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

Application of food (seaweed, SW) stimuli to the lips evokes a burst of met acerebral cell (MCC) spikes, and it was found in free-moving animals that r epeated presentation of the stimulus was associated with a rapid decrement of the evoked responses, even in the absence of ingestion of the food. To a id in discriminating between mechanisms that may be responsible for this de crement, SW was applied repeatedly to the lip ipsilateral or contralateral to one of the paired MCCs, and then generalization of the response decremen t was tested by applying a SW stimulus to the opposite (nonstimulated) rece ptive field. There was statistically significant generalization of response decrement and the amount of generalization appeared to be a function of wh ether the decrementing stimuli were presented on the side ipsilateral vs. c ontralateral to the recorded MCC. The overall data suggest that MCC respons e decrement to repeated food stimuli results in a process analogous to beha vioral habituation, and the data are consistent with a simple neural model. (C) 1999 Elsevier Science Ireland Ltd. All rights reserved.