Management of carpal tunnel syndrome in renal dialysis patients using an extended carpal tunnel release procedure

BACKGROUND

Chronic dialysis patients are susceptible to median nerve compression. This may be due to oedema or vascular insufficiency related to a dialysis shunt or fistula. Patients with renal failure may also develop amyloid disease. Amyloid infiltration of the synovium within the carpal canal may be a contributing factor to the nerve compression. Traditional carpal tunnel release, although simple to perform, is associated with a much higher recurrence rate in this group than in nonrenal patients. Our aim was to modify the carpal tunnel release procedure and prevent these recurrences.

METHODS

A retrospective review of 24 extended carpal tunnel decompressions in 19 dialysis patients was performed, with reference to patient records. The surgical technique is detailed and the clinical results analysed.

RESULTS

All patients noted an early and sustained improvement in symptoms; those patients with established sensory or motor signs had poorer results following surgery. There were no instances of recurrence of nerve compression during this follow-up period, range 2-6 years.

CONCLUSIONS

Carpal tunnel decompression enhances hand function and quality of life in this group.

Hedgehog and Fgf signaling pathways regulate the development of tphR-expressing serotonergic raphe neurons in zebrafish embryos

Serotonin (5HT) plays major roles in the physiological regulation of many behavioral processes, including sleep, feeding, and mood, but the genetic mechanisms by which serotonergic neurons arise during development are poorly understood. In the present study, we have investigated the development of serotonergic neurons in the zebrafish. Neurons exhibiting 5HT-immunoreactivity (5HT-IR) are detected from 45 h postfertilization (hpf) in the ventral hindbrain raphe, the hypothalamus, pineal organ, and pretectal area. Tryptophan hydroxylases encode rate-limiting enzymes that function in the synthesis of 5HT. As part of this study, we cloned and analyzed a novel zebrafish tph gene named tphR. Unlike two other zebrafish tph genes (tphD1 and tphD2), tphR is expressed in serotonergic raphe neurons, similar to tph genes in mammalian species. tphR is also expressed in the pineal organ where it is likely to be involved in the pathway leading to synthesis of melatonin. To better understand the signaling pathways involved in the induction of the serotonergic phenotype, we analyzed tphR expression and 5HT-IR in embryos in which either Hh or Fgf signals are abrogated. Hindbrain 5HT neurons are severely reduced in mutants lacking activity of either Ace/Fgf8 or the transcription factor Noi/Pax2.1, which regulates expression of ace/fgf8, and probably other genes encoding signaling proteins. Similarly, serotonergic raphe neurons are absent in embryos lacking Hh activity confirming a conserved role for Hh signals in the induction of these cells. Conversely, over-activation of the Hh pathway increases the number of serotonergic neurons. As in mammals, our results are consistent with the transcription factors Nk2.2 and Gata3 acting downstream of Hh activity in the development of serotonergic raphe neurons. Our results show that the pathways involved in induction of hindbrain serotonergic neurons are likely to be conserved in all vertebrates and help establish the zebrafish as a model system to study this important neuronal class.

The Mexican hat splint--a new splint for the treatment of closed mallet finger

A new splint for the treatment of closed mallet finger injuries is described. This is a modified aluminium-foam ('Zimmer') splint, which takes account of the skin circulation at the distal interphalangeal joint, and is specifically designed to alleviate the potential problems which can be seen with the traditional 'mallet finger' splints.

A mutation in the Gsk3-binding domain of zebrafish Masterblind/Axin1 leads to a fate transformation of telencephalon and eyes to diencephalon

Zebrafish embryos homozygous for the masterblind (mbl) mutation exhibit a striking phenotype in which the eyes and telencephalon are reduced or absent and diencephalic fates expand to the front of the brain. Here we show that mbl(-/-) embryos carry an amino-acid change at a conserved site in the Wnt pathway scaffolding protein, Axin1. The amino-acid substitution present in the mbl allele abolishes the binding of Axin to Gsk3 and affects Tcf-dependent transcription. Therefore, Gsk3 activity may be decreased in mbl(-/-) embryos and in support of this possibility, overexpression of either wild-type Axin1 or Gsk3beta can restore eye and telencephalic fates to mbl(-/-) embryos. Our data reveal a crucial role for Axin1-dependent inhibition of the Wnt pathway in the early regional subdivision of the anterior neural plate into telencephalic, diencephalic, and eye-forming territories.

Dental infections masquerading as skin lesions

Dental infection is a common cause of facial sinus; the external opening can masquerade as a variety of lesions. Surgical excision of the skin component alone fails to address the underlying problem and results in recurrence. Recognition and treatment of the underlying dental infection is required to allow the resolution of the associated skin lesion. Two illustrative cases are presented.

The nodal pathway acts upstream of hedgehog signaling to specify ventral telencephalic identity

The Nodal and Hedgehog signaling pathways influence dorsoventral patterning at all axial levels of the CNS, but it remains largely unclear how these pathways interact to mediate patterning. Here we show that, in zebrafish, Nodal signaling is required for induction of the homeobox genes nk2.1a in the ventral diencephalon and nk2.1b in the ventral telencephalon. Hedgehog signaling is also required for telencephalic nk2.1b expression but may not be essential to establish diencephalic nk2.1a expression. Furthermore, Shh does not restore ventral diencephalic development in embryos lacking Nodal activity. In contrast, Shh does restore telencephalic nk2.1b expression in the absence of Nodal activity, suggesting that Hedgehog signaling acts downstream of Nodal activity to pattern the ventral telencephalon. Thus, the Nodal pathway regulates ventral forebrain patterning through both Hedgehog signaling-dependent and -independent mechanisms.

A nodal signaling pathway regulates the laterality of neuroanatomical asymmetries in the zebrafish forebrain

Animals show behavioral asymmetries that are mediated by differences between the left and right sides of the brain. We report that the laterality of asymmetric development of the diencephalic habenular nuclei and the photoreceptive pineal complex is regulated by the Nodal signaling pathway and by midline tissue. Analysis of zebrafish embryos with compromised Nodal signaling reveals an early role for this pathway in the repression of asymmetrically expressed genes in the diencephalon. Later signaling mediated by the EGF-CFC protein One-eyed pinhead and the forkhead transcription factor Schmalspur is required to overcome this repression. When expression of Nodal pathway genes is either absent or symmetrical, neuroanatomical asymmetries are still established but are randomized. This indicates that Nodal signaling is not required for asymmetric development per se but is essential to determine the laterality of the asymmetry.

Programmed cell death in zebrafish rohon beard neurons is influenced by TrkC1/NT-3 signaling

Rohon Beard (RB) cells are embryonic primary sensory neurons that are removed by programmed cell death during larval development in zebrafish. RB somatosensory functions are taken over by neurons of the dorsal root ganglia (DRG), suggesting that RB cell death may be triggered by the differentiation of these ganglia, as has been proposed to be the case in Xenopus. However, here we show that the timing of RB cell death correlates with reduced expression of trkC1, the receptor for neurotrophin NT-3, but not with the appearance of DRG, which differentiate only after most RB cells die. trkC1 is expressed in subpopulations of RB neurons during development, and cell death is initiated only in trkC1-negative neurons, suggesting a role for TrkC1 and its ligand, NT-3, in RB cell survival. In support of this, antibodies that deplete NT-3 induce RB cell death while exogenous application of NT-3 reduces death. In addition, we show that RB cell death can be prevented using a caspase inhibitor, zVADfmk, showing that during normal development, RB cells die by a caspase-dependent programmed cell death pathway possibly triggered by reduced signaling via TrkC1.

Midline signals regulate retinal neurogenesis in zebrafish

In zebrafish, neuronal differentiation progresses across the retina in a pattern that is reminiscent of the neurogenic wave that sweeps across the developing eye in Drosophila. We show that expression of a zebrafish homolog of Drosophila atonal, ath5, sweeps across the eye predicting the wave of neuronal differentiation. By analyzing the regulation of ath5 expression, we have elucidated the mechanisms that regulate initiation and spread of neurogenesis in the retina. ath5 expression is lost in Nodal pathway mutant embryos lacking axial tissues that include the prechordal plate. A likely role for axial tissue is to induce optic stalk cells that subsequently regulate ath5 expression. Our results suggest that a series of inductive events, initiated from the prechordal plate and progressing from the optic stalks, regulates the spread of neuronal differentiation across the zebrafish retina.

Ace/Fgf8 is required for forebrain commissure formation and patterning of the telencephalon

Fibroblast growth factors (Fgfs) form a large family of secreted signalling proteins that have a wide variety of roles during embryonic development. Within the central nervous system (CNS) Fgf8 is implicated in patterning neural tissue adjacent to the midbrain-hindbrain boundary. However, the roles of Fgfs in CNS tissue rostral to the midbrain are less clear. Here we examine the patterning of the forebrain in zebrafish embryos that lack functional Fgf8/Ace. We find that Ace is required for the development of midline structures in the forebrain. In the absence of Ace activity, midline cells fail to adopt their normal morphology and exhibit altered patterns of gene expression. This disruption to midline tissue leads to severe commissural axon pathway defects, including misprojections from the eye to ectopic ipsilateral and contralateral targets. Ace is also required for the differentiation of the basal telencephalon and several populations of putative telencephalic neurons but not for overall regional patterning of forebrain derivatives. Finally, we show that ace expression co-localises with anterior neural plate cells that have previously been shown to have forebrain patterning activity. Removal of these cells leads to a failure in induction of ace expression indicating that loss of Ace activity may contribute to the phenotypes observed when anterior neural plate cells are ablated. However, as ace mutant neural plate cells still retain at least some inductive activity, then other signals must also be produced by the anterior margin of the neural plate.

Silberblick/Wnt11 mediates convergent extension movements during zebrafish gastrulation

Vertebrate gastrulation involves the specification and coordinated movement of large populations of cells that give rise to the ectodermal, mesodermal and endodermal germ layers. Although many of the genes involved in the specification of cell identity during this process have been identified, little is known of the genes that coordinate cell movement. Here we show that the zebrafish silberblick (slb) locus encodes Wnt11 and that Slb/Wnt11 activity is required for cells to undergo correct convergent extension movements during gastrulation. In the absence of Slb/Wnt11 function, abnormal extension of axial tissue results in cyclopia and other midline defects in the head. The requirement for Slb/Wnt11 is cell non-autonomous, and our results indicate that the correct extension of axial tissue is at least partly dependent on medio-lateral cell intercalation in paraxial tissue. We also show that the slb phenotype is rescued by a truncated form of Dishevelled that does not signal through the canonical Wnt pathway, suggesting that, as in flies, Wnt signalling might mediate morphogenetic events through a divergent signal transduction cascade. Our results provide genetic and experimental evidence that Wnt activity in lateral tissues has a crucial role in driving the convergent extension movements underlying vertebrate gastrulation.

Toward optimal classifier system performance in non-Markov environments

Wilson's (1994) bit-register memory scheme was incorporated into the XCS classifier system and investigated in a series of non-Markov environments. Two extensions to the scheme were important in obtaining near-optimal performance in the harder environments. The first was an exploration strategy in which exploration of external actions was probabilistic as in Markov environments, but internal "actions" (register settings) were selected deterministically. The second was use of a register having more bit-positions than were strictly necessary to resolve environmental aliasing. The origins and effects of the two extensions are discussed.

Bmp activity establishes a gradient of positional information throughout the entire neural plate

Bone morphogenetic proteins (Bmps) are key regulators of dorsoventral (DV) patterning. Within the ectoderm, Bmp activity has been shown to inhibit neural development, promote epidermal differentiation and influence the specification of dorsal neurons and neural crest. In this study, we examine the patterning of neural tissue in mutant zebrafish embryos with compromised Bmp signalling activity. We find that although Bmp activity does not influence anteroposterior (AP) patterning, it does affect DV patterning at all AP levels of the neural plate. Thus, we show that Bmp activity is required for specification of cell fates around the margin of the entire neural plate, including forebrain regions that do not form neural crest. Surprisingly, we find that Bmp activity is also required for patterning neurons at all DV levels of the CNS. In swirl/bmp2b(−) (swr(−)) embryos, laterally positioned sensory neurons are absent whereas more medial interneuron populations are hugely expanded. However, in somitabun(−) (sbn(−)) embryos, which probably retain higher residual Bmp activity, it is the sensory neurons and not the interneurons that are expanded. Conversely, in severely Bmp depleted embryos, both interneurons and sensory neurons are absent and it is the most medial neurons that are expanded. These results are consistent with there being a gradient of Bmp-dependent positional information extending throughout the entire neural and non-neural ectoderm.

Development of noradrenergic neurons in the zebrafish hindbrain requires BMP, FGF8, and the homeodomain protein soulless/Phox2a

We report that the zebrafish mutation soulless, in which the development of locus coeruleus (LC) noradrenergic (NA) neurons failed to occur, disrupts the homeodomain protein Phox2a. Phox2a is not only necessary but also sufficient to induce Phox2b+ dopamine-beta-hydroxylase+ and tyrosine hydroxylase+ NA neurons in ectopic locations. Phox2a is first detected in LC progenitors in the dorsal anterior hindbrain, and its expression there is dependent on FGF8 from the mid/hindbrain boundary and on optimal concentrations of BMP signal from the epidermal ectoderm/future dorsal neural plate junction. These findings suggest that Phox2a coordinates the specification of LC in part through the induction of Phox2b and in response to cooperating signals that operate along the mediolateral and anteroposterior axes of the neural plate.

A role for the extraembryonic yolk syncytial layer in patterning the zebrafish embryo suggested by properties of the hex gene

Recent studies in mouse suggest that the extraembryonic endoderm has an important role in early embryonic patterning [1]. To analyze whether similar mechanisms operate in other vertebrates, we cloned the zebrafish homologue of Hex, a homeobox gene that is expressed asymmetrically in the mouse visceral endoderm [2]. Early expression of zebrafish hex is restricted to the dorsal portion of the yolk syncytial layer (YSL), an extraembryonic tissue. By the onset of gastrulation, hex is expressed in the entire dorsal half of the YSL, which directly underlies the cells fated to form the neural plate. We show that hex expression is initially regulated by the maternal Wnt pathway and later by a Bmp-mediated pathway. Overexpression experiments of wild-type and chimeric Hex constructs indicate that Hex functions as a transcriptional repressor and its overexpression led to the downregulation of bmp2b and wnt8 expression and the expansion of chordin expression. These findings provide further evidence that the zebrafish YSL is the functional equivalent of the mouse visceral endoderm and that extraembryonic structures may regulate early embryonic patterning in many vertebrates.

The surgical treatment of drooling in Leicester: 12 years experience

The experience of the surgical treatment of drooling in the 12-year period 1985-1997 has been retrospectively reviewed. Details of 71 out of a total of 79 patients were available. Of these, 69% underwent bilateral submandibular duct diversion and unilateral parotid duct ligation. Excellent or good control of drooling was obtained in 65 patients (92%) which compares favourably with other series. A ranula occurred in 10% and settled spontaneously. Transient airway obstruction occurred in one patient.

Zebrafish aussicht mutant embryos exhibit widespread overexpression of ace (fgf8) and coincident defects in CNS development

During the development of the zebrafish nervous system both noi, a zebrafish pax2 homolog, and ace, a zebrafish fgf8 homolog, are required for development of the midbrain and cerebellum. Here we describe a dominant mutation, aussicht (aus), in which the expression of noi and ace is upregulated. In aus mutant embryos, ace is upregulated at many sites in the embryo, while noi expression is only upregulated in regions of the forebrain and midbrain which also express ace. Subsequent to the alterations in noi and ace expression, aus mutants exhibit defects in the differentiation of the forebrain, midbrain and eyes. Within the forebrain, the formation of the anterior and postoptic commissures is delayed and the expression of markers within the pretectal area is reduced. Within the midbrain, En and wnt1 expression is expanded. In heterozygous aus embryos, there is ectopic outgrowth of neural retina in the temporal half of the eyes, whereas in putative homozygous aus embryos, the ventral retina is reduced and the pigmented retinal epithelium is expanded towards the midline. The observation that aus mutant embryos exhibit widespread upregulation of ace raised the possibility that aus might represent an allele of the ace gene itself. However, by crossing carriers for both aus and ace, we were able to generate homozygous ace mutant embryos that also exhibited the aus phenotype. This indicated that aus is not tightly linked to ace and is unlikely to be a mutation directly affecting the ace locus. However, increased Ace activity may underly many aspects of the aus phenotype and we show that the upregulation of noi in the forebrain of aus mutants is partially dependent upon functional Ace activity. Conversely, increased ace expression in the forebrain of aus mutants is not dependent upon functional Noi activity. We conclude that aus represents a mutation involving a locus normally required for the regulation of ace expression during embryogenesis.

Mutations in the zebrafish unmask shared regulatory pathways controlling the development of catecholaminergic neurons

The mechanism by which pluripotent progenitors give rise to distinct classes of mature neurons in vertebrates is not well understood. To address this issue we undertook a genetic screen for mutations which affect the commitment and differentiation of catecholaminergic (CA) [dopaminergic (DA), noradrenergic (NA), and adrenergic] neurons in the zebrafish, Danio rerio. The identified mutations constitute five complementation groups. motionless and foggy affect the number and differentiation state of hypothalamic DA, telencephalic DA, retinal DA, locus coeruleus (LC) NA, and sympathetic NA neurons. The too few mutation leads to a specific reduction in the number of hypothalamic DA neurons. no soul lacks arch-associated NA cells and has defects in pharyngeal arches, and soulless lacks both arch-associated and LC cell groups. Our analyses suggest that the genes defined by these mutations regulate different steps in the differentiation of multipotent CA progenitors. They further reveal an underlying universal mechanism for the control of CA cell fates, which involve combinatorial usage of regulatory genes.

Isolation, expression and regulation of a zebrafish paraxis homologue

The formation of somites involves the subdivision of segmented presomitic mesoderm into segmentally arranged somite blocks. In mice and chicks, the basic-helix-loop-helix (bHLH) gene, paraxis, is involved in this process. Here, we report the isolation of a zebrafish homologue of paraxis, par1. par1 is expressed in presomitic paraxial mesoderm from late gastrula stages, and expression is maintained in ventrolateral cells after somite formation. In spt- embryos, par1 expression is both delayed and severely reduced whereas in flh- embryos, ectopic transcripts are detected in axial mesoderm. Spatial regulation of par1 expression within the somites is affected in several mutants with defects in axial midline tissues.

A small population of anterior cells patterns the forebrain during zebrafish gastrulation

During gastrulation in vertebrates, dorsal ectoderm is induced to form neural tissue that later gives rise to the brain and spinal cord. This induction depends on signals arising from a group of cells on the dorsal side of the gastrula. This group of cells constitutes the organizer. It is thought that the organizer initially induces neural tissue with anterior, or forebrain, character, and that other signals subsequently posteriorize neural tissue in the trunk. Here we show that development of the anterior central nervous system of the zebrafish embryo also depends on a small group of ectodermal cells located in the prospective head region. Removal of these ectodermal cells during gastrulation perturbs subsequent neural patterning and results in widespread cell death. Transplantation of these cells shows that they can induce forebrain-specific gene expression in more posterior regions of the neural plate. Our results indicate that an early step in neural patterning is the establishment of a small population of signalling cells within the most anterior region of the embryo. These cells are required for patterning and survival of the anterior brain.

Analysis of axon tract formation in the zebrafish brain: the role of territories of gene expression and their boundaries

Mutant analysis in the zebrafish is revealing the genes that are expressed in the early neuroepithelium and that regulate factors responsible for the guidance of commissural axons. We review work on the developing zebrafish brain illustrating the way in which territories of regulatory gene expression influence the formation and positioning of axon pathways.

Anf: a novel class of vertebrate homeobox genes expressed at the anterior end of the main embryonic axis

Five novel genes homologous to the homeobox-containing genes Xanf-1 and Xanf-2 of Xenopus and Hesx-1/Rpx of mouse have been identified as a result of a PCR survey of cDNA in sturgeon, zebrafish, newt, chicken and human. Comparative analysis of the homeodomain primary structure of these genes revealed that they belong to a novel class of homeobox genes, which we name Anf. All genes of this class investigated so far have similar patterns of expression during early embryogenesis, characterized by maximal transcript levels being present at the anterior extremity of the main embryonic body axis. The data obtained also suggest that, despite considerable high structural divergence between their homeodomains, all known Anf genes may be orthologues, and thus represent one of the most quickly evolving classes of vertebrate homeobox genes.

The Pax protein Noi is required for commissural axon pathway formation in the rostral forebrain

No-isthmus (Noi) is a member of the zebrafish Pax family of transcriptional regulators that is expressed in restricted domains of the developing CNS. In the developing eye and optic nerve, the Noi+ cells are primitive glial cells that line the choroid fissure and optic stalk/nerve to its junction with the optic tract. This pattern of Noi expression is retained in the adult, defining the optic nerve astroglia, which wrap the left and right nerves separately at the midline, thus forming the bodily crossed optic chiasm found in fish. In embryos carrying mutations in the noi gene, the choroid fissure fails to close, glial cells of the optic nerve fail to differentiate and optic axons exhibit abnormal trajectories exiting the eye and at the midline of the diencephalon. Optic axons select inappropriate pathways into the contralateral optic nerve, rostrally towards the anterior commissure and along the ipsilateral optic tract. Noi+ cells also border the pathway of axons in the postoptic commissure, which is located adjacent to the optic chiasm. These postoptic commissural axons are defasciculated and also exhibit pathfinding defects in noi- embryos. These results indicate that Noi is required in cells that line the pathways taken by optic and non-optic commissural axons for guidance across the midline of the diencephalon. We find that expression of two members of the Netrin family of axon guidance molecules and the signalling protein Sonic hedgehog is disturbed in noi- embryos, whereas several members of the Eph family of receptors and ligands show no obvious alterations in expression at the diencephalic midline.

The zebrafish homologue of the ret receptor and its pattern of expression during embryogenesis

The c-ret proto-oncogene, a member of the receptor tyrosine kinase gene superfamily, plays a critical role in the development of the excretory system and the enteric and autonomic nervous systems of mammalian embryos. To study the potential function of the c-ret locus in lower vertebrates, we have isolated its zebrafish homologue, ret1 and established its expression pattern during embryogenesis. Ret1 mRNA first appears during early somitogenesis in the presumptive brain, spinal cord and excretory system. Within the CNS, expression of ret1 is detected in primary motor and sensory (Rohon-Beard) neurons. Ret1 transcripts are also expressed in subsets of neural crest cells and cranial ganglia as well as in the enteric nervous system. In the excretory system, expression is detected in the developing nephric duct and the pronephros. Our findings reveal a remarkable similarity in the expression pattern of c-ret between higher and lower vertebrates, suggesting that the function of this locus has been conserved throughout vertebrate evolution. Furthermore, the conservation of ret1 expression in cell types which remain unaffected by the mammalian c-ret mutations, such as motor and sensory neurons, suggests a function of this receptor in these cell lineages.

floating head and masterblind regulate neuronal patterning in the roof of the forebrain

The epiphysial region of the dorsal diencephalon is the first site at which neurogenesis occurs in the roof of the zebrafish forebrain. We show that the homeobox containing gene floating head (flh) is required for neurogenesis to proceed in the epiphysis. In flh- embryos, the first few epiphysial neurons are generated, but beyond the 18 somite stage, neuronal production ceases. In contrast, in masterblind- (mbl-) embryos, epiphysial neurons are generated throughout the dorsal forebrain. We show that mbl is required to prevent the expression of flh in dorsal forebrain cells rostral to the epiphysis. Furthermore, epiphysial neurons are not ectopically induced in mbl-/flh- embryos, demonstrating that the epiphysial phenotype of mbl- embryos is mediated by ectopic Flh activity. We propose a role for Flh in linking the signaling pathways that regulate regional patterning to the signaling pathways that regulate neurogenesis.

Controlled reperfusion of cardiac grafts from non-heart-beating donors

BACKGROUND

Hearts harvested from non-heart-beating donors sustain severe injury during procurement and implantation, mandating interventions to preserve their function. We tested the hypothesis that limiting oxygen delivery during initial reperfusion of such hearts would reduce free-radical injury.

METHODS

Rabbits sustained hypoxic arrest after ventilatory withdrawal, followed by 20 minutes of in vivo ischemia. Hearts were excised and reperfused with blood under conditions of high arterial oxygen tension (PaO2) (approximately 400 mm Hg), low PaO2 (approximately 60 to 70 mm Hg), high pressure (80 mm Hg), and low pressure (40 mm Hg), with or without free-radical scavenger infusion. Non-heart-beating donor groups were defined by the initial reperfusion conditions: high PaO2/ high pressure (n = 8), low PaO2/high pressure (n = 7), high PaO2/low pressure (n = 8), low PaO2/low pressure (n = 7), and high PaO2/high pressure/free-radical scavenger infusion (n = 7).

RESULTS

After 45 minutes of reperfusion, low PaO2/ high pressure and high PaO2/low pressure had a significantly higher left ventricular developed pressure (63.6 +/- 5.6 and 63.1 +/- 5.6 mm Hg, respectively) than high PaO2/high pressure (40.9 +/- 4.5 mm Hg; p < 0.0000001 versus both). However, high PaO2/high pressure/free-radical scavenger infusion displayed only a trend toward improved ventricular recovery compared with high PaO2/ high pressure.

CONCLUSIONS

Initially reperfusing nonbeating cardiac grafts at low PaO2 or low pressure improves recovery, but may involve mechanisms other than decreased free-radical injury.

Non-heart-beating donors: a model of thoracic allograft injury

4ACKGROUND. Non-heart-beating donors (NHBDs) have been proposed for the critical shortage of donors for cardiac and pulmonary transplantation. We determined the effects of prearrest hypoxia and postarrest warm ischemia on cardiac and pulmonary allografts procured from NHBDs undergoing hypoxic arrest. METHODS. Rabbit hearts and lungs were procured from separate donors and placed on isolated blood perfusion circuits. Controls were excised and perfused without ischemia. Heart from NHBDs underwent either prearrest hypoxic perfusion alone or consecutive periods of prearrest hypoxic perfusion and 20 minutes of postarrest warm ischemia. A third group of hearts underwent 30 minutes of warm, global ischemia alone. Two groups of pulmonary allografts were studied using similar hypoxic perfusion/20-minute ischemia and 30-minute ischemia donors. RESULTS. Prearrest hypoxic perfusion clearly causes significant dysfunction of cardiac allografts from NHBDs compared with nonischemic controls. Prearrest hypoxic perfusion combined with postarrest ischemia results in an additive degree of dysfunction more severe than a similar period of warm ischemia alone. Both groups of experimental lungs displayed function similar to that of nonischemic controls in terms of pulmonary hemodynamics, airway resistance, and oxygenation potential. CONCLUSIONS. We conclude that prearrest hypoxic perfusion significantly contributes to the dysfunction of NHBD cardiac allografts. Pulmonary allografts may be more amenable to procurement of NHBDs.

Comparison of total resistive work of breathing in two generations of ventilators in an animal model

Spontaneous breathing through an endotracheal tube and ventilator circuit is associated with an increased work of breathing (WOB). Recently, pediatric ventilators have introduced improved features to optimize patient-ventilator interactions. We performed an experiment utilizing an animal model to compare total resistive WOB of two widely used ventilators, the Siemens Servo Ventilator 300 (SV300) with patient-optimized features, such as flow-triggering and rapid response time, and the Siemens 900C (S900C) without those features. A total of 120 experiments of 10 minutes duration each were performed in 6 anesthetized, intubated lambs. In each experiment, the animal was randomized to either pressure support ventilation (PSV) of 5 cm H2O, or continuous positive airway pressure (CPAP) with 0 cmH2O end expiratory pressure (ZEEP) while supported by the SV300 or the S900C. Each animal was used as its own control. WOB was measured with a Bicore monitoring device as WOB of the animal (WOBp), WOB of the ventilator (WOBv), and the pressure time product (PTP) for each breath during the experiment. Oxygen consumption (Vo2) of the animal was measured using breath-by-breath gas analysis with a customized metabolic monitoring system. A Wilcoxon signed rank sum test was used for analysis. All comparisons between the ventilators for both CPAP and PSV showed a statistically significant difference (p < 0.001). WOBp was reduced by 47% during pressure support ventilation (PSV) and by 47% during CPAP when the SV300 was used compared to the S900C. We conclude that WOB is significantly lower in animals ventilated with the SV300 than with the S900C ventilator, and we speculate that ventilators with the features of the SV300 may offer advantages in ventilating pediatric patients.

Antibodies against Pax6 immunostain amacrine and ganglion cells and neuronal progenitors, but not rod precursors, in the normal and regenerating retina of the goldfish

Pax6 is a developmental regulatory gene that plays a key role in the development of the embryonic brain, eye, and retina. This gene is also expressed in discrete groups of neurons within the adult brain. In this study, antibodies raised against a fusion protein from a zebra fish pax6 cDNA were used to investigate the expression of the pax6 gene in the mature, growing, and regenerating retina of the goldfish. On western blots of retinal proteins, the pax6 antibodies recognize a single band at the approximate size of the zebra fish pax6 protein. In retinal sections, the antibodies label the nuclei of mature amacrine and some ganglion cells. At the retinal margin, where neurogenesis and cellular differentiation continually occur in goldfish, the antibodies label neuronal progenitors and the newly postmitotic neurons. Following injury and during neuronal regeneration, the antibodies label mitotically active progenitors of regenerating neurons. Rod precursors, proliferating cells that normally give rise solely to rod photoreceptors and are the presumed antecedents of the injury-stimulated neuronal progenitors, are not immunostained by antibodies to the pax6 protein. The results of this study document the identity of pax6-expressing cells in the mature retina and demonstrate that in the goldfish pax6 is expressed in neuronal progenitors during both retinal growth and regeneration.

Pax proteins and eye development

Homologous members of the Pax gene family are required for eye development in Drosophila and vertebrates. Despite superficial similarities in the phenotypes of vertebrates with mutations in pax-6 and Drosophila eyeless mutants, it remains uncertain whether the two proteins encoded by these genes have comparable functions. The genetic cascade triggered by eyeless leads to eye formation, whereas pax-6 is not necessary for optic vesicle formation, but is required at other stages of eye development. A second vertebrate Pax gene, pax-2, is also required during eye development and appears to play a role during closure of the choroid fissure.

Midline signalling is required for Pax gene regulation and patterning of the eyes

Pax6 and Pax2 are members of the Pax family of transcription factors that are both expressed in the developing visual system of zebrafish embryos. Pax6 protein is present in all cells that form the neural retina and pigment epithelium, whereas Pax2 is located primarily in cells that will give rise to the optic stalk. In this study, we have addressed the role of midline signalling in the regulation of Pax2 and Pax6 distributions and in the subsequent morphogenesis of the eyes. Midline signalling is severely perturbed in cyclops mutant embryos resulting in an absence of ventral midline CNS tissue and fusion of the eyes. Mutant embryos ectopically express Pax6 in a bridge of tissue around the anterior pole of the neural keel in the position normally occupied by cells that form the optic stalks. In contrast, Pax2 protein is almost completely absent from this region in mutant embryos. Concommitant with the changes in Pax protein distribution, cells in the position of the optic stalks differentiate as retina. These results suggest that a signal emanating from the midline, which is absent in cyclops mutant embryos, may be required to promote Pax2 and inhibit Pax6 expression in cells destined to form the optic stalks. Sonic hedgehog (Shh also known as Vhh-1 and Hhg-1) is a midline signalling molecule that is absent from the neuroepithelium of cyclops mutant embryos at early developmental stages. To test the possibility that Shh might be able to regulate the spatial expression of Pax6 and Pax2 in the optic primordia, it was overexpressed in the developing CNS. The number of cells containing Pax2 was increased following shh overexpression and embryos developed hypertrophied optic stalk-like structures. Complimentary to the changes in Pax2 distribution, there were fewer Pax6-containing cells and pigment epithelium and neural retina were reduced. Our results suggest that Shh or a closely related signalling molecule emanating from midline tissue in the ventral forebrain either directly or indirectly induces the expression of Pax2 and inhibits the expression of Pax6 and thus may regulate the partitioning of the optic primordia into optic stalks and retinal tissue.

Expression of zebrafish GATA 3 (gta3) during gastrulation and neurulation suggests a role in the specification of cell fate

In order to understand the role of the transcription factor GATA 3 in vertebrate development, we have examined its expression and some aspects of its regulation during gastrulation and neurulation in the zebrafish. The complete coding sequence of the cDNA encoding the zebrafish GATA 3 homologue, termed gta3, is described. Analysis of expression patterns by in situ hybridisation shows the gene to be expressed during gastrulation in the ventral region of the embryo which includes tissue fated to form the non-neural ectoderm. By the end of gastrulation, there is a clear border to the gta3 expression domain that is close to the edge of the neural plate. Subsequently, gta3 expresses in the pronephric duct and in defined regions of the central nervous system which include specific cells in each segment of the spinal cord and nuclei in the brain. Double labelling embryos with a probe for gta3 and antibodies which identify differentiated neurons suggest that gta3 is dynamically expressed during the early differentiation phase of a subset of neurons but not in the terminal phase. Analysis of gta3 expression in dorsalised embryos and in cyc and spt mutant embryos indicates that the neural expression of the gene is subject to control by signals from the mesoderm, including both the notochord and the somites, which influence the segmental organisation of expression in the spinal cord.

Expression of zebrafish nk2.2 is influenced by sonic hedgehog/vertebrate hedgehog-1 and demarcates a zone of neuronal differentiation in the embryonic forebrain

We have isolated zebrafish nk2.2, a member of the Nk-2 family of homeobox genes. nk2.2 is expressed in a continuous narrow band of cells along a boundary zone demarcating the location at which two of the earliest nuclei in the brain differentiate. This band of cells is located within a few cell diameters of cells expressing the signalling molecule sonic hedgehog/vertebrate hedgehog-1 (shh/vhh-1). Injection of shh/vhh-1 RNA results in ectopic expression of nk2.2 and concomitant abnormalities in the forebrain and eyes. Moreover, cyclops mutant embryos, which initially lack neurectodermal expression of shh/vhh-1, show a concomitant lack of nk2.2 expression. Together, these results suggest a requirement of shh/vhh-1 protein for the spatial regulation of nk2.2 expression.

Regulatory gene expression boundaries demarcate sites of neuronal differentiation in the embryonic zebrafish forebrain

During development of the zebrafish forebrain, a simple scaffold of axon pathways is pioneered by a small number of neurons. We show that boundaries of expression domains of members of the eph, forkhead, pax, and wnt gene families correlate with the positions at which these neurons differentiate and extend axons. Analysis of genetically or experimentally altered forebrains indicates that if a boundary is maintained, there is appropriate neural differentiation with respect to the boundary. Conversely, in the absence of a boundary, there is concomitant disruption of neural patterning. We also show that a strip of cells within the dorsal diencephalon shares features with ventral midline cells. This strip of cells fails to develop in mutant fish in which specification of the ventral CNS is disrupted, suggesting that its development may be regulated by the same inductive pathways that pattern the ventral midline.

Spatially regulated expression of three receptor tyrosine kinase genes during gastrulation in the zebrafish

We describe the isolation and early developmental expression of three novel zebrafish genes (rtk1-3) that encode members of the eph family of receptor tyrosine kinases. At the onset of gastrulation, rtk1 is expressed in the shield region corresponding to the future dorsal side of the embryo. As gastrulation proceeds, both rtk1 and rtk2 are expressed within the axial hypoblast along the entire axis of the embryo. After the gastrula stage is complete, expression of both genes is maintained in precursor cells of the notochord in the tail bud but is downregulated in other regions of the axial hypoblast, rtk3 is expressed in anterior axial hypoblast including the ‘pillow’ at the anterior tip of the hypoblast and in paraxial tissue in posterior regions of the embryo. We show that the precise spatial regulation of expression of rtk genes, ntl and goosecoid along the anteroposterior axis is maintained in embryos that have no dorsoventral axis. This indicates that the mechanisms that regulate gene expression along the anteroposterior and dorsoventral axes of the hypoblast may be independent.

Border disputes: do boundaries play a role in growth-cone guidance?

One of the earliest indications of regional patterning in the CNS is the spatially restricted expression of regulatory genes within the neuroepithelium. Many of these genes encode transcription factors and, although little is known of their downstream targets, it seems likely that they control the identity of cells in different regions of the CNS. This review discusses how the expression of these patterning genes might influence the location at which the first axon pathways in the CNS are pioneered. Evidence is described that suggests that the boundary regions between adjacent domains of regulatory gene expression influence where the first axons will extend.

Axonal trajectories and distribution of GABAergic spinal neurons in wildtype and mutant zebrafish lacking floor plate cells

The role of the midline floor plate cells in the neuronal differentiation of the spinal cord was examined by comparing putative GABAergic neurons in wildtype zebrafish embryos with those in cyc-1 mutant embryos. The mutation produces a pleiotropic recessive lethal phenotype and is severe in rostral brain regions, but its direct effect in the caudal hindbrain and the spinal cord is apparently restricted to the depletion of the midline floor plate cells. In wildtype embryos, an antibody against the neurotransmitter GABA labeled the cell bodies, axons, and growth cones of three classes of previously identified neurons; dorsal longitudinal neurons (DoLA), commissural secondary ascending neurons (CoSA), and ventral longitudinal neurons (VeLD). A novel ventral cell type, Kolmer-Agduhr (KA) neurons, was also labeled. In the cyc-1 mutant, abnormalities were observed in some, but not all, of the GABAreactive CoSA, VeLD, and KA axons, while the axonal trajectories of DoLA neurons were not affected. Furthermore, the number of KA cells was reduced in the mutant while the numbers of the other GABAreactive cells were unperturbed. These observations corroborate our earlier hypothesis that the floor plate cells are one of several guidance cues that direct axonal outgrowth near the ventral midline of the spinal cord. They also suggest that the floor plate cells may play a role in the cellular differentiation of the spinal cord of zebrafish embryos.

Zebrafish pax[b] is involved in the formation of the midbrain-hindbrain boundary

Among the genes thought to be involved in patterning the nervous system are a family of developmentally regulated paired box-containing (Pax) genes. Mutations in some of these Pax genes lead to severe developmental abnormalities. Zebrafish pax[b](pax[zf-b]) is a member of the Pax gene family that is expressed in the presumptive posterior midbrain from the end of gastrulation and, at later stages, in other localized regions of the developing embryo. Here we show that injection of antibodies raised against the pax[b] protein causes a localized malformation at the midbrain-hindbrain boundary. In situ hybridizations demonstrate that antibody injection causes downregulation of pax[b] transcripts in the posterior midbrain and alteration of wnt-1 and eng-2 expression in this area. The data demonstrate an involvement of pax[b] in the formation of the midbrain-hindbrain junction.

Acquisition of regional and cellular identities in the developing zebrafish nervous system

In the past year, several new techniques have been used with great success in the study of nervous system development in the zebrafish. Perhaps the most exciting results have come from experiments in which single identified cells or small groups of cells have been transplanted between embryos in order to examine cell determination and the site of action of genetic mutations.