Brain stimulation reward and dopamine terminal fields. II. Septal and cortical projections

The boundaries and relative sensitivities of the substrates of septal and cortical brain stimulation reward were mapped in relation to the dopamine terminal fields in these regions using a dorsal-ventral moveable electrode. Brain stimulation was rewarding at all levels of the posterior lateral septum and not just in the region of dopamine terminal innervation. Reward thresholds, ease of training, maximum response rates and stability of responding were all unrelated to the proximity of the stimulating electrode to the band of dopamine terminals revealed by glyoxylic acid-induced dopamine fluorescence. Stimulation was also rewarding in the anterior lateral septum; the best sites were in the ventral portions of this region although dopamine terminal fluorescence was uniform throughout. Thus the anatomy of the brain stimulation reward substrate of the lateral septal nucleus does not bear a special relation to the anatomy of dopamine terminals within this region. Stimulation was also rewarding in each of the dopamine terminal fields of the cerebral cortex. The best self-stimulation was obtained with electrodes in the medial frontal cortex; sulcal frontal cortex was next best, entorhinal cortex was next, and pyriform cortex, though reliably positive, supported the weakest self-stimulation. Variations in self-stimulation threshold were seen as electrodes were moved through homogeneous regions of dopamine terminal density in some regions, while stable thresholds were associated with movements through areas of varying dopamine terminal density in others; thus, again, there was no special relation between goodness of self-stimulation and density of dopaminergic innervation. These data suggest that rewarding brain stimulation in these regions is not due to direct activation of either the dopaminergic terminals or the cells that they innervate.