetes, which are risk factors of hippocampal neurodegeneration and cognitive deficits. Along with the adipose-hippocampus crosstalk, chronically inflamed adipose tissue secretes inflammatory cytokine could trigger neuroinflammatory responses in the hippocampus, and in turn, impairs hippocampal neuroplasticity under obese and diabetic conditions. Hence, caloric restriction and physical exercise are critical non-pharmacological interventions to halt the pathogenesis from obesity to hippocampal neurodegeneration. In response to physical exercise, peripheral organs, including the adipose tissue, skeletal muscles, and liver, can secret numerous exerkines, which bring beneficial effects to metabolic and brain health. In this review, we summarized how chronic inflammation in adipose tissue could trigger neuroinflammation and hippocampal impairment, which potentially contribute to cognitive deficits in obese and diabetic conditions. We also discussed the potential mechanisms underlying the neurotrophic and neuroprotective effects of caloric restriction and physical exercise by counteracting neuroinflammation, plasticity deficits, and cognitive impairments. This review provides timely insights into how chronic metabolic disorders, like obesity, could impair brain health and cognitive functions in later life.

Sex-dependent effects of chronic stress on reinstatement of palatable food seeking and involvement of dopamine D1-like receptors

Recent work in our lab has shown that chronic stress exposure causes sex-dependent changes in subsequent relapse-like behavior in rats with a history of palatable food self-administration. Although these effects are mediated by dopamine D₁-like receptors in male rats, such dopaminergic mechanisms have not been investigated in female animals. Thus, male and female rats were trained to respond for highly palatable food reinforcers in daily sessions. During subsequent extinction training, stress was manipulated (0 or 3 h restraint/day for 7 days). To assess dopaminergic involvement, we administered either SCH-23390 (10.0 μg/kg), a dopamine D₁-like receptor antagonist, or vehicle prior to daily treatments. Rats were then tested for cue- and pellet priming-induced reinstatement. Results showed that a history of chronic stress caused an increase in pellet priming-induced reinstatement in males and a decrease in cue-induced reinstatement in females. SCH-23390 combined with stress prevented those effects in males, but not in females. In females, a history of SCH-23390 administration caused an overall increase in responding that was apparent during cue-, but not pellet priming-, induced reinstatement testing. These results establish that both the effects of chronic stress on reinstatement of food seeking and the involvement of dopamine in those effects are dependent on biological sex. Such findings should inform the development of sex-specific interventions for dietary relapse and other stress-related health problems.

Effects of chronic stress on reinstatement of palatable food seeking: Sex differences and relationship to trait anxiety

Previous research in our lab has established a causal role for chronic stress exposure in subsequent increases in relapse-like behaviors in male rats with a history of palatable food self-administration. Given that many of the neurobehavioral consequences of stress are sex dependent, we aimed to determine whether sex differences exist with regard to the effects of chronic stress on relapse. Additionally, because high trait anxiety confers vulnerability to stress-related disorders, we examined whether individual differences in trait anxiety were related to differences in relapse-like behavior after chronic stress exposure. Following elevated plus maze testing for classification into high- or low-anxiety phenotypes, male and female rats responded for highly palatable food pellets. During subsequent extinction training, stress was manipulated (0 or 90 min restraint/day for 7 days). Rats were then tested for cue- and pellet priming-induced reinstatement of palatable food seeking. Results showed that female rats displayed higher levels of responding during cue-induced reinstatement tests compared to males, and that a history of chronic stress caused an attenuation of cue-induced reinstatement in female, but not male, rats. Regarding pellet priming-induced reinstatement, there was a three-way interaction such that neither stress history nor anxiety phenotype was related to reinstatement in females, but a history of stress in males caused increased and decreased responding in low- and high-anxiety rats, respectively. These results suggest that biological sex and trait anxiety level may help to explain differences in vulnerability to relapse among individuals exposed to chronic stress. Such information may be useful in designing more personalized and effective treatments for obesity and eating disorders.