Modelling a Respiratory Central Pattern Generator Neuron in Lymnaea Stagnalis

Lymnaea stagnalis, often termed the great pond snail, is characterized in part by its ability to take in oxygen both cutaneously and aerially (via its rudimentary lung). The central nervous system of the Lymnaea is composed of a relatively small number of large, identifiable neurons. In 1990, Syed et al. [1] established that respiratory rhythmogenesis in the Lymnaea is controlled by a 3-neuron central pattern generator (CPG) as depicted in Figure 1. Syed et al. [1, 2] were able to identify and culture the three neurons that make up the CPG, both singly and together, where they reform the same connections as are present in vivo. Based on various experimental manipulations, they described the following characteristics of this network. One of these neurons, the RPeD1 (Right Pedal Dorsal 1) neuron, is spontaneously active and is responsible for the initiation of respiration, upon receipt of input from the respiratory orifice. The other two neurons, VD4 (Visceral Dorsal 4) and Ip3I (Input 3), are quiescent except during active respiration. The VD4 neuron (which is responsible for inspiration) is connected via reciprocal inhibitory synaptic connections to both the RPeD1 neuron and the Ip3I neuron (which is responsible for expiration). The Ip3I neuron has excitatory synaptic con-