Motor Neurone Coordination and Sensory Modulation in the Feeding System of the Mollusc Pleurobranchaea Californica

Abstract

The electrophysiological basis of coordinated motor neuron activity associated with the intrinsic feeding rhythm of the buccal ganglion and the sensory modulation of this rhythm was examined in P. californica. Paired intracellular microelectrode recordings from antagonist motor neurons showed that each received alternating barrages of EPSP [excitatory postsynaptic potential] and IPSP [inhibitory postsynaptic potential]; as 1 of the pair was depolarized, its antagonist was hyperpolarized. PSP of opposite signs in antagonists were 1:1 suggesting that common presynaptic interneurons were responsible. There was no evidence for direct synaptic interaction between antagonist motor neurons. Paired recordings from synergist neurons showed that they received similar barrages of PSP which alternately depolarized and hyperpolarized the motor neurons. Underlying these parallel changes in potential were 1:1 PSP of the same sign, again suggesting driving by common presynaptic interneurons. The feeding rhythm recorded from the buccal ganglion with the buccal mass attached was compared quantitatively with that recorded from the same ganglion after deafferation. There were significant differences in parameters of the rhythm measured under the 2 conditions. Rhythmic afferent activity was recorded from the distal stumps of buccal roots, during rhythmic feeding movements of the buccal mass. The spiking of different units was associated with different phases of the movement cycle.