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The effects of aging on non-associative learning in the nematode caenorhabditis elegans Beck, Christine Daily O'Brien


With the advantages of simplicity and a we11-understood anatomy, development and genome, C.elegans may be an effective model of the role of the genome in the effects of aging on learning and memory. The purpose of this thesis is to begin this research by describing the effects of aging in C.elegans on a simple form of learning, habituation,in the tap withdrawal reflex. First,the effects of aging on the spontaneous locomotor behavior and simple reflexive behavior of C.elegans were examined. Worms were tested at 4, 7 and 12 days post-hatching. The average life-span of worms raised in the conditions of this laboratory (solid medium, 21ºC) was 14 to 16 days. The amount of spontaneous activity did not change with age, but the nature of that activity did change. Worms moved more slowly and both spontaneous and reflexive reversals decreased in magnitude at day 12. Worms at all ages exhibited graded responses to taps of different intensities. The effects of aging on habituation and dishabituation were then examined. There appeared to be a dissociation of response frequency and magnitude: all ages tested (4, 7 and 12 days post-hatching) showed similar changes in magnitude of reversals due to habituation and dishabituation. However at day 7 the proportion of worms reversing did not decrease during habituation training as it did at the other ages (days 4 and 12) tested. There was also an age-related change in the recovery from habituation; day 12 worms did not recover within 30 min of the last habituation stimulus, unlike worms tested at day 4 and 7 which recovered back to baseline levels by 30 min. Finally the effects of tail-touch habituation training on inhibition of the reversal response to tap was examined at the three test ages. At all ages tail-touch habituation training decreased the inhibition of reversal to tap by tail-touch. Clearly, even day 12 worms are capable of habituation independent of fatigue effects. The age-related changes seen may be produced by From these experiments it is clear that although the behavior of C. elegans does change with age, aged worms are capable of the simple form of learning, habituation. Further behavioral tests with normal and mutant worms may help elucidate the nature of the age-related changes in learning and memory in C.elegans and the genetic mechanisms which underlie them.

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