Modulatory effects of a single neurons on the activity of the pyloric pattern generator in Crustacea.

The firing of a single neuron (named anterior pyloric modulator: APM) of the esophageal ganglion considerably modifies the pyloric rhythm of the rock lobster. These modifications, characterized by a long delay to onset and a long duration, include increased frequency and amplitude of oscillations of the motor neurons, changes in the efficacy of certain synapses within the network, and voltage-dependent modifications of membrane properties of some motor neurons. APM thus seems to be a true modulatory neuron. The APM-provoked changes resemble changes seen in the whole animal, making this a suitable system for an analysis of modulation on several levels.