Is crystalloid co-loading necessary to prevent spinal hypotension during elective cesarean delivery? A randomized double-blind trial

BACKGROUND

Hypotension is common during spinal anesthesia for cesarean delivery. Preventive strategies include fluid loading and phenylephrine. We hypothesized that if prophylactic phenylephrine infusion is used, omission of fluid loading would be non-inferior to fluid co-loading in maintaining cardiac output. We assumed that if there was a difference, the increase in cardiac output would be greater in the no-loading than in the co-loading group.

METHODS

Term pregnant women scheduled for elective cesarean delivery were randomized to receive 1 L crystalloid co-loading or maintenance fluids only. Phenylephrine was titrated to maintain blood pressure. Changes in cardiac output following spinal anesthesia were the primary outcome. The study was powered as a non-inferiority trial, allowing the no-loading arm to have a 50% greater change in cardiac output. Heart rate, dose of phenylephrine, occurrence of nausea and vomiting, Apgar scores and neonatal acid base status were secondary outcomes.

RESULTS

Data from 63 women were analyzed. In contrast to our hypothesis, there was 33% less increase in cardiac output with no loading (ratio 0.67, 95% CI 0.15 to 1.36), and 60% greater reduction of cardiac output with no loading (ratio 1.6, 95% CI 1.0 to 2.7). Total dose of phenylephrine was higher in the no-loading group. There may be a less favorable neonatal acid base status without volume loading.

CONCLUSION

Omission of crystalloid co-loading leads to a decrease in cardiac output which has a potentially unfavorable impact on neonatal acid base status. We conclude that crystalloid co-loading may be useful in the presence of phenylephrine infusion.

Renal failure: a non-cardiac source of high sensitivity cardiac troponin T

Background

Circulating high sensitivity cardiac troponin T (hs-cTnT) levels are frequently elevated in patients with end-stage renal disease (ESRD). The underlying pathophysiology is largely unknown. Currently, accumulation of hs-cTnT due to impaired renal clearance, as well as increased production caused by chronic cardiomyocyte injury is being discussed.

Purpose

The aim of this study was to assess the relative contribution of impaired renal clearance as a non-cardiac source of elevated hs-cTnT concentrations, using renal transplantation as an in vivo model of rapidly improved renal function and on a short-term basis rather unchanged cardiac pathology.

Methods

This single-centre study was a secondary analysis within a prospective active surveillance study program for perioperative myocardial infarction/injury (PMI). 42 consecutive high-risk patients undergoing renal transplantation without evidence of PMI were included. Serial creatinine and hs-cTnT (Elecsys, Roche) measurements were performed pre-transplant (baseline) and post-transplant on day (d) 1, between d2 and d5, and between d14 and d180. The effect of time and creatinine on hs-cTnT was estimated with a log-level non-linear mixed-effects model, where time and creatinine were treated as the fixed effects and subject as the random effect. Natural cubic splines were used to account for nonlinearity in the fixed effects.

Results

Baseline median serum creatinine concentration was 616 umol/L [interquartile range (IQR) 477–825], and significantly fell to 425 umol/L (IQR 313–619) on d1, 285 umol/L (IQR 194–509) on day2–5, and 116 umol/L (IQR 100–166) on d14–180 (p<0.001, p<0.001, and p=0.043, respectively; Figure 1A).

Pre-transplant hs-cTnT concentrations were above the 99th percentile (14ng/L) in all patients, median hs-cTnT concentration was 50 ng/L (IQR 35–70). In parallel to the fall in serum creatinine from baseline to d1, hs-cTnT concentrations significantly fell to 28 ng/L (IQR 15–40) on d1 (p<0.001), and then remained constant on d2–5 (27 ng/L (IQR 18–35)), and on d14–180 (24 ng/L (IQR 19–28); Figure 1B).

The mixed-effect model showed a significant decrease of hs-cTnT between baseline and d1 (p<0.001), whereas no significant change between d1 and d2 (p=0.82) occurred (Figure 2).

Conclusion

In contrast to the continuously falling serum creatinine levels, hs-cTnT concentrations reduced by about 50% only within the first 24 hours with a functional graft and then remained elevated above the 99th percentile. This suggests, that ESRD is a non-cardiac source of elevated circulating hs-cTnT concentrations, which contributes about 50%, while the other 50% seem related to chronic cardiomyocyte injury. Further studies assessing the long-term effect of renal transplantation on hs-cTnT levels and cardiac function are needed.

Funding Acknowledgement

Type of funding sources: Public Institution(s). Main funding source(s): Swiss National Science FoundationSwiss Heart Foundation

Efficacy and safety of carbetocin given as an intravenous bolus compared with short infusion for Caesarean section - double-blind, double-dummy, randomized controlled non-inferiority trial

Background

Carbetocin is a synthetic oxytocin-analogue, which should be administered as bolus according to manufacturer's recommendations. A higher speed of oxytocin administration leads to increased cardiovascular side-effects. It is unclear whether carbetocin administration as short infusion has the same efficacy on uterine tone compared with bolus administration and whether haemodynamic parameters differ.

Methods

In this randomized, double-blind, non-inferiority trial, women undergoing planned or unplanned Caesarean section (CS) under regional anaesthesia received a bolus and a short infusion, only one of which contained carbetocin 100 mcg (double dummy). Obstetricians quantified uterine tone two, three, five and 10 min after cord-clamping by manual palpation using a linear analogue scale from 0 to 100. We evaluated whether the lower limit of the 95% CI of the difference in maximum uterine tone within the first five min after cord-clamping did not include the pre-specified non-inferiority limit of -10.

Results

Between December 2014 and November 2015, 69 patients were randomized to receive carbetocin as bolus and 71 to receive it as short infusion. Maximal uterine tone was 89 in the bolus and 88 in the short infusion group (mean difference -1.3, 95% CI -5.7 to 3.1). Bp, calculated blood loss, use of additional uterotonics, and side-effects were comparable.

Conclusions

Administration of carbetocin as short infusion does not compromise uterine tone and has similar cardiovascular side-effects as a slow i.v. bolus. In accordance with current recommendations for oxytocin, carbetocin can safely be administered as short -infusion during planned or unplanned CS.

Clinical trial registration

ClinicalTrials.gov NCT02221531 and www.kofam.ch SNCTP000001197.

Effect of age on intraoperative cerebrovascular autoregulation and near-infrared spectroscopy-derived cerebral oxygenation

BACKGROUND

Age is an important risk factor for perioperative cerebral complications such as stroke, postoperative cognitive dysfunction, and delirium. We explored the hypothesis that intraoperative cerebrovascular autoregulation is less efficient and brain tissue oxygenation lower in elderly patients, thus, increasing the vulnerability of elderly brains to systemic insults such as hypotension.

METHODS

We monitored intraoperative cerebral perfusion in 50 patients aged 18-40 and 77 patients >65 yr at two Swiss university hospitals. Mean arterial pressure (MAP) was measured continuously using a plethysmographic method. An index of cerebrovascular autoregulation (Mx) was calculated based on changes in transcranial Doppler flow velocity due to changes in MAP. Cerebral oxygenation was assessed by the tissue oxygenation index (TOI) using near-infrared spectroscopy. End-tidal CO₂, O₂, and sevoflurane concentrations and peripheral oxygen saturation were recorded continuously. Standardized anaesthesia was administered in all patients (thiopental, sevoflurane, fentanyl, atracurium).

RESULTS

Autoregulation was less efficient in patients aged >65 yr [by 0.10 (se 0.04; P=0.020)] in a multivariable linear regression analysis. This difference was not attributable to differences in MAP, end-tidal CO₂, or higher doses of sevoflurane. TOI was not significantly associated with age, sevoflurane dose, or Mx but increased with increasing flow velocity [by 0.09 (se 0.04; P=0.028)] and increasing MAP [by 0.11 (se 0.05; P=0.043)].

CONCLUSIONS

Our results do not support the hypothesis that older patients' brains are more vulnerable to systemic insults. The difference of autoregulation between the two groups was small and most likely clinically insignificant.

Zebrafish immunoglobulin IgD: unusual exon usage and quantitative expression profiles with IgM and IgZ/T heavy chain isotypes

The zebrafish is an emerging model for comparative immunology and biomedical research. In contrast to the five heavy chain isotype system of mice and human (IgD, IgM, IgA, IgG, IgE), zebrafish harbor gene segments for IgD, IgM, and novel heavy chain isotype called IgZ/T which appears restricted to bony fishes. The purpose of this study was to design and validate a suite of quantitative real time RT-PCR protocols to measure IgH expression in a vertebrate model which has considerable promise for modeling both pathogenic infection and chronic conditions leading to immune dysfunction. Specific primers were designed and following verification of their specificty, relative expression levels of IgD, IgM, and IgZ/T were measured in triplicate for zebrafish raised under standard laboratory conditions. During embryonic stages, low levels of each heavy chain isotype (IgH) were detected with each increasing steadily between 2 and 17 weeks post fertilization. Overall IgM>IgZ>IgD throughout zebrafish development with the copy number of IgM being several fold higher than that of IgD or IgZ/T. IgD exon usage was also characterized, as its extremely long size and presence of a stop codon in the second IgD exon in zebrafish, raised questions as to how this antibody might be expressed. Zebrafish IgD was found to be a chimeric immunoglobulin, with the third IgD exon spliced to the first IgM constant exon thereby circumventing the first and second IgD exons. Collectively, the qRT-PCR results represent the first comparative profile of IgD, IgM, IgZ/T expression over the lifespan of any fish species and the primers and assay parameters reported should prove useful in enabling researchers to rapidly quantify changes in IgH expression in zebrafish models of disease where altered IgH expression is manifested.

Primary structure of the M subunit of the reaction center from Rhodopseudomonas sphaeroides

The reaction center is a membrane-bound bacteriochlorophyll-protein complex that mediates the primary photochemical events in the photosynthetic bacterium Rhodopseudomonas sphaeroides. The previously determined amino-terminal sequences of the three subunits of the reaction center protein were used to design synthetic mixed oligonucleotide probes for the structural genes encoding the subunits. One of these probes was used to isolate and clone a fragment of DNA from R. sphaeroides that contained the gene encoding the M subunit. The nucleotide sequence of this gene was determined by the dideoxy method. In addition, a number of tryptic and chymotryptic peptides from the M protein were isolated and subjected to sequence analysis, and the sequence of the carboxyl terminus was determined. Together with the amino-terminal sequence, the data establish the primary structure of the M protein. The distribution of hydrophobic residues in the amino acid sequence suggests the presence of five membrane-spanning segments. A significant homology was found between the amino acid sequence of the M subunit and a thylakoid membrane protein (M(r) 32,000) from spinach that has been implicated in herbicide and quinone binding.

Bupivacaine concentrations in the lumbar cerebrospinal fluid of patients during spinal anaesthesia

BACKGROUND

Data on bupivacaine concentrations in the cerebral spinal fluid (CSF) during spinal anaesthesia are scarce. The purpose of this study was to determine the concentration of bupivacaine in the lumbar CSF of patients with an adequate level of spinal anaesthesia after injection of plain bupivacaine 0.5%.

METHODS

Sixty patients with an adequate level of spinal block after standardized administration of plain bupivacaine 20 mg in men and of 17.5 mg in women were studied. To measure the CSF bupivacaine concentration, we performed a second lumbar spinal puncture and obtained a CSF sample at a randomized time point 5-45 min after the bupivacaine injection. In addition, we calculated the half-life of bupivacaine in the CSF and tested the hypothesis that the level of spinal block is related to the lumbar CSF bupivacaine concentration.

RESULTS

Men and women had CSF bupivacaine concentrations ranging from 95.4 to 773.0 microg ml(-1) (median 242.4 microg ml(-1)) and from 25.9 to 781.0 microg ml(-1) (median 187.6 microg ml(-1)), respectively. The large variability of bupivacaine concentrations obtained at similar times after subarachnoid administration made calculation of a meaningful half-life of bupivacaine in CSF impossible. There was no association between CSF bupivacaine concentration and spinal block level, and CSF bupivacaine concentrations for the same spinal block level differed between patients by six-fold.

CONCLUSIONS

There is a large variability of CSF bupivacaine concentrations in patients with an adequate level of spinal anaesthesia.

Immunoglobulin light chain (IgL) genes in zebrafish: Genomic configurations and inversional rearrangements between (V(L)-J(L)-C(L)) gene clusters

In mammals, Immunoglobulin light chain (IgL) are localized to two chromosomal regions (designated kappa and lambda). Here we report a genome-wide survey of IgL genes in the zebrafish revealing (V(L)-J(L)-C(L)) clusters spanning 5 separate chromosomes. To elucidate IgL loci present in the zebrafish genome assembly (Zv6), conventional sequence similarity searches and a novel scanning approach based on recombination signal sequence (RSS) motifs were applied. RT-PCR with zebrafish cDNA was used to confirm annotations, evaluate VJ-rearrangement possibilities and show that each chromosomal locus is expressed. In contrast to other vertebrates in which IgL exon usage has been studied, inversional rearrangement between (V(L)-J(L)-C(L)) clusters were found. Inter-cluster rearrangements may convey a selective advantage for editing self-reactive receptors and poise zebrafish by virtue of their extensive numbers of V(L), J(L) and C(L) to have greater potential for immunoglobulin gene shuffling than traditionally studied mice and human models.

Characterization of terminal deoxynucleotidyl transferase and polymerase mu in zebrafish

Terminal deoxynucleotidyl transferase (TdT) contributes to the junctional diversity of immunoglobulin and T-cell receptors by incorporating nucleotides in a template-independent manner. A closely related enzyme, polymerase mu (polmu), a template-directed polymerase, plays a role in general end-joining double-strand break repair. We cloned zebrafish TdT and polmu and found them to be 43% identical in amino acid sequence. Comparisons with sequences of other species revealed conserved residues typical for TdT in the zebrafish sequence that support the template independence of this enzyme. Some but not all of these features were identified in zebrafish polmu. In adult fish, TdT expression was most prominent in thymus, pro- and mesonephros, the primary lymphoid organs in teleost fish and in spleen, intestine, and the tissue around the intestine. Polmu expression was detected not only in pro- and mesonephros, the major sites for B-lymphocyte development, but also in ovary and testis and in all tissue preparations to a low extent. TdT expression starts at 4 dpf and increases thereafter. Polmu is expressed at all times to a similar extent. In situ studies showed a strong expression of TdT and polmicro in the thymic cortex of 8-week-old fish. The characterization of zebrafish TdT and polmu provide new insights in fish lymphopoiesis and addresses the importance and evolution of TdT and polmu themselves.

The accuracy of non-invasive carbon dioxide monitoring: a clinical evaluation of two transcutaneous systems

We determined the accuracy of two transcutaneous carbon dioxide monitoring systems (SenTec Digital Monitor with V-Sign Sensor and TOSCA 500 with TOSCA Sensor 92) for the measurement of single values and trends in the arterial partial pressure of carbon dioxide in 122 adult patients during major surgery and in 50 adult patients in the intensive care unit. One or several paired measurements were performed in each patient. The first measurement was used to determine the accuracy of a single value of transcutaneous carbon dioxide; the difference between the first and the last measurements was used to analyse the accuracy and to track trends. We defined a 95% limit of agreement of <or=1 kPa as being clinically useful. There was insufficient agreement between transcutaneous carbon dioxide partial pressure values derived from the two systems and arterial carbon dioxide values for both single values and trends as defined by our suggested limit of agreement. We conclude that these systems cannot replace conventional blood gas analysis in the clinical setting studied.

Effects of simulated hypovolaemia on haemodynamics, left ventricular function, mesenteric blood flow and gastric Pco2

BACKGROUND

Compensated clinically silent hypovolaemia may lead to low cardiac output, hypoperfusion and ischaemia. We investigated the cardiovascular effects of simulated hypovolaemia to determine whether it caused mesenteric ischaemia detectable by gastric tonometry.

METHODS

Thirteen healthy volunteers, aged 21-36 years, were investigated. Lower body negative pressure (LBNP) was used to simulate normotensive hypovolaemia. Cardiovascular parameters were measured using echocardiography. Mesenteric blood flow was investigated using Doppler sonography of the superior mesenteric artery (SMA). Gastric Pco(2) (P(g)co(2)) was measured using gas tonometry. Data were collected at baseline, LBNP and during a recovery period.

RESULTS

Normotensive hypovolaemia was induced successfully in 11 volunteers. There were no significant differences in mean arterial pressure between the three data points (91 +/- 6, 93 +/- 10 and 95 +/- 9 mmHg, respectively). With the induction of LBNP, the heart rate increased from 64 +/- 16 to 73 +/- 16 beats/min (P < 0.001), the cardiac index decreased from 2.7 +/- 1.0 to 1.8 +/- 0.6 l/min/m(2) (P= 0.002) and the systemic vascular resistance increased from 1535 +/- 445 to 2270 +/- 550 dyn s/cm(5) (P < 0.001). The SMA mean flow velocity decreased from 53 +/- 18 to 37 +/- 20 cm/s (69 +/- 20%) (P= 0.007), and increased to 56 +/- 34 cm/s (106 +/- 38%) (P= 0.001) during reperfusion. The SMA resistance increased from 92 +/- 30 to 174 +/- 110 mmHg/l/min (P= 0.004). These changes were reversible after termination of LBNP. By contrast, there were no significant differences in P(g)co(2) between the three data points.

CONCLUSIONS

In these volunteers, the mesenteric vascular bed contributed importantly to the maintenance of arterial pressure during normotensive hypovolaemia. However, this compensated hypovolaemia did not compromise the mesenteric perfusion sufficiently to increase P(g)co(2) and to allow detection by tonometry.

Monitoring the injured brain: ICP and CBF

Raised intracranial pressure (ICP) and low cerebral blood flow (CBF) are associated with ischaemia and poor outcome after brain injury. Therefore, many management protocols target these parameters. This overview summarizes the technical aspects of ICP and CBF monitoring, and their role in the clinical management of brain-injured patients. Furthermore, some applications of these methods in current research are highlighted. ICP is typically measured using probes that are inserted into one of the lateral ventricles or the brain parenchyma. Therapeutic measures used to control ICP have relevant side-effects and continuous monitoring is essential to guide such therapies. ICP is also required to calculate cerebral perfusion pressure which is one of the most important therapeutic targets in brain-injured patients. Several bedside CBF monitoring devices are available. However, most do not measure CBF but rather a parameter that is thought to be proportional to CBF. Frequently used methods include transcranial Doppler which measures blood flow velocity and may be helpful for the diagnosis and monitoring of cerebral vasospasm after subarachnoid haemorrhage or jugular bulb oximetry which gives information on adequacy of CBF in relation to the metabolic demand of the brain. However, there is no clear evidence that incorporating data from CBF monitors into our management strategies improves outcome in brain-injured patients.

Imaging of cerebral blood flow and metabolism in brain injury in the ICU

The heterogeneity of the initial insult and subsequent pathophysiology has made both the study of human head injury and design of randomised controlled trials exceptionally difficult. The combination of multimodality bedside monitoring and functional brain imaging positron emission tomography (PET) and magnetic resonance (MR), incorporated within a Neurosciences Critical Care Unit, provides the resource required to study critically ill patients after brain injury from initial ictus through recovery from coma and rehabilitation to final outcome. Methods to define cerebral ischemia in the context of altered cerebral oxidative metabolism have been developed, traditional therapies for intracranial hypertension re-evaluated and bedside monitors cross-validated. New modelling and analytical approaches have been developed.

["Postoperative cognitive dysfunction--do anaesthetics harm memory?"]

Nach Operationen können zwei Formen von kognitiven Störungen auftreten: Das postoperative Delir und die postoperative kognitive Dysfunktion. Letztere äussert sich durch diskrete Störungen des Gedächtnisses, der Aufmerksamkeit und der Sprache, die während Monaten persistieren können. Die wichtigsten Risikofaktoren für die Entwicklung der postoperativen kognitiven Dysfunktion sind ein höheres Alter und die Art des Eingriffs. Bei Patienten, die älter als 60 Jahre alt sind, kann bei rund 25% eine Woche nach einem grösseren Eingriff eine postoperative kognitive Dysfunktion festgestellt werden, drei Monate postoperativ bei 10%. Nach herzchirurgischen Eingriffen ist die Inzidenz noch höher: Bei rund der Hälfte der Patienten kann bei Spitalaustritt eine postoperative kognitive Dysfunktion festgestellt werden, nach sechs Monaten noch bei einem Viertel. Die Pathogenese und die Rolle der Anästhesie bei der Entwicklung der postoperativen kognitiven Dysfunktion sind unklar. Es gibt keine Studien, die den Effekt der Anästhesie unabhängig von einer Operation oder einer Hospitalisation untersuchen. Weder neuere, kurzwirksame Medikamente noch die Wahl der Anästhesietechnik (Regionalanästhesie oder Allgemeinanästhesie) können die postoperative kognitive Dysfunktion verhindern. Eine Prophylaxe oder Therapie ist zum jetzigen Zeitpunkt nicht bekannt.

Physiological thresholds for irreversible tissue damage in contusional regions following traumatic brain injury

Cerebral ischaemia appears to be an important mechanism of secondary neuronal injury in traumatic brain injury (TBI) and is an important predictor of outcome. To date, the thresholds of cerebral blood flow (CBF) and cerebral oxygen utilization (CMRO(2)) for irreversible tissue damage used in TBI studies have been adopted from experimental and clinical ischaemic stroke studies. Identification of irreversibly damaged tissue in the acute phase following TBI could have considerable therapeutic and prognostic implications. However, it is questionable whether stroke thresholds are applicable to TBI. Therefore, the aim of this study was to determine physiological thresholds for the development of irreversible tissue damage in contusional and pericontusional regions in TBI, and to determine the ability of such thresholds to accurately differentiate irreversibly damaged tissue. This study involved 14 patients with structural abnormalities on late-stage MRI, all of whom had been studied with (15)O PET within 72 h of TBI. Lesion regions of interest (ROI) and non-lesion ROIs were constructed on late-stage MRIs and applied to co-registered PET maps of CBF, CMRO(2) and oxygen extraction fraction (OEF). From the entire population of voxels in non-lesion ROIs, we determined thresholds for the development of irreversible tissue damage as the lower limit of the 95% confidence interval for CBF, CMRO(2) and OEF. To test the ability of a physiological variable to differentiate lesion and non-lesion tissue, we constructed probability curves, demonstrating the ability of a physiological variable to predict lesion and non-lesion outcomes. The lower limits of the 95% confidence interval for CBF, CMRO(2) and OEF in non-lesion tissue were 15.0 ml/100 ml/min, 36.7 mumol/100 ml/min and 25.9% respectively. Voxels below these values were significantly more frequent in lesion tissue (all P < 0.005, Mann-Whitney U-test). However, a significant proportion of lesion voxels had values above these thresholds, so that definition of the full extent of irreversible tissue damage would not be possible based upon single physiological thresholds. We conclude that, in TBI, the threshold of CBF below which irreversible tissue damage consistently occurs differs from the classical CBF threshold for stroke (where similar methodology is used to define such thresholds). The CMRO(2) threshold is comparable to that reported in the stroke literature. At a voxel-based level, however (and in common with ischaemic stroke), the extent of irreversible tissue damage cannot be accurately predicted by early abnormalities of any single physiological variable.

Predicting the response of intracranial pressure to moderate hyperventilation

BACKGROUND

Hyperventilation may cause brain ischaemia after traumatic brain injury. However, moderate reductions in PaCO(2) are still an option in the management of raised intracranial pressure (ICP) under some circumstances. Being able to predict the ICP-response to such an intervention would be advantageous. We investigated the ability of pre-hyperventilation ICP and cerebrospinal compensatory reserve to predict the reduction in ICP achievable with moderate hyperventilation in head injured patients.

METHODS

Thirty head injured patients requiring sedation and mechanical ventilation were investigated. ICP was monitored via an intraparenchymal probe and intracranial cerebrospinal compensatory reserve was assessed using an index (R(ap)) based on the relationship between mean ICP and its pulse amplitude. Measurements were made at a constant level of PaCO(2) during a 20-minute baseline period. The patients were then subjected to an acute decrease in PaCO(2) of approximately 1 kPa and, after an equilibration period of 10 minutes, measurements were again made at a constant level of PaCO(2) for a further 20 minutes. A multiple linear regression model, incorporating baseline PaCO(2), ICP, and R(ap) was used to identify the relevant predictors of ICP reduction.

FINDINGS

Baseline ICP and R(ap) were both significant predictors of ICP-reduction (p=0.02 and 0.001 respectively) with R(ap) being the more powerful parameter.

CONCLUSIONS

A model based on cerebrospinal compensatory reserve and ICP can predict the achievable ICP-reduction and may potentially be used to optimise patient selection and intensity of hyperventilation.

The immunoglobulin heavy-chain locus in zebrafish: identification and expression of a previously unknown isotype, immunoglobulin Z

The only immunoglobulin heavy-chain classes known so far in teleosts have been mu and delta. We identify here a previously unknown class, immunoglobulin zeta, expressed in zebrafish and other teleosts. In the zebrafish heavy-chain locus, variable (V) gene segments lie upstream of two tandem diversity, joining and constant (DJC) clusters, resembling the mouse T cell receptor alpha (Tcra) and delta (Tcrd) locus. V genes rearrange to (DJC)(zeta) or to (DJC)(mu) without evidence of switch rearrangement. The zebrafish immunoglobulin zeta gene (ighz) and mouse Tcrd, which are proximal to the V gene array, are expressed earlier in development. In adults, ighz was expressed only in kidney and thymus, which are primary lymphoid organs in teleosts. This additional class adds complexity to the immunoglobulin repertoire and raises questions concerning the evolution of immunoglobulins and the regulation of the differential expression of ighz and ighm.

Association between outcome, cerebral pressure reactivity and slow ICP waves following head injury

OBJECTIVE

To investigate the relationships between slow vasogenic waves ('B waves') of intracranial pressure (ICP), pressure-reactivity and outcome after traumatic brain injury.

MATERIAL AND METHOD

193 head-injured patients (age 34 +/- 16.7 years; median GCS 6) were monitored from 1997 to 2002. ICP, arterial blood pressure (ABP) were continuously monitored. Pressure-reactivity index (PRx) and magnitude of ICP slow waves were evaluated using the bed-side computers.

RESULTS

Distribution of PRx in different outcome groups indicated that pressure-reactivity was significantly worse in patients with fatal outcome. A magnitude of spontaneous slow waves of ICP was gradually decreasing in poorer outcome grades. Mortality indicated threshold rise from 20% to 70% when averaged PRx increased above 0.3 (p < 0.01). There was no threshold for mortality observed along distribution of magnitude of ICP slow waves. Mortality gradually increased when the magnitude of slow waves decreased (R = -0.26; p < 0.0001).

CONCLUSION

Inadequate pressure-reactivity and low magnitude of slow vasogenic waves of ICP are associated with fatal outcome after head injury. Based on brain monitoring data, differentiation between favourable outcome and severe disability is more problematic than differentiation between survivors and non-survivors.

Effects of moderate hyperventilation on cerebrovascular pressure-reactivity after head injury

In volunteers, hyperventilation improves autoregulation. However, in head-injured patients, hyperventilation-induced deterioration and improvement of autoregulation have been reported. We have re-examined this question using an index of pressure reactivity. Thirty patients with severe or moderate head-injury were studied. Arterial blood pressure, cerebral perfusion pressure (CPP), and intracranial pressure (ICP) were recorded over 20 minute epochs separated by ten minutes of equilibration at baseline and during moderate (>3.5 kPa) hyperventilation. End-tidal CO2 was constant during each phase of data acquisition. Pressure reactivity was assessed using an index 'PRx' based on the response of ICP to spontaneous blood pressure changes. Hyperventilation decreased PaCO2 from 5.1 +/- 0.4 to 4.4 +/- 0.4 kPa (p < 0.0001). ICP decreased by 3.7 +/- 2.2 mmHg (p < 0.001). CPP increased by 5.9 +/- 8.2 mmHg (p < 0.001). Overall, PRx did not change significantly with hyperventilation. However, there was a significant negative correlation between baseline PRx and the change in PRx (r = -0.71, p < 0.0001). This suggests that patients with disturbed pressure-reactivity may improve, whereas patients with intact pressure reactivity remain largely unchanged. Our data suggest that the response of pressure reactivity to hyperventilation is heterogeneous. This could be due to hyperventilation-induced changes in cerebral metabolism, or the change in CPP.

Expression of the winged helix/forkhead gene, foxn4, during zebrafish development

The winged-helix/forkhead transcription factor gene, foxn4, is expressed in the nervous system of developing and adult zebrafish. Prominent expression sites include the olfactory placode, the basal layer of the olfactory epithelium, the neuroepithelium of the developing retina, the germinal zone of the differentiated eye, regions of motoneuron development in the neural tube and periventricular regions of the brain. The adult thymus is the only major site of foxn4 expression outside of the nervous system.

T cells and the thymus in developing zebrafish

The expression of genes encoding T cell receptor (TCR) alpha was used to follow the development of the thymus and to analyze the distribution of T cells in zebrafish. In the thymus, expression was first detected, by in situ hybridization, at four days post fertilization. In RNA extracted from whole fish, TCRalpha transcripts were also detected at four days and reached adult levels at three weeks. At six weeks, TCRalpha was expressed throughout the thymus, whereas rag1 expression was localized to the peripheral regions. Expression of TCRalpha outside the thymus was detected at nine days. In adult peripheral organs, the greatest expression was in the pronephros, mesonephros and intestine; expression in the spleen became greater as fish age. Three new, relatively highly expressed, TCR Valpha families were identified.

Intracranial hypertension: what additional information can be derived from ICP waveform after head injury?

OBJECTIVE

Although intracranial hypertension is one of the important prognostic factors after head injury, increased intracranial pressure (ICP) may also be observed in patients with favourable outcome. We have studied whether the value of ICP monitoring can be augmented by indices describing cerebrovascular pressure-reactivity and pressure-volume compensatory reserve derived from ICP and arterial blood pressure (ABP) waveforms.

METHOD

96 patients with intracranial hypertension were studied retrospectively: 57 with fatal outcome and 39 with favourable outcome. ABP and ICP waveforms were recorded. Indices of cerebrovascular reactivity (PRx) and cerebrospinal compensatory reserve (RAP) were calculated as moving correlation coefficients between slow waves of ABP and ICP, and between slow waves of ICP pulse amplitude and mean ICP, respectively. The magnitude of 'slow waves' was derived using ICP low-pass spectral filtration.

RESULTS

The most significant difference was found in the magnitude of slow waves that was persistently higher in patients with a favourable outcome (p<0.00004). In patients who died ICP was significantly higher (p<0.0001) and cerebrovascular pressure-reactivity (described by PRx) was compromised (p<0.024). In the same patients, pressure-volume compensatory reserve showed a gradual deterioration over time with a sudden drop of RAP when ICP started to rise, suggesting an overlapping disruption of the vasomotor response.

CONCLUSION

Indices derived from ICP waveform analysis can be helpful for the interpretation of progressive intracranial hypertension in patients after brain trauma.

Effects of propofol on cerebral oxygenation and metabolism after head injury

BACKGROUND

Flow-metabolism coupling is thought to be deranged after traumatic brain injury, while the effects of propofol on flow-metabolism coupling are controversial. We have used a step increase in target plasma propofol concentration in head injured patients to explore flow-metabolism coupling in these patients.

METHODS

Ten patients with a moderate to severe head injury received a step increase in propofol target controlled infusion of 2 microg x ml(-1). Cerebral tissue gas measurements were recorded using a multimodal sensor, and regional chemistry was assessed using microdialysis. Arterial-jugular venous oxygen differences (AVDO(2)) were measured and all patients had cortical function monitoring (EEG).

RESULTS

The step increase in propofol led to a large increase in EEG burst-suppression ratio (0% (range 0-1.1) to 46.1% (range 0-61.7), P<0.05); however, this did not significantly change tissue gas levels, tissue chemistry, or AVDO(2).

CONCLUSIONS

Flow-metabolism coupling remains intact during a step increase in propofol after traumatic brain injury. The EEG burst-suppression induced by propofol after traumatic brain injury does not appear to be a useful therapeutic tool in reducing the level of regional ischaemic burden.

Predictive value of Glasgow Coma Scale after brain trauma: change in trend over the past ten years

BACKGROUND

Age and the Glasgow Coma Scale (GCS) score on admission are considered important predictors of outcome after traumatic brain injury. We investigated the predictive value of the GCS in a large group of patients whose computerised multimodal bedside monitoring data had been collected over the previous 10 years.

METHODS

Data from 358 subjects with head injury, collected between 1992 and 2001, were analysed retrospectively. Patients were grouped according to year of admission. Glasgow Outcome Scores (GOS) were determined at six months. Spearman's correlation coefficients between GCS and GOS scores were calculated for each year.

RESULTS

On average 34 (SD: 7) patients were monitored every year. We found a significant correlation between the GCS and GOS for the first five years (overall 1992-1996: r = 0.41; p<0.00001; n = 183) and consistent lack of correlations from 1997 onwards (overall 1997-2001: r = 0.091; p = 0.226; n = 175). In contrast, correlations between age and GOS were in both time periods significant and similar (r = -0.24 v r = -0.24; p<0.002).

CONCLUSIONS

The admission GCS lost its predictive value for outcome in this group of patients from 1997 onwards. The predictive value of the GCS should be carefully reconsidered when building prognostic models incorporating multimodality monitoring after head injury.

Genome structure and thymic expression of an endogenous retrovirus in zebrafish

In a search for previously unknown genes that are required for lymphocyte development in zebrafish, a retroviral sequence was identified in a subtracted thymus cDNA library and in genomic DNA libraries. The provirus is 11.2 kb and contains intact open reading frames for the gag, pol, and env genes, as well as nearly identical flanking long terminal repeat sequences. As determined by in situ hybridization, the thymus appears to be a major tissue for retroviral expression in both larval and adult fish. Several viral transcripts were found by Northern blotting in the adult thymus. The provirus was found at the same genomic locus in sperm from four fish, suggesting that it is an endogenous retrovirus. Phylogenetic analysis indicates that it is closest to, yet distinct from, the cluster of murine leukemia virus-related retroviruses, suggesting that this virus represents a new group of retroviruses.

J chain in the nurse shark: implications for function in a lower vertebrate

J chain is a small polypeptide covalently attached to polymeric IgA and IgM. In humans and mice, it plays a role in binding Ig to the polymeric Ig receptor for transport into secretions. The putative orthologue of mammalian J chain has been identified in the nurse shark by sequence analysis of cDNA and the polypeptide isolated from IgM. Conservation with J chains from other species is relatively poor, especially in the carboxyl-terminal portion, and, unlike other J chains, the shark protein is not acidic. The only highly conserved segment in all known J chains is a block of residues surrounding an N-linked glycosylation site. Of the eight half-cystine residues that are conserved in mammalian J chains, three are lacking in the nurse shark, including two in the carboxyl-terminal segment that have been reported to be required for binding of human J chain-containing IgA to secretory component. Taken together with these data, the relative abundance of J chain transcripts in the spleen and their absence in the spiral valve (intestine) suggest that J chain in nurse sharks may not have a role in Ig secretion. Analysis of J chain sequences in diverse species is in agreement with accepted phylogenetic relationships, with the exception of the earthworm, suggesting that the reported presence of J chain in invertebrates should be reassessed.

Cerebrovascular pressure reactivity is related to global cerebral oxygen metabolism after head injury

BACKGROUND

After head injury, impaired cerebrovascular autoregulation has been associated with abnormally high or low cerebral blood flow. The physiological relevance of cerebral blood flow levels is difficult to assess in these patients, whose cerebral metabolic rate for oxygen (CMRO(2)) is known to be abnormal. Investigation of these relations requires quantitative measures of cerebral blood flow and CMRO(2), to allow assessment of oxygen supply and demand relations.

OBJECTIVES

To investigate the relation between dysautoregulation and global cerebral oxygen metabolism following head injury.

METHODS

Using positron emission tomography, global cerebral blood flow, CMRO(2), and oxygen extraction fraction were determined in 22 patients who were investigated in 26 examinations on days 1 to 11 (mean (SD), 3.5 (2.3)) after head injury. Cerebrovascular pressure reactivity was assessed using a pressure reactivity index, calculated as the moving linear correlation coefficient between mean arterial blood pressure and intracranial pressure. Outcome was assessed six months after injury using the Glasgow outcome scale.

RESULTS

Low CMRO(2) was associated with disturbed pressure reactivity (inverse function, R(2) = 0.21, p = 0.018) and there was a correlation between disturbed pressure reactivity and oxygen extraction fraction (quadratic function, R(2) = 0.55, p = 0.0001). There was no significant relation between pressure reactivity and cerebral blood flow. An unfavourable outcome was associated with disturbed pressure reactivity. There was no significant relation between outcome and CMRO(2) or oxygen extraction fraction.

CONCLUSIONS

There is a close relation between dysautoregulation and abnormal cerebral metabolism but not blood flow. Further studies are needed to determine whether metabolic dysfunction is a result of or a cause of disturbed pressure reactivity, and to establish if there is a relation between cerebral oxygen metabolism and outcome.

Cerebral oxygen vasoreactivity and cerebral tissue oxygen reactivity

There has long been an appreciation that cerebral blood flow is modulated to ensure adequate cerebral oxygen delivery in the face of systemic hypoxaemia. There is increasing appreciation of the modulatory role of hyperoxia in the cerebral circulation and a consideration of the effects of such modulation on the maintenance of cerebral tissue oxygen concentration. These newer findings are particularly important in view of the fact that cerebrovascular and tissue oxygen responses to hyperoxia may change in disease. Such alterations provide important insights into pathophysiological mechanisms and may provide novel targets for therapy. However, before the modulatory effects of hyperoxia can be used for diagnosis, to predict prognosis or to direct therapy, a more detailed analysis and understanding of the physiological concepts behind this modulation are required, as are the limitations of the measurement tools used to define the modulation. This overview summarizes the available information in this area and suggests some avenues for further research.

Validation of a tonometric noninvasive arterial blood pressure monitor in the intensive care setting

Intra-arterial measurement is considered the gold standard for continuous, beat-to-beat arterial blood pressure monitoring. However, arterial cannulation can be difficult and may cause complications such as thrombosis and ischaemia. Recently, a tonometric system, the Colin CBM-7000 has been developed for noninvasive beat-to-beat measurement of arterial blood pressure from the radial artery. We assessed the level of agreement between the CBM-7000 and invasive radial artery measurements in 15 patients on a neuro-intensive care unit. Agreement of systolic, diastolic and mean arterial pressure values was limited, with approximately 34% of mean arterial pressures differing by over 10 mmHg. In many cases, this was due to a downward drift of the noninvasive measurements over time. Furthermore, there was a tendency to underestimate low pressures and overestimate high pressures. In our opinion, the Colin CBM-7000 cannot be recommended for continuous blood pressure monitoring in the intensive care setting.

Hyperoxia and the cerebral hemodynamic responses to moderate hyperventilation

BACKGROUND

A reduction in the arterial partial pressure of CO2 (PaCO2) leads to a rapid reduction in cerebral blood flow (CBF). However, despite continuing hypocapnia there is secondary recovery of CBF over time as a result of increases in lactic acid production. Hyperoxia is thought to modulate the production of lactic acid. This study examined the kinetics of middle cerebral artery flow velocity (MCA FV) reduction during hyperventilation, and its modulation by hyperoxia.

METHODS

Cerebral blood flow was assessed using transcranial Doppler ultrasound in nine healthy, awake human volunteers. Subjects were ventilated, via a mouthpiece, to achieve a stable end-tidal CO2 (PETCO2). After a 20-min baseline period the minute volume on the ventilator was passively increased by approximately 20% to reduce PETCO2 by 0.75-1 kPa. After a 10-min stabilization period the new PETCO2 level was maintained at a constant level for 20 min, and MCA FV recovery was measured during this 20-min period. Subjects undertook the protocol breathing air and breathing 100% oxygen.

RESULTS

The PETCO2 level was (mean +/- SD) 4.9 +/- 0.4 kPa (normoxia baseline), 4.0 +/- 0.3 kPa (normoxia hyperventilation), 4.6 +/- 0.4 kPa (hyperoxia baseline) and 3.9 +/- 0.4 kPa (hyperoxia hyperventilation). CO2 reactivity was significantly lower with normoxia than hyperoxia (16.5 +/- 3.8 vs. 21.2 +/- 4.6 % kPa-1; P< 0.05). Middle cerebral artery FV recovery was significantly more rapid with normoxia than hyperoxia (0.23 +/- 0.17 vs. 0.08 +/- 0.1 % baseline min-1; P< 0.01).

CONCLUSIONS

Our results suggest that cerebral hemodynamic responses to moderate hyperventilation are different in normoxic and hyperoxic conditions. Clinical assessment of CO2 reactivity and CBF recovery during hyperventilation should take the degree of arterial oxygenation into account.

Assessment of the Ventrix parenchymal intracranial pressure monitoring probe (NL950-P) and Monitor (NL950-100) in a 3 Tesla magnetic resonance scanner

Magnetic resonance (MR) imaging and spectroscopy provide important information in patients with acute head injury. However, optimal patient management requires intracranial pressure (ICP) monitoring. There are few reports on the use of ICP sensors in an MR environment. We tested the Ventrix parenchymal intracranial pressure monitoring probe and monitor (Integra Neurosciences, USA), modified by the use of a fibre-optic extension cable, within a 3 Tesla MR system. The device performed well in the MR environment, but one element within the fibre-optic extension was significantly ferromagnetic. The ICP probe produced a small susceptibility artefact on spin echo images, and a larger artefact on gradient echo images. The MR safety of the integrated system is probably acceptable, but could be easily improved with minor modifications. Although the system is MR compatible and produces generally acceptable imaging even at 3 Tesla, there is significant degradation of image quality during gradient echo sequences.

Continuous assessment of cerebral autoregulation: clinical and laboratory experience

The method for the continuous assessment of cerebral autoregulation using slow waves of MCA blood flow velocity (FV) and cerebral perfusion pressure (CPP) or arterial pressure (ABP) has been introduced seven years ago. We intend to review its clinical applications in various scenarios. Moving correlation coefficient (3-6 min window), named Mx, is calculated between low-pass filtered (0.05 Hz) signals of FV and CPP or ABP (when ICP is not measured directly). Data from ventilated 243 head injuries and 15 patients after poor grade subarachnoid haemorrhage, 38 patients with Carotid Artery stenosis, 35 patients with hydrocephalus and fourteen healthy volunteers is presented. Good agreement between the leg-cuff test and Mx has been confirmed in healthy volunteers (r = 0.81). Mx also correlated significantly with the static rate of autoregulation and transient hyperaemic response test. Autoregulation was disturbed (p < 0.021) by vasospasm after SAH and worse in patients with hydrocephalus in whom CSF circulation was normal (p < 0.02). In head injury, Mx indicated disturbed autoregulation with low CPP (< 55 mmHg) and too high CPP (> 95 mmHg). Mx strongly discriminated between patients with favourable and unfavourable outcome (p < 0.00002). This method can be used in many clinical scenarios for continuous monitoring of cerebral autoregulation, predicting outcome and optimising treatment strategies.

B cells develop in the zebrafish pancreas

The zebrafish, with its transparent free-living embryo, is a useful organism for investigating early stages in lymphopoiesis. Previously, we showed that T cells differentiate in the thymus by day 4, but no sites for B cell differentiation were seen until 3 weeks. We report here that on day 4, we detect rearrangements of genes encoding B cell receptors in DNA extracted from whole fish. Also by day 4, rag1 transcripts are seen in the pancreas, an organ not previously associated with lymphopoiesis; by day 10, Igmu transcripts are detected here. Thus, in zebrafish, the pancreas assumes the role of both the liver in fetal mice and the spleen in neonatal mice.

Should we measure cerebral blood flow in head-injured patients?

Inadequate cerebral blood flow (CBF) after head injury is an important cause of secondary ischaemic damage. Rapid identification of episodes of hypo- or hyperperfusion would allow timely intervention and would possibly improve outcome. Despite a large number of methods to estimate CBF, this concept is only marginally implemented in clinical practice. The methods to detect such episodes are limited for technical reasons, but also because the thresholds of ischaemia and hyperaemia are variable after head injury. Furthermore, we are not always able to manipulate CBF in a controlled manner. Accordingly, it is not surprising that attempts to compare a CBF-targeted strategy with another management option have failed to demonstrate a clear benefit. Methods need to be developed that allow either identification of thresholds for critically low or high CBF in individual patients, allow monitoring oxygen extraction fraction, representing circulatory reserve, or alternatively provide a measure of the volume of ischaemic or hyperaemic brain.

Assessment of the Caradyne WhisperFlow for administration of continuous positive airway pressure in a 3 Tesla magnetic resonance scanner

Demand for magnetic resonance investigations in critically ill patients is increasing. While these patients frequently need ventilatory support, not all of them require controlled ventilation and many may be treated with continuous positive airway pressure. Controlled ventilation, with the concurrent need for sedation, may be inappropriate when airway physiology is being studied and may retard weaning. No commercially available ventilator designed for the magnetic resonance environment can deliver high flow continuous positive airway pressure. We tested the Caradyne Whisperflow flow generator and five Whisperflow valves (2.5-15 cmH2O airway pressure) within a 3 Tesla environment for safety and possible dysfunction. All components had minimal ferromagnetic properties and tests showed no clinically relevant change in flow delivery or oxygen concentration in the magnetic field. In addition, the airway pressure generated by the valves was not affected by the magnetic field. We conclude that the tested system can be safely used in a 3 Tesla magnetic resonance environment.

Perioperative management of a child with very-long-chain acyl-coenzyme A dehydrogenase deficiency

Very-long-chain acyl-coenzyme A dehydrogenase deficiency is an inborn error of fatty acid metabolism. The clinical presentation of this disease in children is either a severe form with onset of symptoms in the first months of life, cardiomyopathy, metabolic acidosis, myopathy and a high mortality, or a less severe form manifesting mainly with hypoglycaemia. Perioperative fasting and (even emotional) stress can trigger metabolic decompensation through the altered metabolism of endogenous fatty acids resulting in hypoglycaemia, acute cardiac and hepatic dysfunction and rhabdomyolysis. We report the perioperative management of a 9-year-old boy suffering from the severe form of this disease who underwent circumcision. Metabolism was kept stable in this child by using a glucose--electrolyte infusion throughout the perioperative period to avoid the biochemical consequences of fasting and a benzodiazepine--opioid technique combined with regional anaesthesia to minimize the stress response. Considering reports about a possible interference of propofol with fatty acid oxidation and to avoid the unnecessary administration of fatty acids, propofol should not be used in these patients.

Ikaros expression as a marker for lymphoid progenitors during zebrafish development

The Ikaros gene encodes a transcription factor that, in mice, has been shown to be essential for the correct differentiation of B and T lymphocytes and is expressed in all cells of the lymphoid lineage, including pluripotent hematopoietic stem cells. During development in zebrafish, Ikaros expression begins in lateral mesoderm, and continues in the intermediate cell mass (ICM), which is derived from lateral mesoderm and has been shown to generate primitive hematopoietic precursors. Cells expressing Ikaros were then seen on the ventral side of the dorsal aorta, known to be a location of definitive hematopoietic precursors in birds and mammals. Ikaros-expressing cells were also found in the pharyngeal region, near the forming thymus. Later, such cells were seen in the pronephros, the site of hematopoiesis in adult fish. The timing of appearance of Ikaros-expressing cells suggests that, similar to other vertebrates, lymphocytes in the thymus arise from hematopoietic tissue located near the dorsal aorta or in the ICM.

Cerebral autoregulation following head injury

OBJECT

The goal of this study was to examine the relationship between cerebral autoregulation, intracranial pressure (ICP), arterial blood pressure (ABP), and cerebral perfusion pressure (CPP) after head injury by using transcranial Doppler (TCD) ultrasonography.

METHODS

Using ICP monitoring and TCD ultrasonography, the authors previously investigated whether the response of flow velocity (FV) in the middle cerebral artery to spontaneous variations in ABP or CPP provides reliable information about cerebral autoregulatory reserve. In the present study, this method was validated in 187 head-injured patients who were sedated and receiving mechanical ventilation. Waveforms of ICP, ABP, and FV were recorded over intervals lasting 20 to 120 minutes. Time-averaged mean FV and CPP were determined. The correlation coefficient index between FV and CPP (the mean index of autoregulation [Mx]) was calculated over 4-minute epochs and averaged for each investigation. The distribution of averaged mean FV values converged with the shape of the autoregulatory curve, indicating lower (CPP < 55 mm Hg) and upper (CPP > 105 mm Hg) thresholds of autoregulation. The relationship between the Mx and either the CPP or ABP was depicted as a U-shaped curve. Autoregulation was disturbed in the presence of intracranial hypertension (ICP > or = 25 mm Hg) and when mean ABP was too low (ABP < 75 mm Hg) or too high (ABP > 125 mm Hg). Disturbed autoregulation (p < 0.005) and higher ICP (p < 0.005) occurred more often in patients with unfavorable outcomes than in those with favorable outcomes.

CONCLUSIONS

Autoregulation not only is impaired when associated with a high ICP or low ABP, but it can also be disturbed by too high a CPP. The Mx can be used to guide intensive care therapy when CPP-oriented protocols are used.

Immunoglobulin variable-region diversity in the zebrafish

As part of an investigation of the immune system in the developing zebrafish, Danio rerio, we cloned and characterized a genomic V(H) segment and a number of cDNAs encoding IgM heavy chains. The genomic V(H) has the characteristic features of V(H) in other vertebrates, including a leader segment interrupted by a short intron, and regulatory and recombination signal sequences. The V(H) sequences of 75 cDNA clones fell into four distinct groups or families. All of these families cluster most closely with other teleost V(H); one of the families, V(H)3, is also closely related to other vertebrate V(H). Analysis by Southern blotting suggests that there are a number of germline genes corresponding to each family. Most variability within the V(H)1 family is confined to codons 30-32, at the end of the first framework region and in the beginning of the first complementarity-determining region. The nucleotide sequence of the genomic V(H) in this region contains motifs associated with a relatively high frequency of somatic mutation. There is much variability in segments of the clones corresponding to the third complementarity-determining region. The cDNA sequences encoding the fourth framework region are consistent with the contribution of four distinct J(H) segments.

Sequence and expression pattern of J chain in the amphibian, Xenopus laevis

We have determined the cDNA sequence encoding J chain, a polypeptide accessory molecule associated with polymeric Ig, from the anuran amphibian, Xenopus laevis (South African clawed frog). The translated polypeptide consists of 164 amino acid residues, including the signal sequence, and is somewhat longer than the corresponding sequence in mouse and cow, the two mammalian species in which the signal sequence of J chain has been determined. J chain in several mammalian species (human, mouse, cow and rabbit) has eight Cys residues. In the human chain, two of these Cys residues, the second and third in the sequence, have been shown to form disulfide bridges to heavy chains in IgM or IgA; the remaining Cys residues form intrachain disulfide bonds. The Xenopus J chain contains only seven of these Cys residues. Ser is found at the position corresponding to the third Cys in mammalian J chains. Northern blot analysis, performed on RNA isolated from various organs of 3-month old frogs, indicated that the highest level of expression was in the intestine. Transcripts corresponding to J chain were also detected in the spleen and at very low levels in the thymus.

Expression of zebrafish rag genes during early development identifies the thymus

Recent experiments have demonstrated that zebrafish is a vertebrate in which it is possible to carry out large-scale mutagenic screens to identify genes involved in specific developmental pathways. To follow development of the immune system in zebrafish, we have analyzed the expression of the recombination activating genes, rag1 and rag2, which we have previously isolated and characterized. These genes catalyze the rearrangement of immunoglobulin genes in immature B lymphocytes and of T cell receptor genes in immature T lymphocytes and are therefore appropriate markers to follow the development of organs containing these cells. By whole-mount in situ hybridization, we detected expression of both rag genes in a paired organ in the head, beginning on the fourth day after fertilization. Histological examination of this organ indicated that it corresponds to the thymus, as described for other fish, an organ that has not previously been identified in zebrafish. By histological analysis, the thymus primordium appears at 54 hr but does not enlarge significantly until 30 hr later. The thymus continues to enlarge and reaches its mature histological organization at 1 month. The pronephros, the major hematopoietic organ in the adult fish, begins to develop hematopoietic tissue about 2 weeks after fertilization. By 1 month, mature lymphocytes are distinguishable in the tissue surrounding renal tubules. Lymphocytes appear in the kidney too late for screening by whole-mount in situ hybridization; however, the pattern of rag1 expression in the thymus forms the basis of an assay for mutations affecting development of the thymus or its constituent lymphocytes.

Characterization and expression of the recombination activating genes (rag1 and rag2) of zebrafish

The closely linked recombination activating genes, rag1 and rag2, encode components of the recombinase involved in V(D)J recombination of the immunoglobulin and T-cell receptor genes. These genes are expressed together exclusively in immature lymphocytes and are useful markers for following the development of lymphoid tissues. We cloned the rag locus of the zebrafish Danio rerio and sequenced the open reading frames of the rag1 and rag2 genes. Although the gene organization is similar to that in other species, the rag1 gene is unusual in possessing two introns within the coding region. In another teleost, the rainbow trout, the rag1 gene is interrupted by a single intron. Introns are not present in the rag1 gene of any other species examined to date. Expression of both rag1 and rag2 begins late in embryonic development, on day 4, by northern RNA blot analysis. Expression of rag1 was detected in the adult zebrafish thymus, pronephros, mesonephros, and ovary. This pattern of expression is consistent with previous histological studies of adult teleosts, which implicate the kidney as the major site of hematopoiesis and the thymus as the major lymphocyte-containing organ.