Motor neurone coordination and sensory modulation in the feeding system of the mollusc Pleurobranchaea californica.

This study on the marine mollusc, Pleurobranchaea californica, examined the electrophysiological basis of coordinated motor neurone activity associated with the intrinsic feeding rhythm of the buccal ganglion, and the sensory modulation of this rhythm. Paired intracellular microelectrode recordings from antagonist motor neurones showed that each received alternating barrages of EPSPs and IPSPs; as one of the pair was depolarized, its antagonist was hyperpolarized. PSPs of opposite polarity in antagonists were one-for-one with each other, suggesting that common presynaptic interneurones were responsible. There was no evidence for direct synaptic interaction between antagonist motor neurones. Paired recordings from synergist motor neurones showed that they received similar barrages of PSPs which alternately depolarized and hyperpolarized them. Underlying these parallel changes in potential were one-to-one PSPs of the same polarity, again suggesting driving by common presynaptic interneurones. The feeding rhythm that was recorded from the buccal ganglion with the buccal mass attached was compared quantitatively with that recorded from the same ganglion after deafferentation. There were significant differences in parameters of the rhythm measured under the two 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. Sensory cells with central somata were stimulated individually in the isolated ganglion, and two effects were recorded. Some sensory neurones excited withdrawal motor neurones and inhibited eversion motor neurones; others inhibited withdrawal motor neurones.