Tonic Dopamine Modulates Exploitation of Reward Learning

The impact of dopamine on adaptive behavior in a naturalistic environment is largely unexamined. Experimental work suggests that phasic dopamine is central to reinforcement learning whereas tonic dopamine may modulate performance without altering learning per se; however, this idea has not been developed formally or integrated with computational models of dopamine function. We quantitatively evaluate the role of tonic dopamine in these functions by studying the behavior of hyperdopaminergic DAT knockdown mice in an instrumental task in a semi-naturalistic homecage environment. In this “closed economy” paradigm, subjects earn all of their food by pressing either of two levers, but the relative cost for food on each lever shifts frequently. Compared to wild-type mice, hyperdopaminergic mice allocate more lever presses on high-cost levers, thus working harder to earn a given amount of food and maintain their body weight. However, both groups show a similarly quick reaction to shifts in lever cost, suggesting that the hyperdominergic mice are not slower at detecting changes, as with a learning deficit. We fit the lever choice data using reinforcement learning models to assess the distinction between acquisition and expression the models formalize. In these analyses, hyperdopaminergic mice displayed normal learning from recent reward history but diminished capacity to exploit this learning: a reduced coupling between choice and reward history. These data suggest that dopamine modulates the degree to which prior learning biases action selection and consequently alters the expression of learned, motivated behavior

CommunityRx, a social care assistance intervention for family and friend caregivers delivered at the point of care: Two concurrent blinded randomized controlled trials

Background: CommunityRx is an evidence-based social care intervention delivered to family and friend caregivers (“caregivers”) at the point of healthcare to address health-related social risks (HRSRs). Two CommunityRx randomized controlled trials (RCTs) are being fielded concurrently on Chicago’s South Side, a predominantly African American/Black community. CommunityRx-Hunger is a double-blind RCT enrolling caregivers of hospitalized children. CommunityRx-Dementia is a single-blind RCT enrolling caregivers of community-residing people with dementia. RCTs with caregivers face recruitment barriers, including caregiver burden and lack of systematic strategies to identify caregivers in clinical settings. COVID-19 pandemic-related visitor restrictions exacerbated these barriers and prompted the need for iteration of the protocols from in-person to remote operations. This study describes these protocols and methods used for successful iteration to overcome barriers. Methods and findings: CommunityRx uses individual-level data to generate personalized, local community resource referrals for basic, health and caregiving needs. In early 2020, two in-person RCT protocols were pre-tested. In March 2020, when pandemic conditions prohibited face-to-face clinical enrollment, both protocols were iterated to efficient, caregiver-centered remote operations. Iterations were enabled in part by the Automated Randomized Controlled Trial Information-Communication System (ARCTICS), a trial management system innovation engineered to integrate the data collection database (REDCap) with community resource referral (NowPow) and SMS texting (Mosio) platforms. Enabled by engaged Community Advisory Boards and ARCTICS, both RCTs quickly adapted to remote operations. To accommodate these adaptations, launch was delayed until November (CommunityRx-Hunger) and December (CommunityRx-Dementia) 2020. Despite the delay, 65% of all planned participants (CommunityRx-Hunger n = 417/640; CommunityRx-Dementia n = 222/344) were enrolled by December 2021, halfway through our projected enrollment timeline. Both trials enrolled 13% more participants in the first 12 months than originally projected for in-person enrollment. Discussion: Our asset-based, community-engaged approach combined with widely accessible institutional and commercial information technologies facilitated rapid migration of in-person trials to remote operations. Remote or hybrid RCT designs for social care interventions may be a viable, scalable alternative to in-person recruitment and intervention delivery protocols, particularly for caregivers and other groups that are under-represented in traditional health services research. Trial registration: ClinicalTrials.gov: CommunityRx-Hunger (NCT04171999, 11/21/2019); CommunityRx for Caregivers (NCT04146545, 10/31/2019).</p

Sucrose Exposure in Early Life Alters Adult Motivation and Weight Gain

The cause of the current increase in obesity in westernized nations is poorly understood but is frequently attributed to a ‘thrifty genotype,’ an evolutionary predisposition to store calories in times of plenty to protect against future scarcity. In modern, industrialized environments that provide a ready, uninterrupted supply of energy-rich foods at low cost, this genetic predisposition is hypothesized to lead to obesity. Children are also exposed to this ‘obesogenic’ environment; however, whether such early dietary experience has developmental effects and contributes to adult vulnerability to obesity is unknown. Using mice, we tested the hypothesis that dietary experience during childhood and adolescence affects adult obesity risk. We gave mice unlimited or no access to sucrose for a short period post-weaning and measured sucrose-seeking, food consumption, and weight gain in adulthood. Unlimited access to sucrose early in life reduced sucrose-seeking when work was required to obtain it. When high-sugar/high-fat dietary options were made freely-available, however, the sucrose-exposed mice gained more weight than mice without early sucrose exposure. These results suggest that early, unlimited exposure to sucrose reduces motivation to acquire sucrose but promotes weight gain in adulthood when the cost of acquiring palatable, energy dense foods is low. This study demonstrates that early post-weaning experience can modify the expression of a ‘thrifty genotype’ and alter an adult animal's response to its environment, a finding consistent with evidence of pre- and peri-natal programming of adult obesity risk by maternal nutritional status. Our findings suggest the window for developmental effects of diet may extend into childhood, an observation with potentially important implications for both research and public policy in addressing the rising incidence of obesity.</p

Sucrose exposure in early life alters adult motivation and weight gain.

The cause of the current increase in obesity in westernized nations is poorly understood but is frequently attributed to a 'thrifty genotype,' an evolutionary predisposition to store calories in times of plenty to protect against future scarcity. In modern, industrialized environments that provide a ready, uninterrupted supply of energy-rich foods at low cost, this genetic predisposition is hypothesized to lead to obesity. Children are also exposed to this 'obesogenic' environment; however, whether such early dietary experience has developmental effects and contributes to adult vulnerability to obesity is unknown. Using mice, we tested the hypothesis that dietary experience during childhood and adolescence affects adult obesity risk. We gave mice unlimited or no access to sucrose for a short period post-weaning and measured sucrose-seeking, food consumption, and weight gain in adulthood. Unlimited access to sucrose early in life reduced sucrose-seeking when work was required to obtain it. When high-sugar/high-fat dietary options were made freely-available, however, the sucrose-exposed mice gained more weight than mice without early sucrose exposure. These results suggest that early, unlimited exposure to sucrose reduces motivation to acquire sucrose but promotes weight gain in adulthood when the cost of acquiring palatable, energy dense foods is low. This study demonstrates that early post-weaning experience can modify the expression of a 'thrifty genotype' and alter an adult animal's response to its environment, a finding consistent with evidence of pre- and peri-natal programming of adult obesity risk by maternal nutritional status. Our findings suggest the window for developmental effects of diet may extend into childhood, an observation with potentially important implications for both research and public policy in addressing the rising incidence of obesity

Glucose challenge.

<p>(a) Weights after a 21 hour fast and prior to glucose challenge. (b) blood glucose levels at fasting baseline (timepoint 0) and following i.p. injection of dextrose (2 g/kg). N = 6 (no sucrose) and 8 (unlimited).</p

Concurrent choice.

<p>Average lever presses during (a) choice and (b) no choice conditions (n = 8). (c) Total food consumed (earned sucrose+freely available chow) during choice sessions (n = 8). (d) Percentage of total intake comprised of earned sucrose pellets during choice sessions (n = 8). Box plots: as described in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0003221#pone-0003221-g001" target="_blank">figure 1</a>; * p<.05; **p<.005; *** p<.0001.</p

Experimental timeline, progressive ratio and activity.

<p>(a) Timeline indicating the order of experimental manipulations and tests. Two cohorts of mice were used and administered the experimental manipulation and testing procedures as indicated above and below the timeline. Breakpoint in progressive ratio (PR7) for the sucrose exposed and non-sucrose exposed mice tested under (b) food restriction and (c) sated conditions (n = 8). (d) Total distance traveled in the open field (1 hr) (n = 7). (e) Total number of wheel turns in 1 week (n = 7, 8). Box plots: Middle lines represent the median values, the top and bottom of the boxes represent the 25th and 75th percentiles, the whiskers represent the 10th and 90th percentiles and the dots represent mean values ; * p = .05.</p

High sugar/high fat dietary challenge.

<p>(a) Percent weight gain 3-weeks prior to (left) and during (right) the 3-week HS/HF exposure period in adulthood. (b) Body weight at the beginning and subsequent three weeks of HS/HF dietary options. (c) Metabolic efficiency as gram body weight increase per kcal consumed across the HS/HF dietary challenge. (d) Weekly consumption of standard chow (solid lines) and HS/HF options (dashed lines). N = 5–7; ±SEM, * p<.05.</p