REDUCED COGNITIVE DYSFUNCTIONS IN RATS WHEN THE TEMPORAL-ENTORHINAL CORTICES AND HIPPOCAMPAL REGION ARE DENERVATED SIMULTANEOUSLY

Transections of the fiber connections between the temporal cortex (TC) and the lateral entorhinal cortex (LEG) result in decreased ability t o retain visual information, whereas transections of the hippocampal p erforant path (PP) fibers cause decreased ability to acquire visual in formation. It was assumed that a combination of these two lesion types would mimic the pathology of some neurogenerative disorders and produ ce severe impairment in both acquiring and retaining new information. Surprisingly, TC/LEC + PP lesions did not cause any effects in a visua l discrimination task, whereas separate TC/LEC or PP lesions affected behavior as described above (Experiment 1). In Experiment 2, a novelty test was employed to validate further the lack of effects seen to fol low TC/LEC + PP lesions. Initially, an effect of TC/LEC + PP lesions a ppeared, but vanished as testing proceeded. Separate TC/LEC or PP lesi ons resulted in reduced preference for novelty throughout all test ses sions. Experiment 3 was undertaken to highlight potential neurochemica l mechanisms involved in the compensatory processes apparently initiat ed by the combined lesions. Relatively enhanced cholinergic activity i n the hippocampus was found in TC/LEC + PP animals, whereas glutamater gic measures seemed to be unresponsive. The results are discussed in t erms of possible compensatory mechanisms underlying the recovery of fu nction seen in rats bearing TC/LEC + PP transections.