Fig. 3. Reticulospinal somata backfilled with dextran biotin from near the chronic recording site. (A) Horizontal section highlighting hindbrain segmentation. Reticulospinal neurons ipsilateral to the injection site are seen in rhombomeres (r-) 4 and 5 and contralateral in r3, r4 and r6 (Bi-Biv). Transverse sections of representative reticulospinal neurons in r2, r4, r5 and r7, respectively. (Bi) Two ipsilateral reticulospinal neurons in r2. (Bii) Bilateral reticulospinal neurons labeled in r4. Note the Mauthner cell ventral dendrite on the left (arrow). (Biii) Bilateral reticulospinal neurons in r5 at the level of the decussation of the M-axons (asterisk). (Biv) Bilateral reticulospinal neurons located in r7. Midline is to the left in Bi and is centered in Bii-Biv.