Intersegmental coordination in the crayfish swimmeret system reconsidered

Abstract

AbstractStein ('71, '74) demonstrated that lesions in areas 78 and 81 of the nerve cord of the crayfish Procambarus affected intersegmental coordination. In these areas he found neurons which appeared to be local interneurons and whose discharge was correlated with motor discharge in the swimmeret roots. He suggested that these neurons might be responsible for intersegmental coordination and termed them coordinating fibres. We reexamined the same areas of the ventral nerve cord in the crayfish Cherax by recording extracellularly from small bundles of axons during rhythmic activity in the swimmeret motor nerves. All the units we located that exhibited correlated discharge appeared to be plurisegmental. Physiological examination revealed that such units may be sensory, motor, or interneurons. We confirmed this finding morphologically by staining some of the units intracellularly with cobalt. Deafferentation experiments and the effects of stimulating units showing correlated discharge suggest that all three types of neurons may be involved in intersegmental coordination. We conclude that the that the present coordinating fibre model should be abandoned.