Neural and biomechanical mechanisms underlying the generation of feeding responses of different amplitude by the multifunctional feeding apparatus of Aplysia californica.

摘要

How do biomechanics interact with neural control to generate responses of different intensity? In order to study this question, two mutually exclusive feeding responses, swallowing and rejection, were studied in the marine mollusk Aplysia californica.; The kinematics of the food stimulus, a polyethylene tube, was characterized during swallowing and rejection responses. During small amplitude Type A swallows, the tube translated inwards. During large amplitude Type B swallows, the tube translated inwards more strongly and rotated. During small amplitude Type A rejections, the tube translated outward. During large amplitude Type B rejections, the tube translated outwards more strongly and rotated.; The neural and biomechanical mechanisms underlying different amplitude responses were studied. Type A swallows began with a weak protraction. During retraction, jaw muscle contraction pushed the closed radula back and translated the tube inward. Type B swallows began with a more intense protraction, which set up the radula/odontophore to be a retractor. Strong protraction also stretched the hinge muscle. Thus both the radula closer muscle (I4) and the hinge muscle acted to increase swallowing amplitude. Two identified buccal ganglion motor neurons, B8 and B7, contributed to these movements, respectively. Their functions changed with the biomechanical context. The retractor muscle I1/I3 reinforced jaw closure at the peak of protraction as food was grasped.; During rejection, as the radula closed at the onset of protraction, it elongated and stretched the protractor muscle (I2), therefore increasing I2's ability to exert force. Both shape change and greater I2 contraction were necessary for the expression of the larger amplitude Type B rejections. Identified multiaction interneurons B4 and B5 are partially responsible for delaying the activation of the I1/I3 muscle, so that radula opening was not opposed by activation of the retractor muscles at peak protraction.; These results suggest a multifunctional usage of the buccal muscles and motor neurons in generating different amplitude feeding responses. Several biomechanics-based neural criteria were provided for future studies of the interneuronal mechanisms underlying intensity change.