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A remarkable property of tetrapod bone is its ability to detect and remodel areas where damage has accumulated through prolonged use. This process, believed vital to the long-term health of bone, is considered to be initiated and orchestrated by osteocytes, cells within the bone matrix. It is therefore surprising that most extant fishes (neoteleosts) lack osteocytes, suggesting their bones are not constantly repaired, although many species exhibit long lives and high activity levels, factors that should induce considerable fatigue damage with time. Here, we show evidence for active and intense remodeling occurring in the anosteocytic, elongated rostral bones of billfishes (e.g., swordfish, marlins). Despite lacking osteocytes, this tissue exhibits a striking resemblance to the mature bone of large mammals, bearing structural features (overlapping secondary osteons) indicating intensive tissue repair, particularly in areas where high loads are expected. Billfish osteons are an order of magnitude smaller in diameter than mammalian osteons, however, implying that the nature of damage in this bone may be different. Whereas billfish bone material is as stiff as mammalian bone (unlike the bone of other fishes), it is able to withstand much greater strains (relative deformations) before failing. Our data show that fish bone can exhibit far more complex structure and physiology than previously known, and is apparently capable of localized repair even without the osteocytes believed essential for this process. These findings challenge the unique and primary role of osteocytes in bone remodeling, a basic tenet of bone biology, raising the possibility of an alternative mechanism driving this process.anosteocytic bone | osteon | bone toughness | damage-driven remodeling | fish skeleton

SUMMARYThe histological diversity of the skeletal tissues of fishes is impressive compared with that of other vertebrate groups, yet our understanding of the functional consequences of this diversity is limited. In particular, although it has been known since the mid1800s that a large number of fish species possess acellular bones, the mechanical advantages and consequences of this structural characteristic -and therefore the nature of the evolution of this feature -remain unclear. Although several studies have examined the material properties of fish bone, these have used a variety of techniques and there have been no direct contrasts of acellular and cellular bone. We report on a comparison of the structural and mechanical properties of the ribs and opercula between two freshwater fish -the common carp Cyprinus carpio (a fish with cellular bone) and the tilapia Oreochromis aureus (a fish with acellular bone). We used light microscopy to show that the bones in both fish species exhibit poor blood supply and possess discrete tissue zones, with visible layering suggesting differences in the underlying collagen architecture. We performed identical micromechanical testing protocols on samples of the two bone types to determine the mechanical properties of the bone material of opercula and ribs. Our data support the consensus of literature values, indicating that Youngʼs moduli of cellular and acellular bones are in the same range, and lower than Youngʼs moduli of the bones of mammals and birds. Despite these similarities in mechanical properties between the bone tissues of the fish species tested here, cellular bone had significantly lower mineral content than acellular bone; furthermore, the percentage ash content and bone mineral density values (derived from micro-CT scans) show that the bone of these fishes is less mineralized than amniote bone. Although we cannot generalize from our data to the numerous remaining teleost species, the results presented here suggest that while cellular and acellular fish bone may perform similarly from a mechanical standpoint, there are previously unappreciated differences in the structure and composition of these bone types.

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Dogs envenomed by V. palaestinae appear to sustain some degree of myocardial injury, as reflected by increased serum cTn concentrations and by the occurrence of arrhythmias. The latter should alert clinicians to a potentially ongoing cardiac injury. An increase in cTn-T may be of clinical relevance and indicate a cardiac injury in V. palaestinae envenomations in dogs.

Case Description—A 15-kg (33-lb) pregnant female mixed-breed dog of unknown age was referred because of a 10-day history of difficulty breathing. Clinical Findings—Physical examination findings were dyspnea, tachypnea, decreased bronchovesicular sounds (bilateral), muffled heart sounds, and abdominal distention with palpable fetuses. Hematologic abnormalities included anemia, leukocytosis, and thrombocytosis. Abnormalities detected during serum biochemical analysis included decreases in concentrations of albumin, sodium, triglycerides, and total calcium and increases in activities of alkaline phosphatase, alanine aminotransferase, γ-glutamyltransferase, aspartate aminotransferase, lactate dehydrogenase, and creatine kinase. Thoracic radiography revealed a diaphragmatic hernia with fetuses and a soft tissue or fluid opacity within the thoracic cavity. Treatment and Outcome—Exploratory celiotomy, ovariohysterectomy, partial sternotomy, placement of a right-sided thoracostomy tube, and herniorrhaphy were performed. After surgery, pneumothorax developed, and the thoracostomy tube was used to remove pleural effusion and free air. The pneumothorax did not resolve after continuous drainage of the thoracic cavity for 4 days. Autologous blood pleurodesis was performed by infusion of 80 mL (6 mL/kg [2.73 mL/lb]) of whole blood. The pneumothorax resolved immediately after injection of the blood. Conclusions and Clinical Relevance—Blood pleurodesis was used for resolution of pneumothorax in a dog after correction of a diaphragmatic hernia. Blood pleurodesis may provide a simple, safe, and inexpensive medical treatment for resolution of persistent (duration > 5 days) pneumothorax when surgery is not an option.