ENCODING AND SELECTIVE ACTIVATION OF METABOLIC MEMORIES IN THE RAT

Experiment 1 used Pavlovian conditioning procedures to show that rats formed distinct memorial representations of 2 (peanut oil and sucrose pellets) unconditioned stimuli (USs) that could be activated by 2 diff erent conditioned stimuli (CSs). After training in Experiment 2, rats injected with the lipid antimetabolite Na-2-mercaptoacetate (MA) respo nded more to the CS for oil than to the CS for sucrose. This pattern w as not shown by rats that received isotonic saline or systemic 2-deoxy -d-glucose (a glucose antimetabolite). By contrast, intracerebroventri cular infusion of the glucose antimetabolite 5-thioglucose selectively promoted responding to the CS for sucrose (Experiment 4). Thus, lipop rivic and glucoprivic treatments selectively promoted the activation o f the memories of fat and carbohydrate USs, respectively. In Experimen t 3, the capacity of MA to augment responding to a CS for oil was abol ished for rats that received subdiaphragmatic vagal deafferentation. T his indicates that the capacity of lipoprivic signals to selectively a ctivate the representations of fat USs may depend on vagal afferent fi bers.