The thickness of the ventral midline of the spinal cord was determined in
9 human embryos aged five weeks (developmental stages 13-15). This part of
the spinal cord consists of floor plate, mantle and marginal layers. The floor
plate ependymal cells form pseudostratified columnar epithelium. The thickness
of the investigated structure varied from 20 to 50 micrometers at different
levels of the spinal cord

Bruska, M.

Pytel, A.

Sroka, A.

Woźniak, W.

Łupicka, J.

English

Via Medica Journals

Folia Morphol. Vol. 67, No. 3, pp. 205–208Copyright © 2008 Via MedicaISSN 0015–5659www.fm.viamedica.plO R I G I N A L   A R T I C L E205Address for correspondence: Prof. W. Woźniak, Department of Anatomy, University of Medical Sciences, Święcickiego 6, 60–781 Poznań,Poland, tel: +48 61 854 65 64, e-mail: wwozniak@ump.edu.plThe thickness of the ventral midlineof the spinal cord in human embryosduring the fifth weekW. Woźniak, J. Łupicka, A. Sroka, M. Bruska, A. PytelDepartment of Anatomy, University of Medical Sciences, Poznań, Poland[Received 21 July 2008; Accepted 21 July 2008]The thickness of the ventral midline of the spinal cord was determined in9 human embryos aged five weeks (developmental stages 13–15). This part ofthe spinal cord consists of floor plate, mantle and marginal layers. The floorplate ependymal cells form pseudostratified columnar epithelium. The thick-ness of the investigated structure varied from 20 to 50 micrometers at differentlevels of the spinal cord. (Folia Morphol 2008; 67: 205–208)Key words: human neuroembryology, spinal cord, ventral midlinecells, floor plateINTRODUCTIONDifferentiation of neuronal types and the estab-lishment of appropriate connections between neu-rons and their targets are critical phases of the earlydevelopment of the nervous system, and theseevents form the basis for the proper operation ofthe mature nervous system. Cells at the midline ofthe neural tube control axon projections and influ-ence motor neurons and several types of interneu-ron differentiation [2, 12, 16].The formation of precise neuronal circuits de-pends upon the ability of the growth cone, whichguides axons, to navigate over a long distance. Theguidance cues exist in either diffusible or cell sur-face-associated forms [7, 21]. Growth cone-associ-ated cell surface receptors interpret these signals aspositive/attractive (netrin) or negative/repulsive (slitand semaphorin proteins) forces [15, 24].The midline of the developing central nervoussystem represents an important choice point forpathfinding axons [8]. Recent experiments show thataxial mesoderm can stimulate formation of specificventral cell types in the spinal cord, including floorplate and motor neurons. Generation of these celltypes is dependent on the secreted signalling mole-cule Sonic hedgehog (Shh), which is produced byaxial mesodermal midline cells of the notochord. Shhsignalling from the notochord induces developmentof the ventral midline cells and the floor plate whichalso expresses Shh together with other genes [4].The ependymal lining floor plate has been inves-tigated in ultrastructural and cytochemical studieson the human spinal cord by Gamble [3], Malinskyand Brichova [13] and Tanaka et al. [20]. In thepresent study we investigated the thickness and his-tological structure of the ventral midline of the spi-nal cord in human embryos aged five weeks.Although morphological criteria do not permitdelimination of the ventral midline cells and the floorplate in the transverse plane, it is possible to mea-sure the thickness of the ventral midline cells of thespinal cord in the sagittal plane.MATERIAL AND METHODSA study was made on human embryos aged fiveweeks (developmental stages 13, 14 and 15, Table 1).The embryos were from the Collection of the De-partment of Anatomy of the University of MedicalSciences in Poznań. All embryos were embeddedin toto in paraplast and serially sectioned in the206Folia Morphol., 2008, Vol. 67, No. 3horizontal plane. Measurements of the ventral mid-line of the spinal cord were made on sections fromvarious levels of the spinal cord with the aid ofa Leica Olympus Microscope using program AxioVision LEwith the Canon Module. The thickness of the ventralmidline was determined together with the floor plate.The structure of the ventral midline of the spinalcord was also investigated in histological sections.RESULTSIn embryos at stage 13 the mantle layer of theventral midline of the spinal cord consists of 4 rowsof cells with oval nuclei. The ependyma at this partis formed of columnar cells with basally located nu-clei. The marginal layer is clearly visible (Fig. 1). Thethickness of the ventral midline in the embryos stud-ied varied from 20 to 40 mm at different levels ofthe spinal cord and was greater in the cervical andupper thoracic segments than in the lumbar seg-ment of the spinal cord (Table 2).In embryos at stage 14 the mantle layer of theventral midline is thicker than that of embryos instage 13 and consists of 5 or 6 rows of cells (Fig. 2).The ependymal layer consists of pseudostratifiedcolumnar epithelium. In the mantle layer the cross-ing commissural axons are visible (Fig. 3). The thick-ness of this ventral midline cells varies from 30 to50 mm (Table 2).In embryos at stage 14 the central canal of thespinal cord diminishes and the anterior horns arewell developed. The structure and thickness of theventral midline of the spinal cord are similar to thatof embryos at stage 14 (Fig. 4).DISCUSSIONThe ventral midline cells of the central nervoussystem are important in the neural tube, playinga role in the differentiation part of motor neuronsand the establishment of commissural projections[2, 14]. The differentiation of neurons in the ventralneural tube is dependent on inductive signals fromthe notochord and floor plate, which is formed ofspecialized glia in a narrow strip at the ventral mid-line [1, 14, 17, 18, 22].According to O’Rahilly and Müller [16], the floorplate is formed by the ventromedial cells of the epi-notochordal part of the neural plate or tube and isinduced by the notochord. It differs regionally. Cellsin the midbrain can induce the production of dopam-inergic neurons, whereas those of the rhomben-cephalon develop into the septum medullae.According to many authors, beginning with thedescriptions of His [5], the floor plate is made up ofcolumnar ependymal cells that span the width of theneural tube at its ventral midline. The anterior bound-ary of the floor plate has been placed at the hind-brain-midbrain junction [9, 10] but there are severalFigure 1. Horizontal section of the spinal cord of an embryo atstage 13. Staining with toluidine blue, ¥ 400; E — ependymal ofthe floor plate, M — mantle layer, m — marginal layer.Table 1. Crown-rump length, developmental stage, and age in days of the embryos examinedCatalogue C-R length Developmental Age in postovulatory Plane ofnumber  [mm]  stage  days sectionB 171 4 13 32 HorizontalB 194 6 13 32 HorizontalB 218 4.5 13 32 HorizontalA 19 7 14 32 HorizontalB 207 6 14 32 HorizontalP 41 5 14 33 HorizontalB 115 8 15 33 HorizontalPJK 20 7 15 33 HorizontalPJK 21 10 15 37 Horizontal207W. Woźniak et al., Human embryonic midline cellsreasons for believing that this plate extends throughthe midbrain into the posterior diencephalon andends near the mammillary region [2, 11, 17, 18].In the present study it was shown that in the earlyembryonic human spinal cord the ventral midline ofthe spinal cord consists of ependymal lining cells,mantle, and marginal layers. The thickness of the partof the spinal cord under investigation slightly increas-es at stages 14 and 15, and during these stages com-missural axons are visible crossing the marginal layer.Table 2. Thickness of the ventral midline of the spinal cord in the embryos examinedCatalogue number Developmental Level of section Thickness in micrometersof embryo stageB 171 13 Upper thoracic 40Lumbar 30B 194 13 Cervical 30Lower thoracic 20B 218 13 Upper thoracic 20Lower thoracic 20Lumbar 20P 41 14 Lower cervical 40Upper thoracic 40Lower thoracic 30A 19 14 Upper thoracic 30Lower thoracic 40B 207 14 Cervical 50Upper thoracic 50Lumbar 40B 115 15 Cervical 40Upper thoracic 40Lower thoracic 40PJK 21 15 Cervical 30Upper thoracic 30Lower thoracic 30PJK 20 15 Cervical 50Upper thoracic 40Lower thoracic 40Figure 2. Horizontal section of the spinal cord in an embryo atstage 14. Bodian’s protargol, ¥ 100; A — anterior horn,B — ventral midline cells.Figure 3. Horizontal section through the ventral part of the spinalcord in an embryo at stage 14. Bodian’s protargol, ¥ 400; E —ependyma of the floor plate, M — mantle layer, m — marginallayer with commissural fibres.208Folia Morphol., 2008, Vol. 67, No. 3Sturrock [19] in mouse, Yoshioka and Tanaka inrats [23] and Gamble [3] and Malinsky and Brichova [13]in humans found that the floor plate ependymal cellsdifferentiate during an earlier stage of embryonicdevelopment and are closely associated with thegrowth of decussating nerve fibres in the marginallayer, as was observed in our study. Midline-associ-ated glial cells appear to be a source of contact-dependent or diffusible guidance cues for commis-sural axons [6].REFERENCES1. Briscoe J, Ericson J (2001) Specification of neuronal fatesin the ventral neural tube. Curr Opin Neurobiol, 11:43–49.2. Colamarino SA, Tessier-Lavigne M (1995) The role ofthe floor plate in axon guidance. Annu Rev Neurosci,18: 497–529.3. Gamble HJ (1969) Electron microscope observations onthe human fetal and embryonic spinal cord. J Anat,104: 435–453.4. 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The thickness of the ventral midline of the spinal cord in human embryos during the fifth week

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The thickness of the ventral midline of the spinal cord in human embryos during the fifth week

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