Figure 3.

Horizontally stacked images of the Mauthner cell and reticulospinal neurons in r4–r6. Camera lucida reconstructions from serial horizontal sections of paired, recorded, and intracellularly labeled the M-cells in r4 (black) and RSNs in r4–r6. The somata of all of types of RSNs fell into tidy segments, but their dendrites protruded away from their own segments and projected to the adjacent segments. A, B, Left MiD2cm cell in r5 (A) and MiD3cm cell in r6 (B) with bilateral M-cells. Both were located dorsally and had a stem axon that projected to the contralateral spinal cord as the M-cell. Broken lines indicate the midline (same in following traces of Figs. 3, 4). Filled arrowheads indicate the lateral dendrites, and open arrowheads indicate the ventral dendrites, which is the same in the following traces in Figures 3 and 4. C, D, MiD2i cell in r5 (C) and MiD3i cell in r6 (D), which had an axon that projected to the ipsilateral spinal cord. E, F, MiM1 cells in r4, of which an axon projected to the ipsilateral spinal cord were subdivided into dorsally located MiM1D (E) and more ventrally located MiM1V cells (F): MiM1D cell possesses two main ventral dendrites that project ventrolaterally, and MiM1V cell possesses a large lateral dendrite. Both possess a rostral dendrite that projects rostroventrally (gray arrowheads). G–I, Ventrally located MiV1 cell in r4 (G), MiV2 cell in r5 (H), and MiV3 cell in r6 (I), which had an axon that projected to the ipsilateral spinal cord. These cells had a major thick lateral dendrite. Four of 10 MiV3 cells had an axon that projected rostrally and then caudally turned back (arrow). Up is rostral. The calibration in A is also applicable to B–I.