PREFERENCE CONDITIONING ALTERS TASTE RESPONSES IN THE NUCLEUS OF THE SOLITARY TRACT OF THE RAT

Aversive conditioning has an impact on the neural signal for the gusta tory conditioned stimulus (CS). Here, we determined whether the code i s also affected by preference conditioning. We paired the taste of MgC l2 (CS+) with intragastric nutrients in some rats (MG), and citric aci d (CS+) with nutrients in others (CI). A control group (Control) exper ienced both tastants without nutrients. Preferences (>90%) developed f or each CS+. We recorded responses to 16 taste stimuli in the nucleus of the solitary tract. Responsiveness of acid-oriented neurons to MgCl 2 in MG rats was lower than in Controls, and its profile was more dist inct from those of acidic and bitter stimuli. Total activity to citric acid was unchanged in CI rats. However its temporal profile showed a decreased phasic component, making citric acid temporally distinct fro m nonsugars. Therefore, the responses to both CS+ were modified, each in its own manner, to be more distinct from those of aversive stimuli. The effects of preference conditioning, however, were weaker than tho se of aversive conditioning.