Consistent changes in muscle metabolism underlie dive performance across multiple lineages of diving ducks

Diving animals must sustain high activity with limited O2 stores to successfully capture prey. Studies suggest that increasing body O2 stores supports breath-hold diving, but less is known about metabolic specializations that underlie underwater locomotion. We measured maximal activities of 10 key enzymes in locomotory muscles (gastrocnemius and pectoralis) to identify biochemical changes associated with diving in pathways of oxidative and substrate-level phosphorylation and compared them across three groups of ducks-the longest diving sea ducks (eight spp.), the mid-tier diving pochards (three spp.) and the non-diving dabblers (five spp.). Relative to dabblers, both diving groups had increased activities of succinate dehydrogenase and cytochrome c oxidase, and sea ducks further showed increases in citrate synthase (CS) and hydroxyacyl-CoA dehydrogenase (HOAD). Both diving groups had relative decreases in capacity for anaerobic metabolism (lower ratio of lactate dehydrogenase to CS), with sea ducks also showing a greater capacity for oxidative phosphorylation and lipid oxidation (lower ratio of pyruvate kinase to CS, higher ratio of HOAD to hexokinase). These data suggest that the locomotory muscles of diving ducks are specialized for sustaining high rates of aerobic metabolism, emphasizing the importance of body O2 stores for dive performance in these species.

Solving the conundrum of intra-specific variation in metabolic rate: A multidisciplinary conceptual and methodological toolkit: New technical developments are opening the door to an understanding of why metabolic rate varies among individual animals of a species: New technical developments are opening the door to an understanding of why metabolic rate varies among individual animals of a species

Researchers from diverse disciplines, including organismal and cellular physiology, sports science, human nutrition, evolution and ecology, have sought to understand the causes and consequences of the surprising variation in metabolic rate found among and within individual animals of the same species. Research in this area has been hampered by differences in approach, terminology and methodology, and the context in which measurements are made. Recent advances provide important opportunities to identify and address the key questions in the field. By bringing together researchers from different areas of biology and biomedicine, we describe and evaluate these developments and the insights they could yield, highlighting the need for more standardisation across disciplines. We conclude with a list of important questions that can now be addressed by developing a common conceptual and methodological toolkit for studies on metabolic variation in animals.

Mitochondrial function declines with age within individuals but is not linked to the pattern of growth or mortality risk in zebra finch

Mitochondrial dysfunction is considered a highly conserved hallmark of ageing. However, most of the studies in both model and non-model organisms are cross-sectional in design; therefore, little is known, at the individual level, on how mitochondrial function changes with age, its link to early developmental conditions or its relationship with survival. Here we manipulated the postnatal growth in zebra finches (Taeniopygia guttata) via dietary modification that induced accelerated growth without changing adult body size. In the same individuals, we examined blood cells mitochondrial functioning (mainly erythrocytes) when they were young (ca. 36 weeks) and again in mid-aged (ca. 91 weeks) adulthood. Mitochondrial function was strongly influenced by age but not by postnatal growth conditions. Across all groups, within individual ROUTINE respiration, OXPHOS and OXPHOS coupling efficiency significantly declined with age, while LEAK respiration increased. However, we found no link between mitochondrial function and the probability of survival into relatively old age (ca. 4 years). Our results suggest that the association between accelerated growth and reduced longevity, evident in this as in other species, is not attributable to age-related changes in any of the measured mitochondrial function traits.

Tissue-specific reductions in mitochondrial efficiency and increased ROS release rates during ageing in zebra finches, Taeniopygia guttata

Mitochondrial dysfunction and oxidative damage have long been suggested as critically important mechanisms underlying the ageing process in animals. However, conflicting data exist on whether this involves increased production of mitochondrial reactive oxygen species (ROS) during ageing. We employed high-resolution respirometry and fluorometry on flight muscle (pectoralis major) and liver mitochondria to simultaneously examine mitochondrial function and ROS (H₂O₂) release rates in young (3 months) and old (4 years) zebra finches (Taeniopygia guttata). Respiratory capacities for oxidative phosphorylation did not differ between the two age groups in either tissue. Respiratory control ratios (RCR) of liver mitochondria also did not differ between the age classes. However, RCR in muscle mitochondria was 55% lower in old relative to young birds, suggesting that muscle mitochondria in older individuals are less efficient. Interestingly, this observed reduction in muscle RCR was driven almost entirely by higher mitochondrial LEAK-state respiration. Maximum mitochondrial ROS release rates were found to be greater in both flight muscle (1.3-fold) and the liver (1.9-fold) of old birds. However, while maximum ROS (H₂O₂) release rates from mitochondria increased with age across both liver and muscle tissues, the liver demonstrated a proportionally greater age-related increase in ROS release than muscle. This difference in age-related increases in ROS release rates between muscle and liver tissues may be due to increased mitochondrial leakiness in the muscle, but not the liver, of older birds. This suggests that age-related changes in cellular function seem to occur in a tissue-specific manner in zebra finches, with flight muscle exhibiting signs of minimising age-related increase in ROS release, potentially to reduce damage to this crucial tissue in older individuals.

Adaptive increases in respiratory capacity and O2 affinity of subsarcolemmal mitochondria from skeletal muscle of high-altitude deer mice

Aerobic energy demands have led to the evolution of complex mitochondrial reticula in highly oxidative muscles, but the extent to which metabolic challenges can be met with adaptive changes in physiology of specific mitochondrial fractions remains unresolved. We examined mitochondrial mechanisms supporting adaptive increases in aerobic performance in deer mice (Peromyscus maniculatus) adapted to the hypoxic environment at high altitude. High-altitude and low-altitude mice were born and raised in captivity, and exposed as adults to normoxia or hypobaric hypoxia (12 kPa O₂ for 6-8 weeks). Subsarcolemmal and intermyofibrillar mitochondria were isolated from the gastrocnemius, and a comprehensive substrate titration protocol was used to examine mitochondrial physiology and O₂  kinetics by high-resolution respirometry and fluorometry. High-altitude mice had greater yield, respiratory capacity for oxidative phosphorylation, and O₂ affinity (lower P₅₀ ) of subsarcolemmal mitochondria compared to low-altitude mice across environments, but there were no species difference in these traits in intermyofibrillar mitochondria. High-altitude mice also had greater capacities of complex II relative to complexes I + II and higher succinate dehydrogenase activities in both mitochondrial fractions. Exposure to chronic hypoxia reduced reactive oxygen species (ROS) emission in high-altitude mice but not in low-altitude mice. Our findings suggest that functional changes in subsarcolemmal mitochondria contribute to improving aerobic performance in hypoxia in high-altitude deer mice. Therefore, physiological variation in specific mitochondrial fractions can help overcome the metabolic challenges of life at high altitude.

Inter-individual variation in mitochondrial phosphorylation efficiency predicts growth rates in ectotherms at high temperatures

There is increasing evidence that aquatic ectotherms are especially vulnerable to global warming since their metabolic demands increase with ambient temperature while water-oxygen content decreases. The possible role of shrinking aerobic scope in limiting performance has been much discussed; however, less attention has been given to whether tissue-level changes in the efficiency of oxygen usage occur at elevated temperatures. Here, we show that this varies widely among individuals, with consequences for performance. We examined the inter-individual variation in growth rate and mitochondrial function from white muscle and liver of brown trout (Salmo trutta) acclimated to either high (19.5°C) or near-optimal temperature (12°C). Liver (but not muscle) mitochondria showed a positive relationship between growth rate and maximal oxidative phosphorylation at both temperatures, and a negative relationship between growth rate and ROS release. There was a positive correlation in both tissues between individual mitochondrial phosphorylation efficiency and growth rate, but only at 19.5°C. In this representative of aquatic ectotherms, an individual's liver mitochondrial efficiency thus seems to dictate its capacity to grow at elevated temperatures. This suggests that individual heterogeneity in cellular function may cause variation in the thermal limits of aquatic ectotherms and could adversely affect wild populations in warming environments.

Avian red blood cell mitochondria produce more heat in winter than in autumn

Endotherms in cold regions improve heat-producing capacity when preparing for winter. We know comparatively little about how this change is fueled by seasonal adaptation in cellular respiration. Thus, we studied the changes of mitochondrial function in red blood cells in sympatric Coal (Periparus ater), Blue (Cyanistes caeruleus), and Great (Parus major) tits between autumn and winter. These species differ more than twofold in body mass and in several aspects of their foraging ecology and social dominance, which could require differential seasonal adaptation of energy expenditure. Coal and Great tits in particular upregulated the mitochondrial respiration rate and mitochondrial volume in winter. This was not directed toward ATP synthesis, instead reflecting increased uncoupling of electron transport from ATP production. Because uncoupling is exothermic, this increased heat-producing capacity at the sub-cellular level in winter. This previously unexplored the route of thermogenesis in birds should be addressed in future work.

Astrocyte-mediated disruption of ROS homeostasis in Fragile X mouse model

Astrocytes, glial cells within the brain, work to protect neurons during high levels of activity by maintaining oxidative homeostasis via regulation of energy supply and antioxidant systems. In recent years, mitochondrial dysfunction has been highlighted as an underlying factor of pathology in many neurological disorders. In animal studies of Fragile X Syndrome (FXS), the leading genetic cause of autism, higher levels of reactive oxygen species, lipid peroxidation, and protein oxidation within the brain indicates that mitochondria function is also altered in FXS. Despite their integral contribution to redox homeostasis within the CNS, the role of astrocytes on the occurrence or progression of neurodevelopmental disorders in this way is rarely considered. This study specifically examines changes to astrocyte mitochondrial function and antioxidant expression that may occur in FXS. Using the Fmr1 knockout (KO) mouse model, mitochondrial respiration and reactive oxygen species (ROS) emission were analyzed in primary cortical astrocytes. While mitochondrial respiration was similar between genotypes, ROS emission was significantly elevated in Fmr1 KO astrocytes. Notably, NADPH-oxidase 2 expression in Fmr1 KO astrocytes was also enhanced but only changes in catalase antioxidant enzyme expression were noted. Characterization of astrocyte factors involved in redox imbalance is invaluable to uncovering potential sources of oxidative stress in neurodevelopmental disorders and more specifically, the intercellular mechanisms that contribute to dysfunction in FXS.

Convergent changes in muscle metabolism depend on duration of high-altitude ancestry across Andean waterfowl

High-altitude environments require that animals meet the metabolic O2 demands for locomotion and thermogenesis in O2-thin air, but the degree to which convergent metabolic changes have arisen across independent high-altitude lineages or the speed at which such changes arise is unclear. We examined seven high-altitude waterfowl that have inhabited the Andes (3812-4806 m elevation) over varying evolutionary time scales, to elucidate changes in biochemical pathways of energy metabolism in flight muscle relative to low-altitude sister taxa. Convergent changes across high-altitude taxa included increased hydroxyacyl-coA dehydrogenase and succinate dehydrogenase activities, decreased lactate dehydrogenase, pyruvate kinase, creatine kinase, and cytochrome c oxidase activities, and increased myoglobin content. ATP synthase activity increased in only the longest established high-altitude taxa, whereas hexokinase activity increased in only newly established taxa. Therefore, changes in pathways of lipid oxidation, glycolysis, and mitochondrial oxidative phosphorylation are common strategies to cope with high-altitude hypoxia, but some changes require longer evolutionary time to arise.

Measurement of mitochondrial respiration in permeabilized fish gills

Physiological investigations of fish gills have traditionally centred on the two principal functions of the gills: gas exchange and ion regulation. Mitochondrion-rich cells (MRCs) are primarily found within the gill filaments of fish, and are thought to proliferate in order to increase the ionoregulatory capacity of the gill in response to environmentally induced osmotic challenges. However, surprisingly little attention has been paid to the metabolic function of mitochondria within fish gills. Here, we describe and validate a simple protocol for the permeabilization of fish gills and subsequent measurement of mitochondrial respiration rates in vitro Our protocol requires only small tissue samples (8 mg), exploits the natural structure of fish gills, does not require mechanical separation of the gill tissue (so is relatively quick to perform), and yields accurate and highly reproducible measurements of respiration rates. It offers great potential for the study of mitochondrial function in gills over a wide range of fish sizes and species.

Cardiovascular responses to progressive hypoxia in ducks native to high altitude in the Andes

The cardiovascular system is critical for delivering O2 to tissues. Here we examine the cardiovascular responses to progressive hypoxia in four high-altitude Andean duck species compared to four related low-altitude populations in North America, tested at their native altitude. Ducks were exposed to stepwise decreases in inspired partial pressure of O2 while we monitored heart rate, O2 consumption rate, blood O2 saturation, haematocrit (Hct), and blood haemoglobin concentration [Hb]. We calculated O2 pulse (the product of stroke volume and the arterial-venous O2 content difference), blood O2 concentration, and heart rate variability. Regardless of altitude, all eight populations maintained O2 consumption rate with minimal change in heart rate or O2 pulse, indicating that O2 consumption was maintained by either a constant arterial-venous O2 content difference (an increase in the relative O2 extracted from arterial blood) or by a combination of changes in stroke volume and the arterial-venous O2 content difference. Three high-altitude taxa (yellow-billed pintails, cinnamon teal, and speckled teal) had higher Hct and [Hb], increasing the O2 content of arterial blood, and potentially providing a greater reserve for enhancing O2 delivery during hypoxia. Hct and [Hb] between low- and high-altitude populations of ruddy duck were similar, representing a potential adaptation to diving life. Heart rate variability was generally lower in high-altitude ducks, concurrent with similar or lower heart rates than low-altitude ducks, suggesting a reduction in vagal and sympathetic tone. These unique features of the Andean ducks differ from previous observations in both Andean geese and bar-headed geese, neither of which exhibit significant elevations in Hct or [Hb] compared to their low-altitude relatives, revealing yet another avian strategy for coping with high altitude.

Control of breathing and respiratory gas exchange in high-altitude ducks native to the Andes

We examined the control of breathing and respiratory gas exchange in six species of high-altitude duck that independently colonized the high Andes. We compared ducks from high-altitude populations in Peru (Lake Titicaca at ∼3800 m above sea level; Chancay River at ∼3000-4100 m) with closely related populations or species from low altitude. Hypoxic ventilatory responses were measured shortly after capture at the native altitude. In general, ducks responded to acute hypoxia with robust increases in total ventilation and pulmonary O₂ extraction. O₂ consumption rates were maintained or increased slightly in acute hypoxia, despite ∼1-2°C reductions in body temperature in most species. Two high-altitude taxa - yellow-billed pintail and torrent duck - exhibited higher total ventilation than their low-altitude counterparts, and yellow-billed pintail exhibited greater increases in pulmonary O₂ extraction in severe hypoxia. In contrast, three other high-altitude taxa - Andean ruddy duck, Andean cinnamon teal and speckled teal - had similar or slightly reduced total ventilation and pulmonary O₂ extraction compared with low-altitude relatives. Arterial O₂ saturation (S _aO2 ) was elevated in yellow-billed pintails at moderate levels of hypoxia, but there were no differences in S _aO2  in other high-altitude taxa compared with their close relatives. This finding suggests that improvements in S _aO2  in hypoxia can require increases in both breathing and haemoglobin-O₂ affinity, because the yellow-billed pintail was the only high-altitude duck with concurrent increases in both traits compared with its low-altitude relative. Overall, our results suggest that distinct physiological strategies for coping with hypoxia can exist across different high-altitude lineages, even among those inhabiting very similar high-altitude habitats.

The Mitochondrial Basis for Adaptive Variation in Aerobic Performance in High-Altitude Deer Mice

Mitochondria play a central role in aerobic performance. Studies aimed at elucidating how evolved variation in mitochondrial physiology contributes to adaptive variation in aerobic performance can therefore provide a unique and powerful lens to understanding the evolution of complex physiological traits. Here, we review our ongoing work on the importance of changes in mitochondrial quantity and quality to adaptive variation in aerobic performance in high-altitude deer mice. Whole-organism aerobic capacity in hypoxia (VO2max) increases in response to hypoxia acclimation in this species, but high-altitude populations have evolved consistently greater VO2max than populations from low altitude. The evolved increase in VO2max in highlanders is associated with an evolved increase in the respiratory capacity of the gastrocnemius muscle. This appears to result from highlanders having more mitochondria in this tissue, attributed to a higher proportional abundance of oxidative fiber-types and a greater mitochondrial volume density within oxidative fibers. The latter is primarily caused by an over-abundance of subsarcolemmal mitochondria in high-altitude mice, which is likely advantageous for mitochondrial O2 supply because more mitochondria are situated adjacent to the cell membrane and close to capillaries. Evolved changes in gastrocnemius phenotype appear to be underpinned by population differences in the expression of genes involved in energy metabolism, muscle development, and vascular development. Hypoxia acclimation has relatively little effect on respiratory capacity of the gastrocnemius, but it increases respiratory capacity of the diaphragm. However, the mechanisms responsible for this increase differ between populations: lowlanders appear to adjust mitochondrial quantity and quality (i.e., increases in citrate synthase [CS] activity, and mitochondrial respiration relative to CS activity) and they exhibit higher rates of mitochondrial release of reactive oxygen species, whereas highlanders only increase mitochondrial quantity in response to hypoxia acclimation. In contrast to the variation in skeletal muscles, the respiratory capacity of cardiac muscle does not appear to be affected by hypoxia acclimation and varies little between populations. Therefore, evolved changes in mitochondrial quantity and quality make important tissue-specific contributions to adaptive variation in aerobic performance in high-altitude deer mice.

Effects of hypoxia at different life stages on locomotory muscle phenotype in deer mice native to high altitudes

Animals native to high altitude must overcome the constraining effects of hypoxia on tissue O₂ supply to support routine metabolism, thermoregulation in the cold, and exercise. Deer mice (Peromyscus maniculatus) native to high altitude have evolved an enhanced aerobic capacity in hypoxia, along with increased capillarity and oxidative capacity of locomotory muscle. Here, we examined whether exposure to chronic hypoxia during development or adulthood affects muscle phenotype. Deer mice from a highland population were bred in captivity at sea level, and exposed to normoxia or one of four treatments of hypobaric hypoxia (12kPa O₂, simulating hypoxia at ~4300m): adult hypoxia (6-8weeks), post-natal hypoxia (birth to adulthood), pre-natal hypoxia (before conception to adulthood), and parental hypoxia (in which mice were conceived and raised in normoxia, but their parents were previously exposed to hypoxia). Litter size was similar across treatments, and pups survived the hypoxia exposures and grew to similar body masses at ~6-8months of age. Hypoxia had no effect on the masses of gastrocnemius and soleus muscles. There was a strong concordance between two distinct histological methods for staining capillaries in the gastrocnemius - alkaline phosphatase activity and binding of Griffonia simplicifolia lectin I - each of which showed that capillarity and muscle fibre size were largely unaffected by hypoxia. Maximal activities of several metabolic enzymes (cytochrome c oxidase, citrate synthase, isocitrate dehydrogenase, and lactate dehydrogenase) in the gastrocnemius were also largely unaffected by hypoxia. Therefore, the evolved muscle phenotype of high-altitude deer mice is relatively insensitive to hypoxia across life stages.

Hybridization increases mitochondrial production of reactive oxygen species in sunfish

Mitochondrial dysfunction and oxidative stress have been suggested to be possible mechanisms underlying hybrid breakdown, as a result of mito-nuclear incompatibilities in respiratory complexes of the electron transport system. However, it remains unclear whether hybridization increases the production of reactive oxygen species (ROS) by mitochondria. We used high-resolution respirometry and fluorometry on isolated liver mitochondria to examine mitochondrial physiology and ROS emission in naturally occurring hybrids of pumpkinseed (Lepomis gibbosus) and bluegill (L. macrochirus). ROS emission was greater in hybrids than in both parent species when respiration was supported by complex I (but not complex II) substrates, and was associated with increases in lipid peroxidation. However, respiratory capacities for oxidative phosphorylation, phosphorylation efficiency, and O₂  kinetics in hybrids were intermediate between those in parental species. Flux control ratios of capacities for electron transport (measured in uncoupled mitochondria) relative to oxidative phosphorylation suggested that the limiting influence of the phosphorylation system is reduced in hybrids. This likely helped offset impairments in electron transport capacity and complex III activity, but contributed to augmenting ROS production. Therefore, hybridization can increase mitochondrial ROS production, in support of previous suggestions that mitochondrial dysfunction can induce oxidative stress and thus contribute to hybrid breakdown.

Respiratory mechanics of eleven avian species resident at high and low altitude

The metabolic cost of breathing at rest has never been successfully measured in birds, but has been hypothesized to be higher than in mammals of a similar size because of the rocking motion of the avian sternum being encumbered by the pectoral flight muscles. To measure the cost and work of breathing, and to investigate whether species resident at high altitude exhibit morphological or mechanical changes that alter the work of breathing, we studied 11 species of waterfowl: five from high altitudes (>3000 m) in Perú, and six from low altitudes in Oregon, USA. Birds were anesthetized and mechanically ventilated in sternal recumbency with known tidal volumes and breathing frequencies. The work done by the ventilator was measured, and these values were applied to the combinations of tidal volumes and breathing frequencies used by the birds to breathe at rest. We found the respiratory system of high-altitude species to be of a similar size, but consistently more compliant than that of low-altitude sister taxa, although this did not translate to a significantly reduced work of breathing. The metabolic cost of breathing was estimated to be between 1 and 3% of basal metabolic rate, as low or lower than estimates for other groups of tetrapods.

Passive regeneration of glutathione: Glutathione reductase regulation from the freeze-tolerant North American wood frog, Rana sylvatica

Wood frogs inhabit a broad range across North America, extending from the southern tip of the Appalachian Mountains to the northern boreal forest. Remarkably they can survive the winter in a frozen state, where as much as 70% of their body water is converted into ice. During the frozen state, their hearts cease to pump blood, causing their cells to experience ischemia which can dramatically increase the production of reactive oxygen species produced within the cell. To overcome this, wood frogs have elevated levels of glutathione, a primary antioxidant. We examined the regulation of glutathione reductase, the enzyme involved in recycling glutathione, in both the frozen and unfrozen state (control). Glutathione reductase activity from both the control and frozen state showed dramatic reduction in substrate specificity (Km) for oxidized glutathione (50%) when measured in the presence of glucose (300mM) and a increase (157%) when measured in the presence of levels of urea (75mM) encountered in the frozen state. However, when we tested the synergistic effect of urea and glucose simultaneously, we observed a substantial reduction in the Km for oxidized glutathione (43%) to a value similar to that of glucose alone. In fact, we found no observable differences in the kinetic and structural properties of glutathione reductase between the two states. Therefore, a significant increase in the affinity for oxidized glutathione in the presence of endogenous levels of glucose, suggests that increased glutathione recycling may result due to passive regulation of glutathione reductase by rising levels of glucose during freezing.

Mitochondrial physiology in the skeletal and cardiac muscles is altered in torrent ducks, Merganetta armata, from high altitudes in the Andes

Torrent ducks inhabit fast-flowing rivers in the Andes from sea level to altitudes up to 4500 m. We examined the mitochondrial physiology that facilitates performance over this altitudinal cline by comparing the respiratory capacities of permeabilized fibers, the activities of 16 key metabolic enzymes and the myoglobin content in muscles between high- and low-altitude populations of this species. Mitochondrial respiratory capacities (assessed using substrates of mitochondrial complexes I, II and/or IV) were higher in highland ducks in the gastrocnemius muscle - the primary muscle used to support swimming and diving - but were similar between populations in the pectoralis muscle and the left ventricle. The heightened respiratory capacity in the gastrocnemius of highland ducks was associated with elevated activities of cytochrome oxidase, phosphofructokinase, pyruvate kinase and malate dehydrogenase (MDH). Although respiratory capacities were similar between populations in the other muscles, highland ducks had elevated activities of ATP synthase, lactate dehydrogenase, MDH, hydroxyacyl CoA dehydrogenase and creatine kinase in the left ventricle, and elevated MDH activity and myoglobin content in the pectoralis. Thus, although there was a significant increase in the oxidative capacity of the gastrocnemius in highland ducks, which correlates with improved performance at high altitudes, the variation in metabolic enzyme activities in other muscles not correlated to respiratory capacity, such as the consistent upregulation of MDH activity, may serve other functions that contribute to success at high altitudes.

A hydrogen peroxide safety valve: The reversible phosphorylation of catalase from the freeze-tolerant North American wood frog, Rana sylvatica

BACKGROUND

The North American wood frog, Rana sylvatica, endures whole body freezing while wintering on land and has developed multiple biochemical adaptations to elude cell/tissue damage and optimize its freeze tolerance. Blood flow is halted in the frozen state, imparting both ischemic and oxidative stress on cells. A potential build-up of H2O2 may occur due to increased superoxide dismutase activity previously discovered. The effect of freezing on catalase (CAT), which catalyzes the breakdown of H2O2 into molecular oxygen and water, was investigated as a result.

METHODS

The present study investigated the purification and kinetic profile of CAT in relation to the phosphorylation state of CAT from the skeletal muscle of control and frozen R. sylvatica.

RESULTS

Catalase from skeletal muscle of frozen wood frogs showed a significantly higher Vmax (1.48 fold) and significantly lower Km for H2O2 (0.64 fold) in comparison to CAT from control frogs (5°C acclimated). CAT from frozen frogs also showed higher overall phosphorylation (1.73 fold) and significantly higher levels of phosphoserine (1.60 fold) and phosphotyrosine (1.27 fold) compared to control animals. Phosphorylation via protein kinase A or the AMP-activated protein kinase significantly decreased the Km for H2O2 of CAT, whereas protein phosphatase 2B or 2C action significantly increased the Km.

CONCLUSION

The physiological consequence of freeze-induced CAT phosphorylation appears to improve CAT function to alleviate H2O2 build-up in freezing frogs.

GENERAL SIGNIFICANCE

Augmented CAT activity via reversible phosphorylation may increase the ability of R. sylvatica to overcome oxidative stress associated with ischemia.

Purification and characterization of a urea sensitive lactate dehydrogenase from the liver of the African clawed frog, Xenopus laevis

The African clawed frog, Xenopus laevis, is able to withstand extremely arid conditions by estivating, in conjunction with dehydration tolerance and urea accumulation. Estivating X. laevis reduce their metabolic rate and recruit anaerobic glycolysis, driven by lactate dehydrogenase (LDH; E.C. 1.1.1.27) enzymes that reversibly convert pyruvate and NADH to lactate and NAD(+), to meet newly established ATP demands. The present study investigated purified LDH from the liver of dehydrated and control X. laevis. LDH from dehydrated liver showed a significantly higher K m for L-lactate (1.74 fold), NAD(+) (2.41 fold), and pyruvate (1.78 fold) in comparison to LDH from the liver of control frogs. In the presence of physiological levels of urea found in dehydrated animals, the K m values obtained for dehydrated LDH all returned to control LDH K m values. Dot blot analysis showed post-translational modifications may be responsible for the kinetic modification as the dehydrated form of LDH showed more phosphorylated serine residues (1.54 fold), less methylated lysine residues (0.43 fold), and a higher level of ubiquitination (1.90 fold) in comparison to control LDH. The physiological consequence of dehydration-induced LDH modification appears to adjust LDH function in conjunction with urea levels in dehydrated frogs. When urea levels are high during dehydration, LDH retains its normal function. Yet, as urea levels drop during rehydration, LDH function is reduced, possibly shunting pyruvate to the TCA cycle.

Characterization of fructose-1,6-bisphosphate aldolase during anoxia in the tolerant turtle, Trachemys scripta elegans: an assessment of enzyme activity, expression and structure

One of the most adaptive facultative anaerobes among vertebrates is the freshwater turtle, Trachemys scripta elegans. Upon a decrease in oxygen supply and oxidative phosphorylation, these turtles are able to reduce their metabolic rate and recruit anaerobic glycolysis to meet newly established ATP demands. Within the glycolytic pathway, aldolase enzymes cleave fructose-1,6-bisphosphate to triose phosphates facilitating an increase in anaerobic production of ATP. Importantly, this enzyme exists primarily as tissue-specific homotetramers of aldolase A, B or C located in skeletal muscle, liver and brain tissue, respectively. The present study characterizes aldolase activity and structure in the liver tissue of a turtle whose survival greatly depends on increased glycolytic output during anoxia. Immunoblot and mass spectrometry analysis verified the presence of both aldolase A and B in turtle liver tissue, and results from co-immunoprecipitation experiments suggested that in the turtle aldolase proteins may exist as an uncommon heterotetramer. Expression levels of aldolase A protein increased significantly in liver tissue to 1.59±0.11-fold after 20 h anoxia, when compared to normoxic control values (P<0.05). A similar increase was seen for aldolase B expression. The overall kinetic properties of aldolase, when using fructose-1,6-bisphosphate as substrate, were similar to that of a previously studied aldolase A and aldolase B heterotetramer, with a K_m of 240 and 180 nM (for normoxic and anoxic turtle liver, respectively). Ligand docking of fructose-1,6-bisphosphate to the active site of aldolase A and B demonstrated minor differences in both protein:ligand interactions compared to rabbit models. It is likely that the turtle is unique in its ability to regulate a heterotetramer of aldolase A and B, with a higher overall enzymatic activity, to achieve greater rates of glycolytic output and support anoxia survival.

Real-time protein unfolding: a method for determining the kinetics of native protein denaturation using a quantitative real-time thermocycler

Protein stability can be monitored by many different techniques. However, these protocols are often lengthy, consume large amounts of protein, and require expensive and specialized instruments. Here we present a new protocol to analyze protein unfolding kinetics using a quantified real-time thermocycler. This technique enables the analysis of a wide range of denaturants (and their interactions with temperature change) on protein stability in a multi-well platform, where samples can be run in parallel under virtually identical conditions and with highly sensitive detection. Using this set-up, researchers can evaluate the half-maximal rate of protein denaturation (Knd), maximum rate of denaturation (Dmax), and the cooperativity of individual denaturants in protein unfolding (µ-coefficient). Both lysozyme and hexokinase are used as model proteins and urea as a model denaturant to illustrate this new method and the kinetics of protein unfolding that it provides. Overall, this method allows the researcher to explore a large number of denaturants, at either constant or variable temperatures, within the same assay, providing estimates of denaturation kinetics that have been previously inaccessible.

Regulation of tail muscle arginine kinase by reversible phosphorylation in an anoxia-tolerant crayfish

Freshwater crayfish, Orconectes virilis, can experience periodic exposures to hypoxia or anoxia due to low water flow (in summer) or ice cover (in winter) in their natural habitat. Hypoxia/anoxia disrupts energy metabolism and triggers mechanisms that to support ATP levels while often also suppressing ATP use. Arginine kinase (AK) (E.C. 2.7.3.3) is a crucial enzyme involved in energy metabolism in muscle, gating the use of phosphagen stores to buffer ATP levels. The present study investigated AK from tail muscle of O. virilis identifying changes to kinetic properties, phosphorylation state and structural stability between the enzyme from aerobic control and 20 h anoxic crayfish. Muscle AK from anoxia-exposed crayfish showed a significantly higher (by 59%) K (m) for L: -arginine and a lower I(50) value for urea than the aerobic form. Several lines of evidence indicated that AK was converted to a high phosphate form under anoxia: (a) aerobic and anoxic forms of AK showed well-separated elution peaks on DEAE ion exchange chromatography, (b) ProQ Diamond phosphoprotein staining showed a 64% higher bound phosphate content on anoxic AK compared with the aerobic form, and (c) treatment of anoxic AK with alkaline phosphatase reduced K (m) L: -arginine to aerobic levels whereas incubation of aerobic AK with protein kinase A catalytic subunit raised the K (m) to anoxic levels. The physiological consequence of anoxia-induced AK phosphorylation may be to suppress AK activity in the phosphagen-synthesizing direction and, together with reduced cellular pH and ATP levels, promote the phosphagen-catabolizing direction under anoxic conditions. This is first time that AK has been shown to be regulated by reversible phosphorylation.

Use of sublingual glyceryl trinitrate as a supplement to volatile inhalational anaesthesia in a case of uterine inversion

We present a case of uterine inversion in which glyceryl trinitrate was used via the sublingual route, as opposed to the intravenous route, in association with volatile inhalational anaesthesia in order to achieve relaxation of the uterus. A transient, but significant, hypotensive response occurred, which was easily corrected with a colloid infusion and vasopressors. Sublingual glyceryl trinitrate is easily administered, has a fast onset of action and may have a role in situations where rapid relaxation of the uterus is required.

The assessment of intramuscular discrimination using signal detection theory: its potential contribution to chiropractic

INTRODUCTION

Most studies on sensory changes after manual therapies have focused on pain sensitivity. This ignores the wider range of sensory alternations that may be important in assessing patient functioning and neglects the issue of bias, which is inherent in most methods of pain assessment employing threshold methodology. Signal detection theory (SDT) addresses the issue of bias and provides a measurement of intramuscular discrimination--the ability to discriminate between two stimuli--which can be assessed over the full range of sensation. This paper will discuss the strengths and limitations of SDT and report on the effects of trigger point therapy and manipulation on intramuscular discrimination to illustrate the potential contribution of this methodology to chiropractic.

METHODS

Intramuscular needle electrodes were used to provide a pair of electrical stimuli to the forearm extensor muscles. Subjects were asked to assess the differences between stimuli before and after treatment. The treatments consisted of manual trigger point therapy applied to the forearm extensors, cervical spine manipulation and a control treatment.

RESULTS

After the trigger point therapy, there was a significant improvement in the ability of the subjects to discriminate between intramuscular signals to treated muscle. Some individual subjects showed alterations in ability to discriminate after cervical spine manipulation but the effect was not significant in the group as a whole.

CONCLUSIONS

The methodology of signal detection theory provides a promising, bias-free method of assessing changes in intramuscular sensation after various treatments. In these experiments, trigger point therapy was found to enhance intramuscular discrimination, suggesting that a peripheral reflex may be involved.

Sacroiliac joint manipulation decreases the H-reflex

Joint manipulation is widely utilized clinically to decrease pain and increase the range of motion of joints displaying limited mobility. Evidence of efficacy is based on subjective reports of symptom improvement as well as on the results of clinical trials. Experiments were designed to determine whether or not sacroiliac joint manipulation affects the amplitude of the Hoffman (H) reflex. Surface EMG recordings of the reflex response to electrical stimulation of the tibial nerve in the popliteal fossa were made from the soleus muscle. The averaged amplitudes of H-reflexes were compared on both legs before and after either sacroiliac joint manipulation or a sham procedure. H-reflex amplitude was significantly decreased (12.9%) in the ipsilateral leg (p < 0.001) following a sacroiliac joint manipulation while there was no significant alteration following the sham intervention. There was no significant alteration in reflex excitability in the contralateral leg to the sacroiliac joint manipulation. To further investigate the mechanism of these reflex alterations, the local anaesthetic cream EMLA (Astra Pharmaceuticals) was applied to the skin overlying the sacroiliac joint and the experiments were repeated on a different group of subjects. This was intended to determine if excitation of cutaneous afferents was responsible for the reflex excitability changes. There was still a significant decrease in reflex excitability (10.6%) following sacroiliac joint manipulation (p < 0.001). These findings indicate that joint manipulation exerts physiological effects on the central nervous system, probably at the segmental level. The fact that the changes persisted in the presence of cutaneous anaesthesia suggests that the reflex changes are likely to be mediated by joint and/or muscle afferents.

The effect of therapeutic muscle stretch on neural processing

Therapeutic muscle stretch is a commonly used procedure despite little evidence in support of efficacy or information about the mechanisms underlying the various methods. The purpose of this work was to compare the sequential application of static and ballistic muscle stretch with static muscle stretch alone, using the electrically elicited Hoffmann reflex (H-reflex) as a measure of excitability of homonymous motoneurons. The foot was passively dorsiflexed and either maintained in this position or rapidly and repeatedly dorsiflexed at a velocity of 1.0 radian/sec. Hoffmann reflexes were taken using established criteria under control conditions and during stretch conditions. An analysis of variance indicated a significant difference (p < 0.05) between condition means, with H-reflex amplitude reducing to 60 and 15% of the control value during static and ballistic stretch, respectively. Since reductions in alpha-motoneuron pool excitability correlate with increased flexibility, ballistic stretch applied following static stretch appears more effective than static stretch alone.

Discriminability of electrocutaneous stimuli after topical anesthesia: detection-theory measurement of sensitivity to painful stimuli

In three experiments on the psychophysical measurement of pain, electrocutaneous currents were applied to the volar surface of the forearm. In the first experiment, a conventional category scaling method was compared with the rating method of signal detection. The results of both methods were analyzed in detection-theory terms to derive receiver operating characteristic curves and measures of the discriminability of adjacent currents. The rating method yielded larger discriminability values than the category scale did, and that method was therefore used in the subsequent experiments to examine the effect of a topical anesthetic on discriminability. When the stimuli were applied through surface electrodes, no effect of the topical anesthetic on discriminability was found, but when the stimuli were applied to a more localized area by intradermal needle electrodes, a dose-dependent effect of the anesthetic on discriminability occurred. For this experiment, the slope of the cumulative sensitivity function increased with increasing elapsed time since the removal of the anesthetic. This result is congruent with the theory that discriminability can serve as a measure of sensitivity to painful stimuli.

The behaviour of different factor VIII concentrates in a chromogenic factor X-activating system

A chromogenic factor Xa generation method has been developed for comparing the co-factor activity of factor VIII concentrates at physiological factor VIII concentrations (1 iu/ml). In the presence of thrombin all concentrates gave similar rapid rates of factor Xa generation, but in the absence of thrombin there were major differences between the rates of Xa generation between different products. High purity products, particularly those prepared by monoclonal antibody purification from plasma and recombinant sources, gave more rapid Xa generation than most intermediate-purity products. There was a very strong correlation between the rate of Xa generation and the difference in factor VIII potency by one-stage and two-stage assays. These results suggest the possible presence of small amounts of activated factor VIII in some concentrates, but differences in von Willebrand factor content could also contribute towards the different rates of factor Xa generation observed.

Pre-spinal convergence between thoracic and visceral nerves of the rat

Dichotomizing sensory axons have been demonstrated in a number of species and are of significance in understanding the possible mechanisms underlying referred pain. The present study reviews work employing fluorescent dyes as tracers to demonstrate afferent dichotomization in the peripheral nervous system. Dichotomization between the intercostal and splanchnic nerves of the rat was demonstrated by means of intraneural transport of Diamidino yellow or Fast blue. Frequency of pre-spinal somato-visceral convergence averaged 2% (range 0.1-21%). Average frequency of convergence was 8.3% (range 2-23.1%) between internal and external intercostal nerves. Control experiments in which axoplasmic transport was inhibited by vinblastine ruled out the possibility of errors from non-axoplasmic transport of the markers. Thoraco-visceral pre-spinal convergence occurs in the rat and is variable in extent.

Need satisfaction in terminal care settings

Research comparing hospice and conventional programs of care for the terminally ill has identified few measurable differences in the care provided to patients and their families. Nonetheless, hospice recipients frequently express a higher level of satisfaction with their program of care. This study compared the ability of hospice and conventional care settings to meet the basic emotional needs of families during a member's dying and death from cancer. In addition, the relationship of basic needs satisfaction, perceptions about the nurse, and overall satisfaction with the program of care were explored. One hundred bereaved familial care givers completed a mail questionnaire concerning their perceptions of care at the site of a family member's death. The sites were (1) the home, with care provided by a Medicare certified, community-based hospice program: (2) a hospital affiliated with a Medicare certified, community-based hospice program; (3) a hospital with its own hospice program; and (4) a conventional (non-hospice) hospital. Analyses of quantitative data supported two hypotheses about significant differences between hospice and conventional care. The conventional care group demonstrated the lowest levels of basic needs satisfaction, satisfaction with the psycho-social support of the nurse, and overall program satisfaction. As predicted, overall satisfaction with care was consistent across hospice groups. However, home hospice care provided the highest quality of basic needs satisfaction and the highest level of satisfaction with the nurse. Significant Pearson correlations supported the hypothesis that overall satisfaction is negatively related to unmet basic needs (r = -0.69) and positively related to the psycho-social support received from nurses (r = 0.73).(ABSTRACT TRUNCATED AT 250 WORDS)

High molecular weight aggregate content of heated and unheated factor VIII products determined by fast-protein liquid chromatography

The molecular-weight distribution of proteins in factor VIII concentrates has been analysed by fast-protein liquid chromatography. The proportion of high-molecular-weight (HMW) aggregates in one product increased on freeze-drying and heating, with fibrinogen and fibronectin being the main protein components of the HMW peak. In all other concentrates, the HMW peak was less than or equal to 5% of the total protein content and there were no differences in HMW content according to purity or method of viral inactivation.

Inhibition of interleukin-2 secretion by factor VIII concentrates: a possible cause of immunosuppression in haemophiliacs

The inhibitory effect of factor VIII concentrate products on IL-2 secretion by human T-cells was investigated. The six products used widely in the U.K. showed very different activities varying from almost total inhibition to no significant effect. There appeared to be no obvious relationship between inhibitory activity and protein composition but factor VIII itself was not responsible for the effect as affinity purified products were entirely non-inhibitory. The two wet-heated products were most inhibitory whereas dry-heated products were less inhibitory or non-inhibitory. However, a wet-heated version of a non-inhibitory dry-heated product was also non-inhibitory, suggesting that the composition of the concentrate rather than anti-viral treatment is important for immunosuppressive activity. A product treated by the solvent/detergent procedure showed considerable inhibitory activity. Immunoglobulin and albumin products did not inhibit IL-2 secretion to any significant extent, but factor IX concentrates were inhibitory. We suggest that inhibition of IL-2 secretion by factor VIII concentrates may be related to the immunosuppression observed in haemophiliacs treated with high dose factor VIII products and that our results should be considered by clinicians and manufacturers of factor VIII products.

Assay discrepancies with highly purified factor VIII concentrates

We have assayed two different monoclonal-antibody-purified concentrates (A and B) and one conventional concentrate (C), against the 3rd International Standard for factor VIII concentrate, using one-stage, two-stage and chromogenic methods. One-stage assays performed with immunodepleted plasmas gave lower potencies than with haemophilic plasma for all concentrates, though the discrepancies were most marked for the two highly purified products. The absence of von Willebrand factor in one of the immunodepleted plasmas appeared to contribute towards the low potencies observed. In addition, potencies of product A were 50% higher by one-stage assays (haemophilic plasma) than by two-stage or chromogenic methods. These results indicate the need for careful evaluation of assay methodologies for assessment of factor VIII:C activity in highly purified concentrates.

Effects of environmental temperature on the development of a noradrenergic thermoregulatory mechanism in the rat

Rats reared at 30 degrees C do not exhibit the same thermoregulatory competence during cold exposure as do rats reared at 20 degrees C. They are even more clearly distinguished by the absence of an hypothermic response to intrahypothalamic noradrenaline (IH-NA). In one series of experiments, different groups of rats all received 120 days 30 degrees C-exposure and 20 days 20 degrees C-exposure. The 20 degrees C-exposure occurred at different ages in different treatment groups. At 140 days of age, bilateral IH-NA injections (each 10 micrograms/1 microliter CSF) were administered in conscious rats and the body temperature response observed. An hypothermic response to IH-NA was observed in groups whose exposure to 20 degrees C terminated between 20 and 80 days of age. In a second series of experiments, duration of rearing at 20 degrees C varied but always started at 40 days of age. Responses to IH-NA in 140-day-old adults indicated that the exposure required to induce 50% of the hypothermic response of control (20 degrees C-reared) rats was approximately 17 days. These data suggest that there is an hypothalamic noradrenergic mechanism implicated in the control of body temperature whose development is affected by environmental temperature in a duration-dependent manner. The period during which this effect may be exerted extends into adulthood.

Contralateral intramuscular acupuncture-like electrical stimulation differentially changes the short-latency responses to muscle stretch

Measurements were made from the human first dorsal interosseous and extensor digitorum communis muscles of the surface electromyographic activity reflexly produced by brief stretch of the muscle. For the first dorsal interosseous muscle, reflex EMG activity was also produced by electrical stimulation of the ulnar nerve at the wrist. The procedures were carried out before, during, and after 25 min of nonspecific, low-frequency electrical stimulation to the contralateral arm delivered through intramuscular electrodes. Control stimulation was delivered subcutaneously. The EMG recorded during a maintained contraction was rectified, filtered, and averaged. Two reflex components (M1 and M2) of the EMG response to muscle stretch or ulnar nerve stimulation were investigated. During nonspecific intramuscular stimulation to the contralateral arm, M1 responses of the extensor digitorum communis were depressed, initially by 37%. The effect began to fade during stimulation but extended beyond it. Reflex responses were elicited alternately by brief stretch of the first dorsal interosseus muscle and by electrical stimulation of the ulnar nerve in the same experiment. Nonspecific intramuscular stimulation to the contralateral arm depressed the M1 response to stretch, but had no effect on the M1 response to electrical stimulation. It is concluded that nonspecific intramuscular electrical stimulation reduces the amplitude of the M1 component of the response to brief stretch of contralateral muscle, either through depression of fusimotor activity or inhibition of oligosynaptic pathways that contribute to the early reflex response.

Brain stem projections of the glossopharyngeal nerve and its carotid sinus branch in the rat

Transganglionic transport of horseradish peroxidase or lectin-conjugated horseradish peroxidase from an application site in the cervical trunk of the glossopharyngeal (IXth cranial) nerve of the rat produced extraperikaryal reaction product characteristic of axon terminal processes in three regions of the brain stem: (1) the nucleus of the tractus solitarius, from approximately 2.5 mm rostral to the obex to approximately 3 mm caudal to the obex; (2) the spinal trigeminal nucleus at the level of obex; (3) the cuneate fasciculus, approximately 3 mm caudal to the obex. In contrast, labelling of the carotid sinus nerve, a branch of the glossopharyngeal nerve which conveys chemoreceptor and baroreceptor afferent fibers from the carotid bifurcation, revealed a restricted central projection to within 1 mm of the obex and corresponding to the intermediate region of the glossopharyngeal nerve projection to the nucleus of the tractus solitarius. Two distinct aggregations of label were observed: (1) rostral to the obex, within the lateral and dorsomedial subnuclei of the nucleus of the tractus solitarius; (2) caudal to the obex, within the commissural and ventrolateral subnuclei of the nucleus of the tractus solitarius. Between these two sites the density of labelling was reduced. Retrogradely labelled neurons were demonstrated in the inferior salivatory nucleus and in the nucleus ambiguus after application of lectin-conjugated horseradish peroxidase to the glossopharyngeal nerve. Of the labelled neurons in the nucleus ambiguus (approximately 100), 25% contributed fibers to the carotid sinus nerve. The concentration of extraperikaryal reaction product located rostral to the obex after labelling of the carotid sinus nerve closely matches descriptions of the region of afferent terminations from carotid and aortic baroreceptors in the cat. The concentration of label caudal to the obex may therefore correspond to the region of afferent terminations from carotid chemoreceptors. This study may therefore provide some basis for a separation of the central synapses of primary afferent fibers from the carotid baroreceptors and chemoreceptors in the rat. The labelled neurons of the nucleus ambiguus provide the anatomical substrate for centrifugal control of carotid chemoreceptor activity.

Static and dynamic response characteristics, receptive fields, and interaction with noxious input of midline medullary thermoresponsive neurons in the rat

Thermal clamping of deep-body temperature and 16 fields covering the total truncal skin surface enabled characterization of thermal transmission neurons distributed in a midline medullary location. The total data set comprised 136 neurons from 54 female rats. Relative abundance of neuronal types was 27 to 34 to 75 for cold-responsive, warm-responsive, and thermally unresponsive neurons. Response maxima of thermoresponsive neurons to static thermal stimulation of the total truncal surface were 55 +/- 4 ips (mean +/- SE) at 5 degrees C for cold-responsive neurons and 6.0 +/- 1.6 ips at 35 degrees C for warm-responsive neurons. Dynamic thermal stimulation of the total truncal surface at rates up to +/- 1.6 degrees C/s failed to reveal a clear dynamic thermosensitivity in either cold- or warm-responsive neuronal pools. Instead, the data suggest a preferential passing of the static response relative to the dynamic response. Cutaneous thermal receptive fields were diffuse, occupying most of the truncal surface. Subparts of these fields drove thermoresponsive neurons to variable extents, suggesting convergence from unequally represented multiple cutaneous sources. Noxious stimulation at widely distributed body sites consistently augmented activity in cold-responsive neurons. A thermoregulatory rather than somatesthetic role is proposed for the midline medullary neurons studied here.

Reflex origin for the slowing of motoneurone firing rates in fatigue of human voluntary contractions

During fatigue from a sustained maximal voluntary contraction (m.v.c.) the mean motoneurone discharge rates decline. In the present experiments we found no recovery of firing rates after 3 min of rest if the fatigued muscle was kept ischaemic, but near full recovery 3 min after the blood supply was restored. Since 3 min is thus sufficient time for recovery of any central changes in excitability, the results support the hypothesis that, during fatigue, motoneurone firing rates may be regulated by a peripheral reflex originating in response to fatigue-induced changes within the muscle.

Rearing rats (Rattus norvegicus) at 30 degrees C does not alter sensitivity to noradrenaline

Rats reared from birth at 30 degrees C show a permanent deficit in body temperature regulation. To test the ability of heat-reared rats to respond to an adrenergic drive, carbon dioxide production was measured at five doses of noradrenaline in rats reared at either 20 or 30 degrees C. Noradrenaline-induced carbon dioxide production was greater at all doses in 20 degrees C rats, but sensitivity to noradrenaline was the same in heat-reared and control animals. These findings support the conclusion that the thermoregulatory deficit induced by heat rearing is due to a change induced in the nervous system.

Intramuscular acupuncture-like electrical stimulation inhibits stretch reflexes in contralateral finger extensor muscles

Electro-acupuncture is one of many physical measures used to relieve musculoskeletal pain and to improve the associated restricted range of motion. Experiments were designed to determine whether or not acupuncture-like stimulation inhibits stretch reflexes in an arm extensor muscle in human volunteers. Surface electromyographic recordings were made on the right extensor digitorum communis muscle and averaging techniques were used to study the reflex responses to brief deflection of the finger with a solenoid-driven probe. The ratio M1:M2 of two components of the reflex was reduced during continuous acupuncture-like stimulation of the contralateral first dorsal interosseus and extensor digitorum communis muscles near their motor points (acupuncture points LI 4 and LI 11). Concomitant changes in skin temperature were observed on the forehead and in the arm in which acupuncture-like stimulation was used. In control experiments, when the acupuncture needles were inserted subcutaneously and stimulated with the same current parameters at distinctly uncomfortable intensities, no change in the reflexes occurred. These findings show that acupuncture-like stimulation exerts physiologic effects on the central nervous system, mediated presumably by muscle afferent fibers. The effects may be relevant to relief of muscle spasm and musculoskeletal pain, and restoration of mobility.

The dynamic properties of trigeminal thermoreceptors following heat-rearing in rats

Dynamic properties of thermoresponsive units at the caudal trigeminal nucleus are not modified by heat-rearing. The modification of the thermoregulatory system by heat-rearing is unlikely to be a consequence of altered thermoreceptive function at this level. Rats were reared at ambient temperatures of 30 degrees C (heat-reared) and 20 degrees C (controls). Extracellular recordings of thermoresponsive units at the caudal trigeminal nucleus were made while the facial receptive fields of these thermoresponsive units were stimulated with 6 different rates of temperature change (+0.5, +0.1, +0.02, -0.02, -0.1 and -0.5 degrees C/sec). All thermoresponsive units encountered were cold-sensitive. The static maxima were clustered around 13.5 degrees C and did not differ between treatment groups. Dynamic maxima occurred at temperatures around 29-30 degrees C and were not different in thermoresponsive neurones from the two treatment groups. There was no difference between the two treatment groups in the dynamic activity of trigeminal cold-responsive neurones at any of the 42 combinations of temperature and rate of temperature change examined.

Evidence for on-off control of heat dissipation from the tail of the rat

Anterior hypothalamic temperature, tail vasoactivity, and tail heat loss were observed in unanaesthetised rats resting at an ambient temperature that was varied between 25 and 35 degrees C between experiments, but was held constant within an experiment. Vasodilation and vasoconstriction at the tail were qualitatively detectable by the appearance and disappearance of temperature differences between the tail surface overlying the ventral arterial supply, and the lateral venous drainage. Vasodilation detected this way was an abrupt singular event (being either on or off), and preceded subsequent exponential changes in tail surface temperature and heat loss. Within the ambient temperature range of 29--33 degrees C, the following sequence occurred in a 20-min cycle, despite the noncycling constant environmental and metabolic heat loads: tail vasodilation - 0.2 to 0.4 degrees C fall in hypothalamic temperature - tail vasoconstriction - 0.2 to 0.4 degrees C rise in hypothalamic temperature. This behaviour, consistent with the limit-cyclic behaviour of some nonlinear controllers, as well as the abrupt two-state nature of vasoactivity at the rat tail, provides evidence that the mechanism can be described by an on-off control model. In addition, angiography suggests that vasoconstriction rather than countercurrent heat exchange provides the major barrier to core to tail heat flow during the "off" phase.