Figure 4

N3t interneuron has multiple roles in the feeding system. (A) The semi-intact preparation used for electrophysiological recording and sucrose stimulation showing the location of the feeding interneurons, N1M and N3t. (B) An experiment showing that the food stimulus, sucrose, reduces the suppressive inhibitory control of the N3t cell and releases rhythmic fictive feeding. It is therefore important in switching the feeding system from quiescence to feeding. When it changes from tonic firing to rhythmic activity it becomes part of the CPG. The change in the pattern of activity is emphasized by the top trace where the number of spikes is accumulated in 3 s bins. (C) Expansion of the boxed area in (B) shows the first cycle of fictive feeding activity in the N1M after the sucrose-induced reduction in N3t firing rate. The arrow under the N3t trace indicates the point at which N3t starts to hyperpolarize and its tonic firing begins to decrease. This decrease in firing is followed by complete suppression of N3t firing when the N1M becomes active and synaptically inhibits the N3t. The subsequent phasic N1M-N3t reciprocal inhibition leads to alternating patterns of N1M/N3t firing seen throughout the feeding pattern that follows. (D) Hunger and satiety influences spontaneous feeding activity by influencing the level of tonic inhibition of the feeding CPG interneuron N1M. In satiated animals, the N3t fires continuously and the consequent inhibitory effects on the N1M prevent spontaneous feeding. In hungry animals, even with no food present, there are occasional feeding bursts in the N1M due to the lower rate of firing in the N3t. In feeding animals the tonic N3t firing is weak and insufficient to prevent sustained bursting in the N1M. Dots indicate inhibitory chemical synaptic connections. Adapted from [26] with permission from Elsevier. See Abbreviations for all definitions of neuron types.