Fusion of the cervical vertebrae of mammals

Morphogenesis of the cervical vertebrae has been investigated in Dipis sagitt. and in Rattus norvegicus. The main distinctive feature of the Dipis embryos at the mesenchymal stage is their very thin perichordal intervertebral rings. As a result, short cartilaginous vertebral bodies and thin intervertebral discs develop, cervical segments lengthen more slowly than those of the Rattus. Because of the small length of the Dipis cervical segments, the cartilaginous neural arches and the transverse processes of 2-6 vertebrae draw nearer and fuse. Owing to the insufficient development of the Dipis intervertebral discs and the nuclei pulposae, the normal formation of the vertebral epiphyses is disturbed, this results in fusion of the neighbouring osseous vertebral bodies.     

Congenital kyphoscoliosis and spinal cord lesion produced in the rat by beta-aminopropionitrile

Pregnant rats received the lathyrogen beta-aminopropionitrile (1,500 mg/kg) intraperitoneally on day 16 (plug day = 0 day). Kyphoscoliosis was produced in a high incidence in the fetuses at the level of the upper thoracic spine as early as 24 hours after treatment. Although most of the affected newborns died within two weeks, survivors were studied until 20 weeks after birth. Survivors developed paraplegia in consequence of kyphoscoliosis. Both spinal deformity and motor disturbance were progressive. Biochemical and electron microscopic observations suggested that beta-aminopropionitrile treatment resulted in an inhibition of collagen formation in the spinal column and surrounding longitudinal ligaments of the fetuses six hours after the treatment. In addition, electron micrographs of vertebral bodies showed a decrease of proteoglycan granules in the extracellular matrix. Therefore, rupture and collapse of weakened ligaments and vertebral bodies might result in severe spinal deformity and spinal cord lesion.     

The arterial supply of the cervical vertebral body in newborns

The cervical vertebral column is mainly supplied by both vertebral arteries. A regular ladder pattern of arteries is on the dorsal plane as well as on the ventral plane of the cervical vertebral bodies, opposite to the thoracal and the lumbar area of the vertebral column with only a dorsal ladder pattern of arteries. The cervical arterial anastomoses are built by the segmental arteries of the vertebral arteries, in the back of the cervical vertebral bodies by the arteriae canalis vertebralis anteriores and in the front by the rami anteriores (corporum vertebrarum). The thyrocervical and the costocervical trunks are an additional blood supply especially to the ventral anastomoses. A loss of a segmental artery may have no effect because of the good anastomoses. Some decades of aa. nutriciae come in the vertebral body from all sides, but only 2 up to 4 rr. centrales anteriores and 2 rr. centrales posteriores join in the middle of the vertebral body. There are parallels to the arterial blood supply of the thoracal and the lumbar vertebral bodies. The longitudinal ligaments are supplied by both ladder patterns of arteries.     

Remodelling of the vertebral axis during metamorphic shrinkage in the pearlfish

Body shortening was observed in the pearlfish Carapus homei during metamorphosis. The tenuis larva at first possessed a suite of osseous vertebral bodies of similar length. The reduction in both the number and size of vertebrae followed increasing decalcification, degeneration of organic tissue and shortening. This involved a complete degradation and disappearance of the caudal tip vertebrae, and there was a reduction in the size of most of the remaining vertebrae. The further development of the vertebrae began with ossification of the neural and haemal arches before that of the vertebral body. This second part of the development followed a gradient: a gradual decreases towards the caudal tip in the size of the vertebrae and their completeness.     

Deformation of the notochord by pressure from the swim bladder may cause malformation of the vertebral column in cultured Atlantic cod Gadus morhua larvae: a case study

This study describes a malformation that frequently occurs in Atlantic cod Gadus morhua in intensive culture systems. The malformation is characterised by a slight upward tilt of the head and an indented dorsal body contour at the transition between the head and the trunk, and is first evident to the fish farmer when the cod reach the juvenile stage. These abnormalities are associated with malformations of the neurocranium, the cranial region of the vertebral column and the cranial part of the epaxial lateral muscles. The pathogenesis involves deformation of the notochord, which can be observed in larvae about 7 d post-hatch (dph) and onwards. The deformation consists of an increase in dorsal curvature of the notochord in the region above the swim bladder. In the same region, the notochord has an abnormal cross-sectional outline, characterised by a groove-shaped, longitudinal impression along the ventral surface of the sheath. In most cases, the swim bladder fills the impression, and in severely affected larvae it forms a hernia-like lesion in the notochord. The deformation of the notochord seems to be conveyed to the vertebral body anlagen (chordacentra), which in teleosts are formed by mineralisation within the notochordal sheath. The vertebral bodies adopt an abnormal wedge shape, with a ventral concavity, and the neural arches are most often S-shaped. A continuous range of degrees of the malformation can be observed. All these pathomorphological characteristics are compatible with the notion that the notochord has been subjected to an upward mechanical force, probably generated by a persistent increase in pressure between the swim bladder and the notochord during the period of development of the vertebral anlagen. Our results thus indicate that the critical time window with regard to development of the malformation is from 18 to 36 dph, when the initial formation of the vertebrae takes place. Chronic overinflation of the swim bladder or pathological dilatation of the digestive tract may cause the lesions, and aetiology may be related to factors that influence the function of these organs.     

Configuration of the cervical part of the spinal column in various age periods

In order to estimate pathological deformities of the spinal column, it is necessary to know its normal configuration during various age periods. For this 240 men and women in age groups from 15 up to 60 years and older, having not any complaints, have been investigated. Each patient is subjected to a standard x-ray examination of the cervical part of the spinal column in 2 projections with a subsequent roentgenography In the roentgenograms (lateral projection) angles between ventral bodies CII and CVII are measured, as well as angles in every segment. Indices of the cervical lordosis for every age group in men and women are estimated. The form of the cervical part of the spinal cord in men and women is not equal and changes in different age periods. During the middle age lordosis decreases both in men and women and again increases in the elderly age.     

Length of the spinal dural sac, sex differences and correlation with the length of the spinal cord and vertebral column in adults

In 94 corpses (59 male and 35 female) of mature persons the length of the spinal dura mater sac has been studied. The average length of the sac is 621 +/- 3 mm. In men its average length is 636 +/- 4 mm, it makes 40 mm more in length than that in women (596 +/- 4 mm). The length of various parts in the dura mater sac is not the same: the cervical part makes 23% of the whole length, the thoracic--47%, the lumbar--23%, the sacral--7%. In men the cervical part of the sac in average is 6 mm longer than the lumbar part, and in women--quite the reverse, it is 7 mm shorter than the lumbar part. The sacral part of the sac in women is 3 mm longer that that in men. The sex differences noted are statistically significant. It is stated that the length of the spinal cord, its dura mater and the vertebral column are related as 1:1.5:1.7, the length of their cervical parts--as 1:1.5:1.4. the thoracic--as 1:1.3:1.3, the lumbar--as 1:2.4:3, the sacrococcygeal--as 1:1.4:4.9, respectively. During ontogenesis the greatest increase in the dura mater sac takes place in the cervical part as compared to the spinal cord and the vertebral column; in the thoracic part the intensity of their growth is equal: in the lumbar and in the sacrococcygeal part the increase of the vertebral column is the greatest.     

Effects of a brief sensorimotor training on the development of behavioral inhibition in the mouse

In the young C57Bl6 mouse, the hyperexcitability phase (`pop-corn' stage) which normally occurs around the 16–18th postnatal day and lasts 3–6 days, was greatly shortened by an intensive sensorimotor training when the `pop-corn' stage appeared. It was prevented when the animals were trained for 4 days before it appeared. This might suggest, at least in part, that an early short duration sensorimotor training increased the rate of maturation of the inhibitory systems that sustain the development of the motor behavior.     

“Naked” spinal cord on a non-segmented baton-like bony structure in the tail of the electric fish Eigenmannia virescens (Gymnotoidei)

Summary The caudal spinal cord of Eigenmannia virescens is not enclosed in a neural canal of the vertebral column. In fact, a segmented vertebral column with neural and ventral arches is lacking and replaced by a non-segmented baton-like bony structure on which the free spinal cord is located. The baton consists of calcified bone tissue with bone cells. Individual differences exist as far as the length of the rod is concerned. The electromotor neurons of this caudal part of the spinal cord are histochemically acetylcholinesterase-positive. The electrocytes which surround this part of the spinal cord show strong enzymatic actitivity on the posterior innervated face. However, there is also activity on the non-innervated lateral and anterior faces.     

Built for speed: strain in the cartilaginous vertebral columns of sharks

In most bony fishes vertebral column strain during locomotion is almost exclusively in the intervertebral joints, and when these joints move there is the potential to store and release strain energy. Since cartilaginous fishes have poorly mineralized vertebral centra, we tested whether the vertebral bodies undergo substantial strain and thus may be sites of energy storage during locomotion. We measured axial strains of the intervertebral joints and vertebrae in vivo and ex vivo to characterize the dynamic behavior of the vertebral column. We used sonomicrometry to directly measure in vivo and in situ strains of intervertebral joints and vertebrae of Squalus acanthias swimming in a flume. For ex vivo measurements, we used a materials testing system to dynamically bend segments of vertebral column at frequencies ranging from 0.25 to 1.00 Hz and a range of physiologically relevant curvatures, which were determined using a kinematic analysis. The vertebral centra of S. acanthias undergo strain during in vivo volitional movements as well as in situ passive movements. Moreover, when isolated segments of vertebral column were tested during mechanical bending, we measured the same magnitudes of strain. These data support our hypothesis that vertebral column strain in lateral bending is not limited to the intervertebral joints. In histological sections, we found that the vertebral column of S. acanthias has an intracentral canal that is open and covered with a velum layer. An open intracentral canal may indicate that the centra are acting as tunics around some sections of a hydrostat, effectively stiffening the vertebral column. These data suggest that the entire vertebral column of sharks, both joints and centra, is mechanically engaged as a dynamic spring during locomotion.     

Investigation of impact loading rate effects on the ligamentous cervical spinal load-partitioning using finite element model of functional spinal unit C2–C3

The cervical spine functions as a complex mechanism that responds to sudden loading in a unique manner, due to intricate structural features and kinematics. The spinal load-sharing under pure compression and sagittal flexion/extension at two different impact rates were compared using a bio-fidelic finite element (FE) model of the ligamentous cervical functional spinal unit (FSU) C2–C3. This model was developed using a comprehensive and realistic geometry of spinal components and material laws that include strain rate dependency, bone fracture, and ligament failure. The range of motion, contact pressure in facet joints, failure forces in ligaments were compared to experimental findings. The model demonstrated that resistance of spinal components to impact load is dependent on loading rate and direction. For the loads applied, stress increased with loading rate in all spinal components, and was concentrated in the outer intervertebral disc (IVD), regions of ligaments to bone attachment, and in the cancellous bone of the facet joints. The highest stress in ligaments was found in capsular ligament (CL) in all cases. Intradiscal pressure (IDP) in the nucleus was affected by loading rate change. It increased under compression/flexion but decreased under extension. Contact pressure in the facet joints showed less variation under compression, but increased significantly under flexion/extension particularly under extension. Cancellous bone of the facet joints region was the only component fractured and fracture occurred under extension at both rates. The cervical ligaments were the primary load-bearing component followed by the IVD, endplates and cancellous bone; however, the latter was the most vulnerable to extension as it fractured at low energy impact.     

Paradox segmentation along inter- and intrasomitic borderlines is followed by dysmorphology of the axial skeleton in the open brain (opb) mouse mutant

In open brain (opb) mutant embryos, developmental defects of the trunk spinal cord were spatially correlated with severe defects of the epaxial somite derivatives including sclerotomes, whereas hypaxial somite derivatives are much less affected. Later in development, the neural arches (epaxial sclerotome derivatives) formed but were severely disorganized, and also the distal ribs (hypaxial sclerotome derivatives) were malformed. Adjacent neural arches and vertebral bodies were often fused where joints should have formed suggesting defects of the intrasomitic borderlines. Moreover, neural arches frequently and ribs sometimes were split into halves at distinct levels along the dorso-ventral body axis. This suggests that ‘resegmentation’ of sclerotomes across the somite borders did not completely occur. These prominent skeletal defects were preceded by reduced expression of Pax1 along the intrasomitic borderlines, and incomplete maintenance of somite borders between central sclerotome moieties. The defects of the axial skeleton were accompanied by segmentation defects of the myotomes which were split distally, and also partly fused from adjacent segments across somite borders. The segmentation defects observed suggest that in opb mutants both segmental borderlines, the somite borders and the intrasomitic borderlines (fissures), were affected and behaved paradoxically. Dev. Genet. 22:359–373, 1998. © 1998 Wiley-Liss, Inc.     

Development of osteological structures in the sea bream: vertebral column and caudal fin complex

The development of cartilaginous structures in cultured sea bream Sparus aurata larvae and the timing of their ossification was studied. In cultivated sea bream larvae the first cartilaginous structure to be identified was hypural 1 at 4.1 mm notochord length ( L _N). By 5.3 mm L _N, prior to the onset of ossification, it was possible to distinguish the following cartilaginous structures: all 23 neural arches, all 13 haemal arches and two of the four pairs of parapophyses. The neural arches 1–4 and 15–23 were formed on the notochord and elongated dorsally, while neural arches 5–14 appeared on the dorsal side of the spinal cord and elongated ventrally. Initiation of ossification occurred at 5.7–6.0 mm standard length ( L _S) when the cartilaginous ontogeny of the vertebral column was completed. Ossification was coincident with dorsal flexion at the posterior end of the notochord and occurred in a sequential manner: (1) dorsoanteriorly, the cartilaginous neural arches and the centra were the first structures to ossify; (2) ventrad at the centre, at 7.0–7.5 mm L _S; (3) posteriorly at 7.1 mm L _S the hypural complex and urostyle (24th centrum) were ossified; and (4) dorsad at the centre (neural arches and spines).     

Time of origin of cells in the histiogenesis of the spinal cord]

In order to establish the moment of appearance of neuroblasts and ectoglia of the spinal cord the autoradiographic study with the use of H3-thymidine and C14-thmidine injected to pregnant mice with the intervals between injections 121/2 or 24 hours was undertaken. It was establised that spinal neurons were removed from the nervous tube beginning from the 10th up to 13th days of embroyogenesis. The motoneurons of the anterior horn were the first to appear (10th-12th days), the neurons of the intermideate zone were the next to appear (11th - 12th days) and the last were the neurons of posterior horn (13th day). Beginning from the 13th day of embryogenesis there appeared the ectoglia which migrated following meurblasts two days later. The saturation of the grey matter with glial cells and the saturation of the white matter with Schwann cells was brought about by means of additional multiplication at the site of the glioblasts removed from the nervous tube. The main function of the matrix layer neuroepithelium of the nervous tube as a provider of cells to the spinal cord terminated on the 15th day of embryogenesis.