Fig. 2. Soma ablation in Lymnaea. (A) Photomicrograph of a Lucifer yellow-filled RPeD1. RPeD1 sends neuritic branches to other ganglia, where it synapses with other members of the aerial respiratory network, and also sends processes to the pneumostome area, where it receives both tactile and chemosensory input. The soma diameter of RPeD1 is approximately 75 µmol l^-1. (B) A similar RPeD1 Lucifer yellow fill, except that gentle poking of it with a glass microelectrode has ablated its soma. The isolated neurite remains viable, as detected electrophysiologically for at least 2 weeks and behaviourally for at least 1 month. (C) A cartoon of the aerial respiratory central pattern generator (CPG; RPeD1, VD4 and IP3; see Syed et al., 1990) showing how synaptic connections are made in these unipolar neurons. Removal of RPeD1's soma does not disrupt either the pre- or postsynaptic specialization areas of the neuron. The closed circles represent an inhibitory chemical synaptic input, the bars represent excitatory synaptic input, and a combined bar and filled circle represents a conjoint inhibitory/excitatory input. All synapses are chemical and involve, at a minimum, the classical transmitters acetylcholine and dopamine and peptide transmitters of the RFamide family.