New aspects of the histology of the mandibular condyle in the rat

The function of the multipotential mesenchymal cells in the mandibular condyle was studied histochemically and histologically in 27 Long Evans/Turku rats. Sagittal sections from the temporomandibular joint were stained with haematoxylin and eosin, toluidine blue, or van Gieson's stain. A weakly orthochromatically stained fibrous layer was followed in the upper region by a weakly metachromatically stained mesenchymal cell layer. Deep within this was a strongly metachromatically stained layer of immature chondroblasts. The metachromasia of the matrix of these layers disappeared abruptly in an anterior direction and gradually in a posterior direction. The changes in the staining reactions are explained by the fact that mesenchymal cells can differentiate into chondrogenic or osteogenic cells depending on the environmental conditions. A new hypothesis is presented according to which regulation of the direction of condylar growth is achieved by choosing the cells for chondrogenesis more posteriorly or anteriorly from among the mesenchymal cells covering the whole condylar cartilage.     

Weaning and the histology of the mandibular condyle in the rat.

Eighty-eight Long Evans/Turku rats were used in the study. The effect of the articulatory function on the mandibular condyle was observed histologically during normal growth, when the rat is changing its diet from milk to whole pellets as a part of weaning. Six animals each were killed at the age of 10, 15, 20, 25, 30, 35, 40 and 50 days for histological tissue processing. For further information, 30 animals were fed a soft diet (6 animals each were killed at the age of 25, 30, 35, 40 and 50 days), and 10 animals were fed hardened pellets (2 animals each were killed at the ages of 25, 30, 35, 40 and 50 days). An even and regular transition from mesenchymal cells via immature chondroblasts into mature chondroblasts and hypertrophied chondrocytes was found at 10, 15 and 20 days during normal growth and also at 25, 30, 35, 40 and 50 days when animals were fed a soft diet. This maturing process appeared to be disturbed at the age of 25, 30, 35 and 40 days in the superior aspect of the condyle in animals fed ordinary pellets. The density of the mesenchymal cell layer was decreased, and the amount of intercellular matrix seemed to be evaluated in mesenchymal and intermediate cell layers. These features were later manifest deeper in the cartilage as acellular regions and as cell clusters. The changes were similar but more severe when the animals were fed hardened pellets.(ABSTRACT TRUNCATED AT 250 WORDS)     

Morphometric study of the mandibular condyle of the rat during postnatal development

A morphometric technique for the use of the temporomandibular joint (TMJ) of the rat as an experimental model was developed to study TMJ growth from birth to 120 days of age. Experimental conditions for the reduction and embedding of the specimen, as well as for data collection were standardized. Morphometric data were obtained from projected drawings and the areas occupied by the various structures were determined by counting points with a specially constructed integration grid. The areas occupied by the layers making up the mandibular condyle remained relatively constant, forming an architectural pattern from the 30th postnatal day on. Between the 10th and 30th day they underwent modifications interpreted to be functional adaptations conditioned by changes in the animal's feeding habits.     

Effects of grape seed proanthocyanidins extract on rat mandibular condyle

We investigated the effects of grape seed proanthocyanidins extract (GSPE) on bone formation by examining total and cortical bone mass, density, architecture, and strength non-invasively using mandibular condyles of Ca-restricted rats. Forty Wistar male rats, each 5 weeks old, were divided into control (C), low-Ca diet (LCaD), low-Ca diet-standard diet (LcaD x SD), and low-Ca diet x Estandard diet with supplementary GSPE (LcaD x SD+GSPE) groups. In LCaD x SD group, after the bone debility was induced by low-Ca diet, a standard diet therapy was given. In LCaD x SD+GSPE group, after the bone debility was induced by low-Ca diet, a standard diet therapy with supplementary GSPE was given. Each mandibular condyle was examined using peripheral quantitative computed tomography (pQCT). There were no significant inter-group differences in body weight seen throughout the experimental period. In LcaD x SD+GSPE, cortical bone cross-sectional area and mineral content were not significantly different from C, while bone mineral content was significantly higher in LcaD x SD+GSPE than in LcaD x SD. Cortical bone density of LcaD x SD+GSPE was not significantly different from that of C, however, that value in LCaD and LcaD x SD was significantly lower than that. The cross-sectional (bending) moment of inertia values in LcaD x SD+GSPE were the highest among all groups, though they did not differ significantly from those in C. Further, the cross-sectional (bending) Stress/Strain Index (SSI) values in LcaD x SD+GSPE were statistically similar to those in C, however, not significant higher than in LcaD x SD. These results suggest that GSPE treatment would increase both bone mass and bone strength on the rat mandibular condyles.     

Age-related changes in microarchitecture and mineralization of cancellous bone in the porcine mandibular condyle

The mandibular condyle is considered a good model for developing cancellous bone because of its rapid growth and high rate of remodeling. The aim of the present study was to analyze the simultaneous changes in microarchitecture and mineralization of cancellous bone during development in a three-dimensional fashion. Eight mandibular condyles of pigs aged 8 weeks prepartum to 108 weeks postpartum were scanned using microCT with an isotropic spatial resolution of 10 microm. The number of trabeculae decreased during development, whereas both the trabecular thickness and the distance between the trabeculae increased. The bone surface to volume ratio decreased during development, possibly limiting the amount of (re)modeling. Both the mean degree of mineralization and intratrabecular differences in mineralization between the surfaces and cores of trabecular elements increased during development. The trabecular surfaces were more highly mineralized in the older condyles compared to the younger ones. Together with the observed decrease in the relative size of trabecular surface, this finding suggests a decrease in (re)modeling activity during development. In accordance with the general growth and development of the pig, it was concluded that most developmental changes in cancellous bone occur until the age of 40 weeks postpartum.     

Biomechanical consequences of developmental changes in trabecular architecture and mineralization of the pig mandibular condyle

The purpose of the present study was to examine the changes in apparent mechanical properties of trabecular bone in the mandibular condyle during fetal development and to investigate the contributions of altering architecture, and degree and distribution of mineralization to this change. Three-dimensional, high-resolution micro-computed tomography (microCT) reconstructions were utilized to assess the altering architecture and mineralization during development. From the reconstructions, inhomogeneous finite element models were constructed, in which the tissue moduli were scaled to the local degree of mineralization of bone (DMB). In addition, homogeneous models were devised to study the separate influence of architectural and DMB changes on apparent mechanical properties. It was found that the bone structure became stiffer with age. Both the mechanical and structural anisotropies pointed to a rod-like structure that was predominantly oriented from anteroinferior to posterosuperior. Resistance against shear, also increasing with age, was highest in the sagittal plane. The reorganization of trabecular elements, which occurred without a change in bone volume fraction, contributed to the increase in apparent stiffness. The increase in DMB, however, contributed more dominantly. Incorporating the observed inhomogeneous distribution of mineralization decreased the apparent stiffness, but increased the mechanical anisotropy. This denotes that there might be a directional dependency of the DMB of trabecular elements, i.e. differently orientated trabecular elements might have different DMBs. In conclusion, the changes in DMB and its distribution are important to consider when studying mechanical properties during development and should be considered in other situations where differences in DMB are expected.     

Asymmetry of the mandibular condyle in Haida Indians

The condyles of 72 aged and sexed Haida Indians were measured for anteroposterior and mediolateral diameter and their approximate areas calculated. Dental wear was assessed for the same individuals. Asymmetry of condyle size did not appear to change with age. In a pair-wise analysis, no relationship was found between the largest of a pair of condyles and the most worn side of the dentition. The difference in size between each pair of condyles (normalized for individual size) was plotted as a histogram and found to have a normal distribution with a mean of 0 and no skewness. Condyle asymmetry does not appear to be related to differential chewing forces but more closely fits the model of fluctuating asymmetry.     

The expanded mandibular condyle of the Megaladapidae

The Megaladapidae have a posterior expansion of the articular surface of the mandibular condyle. Several other strepsirhine species exhibit a similar condylar surface. In this study, I propose two behavioral scenarios in which the posterior articular expansion might function: 1) contact with the postglenoid process and resistance to joint stress during browsing, and 2) movement against the postglenoid process during the fast closing and power strokes of mastication, as a consequence of large transverse jaw movements and associated with a strong mandibular symphysis. These models are evaluated through dissection of the TMJ in Lepilemur and from comparative anatomical observations on strepsirhines and ungulates. In Lepilemur the mandibular symphysis is unfused, but compared to the unfused symphyses of other strepsirhines is strengthened by interlocking bony projections (Beecher [1977] Am. J. Phys. Anthropol. 47:325–336). An accessory articular meniscus is found between the posterior articular expansion and the postglenoid process in Lepilemur, suggesting that significant movement occurs in this part of the TMJ. The symphysis is fused in adult specimens of Megaladapis. A posterior articular expansion is common among ungulates, and its presence is associated not with browsing but with symphyseal fusion. This supports the second model and suggests that the posterior articular expansion functions as a movement surface during mastication. Schwartz and Tattersall ([1987] J. Hum. Evol. 16:23–40) cite the posterior articular expansion as a synapomorphy uniting an Adapis-Leptadapis clade with a Megaladapidae-Daubentonia-Indridae clade. The comparative evidence suggests that the posterior articular expansion has evolved convergently in adapines, notharctines, megaladapids, hapalemurids, and indrids as part of a functional complex related to herbivory. However, close morphological similarity of the posterior articular expansion among genera within these strepsirhine subfamilies and families indicates that it is probably a reliable synapomorphy at lower taxonomic levels. Am J Phys Anthropol 103:263–276, 1997. © 1997 Wiley-Liss, Inc.     

Physiological and metabolic changes associated with weaning in the tammar wallaby,Macropus eugenii

Summary The tammar wallaby (Macropus eugenii) is a small macropodid marsupial in which the major part of weaning occupies the period between 28 and 36 weeks of pouch life. Before weaning the diet of the tammar is high in carbohydrate and low in lipid/volatile fatty acid whereas the reverse applies after weaning. The adult tammar is a forestomach fermenter. The aim of this study was to elucidate some of the physiological and metabolic changes associated with this major change in the diet.Hepatic glycogen content increased gradually early in development to a maximum of 7% of liver weight at 28–30 weeks of pouch life. It then fell precipitously to less than 1% of liver weight at 36 weeks before recovering to the adult level of about 3% liver weight. Plasma glucose levels were maintained at about 10 mM until 36 weeks, after which they fell gradually to adult values of about 4 mM. Hepatic hexokinase activity increased several-fold between 18 and 30 weeks of pouch life, remained high until 42 weeks, and then fell to the adult level. The hepatic activities of fructose-bisphosphatase and particulate phosphoenolpyruvate carboxykinase (PEPCK) were unchanged during development but soluble hepatic PEPCK activity, which was low until 28 weeks of pouch life, increased 3–4 fold between 30 and 36 weeks and then fell slightly to the adult level. Hepatic pyruvate kinase increased in activity up to 28 weeks and then fell to about half peak values at 36 weeks and 20% of peak activity in the adult. There was a greater than ten-fold increase in the ratio of soluble PEPCK activity to pyruvate kinase activity between 28 and 36 weeks of development. It has previously been reported that hepatic gluconeogenesis is inducible in pouch young but constitutive in adults. We conclude that the change in regulation of hepatic gluconeogenesis at the PEPCK/pyruvate kinase level is part of the weaning process.The urea content of the plasma changed little during development but plasma ammonia increased consistently through pouch life. Urine urea content was low until about 28 weeks of age and then increased rapidly to adult levels. Urine ammonia increased from about 20 mM early in pouch life to a maximum of more than 100 mM at 28 weeks. Thereafter, urine ammonia content fell rapidly to the adult value of about 20 mM. For the first 27 weeks of pouch life, urine pH was consistently between 4.4 and 5.7, but subsequently it rose and became more variable. Urine pH in adults was 8.1±0.3. The activities of the five enzymes of the ornithine-urea cycle increased 3–5 fold in activity between 28 and 36 weeks of pouch life.These findings indicate that there are major changes in metabolic regulation associated with weaning in the tammar. During weaning, glucose becomes essentially unavailable to the young animal and there is an increase in the rate of hepatic gluconeogenesis which is attributable primarily to increased activity of soluble PEPCK. Metabolism, which is acidotic before weaning, becomes alkalotic and there is a decrease in urinary ammonia content as proton excretion decreases. As ammonia excretion falls, the activity of the urea cycle increases and the concentration of urea in the urine rises. Weaning in the tammar is therefore a complex and well-orchestrated process which may be associated with the change in diet.     

Ultrastructural changes in rat epididymis after vasectomy

Summary Epididymal biopsies from rats that had undergone unilateral or bilateral vasectomies from one to eight months previously were compared with biopsies from their contralateral side or from normal controls to ascertain what ultrastructural changes had occurred. After vasectomy, spermatozoa appeared to dissolve in the lumen of the caput epididymidis and to be absorbed by the principal cells. About 5 weeks after vasectomy, numerous lamellar accumulations became apparent in the supernuclear region. Their resemblance to lysosomes or residual bodies was confirmed by an acid phosphatase reaction. After 10 weeks, similar lamellar and polymorphic accumulations on the contralateral side of animals with unilateral vasectomies indicated that resorption had also increased on the unligated side.Publication No. 627 of the Oregon Regional Primate Research Center. This study was supported by NIH Grants No. RR-00163 and HD-05969.The author wishes to thank Ms. J. Hren for her excellent technical assistance.     

Changes in mechanical properties of bone within the mandibular condyle with age

The purpose of the study was to compare indentation modulus (IM) and hardness of condylar bone in young and adult dogs. In addition we desired to examine histologic sections for bone formation activity in the two groups. Mandibular condyles were obtained from adult (1- to 2-year-old) and young (approximately 5-m old) dogs. Two sections/condyle were obtained and one was processed for histomorphometry and the other for mechanical analyses. Indents were made on moist condylar trabecular bone to a depth of 500 nm at a loading rate of 10 nm/s using a custom-made hydration system to obtain IM and hardness. Histomorphometric analyses measured the bone volume/total volume (BV/TV%) and ratio of labeled to unlabeled bone within the condyle. Data were analyzed using a repeated-measures factorial analysis of variance and Tukey-Kramer method. Overall, the IM of the adult condyles (10.0+/-3.4 GPa, Mean+/-SD) were significantly (P<0.0001) higher than in young dogs (5.6+/-2.6 GPa). There was a greater bone mass in the young (60.2%) versus the adult condyles (42%). Also, significantly more labeled bone in the young (66.1%) condylar bone suggested higher bone forming activity than in adult condyles (27.5%). With age there is a change in mass and material properties in the trabecular bone of the mandibular condyle in dogs.     

Size and shape of the mandibular condyle in primates

The relationships between the size of the articular surface of the mandibular condyle and masticatory muscle size, tooth size, diet, and biomechanical variables associated with mastication were studied by taking 12 measurements on skulls of 253 adult female anthropoid primates, including three to ten specimens from each of 32 species. In regressions of condylar length, width, or area against body weight, logarithmic transformations substantially improve the fit of the equations compared with untransformed data. There is a strong relationship between condylar measurements and body weight, with all correlations being .94 or higher. The slopes of the allometric regressions of length, width, and area of the condylar head indicate slight positive allometry with body size. Folivorous primates have smaller condyles than frugivorous primates, and colobines have smaller condyles than cebids, cercopithecines, or hominoids. When colobines are eliminated, the differences between frugivores and folivores are not significant. However, the two species with the relatively largest condyles are Pongo pygmaeus and Cercocebus torquatus, suggesting that there may be a relationship between unusually large condylar dimensions and the ability to crack hard nuts between the teeth. Cranial features having strong positive correlations with condylar dimensions include facial prognathism, maxillary incisor size, maxillary postcanine area, mandibular ramus breadth, and temporal fossa area. These data are interpreted as indicating that relatively large condyles are associated with relatively large masticatory muscles, relatively inefficient mandibular biomechanics, and a large dentition. These relationships support the growing evidence that the temporomandibular joint is a stress-bearing joint in normal function.     

Ultrastructural changes in the neurohypophysis of the aged male rat

Summary The neurohypophyses (neural lobes of the pituitary) of young adult (3–6 months) and aged (12–30 months) male rats were studied by means of electron microscopy. Stereomorphometric analyses were performed to determine the size, number and relative volume of the hormone-containing vesicles. The principal observations included: 1) the conspicuous depletion in aged rats of the granular hormone-containing vesicles from the axon terminals and the Herring bodies, with a decrease in the relative volume fraction of the vesicles from 4.8 Vv % in the control animals to 1.1 Vv % in the aged rats; 2) a change in the size-distribution of the hormone vesicles; 3) an increase in the extracellular space around the nerve terminals, axons and capillaries; and 4) lipid accumulations and signs of activation in the pituicytes. The possible physiological significance of the findings is discussed in the light of several regulatory functions known to be altered during the process of ageing.     

Ultrastructural changes in the rat submaxillary gland following isoprenaline

Summary The ultrastructural appearance of acinar cells of the submaxillary gland have been examined at various time intervals following an injection of isoprenaline; the changes observed in previously untreated rats were compared with those in animals which had received differing periods of chronic treatment. The depletion and re-accumulation of secretory material was found to follow a similar time course irrespective of earlier treatment but there were quantitative differences in magnitude of response. An injection of the drug resulted in almost total depletion of secretory granules in previously untreated animals while in those which had received chronic treatment the depletion was less complete. This difference is discussed in relation to the decline in the hyperplasic response with prolonged drug treatment. The secretory granules showed better preservation of membranes and frequently contained dense configurations after chronic treatment.I am indebted to S. Glanvill, B. Mason, and D. O'Reilly for their skilled assistance.