Medial prefrontal serotonin in the rat is involved in goal-directed behaviour when affect guides decision making

RATIONALE: Across species, serotonin (5-HT) depletion in the prefrontal cortex (PFC) has been shown to cause impaired performance on tests of cognitive flexibility and the processing of affective information (e.g. information with an ‘emotional’ content). While recent work has explored the specific role of the orbital PFC herein, the role of the medial PFC remains unclear. OBJECTIVES: The aim of our current experiments was to study the role of medial PFC 5-HT in both the processing of affective information and reversal learning across stimulus modalities. MATERIALS AND METHODS: To this end, we selectively destroyed 5-HT terminals in the medial PFC of male Wistar rats by means of local infusion of the toxin 5,7-dihydroxytryptamine. Both control and lesioned animals were tested in two reversal learning paradigms with either spatial or odour cues and an affective switch from non-preferred to preferred food rewards. RESULTS: Our results indicate that a pellet switch during reversal learning impaired performance in control animals but not in lesioned animals, independent of the stimulus modality. CONCLUSION: These results indicate that lesioned animals are not guided in their behaviour by the affective value of the reward like intact animals and thus that medial prefrontal 5-HT is needed for affective processing in goal-directed behaviour.