Midbrain

The sense probe staining is shown in Figure 6a,b. Between forebrain and midbrain, moderate labeling was observed in neurons of the anterior glomerular nucleus, in neurons bordering the margins of the glomerular nucleus and in few large neurons in its inner part (Figure 6c,d). In the longitudinal tori, NT-6 mRNA was intensely expressed in numerous positive neurons located mainly in the most ventral part (Figure 6e), and along the margin with the optic tectum (Figure 6f). In the optic tectum, positive neurons were observed in the periventricular grey zone (Figures 6g and 7a). However, NT-6 mRNA expressing neurons were few in the most rostral part of the periventricular grey zone (Figure 6f) while became more numerous caudally (Figures 6g and 7a). Furthermore, the neurons lining the margin between the optic tectum and tegmentum were intensely labeled (Figure 6g). In the tegmentum, a positive signal was detected in neurons of Layers 1, 3 and 4 of semicircular tori (TS-1, TS-3, and TS-4) (Figure 6c).

**Figure 6.** Expression of NT-6 mRNA in transverse section of caudal diencephalon/midbrain of adult *N. furzeri.* On the top, schematic drawings of *N. furzeri* brain, with red dots indicating NT-6 mRNA distribution over the different brain areas. Caudal diencephalon/midbrain: (**a**) sense probe staining in the anterior midbrain tegmentum; (**b**) high magnification of sense probe staining in the NG; (**c**) overview of tegmentum, with probe signal in neurons of TS and NG; (**d**) high magnification of positive neurons, scattered along the margin of NG; (**e**) probe signal in the dorsal and ventral part of TL and along the margin with OT; (**f**) few positive cells of PGZ in the anterior part of OT; and (**g**) numerous positive cells in the most caudal part of OT and intense staining at the margin between OT and the midbrain tegmentum (arrow). Scale bars: (**a**,**c**) 50 μm; and (**b**,**d**–**g**) 25 μm. Abbreviations: NG, glomerular nucleus; OT, optic tectum; PGZ, periventricular grey zone; TL, longitudinal tori; TS, semicircular tori.
