The cord stretch receptors in the abdominal nerve cord of the crayfish Cherax destructor: physiology and relationships.

The physiology and relationships of tonic cord stretch receptor neurons in the crayfish Cherax destructor were examined with intracellular and extracellular recording. Cord stretch evoked slow depolarisations leading to action potentials in tonic cord stretch receptor neurons. Intermittent post-synaptic potentials were also seen in cord stretch receptor neurons but were not the primary cause of the action potentials. Cord stretch still evoked action potentials in cord stretch receptor neurons when all synaptic activity, monitored at another known chemical synapse, was blocked using high [Mg(2+)] and low [Ca(2+)] in the bath. One source of facilitating excitatory post-synaptic potentials in the cord stretch receptor neurons was from mechanosensory hairs on the dorsal abdominal surface. Tonic cord stretch receptor neuron activity was associated with an increase in the activity of the abdominal slow extensor inhibitor motor neuron and at least one abdominal flexor excitor motor neuron in its segment, and reduced activity in the abdominal slow flexor inhibitor motor neuron. Activation of individual cord stretch receptor neurons produced a local resistance reflex. Cord stretch, activating many receptors, produced several other outcomes. One was the "extensor state" described in earlier literature. The tonic cord stretch receptor neurons of Cherax destructor appear to be stretch-sensitive interneurons that receive inputs from other elements of the abdominal control system and mediate polysynaptic reflex activity in postural motor neurons.