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Fig. 4 Structural and functional patterning within the alx stripe. (A) Patch recording of an alx:GFP+ neuron in hindbrain segment 7 of a 5-dpf fish, while simultaneously recording motor activity in a ventral root. (A, panel 1) Cross-section view of the patched cell (red) within the alx stripe (green). (A, panel 2) Recording from the alx cell on the left is shown below the simultaneous ventral root recording. (B) Variation in axonal projections into spinal cord of hindbrain alx neurons. (B, panel 1) An example of a reconstruction of a single alx neuron (red) within the alx:GFP transgenic line (lateral view). (A, panel 2) Lateral views of 3D reconstructions of neurons from different dorsoventral locations in the medial glutamatergic stripe in rhombomere 7, with the most dorsal one at the top (normalized dorsoventral positions: 0.51, 0.28, and 0.16 from ventral edge of stripe, rostral to the left). (C) A plot of the total 3D axonal length of 10 labeled alx neurons (two of them overlap, shown with white circle) vs. their dorsal ventral location in the stripe. More ventral neurons have systematically longer axonal length (P < 0.0001). Red, green, and blue points correspond with the three neurons in B. (D) Plot of the input resistance of a neuron vs. its dorsoventral location in a stripe. More-dorsal neurons have systematically higher input resistances in both more- (black dots, P < 0.05) and less-exposed brain preparations (gray squares, P < 0.01). See text for further details. (E) Examples of calcium imaging of alx neurons from different locations in the stripe during different frequencies of swimming in 5-dpf fish. (E, panels 1–3) Cross-sections images of alx:DsRed fish with locations of the neurons (dots) shown relative to the stripes. (E, panels 4–6) Calcium responses of the neurons on the left in two example trials at swimming frequencies near those when the neurons are first recruited. (F) Plot of the minimum swimming frequency at which a neuron responds vs. the dorsoventral location of the neuron, including both alx:DsRed+ alx:DsRed neurons in the region of the alx stripe (P < 0.05 for each correlation). Neurons from Fig. 4B are shown in color. (Scale bars, 200 μm.)