PMC

Upper drawing shows a three-dimensional model of the human red nucleus. The rostral end of this model is toward the left side. The lower drawing shows serial sections of the magnocellular red nucleus (also shown in –) for reconstructing the magnocellular red nucleus. Large dots indicate giant neurons. Top extension with diamond-shaped cross-section is the cerebral aqueduct in the mid-saggital plane, dmpN – dorsomedial part of parvicellular red nucleus, FR – fasciculus retroflexus, mNr – magnocellular red nucleus, NB – nucleus accessorius medialis of Bechterew, ND – nucleus of Darkschewitsch, vlpNr – ventrolateral part of parvicellular red nucleus.

High magnification photographs of pigmented neurons (A) outside the magnocelluar red nucleus and giant neurons (B) of the magnocellular red nucleus in . Scale bar  = 100 µm.

The magnocellular red nucleus wraps around the caudal pole of the parvicellular red nucleus. The black arrowheads indicate giant neurons. Black and white arrowheads indicate pigmented large neurons. The number in the left corner is the rostrocaudal distance (in micrometers) from the rostral tip of the red nucleus. CLi – caudal linear nucleus, MLF – medial longitudinal fasciculus, mNr – magnocellular red nucleus, NIII – oculomotor nerve, PBP – parabrachial pigmented nucleus, SCP – superior cerebellar peduncle, SNc – substantia nigra pars compacta, vlpNr – ventrolateral part of parvicellular red nucleus, III – oculomotor nucleus. Scale bar  = 100 µm.

Pitx2 expression is transient in the ventral midbrain. (A–L) Adjacent coronal sections of Pitx2^Cre/+;NL midbrains processed for βGAL histochemistry (A, B, E, F, I, J), Pitx2 mRNA (C, G, K) or PITX2 immunofluorescence (D, H, L). The dotted line demarcates the red nucleus. (A) At E14.5, Pitx2-lineage neurons are located in the superior colliculus (SC) and red nucleus (RN). (B) High magnification of panel A shows only a few Pitx2-lineage cells in the red nucleus, despite high red nucleus Pitx2 mRNA (C). (D) Immunofluorescence indicates only a few PITX2-positive red nucleus cells. (E, F, I, J) At E16.5–E18.5, β-galactosidase activity shows Pitx2-lineage neurons in the superior colliculus and red nucleus. (G, H, K, L) The E16.5–E18.5 red nucleus continues to express Pitx2 mRNA, although PITX2 protein is absent. (M) Coronal section of an E14.5 Pitx2^Cre/+;ZsGrn midbrain showing ZsGrn fluorescence in the superior colliculus. Few cells are fluorescent in the ventral midbrain as seen in a high magnification image of the red nucleus (N). (O) A neighboring section to M processed for Pitx2 in situ hybridization shows Pitx2 mRNA in the superior colliculus, ventromedial population, and red nucleus. (P) Higher magnification of the red nucleus in O. Dotted areas denote the ventromedial population and red nucleus. Scale bar in A is 125 μm and applies to panels A, E, and I. Scale bar in B is 32μm and applies to panels B–D, F–H, and J–L. Scale bars in M and N are 100μm and 50 μm and apply to panels M, O and N, P, respectively.