Central actions of R15, a putative peptidergic neuron in Aplysia

We report that the bursting pacemaker neuron R15 has central actions on other identified neurons in the abdominal ganglion of Aplysia california. The follower cells are located on the dorsal surface of the left lower quadrant of the ganglion and include members of the LC cell cluster. A spontaneous burst of impulses in R15 produces a slow, graded, excitatory potential of up to 8 mV in follower cells. The response begins about 2-3 s after the first impulse in an R15 burst, and reaches its peak at about 4-6 s (corresponding approximately to the end of the R15 burst). In some preparations a biphasic response was seen composed of the early depolarization followed by a slower excitatory or inhibitory phase. All the responses were blocked when R15 was hyperpolarized to prevent spiking. The magnitude of the response was reduced in a graded fashion by prematurely terminating the R15 burst with hyperpolarizing current and was increased when depolarizing current was injected into R15 during a burst. Central actions of R15 were observed in only 28% of our preparations, and their presence may depend on unknown physiological factors. The effects are likely to be mediated by R15 neuropeptides. The accessibility of both R15 and its targets in this preparation should facilitate further analysis of this interaction.