Spatial relations in the oral cavity and the mechanism of secondary palate closure in the rat

Morphometric analysis of secondary palate development in human embryos

Rapid shelf elevation and contact of the secondary palate and fusion reportedly occur due to a growth-related equilibrium change in the structures within the oro-nasal cavity. This study aimed to quantitatively evaluate complex three-dimensional morphological changes and their effects on rapid movements, such as shelf elevation and contact, and fusion. Morphological changes during secondary palate formation were analyzed using high-resolution digitalized imaging data (phase-contrast X-ray computed tomography and magnetic resonance images) obtained from 22 human embryonic and fetal samples. The three-dimensional images of the oro-nasal structures, including the maxilla, palate, pterygoid hamulus, tongue, Meckel's cartilage, nasal cavity, pharyngeal cavity, and nasal septum, were reconstructed manually. The palatal shelves were not elevated in all the samples at Carnegie stage (CS)21 and CS22 and in three samples at CS23. In contrast, the palatal shelves were elevated but not in contact in one sample at CS23. Further, the palatal shelves were elevated and fused in the remaining four samples at CS23 and all three samples from the early fetal period. For each sample, 70 landmarks were subjected to Procrustes and principal component (PC) analysis. PC-1 accounted for 67.4% of the extracted gross changes before and after shelf elevations. Notably, the PC-1 values of the negative and positive value groups differed significantly. The PC-2 value changed during the phases in which the change in the PC-1 value was unnaturally slow and stopped at CS22 and the first half of CS23. This period, defined as the "approach period", corresponds to the time before dynamic changes occur as the palatal shelves elevate, the tongue and mandibular tip change their position and shape, and secondary palatal shelves contact and fuse. During the "approach period", measurements of PC-2 changes showed that structures on the mandible (Meckel's cartilage and tongue) and maxilla (palate and nasal cavity) did not change positions, albeit both groups of structures appeared to be compressed anterior-posteriorly. However, during and after shelf elevation, measurements of PC-1 changes showed significant changes between maxillary and mandibular structures, particularly positioning of the shelves above the tongue and protrusion of the tongue and mandible. These results suggest an active role for Meckel's cartilage growth in repositioning the tongue to facilitate shelf elevation. The present data representing three distinct phases of secondary palate closure in humans can advance the understanding of morphological growth changes occurring before and after the horizontal positioning of palatal shelves and their fusion to close the secondary palate in humans successfully.

Histomorphological study of palatal shelf elevation during murine secondary palate formation

During mammalian secondary palate development, the palatal shelves undergo dramatic morphological changes to elevate from a vertical to a horizontal plane in the oral-nasal cavity. We found that E14.5 mouse embryos displayed marked variations in shelf morphology that represent various intermediate states of the elevation process. With these variations, we reconstructed the sequence of shelf morphological changes that take place during the elevation process and discovered distinct patterns in different regions along the anterior-posterior (AP) axis. Moreover, our study revealed that during the elevation process, shelf morphological changes are accompanied by tongue morphological changes, which also show distinct characteristics along the AP axis. We further discuss how to divide the palate along the AP axis based on morphological criteria. Our study provides a framework that recognizes variation in timing of palatal morphogenesis along the AP axis that will aid in the investigation of the mechanisms regulating palatal shelf elevation.

Development of a suspension organ culture of the fetal rat palate

On the basis of an already established suspension organ culture system of mouse palate anlagen, we developed a corresponding culture system for rat palate anlagen. In order to optimize the culture results we systematically studied the influence of main "culture conditions" such as dissection technique, rotation speed, gassing schedule, and developmental stage at the onset of culture for mice and rat palate anlagen. This system allows culturing rat palate anlagen from day 15 of gestation to day 18 + 8 h (80 h) under serum- and antibiotic-free conditions using a chemically defined medium, resulting in 90% fused palates. The explants, containing the maxillary vault and the palatal shelves, were cultured in siliconized culture flasks at a rotation speed of 12 rpm and a temperature of 37 degrees C (Table 1).

Congenital oral synechiae

Major congenital synechiae of the oral cavity constitute a clinically confusing spectrum of abnormalities. On the basis of clinical data, we propose two categories: 1) abnormalities secondary to persistence of the buccopharyngeal membrane and 2) abnormalities secondary to formation of ectopic membranes. An ectopic membrane results from abnormal fusion and can be subclassified as a subglossopalatal membrane, glossopalatal ankylosis, or syngnathia. This classification is supported by embryologic studies and is used to reclassify all cases reported since 1900. Distinct differences, such as the presence of associated limb anomalies, emerge; these are reviewed and add support to the proposed classification.

Catecholamine modulation of embryonic palate mesenchymal cell DNA synthesis

Development of the mammalian embryonic palate depends on the precise temporal and spatial regulation of growth. The factors and mechanisms underlying differential growth patterns in the palate remain elusive. Utilizing quiescent populations of murine embryonic palate mesenchymal (MEPM) cells in vitro, we have begun to investigate hormonal regulation of palatal cell proliferation. MEPM cells in culture were rendered quiescent by 48 hr serum deprivation and were subsequently released from growth arrest by readdition of medium containing 10% (v/v) serum. The progression of cells into S-phase of the cell cycle was monitored by autoradiographic analysis of tritiated thymidine incorporation. Palate mesenchymal cell entry into S-phase was preceded by a 6- to 8-hr prereplicative lag period, after which time DNA synthesis increased and cells reached a maximum labeling index by 22 hr. Addition of 10 microM isoproterenol to cell cultures at the time of release from growth arrest lengthened the prereplicative lag period and delayed cellular entry into S-phase by an additional 2 to 4 hr. The rate of cellular progression through S-phase remained unaltered. The inhibitory effect of isoproterenol on the initiation of MEPM cell DNA synthesis was abolished by pretreatment of cells with propranolol at a concentration (100 microM) that prevented isoproterenol-induced elevations of cAMP. Addition of PGE2 to cell cultures, at a concentration that markedly stimulates cAMP formation, mimicked the inhibitory effect of isoproterenol on cellular progression into S-phase. These findings demonstrate the ability of the beta-adrenergic catecholamine isoproterenol to modulate MEPM cell proliferation in vitro via a receptor-mediated mechanism and raise the possibility that the delayed initiation of DNA synthesis in these cells is a cAMP-dependent phenomenon.

Teratogenicity of arotinoid ethyl ester (RO 13-6298) in mice

Arotinoid ethyl ester (RO 13-6298) is a new and very potent retinoid that exerts a profound influence on epithelial and mesenchymal differentiation in doses 500 times lower than those of compounds of the first and second retinoid generation. In the present study the teratogenicity of arotinoid ethyl ester was investigated in NMRI mice employing different treatment schedules. Recording of abnormalities was performed on day 18 (day 0 = day of conception) according to Wilson and with cleared skeletal preparations. Intraperitoneal application of the drug at a dosage of 10 micrograms/kg/day for three consecutive days (days 9-11 or 12-14) caused severe malformations, particularly in the skeletal system and the cavernous organs. Skeletal elements were reduced in number, shortened, or abnormally shaped. Ossification was diminished. Atresia of anus and urethra were frequent. Single application of 200 micrograms/kg between days 8 and 14 also caused multiple and severe malformations. However, no stage-specific pattern of abnormalities was detectable. Some skeletal malformations indicated more or less vulnerable stages that were in concordance with special developmental steps. Others, however, seemed to be equally susceptible over a longer period, eg, rays 1 and 5 of the hand or foot and the development of the mandibular joints. The pattern of abnormalities caused by these very low doses of RO 13-6298 is comparable to that obtained with other retinoids and is achieved within the same relative dose-response range. Preconceptional treatment of the animals did not induce any malformations.

A morphometric analysis of craniofacial growth and changes in spatial relations during secondary palatal development in human embryos and fetuses

Staged human embryos and fetuses in the Carnegie Embryological Collection were morphometrically analyzed to show craniofacial dimensions and changes in spatial relations, and to identify patterns that would reflect normal developmental events during palatal formation. Normal embryos aged 7-8 weeks postconception (Streeter-O'Rahilly stages 19-23) and fetuses aged 9-10 weeks postconception, in eight groups with mean crown-rump (CR) lengths of 18-49 mm, were studied with cephalometric methods developed for histologic sections. In the 4-week period studied, facial dimensions increased predominantly in the sagittal plane with extensive changes in length (depth) and height, but limited changes in width. Growth of the mandible was more rapid than the nasomaxillary complex, and the length of Meckel's cartilage exceeded the length of the oronasal cavity at the time of horizontal movement of the shelves during stage 23. Simultaneously with shelf elevation, the upper craniofacial complex lifted, and the tongue and Meckel's cartilage extended forward beneath the primary palate. Analysis of spatial relations in the oronasal cavity showed that the palatomaxillary processes became separated from the tongue--mandibular complex as the head extended, and the tongue became positioned forward with growth of Meckel's cartilage. As the head position extended by 35 degrees, the cranial base angulation was unchanged and the primary palate maintained a 90 degrees position to the posterior cranial base. However, the sagittal position of the maxilla relative to the anterior cranial base increased by 20 degrees between stages 19 and 23. In the late embryonic and early fetal periods, the mean cranial base angulation of approximately 128 degrees and the mean maxillary position angulation of approximately 84 degrees were similar to the angulations previously shown to be present later prenatally and post-natally. The results suggest that human patterns of cranial base angulation and maxillary position to the cranial base develop during the late embryonic period when the chondrocranium and Meckel's cartilage form the primary skeleton.

Developmental mechanisms in normal and abnormal palate formation with particular reference to the aetiology, pathogenesis and prevention of cleft palate

Palatal development was studied macroscopically, microscopically and ultrastructurally in foetuses of inbred Wistar rats and Alligator mississippiensis. In the rat, elevation of the palatal shelves from a vertical position lateral to the tongue to a horizontal position above the tongue, occurs very rapidly. This reorientation is postulated to be caused by an intrinsic turgor shelf force generated by the hydration of mesenchymal mucopolysaccharides (predominantly hyaluronic acid). Cleft palate was induced in rat foetuses using 5-fluoro-2-desoxyuridine and was associated with greatly decreased mucopolysaccharide synthesis. The alligator is the only animal which develops in an external egg and which possesses a true mammal-like secondary palate: it is therefore a useful animal model system because longitudinal studies and direct surgical and pharmacological manipulations can be performed. The palatal shelves of alligators grow horizontally above the dorsum of the tongue from their first appearance. This de novo horizontal shelf growth is associated with an increase amount of space in the alligator oronasal cavity due to the small, fatty, alligator tongue. It is postulated that the evolution of the large muscular mammalian tongue constrains the palatal shelves to grow vertically until sufficient space can be created to form the common nasal passage simultaneous with shelf elevation.

The effect of vitamin A on fusion of mouse palates. I. Retinyl palmitate and retinoic acid in vivo

C57B1 mice were given orally one, two , or three doses of ritinyl palmitate or retinoic acid on day 11, 12, 13, or 14 or pregnancy to determine 1) if it was possible to produce cleft palate at any time during palatal development of the mouse embryo, and 2) the maternal and fetal levels of vitamin A associated with the production of clefts. Whereas a single dose of either substance was sufficient to cause clefts on day 11 or day 12, three doses at 3-hour intervals were necessary to cause clefts on day 14. Most of these clefts were incomplete. Measurement of vitamin A levels in maternal serum and fetuses of dams after administration of retinyl palmitate or retinoic acid on day 11 and day 14 of pregnancy showed that transplacental passage of retinyl palmitate, retinol, and retinoic acid had taken place. Analysis of fetal serum on day 14 showed increase in levels of retinyl palmitate, retinol, and retinoic acid after dosing with retinyl palmitate, and in retinoic acid alone after dosing with retinoic acid. In both cases peak levels were observed within 3 hours. Our findings suggest that the effect of vitamin A on the developing mouse palate is direct, occurring soon after its administration, and that duration of exposure is as important as its concentration in vivo. The apparent change in sensitivity of mouse palate between day 11 and day 14 of pregnancy is discussed.

Ontogeny of oral function in hamsters (Mesocricetus auratus)

The oral apparatus of neonatal and juvenile golden hamsters was investigated by clearing and staining of whole crania, videotaping of behavior, and electromyography of several jaw muscles. Chewing developed during the first postnatal week and matured in the second; however, suckling was still the primary mode of feeding. Micromovements of the jaws occurred early when the osseous skeleton and joints developed. Macromovements correlated well with EMG records and were limited to jaw opening at birth. Muscles of the oral floor generated large bursts of activity during jaw opening and tongue protrusion from 0 days postnatal (dpn), when simple and stereotyped gaping was induced, until 14 dpn, when movements were spontaneous and not stereotyped nor inducible. However, adductor muscle activity was brief, low in amplitude, and primarily involved with jaw stabilization until 4 dpn, when these muscles became active during closing the jaws; closing activity increased in frequency and amplitude until the end of the second week. Development of frequent, coordinated macromovements of chewing was associated with the refinement of joint structure and dental occlusion and with the growth of the craniofacial skeleton. Jaw movements and associated EMG's correlated better with available data on development of neural circuitry than with that for musculoskeletal development.

Effects of craniofacial structures on mouse palatal closure in vitro

Heads of Swiss-Webster mouse fetuses of four ages spanning days 12-13 of gestation, were partially dissected by removing the brain (B), tongue (T) and mandible (M) alone or in combination (BT, BM, BTM). Preparations were suspended in a gassed, circulating culture system such that palatal closure must take place against gravity. Closure occurred earlier than in vivo and required the posterior half of the mandible be intact and the tongue removed.

The mechanism of palatal shelf elevation and the pathogenesis of cleft palate

Both normal Wistar rat fetuses and those with cleft palate induced by 5-Fluoro-2-Desoxyuridine were studied with a view to elucidating the mechanism of palatal shelf elevation and the pathogenesis of cleft palate. It was postulated that normal shelf elevation is brought about rapidly by an intrinsic turgor shelf force generated by binding of water to mucopolysaccharides. Interference with mucopolysaccharide synthesis would seem to be an important factor in the pathogenesis of some types of cleft palate.

Graphic reconstructions of craniofacial structures during secondary palate development in rats

Lateral and ventral graphic reconstructions of coronally sectioned rat fetuses at four stages of secondary palate development were made to illustrate the size, form, and spatial relations of craniofacial structures at each stage, and to indicate changes between stages. The results illustrated extensive changes in the nasomaxillary and tongue-mandibular complexes and spatial relations in the oronasal cavity during this 2-day period. During closure of the palate the palatine processes and molar dental laminae moved medially, the vertical dimension between the cranial base and Meckel's cartilage increased, and the Meckel's cartilage changed in shape from a "U" to a "V". During the 2-day period extensive increases in anteroposterior and vertical dimensions and limited changes in lateral dimensions resulted in a change in shape of the complete orofacial region. More extensive investigations, preferably quantitative, of the changes shown are indicated to identify the relative contribution of various craniofacial components and to establish the role of differential growth in secondary palate closure.

Radioautographic study of mesenchymal cell activity in the secondary palate of the rat

In this radioautographic study of the developing secondary palate of the rat, it has been shown that there was not the increased nuclear labeling indicative of increased mitotic activity in the mesenchyme said to be responsible for medial rotation of the palatal shelves. Variations in labeling index in different regions of the developing palate appeared mainly because of developing bone and mucous glands.

The course of the palatine arteries during secondary palate development in the rat

The course of the palatine arteries was studied in 96 rat fetuses. The descending palatine arteries were a major blood supply to the incisive area of the primary palate. When shelves were elevated, the arteries became positioned more medially and changed from a semicircular to a V-shaped form in the pre-maxilla.