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Neuronal plasticity and recovery of function in a polyclad flatworm



NEURONAL recovery of function, although well known in the lower metazoa, has received comparatively little attention or critical investigation. We have been able to demonstrate not only recovery of function but also the recruitment of pathways mediating aspects of feeding behaviour in the marine polyclad flatworm, Notoplana acticola. Unlike some freshwater planarians which regenerate lost parts readily and may even grow new brains, polyclads have limited powers of regeneration and the brain seems to be essential for any repair which takes place1. Three aspects of feeding behaviour were utilised in this study. When a normal intact flatworm is presented with food (dead adult brine shrimp) at its posterior laterial margin, that part of the margin in contact with the food is extended and grips the shrimp. This local response is followed by an ipsilateral turning and contraction which brings the anterior margin in contact with the food which it grips and then passes the shrimp towards the midventral mouth. After feeding on two or three shrimp, the worms are satiated and no longer respond to the presence of food. Both turning and satiation are altered when the brain is removed. Decerebrate animals do not turn, the local response is prolonged, and the food is passed directly to the mouth where it is swallowed. After the stomach is filled the worms continue to collect food which is piled under the mouth. This localised feeding response (LFR) continues to occur as long as food is presented. The presence of the brain is necessary to inhibit the LFR as well as to initiate turning and satiation.

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  1. 1

    Olmstcad, J. M. D., J. exp. Zool., 36, 49–56 (1922).

  2. 2

    Best, J. B., and Rubinstein, I., Science, 135, 916–918 (1962).

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