Habituation is a fundamental form of non-associative learning and memory that allows organisms to ignore irrelevant, repeated stimulation. Previous studies have shown that C. elegans exhibit both short-term and long-term habituation to a non-localized mechanical stimulus, or tap. Following repeated tap stimulation, there is a decrease in both reversal rate (to approximately 40%) and reversal distance, and a corresponding increase in accelerations. Previously we showed that a D1-like dopamine receptor DOP-1, and dopamine deficient mutant,
cat-2 habituated faster than wildtype animals and that this effect may be acting at the level of the sensory neurons (Sanyal et al, 2004). To further investigate the mechanism underlying this modulation of behavioral plasticity, we have investigated the habituation phenotypes of candidate signal transduction mutants. Dopamine receptors are in the superfamily of G-protein coupled receptors, so it is likely that the DOP-1 receptor is signaling through G proteins. Preliminary results indicate that Gq-alpha (
egl-30))is the effector of DOP-1 in tap habituation, as
egl-30 loss of function mutants show a precocious habituation phenotype similar to
dop-1 mutants. In contrast, Go-alpha (
goa-1) mutants show resistance to habituation, suggesting that Go may participate in an antagonistic pathway to
dop-1. We are currently using the genetically encoded FRET based calcium sensor, cameleon to examine the effects of
dop-1,
goa-1, and
egl-30 on the mechanosensory response of the touch receptor neurons ALM, PLM, and AVM. We have also begun using enhanced genetically-encoded calcium sensors to image from the downstream command interneurons. In particular, by imaging from the command interneurons, we will determine how habituation training affects interneuron responses to touch neuron stimulation as well as stimulation of other presynaptic inputs such as the polymodal ASH nociceptors. This will provide insight into how different sensory modalities are integrated and processed by the C. elegans nervous system.