Figure 2.

Two different gastric motor patterns elicited in vitro by cyclic activation of the CG and/or GI projection interneurons. Top schematics, Previously identified synaptic relationships between the CG and GI neurons and the gastric network (Combes et al., 1999a). The CG neuron excites the LPG and GM neurons, whereas the GI neuron inhibits the LG–MG neurons. Open circles in each schematic denote motoneuron subtypes that are coactive with the rhythmically stimulated interneuron(s) (indicated with bold connections). Hatched circles indicate motoneurons that fire in antiphase with the stimulated projection neuron(s). Bottom, Motoneuron burst phase relationships in output patterns elicited by activation of either one or both interneurons. A, Cyclic activation of a CG neuron alone generates a type 1 pattern (i.e., with LPG and GM neurons firing in phase opposition; ellipse). B, Cyclic activation of a GI neuron alone also produces a type 1 pattern. C, Simultaneous activation of the CG and GI interneurons drives gastric mill activity in a type 2 pattern in which LPG and GM motoneurons discharge in synchrony with the projection neurons (ellipse). Data are summarized from Combes et al. (1999a).