Magnetomicrometry

We live in an era of wearable sensing, where our movement through the world can be continuously monitored by devices. Yet, we lack a portable sensor that can continuously monitor muscle, tendon, and bone motion, allowing us to monitor performance, deliver targeted rehabilitation, and provide intuitive, reflexive control over prostheses and exoskeletons. Here, we introduce a sensing modality, magnetomicrometry, that uses the relative positions of implanted magnetic beads to enable wireless tracking of tissue length changes. We demonstrate real-time muscle length tracking in an in vivo turkey model via chronically implanted magnetic beads while investigating accuracy, biocompatibility, and long-term implant stability. We anticipate that this tool will lay the groundwork for volitional control over wearable robots via real-time tracking of muscle lengths and speeds. Further, to inform future biomimetic control strategies, magnetomicrometry may also be used in the in vivo tracking of biological tissues to elucidate biomechanical principles of animal and human movement.

Validation of a novel Multi-Gas sensor for volcanic HCl alongside H2S and SO2 at Mt. Etna

Volcanic gas emission measurements inform predictions of hazard and atmospheric impacts. For these measurements, Multi-Gas sensors provide low-cost in situ monitoring of gas composition but to date have lacked the ability to detect halogens. Here, two Multi-Gas instruments characterized passive outgassing emissions from Mt. Etna's (Italy) three summit craters, Voragine (VOR), North-east Crater (NEC) and Bocca Nuova (BN) on 2 October 2013. Signal processing (Sensor Response Model, SRM) approaches are used to analyse H₂S/SO₂ and HCl/SO₂ ratios. A new ability to monitor volcanic HCl using miniature electrochemical sensors is here demonstrated. A "direct-exposure" Multi-Gas instrument contained SO₂, H₂S and HCl sensors, whose sensitivities, cross-sensitivities and response times were characterized by laboratory calibration. SRM analysis of the field data yields H₂S/SO₂ and HCl/SO₂ molar ratios, finding H₂S/SO₂ = 0.02 (0.01-0.03), with distinct HCl/SO₂ for the VOR, NEC and BN crater emissions of 0.41 (0.38-0.43), 0.58 (0.54-0.60) and 0.20 (0.17-0.33). A second Multi-Gas instrument provided CO₂/SO₂ and H₂O/SO₂ and enabled cross-comparison of SO₂. The Multi-Gas-measured SO₂-HCl-H₂S-CO₂-H₂O compositions provide insights into volcanic outgassing. H₂S/SO₂ ratios indicate gas equilibration at slightly below magmatic temperatures, assuming that the magmatic redox state is preserved. Low SO₂/HCl alongside low CO₂/SO₂ indicates a partially outgassed magma source. We highlight the potential for low-cost HCl sensing of H₂S-poor HCl-rich volcanic emissions elsewhere. Further tests are needed for H₂S-rich plumes and for long-term monitoring. Our study brings two new advances to volcano hazard monitoring: real-time in situ measurement of HCl and improved Multi-Gas SRM measurements of gas ratios.

Crystal structure of bis-(1,3-di-amino-propane-κ(2) N,N')bis-[2-(4-nitro-phen-yl)acetato-κO]zinc(II)

In the structure of the title compound, [Zn(C₈H₆NO₄)₂(C₃H₁₀N₂)₂], the Zn^II atom is located on a center of symmetry with one independent Zn—O distance of 2.199 (2) Å, and two Zn—N distances of 2.157 (2) and 2.144 (2) Å. The overall coordination geometry around the Zn^II atom is octa­hedral. Several types of hydrogen-bonding inter­actions are evident. Both intra­molecular [2.959 (3) Å] and inter­molecular [3.118 (3) and 3.124 (3) Å inter­actions occur between the O atoms of the acetate group and the amino N atoms, and weak inter­molecular C—H—O inter­actions involving the nitro groups, leading to an extended chain of the molecules aligned along the ac plane.

Chasing maximal performance: a cautionary tale from the celebrated jumping frogs of Calaveras County

Maximal performance is an essential metric for understanding many aspects of an organism's biology, but it can be difficult to determine because a measured maximum may reflect only a peak level of effort, not a physiological limit. We used a unique opportunity provided by a frog jumping contest to evaluate the validity of existing laboratory estimates of maximum jumping performance in bullfrogs (Rana catesbeiana). We recorded video of 3124 bullfrog jumps over the course of the 4-day contest at the Calaveras County Jumping Frog Jubilee, and determined jump distance from these images and a calibration of the jump arena. Frogs were divided into two groups: 'rental' frogs collected by fair organizers and jumped by the general public, and frogs collected and jumped by experienced, 'professional' teams. A total of 58% of recorded jumps surpassed the maximum jump distance in the literature (1.295 m), and the longest jump was 2.2 m. Compared with rental frogs, professionally jumped frogs jumped farther, and the distribution of jump distances for this group was skewed towards long jumps. Calculated muscular work, historical records and the skewed distribution of jump distances all suggest that the longest jumps represent the true performance limit for this species. Using resampling, we estimated the probability of observing a given jump distance for various sample sizes, showing that large sample sizes are required to detect rare maximal jumps. These results show the importance of sample size, animal motivation and physiological conditions for accurate maximal performance estimates.

Membrane muscle function in the compliant wings of bats

Unlike flapping birds and insects, bats possess membrane wings that are more similar to many gliding mammals. The vast majority of the wing is composed of a thin compliant skin membrane stretched between the limbs, hand, and body. Membrane wings are of particular interest because they may offer many advantages to micro air vehicles. One critical feature of membrane wings is that they camber passively in response to aerodynamic load, potentially allowing for simplified wing control. However, for maximum membrane wing performance, tuning of the membrane structure to aerodynamic conditions is necessary. Bats possess an array of muscles, the plagiopatagiales proprii, embedded within the wing membrane that could serve to tune membrane stiffness, or may have alternative functions. We recorded the electromyogram from the plagiopatagiales proprii muscles of Artibeus jamaicensis, the Jamaican fruit bat, in flight at two different speeds and found that these muscles were active during downstroke. For both low- and high-speed flight, muscle activity increased between late upstroke and early downstroke and decreased at late downstroke. Thus, the array of plagiopatagiales may provide a mechanism for bats to increase wing stiffness and thereby reduce passive membrane deformation. These muscles also activate in synchrony, presumably as a means to maximize force generation, because each muscle is small and, by estimation, weak. Small differences in activation timing were observed when comparing low- and high-speed flight, which may indicate that bats modulate membrane stiffness differently depending on flight speed.

Pharmacological MRI of stem cell transplants in the 3-nitroproprionic acid-damaged striatum

Blood oxygen level dependent (BOLD) pharmacological magnetic resonance imaging (phMRI) affords the non-invasive visualization of brain activity resulting from the administration of pharmacological compounds. Once the compound-responsive cells are lost, no change in activity is expected to occur. This principle therefore allows the assessment of neuronal loss or lack of signal transmission. These investigations can provide evidence of pathology in the absence of significant tissue loss and can be highly specific to determine which type of cell has been lost. Conversely, transplantation of cells replacing the lost neurons should restore normal signal transmission. We here demonstrate the application of phMRI to differentiate between rats with 3-nitroproprionic acid (3-NPA)-induced striatal lesions and 3-NPA-lesioned animals with neural stem cell transplants or controls. 3-NPA-induced lesions mainly involve striatal projection neurons that are responsive to dopamine agonists. The D2-agonist bromocriptine acts on these projection cells and loss of these through 3-NPA administration resulted in a significant decrease of locomotor activity and a substantial attenuation of the BOLD-response in the striatum. In contrast, lesioned animals that were grafted with neural stem cells exhibited an activity pattern akin to controls. Hence, grafting of neural stem cells exerts a functionally significant effect on striatal signal transmission that could underpin behavioral recovery.

Preservation of striatal tissue and behavioral function after neural stem cell transplantation in a rat model of Huntington’s disease

Cell replacement has the potential to become a frontline therapy to remedy behavioral impairments in Huntington's disease. To determine the efficacy of stem cell transplantation, behavioral assessment and in vivo monitoring of the lesion environment are paramount. We here demonstrate that neural stem cells from the MHP36 cell line prevented the development of a deficit on the beam walk test while providing partial recovery of learning in the water maze. However, no beneficial effect on rats' impairment in the staircase test was observed. By quantification of the lesion from serial magnetic resonance images, no effect of neural stem cells on lesion volume was observed. Instead, a preservation of striatal volume over time and its correlation with performance on the beam walk test suggested that sparing of behavioral function was associated with a stagnation of ongoing tissue loss rather than a reduction in lesion size. Serial imaging therefore warrants further implementation in clinical trials of neural grafts to monitor in vivo changes in the damaged brain due to transplantation.

Selective loss of natural killer T cells by apoptosis following infection with lymphocytic choriomeningitis virus

Natural killer T (NKT) cells, a unique subpopulation of T cells, coexpress markers also present on NK cells and recognize the major histocompatibility complex class I-like CD1d1 molecule. We studied the effect of an acute virus infection on NKT cells. Mice were infected with the nonhepatotropic Armstrong strain of lymphocytic choriomeningitis virus (LCMV), and at various times postinfection, mononuclear cells from the liver, peritoneum, and spleen were isolated. It was found that within 2 to 3 days, there was a selective loss of NKT cells from the liver with an apparent rapid recovery within 8 to 14 days. There was no increase in peritoneal or splenic NKT cells, indicating that NKT cells did not traffic to these tissues. This loss of NKT cells was independent of gamma interferon (IFN-gamma) and interleukin 12 (IL-12) production, but did occur in mice treated with poly(I-C), a classical inducer of IFN-alpha/beta. The reduction in NKT cells was CD28 and fas/fasL independent and occurred via apoptosis. It was not observed in LCMV-infected DNA fragmentation factor 45-deficient mice, and an increase in active caspase 3-specific staining was found in liver NKT cells from LCMV-infected and poly(I-C)-treated mice compared to uninfected wild-type mice. Interestingly, it was also found that liver NKT cells from LCMV-infected mice were themselves infected. These results suggest that the loss of NKT cells following an acute LCMV infection could be due to the induction of IFN-alpha/beta resulting in NKT-cell apoptosis and is important for the host's immune response to LCMV.

Central leptin stimulates ingestive behavior and urine flow in the near term ovine fetus

Leptin inhibits ingestive behavior and induces diuresis and natriuresis. To examine whether leptin influences fetal physiologic functions, we investigated the effect of central leptin on ovine fetal swallowing activity and urine flow. Six pregnant ewes with singleton fetuses (130 +/- 2 d gestation) were prepared with maternal and fetal arterial and venous catheters, fetal lateral intra-ventricle cannula, fetal bladder and amniotic fluid catheters. Electromyogram wires were placed in the fetal thyrohyoid muscle and upper and lower nuchal esophagus and electrodes were implanted on the parietal dura. Five days after surgery, recombinant human leptin was infused into the lateral ventricle and the fetus monitored for 8 h. Central leptin increased fetal swallowing activity during low-voltage electrocortical activity from basal values (0.96 +/- 0.08 swallows/min) at 2 h (1.41 +/- 0.24 swallows/min), 4 h (2.81 +/- 0.57 swallows/min), 6 h (2.53 +/- 0.59 swallows/min) and 8 h (2.08 +/- 0.39 swallows/min, p < 0.05). In comparison to basal values, low voltage electrocortical activity decreased (57 +/- 5% to 42 +/- 4%) and high voltage electrocortical increased (43 +/- 5% to 61 +/- 4%). In response to leptin, fetal urine flow initially decreased from basal values at 2 h (0.12 +/- 0.03 to 0.08 +/- 0.02 ml/kg/min, p < 0.05) then subsequently increased at 4 h and 6 h (0.20 +/- 0.04; 0.21 +/- 0.04 ml/kg/min, respectively, p < 0.05). Central leptin significantly increases near term ovine fetal swallowing activity and urine output, suggesting that leptin contributes to in utero development of ingestive behavior.

Central neuropeptide Y stimulates ingestive behavior and increases urine output in the ovine fetus

We hypothesized that central neuropeptide Y (NPY) increases swallowing activity and alters renal function in the near-term ovine fetus. Six ewes with singleton fetuses (130 +/- 2 days of gestation; 148 days = term) were chronically prepared with arterial and venous catheters, a fetal lateral cerebroventricular cannula, and fetal bladder and amniotic fluid catheters. For determination of fetal swallowing, electromyogram wires were placed in the fetal thyrohyoid muscle and the upper and lower nuchal esophagus. Electrodes were implanted on the parietal dura for determination of fetal electrocorticogram (ECoG). After 5 days of recovery, fetal swallowing, ECoG, blood pressure, and heart rate were monitored during a 3-h basal period. At t = 3 h, ovine NPY (0.05 mg/kg) was administered into the lateral ventricle, and fetuses were monitored for an additional 8 h. A control study of central administration of artificial cerebral spinal fluid was performed on an alternate day. Central NPY significantly increased swallowing activity during low-voltage ECoG from basal activity (1.26 +/- 0.15 swallows/min) at 4 h (1.93 +/- 0.37 swallows/min), 6 h (1.69 +/- 0.27 swallows/min), and 8 h (2.38 +/- 0.31 swallows/min). NPY significantly increased fetal urine flow (basal: 0.13 +/- 0.02; 4 h: 0.21 +/- 0.04; 6 h: 0. 19 +/- 0.03 ml.kg(-1).min(-1)). These results demonstrate that central NPY stimulates fetal swallowing activity and increases urine output, which may contribute to the in utero development of ingestive behavior.

Muscle and tendon contributions to force, work, and elastic energy savings: a comparative perspective

Muscle-tendon architecture underlies muscle function. Whereas muscles generally contribute most to mechanical work, tendons provide the majority of elastic energy savings. Isometric or eccentric contractions enhance force and further reduce energy cost. However, elastic savings is probably constrained by the need to reduce compliance for accurate control of position.

Fetal diuretic responses to maternal hyponatremia: contribution of placental sodium gradient

Maternal hyponatremia induces fetal hyponatremia and increased fetal urine flow. We sought to examine the relative contributions of the placental Na(+) gradient vs. the absolute decrease in fetal plasma Na(+) in the fetal diuretic response to hyponatremia. Seven ewes with singleton fetuses (130 +/- 2 days) were prepared. Ewes received intravenous 1-desamino-8-D-arginine vasopressin (20 microg) and warm tap water (2 liters). Maternal plasma Na(+) was decreased to achieve two levels of maternal hyponatremia. Maternal and fetal blood volume were measured with radiolabeled red blood cells. In response to the first decrease in maternal plasma Na(+), fetal plasma Na(+) did not change initially. Subsequently, fetal plasma Na(+) decreased, normalizing the gradient. The second decrease in maternal plasma Na(+) similarly induced a reduced and normalized placental gradient at lower fetal plasma Na(+) values. Fetal urine flow increased in direct proportion to the degree of fetal hyponatremia (13, 38, 63, 100%, respectively). Maternal, although not fetal, blood volume significantly increased in response to hyponatremia. These results suggest that chronic fetal hyponatremia will result in a persistent diuresis, despite placental equilibration.

Maternal 1-deamino-8-D-arginine-vasopressin-induced sequential decreases in plasma sodium concentration: ovine fetal renal responses

OBJECTIVE

Acute maternal plasma hypotonicity induces a reduced placental osmotic gradient that contributes to augmented maternal-to-fetal water flow. Subsequently, maternal plasma hyponatremia results in fetal plasma hyponatremia, increased fetal urinary flow, and ultimately increased amniotic fluid volume. We hypothesized that both the degree of reduction in the placental osmotic gradient and the degree of fetal plasma hyponatremia influence fetal urinary diuretic responses. To differentiate the roles of these factors, we determined fetal urinary responses to graded levels of plasma hyponatremia during a constant placental osmotic gradient. Furthermore, we sought to establish the minimum level of plasma hyponatremia necessary to facilitate an increase in fetal urine production.

STUDY DESIGN

Seven pregnant ewes (130 +/- 2 days) were prepared with maternal and fetal vascular catheters and a fetal bladder catheter. After 6 days of recovery, fetal urinary flow and urine and plasma compositions were measured during a 2-hour control period. At 2 hours, tap water (2 L, 38 degreesC) with a 20-g bolus of 1-deamino-8-d-arginine-vasopressin was administered to the ewe. Maternal plasma sodium concentration was decreased from control by 5 to 7, 10 to 12, and 15 to 17 mEq/L, and held at each level (levels 1, 2, and 3) for 60 minutes.

RESULTS

1-Deamino-8-d-arginine-vasopressin administration induced sequential decreases in maternal and fetal plasma sodium concentrations (control 146.9 +/- 0.5 mEq/L and 141.0 +/- 0.5 mEq/L, respectively) at level 1 (140.1 +/- 0.6 mEq/L and 136.7 +/- 0.7 mEq/L, respectively), level 2 (132.5 +/- 0.7 mEq/L and 130.6 +/- 1.1 mEq/L, respectively), and level 3 (125.4 +/- 1.2 mEq/L and 123.0 +/- 1.5 mEq/L, respectively). The maternal-fetal placental osmolality and sodium gradients were constant at each hypotonicity level. Fetal urinary flow significantly increased in association with the degree of hyponatremia (from 0.17 +/- 0.03 mL/kg/min to 0. 26 +/- 0.04 mL/kg/min, 0.33 +/- 0.05 mL/kg/min, and 0.38 +/- 00.5 mL/kg/min at levels 1, 2, and 3, respectively).

CONCLUSIONS

These results indicate the following: (1) Sequential decreases in maternal plasma tonicity result in parallel decreases in fetal plasma tonicity. (2) The fetal urinary diuretic response is highly correlated with the degree of fetal plasma hypotonicity, despite a constant placental osmotic gradient. A fetal therapeutic response (53% increase in fetal urine production) may be induced by a maternal plasma sodium concentration decrease of only 5 to 7 mEq/L.

Energetics of bipedal running. I. Metabolic cost of generating force

Similarly sized bipeds and quadrupeds use nearly the same amount of metabolic energy to run, despite dramatic differences in morphology and running mechanics. It has been shown that the rate of metabolic energy use in quadrupedal runners and bipedal hoppers can be predicted from just body weight and the time available to generate force as indicated by the duration of foot-ground contact. We tested whether this link between running mechanics and energetics also applies to running bipeds. We measured rates of energy consumption and times of foot contact for humans (mean body mass 78.88 kg) and five species of birds (mean body mass range 0.13-40.1 kg). We find that most (70-90%) of the increase in metabolic rate with speed in running bipeds can be explained by changes in the time available to generate force. The rate of force generation also explains differences in metabolic rate over the size range of birds measured. However, for a given rate of force generation, birds use on average 1.7 times more metabolic energy than quadrupeds. The rate of energy consumption for a given rate of force generation for humans is intermediate between that of birds and quadrupeds. These results support the idea that the cost of muscular force production determines the energy cost of running and suggest that bipedal runners use more energy for a given rate of force production because they require a greater volume of muscle to support their body weight.

Energetics of bipedal running. II. Limb design and running mechanics

Compared with quadrupeds, bipedal runners of the same weight have longer legs, take longer steps and can presumably use slower, more economical muscle fibers. One might predict that bipedal running is less expensive, but it is not. We hypothesized that bipeds recruit a larger volume of muscle to support their weight, eliminating the potential economy of longer legs and slower steps. To test our hypothesis, we calculated the relative volume of muscle needed to support body weight over a stride in small dogs (Canis familiaris) and wild turkeys (Meleagris gallopavo) of the same weight. First, we confirmed that turkeys and dogs use approximately the same amount of energy to run at the same speed, and found that turkeys take 1. 8-fold longer steps. Higher muscle forces and/or longer muscle fibers would require a greater volume of active muscle, since muscle volume is proportional to the product of force and fascicle length. We measured both mean fascicle length and mean mechanical advantage for limb extensor muscles. Turkeys generated approximately the same total muscle force to support their weight during running and used muscle fascicles that are on average 2.1 times as long as in dogs, thus requiring a 2.5-fold greater active muscle volume. The greater volume appears to offset the economy of slower rates of force generation, supporting our hypothesis and providing a simple explanation for why it costs the same to run on two and four legs.

Somatotropin treatment reduces energy intake without altering protein intake in pigs selecting between high and low protein diets

The current experiment examined the effect of somatotropin (STH) on feed intake and diet selection in pigs selecting between high (24% CP) and low (12% CP) protein diets. Sixteen pigs (initial weight 69 +/- 2 kg) were individually penned and allowed to select between the diets for a 7-d pretreatment period and a 14-d treatment period during which time they received daily, subcutaneous injections of porcine somatotropin (0 or 4 mg/d). A 6-d withdrawal period followed. Feed intake was recorded daily. Over the 14-d treatment period, feed intake in pigs treated with STH was 21% less than that in the control group (2.49 vs. 3.17 kg/d, P < 0.01). The decrease in total intake was accounted for entirely by a decrease in the amount of the 12% CP diet selected (1.00 vs. 2.00 kg/d, P <0.01). STH-treated pigs altered their selection pattern such that energy intake was reduced, but total protein intake was unaffected. Control pigs selected a diet that was 15-16% crude protein throughout the study. STH-treated pigs selected a higher protein diet (18%, P < 0.02). During the withdrawal period, total feed intake began to normalize, such that by the third day of withdrawal, intake was not different than that in the control group. The recovery of total intake was accomplished by increased consumption of both diets rather than a specific normalization of low protein diet consumption. The results indicate that pigs treated with STH decrease feed intake, which is due to a decrease in the amount of 12% CP diet consumed. The change in dietary selection pattern is likely associated with a change in energy retention (carcass lipid + protein) associated with the STH-induced changes in composition of gain.

Muscular force in running turkeys: the economy of minimizing work

During running, muscles and tendons must absorb and release mechanical work to maintain the cyclic movements of the body and limbs, while also providing enough force to support the weight of the body. Direct measurements of force and fiber length in the lateral gastrocnemius muscle of running turkeys revealed that the stretch and recoil of tendon and muscle springs supply mechanical work while active muscle fibers produce high forces. During level running, the active muscle shortens little and performs little work but provides the force necessary to support body weight economically. Running economy is improved by muscles that act as active struts rather than working machines.

Design of the oxygen and substrate pathways. I. Model and strategy to test symmorphosis in a network structure

This first paper in a series develops a model of structure-function relationships for the oxygen and substrate pathways of oxidative metabolism in working muscle. This will be used in the subsequent experimental papers in asking how biological structures are designed if they serve more than one function and whether one function can be served by more than one structural pathway. We have used the concept of symmorphosis to address this question; in its original form, it postulates that no more structure is built and maintained at each step in a pathway than is required to meet functional demands. The concept of symmorphosis was developed to deal with the problem of modelling the pathway for oxygen from the environment to mitochondria, essentially a single series of interconnected transfer steps. In the present context, the application of this concept is more complex. Both oxygen and substrates are transported directly from the blood to the mitochondria in what appear to be shared steps. The flows along this direct pathway are adjusted during muscular work. However, substrates have an additional option. They can be stored intracellularly as lipid droplets or glycogen, and thus their supply to mitochondria can occur in two steps separated in time: from capillaries to stores during rest, and from stores to mitochondria during work. The integrated pathways have a network structure and the functional flows are partitioned to different branches of the network, and we must ask whether the partitioning of fluxes is related to design constraints. The principle of symmorphosis predicts that the best use is made of the available options and that the design of each step is matched to the specific functional demand in view of a balance to be achieved over the entire network. This will be tested in subsequent papers by determining maximal flows for oxygen, carbohydrates and lipids through each of the transport steps and their respective structural capacities, comparing dogs and goats, animals of the same size whose maximal oxidative capacities differ by more than twofold. Finally, we will ask whether the principle of symmorphosis can be extended to apply to network systems.

Design of the oxygen and substrate pathways. III. Partitioning energy provision from carbohydrates

This paper quantifies maximal fluxes through the pathway supplying carbohydrates to the mitochondria of muscle cells. Continuous infusions of D-[3-(3)H]glucose together with indirect calorimetry were used to investigate the partitioning of the supply of carbohydrates through the two branches of the pathway: from circulating glucose and from glycogen stores within the muscle cells to the mitochondria. The relative contribution of circulating glucose to total carbohydrate oxidation was small, accounting for only 13% and 23% of the carbohydrate oxidized at exercise intensities approaching MO2max in dogs and goats, respectively. Unexpectedly, maximal rates of circulating glucose oxidation were nearly the same in the two species (when expressed in absolute terms; dog:goat ratio = 1.2), despite the 2.2-fold difference in aerobic capacity. We conclude that the glycogen stores in the muscle cells are the major source of substrates at maximal rates of oxidation, supplying 60-70% of the total energy. Furthermore, it is this branch of the carbohydrate pathway that is adapted to the large difference in aerobic capacity between dogs and goats.

Design of the oxygen and substrate pathways. II. Defining the upper limits of carbohydrate and fat oxidation

This paper quantifies maximal flows of carbohydrates and lipids through the pathways supplying the mitochondria. Maximal flow rates are the main functional parameter used in testing the principle of symmorphosis, which states that structural capacities are quantitatively matched to functional demand. Only under rate-limiting conditions will all of the structural capacity be used. Dogs and goats were compared to obtain large differences in absolute rates. We exercised the animals for long enough to reach steady-state O2 and CO2 exchange rates at intensities eliciting 40%, 60% and 85% of the maximal rate of oxygen consumption (MO2max). We then calculated rates of fat and carbohydrate oxidation from the ratio of CO2 produced to O2 consumed (the respiratory exchange ratio). The dog's Mo2max was more than twice that of the goat (6517 versus 3026 mumol O2 kg-1 min-1). We found the same pattern of fuel selection as a function of exercise intensity in both species, and it appears to be general to mammals. Maximal rates of fat oxidation were reached at 40% exercise intensity, where 77% of the energy was supplied by fat. As exercise intensity increased, all additional energy was supplied by carbohydrates. We conclude that the partitioning of fuel supply to the fat and carbohydrate pathways follows the same pattern in both dogs and goats.

Design of the oxygen and substrate pathways. VII. Different structural limits for oxygen and substrate supply to muscle mitochondria

This paper integrates the results of a series of studies on the supply of O2 and substrates for oxidative muscle metabolism and draws conclusions on the role of structural design in partitioning and limiting substrate supply. The studies compared dogs and goats exercising at different intensities and combined physiological, biochemical and morphometric investigations. In both species, the rate of fatty acid oxidation reached an upper limit at low exercise intensities, and only glucose consumption was increased at higher exercise intensities. The supply of both glucose and fatty acids from the capillaries reached maximal rates at low exercise intensities; this limitation is related to the design of the sarcolemma as calculations suggest that the endothelium introduces only a small resistance to substrate flux. From these findings, it appears that the capillaries are designed to satisfy O2 supply up to maximal O2 demand. The increase in substrate supply to the mitochondria at higher exercise intensities is achieved by drawing on intracellular stores of glycogen and lipids. The size of these stores is larger in dogs than in goats, providing the athletic species with twice the fuel reserves. These findings are interpreted on the basis of a network model with fluxes partitioned between direct and indirect pathways and with some structures shared by more than one function. Whereas O2 is supplied through a direct pathway, the supply of both substrates is split temporally to allow, during exercise, immediate fuel supply to the mitochondria from intracellular stores; these are replaced from the vasculature, during periods of rest, to a size commensurate with high rates of combustion. Considering this complexity, we conclude that the results are compatible with the principle of symmorphosis applied to a network structure and that the adjustment of design to functional demand involves different structures for O2 and for substrates.

Rats treated with somatotropin select diets higher in protein

It was previously shown that somatotropin (STH) increases growth rate, improves food efficiency and stimulates protein accretion. In rats, STH also increases food intake. This study examined the effect of exogenous STH on rats' selection of diets varying in protein content. It was hypothesized that the increase in food intake in response to STH is driven by an increased protein requirement. Rats were allowed to select between two diets varying in casein (5 and 30%) or given a diet of a single casein level (20%). In each diet group, rats were treated with 0 or 4 mg of porcine STH/d. Rats treated with STH showed greater food intake (20%) and protein accretion (125%), regardless of diet. However, the greater food intake in rats allowed to select was due to greater consumption of the high protein diet. Diet selecting, STH-treated rats consumed 75% more of the 30% casein diet than did the saline-treated controls, while consuming a similar amount of 5% casein diet. Total protein intake (g/d) was 22 and 53% greater in rats injected with STH consuming the 20% casein diet and selection diets, respectively. The results indicate that rats injected with somatotropin select a diet greater in protein when compared with those not receiving somatotropin. It is suggested that the STH-induced increase in protein accretion results in a greater demand for essential amino acids. The mechanism whereby animals are able to monitor this greater need is not clear.

Comparison of daily versus continuous administration of somatotropin on growth rate, feed intake, and body composition in intact female rats

The response to continuous delivery or daily bolus injection of porcine somatotropin (pST) was compared in mature, pituitary-intact female rats (225 g). Growth rate in control rats was approximately 1 g/d over the 14-d study. There was a dose-dependent (0, .4, 1.2, and 3.6 mg of pST/d; P < .001) increase in rate of gain with an interaction (P < .001) of dose and mode of delivery. The slope of the dose-response curve for growth rate was linear on a logarithmic scale for both modes of delivery but was greater for continuous delivery. At the low dose (.4 mg/d) pST stimulated gain (21.7 g/14 d above control, P < .05) when administered by daily injection but failed to stimulate gain (6.0 g/14 d above control, NS) when delivered continuously. At the high dose (3.6 mg/d), gain (above that in control rats) was 49.1 and 79.7 g/14 d for daily and continuous delivery; the two modes were different (P < .05) from each other. Feed intake and liver weights were also stimulated by pST in a dose-dependent manner. The increase in liver size was accompanied by a dose-dependent increase in liver DNA, indicative of an increase in cell number. Increased carcass gain was largely accounted for by increased carcass protein accretion. Rates of carcass lipid accretion were lower than those for protein accretion and were further decreased by pST, particularly by the high dose administered by continuous delivery, where a negative lipid accretion value was observed. Circulating IGF-I was increased by pST (P < .001) but was not affected by the mode of delivery. The results demonstrate that the increased gain observed in mature rats is largely due to lean tissue accretion and is accompanied by an increase in feed intake.

Moving cheaply: energetics of walking in the African elephant

Large animals have a much better fuel economy than small ones, both when they rest and when they run. At rest, each gram of tissue of the largest land animal, the African elephant, consumes metabolic energy at 1/20 the rate of a mouse; using existing allometric relationships, we calculate that it should be able to carry 1 g of its tissue (or a load) for 1 km at 1/40 the cost for a mouse. These relationships between energetics and size are so consistent that they have been characterized as biological laws. The elephant has massive legs and lumbers along awkwardly, suggesting that it might expend more energy to move about than other animals. We find, however, that its energetic cost of locomotion is predicted remarkably well by the allometric relationships and is the lowest recorded for any living land animal.

Interaction of insulin and somatotropin on body weight gain, feed intake, and body composition in rats

This study investigated the interaction of insulin and somatotropin on body weight gain and feed conversion in rats. Female rats (initial wt 215 g) were assigned to one of the following four treatments for a 2-wk period: 1) control; 2) 40 U protamine zinc insulin.kg-1.day-1; 3) 2 mg/day somatotropin; 4) insulin + somatotropin. Relative to the control group (gain, 1.4 g/day; intake, 16.7 g/day) insulin stimulated the rate of gain (250%), feed intake (73%), and fat pad weight (215%). Insulin caused a 270% increase in carcass fat and a 30% increase in carcass protein. Somatotropin also increased gain (178%) but did not have a significant effect on intake or fat pad weight. Somatotropin increased carcass protein 28% but had no effect on carcass fat. The greatest stimulation of body weight gain (392%) was observed with the insulin plus somatotropin combination treatment, indicating an additive effect. There were also additive effects on protein accretion and organ weights. However, feed intake and carcass fat in the combination group were intermediate between that of the control and insulin alone groups, indicating that somatotropin attenuated the ability of insulin to stimulate these parameters. These results indicate that certain effects of insulin and somatotropin, such as the promotion of lean tissue accretion, are additive, whereas other effects, such as those associated with lipid metabolism, oppose each other.

Mismatch between lipid mobilization and oxidation: glycerol kinetics in running African goats

Glycerol kinetics and total fatty acid (FA) oxidation of trained African pygmy goats were measured by continuous infusion of [2-3H]glycerol and indirect calorimetry during treadmill exercise at 40, 60, and 85% maximal O2 consumption (VO2max). Our main goals were 1) to determine whether rates of FA mobilization and utilization are eventually matched as exercise intensity increases, thereby minimizing reesterification to supply more FA to working muscles, and 2) to test the hypothesis that lipolytic rate is proportional to aerobic capacity by comparing low-aerobic goats with published values from highly aerobic dogs and humans. Mean rate of glycerol release in the circulation (Ra glycerol) was 3.83 +/- 0.11 at rest, 7.69 +/- 0.88 at 40% VO2max, reached a maximum of 15.32 +/- 0.95 at 60% VO2max, and returned to 10.53 +/- 0.76 mumol.kg-1 x min-1 at 85% VO2max. Lipolytic rate did not match total FA oxidation, implying that Ra glycerol cannot be used as an index of FA utilization, even during intense exercise. A large fraction of total FA released by lipolysis was reesterified at 60 and 85% VO2max, showing that FA mobilization does not limit whole animal FA oxidation at these intensities. Comparing goat, dog, and human responses reveals that mammalian lipolytic rate is scaled with aerobic capacity. High- and low-aerobic species exercising at the same %VO2max mobilize FA in exact proportion with their metabolic rate, suggesting that the relative contribution of FA to total energy provision is independent of VO2max.

Second neoplasms in patients with carcinomas of the vocal cord: incidence and implications for survival

A retrospective analysis was performed for 218 patients who were managed for carcinomas of the glottic larynx from 1975 to 1988. With a median follow-up of 51 months (range: 24 to 120 months), 41 patients developed a second malignant neoplasm. Six patients had synchronous and 35 had metachronous second malignant neoplasms. The median interval between the diagnosis of glottic carcinoma and a second malignant neoplasm was 31 months. This median interval increased to 43 months when only the metachronous tumors were analyzed. The average annual risk of developing a second malignant neoplasm (SMN) in a 10-year period was 3.1%. Seventy-one percent of them occurred in the upper aerodigestive tract or lungs. When analyzed according to the initial stage of the glottic carcinoma, 23 of 145 (16%) patients with T1 or T2 glottic carcinomas developed a second malignant neoplasm, whereas 18 of 73 (25%) patients T3 or T4 lesions did so. For the T1/T2 group, the average annual risk was 2.5%, as compared to 4.8% for the T3/T4 group (p = 0.023). The development of a second malignant neoplasm adversely affected survival. The 10-year actuarial survival for these patients who did not develop a second malignant neoplasm was 45%, as compared to 19% for those who did develop a second malignant neoplasm (p = 0.008). Although second malignant neoplasms occurred in only 19% of the total patient population, their impact on the survival rate of the overall population was equal to that of glottic carcinomas. The median survival after the diagnosis of a SMN was 6 months. The high incidence of second malignant neoplasms in patients with glottic carcinomas warrants careful follow-up and clinical investigation of the use of chemopreventive agents.

Evidence for a nonsense mutation at the niaD locus of Aspergillus nidulans

Two mutations at theniaDlocus (structural gene for nitrate reductase apo-protein) are genotypically suppressible. Both mutations result in loss of nitrate reductase enzyme activity and cross reacting material and are non complementing, nonleaky and highly revertible. They have the properties of nonsense mutations. This implies that some of the allele specific suppressors, which act on these and alleles at several other loci, are nonsense suppressors.

A sero-epidemiological survey for Bunyaviridae and certain other arboviruses in Pakistan

Complement fixation test reactions to the following viruses were studied in 372 samples (157 rodents, 172 domestic animals, 43 persons) from Pakistan: Bunyaviridae, Phlebovirus: Phlebotomus fever Sicilian (PFS), Phlebotomus fever Naples (PFN), Karimabad (KAR), Salehabad (SAL); Nairovirus: Crimean-Congo haemorrhagic fever (CCHF), Hazara (HAZ), Dera Ghazi Khan (DGK), Dhori (DHO); Uukuvirus: Manawa (MWA); "possible members": Bakau (BAK), Bhanja (BHA). Reoviridae, Orbivirus: Wad Medani (WM). Unclassified: Wanowrie (WAN). Four of these viruses are Phlebotomus-borne (PFS, PFN, KAR, SAL). The other nine ar tick-borne. Antibodies against each virus were detected in sera from rodents. Antibodies against PFS, PFN, KAR, CCHF, DGK, BHA, WM and WAN viruses were detected in sera from domestic animals. Antibodies against PFS, CCHF, DGK, DHO, MWA, BHA, and BHA and WAN viruses were detected in human sera. The presence in Pakistan of KAR, DHO, BHA, and WAN viruses is documented for the first time. Over-all prevalence rates were highest for BHA (12.1%) and WM (10.7%) viruses, followed by DGK, CCHF, PFN and PFS (4.0 to 5.4%) and DHO, KAR, WAN, SAL, MWA, BAK and HAZ (0.3 to 2.1%). Epidemiological factors relating to virus circulation and human disease are discussed.

Diagnosis of nonsense mutations in Aspergillus nidulans

Three genotypically suppressible alleles, a1X4, alcA125, and niaD500, are phenotypically suppressed by aminoglycoside antibiotics. Unsuppressible alleles at these loci are unaffected as are known missense mutations at the yA and gdhA loci. This is consistent with the premise that the suppressible mutations are nonsense and that this highly-allele-specific phenotypic suppression can be used to distinguish nonsense from missense mutations of Aspergillus nidulans. Paromomycin and tobramycin are recommended for screening unknown mutations.

A sero-epidemiological survey for certain arboviruses (Togaviridae) in Pakistan

Complement-fixation test reactions to eight viruses of the family Togaviridae were studied in 372 serum samples (157 rodents, 172 domestic animals, 43 humans) from Pakistan. Antibodies to each tested virus were detected. The highest over-all prevalence rates were for West Nile (WN) (7.8%), Japanese encephalitis (JE) (3.2%) and Zika (ZIKA) (2.4%) viruses, followed by Sindbis (SIN), Chikungunya (CHIK), Uganda S (UGS) and Royal Farm (RF) viruses (1.6 to 1.3%). One human serum (male, age 58 years) reacted with Dengue-1 (DEN) virus antigen (titre 1:32). Antibodies to each virus except RF were detected in human sera; antibodies to RF virus were detected only in rodent and domestic animal sera. The roles of rodents in the epidemiology of WN, JE and ZIKA viruses should be investigated. At least six of these eight viruses cause fevers in humans (fevers of unknown origin comprise about one third of the febrile episodes recorded in Pakistan).