European Journal of Neuroscience, Vol. 30, pp. 289–298, 2009
Dopamine D1-like receptor antagonism in amygdala impairs the acquisition of glucose-conditioned ﬂavor preference in rats
Khalid Touzani,1 Richard J. Bodnar2,4 and Anthony Sclafani1,3,4
Department of Psychology, BrooklynCollege, City University of New York, 2900 Bedford Avenue, Brooklyn, NY 11210, USA Department of Psychology, Queens College, City University of New York, 65-30 Kissena Blvd., Flushing, NY 11367, USA 3 Cognition, Brain and Behavior Subprogram and 4 Neuropsychology Doctoral Subprogram, Graduate Center, City University of New York, 2900 Bedford Avenue, Brooklyn, NY 11210, USA Keywords: carbohydrate,conditioning, forebrain, learning, SCH23390
This study examined the role of dopamine within the amygdala (AMY) in ﬂavor preference learning induced by post-oral glucose. In Experiment 1, rats were trained with a ﬂavor [conditioned stimulus (CS+)] paired with intragastric (IG) infusions of 8% glucose and a different ﬂavor (CS)) paired with IG water infusions. The CS+ preference wasevaluated in two-bottle tests following bilateral injection of the dopamine D1-like receptor antagonist, SCH23390 (SCH), into the AMY at total doses of 0, 12, 24 and 48 nmol. SCH produced dose-dependent reductions in CS+ intake but did not block the CS+ preference except at the two highest doses, which also greatly suppressed the CS intakes. In Experiment 2, new rats were injected daily in the AMY witheither saline or SCH (12 nmol), prior to training sessions with CS+ ⁄ IG glucose and CS) ⁄ IG water. In the two-bottle tests, SCH rats, unlike the control rats, failed to prefer the CS+ (55 vs. 81%). In Experiments 3 and 4, new rats were trained as in Experiment 2, except that brain injections were in the basolateral and central nuclei of the AMY, respectively. SCH rats learned to prefer the CS+to the CS), although their preference was weaker than that displayed by the control rats (Experiment 3: 59 vs. 80%; Experiment 4: 73 vs. 88%). These results show an essential role for D1-like receptor activation in the AMY in the acquisition of ﬂavor preference learning induced by the post-oral reinforcing properties of glucose. A distributed network mediating ﬂavor–nutrient incentive learning isdiscussed.
Learning plays an important role in the development of ﬂavor preferences and food selection in omnivores. There is extensive evidence from laboratory research that animals learn to prefer the ﬂavor of foods and ﬂuids that provide positive nutritional consequences. This is documented by studies showing that animals acquire strong and long-lasting preferences for ﬂavoredfoods and ﬂuids that either contain a nutrient or are paired with intragastric (IG) infusions of nutrients (Capaldi, 1996; Sclafani, 1999). Flavor preference conditioning, like ﬂavor aversion conditioning, is a form of classical conditioning in which a cue ﬂavor [conditioned stimulus (CS)] is associated with the oral and ⁄ or post-oral properties of a nutrient (unconditioned stimulus). There aretwo types of preference conditioning. In ﬂavor–ﬂavor conditioning, a preference develops for a cue ﬂavor that is paired with the preferred ﬂavor of a nutrient (e.g. sweet taste of sugar). In ﬂavor–nutrient conditioning (or post-oral consequence learning), a preference develops for a cue ﬂavor paired with the post-oral effects of a nutrient. The most common paradigm used to study conditioned ﬂavorpreferences is to pair one ﬂavor (the CS+) with the nutrient unconditioned stimulus and a different ﬂavor (the CS)) with water on alternate days and then assess preference learning by presenting the CS+ and CS) ﬂavors in a twobottle choice test. Flavor–nutrient learning, which is the subject of the present study, requires the neural integration of orosensory and viscerosensory information and the...