Cerebral neurons underlying prey capture movements in the pteropod mollusc, Clione limacina

Abstract

The pteropod mollusc Clione limacina feeds on shelled pteropods capturing them with 3 pairs of oral appendages, called buccal cones. A group of electrically-coupled putative motoneurons (A neurons) has been identified in the cerebral ganglia, whose activation induces opening of the oral skin folds and extrusion of the buccal cones. These cells are normally silent and have one or two axons in the ipsilateral head nerves. Electrical coupling between A neurons is relatively weak and normally does not produce 1:1 spike synchronization. Coupling coefficients ranged from 0.05 to 0.25. A second type of putative motoneurons (B neurons) controls retraction and withdrawal of buccal cones. B neurons show spontaneous spike activity which maintains the buccal cones in a continuous retracted state. All B neurons have one axon running into the head nerves. Ipsilateral B motoneurons are electrically coupled to each other. A neurons strongly inhibit B neurons, however, seven identified A motoneurons which were specifically tested do not form monosynaptic contacts with B motoneurons. Appropriate stimuli from the prey activate A motoneurons, which in turn inhibit B motoneurons and evoke extrusion of the buccal cones. One mechanism promoting the speed of this extremely rapid reaction is brief co-activation of antagonistic A and B neuron groups, which provides a notable increase in fluid pressure inside the head. Mechanical stimulation of buccal cones provides excitatory inputs to A motoneurons. Similar stimulation from captured prey would serve to prolong buccal cone protraction during the manipulatory phase of feeding.