Lesions of midline midbrain structures leave medial forebrain bundle self-stimulation intact

Previous work with psychophysically-based collision methods and pharmacolog ical manipulation suggests a role in medial forebrain bundle (MFB) self-sti mulation for neurons lying along the midline between the cerebral hemispher es, in the mid- and/or hindbrain. Also, recently-proposed models of the ana tomical substrate for medial forebrain bundle stimulation reward suggest th at at least part of the directly-activated axons of this substrate arise fr om mid- and/or hindbrain somata, bifurcate, and send bilateral projections to the MFB of each hemisphere. Branches of these axons are thought to cross the midline at some point near the ventral tegmental area. This study exam ines the effects on MFB stimulation reward of lesioning midbrain structures that lie along the midline between hemispheres. In 13 rats, lesions of the median raphe, the decussation of the superior cerebellar peduncle, or the interpeduncular nucleus were all ineffective in altering the stimulation fr equency required to maintain half-maximal levels of operant responding for stimulation reward. These results are discussed in terms of implications fo r recent models of the anatomical substrate for brain stimulation reward. ( C) 1999 Elsevier Science B.V. All rights reserved.