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Biomedical subjects

R M Dillaman

Publications and source records attributed to R M Dillaman.

18 recordsLinked to original sources
PubMed2004

Blubber development in bottlenose dolphins (Tursiops truncatus).

Blubber, the lipid-rich hypodermis of cetaceans, functions in thermoregulation, buoyancy control, streamlining, metabolic energy storage, and locomotion. This study investigated the development of this specialized hypodermis in bottlenose dolphins (Tursiops truncatus) across an ontogenetic series, including fetuses, neonates, juveniles, subadults, and adults. Blubber samples were collected at the level of the mid-thorax, from robust specimens (n = 25) that stranded along the coasts of North Carolina and Virginia. Blubber was dissected from the carcass and its mass, and the depth and lipid content at the sample site, were measured. Samples were prepared using standard histological methods, viewed by light microscopy, and digital images of blubber captured. Images were analyzed through the depth of the blubber for morphological and structural features including adipocyte size, shape, and numbers, and extracellular, structural fiber densities. From fetus to adult, blubber mass and depth increased proportionally with body mass and length. Blubber lipid content increased dramatically with increasing fetal length. Adult and juvenile blubber had significantly higher blubber lipid content than fetuses, and this increase was reflected in mean adipocyte size, which increased significantly across all robust life history categories. In juvenile, subadult, and adult dolphins, this increase in cell size was not uniform across the depth of the blubber, with the largest increases observed in the middle and deep blubber regions. Through-depth counts of adipocytes were similar in all life history categories. These results suggest that blubber depth is increased during postnatal growth by increasing cell size rather than cell number. In emaciated adults (n = 2), lipid mobilization, as evidenced by a decrease in adipocyte size, was localized to the middle and deep blubber region. Thus, in terms of both lipid accumulation and depletion, the middle and deep blubber appear to be the most metabolically dynamic. The superficial blubber likely serves a structural role important in streamlining the animal. This study demonstrates that blubber is not a homogeneous tissue through its depth, and that it displays life history-dependent changes in its morphology and lipid content.

Adipocytes↗
PubMed2004

Metabolic influences of fiber size in aerobic and anaerobic locomotor muscles of the blue crab, Callinectes sapidus.

Diameters of some white locomotor muscle fibers in the adult blue crab, Callinectes sapidus, exceed 500 microm whereas juvenile white fibers are <100 microm. It was hypothesized that aerobically dependent processes, such as metabolic recovery following burst contractions, will be significantly impeded in the large white fibers. In addition, dark aerobic fibers of adults, which rely on aerobic metabolism for both contraction and recovery, grow as large as the white fibers. These large aerobic fibers are subdivided, however, thus decreasing the effective diameter of each metabolic functional unit and enabling aerobic contraction. The two goals of this study were: (1) to characterize the development of subdivisions in the dark levator muscle fibers and (2) to monitor post-contractile metabolism as a function of fiber size in aerobic and anaerobic levator muscles. Dark levator muscle fibers from crabs ranging from <0.1 g to >190 g were examined with transmission electron microscopy to determine the density of mitochondria and subdivision diameters. Across all size classes, there was a constant mitochondrial fractional area (25% of the total subdivision area) and subdivision size (mean diameter of 36.5+/-2.7 microm). Thus, blue crab dark levator fibers are unusual in having metabolic functional units (subdivisions) that do not increase in size during development while the contractile functional units (fibers) grow hypertrophically. The body mass scaling of post-contractile lactate dynamics was monitored during recovery from anaerobic, burst exercise in white and dark muscle, and in hemolymph. There were no differences among size classes in lactate accumulation during exercise in either muscle. However, in white fibers from large crabs, lactate continued to increase after exercise, and lactate removal from tissues required a much longer period of time relative to smaller crabs. Differences in lactate removal among size classes were less pronounced in dark fibers, and post-contractile lactate accumulation was significantly higher in white than in dark fibers from large animals. These data suggest that the large white fibers invoke anaerobic metabolism following contraction to accelerate certain phases of metabolic recovery that otherwise would be overly slow. This implies that, in addition to the typical mass-specific decrease in oxidative capacity that accompanies increases in animal mass, aerobic metabolic processes become increasingly limited by surface area to volume and intracellular diffusion constraints in developing white muscle fibers.

Analysis of Variance↗
PubMed2003

Formation of the arthrodial membrane in the blue crab, Callinectes sapidus.

In this study the pattern of arthrodial membrane deposition in Callinectes sapidus was determined by histological and ultrastructural examination of tissues from the carpus joint of the cheliped collected during premolt, ecdysis, postmolt, and intermolt. Apolysis in the arthrodial membrane occurs at stage D(0) and is synchronous with apolysis of the calcified cuticle. Epicuticle formation begins at early stage D(1) and is completed in late stage D(1). Procuticle deposition starts at D(2) and continues until ecdysis. Numerous cytoplasmic extensions occur throughout the lamellae. Component fibers of the arthrodial membrane are intimately associated with dense plaques on the apical membrane of the underlying hypodermal cells, suggesting a site for fiber polymerization. Deposition of the arthrodial membrane continues after ecdysis, with most of the cuticle thickening occurring during stage C. When stained with PAS and counterstained with hematoxylin, a difference can be discerned between preecdysial and postecdysial procuticle of the arthrodial membrane, a distinction not made in previous studies. The boundary between the arthrodial membrane and calcified cuticle is thicker than either of the two layers and the layers overlap rather than butting up against one another. This pattern suggests that underlying hypodermal cells have to produce multiple types of cuticle over the molt cycle. A summary of the various molting patterns in C. sapidus suggests that the control of these diverse events may prove to be complex.

Animals↗
PubMed2000

Precocial development of axial locomotor muscle in bottlenose dolphins (Tursiops truncatus).

At birth, the locomotor muscles of precocial, terrestrial mammals are similar to those of adults in both mass, as a percent of total body mass, and fiber-type composition. It is hypothesized that bottlenose dolphins (Tursiops truncatus), marine mammals that swim from the instant of birth, will also exhibit precocial development of locomotor muscles. Body mass data from neonatal and adult dolphins are used to calculate Grand's (1992) Neural and Muscular Indices of Development. Using these indices, the bottlenose dolphin is a Condition "3.5" neonate, where Condition 4 is the documented extreme of precocial development in terrestrial mammals. Moreover, myosin ATPase (alkaline preincubation) analyses of the epaxial locomotor m. extensor caudae lateralis show that neonatal dolphins have fiber-type profiles very similar to those of adults. Thus, based on mass and myosin ATPase activity, muscle development in dolphins is precocial. However, succinic dehydrogenase and Nile red histochemistry demonstrate that neonatal dolphin muscle has mitochondrial and lipid distributions different from those found in adults. These data suggest that neonates have a lower aerobic capacity than adults. Dolphin neonates may compensate for an apparent lack of aerobic stamina in two ways: 1) by being positively buoyant, with a relatively increased investment of their total body mass in blubber, and 2) by "free-riding" off their mothers. This study investigates quantitatively the development of a dolphin locomotor muscle and offers suggestions about adaptations required for a completely aquatic existence.

Animals↗
PubMed2000

Nucleation and growth of calcite on native versus pyrolyzed oyster shell folia.

The thin sheets of calcite, termed folia, that make up much of the shell of an oyster are covered by a layer of discrete globules that has been proposed to consist of agglomerations of protein and mineral. Foliar fragments, treated at 475 degrees C for 36 h to remove organic matter, were imaged by atomic force microscopy (AFM) as crystals grew on the foliar surfaces in artificial seawater at calcite supersaturations up to 52-fold. Crystals were also viewed later by scanning electron microscopy. After pyrolysis, the foliar globules persisted only as fragile remnants that were quickly washed away during AFM imaging, revealing an underlying morphology on the foliar laths of a tightly packed continuum of nanometer-scale protrusions. At intermediate supersaturations, crystal formation was seen immediately almost everywhere on these surfaces, each crystal having the same distinctive shape and orientation, even at the outset with crystals as small as a few nanometers. In contrast, nucleation did not occur readily on non-pyrolyzed foliar surfaces, and the crystals that did grow, although slowly at intermediate supersaturations, had irregular shapes. Possible crystallographic features of foliar laths are considered on the basis of the morphology of ectopic crystals and the atomic patterns of various surfaces. A model for foliar lath formation is presented that includes cycles of pulsed secretion of shell protein, removal of the protein from the mineralizing solution upon binding to mineral, and mineral growth at relatively high supersaturation over a time frame of about 1 h for each turn of the cycle.

Animals↗
PubMed1999

Role of the midgut gland in purine excretion in the robber crab, Birgus latro (Anomura: Coenobitidae).

White fecal strands of Birgus latro are composed of small spherules of uric acid with a mean diameter of 1.6 +/- 0.6 microm. Large numbers of membrane-bound spherules with concentric lamellae are present in the R cells of the midgut gland, so we suggest that lengths of white feces are produced by coordinated secretion of these spherules into the lumen of the midgut gland tubules. There are four cell types in the tubules with embryonic (E) cells at the distal tip, B cells in a narrow band at the distal end and R cells making up the bulk of the tubules and gland. F cells are sparsely scattered among the R cells. Midgut gland tissue was assayed for activities of xanthine dehydrogenase and xanthine oxidase, the two forms of xanthine oxidoreductase. Contrary to previous reports, we found that the midgut gland of B. latro contains only high activities of xanthine dehydrogenase. If proteinase inhibitors were omitted from the assays, however, significant activity of xanthine oxidase was measured, a result we regard as an artifact attributable to the partial conversion of xanthine dehydrogenase to xanthine oxidase by endogenous proteinases. R cells were demonstrated to contain peroxisomes, which may be involved in lipid metabolism rather than synthesis of uric acid.

Animals↗
PubMed1995

A theoretical model of circulatory interstitial fluid flow and species transport within porous cortical bone.

A three-dimensional model of interstitial fluid flow and passive species transport within mineralized regions surrounding cross-cortical vessel canals is developed. In contrast to earlier studies, the present model applies to circulatory, non-stress-induced interstitial flow in porous cortical bone. Based on previous experimental observations, the canals are modeled as line sources that pass at an oblique angle through the cortex. Cross-cortical interstitial flow from the endosteal surface to the periosteal surface is also taken into account. It is found that model transport characteristics are qualitatively consistent with reported observations. In addition, parametric studies reveal the following: (1) Solute contact with the matrix is maximized when the ratio of canal radius to cortex thickness (R) is near physiological R values. (2) Solute-matrix contact falls to low levels when R falls below the physiological range. (3) Solute-matrix contact is maximized when the cross-cortical velocity is approximately an order of magnitude smaller than the canal outflow velocity. The first and second findings suggest that within porous bone physiological ranges of R promote near optimal species contact with the mineralized matrix. The third finding suggests that relatively impermeable layers of bone within the cortex can effectively promote solute-matrix contact by limiting cross-cortical flow. Finally, the model suggests that intra-canal resorption associated with reduced external loading may effectively compensate for reduced stress-induced interstitial flow by enhancing circulatory interstitial flow and species transport.

Animals↗
PubMed1994

Decreased femoral arterial flow during simulated microgravity in the rat.

To determine whether the blood supply to the hindlimbs of rats is altered by the tail-suspension model of weightlessness, rats were chronically instrumented for the measurement of femoral artery flow. Ultrasonic transit-time flow probes were implanted into 8-wk-old Wistar-Furth rats under ketamine-xylazine anesthesia, and, after 24 h of recovery, flow was measured in the normal ambulatory posture. Next, rats were suspended and flow was measured immediately and then daily over the next 4-7 days. Rats were subsequently returned to normal posture, and flow was monitored daily for 1-3 days. Mean arterial flow decreased immediately on the rats being suspended and continued to decrease until a new steady state of approximately 60% of control values was attained at 5 days. On the rats returning to normal posture, flow increased to levels observed before suspension. Quantile-quantile plots of blood flow data revealed a decrease in flow during both systole and diastole. The observed decrease in hindlimb blood flow during suspension suggests a possible role in the etiology of muscular atrophy and bone loss in microgravity.

Adaptation, Physiological↗
PubMed1991

Fluid movement in bone: theoretical and empirical.

Evidence from the literature and from our laboratory demonstrates a pronounced and rapid flow of fluids and associated solutes through the extravascular spaces in bone. Minutes after injection, large molecules such as ferritin and horseradish peroxidase (HRP) have been localized throughout the osteocytic lacunae and canaliculi of cortical bone in the chick, rat and dog. Patterns of marker movement preclude diffusion as the mechanism for solute movement and suggest a centrifugal bulk flow of fluids. We have developed a computer model of bone fluid flow that has led to the conclusion that the pattern and rate of fluid movement is governed by the pressure differential across the bone, the vascular architecture, and the porosity of the mineralized matrix. The validity of simulations in which a substance is injected and monitored over time has been tested by comparisons with actual injections of markers in the rat. Evidence is presented for a relationship between blood flow and bone dynamics in growth, repair and pathology of bone. We employed the tail suspension model of weightlessness in the rat to test the effect of posture on the perfusion of cortical bone using injections of HRP. Data indicated that perfusion of the femur was reduced by this treatment. We propose a "rheostat" mechanism, which suggests that bone perfusion may set limits for bone growth and remodeling. Therefore, bone mass reflects the ability of the vasculature to supply oxygen and nutrients to the cells on and within the mineralized matrix.

Animals↗
PubMed1991

A serum substitute promotes osteoblast-like phenotypic expression in cultured cells from chick calvariae.

The effects of medium supplements were tested on embryonic chick calvarial cells in culture. Isolates were divided among four treatment groups: Nu-Serum, chicken serum, fetal bovine serum, or calf serum. Expression of the osteoblastic phenotype was assessed by cell morphology, DNA content, [3H]thymidine incorporation, lactate production, cellular and medium alkaline phosphatase activities, and collagen synthesis. Cells grown in Nu-Serum demonstrated increased alkaline phosphatase activity and a six-fold higher rate of collagen synthesis compared to chicken serum. These cells displayed a polygonal profile, abundant rough endoplasmic reticulum, Golgi apparati, and elaborated an extensive matrix of banded collagen which was well mineralized by day 10 of culture. Although highly mitogenic, chicken serum promoted a more fibroblastoid morphology. Compared to the sera tested, Nu-Serum preferentially promoted the osteoblast-like phenotype in chick calvarial cells in culture.

Alkaline Phosphatase↗
PubMed1990

Bone growth and calcium balance during simulated weightlessness in the rat.

Rats, age 28 days, experiencing tail suspension in modified metabolic cages for 1, 2, and 3 wk were compared with littermate controls. Food and water consumption, urinary and fecal Ca excretion, and serum Ca were measured; hearts, fore- and hindlimb bones, skulls, and mandibles were removed for determination of wet, dry, and ash weights and Ca concentration and for histological examination. Weight gain and Ca intake and excretion were the same for both groups; both displayed net Ca gain. Suspended rats had significantly lower wet, dry, and ash weights of femora and tibiae. Dry weights of the humeri and radii/ulnae were moderately higher, and the skull and mandible dry and ash weights were significantly higher in suspended than in control rats. Cortical thickness of the femur, but not humerus, was less in suspended rats. The data are consistent with the hypothesis that bone growth is influenced by the cardiovascular changes associated with tail suspension.

Animals↗
PubMed1984

Movement of ferritin in the 2-day-old chick femur.

The distribution of intravascularly administered ferritin was examined in histological sections of femurs from 2-day-old chicks. The ferritin was seen in the mineralized portion of the bone as well as in the vessels 5 minutes after injection into the external jugular vein but was essentially absent 4 hours after injection. The concentration of ferritin in the vessels appeared to increase from the endosteal to the periosteal surface. In the mineral the ferritin appeared to move as a front roughly parallel and distal to the canals. A scheme for the movement of fluid and associated material through the mineralized portion of chick bone is presented that suggests that the driving force for the bone fluid is attributable to pressure differentials between adjacent canals. This differential is due to the geometry of the canals and increases as the angle of the canal relative to the endosteal surface decreases.

Animals↗
PubMed1981

X-ray evaluation of SEM technique for determining the crystallography of echinoid skeletons.

Coronal plates of the sea urchin Strongylocentrotus purpuratus have a microstructure typified by smooth textured trabeculae. When plates were decorated with calcite crystals each rhombohedron had the same orientation regardless of its location on the plate. When the sample was oriented so that the three edges of the rhombohedron formed equal 120 degrees angles and the three crystal faces appeared to form equal angles with the plane of the photograph, the c-axis of the plate paralleled the electron beam and the three a-axes were 30 degrees counterclockwise from the edges. These a-axes were then related to a plate edge recorded in a low magnification micrograph. Directions of the a-axes of each plate were also measured using a back-reflection Laue x-ray diffraction camera. A comparison of a-axes measured by the two techniques showed an average difference of 3 degrees, indicating that decorated crystal grew in crystallographic continuity with the plate. Assuming this relationship remains constant, the decoration technique appears to be an accurate and efficient method for evaluating the crystallography of echinoid skeletal units. Analysis of a polar plot of a-axes for 11 plates indicated that the a-axes were not randomly oriented; however, definitive relationships must await more extensive investigations.

Animals↗
PubMed1976

Direct innervation of the mantle edge gland by neurosecretory axons in Helisoma duryi (Mollusca: Pulmonata).

The mantle edge gland of Helisoma duryi is innervated by neurosecretory axons from the pallial nerves. Synaptoid contacts occur between axons and gland cells, and there is ultrastructural evidence for the release of neurosecretory material. The mantle edge gland contributes to the deposition of periostracum during shell formation, and direct neurosecretory innervation may control shell growth and regeneration.

Animals↗
PubMedDate not supplied

Changes in blubber distribution and morphology associated with starvation in the harbor porpoise (Phocoena phocoena): evidence for regional differences in blubber structure and function.

To examine patterns of blubber loss accompanying a decline in body condition, blubber thickness of juvenile harbor porpoises in normal/robust body condition (n=69) was compared with that of starved conspecifics (n=31). Blubber thickness in the thorax of starved porpoises (9-11 mm) was only 50%-60% of that of normal animals (18-20 mm); however, very little tailstock blubber was lost during starvation. Adipocytes in thorax and tailstock blubber were measured in both groups (n=5) to determine whether thickness changes were homogeneous throughout blubber depth. In the thorax of normal porpoises, adipocytes near the epidermis (outer blubber) were smaller (0.11 nL) than inner blubber adipocytes (0.17 nL). Conversely, the size of tailstock adipocytes was uniform. Starved animals had fewer, smaller adipocytes in the inner thorax blubber, suggesting a possible combination of adipocyte shrinkage and loss. Lipids were withdrawn only from the inner layer of thorax blubber during starvation, supporting a hypothesis of regional specialization of function in blubber. Blubber of the thorax serves as the site of lipid deposition and mobilization, while the tailstock is metabolically inert and likely important in locomotion and streamlining. Therefore, some proportion of the blubber of small odontocetes must be considered structural/mechanical rather than an energy reserve.

Adipocytes↗