Slow Active Potentials in Walking-leg Motor Neurones Triggered by Non-spiking Proprioceptive Afferents in the Crayfish

Intracellular recordings have been made from walking-leg motor neurones of the crayfish, Pacifastacus leniusculus, in isolated preparations of the thoracic ganglia. Some motor neurones display slow depolarizations that can drive bursts of spikes and resemble 'plateau' potentials described in other invertebrate and vertebrate neurones. Evidence is presented which suggests that the potentials are regenerative and endogenous to the motor neurones, and are not the result of feedback from a neural network. These potentials can be induced by synaptic inputs from the non-spiking afferent neurones of the thoracic-coxal muscle receptor organ, a basal limb proprioceptor. Reflex input from this receptor is augmented during the active depolarization of the motor neurone. The results are discussed in terms of the control of rhythmic motor output and the central modulation of reflexes in the crayfish's thoracic nervous system.