Decrement of the response of a serotonergic modulatory neuron (the metacerebral cell) in Aplysia, during repeated presentation of appetitive (food) stimuli

Abstract

Application of food (seaweed, SW) stimuli to the lips evokes a burst of metacerebral cell (MCC) spikes, and it was found in free-moving animals that repeated presentation of the stimulus was associated with a rapid decrement of the evoked responses, even in the absence of ingestion of the food. To aid in discriminating between mechanisms that may be responsible for this decrement, SW was applied repeatedly to the lip ipsilateral or contralateral to one of the paired MCCs, and then generalization of the response decrement was tested by applying a SW stimulus to the opposite (non-stimulated) receptive field. There was statistically significant generalization of response decrement and the amount of generalization appeared to be a function of whether the decrementing stimuli were presented on the side ipsilateral vs. contralateral to the recorded MCC. The overall data suggest that MCC response decrement to repeated food stimuli results in a process analogous to behavioral habituation, and the data are consistent with a simple neural model.