Lesions of connections of the medial prefrontal cortex in rats: differential effects on self-stimulation and spontaneous motor activity.

The effects of lesions of the mediodorsal nucleus of the thalamus (MD) and the nucleus caudate putamen (CP) on self-stimulation (SS) of the medial prefrontal cortex (MPC) were investigated. After bilateral electrolytic lesions of the MD or the anteromedial segment of the CP, SS rate and spontaneous motor activity (SMA) were measured. Both MD and CP lesions induced a significant decrease in SS. After 8 days post-lesion, SS rate recovered to pre-lesion levels. SMA did not change significantly after MD lesion. However, SMA showed a significant decrease the 1st and the 5th days after lesioning the CP. The results suggest that the MD and possibly the CP are associated with SS, although it appears that they do not have an essential but rather a modulatory role. The recovery of SS occurs within a few days, presumably due to the compensatory effect of other pathways and structures. The results are also discussed in relation to the effect found after electrolytic lesion of ventrotegmental area and locus coeruleus.