Muscle receptor organs of the crayfish, Cherax destructor: Input to telson motor neurons

Abstract

The stretch receptor cells (SRs) of the abdominal muscle receptor organs (MROs) of crayfish send large axons directly to the last abdominal ganglion. In Precambarus clarkii some unidentified motor neurons and interneurons 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 SRs on several types of tailfan neurons including identified motor neurons in the crayfish, Cherax destructor. SR activation, either with single action potentials, multiple action potentials, or simultaneously from many SRs, produced no spiking activity in any of the nerves of the tailfan. To test for subthreshold activation, we identified and recorded from the pool of large motor neurons responsible for flexion of the telson while stimulating identified SR axons. The only members of this group that received direct input from the SRs were the inhibitory motor neurons. The excitation was probably monosynaptic and was evoked by both phasic and tonic SRs. Activation always occurred in response to input from the SRs of more than one segment but EPSPs were not necessarily evoked by the SRs of all segments. There was no consistent correlation between the strength of the evoked EPSP and either the segment of origin of the SR or the intracellular recording site, although responses from abdominal segments A2 and A3 tended to be stronger. We recorded intracellularly from a number of unidentified interneurons as well but did not find segmental correlation in these either.