Delay discounting as impaired valuation: Delayed rewards in an animal obesity model

Obesity Animal Models for Acupuncture and Related Therapy Research Studies

Obesity and related diseases are considered as pandemic representing a worldwide threat for health. Animal models are critical to validate the effects and understand the mechanisms related to classical or innovative preventive and therapeutic strategies. It is, therefore, important to identify the best animal models for translational research, using different evaluation criteria such as the face, construct, and predictive validity. Because the pharmacological treatments and surgical interventions currently used for treating obesity often present many undesirable side effects, relatively high relapse probabilities, acupuncture, electroacupuncture (EA), and related therapies have gained more popularity and attention. Many kinds of experimental animal models have been used for obesity research studies, but in the context of acupuncture, most of the studies were performed in rodent obesity models. Though, are these obesity rodent models really the best for acupuncture or related therapies research studies? In this study, we review different obesity animal models that have been used over the past 10 years for acupuncture and EA research studies. We present their respective advantages, disadvantages, and specific constraints. With the development of research on acupuncture and EA and the increasing interest regarding these approaches, proper animal models are critical for preclinical studies aiming at developing future clinical trials in the human. The aim of the present study is to provide researchers with information and guidance related to the preclinical models that are currently available to investigate the outcomes of acupuncture and related therapies.

Blunted satiety in fatty Zucker rats

Levels of weight gain have hit an epidemic level with rates of overweight and obesity diagnoses topping all-time highs. Elevated body weight has been linked to increased rates of cardiac problems, blood pressure issues, and risk of developing type 2 diabetes. Leptin, a hormone produced by the body that is involved in energy balance by inhibiting hunger has been implicated as an underlying mechanism that differentially contributes to food-seeking motivation. Using a scientifically validated animal model of obesity, the fatty Zucker rat, which has mutated leptin receptor genes, leptin's role in behavioral motivation can be assessed. Animals were on a 2 -h food access restriction with one-hour access to rewards in session and one hour of free-feeding access. Pre-session and post-session food access differences were evaluated in looking at motivation for food rewards during satiation while responding on differing levels of fixed-ratio schedules. The results showed robust differential behavior from satiation, demonstrating a basis for a biological mechanism involving leptin sensitivity that could underlie obesity. Although further experimentation is needed, understanding leptin could help bridge the gap in our understanding of satiation and non-satiation.

Early-life begging effort reduces adult body mass but strengthens behavioural defence of the rate of energy intake in European starlings

Animals require strategies for coping with periods when food is scarce. Such strategies include storing fat as a buffer, and defending the rate of energy intake by changing foraging behaviour when food becomes difficult to obtain. Storage and behavioural defence may constitute alternative strategies for solving the same problem. We would thus expect any developmental influences that limit fat storage in adulthood to also induce a compensatory alteration in adult foraging behaviour, specifically when food is hard to obtain. In a cohort of hand-reared European starlings, we found that higher manipulated early-life begging effort caused individuals to maintain consistently lower adult body mass over a period of two years. Using an operant foraging task in which we systematically varied the costs of obtaining food, we show that higher early-life begging effort also caused stronger behavioural defence of the rate of energy intake when food was more costly to obtain. Among individuals with the same developmental history, however, those individuals who defended their rate of energy intake most strongly were also the heaviest. Our results are relevant to understanding why there are marked differences in body weight and foraging behaviour even among individuals inhabiting the same environment.