Degenerative patterns following denervation of temporal structures in a rat model of mnemonic dysfunction

The temporal region makes up an important substrate for mnemonic function in both humans and animals. Rats with transection of fibers connecting the temporal and entorhinal cortices display impaired visual memory. The use of hematoxylin and eosin (HE) or Nissl staining has proved insufficient for characterization of the degenerative events that take place after the lesions, and in the present study we therefore applied Fluoro-Jade dye, and zinc autometallography (AMG) in order to describe degenerative changes with AMG. We found that 14 days survival resulted in a much more severe degeneration of cell bodies in the temporal, perirhinal, entorhinal, and postrhinal cortices than was seen after 8 days survival. Corresponding degeneration of cell bodies was optimally observed 7 days following surgery with the Fluoro-Jade staining. HE staining did not reveal degenerative changes with survival times of 8 or 14 days. A substantial increase in AMG staining for zinc ions after lesion revealed an increase in zinc enriched neuronal terminals in the temporal areas and was interpreted as sprouting from local zinc enriched neuronal projections. The present data are related to the memory deficits observed in rats with similar denervations in previous studies.