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The effects of spatial learning on adult neurogenesis in the dentate gyrus Epp, Jonathan Richard

Abstract

In the hippocampus, unlike most areas of the mammalian brain, new neurons are continuously produced throughout life. Studies have demonstrated that spatial learning, a process dependent on the hippocampus, regulates neurogenesis (i.e. the survival of new neurons) in the hippocampus. Studies have found that spatial learning either causes an increase, no change, or a decrease in neurogenesis. It was the goal of this thesis to determine under what conditions neurogenesis is increased, decreased or unaffected by spatial learning using the Morris water task. Experiment 1 demonstrated that there was a critical period in the developmental of new neurons in adult rats, at 6-10 days old, during which spatial learning can increase neurogenesis. Experiment 2 showed that spatial learning at a later time point (days 11-15) decreased cell survival but this decrease occurred gradually and as a result may only be seen if several days are waited after training prior to examining levels of neurogenesis. Experiment 3 demonstrated that although neurogenesis may be increased if spatial training occurs when the new neurons are 6-10 days old in adult rats, this effect can be eliminated or reversed by increasing the difficulty of the spatial task. Finally, in Experiment 4 I showed that the effect of spatial learning is affected by the strain of rats used, possibly due to differences in the rate of maturation of new neurons. Sixteen day old bromodeoxyuridine-labeled cells were increased in both Sprague-Dawley and Long-Evans rats following spatial learning but doublecortin-labeling (which labels a broader age of new neurons) is increased only in Sprague-Dawley rats after spatial learning. Thus, numerous methodological factors must be considered when examining the effects of spatial learning on neurogenesis. There are likely more factors (i.e., stress, age, sex, etc.) that interact with spatial learning and neurogenesis than described here however these studies have clarified many prior conflicting studies.

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