Cervical Flexure Research Articles

Morphogenesis of experimentally induced arnold-chiari malformation

The administration of a single dose of vitamin A to pregnant hamsters, early during the morning of their 8th day of gestation, induces types I and II Arnold-Chiari malformation (ACM), as well as various types of axial skeletal-dysraphic disorders known to be associated with the human disease. This new model provides a means of carrying comparative studies between the axial skeletal defects and neurological anomalies of this complex developmental malformation with those which characterize the other induced disorders related to it. Study of this experimental model has demonstrated that the basichondrocranium of fetuses with ACM is shorter than normal and slightly elevated (lordotic) in relation to the axis of the vertebral column. The shortness of the basichondrocranium of these fetuses is caused by the underdevelopment of the occipital bone specially noticeable in its basal component (basioccipital). This basic defect has resulted in a short and small posterior cerebral fossa which is inadequate to contain the developing nervous structures of that region. The developing cerebellum is displaced downward to an anomalous position just above the foramen magnum; and, the developing medulla is compressed or crowded into the small posterior cerebral fossa of affected fetuses. The lordotic elevation of the basichondrocranium is also responsible for the reduction of the pontine flexure and the increased angle of the cervical flexure of the hindbrain found in these fetuses. All of these neurological anomalies, which are characteristic and diagnostic of clinical ACM as well, are considered here to be secondary to the axial skeletal defects rather than primary abnormalities, as is generally believed. The peculiar type of protrusion of the odontoid process into the cranial cavity found in fetuses with ACM, as well as in those with cranioschisis aperta and occulta, is also considered to be caused by the slight depression of the underdeveloped basioccipital and therefore, comparable to the so-called basilar impression often described in clinical ACM. This study has emphasized various developmental features which are closely related with the morphogenesis of ACM, including: the somitic origin of the occipital bone, and the late growth of the cerebellum which is predominantly postnatal in almost all experimental animals. It has been pointed out that some developmental defects involving the occipital bone and the caudal vertebral column, such as those which characterize ACM type II, may be more closely related than previously recognized. It has been also pointed out that the so-called cerebellar herniation into the cervical spinal canal described in the human disease represents a late addition to this disorder which is related to the relatively late growth of the cerebellum. A prerequisite for the development of this late anomaly is the presence of a small posterior cerebral fossa which is overfilled during the postnatal growth spurt of the cerebellum which is then forced to grow into the available space of the upper cervical spinal canal. A new hypothesis concerning the origin and morphogenesis of axial skeletaldysraphic disorders, including ACM, is introduced in this study. The hypothesis proposes that a primary para-axial mesodermal insufficiency (vitamin A-induced) could affect embryos prior to, during, and after the closure of the neural folds resulting in a variety of developmental malformations which share a common type of axial skeletal defect and different neurological anomalies which reflect the degree of the dysraphic disturbance. ACM, in spite of its lack of a distinct dysraphic defect, represents an example of this type of developmental disorder, and as such it has been classified. Finally, the study introduces the idea that an early surgical intervention (nuchalectomy) in possible candidates of this disorder may prevent the development of the devastating neurological complications which characterize human ACM.

Prenatal Development after Diapause in the Marsupial Macropus rufogriseus

Prenatal development of Macropus rufogriseus was described in eight stages ranging from a quiescent blastocyst to a near-term foetus. Embryos and corpora lutea were induced to resume development after diapause by the removal of suckling pouch young (RPY). The diameter of unilaminar blastocysts ranged from approximately 260 �m at 0 days after RPY to 290 �m after 6 days. At 9 days after RPY (330 �m diameter) the zona pellucida and mucoid coat were apparently absent and endoderm had proliferated (early bilaminar). At 15 days, mesoderm had formed in the trilaminar blastocyst (4.8 mm diameter). By 18 days after RPY the shell membrane had ruptured and was 3.0 �m in thickness (7.0 pm at 0 days after RPY). At this time the pre-foetal embryo had acquired forelimb ridges, mesonephric kidneys, optic stalks and 25 paired somites; persistent features included an amniopore, posterior neuropore and an intact stomodeal membrane; the lung buds and allantois were rudimentary; cervical, lumbosacral and cranial flexures were present. By 20 days after RPY, digital anlagen were noted in the forelimb paddles of the pre-foetal embryo (32 paired somites); the gonadal ridges; glomeruli and optic cups had formed. At 25 days after RPY, the near-term foetus had forelimbs with claws on the separate digits, hindlimb paddles, pontine flexure and cardiac valves; the metanephric kidneys, pigmented and nervous retinas and villous intestine were present. A single birth was recorded at 26 days after RPY (delayed gestation length).

Temporal, morphological, and genetic responses of avian embryos to Azodrin, an organophosphate insecticide.

The effect of Azodrin on avian development was studied using a bobwhite quail line and two chicken lines--a single comb White Leghorn (SCWL) and an Australorp line. The bobwhite quail embryos did not respond to injections of Azodrin until stages 22 to 23 (6 days of incubation); the SCWL embryos, not until stage 18 (3 days of incubation) with increasing susceptibility through stage 20. The threshold concentration, at stage 19, for the SCWL was 0.4 mg/kg, for the Australorp, less. Within one hour of treatment stage-20 embryo shape was altered. There was, however, no immediate response from embryos treated earlier. The effect appeared as a reduced growth rate in the cervical flexure, and may be mediated by interference with the normal energy balance. The response, once initiated, was continuous through 10 days of incubation.

Skullbase malformations in rat fetuses with hypervitaminosis A-induced exencephaly.

AbstractExencephalic fetuses (16th–20th day), offspring of female Wistar rats treated with vitamin A palmitate orally during pregnancy, were studied in serial sections. The median part of the skullbase of the rat is formed by the basioccipital, basisphenoid, and presphenoid. In exencephalic fetuses the basioccipital had a normal shape; the hypophyseal fossa in the basisphenoid was too deep; the presphenoid was malformed. The angle between the cervical vertebral column and basioccipital was increased and those between the basioccipital and basisphenoid, and the basisphenoid and presphenoid were reduced. As a result the longitudinal axis of the skullbase was shortened. In all exencephalic fetuses the pontine and cervical flexures were less well marked than in controls. No anomalies of the rostral part of the notochord were observed. It is concluded that there is a relation between abnormal flexures of the neural tube and the malformation of the skullbase. The resemblance of the skullbase in human anencephaly and rat exencephaly is emphasized.

Changes in the foramen magnum axis during human foetal life.

The present findings showed that in early embryonic life the foramen magnum plane has a direction, more like that found in most animals in the sagittal plane due to the cervical flexure found at this early developmental period. Gradually during the foetal period the inclination of the foramen magnum plane changes to a more perpendicular relationship with the trunk preparing for a future erect posture. It was thought that the most important factor in this change of inclination is the rapid growth of the cerebral cortex. The study was carried out in order to see if possible changes in axial inclination of the foramen magnum axis in the sagittal plane can partly explain the changes in the cephalic flexure during foetal life. The material consisted of 38 selected human foetuses and 4 skulls of newborn babies.

The early brain development of the dog.

AbstractThe neural plate in dog embryos forms cranial to the primitive streak by 15 days and elongates as the primitive streak regresses. The neural folds contact each other at the third rhombomere at the seven somite stage. Neural crest cells are present in the early somite embryos from the optic primordia throughout the brain. Differentiation of these cells results in the anlagen of cranial nerve ganglia. Regional differentiations of the neural plate establish the prosencephalon as a broad cranial segment by four somites, with a closed neural tube, optic vesicles and infundibulum by 15 somites. The mesencephalon is an almost spherical vesicle and the rhombencephalon has become subdivided by 15 somites into seven neuromeres. The cranial flexure begins in the mesencephalon at ten somites, and the cervical flexure at the fourth somite level by 20 somites. The pontine flexure first appears at 32 somites. Secondary divisions of prosencephalon and rhombencephalon from a typical five vesicle brain anlage. The telencephalon is present at 20 somites as a bulge from the roof of the diencephalon. Telencephalic vesicles appear by 30 somites. The mesencephalon elongates slowly but is not divided into neuromeres. The rhombencephalon by 25 days has differentiated into the primordia of the cerebellum and pons cranially (the metencephalon) and the medulla oblongata caudally (the myelencephalon).

The Development of the Embryonic Membranes of the Shrews, Sorex araneus Linn, and Sorex minutus Linn

SUMMARY. 1 The changes in the uterine wall preceding and during the process of implantation of the blastocysts are described. The formation of the uterine crypts results from rearrangement of the cells of the uterine epithelium and they open into the uterine lumen from the time of their inception. This account differs from Hubrecht's (1894), who claimed that the crypts were formed from nests of epithelial cells beneath the epithelium which acquired a secondary opening by the breaking clown of the overlying epithelium. 2 The changes in the structure and arrangement of the embryonic membranes during and after the attachment of the blastocyst to the uterine wall are described in sequence. 3 Amniogenesis is by fold formation after the embryonic plate has been exposed by the disappearance of the cells of Rauber. The amniotic and chorionic parts of the folds are distinct from the beginning and there is no transformation of the one into the other. A transient sero-amniotic connection is formed from the cells of the amniotic wall of the folds at the point where they close, far back over the embryo. The proamnion is large and is invaginated, together with the yolk-sac, by the formation of the cervical flexure. The mesoderm only extends into this region at a late stage in development. 4 The allantoic mesoderm differentiates very early, almost immediately after the formation of the exocoel. The entodermal allantoic diverticulum is formed later, is exceedingly rudimentary and transitory. The allantoic stalk is not provided with a trophoblastic sheath, like that of Crocidura (Sansom, 1937). The allantoic mesoderm fuses with the chorion, forming the allantochorion, very soon after the closure of the amniotic folds, and the adherence of the ehorionic trophoblast to the mucosa. 5 Vestiges of a decidua capsularis corresponding to that of Erinaceus are found in Sorex, but a complete decidua eapsularis is not formed. Small transitory folds, which are quite distinet from the vestiges of the decidua capsularis, are, found in Sorex araneus and it is suggested that these correspond to the so-called “ decidua eapsularis ” of Crocidura. 6 Reichert's membrane is well developed in the Shrews. It is formed between the mesoderm and trophoblast of the chorion and between the entoderm and trophoblast of the bilaminar omphalopleure. Therefore it appears to be of purely trophoblastic origin. It disappears in the placental region after the establishment of the allanto-chorion. Later its free margin forms a supporting collar around the base of the allantoic stalk. 7 The whole of the upper or splanchnic wall of the yolk-sac is invaginated within the lower or bilaminar wall so that the sinus terminalis runs around the rim of the cup so formed. The entodcrm cells of the area vasculosa become enlarged and their cytoplasm charged with granules. The small blood vessels of this region project into the cavity of the yolk-sac, forming villi which are covered with these enlarged entoderm cells and apparently are absorptive organs. The yolk-sac remains large and its bilaminar wall persists throughout development, though its cavity is greatly reduced by invagination and the consequent approximation of its outer and inner walls.

ニシキベラThalassoma cupido(TEMMINCK & SCHLEGEL)の発生に就て

The egg is pelagic, globular, small, its diameter 0•45-0•50mm long, with a single oilglobule measuring 0•07mm in diameter. It takes about 36 hours to hatch after fertilization at water temperatures 22•6-23•9°C. Newly hatched larvae (Fig. 3) are 1•1mm long, provided with 7 black chromatophores equidistantly along the dorsal median line, the foremost one is located at the cervical flexure. No pigment is present at the caudal end. The yolk-sac is projected forwards, forming a lump embracing an oil-globule with a black chromatophore, on its anterior surface. The number of myotomes is about 25 pairs. The larva sixteen hours old after hatching is 1•4mm long with 11 black chromatophores along dorsal median line. The anus is situated a little posterior to the middle of the ventral side of body. The ventral part of body and yolk-sac are not furnished with the black chromatophores. The egg of the present species is smaller than those of Halichoeres poecilopterus and Labrus sp. The newly hatched larva is distinguished from others as shown in the following key for Japanese species of Labridae. a. Black chromatophores of dorsal surface arranged in two rows…………H. poecilopterus. a'. Black chromatophores of dorsal surface arranged in one row b. With one black chromatophore above anus……………………………Labrus. sp. b'. Without black chromatophore above anus c. Oil-globule with a black chromatophore on its anterior surface……………T. cupido. c'. Oil-globule with a black chromatophore on its posterior surface d. Black chromatophores of the back 8…………………………………Labrus sp. d'. Black chromatophores of the back comparatively small, 18 in number……Labrus sp.