Structure and synaptic function of local reflex circuit for crayfish uropod motor control system

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The aim of research is to understand the functional role of local circuit neurones and fundamental roganization of neural circuit relating to behavioral context. Mechanical stimulation of the tailfan in crayfish procambarus clarkii elicits a "dart" -like avoidance reaction. The crayfish closed both uropods and walks forward with extension of the abdomen. The movement of the uropod is mediated by local circuit neurones, including nonspiking and spiking local interneurones and ascending interneurones.Synaptic connection to and from nonspiking local interneurones in the avoidance reaction is investigated in detail by using simultaneous intracellular recordings and stainings. Some nonspiking local interneurones received excitatory exteroceptive sensory inputs directly from hair afferents. Boththe ascending and spiking local interneurones also received direct inputs from the afferents via chemical synapses. Neither direct connection between motor neurones and afferents nor direct inhibitory connection from hair afferents were detected.Inhibitory inputs from hair afferents were transmitted ento nonspiking interneurones via mediated by spiking local interneurones. Indirect excitatory inputs from hair afferents were also transmitted into nonspiking interneurones by intersegmental ascending interneurones. Some nonspiking interneurones made either excitatory or inhibitory connection with other nonspiking interneurones. Membrane potential change of nonspiking local interneurones was, in turn, effective to change the membrane potential of uropod motor neurones by means of gradual release of chemical transmitters.