INTEGRATION OF MECHANOSENSORY STIMULI IN CAENORHABDITIS-ELEGANS

The tap withdrawal reflex in Caenorhabditis elegans demonstrates vario us forms of nonassociative learning. A first step in determining the c ellular mechanisms of this learning is to identify the neuronal circui try that underlies this reflex. Studies by Chalfie et al. (1985) have defined the touch-circuit that mediates the response to a stimulus rel ated to tap-a light touch. We used the touch circuit as a starting poi nt in the identification of the tap withdrawal circuitry. Here we repo rt the effects of lesions of identified neurons on the tap withdrawal reflex. Ablations of the sensory neurons and interneurons of the touch circuit produce effects on the tap withdrawal response that generally confirm and expand upon the roles of these cells in mechanosensory in tegration as proposed by Chalfie et al, (1985). However, no role for t he LUA interneurons could be identified in the production of the tap w ithdrawal response. Furthermore, the effects of ablating some neurons outside the touch circuit suggest roles for two of these cells in the integration of the tap withdrawal response. Ablation of either the mid line neuron DVA or the PVD neurons resulted in a decrease in both the frequency and magnitude of reversals that were elicited by tap. Additi onally, the ablation of either cell decreased the magnitude of acceler ations produced by animals in response to tap.