Electrolytic lesions of the medial septal region leads to an unusual neuronal reorganization in which peripheral sympathetic fibers, originating from the superior cervical ganglia, grow into the cholinergically denervated areas of the hippocampus. Since these lesions disrupt cells and fibers of passage which are non-cholinergic, there has been a debate whether Hippocampal Sympathetic Ingrowth is due only to cholinergic denervation of the hippocampus. Using the intraseptal administration of 192-IgG-Saporin, a specific cholinergic neurotoxin, we have found that hippocampal sympathetic ingrowth occurs in the cholinergically denervated hippocampus at 4, 8 and 12 weeks post Saporin injection. These results clearly suggest that hippocampal sympathetic ingrowth is due to the specific loss of the cholinergic projection from the medial septum.
