Settleable atmospheric particulate matter affects the swimming performance and aerobic metabolic rate of Nile tilapia (Oreochromis niloticus).

Atmospheric particulate matter (APM) produced by the steel industry comprises a complex mixture of particles that includes a wide variety of metals and metallic nanoparticles. These particles settle out onto areas surrounding the industries. There is evidence that this 'settleable' APM (SePM) may cause air-to-water cross-contamination with significant effects on aquatic biota. Recent investigations have reported sublethal impacts on the gill structure and blood oxygen-carrying capacity of fishes, which raises the hypothesis that there will be consequences for gas exchange capacity and ability to support aerobic activities. Therefore, we investigated the effects of an environmentally relevant level of SePM contamination on swimming performance and associated aerobic metabolic rates in Nile tilapia, Oreochromis niloticus. Short-term exposure (96 h) to SePM reduced critical swimming speed, energetic efficiency of aerobic swimming, standard metabolic rate, maximum metabolic rate, and aerobic scope. The compromised swimming performance could have adverse ecological effects by limiting foraging ability, predator evasion, territorial protection, and migration. The impairments to aerobic capacity could also affect overall fish performance by influencing long-term energy balance and allocation to growth and reproduction. Thus, despite being sublethal, SePM contamination is considerably debilitating, and if its limiting effects are not compensated for in the longer term, this may reduce the survival and fitness of fish populations.

Settleable atmospheric particulate matter affects cardiorespiratory responses to hypoxia in Nile tilapia (Oreochromis niloticus).

Atmospheric particulate matter (APM) emitted by iron ore processing industries has a complex composition, including diverse metallic particles and nanoparticles. Settleable APM (SePM) causes air to water cross-contamination and has recently been demonstrated to have harmful sublethal impacts on fish, eliciting stress responses, affecting the immune system, and reducing blood oxygen-carrying capacity. These findings imply potential consequences for fish aerobic performance and energy allocation, particularly in their ability to tolerate respiratory challenges such as aquatic hypoxia. To assess that potential limitation, we analyzed metabolic, cardiorespiratory, and morphological alterations after exposing tilapia, Oreochromis niloticus, to an environmentally relevant concentration of SePM (96 h) and progressive hypoxia. The contamination initiated detectable gill damage, reducing respiratory efficiency, increasing ventilatory effort, and compromising fish capacity to deal with hypoxia. Even in normoxia, the resting respiratory frequency was elevated and limited respiratory adjustments during hypoxia. SePM increased O2crit from 26 to 34% of O2 (1.84 to 2.76 mg O2·L-1). Such ventilatory inefficacy implies higher ventilatory cost with relevant alterations in energy allocation. Progression in gill damage might be problematic and cause: infection, blood loss, ion imbalance, and limited cardiorespiratory performance. The contamination did not cause immediate lethality but may threaten fish populations due to limitations in physiological performance. This was the first investigation to evaluate the physiological responses of fish to hypoxia after SePM contamination. We suggest that the present level of environmental SePM deserves attention. The present results demonstrate the need for comprehensive studies on SePM effects in aquatic fauna.

Targeting the Atypical Chemokine Receptor ACKR3/CXCR7: Phase 1 - Phage Display Peptide Identification and Characterization.

One of the greatest challenges in fighting cancer is cell targeting and biomarker selection. The Atypical Chemokine Receptor ACKR3/CXCR7 is expressed on many cancer cell types, including breast cancer and glioblastoma, and binds the endogenous ligands SDF1/CXCL12 and ITAC/CXCL11. A 20 amino acid region of the ACKR3/CXCR7 N-terminus was synthesized and targeted with the NEB PhD-7 Phage Display Peptide Library. Twenty-nine phages were isolated and heptapeptide inserts sequenced; of these, 23 sequences were unique. A 3D molecular model was created for the ACKR3/CXCR7 N-terminus by mutating the corresponding region of the crystal structure of CXCR4 with bound SDF1/CXCL12. A ClustalW alignment was performed on each peptide sequence using the entire SDF1/CXCL12 sequence as the template. The 23-peptide sequences showed similarity to three distinct regions of the SDF1/CXCL12 molecule. A 3D molecular model was made for each of the phage peptide inserts to visually identify potential areas of steric interference of peptides that simulated CXCL12 regions not in contact with the receptor's Nterminus. An ELISA analysis of the relative binding affinity between the peptides identified 9 peptides with statistically significant results. The candidate pool of 9 peptides was further reduced to 3 peptides based on their affinity for the targeted N-terminus region peptide versus no target peptide present or a scrambled negative control peptide. The results clearly show the Phage Display protocol can be used to target a synthesized region of the ACKR3/CXCR7 N-terminus. The 3 peptides chosen, P20, P3, and P9, will be the basis for further targeting studies.

Comparative cardiovascular physiology: future trends, opportunities and challenges.

The inaugural Kjell Johansen Lecture in the Zoophysiology Department of Aarhus University (Aarhus, Denmark) afforded the opportunity for a focused workshop comprising comparative cardiovascular physiologists to ponder some of the key unanswered questions in the field. Discussions were centred around three themes. The first considered function of the vertebrate heart in its various forms in extant vertebrates, with particular focus on the role of intracardiac shunts, the trabecular ('spongy') nature of the ventricle in many vertebrates, coronary blood supply and the building plan of the heart as revealed by molecular approaches. The second theme involved the key unanswered questions in the control of the cardiovascular system, emphasizing autonomic control, hypoxic vasoconstriction and developmental plasticity in cardiovascular control. The final theme involved poorly understood aspects of the interaction of the cardiovascular system with the lymphatic, renal and digestive systems. Having posed key questions around these three themes, it is increasingly clear that an abundance of new analytical tools and approaches will allow us to learn much about vertebrate cardiovascular systems in the coming years.

Nitrogen excretion during embryonic development of the green iguana, Iguana iguana (Reptilia; Squamata).

Development within the cleidoic egg of birds and reptiles presents the embryo with the problem of accumulation of wastes from nitrogen metabolism. Ammonia derived from protein catabolism is converted into the less toxic product urea or relatively insoluble uric acid. The pattern of nitrogen excretion of the green iguana, Iguana iguana, was determined during embryonic development using samples from allantoic fluid and from the whole homogenized egg, and in hatchlings and adults using samples of blood plasma. Urea was the major excretory product over the course of embryonic development. It was found in higher concentrations in the allantoic sac, suggesting that there is a mechanism present on the allantoic membrane enabling the concentration of urea. The newly hatched iguana still produced urea while adults produced uric acid. The time course of this shift in the type of nitrogen waste was not determined but the change is likely to be related to the water relations associated with the terrestrial habit of the adult. The green iguana produces parchment-shelled eggs that double in mass during incubation due to water absorption; the eggs also accumulate 0.02 mM of urea, representing 82% of the total measured nitrogenous residues that accumulate inside the allantois. The increase in egg mass and urea concentration became significant after 55 days of incubation then were unchanged until hatching.

Autonomic control of cardiorespiratory interactions in fish, amphibians and reptiles

Control of the heart rate and cardiorespiratory interactions (CRI) is predominantly parasympathetic in all jawed vertebrates, with the sympathetic nervous system having some influence in tetrapods. Respiratory sinus arrhythmia (RSA) has been described as a solely mammalian phenomenon but respiration-related beat-to-beat control of the heart has been described in fish and reptiles. Though they are both important, the relative roles of feed-forward central control and peripheral reflexes in generating CRI vary between groups of fishes and probably between other vertebrates. CRI may relate to two locations for the vagal preganglionic neurons (VPN) and in particular cardiac VPN in the brainstem. This has been described in representatives from all vertebrate groups, though the proportion in each location is variable. Air-breathing fishes, amphibians and reptiles breathe discontinuously and the onset of a bout of breathing is characteristically accompanied by an immediate increase in heart rate plus, in the latter two groups, a left-right shunting of blood through the pulmonary circuit. Both the increase in heart rate and opening of a sphincter on the pulmonary artery are due to withdrawal of vagal tone. An increase in heart rate following a meal in snakes is related to withdrawal of vagal tone plus a non-adrenergic-non-cholinergic effect that may be due to humoral factors released by the gut. Histamine is one candidate for this role.

Autonomic control of cardiorespiratory interactions in fish, amphibians and reptiles.

Control of the heart rate and cardiorespiratory interactions (CRI) is predominantly parasympathetic in all jawed vertebrates, with the sympathetic nervous system having some influence in tetrapods. Respiratory sinus arrhythmia (RSA) has been described as a solely mammalian phenomenon but respiration-related beat-to-beat control of the heart has been described in fish and reptiles. Though they are both important, the relative roles of feed-forward central control and peripheral reflexes in generating CRI vary between groups of fishes and probably between other vertebrates. CRI may relate to two locations for the vagal preganglionic neurons (VPN) and in particular cardiac VPN in the brainstem. This has been described in representatives from all vertebrate groups, though the proportion in each location is variable. Air-breathing fishes, amphibians and reptiles breathe discontinuously and the onset of a bout of breathing is characteristically accompanied by an immediate increase in heart rate plus, in the latter two groups, a left-right shunting of blood through the pulmonary circuit. Both the increase in heart rate and opening of a sphincter on the pulmonary artery are due to withdrawal of vagal tone. An increase in heart rate following a meal in snakes is related to withdrawal of vagal tone plus a non-adrenergic-non-cholinergic effect that may be due to humoral factors released by the gut. Histamine is one candidate for this role.

Control of respiration in fish, amphibians and reptiles

Fish and amphibians utilise a suction/force pump to ventilate gills or lungs, with the respiratory muscles innervated by cranial nerves, while reptiles have a thoracic, aspiratory pump innervated by spinal nerves. However, fish can recruit a hypobranchial pump for active jaw occlusion during hypoxia, using feeding muscles innervated by anterior spinal nerves. This same pump is used to ventilate the air-breathing organ in air-breathing fishes. Some reptiles retain a buccal force pump for use during hypoxia or exercise. All vertebrates have respiratory rhythm generators (RRG) located in the brainstem. In cyclostomes and possibly jawed fishes, this may comprise elements of the trigeminal nucleus, though in the latter group RRG neurons have been located in the reticular formation. In air-breathing fishes and amphibians, there may be separate RRG for gill and lung ventilation. There is some evidence for multiple RRG in reptiles. Both amphibians and reptiles show episodic breathing patterns that may be centrally generated, though they do respond to changes in oxygen supply. Fish and larval amphibians have chemoreceptors sensitive to oxygen partial pressure located on the gills. Hypoxia induces increased ventilation and a reflex bradycardia and may trigger aquatic surface respiration or air-breathing, though these latter activities also respond to behavioural cues. Adult amphibians and reptiles have peripheral chemoreceptors located on the carotid arteries and central chemoreceptors sensitive to blood carbon dioxide levels. Lung perfusion may be regulated by cardiac shunting and lung ventilation stimulates lung stretch receptors.

Control of respiration in fish, amphibians and reptiles.

Fish and amphibians utilise a suction/force pump to ventilate gills or lungs, with the respiratory muscles innervated by cranial nerves, while reptiles have a thoracic, aspiratory pump innervated by spinal nerves. However, fish can recruit a hypobranchial pump for active jaw occlusion during hypoxia, using feeding muscles innervated by anterior spinal nerves. This same pump is used to ventilate the air-breathing organ in air-breathing fishes. Some reptiles retain a buccal force pump for use during hypoxia or exercise. All vertebrates have respiratory rhythm generators (RRG) located in the brainstem. In cyclostomes and possibly jawed fishes, this may comprise elements of the trigeminal nucleus, though in the latter group RRG neurons have been located in the reticular formation. In air-breathing fishes and amphibians, there may be separate RRG for gill and lung ventilation. There is some evidence for multiple RRG in reptiles. Both amphibians and reptiles show episodic breathing patterns that may be centrally generated, though they do respond to changes in oxygen supply. Fish and larval amphibians have chemoreceptors sensitive to oxygen partial pressure located on the gills. Hypoxia induces increased ventilation and a reflex bradycardia and may trigger aquatic surface respiration or air-breathing, though these latter activities also respond to behavioural cues. Adult amphibians and reptiles have peripheral chemoreceptors located on the carotid arteries and central chemoreceptors sensitive to blood carbon dioxide levels. Lung perfusion may be regulated by cardiac shunting and lung ventilation stimulates lung stretch receptors.

The role of the vagus nerve in the generation of cardiorespiratory interactions in a neotropical fish, the pacu, Piaractus mesopotamicus.

The role of the vagus nerve in determining heart rate (f(H)) and cardiorespiratory interactions was investigated in a neotropical fish, Piaractus mesopotamicus. During progressive hypoxia f(H) initially increased, establishing a 1:1 ratio with ventilation rate (f(R)). Subsequently there was a hypoxic bradycardia. Injection of atropine abolished a normoxic inhibitory tonus on the heart and the f(H) adjustments during progressive hypoxia, confirming that they are imposed by efferent parasympathetic inputs via the vagus nerve. Efferent activity recorded from the cardiac vagus in lightly anesthetized normoxic fish included occasional bursts of activity related to spontaneous changes in ventilation amplitude, which increased the cardiac interval. Restricting the flow of aerated water irrigating the gills resulted in increased respiratory effort and bursts of respiration-related activity in the cardiac vagus that seemed to cause f(H) to couple with f(R). Cell bodies of cardiac vagal pre-ganglionic neurons were located in two distinct groups within the dorsal vagal motor column having an overlapping distribution with respiratory motor-neurons. A small proportion of cardiac vagal pre-ganglionic neurons (2%) was in scattered positions in the ventrolateral medulla. This division of cardiac vagal pre-ganglionic neurons into distinct motor groups may relate to their functional roles in determining cardiorespiratory interactions.

The basis of vagal efferent control of heart rate in a neotropical fish, the pacu, Piaractus mesopotamicus.

The role of the parasympathetic nervous system, operating via the vagus nerve, in determining heart rate (f(H)) and cardiorespiratory interactions was investigated in the neotropical fish Piaractus mesopotamicus. Motor nuclei of branches of cranial nerves VII, IX and X, supplying respiratory muscles and the heart, have an overlapping distribution in the brainstem, while the Vth motor nucleus is more rostrally located. Respiration-related efferent activity in the cardiac vagus appeared to entrain the heart to ventilation. Peripheral stimulation of the cardiac vagus with short bursts of electrical stimuli entrained the heart at a ratio of 1:1 over a range of frequencies, both below and sometimes above the intrinsic heart rate. Alternatively, at higher bursting frequencies the induced f(H) was slower than the applied stimulus, being recruited by a whole number fraction (1:2 to 1:6) of the stimulus frequency. These effects indicate that respiration-related changes in f(H) in pacu are under direct, beat-to-beat vagal control. Central burst stimulation of respiratory branches of cranial nerves VII, IX and X also entrained the heart, which implies that cardiorespiratory interactions can be generated reflexly. Central stimulation of the Vth cranial nerve was without effect on heart rate, possibly because its central projections do not overlap with cardiac vagal preganglionic neurons in the brainstem. However, bursts of activity recorded from the cardiac vagus were concurrent with bursts in this nerve, suggesting that cardiorespiratory interactions can arise within the CNS, possibly by irradiation from a central respiratory pattern generator, when respiratory drive is high.

Abolition of reflex bradycardia by cardiac vagotomy has no effect on the regulation of oxygen uptake by Atlantic cod in progressive hypoxia.

The functional significance of chemoreflexive hypoxic bradycardia was explored in Atlantic cod Gadus morhua L. (mean mass approximately 800 g, acclimated to a seawater temperature of 11 degrees C) by investigating responses to progressive hypoxia following section of the cardiac branches of cranial nerve X. Cardiac denervation had no effect on oxygen uptake rate (MO(2)), gill ventilation rate (f(G)) or opercular pressure amplitude (P(OP)) under normoxic conditions, but caused a significant increase in heart rate (f(H)), to 50+/-1 beats min(-1) by comparison to 40+/-2 beats min(-1) in sham-operated cod (mean+/-s.e.m., n=9). Sham-operated cod exhibited transient profound bradycardia following oxygen chemoreceptor stimulation by bolus injection of sodium cyanide into the buccal cavity (2 mg in 2 ml seawater), but this cardiac chemoreflex was abolished in denervated cod. Both groups, however, exhibited similar marked transient chemoreflexive hyperventilation following NaCN. When exposed from normoxia (PO(2) approximately 18 kPa) to progressive hypoxia at nominal water PO(2)'s of 8, 6, 5, 4 and 3 kPa, both groups exhibited the same pattern of homeostatic regulation of MO(2), with no significant difference in their mean critical PO(2) (P(crit)) values, which were 7.40+/-0.81 kPa and 8.73+/-0.71 kPa, respectively (n=9). Both groups exhibited significant bradycardia during progressive hypoxia, although denervated fish always had higher mean f(H). The incipient threshold for bradycardia coincided with P(crit) in sham-operated cod whereas, in denervates, the threshold was below their P(crit) and bradycardia presumably reflected direct effects of hypoxia on the myocardium. The sham-operated group displayed a significantly more pronounced ventilatory response than denervates in hypoxia, in particular for P(OP). In sham-operated cod, peak ventilatory responses occurred in deep hypoxia below P(crit) whereas, in denervates, more modest peak responses coincided with P(crit) and, in deep hypoxia, they exhibited a significant decline in f(G) below their normoxic rate. Only a minority of shams lost equilibrium in hypoxia whereas a majority of denervates did, some of which failed to recover. The results indicate that chemoreflexive bradycardia plays no role in the homeostatic regulation of oxygen uptake by cod in hypoxia, but does contribute to maintenance of overall functional integrity below P(crit).

Effects of salinity on rates of protein synthesis and oxygen uptake in the post-larvae and juveniles of the tropical prawn Macrobrachium rosenbergii (de Man).

Protein synthesis is a major determinant of growth and yet little is known about the environmental factors that influence protein synthesis rates in farmed freshwater prawns. To this end, post-larvae and juveniles of Macrobrachium rosenbergii were exposed to various salinities (0, 14, 30 per thousand) to determine whole-animal rates of fractional protein synthesis (k(s)) and oxygen uptake. In the post-larvae that migrate upstream from brackish to freshwater areas, whole-animal k(s) was unaffected by salinity, but rates of oxygen uptake were significantly lower at 14 per thousand. In the freshwater juveniles, a different response was observed, as mean k(s) was significantly higher at 14 per thousand compared with 0 per thousand, but rates of oxygen uptake remained unchanged. Such differences are thought to be related to the energetic costs of osmoregulation and to the ability to maintain osmotic gradients in freshwater. In an additional experiment, acclimation temperature (20, 26, 30 degrees C) had a direct effect on k(s) in juveniles held at 0 per thousand. In all cases, changes in k(s) resulted from alterations in RNA activity at constant RNA capacity. In juveniles at least, whole-animal rates of protein synthesis were highest at 14 per thousand and 30 degrees C which corresponds to the optimal salinity and temperature recommended for the growth and culture of M. rosenbergii.

The unequal influences of the left and right vagi on the control of the heart and pulmonary artery in the rattlesnake, Crotalus durissus.

Autonomic control of the cardiovascular system in reptiles includes sympathetic components but heart rate (f(H)), pulmonary blood flow (Q(pul)) and cardiac shunt patterns are primarily controlled by the parasympathetic nervous system. The vagus innervates both the heart and a sphincter on the pulmonary artery. The present study reveals that whereas both the left and right vagi influence f(H), it is only the left vagus that influences pulmonary vascular resistance. This is associated with the fact that rattlesnakes, in common with some other species of snakes, have a single functional lung, as the other lung regresses during development. Stimulation of the left cervical vagus in anaesthetised snakes slowed the heart and markedly reduced blood flow in the pulmonary artery whereas stimulation of the right cervical vagus slowed the heart and caused a small increase in stroke volume (V(S)) in both the systemic and pulmonary circulations. Central stimulation of either vagus caused small (5-10%) reductions in systemic blood pressure but did not affect blood flows or f(H). A bilateral differentiation between the vagi was confirmed by progressive vagotomy in recovered snakes. Transection of the left vagus caused a slight increase in f(H) (10%) but a 70% increase in Q(pul), largely due to an increase in pulmonary stroke volume (V(S,pul)). Subsequent complete vagotomy caused a 60% increase in f(H) accompanied by a slight rise in Q(pul), with no further change in V(S,pul). By contrast, transection of the right vagus elicited a slight tachycardia but no change in V(S,pul). Subsequent complete vagotomy was accompanied by marked increases in f(H), Q(pul) and V(S,pul). These data show that although the heart receives bilateral vagal innervation, the sphincter on the pulmonary artery is innervated solely by the left vagus. This paves the way for an investigation of the role of the cardiac shunt in regulating metabolic rate, as chronic left vagotomy will cause a pronounced left-right shunt in recovered animals, whilst leaving intact control of the heart, via the right vagus.

The autonomic control and functional significance of the changes in heart rate associated with air breathing in the jeju, Hoplerythrinus unitaeniatus.

The jeju is a teleost fish with bimodal respiration that utilizes a modified swim bladder as an air-breathing organ (ABO). Like all air-breathing fish studied to date, jeju exhibit pronounced changes in heart rate (fH) during air-breathing events, and it is believed that these may facilitate oxygen uptake (MO2) from the ABO. The current study employed power spectral analysis (PSA) of fH patterns, coupled with instantaneous respirometry, to investigate the autonomic control of these phenomena and their functional significance for the efficacy of air breathing. The jeju obtained less than 5% of total MO2 (MtO2) from air breathing in normoxia at 26 degrees C, and PSA of beat-to-beat variability in fH revealed a pattern similar to that of unimodal water-breathing fish. In deep aquatic hypoxia (water PO2)=1 kPa) the jeju increased the frequency of air breathing (fAB) tenfold and maintained MtO2 unchanged from normoxia. This was associated with a significant increase in heart rate variability (HRV), each air breath (AB) being preceded by a brief bradycardia and then followed by a brief tachycardia. These fH changes are qualitatively similar to those associated with breathing in unimodal air-breathing vertebrates. Within 20 heartbeats after the AB, however, a beat-to-beat variability in fH typical of water-breathing fish was re-established. Pharmacological blockade revealed that both adrenergic and cholinergic tone increased simultaneously prior to each AB, and then decreased after it. However, modulation of inhibitory cholinergic tone was responsible for the major proportion of HRV, including the precise beat-to-beat modulation of fH around each AB. Pharmacological blockade of all variations in fH associated with air breathing in deep hypoxia did not, however, have a significant effect upon fAB or the regulation of MtO2. Thus, the functional significance of the profound HRV during air breathing remains a mystery.

Complex physiological traits as biomarkers of the sub-lethal toxicological effects of pollutant exposure in fishes.

Complex physiological traits, such as routine aerobic metabolic rate or exercise performance, are indicators of the functional integrity of fish that can reveal sub-lethal toxicological effects of aquatic pollutants. These traits have proved valuable in laboratory investigations of the sub-lethal effects of heavy metals, ammonia and various xenobiotics. It is not known, however, whether they can also function as biomarkers of the complex potential range of effects upon overall functional integrity caused by exposure to mixtures of chemicals in polluted natural environments. The current study used portable swimming respirometers to compare exercise performance and respiratory metabolism of fish exposed in cages for three weeks to either clean or polluted sites on three urban European river systems: the river Lambro, Milan, Italy; the rivers Blythe, Cole and Tame, Birmingham, UK; and the river Amstel, Amsterdam, The Netherlands. The UK and Italian rivers were variously polluted with high levels of both bioavailable heavy metals and organics, and the Amstel by mixtures of bioavailable organics at high concentrations. In both the UK and Italy, indigenous chub (Leuciscus cephalus) exposed to clean or polluted sites swam equally well in an initial performance test, but the chub from polluted sites could not repeat this performance after a brief recovery interval. These animals were unable to raise the metabolic rate and allocate oxygen towards exercise in the second trial, an effect confirmed in successive campaigns in Italy. Swimming performance was therefore a biomarker indicator of pollutant exposure in chub exposed at these sites. Exposure to polluted sites on the river Amstel did not affect the repeat swimming performance of cultured cloned carp (Cyprinus carpio), indicating either a species-specific tolerance or relative absence of heavy metals. However, measurements of oxygen uptake during swimming revealed increased rates of routine aerobic metabolism in both chub and carp at polluted sites in all of the rivers studied, indicating a sub-lethal metabolic loading effect. Therefore, the physiological traits of exercise performance and metabolic rate have potential as biomarkers of the overall sub-lethal toxic effects of exposure to complex mixtures of pollutants in rivers, and may also provide insight into why fish do not colonize some polluted environments.

Coupling of the respiratory rhythm in fish with activity in hypobranchial nerves and with heartbeat.

Fish have a central respiratory pattern generator (CRPG) in the brain stem that initiates activity in a series of cranial nerves innervating respiratory muscles. These nerves burst sequentially in the order of their rostrocaudal distribution in the central nervous system. When respiratory drive is high, this activity spreads caudally to occipital and anterior spinal neurons that project via the hypobranchial nerves to stimulate hypaxial muscles, causing active jaw abduction. The CRPG may also recruit the heart. Fish, like mammals, show respiratory components in the intrinsic variability of heart rate (HRV). Cardiorespiratory synchrony in the dogfish is driven by bursting activity in the cardiac branches of the vagus nerve, which emanates from preganglionic neurons in the dorsal vagal motor nucleus. A respiratory component in HRV is difficult to discriminate in other species, requiring the use of power spectral analysis and the subsequent elimination of aliased components.

Survey of operating theatre ventilation facilities for minimally invasive surgery in Great Britain and Northern Ireland: current practice and considerations for the future.

Increasing use of minimally invasive surgery (MIS) and other invasive procedures has raised the question of what ventilation facilities are appropriate for such procedures to prevent infection. The Hospital Infection Society (HIS) Working Party on Infection Control in Operating Theatres undertook a survey of practice in Great Britain and Northern Ireland on the ventilation facilities provided for a variety of MIS and other procedures. Five hundred and fifty questionnaires were forwarded to HIS members, and 186 (39%) replies were received. Fifty-eight percent were from district general hospitals (DGHs). Designated theatres for orthopaedic surgery (although not necessarily ultraclean ventilated theatres) were available in more than 80% of hospitals, with approximately 50% of hospitals having designated theatres for a variety of other surgical subspecialities. Approximately two-thirds of urological procedures were performed in conventionally ventilated operating theatres. Most radiological procedures were performed in non-ventilated theatres or treatment rooms. In around half of the DGHs and university/referral hospitals, orthopaedic MIS procedures such as arthroscopy were performed in ultraclean ventilated theatres. This survey revealed considerable variation in the use of conventionally ventilated theatres and ultraclean ventilated theatres. In particular, many radiological and anaesthetic procedures are performed in treatment rooms or ventilated rooms with less than 20 air changes per hour. Whilst it is not clear whether this is acceptable practice given current knowledge, large-scale clinical trials to determine what standards of ventilation are appropriate to minimize infection for these types of procedures would be difficult to conduct. Research is needed on the relative risk of airborne infection for a variety of procedures, including whether all prosthetic implant procedures should be carried out in ultraclean ventilated theatres, as infection associated with implants is often of airborne origin and of considerable clinical significance.

The effects of sustained exercise and hypoxia upon oxygen tensions in the red muscle of rainbow trout.

Teleost fish possess discrete blocks of oxidative red muscle (RM) and glycolytic white muscle, whereas tetrapod skeletal muscles are mixed oxidative/glycolytic. It has been suggested that the anatomy of RM in teleost fish could lead to higher intramuscular O2 partial pressures (PO2) than in mammalian skeletal muscles. This study provides the first direct experimental support for this suggestion by using novel optical fibre sensors to discover a mean (+/- S.E.M., N=6) normoxic steady-state red muscle PO2 (PrmO2) of 61+/-10 mmHg (1 mmHg=133.3 Pa) in free-swimming rainbow trout Oncorhynchus mykiss. This is significantly higher than literature reports for mammalian muscles, where the PO2 never exceeds 40 mmHg. Aerobic RM powers sustained swimming in rainbow trout. During graded incremental exercise, PrmO2 declined from 62+/-5 mmHg at the lowest swim speed down to 45+/-3 mmHg at maximum rates of aerobic work, but then rose again to 51+/-5 mmHg at exhaustion. These measurements of PrmO2 during exercise indicated, therefore, that O2 supply to the RM was not a major limiting factor at exhaustion in trout. The current study found no evidence that teleost haemoglobins with a Root effect cause extremely elevated O2 tensions in aerobic tissues. Under normoxic conditions, PrmO2 was significantly lower than arterial PO2 (119+/-5 mmHg), and remained lower when the arterial to tissue PO2 gradient was reduced by exposure to mild hypoxia. When two sequential levels of mild hypoxia (30 min at a water PO2 of 100 mmHg then 30 min at 75 mmHg) caused PaO2 to fall to 84+/-2 mmHg then 61+/-3 mmHg, respectively, this elicited simultaneous reductions in PrmO2,to 51+/-6 mmHg then 41+/-5 mmHg, respectively. Although these hypoxic reductions in PrmO2 were significantly smaller than those in PaO2, the effect could be attributed to the sigmoid shape of the trout haemoglobin-O2 dissociation curve.