Figure 4.

Structural plasticity following perforant path lesions. Left panels (modified from Steward and Messenheimer, 1978): Mature cat hippocampus histochemically stained for acetyl cholinesterase (AChE) activity at 60 days post-lesion. The density of AChE is dramatically increased in the denervated outer molecular layer (A,B, top right, dark band), consistent with sprouting of the cholinergic septohippocampal axons following lesion. Also note that the thickness of the inner molecular layer is increased due to sprouting of the glutamatergic commissural/associational fibers (C,D, bottom right, double arrows). Right panels (modified from Matthews et al., 1976b): Ultrastructural evidence for synaptic regeneration in the denervated zone at 60 days post-lesion in the mature rat. Serial sections through a complex spine (a,b,c,d, green) show synaptic contacts with a degenerating bouton “D” as well as with a regenerating axon “^*.” a = spine apparatus.