Figure 6 .

Labeling of the output of S1-CST neurons in the spinal cord. (A) Labeling of the CST in the dorsal funiculus of the spinal cord, contralateral to the brain injection site after injection of a rAAV carrying a Cre-dependent tdTomato into S1hl of CCK^Cre mice. CST terminals are preferentially located below the laminae II-III border (n = 3). (B) Quantification of the number of WGA positive neurons after injection of a rAAV.flex.WGA into S1hl of CCK^Cre mice. Quantified are WGA positive neurons that express Lmx1β (n = 4, 320 WGA⁺ neurons), Pax2 (n = 8, 391 WGA⁺ neurons), GlyT2 (n = 3, 275 WGA⁺ neurons), c-Maf (n = 6, 506 WGA⁺ neurons), or PKCγ (n = 4, 201 WGA⁺ neurons). (C,D) Representative images of colabeled WGA positive neurons in the spinal cord with the excitatory marker Lmx1β ((C) and inset) and the inhibitory marker Pax2 ((D) and inset). Neurons expressing eGFP under the GlyT2 promoter (using the GlyT2::eGFP mouse line (E)), and neurons expressing the transcription factor c-Maf (F) were also found positive for WGA. (G,H) Verification of monosynaptic labeling by WGA. CCK^Cre Mice were coinjected with rAAV.flex.WGA and rAAV.flex.Syp-eGFP (encoding a Cre-dependant synaptophysin-eGFP fusion protein) into S1hl. (G) Colabeling of WGA positive neurons in the spinal cord with the neuronal marker NeuN and eGFP labeled presynaptic terminals of S1-CST neurons. Depicted is a representative example of a WGA⁺ neuron in close proximity to a eGFP⁺ presynaptic terminal of a S1-CST neuron3. (H) Quantification of the number of WGA⁺ neurons receiving direct contacts from eGFP⁺ synaptic terminals (n = 4 mice; 25 neurons). CST: corticospinal tract. Error bars represent ±SEM, Scale bars: A and C–F: 100 μm; G: 10 μm.