Dipyridamole-induced neoformation of capillaries in the rat heart. Quantitative stereological study on papillary muscles

Eighteen young male Wistar rats were randomly divided into two groups of equal size. Each experimental animal was treated with the powerful vasodilating drug dipyridamole (4 mg kg-1 intraperitoneally twice daily) for a period of 6 weeks. The control animals received sham injections with saline. The rats were fixed by retrograde vascular perfusion. Seven transverse and two longitudinal sections per animal were randomly selected from the left ventricular papillary muscles for stereological investigation. Length density of capillaries (length of capillaries per unit of tissue volume), surface density of capillaries (surface area of capillaries per unit of tissue volume) and the "true" three-dimensional capillary-fiber ratio (length of capillaries per unit length of myocardial fibers) were estimated by means of the Dimroth-Watson distribution, a mathematical model of directional statistics which assumes that the capillary directions scatter around the longitudinal axis of the muscle. This model was recently introduced into the stereology of myocardial capillaries and leads to a more accurate quantitation of the capillary network than parameters used hitherto, such as the "capillary density" (number of capillary profiles per mm2 of cross sectional area) and the "capillary-fiber ratio" (number of capillary profiles per number of myofiber profiles in cross sections). After chronic dipyridamole treatment, the length density of myocardial capillaries (+5%; p less than 0.02), the surface density of capillaries (+8%, p less than 0.01) and the three-dimensional capillary-fiber ratio (+6%, p less than 0.05) were increased. It is therefore concluded that the vasodilating drug dipyridamole evokes capillary growth in the heart which may be induced by mechanical factors via the enhanced myocardial blood flow. Investigation of the frequency distribution of capillary directions in space in both groups provided evidence that the capillary growth resulted from neoformation of capillaries.     

Cardiac growth in staged human embryos--stages from 15 to 23, post-somitic period

The cardiac growth was studied in 27 human embryos staged in post-somitic period (stages from 15 to 23, Carnegie Institution of Washington). The cardiac volume was determined by morphometric methods (point-counting planimetry on serial sections) and examined relative to gestational age, to crown-rump length and to the embryo body weight. The data were transformed into logarithms and bivariate relations were analyzed according to allometric equations of the form log y = k (log x) + log b. The data were fitted according to 3 techniques: least squares, major axis and reduced major axis. The allometric regressions slopes (k) indicate positive allometry of the cardiac volume relative to the embryonic age and isometry relative to body weight. The present work will be useful when image techniques, as ultrasonography, turn it possible to evaluate quantitatively the embryonic heart.     

Stereology of myocardial hypertrophy induced by physical exercise

Summary Twenty young female Sprague-Dawley rats were randomly assigned to 2 groups. Ten animals served as sedentary controls, the 10 experimental animals were subjected to a training program with gradually increasing intensity of 18 weeks duration on a motor-driven treadmill. The rats were fixed by retrograde vascular perfusion via the abdominal aorta under anesthesia. Two transverse and 2 longitudinal sections per animal were selected at random from the left ventricular papillary muscles for light and electron microscopic stereological investigation. Length density and surface density of myocardial cells and capillaries were estimated with correction for partial anisotropy and curvature by means of the mathematical model of a Dimroth Watson orientation distribution. Left and right ventricular weight increased by 20% in the exercise group (P<0.001), whereas body weight remained unchanged. Physical training led to a significant increase of heart muscle fiber cross-sectional area by 17% (P<0.01). The ultrastructural volumetric composition of the myocardial cell cytoplasm by myofibrils, mitochondria, and sarcoplasmic matrix remained unchanged. Volume density, length density and surface density of capillaries, as well as capillary cross-sectional area and capillary anisotropy parameters were not significantly altered by training. From the data one concludes an increase of the 3-dimensional capillary-fiber ratio by 19% (P<0.001). Thus physical training induces mild absolute biventricular cardiac hypertrophy in young female rats, in which capillary proliferation compensates for the increase of mean oxygen diffusion distance resulting from fiber thickening, by supplying each unit of fiber length by more units of capillary length.     

Impact of Intrauterine Growth Restriction on the Capillarization of the Early Postnatal Rat Heart

Capillarization plays a key role in the growth of the developing heart. We therefore hypothesized that impaired heart development following intrauterine growth restriction (IUGR) may arise from inadequate myocardial capillary growth. The aims of the study were to examine the effect of IUGR on the growth and diffusion radius of intramyocardial capillaries in rats at postnatal day 1. Uteroplacental insufficiency was induced in rats in late gestation (E18, term = E22) by bilateral uterine artery and vein ligation (restricted offspring N = 12; six males and six females); offspring from sham-operated dams were used as controls (N = 10; five males and five females). At postnatal day 1, the hearts were immersion-fixed and heart volume, capillary length density, capillary diffusion radius, and total capillary length were stereologically determined. Restricted offspring were significantly smaller at birth, with a concomitant reduction in heart volume and total myocardial capillary length compared to controls. Capillary growth was not impaired relative to heart size, with no significant differences in capillary length density or diffusion radius in the myocardium of restricted and control offspring. There were no sex differences in any of the parameters examined. In conclusion, there was no evidence to indicate that microvascular development is compromised in the heart of IUGR offspring at 1 day after birth. Total myocardial capillary length, however, was significantly reduced in the growth restricted offspring and further longitudinal studies are required to elucidate the long-term impact, particularly following hypertrophic cardiac growth. Anat Rec, 302:1580–1586, 2019. © 2018 American Association for Anatomy     

Time-course changes in arteriolar and venular portions of capillary in young treadmill-trained rats

This study was designed to examine the time-course changes in capillarity, especially the distribution of arteriolar and venular capillaries, in skeletal muscles during endurance training by running in young female Wistar rats. Exercise training by running started at the age of 5 weeks and lasted for 5 weeks at 25 m min(-1) on a 25% gradient, 10-60 min day(-1), 5 days per week. Morphological findings were obtained from the soleus (SOL) and deep portions of the medial gastrocnemius (GASd) muscles. In SOL, the training significantly increased the capillary-to-fibre ratio (C:F), total capillary density, and density of venular capillaries at Week 1. Significant increases in the C:F and total capillary density were also observed at Weeks 4 and 5. The capillary domain area (CDA) values for total capillary and arteriolar and venular capillaries were significantly decreased after 4 weeks of training. In GASd, the training significantly increased the C:F at Week 1 and from Week 3 onwards. It also significantly increased cross-sectional area of all fibre types. Total capillary density and the CDA values showed no significant difference between control and training groups at all points of time. Significant increases in succinate dehydrogenase (SDH) activity were first noted after 2 weeks in GASd and after 3 weeks in SOL. These findings suggest that, in young growing rats, adaptive changes in the oxygen transport system occurred within 1 week after the onset of training mainly in highly oxidative muscles. The changes in arteriolar and venular capillary densities may help to clarify the growth pattern of the capillary network associated with endurance running training.     

Allometric growth of the adrenal gland in Brazilian fetuses

The growth of the adrenal gland was studied in 60 brazilian fetuses (12-37 weeks post-conception). The right adrenal gland was quantitatively evaluated; its weight, length and thickness were correlated to the fetal body weight, to the Crown-Pump length and to the gestational age by the allometric method (LogY = kLogX + LogB). The width was the only linear measure with positive allometry, and was the one which presented the greatest relative growth, while the thickness had the smallest one. The adrenal weight presented positive allometry relating to the Crown-Rump length (k = 2.32) and to the gestational age (k = 2.40). The importance of these knowledges in the precocious ultrasonographic diagnosis of congenital adrenal pathologies is discussed.     

Allometric growth of the rat peritoneal mast cell mass and of the granular constituents: heparin, histamine and 5-hydroxytryptamine

This paper reports an attempt to measure the normal growth of connective tissue mast cells in rats aged 6 to 24 weeks. We used peritoneal mast cells as a model, and calculated the total mast cell mass and the mass of its components from total peritoneal mast cell numbers and their content of protein, heparin, histamine and 5-hydroxytryptamine (5-HT). The growth process was analysed with the aid of allometric, log-log plots of mast cell quantities versus body weight and linear regression, in order to facilitate comparisons with other systems, notably the lymphoid apparatus. We found that the growth of peritoneal mast cells conformed to the allometric principle (r = 0.91 to 0.93). There were no deviations from linearity or changes in the slope (growth rate constant, k) of the allometric lines within the studied growth interval. K ranged from 1.3 to 1.7, indicating that the mast cell mass and its different components grew at a faster rate than the body as a whole, typical of a late maturing cell system. The mode of growth of the peritoneal mast cells is thus distinctly different from that of the lymphoid system, and neither thymus involution nor sexual maturation appears to influence the growth of these cells.     

Sexually dimorphic proportions of the harbour porpoise (Phocoena phocoena) skeleton

Sexual differences in growth, allometric growth patterns and skeletal proportions were investigated by linear measurements of skeletal parts on 225 harbour porpoises (Phocoena phocoena) from the inner Danish and adjacent waters. Females show larger asymptotic sizes and extended period of growth compared with males. Measurements of the skull and flipper bones show negative allometry, whereas those of the bones of the body generally show positive allometry. There are no statistically significant intersexual differences in allometry except for the pelvic bones, where the males show stronger positive allometry. Throughout the range of individual sizes, females have significantly larger skulls and shorter vertebral columns than males for similarly sized individuals. In fully grown specimens, the condylobasal length of females makes up a smaller proportion of total length, and the vertebrae make up a larger proportion as compared with males. As these characters show negative and positive allometry, respectively, it is suggested that males finish their development at an earlier stage than females, retaining more paedomorphic proportions of the skeleton. Paedomorphosis in fully grown males relative to females is also found in the vertebral epiphyses that mature later in males than females, although the males finish growth at a younger age.     

经bcl-2基因修饰的骨髓间充质干细胞移植对缺血性心功能不全兔心功能及血管新生的影响

目的:探讨经bcl-2基因修饰的骨髓间充质干细胞(BMSCs)移植对急性心肌梗死家兔心肌细胞凋亡、血管再生及心功能的影响。方法:体外分离、培养、纯化兔BMSCs,分别转染腺病毒及重组腺病毒-Bcl-2。结扎兔冠状动脉前降支制作心肌梗死(MI)模型,2周后于心梗边缘区分别注射等量的腺病毒-Bcl-2-BMSCs(MI+Bcl-2-BMSCs组)、腺病毒-BMSCs(MI+BMSCs组)及DMEM液(MI组)。细胞移植4周后经超声测定心功能;荧光显微镜观察BMSCs的存活及分布;TUNEL法检测心肌细胞凋亡;real-time PCR检测VEGF mRNA表达;免疫组化染色法检测CD31表达,计算新生毛细血管密度。以上数据分别与心功能进行相关性分析。结果:与MI组相比,MI+Bcl-2-BMSCs组和MI+BMSCs组的心功能改善、细胞凋亡率降低、VEGF mRNA表达增多、毛细血管密度增加,其中MI+Bcl-2-BMSCs组的变化更为显著(P0.05)。相关性分析显示左室射血分数与心肌细胞凋亡率呈负相关;与VEGF mRNA的表达量及毛细血管密度呈正相关(P0.01)。结论:经bcl-2基因修饰的BMSCs移植可显著减少缺血性心功能不全兔心肌细胞凋亡、促进血管再生、改善心功能。     

Effective Mechanical Advantage Allometry of Felid Elbow and Knee Extensors

Larger terrestrial mammals have generally been found to use more extended limb postures, a mechanism which maintains muscular requirements at larger sizes by improving the effective mechanical advantage (EMA) of limb musculature. Felids, however, have been documented to maintain joint angles across body sizes. If felid morphology scales isometrically, it would mean larger felids have relatively weaker muscles, compromising locomotor activities. Here, we examine the allometric relationships between the EMA of the elbow and knee extensors and body mass, finding that the EMA of the triceps brachii and quadriceps muscles scale with positive allometry. When species-specific joint angles were used rather than felid-average joint angles, EMA scales to body mass with more positive allometry. When the scaling of the muscle and ground reaction force (GRF) lever arms were investigated individually the allometric signal was lost; however, the muscle lever arms generally have allometric slope coefficients that are consistent with positive allometry, while the GRF lever arms demonstrate negative allometric slope coefficients. This suggests there are subtle alterations to limb morphology allowing different felid species to achieve an increased EMA via distinctive mechanisms. The quadriceps EMA was found to scale with sufficient positive allometry to compensate for increases in size without alteration in muscular anatomy; however, this is not the case for the triceps brachii EMA. Anat Rec, 2018. © 2018 Wiley Periodicals, Inc. Anat Rec, 302:775–784, 2019. © 2018 Wiley Periodicals, Inc.     

Allometric relationship between body size and peak VO2 relative to age at menarche

The present study examined allometric coefficients relating peak VO2 and body size relative to the time of menarche. Peak oxygen uptake (peak VO2) during exercise on a bicycle ergometer, stature and body mass were measured at annual intervals in a mixed-longitudinal sample of 40 active girls from 11 to 14 years of age. The girls were interviewed about their menarcheal status at each examination. The data were treated relative to the time before and after menarche: 2 years before (n = 18), 1 year before (n = 26), during the year of menarche (+/- 6 months, n = 32), 1 year after (n = 35) and 2 years after menarche (n = 22). Allometric coefficients were calculated for each of the five menarcheal groups based on logarithmic transformations of peak VO2 and body mass and peak VO2 and stature. The major axis of VO2 and body mass or stature (log transformed) was also calculated. This is the most appropriate slope for comparison with theoretical allometry coefficients. Mean peak VO2 increases from 2.1 +/- 0.19 L 2 years before menarche to 2.3 +/- 0.26 L 2 years after menarche. The slope of the major axis for body mass is always higher (0.508-0.926) than that for the allometric coefficient (0.323-0.591) in each of the menarcheal groups. The major axis slope and allometric coefficient are lowest between body mass and peak VO2 during the year of menarche. The slope of the major axis is below the theoretical allometric coefficients assuming geometric or elastic similarity, 2/3 or 3/4, before and at menarche and increases after menarche. Although the differences are not statistically significant, the results suggest that the relationship between body mass and peak VO2 at menarche is lower compared with relationships before and after this maturational landmark. Allometric coefficients for stature relative to peak VO2 show a similar pattern.     

骨髓间充质干细胞在急性心肌梗死后心室重构中的应用☆

背景：动物实验和初期的临床研究表明,干细胞移植可以取代坏死心肌细胞、增加有功能心肌细胞的数量,改善心功能,从而为心肌梗死的治疗开辟了一条崭新的途径。 目的：观察心肌梗死后自体骨髓间充质干细胞移植及骨髓动员对心功能的影响。 方法：经猪髂前上棘抽取骨髓30 mL,培养得到骨髓间充质干细胞。15只猪分为3组,模型组仅建立心肌梗死模型,干细胞移植组在造模3 h后经冠状动脉注射骨髓间充质干细胞,干细胞动员组在造模3 h后连续5 d注射粒细胞集落刺激因子    150 μg/(kg•d)。 结果与结论：心肌梗死后8周,干细胞动员组、干细胞移植组左心室收缩、舒张末期内径都明显减小,射血分数较心肌梗死前提高,但差异无显著性意义(P > 0.05);干细胞动员组及干细胞移植组血清血管内皮生长因子水平较心肌梗死前有上升趋势(P < 0.05);干细胞动员组和干细胞移植组梗死交界区的毛细血管密度均大于模型组(P < 0.05)。提示心肌梗死后行自体骨髓间充质干细胞移植及骨髓动员均能明显改善心功能,但具体效果仍需进一步大样本实验研究。 关键词：缺血性心脏病;心力衰竭;骨髓间充质干细胞;血管再生;粒细胞集落刺激因子 doi:10.3969/j.issn.1673-8225.2012.10.009     

血小板纤维蛋白支架对心肌梗死的治疗作用

BACKGROUND: The development of biomaterials provides a new idea for myocardial infarction treatment, and so far there are numerous biomaterials, such as fibrin glue, matrigel, emulsion of extracellular matrix and alginate, for myocardial infarction. But there is a lack of studies about the platelet-fibrin scaffold for myocardial infarction. OBJECTIVE: To explore the effect of the platelet-fibrin scaffold on rat myocardial infarction. METHODS: Platelet-fibrin was used to prepare a platelet-fibrin scaffold, and 40 rat models of myocardial infarction were randomly divided into two groups: 200 μL platelet fibrins were injected into the tissues around the rat infarcted myocardium as platelet-fibrin scaffold group, and the same amount of DMEM was injected into the tissues around the rat infarcted myocardium as control group. Subsequently, expressions of vascular endothelial growth factor, hepatocyte growth factor and insulin-like growth factor 1 released from the scaffold were detected. Production of endothelial cells and cardiomyocytes, cardiomyocyte apoptosis, capillary density and cardiac function in rats after implantation were observed. RESULTS AND CONCLUSION: The platelet-fibrin scaffold was successfully prepared. The expression of vascular endothelial growth factor, hepatocyte growth factor and insulin-like growth factor 1 in the scaffold group was (115.7±19.45), (23.98±12.32) and (288.4±16.74) ng/L, respectively. The number of von Willebrand factor-positive cells and a-SA-positive cells in the platelet-fibrin scaffold group was significantly higher than that in the control group (P < 0.05). The number of TUNEL-positive cells in the platelet-fibrin scaffold group was significantly lower than that in the control group (P < 0.05). The capillary density and capillaries with blood flow in the platelet-fibrin scaffold group were significantly higher than those in the control group (P < 0.05). Both the left ventricular end-diastolic volume and left ventricular end-systolic volume in the platelet-fibrin scaffold group were significantly lower than those in the control group (P < 0.05). In conclusion, the platelet-fibrin scaffold can promote the generation of endothelial cells, cardiomyocytes and capillaries, and further improve heart function. Besides, the platelet-fibrin scaffold exerts protective effect on the heart probably by secreting cytokines.     

Multiphasic growth and allometry.

Multiphasic growth assumes increase in body weight, or in other body measures, to be a result of more than one growth phase. Therefore, the concept of allometry can be extended from relation between body measures to relation between phases of growth. For two phases of growth, body weight (W) and tail length (L) can be partitioned into W1 + W2 and L1 + L2. Here, W1 and W2 correspond to phases 1 and 2 of weight and L1 and L2 to phases 1 and 2 of length, where each phase is described by a logistic function. Diphasic functions were applied to growth curves for body weight and for tail length of mice that were progeny of a transgenic male mated to random-bred NMRI females. A group of 20 female and male mice with high body weight at week 12, assumed to be transgenic, and a group of 20 with normal body weight, assumed to be non-transgenic, were selected for comparison. Body weight and tail length were measured about weekly from 3 to 26 weeks of age. Allometric relations between phases for weight (W1 and W2) and tail length (L1 and L2) are presented using predicted values based on estimated parameters of the diphasic growth functions. Differences between ages at maximum gain and ratios of duration of phases were analyzed. Growth in second phase of body weight appeared to be unrelated to growth in first phase of body weight and unrelated to growth in tail length. Growth in each phase of tail length appeared to be close to a simple allometric relation with growth in first phase of body weight. It is now feasible to study multiphasic allometric relations of growth between phases of one body measure and between phases of different body measures by comparing estimates of parameters of the multiphasic growth function.     

Time‐course changes in arteriolar and venular portions of capillary in young treadmill‐trained rats

This study was designed to examine the time‐course changes in capillarity, especially the distribution of arteriolar and venular capillaries, in skeletal muscles during endurance training by running in young female Wistar rats. Exercise training by running started at the age of 5 weeks and lasted for 5 weeks at 25 m min^–1 on a 25% gradient, 10–60 min day^–1, 5 days per week. Morphological findings were obtained from the soleus (SOL) and deep portions of the medial gastrocnemius (GASd) muscles. In SOL, the training significantly increased the capillary‐to‐fibre ratio (C:F), total capillary density, and density of venular capillaries at Week 1. Significant increases in the C:F and total capillary density were also observed at Weeks 4 and 5. The capillary domain area (CDA) values for total capillary and arteriolar and venular capillaries were significantly decreased after 4 weeks of training. In GASd, the training significantly increased the C:F at Week 1 and from Week 3 onwards. It also significantly increased cross‐sectional area of all fibre types. Total capillary density and the CDA values showed no significant difference between control and training groups at all points of time. Significant increases in succinate dehydrogenase (SDH) activity were first noted after 2 weeks in GASd and after 3 weeks in SOL. These findings suggest that, in young growing rats, adaptive changes in the oxygen transport system occurred within 1 week after the onset of training mainly in highly oxidative muscles. The changes in arteriolar and venular capillary densities may help to clarify the growth pattern of the capillary network associated with endurance running training.     

Different patterns in age-related morphometric alteration of myelinated fibers and capillaries of the tibial nerve: a longitudinal study in normal rats

Age-related regression of myelinated fibers in peripheral nerves of the lower limbs is strongly influenced by capillaries and results in balance dysfunction and falls. However, the temporal relationships between alteration patterns of myelinated fibers and capillaries have not yet been clarified. This study aimed to investigate age-related morphological and histological changes of both myelinated fibers and capillaries in peripheral nerves to clarify whether myelinated fibers or capillaries change earlier. Seven male Wistar rats each were randomly selected at 20 weeks (young group), 70 weeks (middle group), and 97 weeks (old group) for histological evaluations. The left and right tibial nerves were removed morphologically and histologically to examine myelinated fibers and capillaries. Axon diameter and myelin thickness were almost unaltered in the middle group compared with the young group but were significantly reduced in the old group when compared with the other two groups. However, the capillary diameter and number of microvascular branch points were substantially reduced in the middle group. The current study demonstrates that myelinated fibers of peripheral nerves show signs of regression in elderly rats, whereas capillaries start to reduce in middle-aged animals. In normal aging of the tibial nerve, capillaries may regress before myelinated fibers.     

Estimation of capillary length density in skeletal muscle by unbiased stereological methods: I. Use of vertical slices of known thickness

Background: The unbiased estimation of the capillary length density in skeletal muscle tissue L_v(cap/mus) has been performed in this study applying a new stereological methodology based on the use of vertical slices and the intersections of cycloid test curves with capillaries in a three-dimensional space defined by systematically chosen fields of vision and the thickness of the sections. Methods: The following simple requirements must be fulfilled: selection of a fixed vertical axis in skeletal muscle, adequate systematic muscle sampling, obtention of vertical slices of constant and known thickness but indifferent in magnitude, superposition of a cycloid test system with the minor axis of cycloid curves positioned perpendicularly to the vertical axis, and counting the intersections between cycloid curves and capillaries. In our study, the vertical axis was defined as that which is parallel to the natural, major axis of the muscle where fibres and capillaries are arranged parallel to this axis. The muscle sampling was performed using the fractionator method, and 25 pm thick sections were chosen. Results: The application of the equation for estimation of L_v(cap/mus) permits determination of an average of 1,480 mm of capillaries per mm³ of muscle tissue, knowing the number of intersections, section thickness, and the points hitting the muscle with a known ratio between cycloid test curve length to a test point. Conclusions: The estimation of L_v(cap/mus) is efficient, unbiasedly obtained, and no assumption on the degree of capillary anisotropy are required. © 1995 Wiley-Liss, Inc.     

Monitoring muscle over three orders of magnitude: Widespread positive allometry among locomotor and body support musculature in the pectoral girdle of varanid lizards (Varanidae)

There is a functional trade-off in the design of skeletal muscle. Muscle strength depends on the number of muscle fibers in parallel, while shortening velocity and operational distance depend on fascicle length, leading to a trade-off between the maximum force a muscle can produce and its ability to change length and contract rapidly. This trade-off becomes even more pronounced as animals increase in size because muscle strength scales with area (length²) while body mass scales with volume (length³). In order to understand this muscle trade-off and how animals deal with the biomechanical consequences of size, we investigated muscle properties in the pectoral girdle of varanid lizards. Varanids are an ideal group to study the scaling of muscle properties because they retain similar body proportions and posture across five orders of magnitude in body mass and are highly active, terrestrially adapted reptiles. We measured muscle mass, physiological cross-sectional area, fascicle length, proximal and distal tendon lengths, and proximal and distal moment arms for 27 pectoral girdle muscles in 13 individuals across 8 species ranging from 64 g to 40 kg. Standard and phylogenetically informed reduced major axis regression was used to investigate how muscle architecture properties scale with body size. Allometric growth was widespread for muscle mass (scaling exponent >1), physiological cross-sectional area (scaling exponent >0.66), but not tendon length (scaling exponent >0.33). Positive allometry for muscle mass was universal among muscles responsible for translating the trunk forward and flexing the elbow, and nearly universal among humeral protractors and wrist flexors. Positive allometry for PCSA was also common among trunk translators and humeral protractors, though less so than muscle mass. Positive scaling for fascicle length was not widespread, but common among humeral protractors. A higher proportion of pectoral girdle muscles scaled with positive allometry than our previous work showed for the pelvic girdle, suggesting that the center of mass may move cranially with body size in varanids, or that the pectoral girdle may assume a more dominant role in locomotion in larger species. Scaling exponents for physiological cross-sectional area among muscles primarily associated with propulsion or with a dual role were generally higher than those associated primarily with support against gravity, suggesting that locomotor demands have at least an equal influence on muscle architecture as body support. Overall, these results suggest that larger varanids compensate for the increased biomechanical demands of locomotion and body support at higher body sizes by developing larger pectoral muscles with higher physiological cross-sectional areas. The isometric scaling rates for fascicle length among locomotion-oriented pectoral girdle muscles suggest that larger varanids may be forced to use shorter stride lengths, but this problem may be circumvented by increases in limb excursion afforded by the sliding coracosternal joint.     

Static genetic and phenotypic allometry of dental traits in inbred and hybrid house mice

Static allometric coefficients were estimated by regression and reduced major axis methods for second and third mandibular molar widths scaled on body weight in 42-day-old inbred and hybrid house mice. Phenotypic slopes were calculated by combining inbred and hybrid strains, and genetic slopes were obtained from differences among the strains. It was hypothesized that the genetic scaling, which reflects the expected evolutionary allometry between populations if they have been produced from directional selection on body weight alone, would exceed the phenotypic scaling. The genetic coefficients were generally higher (average regression estimates in inbreds = 0.65) than the phenotypic ones (comparable average = 0.47), but the differences were non-significant. It was concluded that the higher scaling of tooth dimensions in interspecies versus intraspecies comparisons typically found in previous studies therefore could not necessarily be explained as a secondary response to selection for body size, although more information is needed about trends in the scaling of mammalian teeth at different ages.     

Studying avian encephalization with geometric morphometrics

Encephalization is a core concept in comparative neurobiology, aiming to quantify the neurological capacity of organisms. For measuring encephalization, many studies have employed relative brain sizes corrected for expected allometric scaling to body size. Here we highlight the utility of a multivariate geometric morphometric (GM) approach for visualizing and analyzing neuroanatomical shape variation associated with encephalization. GM readily allows the statistical evaluation of covariates, such as size, and many software tools exist for visualizing their effects on shape. Thus far, however, studies using GM have not attempted to translate the meaning of encephalization to shape data. As such, we tested the statistical relationship between size and encephalization quotients (EQs) to brain shape utilizing a broad interspecific sample of avian endocranial data. Although statistically significant, the analyses indicate that allometry accounts for <10% of total neuroanatomical shape variation. Notably, we find that EQs, despite being corrected for allometric scaling based on size, contain size‐related neuroanatomical shape changes. In addition, much of what is traditionally considered encephalization comprises clade‐specific trends in relative forebrain expansion, particularly driven by landbirds. EQs, therefore, fail to capture 90% of the total neuroanatomical variation after correcting for allometry and shared phylogenetic history. Moving forward, GM techniques provide crucial tools for investigating key drivers of this vast, largely unexplored aspect of avian brain morphology.