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Critical and sensitive periods for reversing the effects of mechanosensory deprivation on development in Caenorhabditis elegans Rai, Susan


Sensory experience at different stages during development can alter structures and functions of the nervous system in different ways suggesting that the timing of the occurring experience is critical. In these studies, I used the nematode Caenorhabditis elegans as a model organism to demonstrate the effects of deprivation of mechanosensory experience on behaviour and development; I identified critical and sensitive periods for reversing the detrimental effects of deprivation by introducing mechanosensory experience during development. Earlier studies found that worms reared in isolation, without the mechanosensory stimulation from conspecifics, respond significantly less to a mechanical tap stimulus and are significantly shorter in body length than worms raised in age-matched colonies. An examination of elements of the synapse between the mechanosensory neurons and the command interneurons showed that in isolate-raised worms, this synapse was weaker (fewer post-synaptic glutamate receptors and fewer pre synaptic vesicles) than the synapses of worms raised in a colony condition. In this thesis, brief mechanical stimulation at any time during development reversed the effects of isolation on the behavioral response to tap and glutamate receptor expression suggesting there is no critical period for these two measures. In addition low levels of stimulation early in development (at the beginning of larval stage LI), but not later, rescued presynaptic vesicular marker pmec-7::SNB-1::GFP vesicle expression suggesting there is a period during which brief mechanosensory stimulation can reverse the effects of isolation very easily. Larger amounts of mechanosensory stimulation resulting from rearing worms in isolation and transferring them to a colony at the start of LI, L2 or L3 rescued the effects of isolation on body growth suggesting there is a critical period to reverse the effects of isolation on worm length that ends during L 3 . These results suggest that development of different systems follow different rules/time courses. Rescuing one aspect of development will not necessarily reverse the total effects of isolation on the developing organism. Different aspects of development will require varying amounts of stimuli at varying time points in development, which would all need to be taken into account to fully rescue the effects of deprivation on the organism.

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