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 l esions of the parabrachial nucleus (PBN) influence the rewarding effec t of medial forebrain bundle (MFB) stimulation. In 10 rats, stimulatio n electrodes were aimed at the lateral hypothalamus and/or ventral teg mental area and a lesioning electrode aimed at the PBN. Rate-frequency curves were collected at each of three stimulation currents at each e lectrode, before and after lesioning. Four rats showed virtually no ch ange in the frequency required to sustain half-maximal performance fol lowing lesioning, and two showed some postlesion decreases. Only two r ats 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, bu t spared the PBN. Thus, the reward effectiveness of MFB stimulation do es not appear to be altered substantially following PBN lesions but ma y decrease following damage to the neighboring pedunculopontine region .