Nonspiking Stretch Receptors of the Crayfish Swimmeret Receive an Efference Copy of the Central Motor Pattern for the Swtmmeret

In crayfish, the movement of each swimmeret is monitored by a pair of nonspiking stretch receptors (NSR) with central somata and dendrites that are embedded in an elastic strand at the base of the appendage. I provide evidence that the neuropile segments of these primary sensory neurones receive synaptic input from the hemiganglionic central pattern generator for the swimmeret. In nonbursting isolated abdominal nerve cords of Pacifastacus leniusculus Dana, the membrane potentials of the NSRs (recorded in the neuropile) are stable; whenever the central pattern generator is active, they oscillate in phase with the motor output. Every perturbation of the central pattern generator's activity is precisely reflected in analogous changes (in phase and/or amplitude) of the NSRs' oscillations. This activity must arise via central, synaptic input to the NSRs, because it occurs when all ganglia except the sixth are deafferented. Lucifer Yellow dye-fills show that the neurites of the NSRs are confined to the ipsilateral lateral neuropile, which is the region of the hemiganglion where swimmeret functions are integrated. These results imply that during rhythmic beating of the swimmerets, the NSRs receive an efference copy of the motor output to the limb whose movements they monitor. In vivo, therefore, the incoming sensory signal must be subject to modulation (gating) by the limb's central pattern generator.