SPATIAL AND DISCRIMINATION-LEARNING IN RODENTS INFECTED WITH THE NEMATODE STRONGYLOIDES-RATTI

Recent work has shown that mice with subclinical parasitic infections suffer impaired spatial learning and memory, as assayed in an open-fie ld water maze. Although the mechanism underlying this effect is not cl ear, the phenomenon has been reported following infection with both a protozoan parasite (Eimeria vermiformis) and a gastrointestinal nemato de (Heligmosomoides polygyrus). In a variety of experiments, we examin ed the effects of a different gastrointestinal nematode, Strongyloides ratti, on the ability of rats and mice to learn a spatial or a discri mination task. Animals were tested at various stages post-infection, w ith different levels of infection, using different lines of S. ratti a nd with varying experimental protocols. All animals learned the tasks, but we found no evidence of an effect of S. ratti infection on learni ng or memory. Even rats infected with approximately 5000 S. ratti larv ae, a dose which has an impact on rat body size, showed no deficit in learning ability. Various reasons for the conflict between our results and those previously reported for E. vermiformis and H. polygyrus are discussed. Our results show that impaired learning and memory followi ng parasitic infection is not a ubiquitous or at least easily replicat ed phenomenon.