Structure and Mechanics of Mammalian Prehensile Tail Vertebrae

abstractPrehensile tails (PTs) – capable of suspending the body weight of the animal – evolved independently as many as 14 times among 40 extant mammalian genera. The structure of the mammalian PT is well studied in New World monkeys, where it evolved twice: once in the atelines (Ateles, Lagothrix, Brachyteles, and Lagothrix) and once in the genus Cebus. Recently, we have expanded our studies to nonprimate taxa such as carnivoran procyonids (raccoons and relatives) and didelphid marsupials (opossums and relatives). Adult PTs share musculoskeletal features that distinguish them from nonprehensile tails, which are thought to be adaptive to the mechanical demands of suspension and/or prehension incurred with locomotion, posture, and manipulation: 1) craniocaudally expanded sacroiliac joint and more proximal region vertebrae, which increase joint and tail stability; 2) more expansive transverse and hemal processes (proximal and distal attachments for primary tail flexors, respectively); and 3) tail vertebrae that are estimated to be structurally stronger and more rigid. Yet, our understanding of the broader adaptive significance of the PT has been hampered by two major deficits. First, structural data are largely limited to cortical and trabecular geometric assessments, which only provide estimates of mechanical properties and therefore limit the mechanical conclusions we can draw. Second, our studies have concentrated solely on the features of the adults, even while we know anecdotally that tail-use behavior changes ontogenetically, and it would be expected that these changes would be reflected in the mechanical properties of the tail vertebrae. The present study demonstrates that cortical geometric assessments correlate with structural mechanical properties of tail vertebrae in an ontogenetic series of squirrel monkeys, and both sets of data reveal a trend of increasing structural strength of the vertebrae with increasing body size (i.e, age)

Annular Lichen Planus in Association with Crohn Disease

BACKGROUND: Lichen planus is an idiopathic inflammatory disease of the skin and mucous membranes. Although the etiology is not established, it has been associated with autoimmune diseases, viral infections, drugs and dental restoration materials. However, the association with inflammatory bowel disease has been very rarely reported in the literature. CASE REPORT: A 19-year-old female patient presented with annular lesions on her upper body and limbs, with a sharply defined border and non-atrophic skin in the center. The lesions were hyperpigmented and had been stable for over one year. The histopathology confirmed the diagnosis of annular lichen planus. She had weight loss, occasional diarrhea, and a severe anemia. The investigation of these symptoms led to the diagnosis of Crohn disease and a sickle cell trait. Therapy with systemic corticosteroids and mesalazine controlled the intestinal disease, with concomitant improvement of the skin lesions. CONCLUSIONS: As lichen planus can be associated with other immunological disorders, the association with inflammatory bowel disease should be considered in the evaluation of the patient

Mouse Hind Limb Skeletal Muscle Functional Adaptation in a Simulated Fine Branch Arboreal Habitat

The musculoskeletal system is remarkably plastic during growth. The purpose of this study was to examine the muscular plasticity in functional and structural properties in a model known to result in significant developmental plasticity of the postcranial skeleton. Fifteen weanling C57BL/6 mice were raised to 16 weeks of age in one of two enclosures: a climbing enclosure that simulates a fine branch arboreal habitat and is traversed by steel wires crossing at 45° relative to horizontal at multiple intersections, and a control enclosure that resembles a parking deck with no wires but the same volume of habitable space. At killing, ex vivo contractility properties of the soleus (SOL) and extensor digitorum longus (EDL) muscles were examined. Our results demonstrate that EDL muscles of climbing mice contracted with higher specific forces and were comprised of muscle fibers with slower myosin heavy chain isoforms. EDL muscles also fatigued at a higher rate in climbing mice compared to controls. SOL muscle function is not affected by the climbing environment. Likewise, mass and architecture of both EDL and SOL muscles were not different between climbing and control mice. Our data demonstrate that functional adaptation does not require concomitant architectural adaptation in order to increase contractile force

Mechanical Effects of Fine-Wire Climbing on the Hindlimb Skeleton of Mice

poster abstractHigh-impact exercise (running/jumping) can stimulate multiple anabolic responses (increased trabecular bone volume, BV/TV) in the skeleton, but is also linked to an increased incidence of skeletal fracture. Thus, it is not an appropriate treatment for patients with elevated fracture risks. However, multi-directional offaxis mechanical loading can also elicit anabolic responses, even when magnitudes are relatively low. This represents a potential alternative to high-impact exercise for improving skeletal mechanical properties. To test this hypothesis, we raised twelve weanling female C57BL/6 mice to 4 months of age in custom enclosures that prevent (control) or require (experimental) manual and pedal grasping while balancing and climbing above narrow wire substrates. At sacrifice, we measured whole mouse bone density (DEXA) and performed architectural (μCT) and mechanical (4-pt bending) analyses of the femur and tibia. Body mass was similar between groups, although exercised mice were leaner (-35% fat mass). Bone mineral density was also similar, while bone mineral content was increased (+7%) in the exercised mice. Femoral midshaft polar moment of inertia was similar between groups, but exercised mice had lower BV/TV (-46%) of the distal femur and greater trabecular spacing (+21%). Exercised femora showed more total displacement (+58%) and post yield displacement (+115%) in bending than controls, and increased material toughness (+40%). Patterns were similar for the tibia. Mechanical data are consistent with high-impact exercise studies, but architectural data are not. Together they suggest that our exercise model may improve bone mechanical properties by redistributing mineral within the skeleton, and not by increasing net bone formation