Penises as Variable-Volume Hydrostatic Skeletons

Clinical studies of magnetic resonance elastography from 1995 to 2021: Scientometric and visualization analysis based on CiteSpace

BACKGROUND

To assess the knowledge framework around magnetic resonance elastography (MRE) and to explore MRE research hotspots and emerging trends.

METHODS

The Science Citation Index Expanded of the Web of Science Core Collection was searched on 22 October 2021 for MRE-related studies published between 1995 and 2021. Excel 2016 and CiteSpace V (version 5.8.R3) were used to analyze the downloaded data.

RESULTS

In all, 1,236 articles published by 726 authors from 540 institutions in 40 countries were included in this study. The top 10 authors published 57.6% of all included articles. The 3 most productive countries were the USA (n=631), Germany (n=202), and France (n=134), and the 3 most productive institutions were the Mayo Clinic (n=240), Charité (n=131), and the University of Illinois (n=56). The USA and the Mayo Clinic had the highest betweenness centrality among countries and institutions, respectively, and played an important role in the field of MRE. In this study, the 24,347 distinct references were clustered into 48 categories via reasonable clustering using specific keywords, forming the knowledge framework. Among the 294 co-occurring keywords, "hepatic fibrosis", "stiffness", "skeletal muscle", "acoustic strain wave", "in vivo", and "non-invasive assessment" were research hotspots. "Diagnostic performance", "diagnostic accuracy", "hepatic steatosis", "chronic hepatitis B", "radiation force impulse", "children", and "echo" were frontier topics.

CONCLUSIONS

Scientometric and visualized analysis of MRE can provide information regarding the knowledge framework, research hotspots, frontier areas, and emerging trends in this field.

The complex ecology of genitalia: Gonopodium length and allometry in the Trinidadian guppy

Male genitalia present an extraordinary pattern of rapid divergence in animals with internal fertilization, which is usually attributed to sexual selection. However, the effect of ecological factors on genitalia divergence could also be important, especially so in animals with nonretractable genitalia because of their stronger interaction with the surrounding environment in comparison with animals with retractable genitalia. Here, we examine the potential of a pervasive ecological factor (predation) to influence the length and allometry of the male genitalia in guppies. We sampled guppies from pairs of low-predation (LP) and high-predation (HP) populations in seven rivers in Trinidad, and measured their body and gonopodium length. A key finding was that HP adult males do not have consistently longer gonopodia than do LP adult males, as had been described in previous work. However, we did find such divergence for juvenile males: HP juveniles have longer gonopodia than do LP juveniles. We therefore suggest that an evolutionary trend toward the development of longer gonopodia in HP males (as seen in the juveniles) is erased after maturity owing to the higher mortality of mature males with longer gonopodia. Beyond these generalities, gonopodium length and gonopodium allometry were remarkably variable among populations even within a predation regime, thus indicating strong context dependence to their development/evolution. Our findings highlight the complex dynamics of genitalia evolution in Trinidadian guppies.

XROMM and diceCT reveal a hydraulic mechanism of tongue base retraction in swallowing

During primate swallowing, tongue base retraction (TBR) drives the food bolus across the oropharynx towards the esophagus and flips the epiglottis over the laryngeal inlet, protecting against penetration and aspiration of food into the airway. Despite the importance of TBR for swallowing performance, the mechanics of TBR are poorly understood. Using biplanar videoradiography (XROMM) of four macaque monkeys, we tested the extrinsic muscle shortening hypothesis, which posits that shortening of the hyoglossus and styloglossus muscles pulls the tongue base posteriorly, and the muscular hydrostat or intrinsic tongue muscle hypothesis, which suggests that, because the tongue is composed of incompressible fluid, intrinsic muscle shortening increases tongue length and displaces the tongue base posteriorly. Our data falsify these hypotheses. Instead we suggest a novel hydraulic mechanism of TBR: shortening and rotation of suprahyoid muscles compresses the tongue between the hard palate, hyoid and mouth floor, squeezing the midline tongue base and food bolus back into the oropharynx. Our hydraulic mechanism is consistent with available data on human tongue swallowing kinematics. Rehabilitation for poor tongue base retraction might benefit from including suprahyoid muscle exercises during treatment.

Morphological changes associated with Nile crocodile (Crocodylus niloticus) phallic glans inflation

The crocodylian phallic glans is the distal inflatable structure that makes the most direct contact with the female cloacal and associated reproductive tract openings during copulation. Therefore, its form and function directly impact female tissue sensory interactions and insemination mechanics. Compared to mammals, less is known about glans functional anatomy among other amniotes, including crocodylians. Therefore, we paired an ex vivo inflation technique with magnetic resonance imaging 3D-reconstructions and corresponding histological analyses to better characterize the morphological glans restructuring occurring in the Nile crocodile (Crocodylus niloticus) at copulation. The expansion of contiguous inflatable spongiform glans tissues is variably constrained by adjacent regions of dense irregular collagen-rich tissues. Therefore, expansion shows regional differences with greater lateral inflation than dorsal and ventral. Furthermore, this enlargement elaborates the cup-like glans lumen, dorsally reorients the glans ridge, stiffens the blunt and bifid glans tip, and putatively works to seal the ventral sulcus spermaticus semen conduit groove. We suggest how these dynamic male structures may interact with structures of the female cloacal urodeum and how these morphological changes, in concert with the varying material properties of the structural tissue compartments visualized in this study, aid copulatory gamete transfer and resulting fecundity. RESEARCH HIGHLIGHTS: Nile crocodile glans inflation produces a reproductively relevant copulatory structure directing insemination and female tissue interactions. Pairing magnetic resonance imaging 3D reconstruction with corresponding histology effectively studies functional anatomy.

Soft tissue rheology and its implications for elastography: Challenges and opportunities

Magnetic resonance elastography and related shear wave ultrasound elastography techniques can be used to estimate the mechanical properties of soft tissues in vivo by using the relationships between wave propagation and the elastic properties of materials. These techniques have found numerous clinical and research applications, tracking changes in tissue properties as a result of disease or other interventions. Most dynamic elastography approaches estimate tissue elastic (or viscoelastic) properties from a simplified version of the equations for the propagation of acoustic waves through a homogeneous linear (visco)elastic medium. However, soft tissue rheology is complex and departs significantly from this idealized picture. In particular, soft tissues are nonlinearly viscoelastic, inhomogeneous and often anisotropic, and their apparent stiffness can vary with the current loading state. All of these features have implications for the reliability and reproducibility of elastography measurements, from data acquisition to analysis and interpretation. New developments in inversion algorithms for elastography are beginning to offer solutions to account for the complex rheology of tissues, including inhomogeneity and anisotropy. There remains considerable potential to further refine elastography to capture the full spectrum of tissue rheology, and thus to better understand the underlying tissue microstructural changes in a broad range of clinical disorders.

Aquatic versus terrestrial crab skeletal support: morphology, mechanics, molting and scaling

The transition from aquatic to terrestrial environments places significant mechanical challenges on skeletal support systems. Crabs have made this transition multiple times and are the largest arthropods to inhabit both environments. Furthermore, they alternate between rigid and hydrostatic skeletons, making them an interesting system to examine mechanical adaptations in skeletal support systems. I hypothesized that terrestrial crabs have modified morphology to enhance mechanical stiffness and that rigid and hydrostatic skeletons scale differently from each other, with stronger allometric relationships on land. Using the aquatic blue crab, Callinectes sapidus, and the terrestrial blackback land crab, Gecarcinus lateralis, I measured and compared body mass, merus morphology (dimensions, cuticle thickness, and I) and mechanics (EI, E, critical stress, and hydrostatic pressure) of rigid and hydrostatic stage crabs encompassing a range of sizes (C. sapidus: 1.5-133 g, N≤24; G. lateralis: 22-70 g, N≤15). Results revealed that rigid G. lateralis has similar morphology (L/D and T/D) than C. sapidus, but the mechanics and most scaling relationships are the same. Hydrostatic land crabs differ from aquatic crabs by having different morphology (thinner cuticle), mechanics (greater internal pressures), and scaling relationship (cuticle thickness). These results suggest that the rigid crab body plan is inherently overbuilt and sufficient to deal with the greater gravitational loading that occurs on land, while mechanical adaptations are important for hydrostatically supported crabs. Compared to other arthropods and hydrostatic animals, crabs possess distinct strategies for adapting mechanically to life on land.

Pharmacologic therapy for Peyronie's disease: what should we prescribe?

INTRODUCTION

Peyronie's disease (PD) is a wound healing disorder of the penis with a myriad of proposed treatment options reported in the literature. Evaluating the available data and therapeutic management of PD can be challenging and confusing, even for the most experienced treating physician. This review provides a comprehensive overview of pharmacologic treatment options for PD, focusing on the best available evidence.

AREAS COVERED

A comprehensive literature search for published articles evaluating oral, topical, and injectable pharmacologic agents for PD was completed. Prospective, controlled trials were given precedence for inclusion.

EXPERT OPINION

Although a multitude of oral agents have been proposed and evaluated in PD patients, results vary widely and a reproducible objective benefit has not yet been strongly established for any single oral agent. Well-designed, large-scale, randomized controlled trials evaluating oral agents in PD patients are lacking. Consistent objective benefit from injectable agents has been supported for years by various non-controlled trials. Recently, injectable collagenase Clostridium histolyticum became the first pharmacologic agent to obtain FDA approval for use in PD patients, supported by data from a large-scale, Phase III randomized controlled trial. Further elucidation of the genetic and mechanistic pathways involved in the development and progression of PD will help define future therapeutic targets.

Protective effects of nutritional supplementation with arginine and glutamine on the penis of rats submitted to pelvic radiation

Radiotherapy is widely used to treat pelvic malignancies, but normal tissues near the target tumour are often affected. Our aims were thus to determine whether the structural organization of the rat penis is altered by radiation, and whether supplementation with L-arginine (ARG) or L-glutamine (GLN) would have protective effects against these alterations. Groups of rats were treated with: no intervention (CONTR); pelvic radiation, followed by sacrifice 7 (RAD7) or 15 (RAD15) days later; and pelvic radiation, daily supplementation with ARG or GLN, followed by sacrifice 7 (RAD7+ARG, RAD7+GLN) or 15 (RAD15+ARG, RAD15+GLN) days after radiation. Structural components in the corpus cavernosum (CC), tunica albuginea of the corpus spongiosum (TACS) and urethral epithelium (UE) were analysed using stereological and immunohistochemical methods. The results showed that in the CC, connective tissue was increased by 18% in RAD15 (p < 0.04), but this change was partially prevented in RAD15+GLN (p < 0.05) and RAD15+ARG (p < 0.04). The fibrous matrix of the CC trabeculae stained evenly for collagen type I. In RAD15, the intensity of the labelling was increased, whereas in RAD15+GLN and RAD15+ARG the staining was similar to that of CONTR. No staining changes were seen in the groups that were sacrificed 7 days after radiation. Cavernosal elastic fibre content in RAD15 was increased by 61% (p < 0.004), and this was prevented in RAD15+ARG (p < 0.004) but not in RAD15+GLN. In TACS, the amino acids protected (p < 0.02) against the radiation-induced 92% increase in elastic fibre content, but only in RAD15. Cell density in the UE, as well as UE thickness, were reduced by 30% in RAD15 (p < 0.004), and there were protective effects of both amino acids. In conclusion, radiation-induced alterations in penile structures tend to be more pronounced 15 days after radiation session. Both ARG and GLN have protective effects against these changes, with the former being slightly more effective.

The diversity of hydrostatic skeletons

A remarkably diverse group of organisms rely on a hydrostatic skeleton for support, movement, muscular antagonism and the amplification of the force and displacement of muscle contraction. In hydrostatic skeletons, force is transmitted not through rigid skeletal elements but instead by internal pressure. Functioning of these systems depends on the fact that they are essentially constant in volume as they consist of relatively incompressible fluids and tissue. Contraction of muscle and the resulting decrease in one of the dimensions thus results in an increase in another dimension. By actively (with muscle) or passively (with connective tissue) controlling the various dimensions, a wide array of deformations, movements and changes in stiffness can be created. An amazing range of animals and animal structures rely on this form of skeletal support, including anemones and other polyps, the extremely diverse wormlike invertebrates, the tube feet of echinoderms, mammalian and turtle penises, the feet of burrowing bivalves and snails, and the legs of spiders. In addition, there are structures such as the arms and tentacles of cephalopods, the tongue of mammals and the trunk of the elephant that also rely on hydrostatic skeletal support but lack the fluid-filled cavities that characterize this skeletal type. Although we normally consider arthropods to rely on a rigid exoskeleton, a hydrostatic skeleton provides skeletal support immediately following molting and also during the larval stage for many insects. Thus, the majority of animals on earth rely on hydrostatic skeletons.

Mechanical Description of a Hyper-Redundant Robot Joint Mechanism Used for a Design of a Biomimetic Robotic Fish

A biologically inspired robot in the form of fish (mackerel) model using rubber (as the biomimetic material) for its hyper-redundant joint is presented in this paper. Computerized simulation of the most critical part of the model (the peduncle) shows that the rubber joints will be able to take up the stress that will be created. Furthermore, the frequency-induced softening of the rubber used was found to be critical if the joints are going to oscillate at frequency above 25 Hz. The robotic fish was able to attain a speed of 0.985 m/s while the tail beats at a maximum of 1.7 Hz when tested inside water. Furthermore, a minimum turning radius of 0.8 m (approximately 2 times the fish body length) was achieved.