STRAIGHT ALLEY ACQUISITION AND EXTINCTION AND OPEN-FIELD ACTIVITY FOLLOWING DISCRETE ELECTROLYTIC LESIONS OF THE MESENCEPHALIC RAPHE NUCLEI

Open field behavior and the acquisition and extinction of a food-rewarded straight alley task were examined in rats with discrete electrolytic lesions of the midbrain raphe nuclei. Increased open field activity was seen following lesions of either the median or dorsal nucleus of the raphe, although the effect of median lesions was much more pronounced. Acquisition and extinction of a runway task were impaired following lesions of the median, but not dorsal, nucleus when trials were separated by 8 min. Animals with combined lesions of the dorsal and median raphe were behaviorally indistinguishable from those subjects with median raphe lesions alone. In a second experiment, it was determined that the acquisition deficit could be eliminated by a decrease in the intertrial interval, suggesting that the original deficit was not due to a motor impairment following median raphe lesions. Although other investigators have reported raphe involvement in aversively motivated behaviors the current study provides the first demonstration that the median raphe is also involved in the performance of tasks which are appetitively motivated. Additionally, we provide the first evidence that deficits in food-rewarded behaviors similar to those seen following damage to certain limbic structures can be produced by lesions within the midbrain. © 1979 Academic Press, Inc.