Brain stem self-stimulation attenuated by lesions of medial forebrain bundle but not by lesions of locus coeruleus or the caudal ventral norepinephrine bundle

Midbrain tegmental intracranial self-stimulation (ICSS) was not attenuated by ipsilateral or bilateral locus coeruleus lesions. Certain of these lesions were followed by histochemical confirmation that the majority of locus coeruleus neurons was destroyed, and biochemical evidence that over 80% of the cortical norepinephrine was depleted. To test the possibility that the surviving ICSS was due to stimulation of another norepinephrine system, histochemically verified ipsilateral or bilateral lesions of the ventral norepinephrine bundle were administered to a second group of midbrain tegmental ICSS animals. These lesions resulted in marked loss of body weight, but had no effect on ICSS. In a third experiment, lesions were made in the medial forebrain bundle (MFB) ipsilateral to midbrain tegmental ICSS electrodes. These lesions resulted in attenuation of ICSS which was directly proportional to the extent of MFB damage. On the basis of these data alone, however, it was not possible to identify the critical fibers supporting ICSS. It was concluded that the locus coeruleus does not play a necessary role in midbrain tegmental ICSS.