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.