HALL, DJ*; PAUL, DH*; MARX, RM; Univ. of Victoria, BC; Univ. of Victoria, BC; Univ. of Victoria, BC: Integration of proprioceptive feedback into central motor circuitry in the sand crab, Emerita analoga (Anomura Hippidae).

We are interested in how motor systems integrate sensory information and how such information modifies an animal’s behavior. In the sand crab, Emerita analoga, two motor programs for uropod beating (‘swimming’ and ‘treading water’) arise from a difference in timing of the power stroke. The power stroke phase in treading water is set by proprioceptive feedback from four ‘giant’ non-spiking stretch receptors (NSRs; Paul, 1976). The distinct behavioral alteration following bilateral ablation of the NSRs demonstrates the importance of their proprioceptive feedback. The mechanism of the feedback is unknown. The properties of E. analoga’s NSRs (Paul & Bruner, 1999) make them a clear entry point for investigating central motor rhythms of composite origin. Three morphologically distinct regions comprise the central portion of these unipolar cells: the proximal end of the large afferent process, a tapering segment, and the much smaller processes arising from both the large and tapering sections of the afferent process. These terminate in at least three regions of the ganglion, raising the possibility of regional differences in synaptic action. Furthermore, there appear to be morphological differences between the projections. We have located input, as well as output, synapses ultrastructurally and continue to investigate their distribution. Modeling shows that the cable properties arising from the NSR morphology delimit the possible function of any synaptic inputs. Localization and identification of input and output synapses will facililate future multi-unit recordings and computational analysis of the neural circuitry underlying the two motor programs. (Supported by NSERC grant # 008183)