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Chemosensory context conditioning in Caenorhabditis elegans Lau, Hsien Lee

Abstract

These studies were designed to investigate how environmental cues are associated during a non-associative learning process by studying chemosensory context conditioning for habituation in the nematode Caenorhabditis elegans. In chemosensory context conditioning for habituation animals that are trained and tested in the presence of either a taste or smell context cue show greater retention of habituation to tap stimuli when compared to animals trained and tested in different environments. This thesis is based on the work of Rankin (2000), in which taste (sodium acetate) context conditioning of habituation, extinction and latent inhibition of the cue were demonstrated. Here, I have shown context conditioning for an olfactory chemosensory cue (diacetyl) and dissociated the taste and smell pathways for this form of learning. odr-7 worms, with non-functional AWA olfactory chemosensory neuron (that detects diacetyl), showed short-term context conditioning to the taste but not to smell; the reverse was true for osm-3 worms with non-functional taste chemosensory neurons. This dissociation allows me to distinguish learning genes from genes involved in the detection of taste or smell. I also demonstrated long-term associative memory (24h) for context conditioning; context conditioning did not enhance normal long-term habituation, however, it produced memory in a training procedure that normally does not produce memory. My results showed that glr-1 (an AMPA-type ionotropic glutamate receptor subunit) and nmr-1 (an NMDA-type ionotropic glutamate receptor subunit) mutant worms did not show either short- or long-term context conditioning. To identify one site of plasticity, I showed that NMR-1 in the RIM interneurons was critical to produce short-term olfactory context conditioning. These studies lay the foundation to elucidate the cellular mechanisms of non-associative and associative learning for both short- and long-term memory, and may provide insights into how interneurons integrate information from multiple sensory systems.

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