New Model of Human Red Nucleus Figure 7. Distribution of WGA-HRP-labelled cells in mesodiencephalic structures (case 3 and 4). A (case 3) and B (case 4): rostral part of ND, C (case 3) and D (case 4): caudal part of ND. E (case 3): dmpNr. F (case 4): vlpNr. dmpNr–dorsomedial part of parvicellular red nucleus, NB–nucleus accessorius medialis of Bechterew, ND–nucleus of Darkschewitsch, vlpNr–ventorlateral part of parvicellular red nucleus. Scale bar = 100 mm in F (also applies to A–E). doi:10.1371/journal.pone.0006623.g007 of this CTT contains fibers emerging from the NB (Fig. 11D). Giant as well as large neurons of the mNr are gathered largely into a dorsal and a ventral group and are scattered among the fibers of the superior cerebellar peduncle (see section 14 in Fig. 10, Fig. 12). These neurons contain coarse Nissl bodies (Fig. 12F and G). At the caudal level of the vlpNr, large, medium and small sized neurons were seen to be gathered between the outer capsule of vlpNr and the pigmented (see next paragraph) cell layer (Fig. 12A– E). This neural zone and scattered giant and large neurons of the mNr form the semi-lunar shell which might correspond to the well-developed semi-lunar shell of mNr seen in infants (Ulfing and Chan, 2001; 2002 [12,13]; Yamaguchi and Goto, 2006 [14]). This adult mNr zone was vestigial, since in some areas these neurons had almost disappeared (Fig. 12C). Many large, pigmented neurons are observed in the surround- ing area outside the red nucleus and superior cerebellar peduncle, such as the parabrachial pigmental nucleus and the rostral and caudal linear nuclei (Fig. 12C and D). There is the possibility that some large pigmented neurons near the red nucleus are mis- identified as mNr neurons. However, these neurons can be excluded clearly from being mNr neurons since cell bodies of the former contain neuromelanin pigment while the latter do not (Fig. 12F, G and H). Discussion Neural Sheet Model of the Parvicellular Red Nucleus (Fig. 13) Ogawa (1939) attributed the origin of the MTT in the cat to three structures: the ND, Nint, and nucleus of the fields of Forel (corresponding to the rostral interstitial nucleus of MLF) and concluded that the human red nucleus corresponds to these nuclei [1]. Thereafter, many researchers subscribed to the view that quadrupedal animals have a well-developed MTT and that humans have a well-developed CTT; they furthermore held that both tracts have the same origins and terminations (see reference in Voogd, 2003 [15]). Cells of origin of these olivary projections have been identified with the HRP method. The subparafasci- cular and parafascicular nuclei in the cat (as defined by [16,17,18,19,20,21,22]) have been redefined as the rostral part of the ND, a structure that projects to the rostral MAO (Onodera, 1984 [3]). The rostral part of the ND in the rat (as shown by Ruigrok and Cella, 1995 [23]) also projects to the rostral MAO (Onodera et al., 2004 [24]). However the rat’s ND proper does not project to the inferior olive [23,25] and does not receive terminals from the substantia nigra pars reticulata (SNr) which projects to the ventrolateral central gray ventral to the rat’s ND PLoS ONE | www.plosone.org 9 August 2009 | Volume 4 | Issue 8 | e6623