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LEARNED MECHANISMS UNDERLYING INTEROCEPTIVE CONTROL OF ENERGY REGULATION IN MALE RATS
Previous research shows that rats have the ability to discriminate between cues arising of different levels of food deprivation. However, it is unclear what associative mechanisms underlie this discriminative control and whether or not a similar mechanism underlies the ability to maintain energy homeostasis. The current study sought to clarify the associative mechanism underlying the utilization of state cues, and how this mechanism may become disrupted following consumption of Western diet (WD). In Experiment 1, male rats were pretrained to establish internal cues as either a (a) conditioned modulators, (b) simple excitors, or (c) irrelevant cues in the control of appetitive behavior. Rats were all subsequently trained in a typical feature negative paradigm where both an internal satiety cue and external visual cue predicted when an ambiguous target cue would not be reinforced (i.e. either the internal or external cue could be learned as a negative occasion setter to discriminate between rewarded and nonrewarded sessions). If the mechanisms underlying the use of internal cues in the control of appetite behavior were similar to those underlying the use of typical, external negative occasion setters, learning about the external negative occasion setters should be overshadowed by learning about internal cues. We expected to see only groups that had internal cues pretrained as conditioned modulators to show this overshadowing of the light; instead, we found that satiety cues overshadowed control by external modulators consistently, independent of pretraining history. This complete overshadowing of external modulators by internal cues indicates a similar mechanism underlying their respective roles in appetitive behavior. In Experiment 2, male rats were trained to use either an internal deprivation state or an external visual cue as a negative occasion setter in a typical feature negative paradigm. Once rats discriminated, half of each group was put on WD for 24d. The effect of diet on the ability of rats to use internal or external cues as negative feature stimulus was assessed in a series of probe tests. Findings indicate that internal, relative to external, cues were better able to inhibit responding to an ambiguous cue on nonreinforced trials in intact animals. Despite these baseline differences, internal and external cues were both impaired in a similar manner relative to chow-fed controls. The observed similarities provide evidence that WD-induced impairments in both internal and external control of appetitive behavior may be a result of similar underlying mechanisms. Taken together, Experiment 1 and Experiment 2 provide evidence for an associative mechanism similar to that of a typical negative occasion setter underlying the role of internal cues in the control of energy regulation.