Fig. 4

Figure 4. The orderly reestablishment of fast and slow excitatory V2a circuit modules underlies stepwise restoration of locomotor function

(A, E, I, and O) Illustration of paired whole-cell patch-clamp recording between a V2a interneuron rostral to the lesion with regrown axons and a V2a interneuron (A and I) or a motor neuron (E and O) caudal to the lesion.

(B, C, F, and G) Paired recordings showing a monosynaptic connection between a rostral fast V2a interneuron and a fast (B) or a slow (C) V2a interneuron or a fast (F) or a slow (G) motor neuron caudal to the lesion at 2–3 wpi.

(D and H) Statistical analysis and connectivity matrix of a rostral fast V2a interneuron induced EPSPs in a fast or a slow V2a interneuron (D), or a fast or a slow motor neuron (H) caudal to the lesion at 2–3 wpi.

(J and K and P and Q) Paired recordings showing a monosynaptic connection between a rostral fast V2a interneuron with regrown axons and a fast (J) or a slow (K) V2a interneuron or a fast (P) or a slow (Q) motor neuron caudal to the lesion at 7–8 wpi.

(M and N and S and T) Paired recordings showing monosynaptic connections between a rostral slow V2a interneuron with regrown axons and a fast (M) or a slow (N) V2a interneuron or a fast (S) or a slow (T) motor neuron caudal to the lesion at 7–8 wpi.

(L and R) Statistical analysis and connectivity matrix of a rostral fast/slow V2a interneuron induced EPSPs in a fast or a slow V2a interneuron (L), a fast or a slow motor neuron (R) caudal to the lesion at 7–8 wpi, respectively.

(U) Proposed model of the reorganization of intraspinal excitatory circuits dominated by a V2a interneuron with regrown axons that underpins the restoration of locomotor rhythm after SCI. All data shown are mean ± SD. ^∗∗∗p < 0.001, significant difference. One dot equals one neuron, and only one pair of neurons was recorded from each fish. See also Figure S4.