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. 2011 Jul 27;366(1574):2086–2099. doi: 10.1098/rstb.2010.0336

Figure 2.

Figure 2.

Homologous identified neurons in sea slugs have divergent or similar roles in behaviour. (a) Tritonia diomedea swims by flexing its body in the dorsal and ventral directions as shown in the diagram to the left. Simultaneous intracellular microelectrode recordings from DSI and C2, two neurons in the central pattern generator (CPG) for the swimming behaviour, display rhythmic bursts of action potentials after a body wall nerve is electrically stimulated (nerve stim.). This comprises the swim motor pattern. (b) The swim CPG in Tritonia contains three neuronal types: DSI, C2 and VSI. There are three DSIs: DSI-A, DSI-B, DSI-C. They are being grouped together for simplicity. The triangles represent excitatory synapses, the circles represent inhibitory synapses and multicomponent synapses are presented by combinations of the two. (c) The swim CPG in Pleurobranchaea has many similarities to that in Tritonia. As1–3 are homologous to the DSIs in Tritonia. There is an As4 that is in the same cell cluster and is in the swim CPG, but is not homologous to the DSIs. Its homologue exists in Tritonia, but the function of this neuron has not been determined in Tritonia. The IVS neuron has not been identified, but its synaptic actions, which can be inferred from recordings of the other neurons, are similar to those of the Tritonia VSI. A1 (which is homologous to C2 in Tritonia) is strongly electrically coupled to neuron A10 and so both are represented together. Homologues of A3 and A10 have not been identified in Tritonia. (d) Pleurobranchaea californica swims with dorsal–ventral body flexions. Intracellular recordings show that the As2,3 neurons and the A1 neuron both exhibit bursting behaviour during the swim motor pattern (adapted from [109], American Physiological Society, with permission). (e) Melibe leonina swims by flexing its body from side-to-side. Intracellular recordings from CeSP (which is homologous to the DSI in Tritonia) and swim interneuron 1 (Si1) show that the CeSP neuron is not rhythmically active during the swim motor pattern.

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