Sodium-mediated plateau potentials in an identified decisional neuron contribute to feeding-related motor pattern genesis in Aplysia

Motivated behaviors such as feeding depend on the functional properties of decision neurons which provide the flexibility required for behavioral adaptation. Here, we analyzed the ionic basis of the endogenous membrane properties of an identified decision neuron (B63) that drive radula biting cycles underlying food-seeking behavior in Aplysia. Each spontaneous bite cycle arises from the irregular triggering of a plateau-like potential and resultant bursting by rhythmic subthreshold oscillations in B63s membrane potential. In isolated buccal ganglion preparations, and after synaptic isolation, the expression of B63s plateau potentials persisted after removal of extracellular calcium, but was completely suppressed in a TTX-containing bath solution, thereby indicating the contribution of a transmembrane Na+ influx. Potassium outward efflux through TEA- and calcium-sensitive channels was found to contribute to each plateaus active termination. This intrinsic plateauing capability, in contrast to B63s membrane potential oscillation, was blocked by the ICAN blocker flufenamic acid (FFA). Conversely, the SERCA blocker cyclopianozic acid (CPA), which abolished the neurons oscillation, did not prevent the expression of experimentally evoked-plateau potentials. These results therefore indicate that the dynamic properties of the decision neuron B63 rely on two distinct mechanisms involving different sub-populations of ionic conductances. NEW & NOTEWORTHYHere, we report an endogenous plateau property underlying bursting in a bilateral pair of buccal ganglion pacemaker neurons (B63) which trigger individual motor pattern cycles for food-seeking behavior in the marine mollusk Aplysia. The ionic mechanisms of this membrane bistability in B63 rely critically on voltage-dependent sodium inward currents. The expression of these plateau properties and the underlying endogenous oscillatory pacemaker drive can be dissociated pharmacologically, indicating that the two intrinsic properties depend on different sets of conductances. Our results thus shed new light on the mechanisms of spontaneous decision making in Aplysia.