Cardiac-like musculature of the intrapulmonary venous wall of the long-clawed shrew (Sorex unguiculatus), common tree shrew (Tupaia glis) and common marmoset (Callithrix jacchus)

Anatomy of the heart with the highest heart rate

Shrews occupy the lower extreme of the seven orders of magnitude mammals range in size. Their hearts are large relative to body weight and heart rate can exceed a thousand beats a minute. It is not known whether traits typical of mammal hearts scale to these extremes. We assessed the heart of three species of shrew (genus Sorex) following the sequential segmental analysis developed for human hearts. Using micro‐computed tomography, we describe the overall structure and find, in agreement with previous studies, a large and elongate ventricle. The atrial and ventricular septums and the atrioventricular (AV) and arterial valves are typically mammalian. The ventricular walls comprise mostly compact myocardium and especially the right ventricle has few trabeculations on the luminal side. A developmental process of compaction is thought to reduce trabeculations in mammals, but in embryonic shrews the volume of trabeculations increase for every gestational stage, only slower than the compact volume. By expression of Hcn4, we identify a sinus node and an AV conduction axis which is continuous with the ventricular septal crest. Outstanding traits include pulmonary venous sleeve myocardium that reaches farther into the lungs than in any other mammals. Typical proportions of coronary arteries‐to‐aorta do not scale and the shrew coronary arteries are proportionally enormous, presumably to avoid the high resistance to blood flow of narrow vessels. In conclusion, most cardiac traits do scale to the miniscule shrews. The shrew heart, nevertheless, stands out by its relative size, elongation, proportionally large coronary vessels, and extent of pulmonary venous myocardium.

Establishment of basal cell carcinoma animal model in Chinese tree shrew (Tupaia belangeri chinensis)

Basal cell carcinoma (BCC) is the most common skin cancer worldwide, with incidence rates continuing to increase. Ultraviolet radiation is the major environmental risk factor and dysregulation of the Hedgehog (Hh) signaling pathway has been identified in most BCCs. The treatment of locally advanced and metastatic BBCs is still a challenge and requires a better animal model than the widely used rodents for drug development and testing. Chinese tree shrews (Tupaia belangeri chinensis) are closely related to primates, bearing many physiological and biochemical advantages over rodents for characterizing human diseases. Here, we successfully established a Chinese tree shrew BCC model by infecting tail skins with lentiviral SmoA1, an active form of Smoothened (Smo) used to constitutively activate the Hh signaling pathway. The pathological characteristics were verified by immunohistochemical analysis. Interestingly, BCC progress was greatly enhanced by the combined usage of lentiviral SmoA1 and shRNA targeting Chinese tree shrew p53. This work provides a useful animal model for further BCC studies and future drug discoveries.

Structure and composition of pulmonary arteries, capillaries, and veins

The pulmonary vasculature comprises three anatomic compartments connected in series: the arterial tree, an extensive capillary bed, and the venular tree. Although, in general, this vasculature is thin-walled, structure is nonetheless complex. Contributions to structure (and thus potentially to function) from cells other than endothelial and smooth muscle cells as well as those from the extracellular matrix should be considered. This review is multifaceted, bringing together information regarding (i) classification of pulmonary vessels, (ii) branching geometry in the pulmonary vascular tree, (iii) a quantitative view of structure based on morphometry of the vascular wall, (iv) the relationship of nerves, a variety of interstitial cells, matrix proteins, and striated myocytes to smooth muscle and endothelium in the vascular wall, (v) heterogeneity within cell populations and between vascular compartments, (vi) homo- and heterotypic cell-cell junctional complexes, and (vii) the relation of the pulmonary vasculature to that of airways. These issues for pulmonary vascular structure are compared, when data is available, across species from human to mouse and shrew. Data from studies utilizing vascular casting, light and electron microscopy, as well as models developed from those data, are discussed. Finally, the need for rigorous quantitative approaches to study of vascular structure in lung is highlighted.

Structural organization of hepatic portal vein in rat with special reference to musculature, intimal folds, and endothelial cell alignment

Structural organization of hepatic portal vein (HPV) was examined in adult rats by means of light and electron microscopy. Three characteristic features were found in the wall structure of rat HPV. (1) Tunica media consisted of two kinds of smooth muscle. The inner circular smooth muscle (CSM) was composed with one or two layer of smooth muscle cells, and was found in the entire length of the HPV and its tributaries. The outer longitudinal smooth muscle (LSM) was limited to a specific region of HPV; in particular it was well-developed at distal half of HPV. CSM counteracts luminal hydrostatic pressure to prevent circumferential hyperextension of venous wall, whereas LSM is likely to counteract a tractive force produced by gravity and movement of small intestine. (2) Intima of HPV showed a unique feature, intimal folds, which protruded into the lumen and were aligned almost circumferentially. Intimal folds were found only at the same region where the LSM was well-developed. Thus, LSM is presumably involved in the formation of intimal folds. (3) The endothelial cells between intimal folds were circumferentially aligned along the folds, although those in the other regions of HPV were arrayed along the longitudinal axis of HPV or the direction of blood flow as reported in other kinds of blood vessel. This finding implied that the circumferential blood flow locally occurs on the surface of intima between the intimal folds.

Structural organization of pulmonary veins in the rat lung, with special emphasis on the musculature consisting of cardiac and smooth muscles

Recent physiological studies have indicated the significant role of pulmonary veins in the total resistance of pulmonary vasculature. The structure of pulmonary veins in the rat was reinvestigated to clarify the different venous segments and their ultrastructure with regard to the musculature including cardiac muscles and smooth muscles with light and electron microscopy. The cardiac muscles were located in the axial and the primary branches of the pulmonary veins within a certain distance limit from the hilum (CM segment) and not in the peripheral region (non-CM segment). The smooth muscles were found indifferent to the presence of cardiac muscles as a continuous layer in segments larger than 180 microm (continuous SM segment) or as a discontinuous layer of circular smooth muscle cells in segments between 50 and 180 microm (partial SM segment). The smooth muscle layer was extremely thin in the CM segments, whereas it became conspicuously thick in the non-CM segment with an irregularly undulating luminal outline, especially in the partial SM segments. There were two elastic laminae in the CM segments: a conspicuous one on the interstitial side of the smooth muscles, and a weaker one between the endothelium and smooth muscles. In the non-CM segment, one elastic lamina was found on the interstitial side of the smooth muscles. Considering the limited range of contraction of cardiac muscles and the thinness of smooth muscle cells in the CM segments, it was concluded that vasoconstriction in the pulmonary veins is executed by smooth muscle cells in the non-CM segments thicker than 50 microm.

Cardiovascular anatomy, physiology, and disease of rodents and small exotic mammals

Cardiovascular disease in small exotic mammals is anecdotally common, but clinical reports of diagnosis and treatment of disease are rare. This article focuses on known causes of cardiovascular disease in the small exotic mammal. Normal anatomy and physiology, as it differs from the dog and cat, is also highlighted. Cardiomyopathy, dirofilariasis, atrial thrombosis, and other acquired and congenital cardiac and vascular diseases of rodents, hedgehogs, sugar gliders, raccoons, opossums, and skunks are reviewed. Expected clinical signs and diagnostic and treatment options, including a formulary, are provided for these species.