The respiratory central pattern generator of Lymnaea: a model, measured and malleable

Great progress has been made, and continues to be made in our understanding of the neuronal mechanisms underlying respiration in a wide variety of mod el systems. The central pattern generator (CPG) controlling aerial respirat ion in the pond-snail Lymaea is a particularly well-studied model. Using in vitro and semi-intact preparations, the neural circuitry that controls aer ial respiration has been characterized as consisting of three identified in terneurons. Furthermore, insight has been gained into the behavioural, cell ular and synaptic mechanisms by which this circuit controls respiratory rhy thmogenesis. It has also been demonstrated that aerial respiratory behaviou r can be modified both by experience and by environmental factors. Studies have shown that, in a behavioural hierarchy, respiration is subservient to the whole-body withdrawal response that respiratory behaviour can be modifi ed through operant conditioning, and that respiratory behaviour is altered by hypoxia. Through research on the Lymnea respiratory CPG we are coming to a better understanding of the construction and malleability of a CPG netwo rk. The malleability of this CPG is of particular interest. No longer can n euronal networks underlying respiratory behaviour be considered hard-wired: they have inherent plasticity. (C) 2000 Elsevier Science B.V. All rights r eserved.