Effects of NMDA lesions of the medial basal forebrain on LH and VTA self-stimulation

Rewarding stimulation of the medial forebrain bundle (MFB) increases Fos-li ke immunoreactivity in many brain areas, including an ipsilateral, basal fo rebrain region extending from the medial preoptic area (MPO) to the lateral preoptic area, and substantia innominata. Excitotoxic lesions of the later al portion of this region have been found to produce large sustained or tra nsient increases in the number of pulses required to maintain half-maximal lever-pressing (required number of pulses) for MFB stimulation. In the pres ent study, changes in self-stimulation of the lateral hypothalamus and vent ral tegmental area were assessed following excitotoxic lesions of more medi al structures, including the MPO and bed nucleus of the stria terminalis. I ncreases in the required number of pulses (up to 0.16 log(10) units) were s een in only 2 of 10 subjects, In two other rats, the reward effectiveness o f the stimulation was moderately increased after the lesion as manifested i n decreases of up to 0.14 log(10) units in the required number. No apprecia ble change from baseline was seen in the remaining six subjects. The simple st interpretation of these results is that neurons with cell bodies in the medial portion of the basal forebrain may make a smaller contribution to th e rewarding effect of MFB stimulation than neurons in the lateral portion. (C) 1999 Elsevier Science Inc.