C-PR neuron of Aplysia has differential effects on "feeding" cerebral interneurons, including myomodulin-positive CBI-12

Head lifting and other aspects of the appetitive central motive state that precedes consummatory feeding movements in Aplysia is promoted by excitatio n of the C-PR neuron. Food stimuli activate C-PR as well as a small populat ion of cerebral-buccal interneurons (CBIs). We wished to determine if firin g of C-PR produced differential effects on the various CBIs or perhaps affe cted all the CBIs uniformly as might be expected for a neuron involved in p roducing a broad undifferentiated arousal state. We found that when C-PR wa s fired, it produced a wide variety of effects on various CBIs. Firing of C -PR evoked excitatory input to a newly identified CBI (CBI-12) the soma of which is located in the M cluster near the previously identified CBI-2. CBI -12 shares certain properties with CBI-2, including a similar morphology an d a capacity to drive rhythmic activity of the buccal-ganglion. Unlike CBI- 2, CBI-12 exhibits myomodulin immunoreactivity. Furthermore when C-PR is fi red, CBI-12 receives a polysynaptic voltage-dependent slow excitation, wher eas, CBI-2 receives relatively little input. C-PR also polysynaptically exc ites other CBIs including CBI-1 and CBI-8/9 but produces inhibition in CBI- S. In addition, firing of C-PR inhibits plateau potentials in CBI-5/6. The data suggest that activity of C-PR may promote the activity of one subset o f cerebral-buccal interneurons, perhaps those involved in ingestive behavio rs that occur during the head-up posture. C-PR also inhibits some cerebral- buccal interneurons that may be involved in behaviors in which C-PR activit y is not required or may even interfere with other feeding behaviors such a s rejection or grazing, that occur with the head down.