Self-stimulation of the MFB following parabrachial lesions.

It has been reported previously that the parabrachial region supports robust self-stimulation. In the present study, we determined whether lesions of the parabrachial nucleus (PBN) influence the rewarding effect of medial forebrain bundle (MFB) stimulation. In 10 rats, stimulation electrodes were aimed at the lateral hypothalamus and/or ventral tegmental area and a lesioning electrode aimed at the PBN. Rate-frequency curves were collected at each of three stimulation currents at each electrode, before and after lesioning. Four rats showed virtually no change in the frequency required to sustain half-maximal performance following lesioning, and two showed some postlesion decreases. Only two rats showed substantial postlesion increases in required frequency; the lesions in these subjects damaged the region ventral to the superior cerebellar peduncle, just caudal to the decussation of the peduncle, but spared the PBN. Thus, the reward effectiveness of MFB stimulation does not appear to be altered substantially following PBN lesions but may decrease following damage to the neighboring pedunculopontine region.