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P4 is a motor neuron in the Aplysia californica pedal ganglia.

Figure 1. Schematic representation of the dorsal Aplysia pedal and pleural ganglia. Left pedal ganglion shows designated sectors, right pedal ganglion shows approximate locations of identified neurons. Identified motor neuron P4 is shown at medioposterior portion of sector II. Modified from Hening et al 1979.

Basic Information

  • No known alias
  • Neurotransmitter is as yet unidentified



P4 is a 80-120um sized cell located posteriomedially in sector II, just anterior to the pedal connective. P4 is considered to be a longitudinal motor neuron, with innervation to the mesosegments of the Aplysia californica foot via Pd 9 (Hening et al. 1979).


P4 causes longitudinal contraction of the second and third segments of the foot and of the tegument, and is considered to be one of the mesosegmental motor neurons. Tail stimulation sometimes excites P4, while head stimulation inhibits this motor neuron. During movement, P4 receives cycling deplorazing and hyperpolarizing waves of stimulation (Hening et al. 1979 - referenced in text but no figure was shown to illustrate the data).


1. Hening, W.A., Walters, E.T., Carew, T.J., Kandel, E.R. (1979) Motorneuronal control of locomotion in Aplysia. Brain Research, 179. 231-253.