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Fig. 1. Illustration of pneumostome opening and the underlying circuitry in
Lymnaea. (A) Schematic diagram of the three neuron CPG and
motorneurons innervating the pneumostome muscles. RPeD1, right pedal dorsal 1
neuron; VD4, visceral dorsal 4; IP3, input 3 interneuron; VK, visceral K
closer motorneurons (MN); VI/J, visceral I/J opener motorneurons; filled
circles, inhibitory connections; open triangles, excitatory connections; grey
triangles, biphasic connections (excitation followed by inhibition). (B) An
example of pneumostome opening in a typical semi-intact preparation. The
pneumostome is located on the bottom right of each panel and is closed, but
reared upward in (i) and fully open in (ii). The two photographs were taken in
quick succession (1 s apart) after lowering the saline level to expose the
pneumostome to the water surface. Scale bar, 3 mm.