Figure 12. tdTomato⁺ cell bodies in Brn3c^Cre/WT; ROSA26^tdTomato/WT mice delineate a novel subdivision of the deep mesencephalic nucleus (“Drury” nucleus).

(a–d) Coronal brain stem schematics and (a1–d1) Brn3c^Cre/WT; ROSA26^tdTomato/WT brain sections, spanning Bregma reference points from −3.52 mm (left) to −4.24 mm (right), adapted from Paxinos mouse atlas plates 60, 62, 64, and 66 respectively. Structures relevant to the Deep Mesencephalic nucleus are labelled with arrows: DpMe – deep mesencephalic nucleus; DpWh – deep white layer of the superior colliculus; DLPAG – dorso- lateral peri-aquaeductal gray; LPAG – lateral peri-aquaeductal gray; DpG – deep gray layer of the superior colliculus; InCo – intercollicular nucleus; Me5 – mesencephalic trigeminal nucleus. The newly identified concentration of cell bodies are encircled with stippled lines in each section in both hemispheres. Within the DpMe of the rostral sections (a1–b1), two separate streams of cell bodies are seen, which are progressively closer to each other more caudally (b1) and eventually fuse towards caudal sections (c1, d1). In sections c1 and d1, the cluster of tdTomato⁺ cells is centered on the boundary of the DpMe, InCo and the LPAG. Given the large number and size of tdTomato⁺ cell bodies, these are distinct from the sparse, large nuclei of the Me5 (see figure 13). Scale bar in d1 = 500 microns.