MUSCLE RECEPTOR ORGANS OF THE CRAYFISH, CHERAX DESTRUCTOR - INPUT TO TELSON MOTOR-NEURONS

The stretch receptor cells (SRs) of the abdominal muscle receptor orga ns (MROs) of crayfish send large axons directly to the last abdominal ganglion. In Procambarus clarkii some unidentified motor neurons and i nterneurons receive direct SR input (Bastiani and Mulloney,'88a,b). We used an isolated, in vitro, preparation of the ventral nerve cord and tailfan to investigate the effects of sensory input from identified S Rs on several types of tailfan neurons including identified motor neur ons in the crayfish, Cherax destructor. SR activation, either with sin gle action potentials, multiple action potentials, or simultaneously f rom many SRs, produced no spiking activity in any of the nerves of the tailfan. To test for subthreshold activation, we identified and recor ded from the pool of large motor neurons responsible for flexion of th e telson while stimulating identified SR axons. The only members of th is group that received direct input from the SRs were the inhibitory m otor neurons. The excitation was probably monosynaptic and was evoked by both phasic and tonic SRs. Activation always occurred in response t o input from the SRs of more than one segment but EPSPs were not neces sarily evoked by the SRs of all segments. There was no consistent corr elation between the strength of the evoked EPSP and either the segment of origin of the SR or the intracellular recording site, although res ponses from abdominal segments A2 and A3 tended to be stronger. We rec orded intracellularly from a number of unidentified interneurons as we ll but did not find segmental correlation in these either. (C) 1997 Wi ley-Liss, Inc.