Research utilizing repeated-measures such as daily assessments with self-report and/or objective measures [e.g., physical activity (PA) monitors] are important in understanding health behaviors and informing practice and policy. However, studies that utilize daily assessment often encounter issues with attrition and non-compliance. The current research yielded high levels of retention and adherence with both self-report and objective daily measures. The purpose of this paper is to highlight and discuss strategies utilized in maximizing retention, minimizing missing data, and some lessons learned from the research experience. Fifty community participants took part in a 4-week study utilizing both daily self-report questionnaires and daily use of PA monitors (Fitbit One™). This study focused on typical daily PA and was not an intervention study (e.g., participants were not randomized nor asked to change their PA behavior). Participants completed the study in two waves (wave 1 n = 10, wave 2 n = 40). The research team utilized several retention strategies including automating the data collection process, a prorated incentive structure, having a dedicated and responsive study staff, and utilizing the 2-wave process to optimize data collection during the 2nd wave. The study had 100% retention and generally positive anonymous feedback post-study. Overall, participants completed the vast majority of daily surveys (97%) and wore their Fitbits (for at least part of the day) on almost all days (99.57%) of the study, although there were individual differences. The strategies discussed and lessons learned may be useful to other researchers using daily measurements for whom adherence and retention are important issues. Future research employing these strategies in different populations, with different measurements, and for longer durations is warranted to determine generalizability.
Animal models of obesity are numerous and diverse in terms of identifying specific neural and peripheral mechanisms related to obesity; however, they are limited when it comes to behavior. The standard behavioral measure of food intake in most animal models occurs in a free-feeding environment. While easy and cost-effective for the researcher, the free-feeding environment omits some of the most important features of obesity-related food consumption—namely, properties of food availability, such as effort and delay to obtaining food. Behavior economics expands behavioral measures of obesity animal models by identifying such behavioral mechanisms. First, economic demand analysis allows researchers to understand the role of effort in food procurement, and how physiological and neural mechanisms are related. Second, studies on delay discounting contribute to a growing literature that shows that sensitivity to delayed food- and food-related outcomes is likely a fundamental process of obesity. Together, these data expand the animal model in a manner that better characterizes how environmental factors influence food consumption.
Diet-induced obesity is a laboratory procedure in which nonhuman animals are chronically exposed to a high-fat, high-sugar diet (i.e. cafeteria diet), which results in weight gain, altered sensitivity to reward, and alterations in the dopamine D system. To date, few (if any) studies have examined age-related diet-induced obesity effects in a rat model or have used an impulsive choice task to characterize diet-induced behavioral alterations in reward processes. We exposed rats to a cafeteria-style diet for eight weeks starting at age 21 or 70 days. Following the diet exposures, the rats were tested on a delay discounting task - a measure of impulsive choice in which preference for smaller, immediate vs larger, delayed food reinforcers was assessed. Acute injections of haloperidol (0.03-0.3 mg/kg) were administered to assess the extent to which diet-induced changes in dopamine D influence impulsive food choice. Across both age groups, rats fed a cafeteria diet gained the most weight and consumed more calories than rats fed a standard diet, with rats exposed during development showing the highest weight gain. No age- or diet-related baseline differences in delay discounting were revealed, however, haloperidol unmasked subtle diet-related differences by dose-dependently reducing choice for the larger, later reinforcer. Rats fed a cafeteria diet showed a leftward shift in the dose-response curve, suggesting heightened sensitivity to haloperidol, regardless of age, compared to rats fed a standard diet. Results indicate that chronic exposure to a cafeteria diet resulted in changes in underlying dopamine D that manifested as greater impulsivity independent of age at diet exposure.
Previous research demonstrated that a remifentanilassociated stimulus facilitated the acquisition of a previously unlearned response; however, it is unclear how long a remifentanil-associated stimulus maintains conditioned reinforcing properties under conditions of daily testing. To address this gap, we exposed adult male rats to response-independent stimulus presentations and deliveries of remifentanil (1.0, 3.2, or 10.0 μg/kg/ infusion). Rats either received the stimulus presentations and remifentanil deliveries together (Paired Pavlovian conditioning) or according to separate clocks (Random control group). In the sessions following Pavlovian conditioning, we allowed rats to emit nose-poke responses for the presentation of the stimulus alone and measured the extent to which the stimulus facilitated and maintained a previously unlearned response. We tested responding for the stimulus presentations across 28 daily sessions to assess the Pavlovian extinction (degradation of the drug-stimulus association) of the conditioned reinforcing properties of the remifentanilassociated stimulus. We observed the highest and most persistent levels of responding in rats with a Paired Pavlovian conditioning history at 3.2 and 10.0 μg/kg/ infusion. In addition, we included analyses of the variability in responding for each group, which revealed individual differences in the susceptibility of the remifentanilassociated stimulus acting as a conditioned reinforcer. These findings demonstrate that a remifentanil-associated stimulus has the ability to sustain drug-seeking behavior and underscores the importance of Pavlovian conditioning in promoting drug abuse.
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