Analysis of postural motoneuron activity in crayfish abdomen. II. Coordination by excitatory and inhibitory connections between motoneurons.

The identified spike trains of the crayfish abdominal postural efferent neurons were recorded simultaneously from one or more segments. The efferent activity was analyzed using cross-correlation histograms, peristimulus time scatter diagrams, and specialized antidromic techniques. The analyses show that the larger, phasically active motoneurons are coordinated in their activity by cross connections made at the motoneuron level. The cross connections are both excitatory and inhibitor in nature and result in significant alterations in spike output. Further, the accessory neuron receives an inhibitory cross connection from a middle-sized extensor excitor motoneuron or motoneurons. In each case, the cross connections appear to be appropriate to the function of the postural system.