Hippocampal sympathetic ingrowth occurs following 192-IgG-saporin administration

Electrolytic lesions of the medial septal region leads to an unusual neuron al reorganization in which peripheral sympathetic fibers, originating from the superior cervical ganglia, grow into the cholinergically denervated are as of the hippocampus. Since these lesions disrupt cells and fibers of pass age which are non-cholinergic, there has been a debate whether Hippocampal Sympathetic Ingrowth is due only to cholinergic denervation of the hippocam pus. Using the intraseptal administration of 192-IgG-Saporin, a specific ch olinergic neurotoxin, we have found that hippocampal sympathetic ingrowth o ccurs in the cholinergically denervated hippocampus at 4, 8 and 12 weeks po st Saporin injection. These results clearly suggest that hippocampal sympat hetic ingrowth is due to the specific loss of the cholinergic projection fr om the medial septum.