Temporal organization of crayfish escape behavior: delayed recruitment of peripheral inhibition

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Abstract
The peripheral inhibitor of the fast flexor muscles in the crayfist was identified by Co staining and intracellular recordings from neurons and muscles. The peripheral inhibitor was effective in blocking muscle spikes and reducing tension. During escape behavior, which could be initiated by a single impulse in an identified central command cell, the peripheral inhibitor often fired a burst of impulses that were delayed relative to the excitatory discharge. Delay and formation of the inhibitor''s burst were centrally programmed. Delay was the result of a polysynaptic pathway from the escape command cell to the inhibitor; the pathway included the flexor motoneurons and a set of corollary discharge interneurons. All of the synapses in the pathway from the command cell to the inhibitor appeared to operate electrically, yet the response of the peripheral inhibitor showed marked facilitation to a pair of command cell impulses as a result of temporal summation and the consequent recruitment of additional interneurons. The peripheral inhibitory circuit was one element of a complex inhibitory network, triggered by the command cell, that helped coordinate the response.