Printed in Great Britain NON-SPIKING STRETCH-RECEPTORS IN THE CRAYFISH SWIMMERET SYSTEM

1. Two neurones have been encountered with the properties of non-spiking stretch-receptors on both sides of each swimmeret-bearing segment of the crayfish Pacifastacus leniusculus. 2. Each neurone depolarizes by up to 35 mV (measured intracellularly in the ganglionic neuropil) in response to experimentally imposed retraction of the appropriate swimmeret, but does not generate spikes. 3. Depolarizing and hyperpolarizing current injected into these neurones can excite or inhibit the spike activity of several swimmeret motorneurones. 4. Intracellular injection of dye shows that both non-spiking stretch-receptors have large diameter axons in the anterior branch of the first root and central cell bodies. One has a cell body in the anterior ipsilateral quadrant of the ganglion (NSSR-A), while the other has a cell body in the posterior ipsilateral quadrant (NSSR-P). 5. Both neurones innervate a peripheral elastic strand which spans the base of the swimmeret, with its posterior attachment on the sternal rib at the posterior rim of the swimmeret socket, and its anterior attachment on the swimmeret basipodite. This strand (Si) is stretched by retraction of the swimmeret. 6. A second strand (S2) stretches from the anterior rim of the swimmeret socket to the mid point of Si, and is innervated by several small diameter axons which also do not appear to have cell bodies in the periphery