Influences of amygdala and medial forebrain bundle on self-stimulation in the septum

Abstract

Effects of lesions and electrical stimulation in the amygdala or medial forebrain bundle on rewarding stimulation of the septum were investigated. Rats were trained to press a bar for septal stimulation. Some rats learned to self-stimulate (pressers) and others did not (nonpressers). Following production of bilateral lesions in the amygdala (AMY), both pressers and nonpressers showed increased rates of self-stimulation. Bilateral lesions in the anterior medial forebrain bundle (MFB) resulted in no significant change. Rats with no lesions were used as controls. Other rats received 3 sets of chronic electrodes, one set each in the septum, AMY, and anterior MFB. After training for septal self-stimulation, the rats received noncontingent electrical stimulation in AMY during septal self-stimulation sessions. The AMY stimulation decreased bar pressing rates. Subsequently the rats received stimulation in MFB during septal self-stimulation sessions. Half of the group showed increased bar-pressing rates during MFB stimulation while the other half showed a long-lasting decrease in response rates. The results suggest that in terms of septal self-stimulation AMY has an inhibitory influence on the septum, and that MFB may carry 2 modulatory systems that influence the septum, one being inhibitory and the other facilitatory.