Figure 3

Locations, synaptic connectivity and sucrose responses of the cerebrobuccal interneurons (CBIs). (A) Cell body locations of the 13 CBIs in the right cerebral ganglion. A similar population of cells occurs on the left side (B) Electrotonic synaptic connections (resistor symbols) between the CBIs (CA1, CV1a, CB1b types) and excitatory chemical synaptic connections (bars) between the CBIs and the N1M CPG interneurons, contralateral (cN1M) and ipsilateral (iN1M). Note that the CBIs can drive the N1Ms (see text) but they also receive excitatory feedback from the N1Ms. (C) Rhythmic responses to sucrose application to the lips recorded intracellularly in three individual CBIs but also extracellularly from their axons in the cerebrobuccal connective (CBC). Suppression of activity in these CBI by intracellular hyperpolarization (not shown here) shows that there were further types of CBIs contributing to the population response recorded in the CBC. (D) The CT2 is the first to fire in a sucrose-driven rhythm (arrowed) and its strong burst of activity precedes the first burst of spikes in the B1 feeding motoneuron. The B1 burst is known to be driven by monosynaptic excitatory synaptic inputs from N1M CPG (bar). This indicates that CT2 fires before the N1M. See Abbreviations for all definitions of neuron types.