Figure 3.

T cells were inhibited during the contraction phase of crawling. A, Inset, experimental setting: in an isolated ganglion, T cells were intracellularly recorded while motoneuron activity was recorded extracellularly in the pair of DP nerves. The recordings show the activity in T and DP in the course of a crawling episode. The largest spike in the DP nerve corresponds to the DE-3 motoneuron. A temporal expansion of the segment indicated by dashed lines is presented below. B, Inset, Correlation analysis. White and gray boxes represent DE-3 bursts; for simplicity, the T-IPSP corresponding to the gray box is the only one drawn. Right vertical dashed line indicates the middle spike of the gray DE-3 burst (t_mid DP). Left line indicates the peak of the middle T-IPSP (t_mid T). The difference between these two values (t_mid DP − t_mid T) divided by the cycle period was used to estimate the correlation described in the polar histogram (n = 253 cycles in 13 ganglia, 6 leeches). The mean period in these experiments was 15 s (14.5 ± 0.6 s). C, Inset, experimental setting: in an isolated ganglion, P cells are intracellularly recorded while motoneuron activity is recorded extracellularly in one DP nerve. The recordings show the activity in P and DP in the course of a crawling episode. Identical results were obtained in 8 pairs of P and DP recordings, tested in 4 ganglia from 4 leeches; these studies included dorsal and ventral P cells. A, C, The numbers on the left of the intracellular recordings indicate the membrane potential in mV.