Abstract
Dopamine receptor activation in the nucleus accumbens (NAc) promotes vigorous environmentally-cued food-seeking in hungry rats. Rats fed ad libitum, however, respond to fewer food-predictive cues, particularly when the value of food reward is low. Here, we investigated whether this difference could be due to differences in the degree of dopamine receptor activation in the NAc. First, we observed that although rats given ad libitum access to chow in their home cages approached a food receptacle in response to reward-predictive cues, the number of such approaches declined as animals accumulated food rewards. Intriguingly, cued approach to food occurred in clusters, with several cued responses followed by successive non-responses. This pattern suggested that behavior was dictated by transitions between two states, responsive and non-responsive. Injection of D1 or D2 dopamine receptor agonists into the NAc dose-dependently increased cue responding by promoting transitions to the responsive state and by preventing transitions to the non-responsive state. In contrast, antagonists of either D1 or D2 receptors promoted long bouts of non-responding by inducing transitions to the non-responsive state and by preventing transitions to the responsive state. Moreover, locomotor behavior during the inter-trial interval was correlated with the responsive state, and was also increased by dopamine receptor agonists. These results suggest that activation of NAc dopamine receptors plays an important role in regulating the probability of approach to food under conditions of normative satiety.
Highlights
For a hungry animal, the decision to respond to a food-predictive cue is a trivial one
From the first day that sucrose reward concentration was reduced from 10% to 3%, a pronounced run-down of cued responses was observed across the 2 h of testing (Figures 1B,C, gray lines)
The low dopamine-dependent response probability in ad libitumfed animals observed here is consistent with many recent studies of regulation of dopamine neurons by messengers, such as cholecystokinin, orexin, ghrelin, leptin, insulin and glucagon-like peptide 1, that signal the body’s nutrient status detected via various mechanisms
Summary
The decision to respond to a food-predictive cue is a trivial one. Dopamine Promotes Cued Approach a rat’s starting position varies from trial to trial Under these conditions, injection of either D1 or D2 dopamine receptor antagonists into the NAc core reduces the proportion of cues to which animals respond by increasing the latency to initiate approach (Nicola, 2010). Injection of either D1 or D2 dopamine receptor antagonists into the NAc core reduces the proportion of cues to which animals respond by increasing the latency to initiate approach (Nicola, 2010) These effects result from a reduction in the magnitude and prevalence of dopamine-dependent cueevoked excitations (du Hoffmann and Nicola, 2014). There may be less activation of NAc dopamine receptors under conditions of relative satiety, leading to a lower probability of responding to food-associated cues
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