Independent regulatory elements in the nestin gene direct transgene expression to neural stem cells or muscle precursors

Changes in intermediate filament gene expression occur at key steps in the differentiation of cell types in the mammalian CNS. Neuroepithelial stem cells express the intermediate filament protein nestin and down-regulate it sharply at the transition from proliferating stem cell to postmitotic neuron. Nestin is also expressed in muscle precursors but not in mature muscle cells. We show here that in transgenic mice, independent cell type-specific elements in the first and second introns of the nestin gene consistently direct reporter gene expression to developing muscle and neural precursors, respectively. The second intron contains an enhancer that functions in CNS stem cells, suggesting that there may be a single transcriptional mechanism regulating the CNS stem cell state. This enhancer is much less active in the PNS. The identification of these elements facilitates analysis of mechanisms controlling the switch in gene expression that occurs when muscle and brain precursors terminally differentiate.

Immortalized stem cells from the central nervous system

A remarkable feature of the early development of the mammalian central nervous system (CNS) is the precise and rapid generation of large numbers of many different neuronal types [1]. We have identified the major neuronal precursor cell and shown that this cell can be immortalized by oncogenes. The immortal precursor cell can be grown in culture and can differentiate when transplanted into the developing brain. The implanted neurons are integrated into the synaptic circuitry of the host brain. These results suggest that implanting cultured precursor cells will provide a powerful strategy to uncover the signals that control the differentiation of this multipotential cell into the many cell types of the adult brain.

Left ventricular transvenous electrode dislodgement after Mustard repair for transposition of the great arteries

An 11-year-old girl who underwent Mustard's operation for complete transposition of the great arteries in infancy, developed Mobitz type II second-degree AV block 8 1/2 years later. A transvenous, active fixation left ventricular lead was inserted and connected to a rate responsive pacemaker. Two years later the lead dislodged due to the child's growth. A new active fixation electrode was positioned in the left ventricle below the pulmonary valve, leaving an electrode loop in the ventricle. Such an approach may prevent lead dislodgement due to growth after intraatrial repair for transposition of the great arteries, but regular radiological or echocardiographic follow-up of lead position is recommended in these patients.

Aerosol penetration and leakage characteristics of masks used in the health care industry

BACKGROUND

Historically, surgical masks have been worn to protect patients from being infected by large, pathogen-containing aerosol droplets emitted by health care personnel. Today, emphasis has shifted from solely protecting the patient to protecting the health care worker as well. As a result of new procedures used in operating rooms and clinical areas, aerosolized hazardous agents in the submicrometer size range are being produced, posing a potential threat to health care workers.

METHODS

Eight surgical masks were tested for aerosol particle penetration through their filter media and through induced face-seal leaks.

RESULTS

The percentage of filter penetration ranged from 20% to nearly 100% for submicrometer-sized particles. In comparison, a dust-mist-fume respirator used in industrial settings had significantly less penetration through its filter medium. When the surgical masks had artificially induced face-seal leaks, the concentration of submicrometer-sized particles inside the mask increased slightly; in contrast, the more protective dust-mist-fume respirator showed a fourfold increase in aerosol penetration into the mask with an artificial leak 4 mm in diameter.

CONCLUSION

We conclude that the protection provided by surgical masks may be insufficient in environments containing potentially hazardous submicrometer-sized aerosols.

Cavopulmonary connection in repair of atrioventricular septal defect with small right ventricle

Between February 1991 and May 1992, 9 patients with a nonrestrictive inlet ventricular septal defect or complete atrioventricular septal defect and hypoplasia of the right ventricle underwent successful two-ventricle correction incorporating a bidirectional cavopulmonary anastomosis. Despite a satisfactory early postoperative course, large serous pleural effusions developed in 5 of them between 2 and 6 weeks after operation. Serial echocardiography showed an evolution of flow patterns in the superior vena cava from marked systolic reversal immediately after operation to nearly continuous forward flow into both pulmonary arteries about 6 weeks later. This pattern was consistent with the transition from cardiac-dependent to respiratory-dependent caval flow. The development of pleural effusions appeared to coincide with the loss of systolic caval flow reversal and resolved after establishment of a predominantly respiratory-dependent flow pattern.

Primary repair and autotransplantation of cardiac valves

The aortic valve is a beautifully designed and balanced structure with precise opening and closing mechanisms. Its design probably cannot be improved upon by man-made mechanical devices, no matter how ingenious. It is logical to use human valves as replacements because of their superior structural configuration. Their chief difficulties are in the troubles of the learning curve of the surgeon to achieve a competent mechanism and the hazard of infection. The pulmonary autograft or translocation of the pulmonary valve to the aortic position offers many advantages, and the long-term results are good. Conservative repair and reconstruction of the aortic valve are increasing in popularity but have a relatively limited application. The mitral valve has a less precise and more adjustable type of mechanism and generous leaflet coaptation. These features make it more amenable to repair, as demonstrated in the clinical series of the technique. Repair is clearly preferable to replacement at present. The tricuspid valve is eminently suitable for reconstruction, but late results are not very good. The disappointing outcome, however, reflects more the severity of underlying cardiac pathology than the effectiveness of the repair.

Percutaneous balloon pericardiotomy for the treatment of cardiac tamponade and large pericardial effusions: description of technique and report of the first 50 cases

OBJECTIVES

This study describes the technique, clinical characteristics and results of the first 50 patients undergoing percutaneous balloon pericardiotomy as part of a multicenter registry.

BACKGROUND

Percutaneous balloon pericardiotomy involves the use of a percutaneous balloon dilating catheter to create a nonsurgical pericardial window.

METHODS

Patients eligible for percutaneous balloon pericardiotomy had either cardiac tamponade (n = 36) or a moderate to large pericardial effusion (n = 14). In addition to clinical follow-up, serial echocardiograms and chest X-ray films were obtained.

RESULTS

The procedure was considered successful in 46 patients after a mean follow-up period of 3.6 +/- 3.3 months. Two patients required an early operation, one for bleeding from a pericardial vessel and one for persistent pericardial catheter drainage. Two patients required a late operation for recurrent tamponade. Minor complications of the procedure included fever in 6 of the first 37 patients (studied before the prophylactic use of antibiotic agents), thoracentesis or chest tube placement in 8 and a small spontaneously resolving pneumothorax in 2. Despite the short-term success of this procedure, the long-term prognosis of the 44 patients with malignant pericardial disease remained poor (mean survival time 3.3 +/- 3.1 months).

CONCLUSIONS

Percutaneous balloon pericardiotomy is successful in helping to manage large pericardial effusions, particularly in patients with a malignant condition. It may become the preferred treatment to avoid a more invasive procedure for patients with pericardial effusion and a limited life expectancy.

Multipotential stem cells in the vertebrate CNS

The functional differences between the many mature neuronal types make the origins of cellular diversity in the nervous system one of the most intriguing problems in biology. This paper discusses recent experiments which explore the mechanisms generating cell diversity in the vertebrate central nervous system, focusing particularly on the immediate precursor to neurons and on neuronal differentiation. Transplantation experiments have been used to explore regional and temporal differences in the cells of the neuroepithelium. The effects of specific genes on neuronal development have been examined by mutational analysis in transgenic mice and in established neuronal stem cell lines. The combination of methods now available allow increasingly powerful dissection of the molecular and cellular mechanisms that generate the large number of different neurons in the vertebrate brain.

Reconstituting animals from immortal precursors

Several recent experiments have shown that immortal neural and muscle cells retain the specific temporal and spatial properties of their precursor cells in the animal. In addition, the immortal cells retain the ability to differentiate in vitro and, after transplantation, in vivo. The results of these experiments suggest that the use of precursor cell lines may lead to powerful approaches for understanding the mechanisms that generate the ordered distribution of cell types in mammals.

Morphology of the ventriculoaortic junction in critical aortic stenosis. Implications for hemodynamic function and clinical management

The clinical presentation of infants with critical aortic stenosis, as well as the results of surgical treatment, differs from obstruction of the left ventricular outflow tract in older children. To investigate a possible anatomic basis for this situation, we performed a detailed morphometric study of 21 hearts from infants who had critical aortic stenosis and 11 normal hearts from infants less than 3 months of age. In each of the hearts with critical aortic stenosis, only one commissure extended to the sinutubular ridge. The other two commissures were represented by folds in the aortic wall that suspended the leaflet below the level of the sinutubular junction. The leaflet thus had a free edge shorter than the circumference of the sinus, in contrast with the normal valve, in which leaflets always were longer than the circumference of their supporting sinus. Analysis of the fibrous triangles on the ventricular aspect of abnormal valves showed a symmetric three-sinus arrangement. In all but one specimen, however, only the triangle related to the mitral valve was fully developed. Although incision of both rudimentary commissures to the aortic wall should achieve some relief of obstruction, these morphologic features strongly mitigate against surgical restoration of normal function or growth in aortic valves having the morphology observed in this series of hearts.

Thrombolysis with tissue-type plasminogen activator following cardiac surgery in children

Three children with major intracardiac or vascular thrombosis following cardiac operations were treated with intravenous recombinant tissue-type plasminogen activator. The first patient, aged 10 yr, developed a left atrial thrombus following replacement of the mitral valve with a Björk-Shiley prosthesis. The second patient, aged 16 months, had a right atrial thrombus following a modified Fontan procedure for tricuspid atresia. Both were successfully treated with a short course of intravenous tissue plasminogen activator. The third patient, aged 19 months, developed the Budd-Chiari syndrome with occlusion of the inferior caval vein following a modified Fontan operation for double inlet left ventricle. Even though near-complete thrombolysis and recanalization of the inferior caval vein was achieved with three courses of tissue plasminogen activator on successive days, she died with failure of multiple organs. In all cases, the diagnosis was established by cross-sectional and Doppler echocardiography, and the response to therapy was monitored using the same technique. Thrombolytic therapy with systemic tissue-type plasminogen activator was safe and effective in the postoperative period, with no major haemorrhagic complications.

An oligodendrocyte precursor cell line from rat optic nerve

We have established permanent cell lines from the optic nerve of the rat with a temperature sensitive immortalizing oncogene (Simian Virus 40 large T-antigen carrying both the tsA58 and U19 mutations). The oncogene was transduced into primary cultures via a replication deficient retrovirus, and infected cells were selected with the antibiotic G418. A clonal cell line (tsU19-5) displayed some properties of oligodendrocyte precursors: it proliferated, bound the monoclonal antibody A2B5 (which recognizes minor ganglioside species), and expressed the intermediate filament vimentin and the enzyme 2',3'-cyclic-nucleotide 3'-phosphodiesterase (CNP) at 33 degrees C (the permissive temperature for the oncogene). At 39 degrees C (the non-permissive temperature), some cells had the potential to differentiate further, and expressed several oligodendrocyte specific components: galactocerebroside, myelin basic protein, proteolipid protein and CNP. These results suggest that conditional oncogenes can establish neural precursor cell lines which are still capable of differentiation in vitro.

Traumatic ventricular septal defect: serial follow-up with Doppler ultrasound

A three-year-old girl presented with a gunshot wound of the chest. Cross-sectional and Doppler echocardiography enabled precise location of the bullet, and assessment of the haemodynamic effects of the traumatic ventricular septal defect. Serial ultrasound examination in the acute stage confirmed that the bullet was well embedded in the left ventricular myocardium, and the ventricular septal defect was restrictive, enabling conservative management.

Renal function after cardiopulmonary bypass in children: comparison of dopamine with dobutamine

We have compared low dose dopamine with dobutamine in conserving renal function in 142 children younger than 10 yr undergoing cardiopulmonary bypass (CPB). Patients were allocated randomly to receive a continuous infusion of either dopamine 2.5 micrograms kg-1 min-1 (group 1) or dobutamine 2.5 micrograms kg-1 min-1 (group 2) from the time of induction of anaesthesia. Administration of inotropes and diuretics was controlled strictly to agreed regimens. There was no clinical or statistically significant difference between the two groups in postoperative urine output, serum concentration of creatinine, fractional sodium excretion or need for diuretic therapy. This was true also of the subgroup of patients who received no other inotropic support. However, the subgroup of patients in group 1 who underwent periods of CPB in excess of 2 h (n = 17) had persistently greater postoperative serum concentrations of creatinine. Low dose dopamine did not appear to be superior to dobutamine for protection of renal function in these patients.

The myth of the aortic annulus: the anatomy of the subaortic outflow tract

Surgical repair of the small aortic root is limited in part by the very structure of the outflow tract from the left ventricle. The root is not constructed on the basis of a ringlike annulus supporting the leaflets of the aortic valve. The only truly circular structure within the outflow tract is the junction of the aortic wall with the underlying ventricular structures, themselves partly muscular and partly fibrous. This circular ventriculoarterial junction is crossed by the semilunar attachments of the leaflets of the aortic valve, producing an interlinking arrangement between the expanded aortic sinuses and three triangles of fibrous tissue placed beneath the apexes of the commissures between the valve leaflets. The triangles form extensions of the left ventricle that are related, in part, to the pericardial cavity surrounding the heart. The arrangements of the attachment of the leaflets in malformed valves with two (or only one) effective leaflets are highly abnormal, although these valves are usually produced on the template of three aortic sinuses. The valve with two leaflets rarely gives problems during childhood. In valves producing "critical stenosis", there is usually only one effective leaflet, a condition due to incomplete liberation of two of the anticipated three commissures. Detailed study shows that, in these malformed hearts, the attachment of the leaflets is much more annular than in normal valves, with inadequate formation of the fibrous triangles.

Identifying and manipulating neuronal stem cells

Fetal brain tissue has been shown to have clear behavioral effects when transplanted into adult lesioned brains. These results have focused attention on the cell types of the embryonic brain. Transplantation experiments using primary cells are beginning to define the plasticity of these cells and the times when they become committed to specific neuronal fates. Growth factors have been defined that regulate the proliferation of these cells in culture. Cell lines have been established that express stem cell properties and that are capable of differentiation when implanted into the developing brain. In this article we review this work on mammalian neuroepithelial stem cells and discuss how these studies might contribute to the therapeutic use of brain transplants.

Results of balloon pulmonary valvuloplasty as a palliative procedure in tetralogy of Fallot

Balloon pulmonary valvuloplasty was attempted in 67 patients with tetralogy of Fallot at a median age of 5 months (range 0.03 to 52 months) for relief of cyanosis. In three patients, the valve could not be crossed and an aortopulmonary shunt was performed. In 35 patients, follow-up angiography was performed 3 to 30 months (average 12) after valvuloplasty. In 24 of these 35 patients (group A), the stenosis had been adequately palliated by valvuloplasty; the other 11 patients (group B) had required an aortopulmonary shunt 1 month (range 0 to 3 months) after valvuloplasty. The two groups were similar (p greater than 0.1) with respect to age at valvuloplasty, pulmonary anulus diameter, ratio of pulmonary artery to descending aorta diameter before valvuloplasty and interval to follow-up angiography. In contrast to patients in group B, patients in group A had a significant immediate improvement in systemic arterial oxygen saturation (p less than 0.01) and a significant increase in pulmonary anulus diameter at follow-up angiography (p less than 0.001). The growth of the branch pulmonary arteries was similar (p greater than 0.1) in the two groups. Among 42 patients who have had surgical correction, a transannular patch for right ventricular outflow tract reconstruction was used in 27 (64%); there was no difference between groups A and B with respect to its use. Eight patients died (three after repair) and death could not be directly attributed to valvuloplasty in any. Balloon valvuloplasty promotes growth of the pulmonary valve anulus and pulmonary arteries and is a useful alternative to an aortopulmonary shunt in patients with small pulmonary arteries or associated complex intracardiac defects.

Comparison of the aortic homograft and the pulmonary autograft for aortic valve or root replacement in children

To assess late results of aortic homograft and pulmonary autograft valves implanted into the left ventricular outflow tract of children, we reviewed the case histories of 146 patients 18 years of age or younger who underwent aortic valve or root replacement between November 1964 and April 1990. One hundred three patients (mean, 12 +/- 3.9 years) received an aortic homograft and 43 (mean, 14 +/- 4.1 years) had their own pulmonary valve transferred to the aortic position. There were 54 valve and 49 root replacements with homografts and 36 valve and seven root replacements with autografts. Hospital mortality rate was 15.5% (16 patients) in the homograft group and 11.6% (five patients) in the autograft group. Survivors were followed up for a total of 867 (homograft) and 297 (autograft) patient-years. The late mortality rate was 16.7% (1.9% per patient-year) for patients with homografts and 13.2% (4.4% per patient-year) for patients with autografts, whereas the incidence for reoperation per patient-year was 2.9% and 2.0%, respectively. At 15 years actuarial rates for homografts and autografts for freedom from reoperation were 54% +/- 8.1% and 68% +/- 11.1%; freedom from endocarditis, 97% +/- 2.4% and 75% +/- 10.2%; and freedom from any complication, 41% +/- 6.5% and 50% +/- 10.3%. Valve degeneration occurred in 19 homografts (2.2% per patient-year), whereas there was no definite instance of primary tissue failure among the pulmonary autografts. This experience would indicate that either the homograft or the autograft valve can be used with acceptable results in children. However, the pulmonary autograft gives better long-term performance and, if growth potential is realized, may be the ideal valve substitute in children.

Replacement of the aortic valve or root with a pulmonary autograft in children

Between January 1967 and December 1988, 34 patients ranging in age from 3 to 18 years (mean, 14 +/- 3.6 years) underwent replacement of the aortic valve or root with their own pulmonary valve. The indication for operation was left ventricular outflow obstruction in 16 patients (47%), aortic regurgitation in 14 (41%), mixed aortic valve disease in 3 (9%), and failure of a previously implanted aortic homograft in 1 (3%). There were four early deaths, all before 1971, giving a hospital mortality of 11.8% (70% confidence interval, 6% to 20%). Surviving patients have been followed up a cumulative total of 214 patient-years, the longest period of observation being 16 years 8 months. Late mortality was 13.3% (70% confidence interval, 7% to 23%), and 4 other patients required removal of the pulmonary autograft for endocarditis. Actuarial rates at 16 years were 74% +/- 11% for freedom from reoperation on the left ventricular outflow tract, 80% +/- 10% for freedom from reoperation on the right ventricular outflow tract, and 77% +/- 10% for late survival. There was no instance of primary structural degeneration in the pulmonary autograft, and all surviving patients were in New York Heart Association functional class I without medication. This experience demonstrates that the pulmonary autograft can achieve good early and medium-term results in young patients. Should growth potential be realized, it might constitute the ideal biological valve for the left ventricular outflow in children.

Critical aortic stenosis in early infancy. Anatomic and echocardiographic substrates of successful open valvotomy

To establish noninvasive criteria by which to manage infants with critical aortic stenosis, we examined 20 heart specimens from infants under 3 months of age and reviewed the clinical course and real time echocardiograms of 20 patients in the same age group. All 20 infants underwent open valvotomy, and in five cases both echocardiographic and postmortem measurements were available for the same heart. The anatomic specimens showed a spectrum of valvular, ventricular, and vascular abnormalities that could be accurately identified by echocardiography. A small left ventricular cavity was usually associated with a narrow ventriculoarterial junction, small ascending aorta, and narrow subaortic region. In these hearts, the mitral valve had a single or grossly hypoplastic papillary muscle with short or "arcuate" tendinous cords. A dilated left ventricular cavity had wider inflow and outflow orifices, and the tension apparatus of the mitral valve was either normal or supported by hypertrophic papillary muscles, at the other end of the spectrum. The survivors (n = 15) and nonsurvivors (n = 5) of open valvotomy showed significant differences in the echocardiographic dimensions of the left ventricle (p less than 0.005), the subaortic region (p less than 0.05), the ventriculoaortic junction (p less than 0.05), the ascending aorta (p less than 0.005), and the mitral valve orifice (p less than 0.001). Moreover, the papillary muscle of the mitral valve was invariably single or hypoplastic with short tendinous cords in the early nonsurvivors. Infants with unfavorable cardiac anatomy tended to present earlier (p less than 0.05) and to have a lower systemic blood pressure (p less than 0.05), and they required prostaglandin E2 to maintain right ventricular support of the circulation through a persistent arterial duct. This study suggests that patients with a small left ventricle (echocardiographic inflow dimension less than 25 mm), a narrow ventriculoaortic junction (less than 5 mm), and a small mitral valve orifice (less than 9 mm) will not achieve a satisfactory surgical result from aortic valvotomy. Such patients should be considered for cardiac transplantation or the Norwood-type of palliation for hypoplastic left heart syndrome.

Operative findings after percutaneous pulmonary balloon dilatation of the right ventricular outflow tract in tetralogy of Fallot

Since 1983 percutaneous balloon dilatation of the right ventricular outflow tract has been performed as an alternative to surgical palliation in selected cases of tetralogy of Fallot at the Royal Liverpool Children's Hospital. From 31 December 1984 to 31 December 1988, 27 of these patients underwent subsequent surgical correction. Age at operation ranged from 7 to 58 months (median 2.7 years). The mean interval between balloon dilatation and correction was 15.6 months (range 3-39 months). Two patients had a systemic pulmonary shunt operation performed before dilatation and a further five required one afterwards. Overall 20 (74%) patients had some anatomical alteration as the result of balloon dilatation, while in seven (26%) there was no discernible change in the right ventricular outflow tract. There was no consistent relation between the ratio of balloon size to pulmonary annulus diameter and the morphological findings. Balloon dilatation may obviate the need for systemic-pulmonary shunt at the expense of some structural damage, particularly to the posterior cusp. The present data suggest that dilatation does not bring about growth of the annulus to such an extent that transannular patch is no longer needed at intracardiac repair.

Proliferation and differentiation of neuronal stem cells regulated by nerve growth factor

Nerve growth factor plays an important part in neuron-target interactions in the late embryonic and adult brain. We now report that this growth factor controls the proliferation of neuronal precursors in a defined culture system of cells derived from the early embryonic brain. Neuronal precursor cells were identified by expression of the intermediate filament protein nestin. These cells proliferate in response to nerve growth factor but only after they have been exposed to basic fibroblast growth factor. On withdrawal of nerve growth factor, the proliferative cells differentiate into neurons. Thus, in combination with other growth factors, nerve growth factor regulates the proliferation and terminal differentiation of neuroepithelial stem cells.