Fig. 1. Expression patterns of Slit1 and Slit2 and Robo1 and Robo2 in the rat embryo. (A) Diagram showing organisation of cranial motoneurons in E12 rat hindbrain; somatic motor (SM) neurons are on the left (red), BM/VM neurons are on the right (blue). Nuclei: III, oculomotor; IV, trochlear; V, trigeminal; VI, abducens; VII, facial; IX, glossopharyngeal; X/XI, vagus and cranial accessory; XII, hypoglossal (inner ear efferent neurons at r4 level omitted). (B,C,H-J) Flat-mount rat hindbrains in situ hybridised with Slit or Robo probes as indicated. Asterisk in H indicates the floor plate. (D-G,K-N) Vibratome sections of E12 rat embryos labelled with fluorescein dextran axon tracer then in situ hybridised; BM/VM projection labelled in D,F,K,M; SM projection labelled in E,G,L,N. Insets in K and M show in situ hybridisation without axon tracing. The axial levels of the vibratome sections are D rhombomere 2(r2); E, r5; F, r2; G, r8; K, r3; L, r7; M, r6; N, r6. (O-R) Peroxidase-stained sections of a rat E12 hindbrain with adjacent sections stained with neurofilament (NF) or anti-Robo1+2 antibodies as labelled. (O,P) r2/3 level; (Q,R) r8. HB or H, hindbrain; MB or M, midbrain; FP, floor plate; r, rhombomere; RL, rhombic lip; SM, somatic motoneurons; TMA, trigeminal motor axons; TG, trigeminal ganglion; VMA, vagus motor axons; HMA, hypoglossal motor axons. Scale bar: 500 µm in B,C,H,I,J,Q,R; 200 µm in D-G,K-N; 300 µm in O,P; 800 µm in insets.