Stem cells and neurogenesis in the adult brain

A new interest in replacing neurons lost to trauma or disease has been generated by findings that challenge the traditional view of the static (irreparable) adult brain. The discovery of stem cells and neurogenesis in the adult central nervous system is responsible for much of this interest.

Open-heart correction of tetralogy of Fallot in an acyanotic dog

Tetralogy of Fallot was diagnosed in an acyanotic 11-month-old dog. Predicted pressure gradient across the pulmonic valve, as assessed by use of continuous wave Doppler echocardiography, was 94.5 mm Hg. Bidirectional shunting was identified by means of selective angiography. Open-heart correction was performed, using a transatrial approach with limited ventriculotomy and cardiopulmonary bypass. The hypertrophied infundibulum was resected, the ventricular septal defect was closed primarily, and a transannular pericardial patch graft was applied. Pressure gradients across the pulmonic valve were 52.9 and 22.8 mm Hg 2 weeks and 4 months after surgery, respectively. Advances in cardiopulmonary bypass, anesthetic management, and use of the transatrial approach may improve the success of open-heart correction of tetralogy of Fallot in dogs.

Report of two sibs with Knobloch syndrome (encephalocoele and viteroretinal degeneration) and other anomalies

We report on two sibs with high myopia, vitreoretinal degeneration (VRD), and occipital encephalocoele or scalp lesion. We review the literature on Knobloch syndrome, discuss possible causes, and suggest a possible involvement of mesoderm in the morphogenesis. One case presents with very early onset of severe eye disease, whereas the other is notable for the very mild scalp defect. In addition, both appear to have an unusual pulmonary lymphatic condition.

The JUN kinase/stress-activated protein kinase pathway is required for epidermal growth factor stimulation of growth of human A549 lung carcinoma cells

Epidermal growth factor (EGF) plays a major role in non-small cell lung cancer cell autocrine growth and has been reported to activate the JUN kinase/stress-activated protein kinase (JNK/SAPK) pathway in model cells. Activation of JNK/SAPK leads to the phosphorylation of c-JUN protooncogene on serines 63 and 73. This mechanism is required for and cooperates in the transformation of rat embryo fibroblasts by Ha-RAS. However, the function of JNK/SAPK in human tumor growth is unknown. We have tested several lung carcinoma cell lines. All exhibited UV-C-inducible JNK/SAPK activity; two exhibited constitutive activity in low serum, and two (M103 and A549) exhibited EGF-inducible JNK/SAPK activity. In A549 cells, EGF induced a rapid and prolonged (up to 24 h) activation of the JNK/SAPK pathway that correlated with a 150-190% growth stimulation. Stably transfected clones of A549 cells expressing c-JUN(S63A,S73A), a transdominant inhibitor of c-JUN, completely blocked the EGF-stimulated proliferation effect but did not alter the basal proliferation rate. Consistent with these results JNK antisense oligonucleotides targeted to JNK1 and JNK2 entirely eliminated the EGF-stimulated JNK/SAPK activity and blocked EGF-stimulated growth but not basal growth. In contrast, specific inhibition of the RAF/ERK pathway by PD98059 (MEK1 inhibitor) completely blocked ERK activation by EGF and basal cell growth but not EGF-stimulated growth, thereby dissociating the growth-promoting roles of each pathway. Our observations indicate, for the first time, that JNK/SAPK may be a preferential effector pathway for the growth properties of EGF in A549 cells.

Stem cells in the central nervous system

In the vertebrate central nervous system, multipotential cells have been identified in vitro and in vivo. Defined mitogens cause the proliferation of multipotential cells in vitro, the magnitude of which is sufficient to account for the number of cells in the brain. Factors that control the differentiation of fetal stem cells to neurons and glia have been defined in vitro, and multipotential cells with similar signaling logic can be cultured from the adult central nervous system. Transplanting cells to new sites emphasizes that neuroepithelial cells have the potential to integrate into many brain regions. These results focus attention on how information in external stimuli is translated into the number and types of differentiated cells in the brain. The development of therapies for the reconstruction of the diseased or injured brain will be guided by our understanding of the origin and stability of cell type in the central nervous system.

Definition by specific antisense oligonucleotides of a role for protein kinase C alpha in expression of differentiation markers in normal and neoplastic mouse epidermal keratinocytes

Epidermal keratinocyte differentiation is a tightly regulated, stepwise process that requires protein kinase C (PKC) activation. Studies using cultured mouse keratinocytes induced to differentiate with Ca2+ have indirectly implicated the alpha isoform of PKC in upregulation of "late" (granular cell) epidermal differentiation markers. Activation of this isoform is also implicated in the suppression of "early" differentiation markers keratin (K) 1 and 10 that characterizes the neoplastic phenotype produced by the v-Ha-ras oncogene. We used antisense oligonucleotides (AS) to directly address the role of PKC alpha in regulating expression of these markers in normal and v-Ha-ras-transduced primary keratinocytes and a keratinocyte cell line (SP-1) containing an activating mutation of the c-Ha-ras gene. Transfection of PKC alpha AS reduced the PKC alpha protein level in a dose-dependent manner, with a maximum effect at doses of 100 nM or higher. Immunoblot analysis with antibodies against PKC alpha, PKC delta, PKC epsilon, and PKC eta confirmed that PKC alpha AS selectively reduced the level of PKC alpha but not the other isoforms. In vitro kinase assays also revealed suppression of Ca(2+)-dependent PKC activity, which is the PKC alpha activity in this cell type, after transfection of PKC alpha AS. When PKC alpha AS-treated normal keratinocytes were stimulated to terminally differentiate with Ca2+, induction of the late differentiation markers loricrin, filaggrin, and SPR-1, as well as transglutaminase K mRNA, was suppressed when compared with their induction in scrambled AS-treated controls. In neoplastic v-Ha-ras-transduced keratinocytes and SP-1 cells, transfection of PKC alpha AS, but not the scrambled AS control, selectively downregulated PKC alpha and restored differentiation-specific expression of K1. These findings directly confirm that PKC alpha is an important component of the signaling pathway regulating terminal differentiation of normal keratinocytes and that activation of PKC alpha contributes to the altered differentiation program of neoplastic murine keratinocytes.

Functional and structural alterations with 24-hour myocardial hibernation and recovery after reperfusion. A pig model of myocardial hibernation

BACKGROUND

Short-term myocardial hibernation of 3 hours resulting from a moderate resting coronary flow reduction has been reproduced in pigs. This study was designed to determine whether any structural changes accompany short-term hibernation caused by a moderate flow reduction maintained for 24 hours and whether any such structural alterations are reversible after reperfusion.

METHODS AND RESULTS

A severe left anterior descending coronary artery (LAD) stenosis was created with a reduction of resting flow to approximately 60% of baseline and maintained for 24 hours. Regional coronary flow was measured by a flowmeter; wall thickening was determined by echocardiography, and local metabolic changes were measured. Of 17 pigs, 11 completed the study protocol of 24 hours. The LAD flow was reduced from 0.91 +/- 0.11 to 0.52 +/- 0.13 mL.min-1.g-1, a 43% mean decrease, at 15 minutes after the LAD stenosis and was maintained at 0.56 +/- 0.11 mL.min-1.g-1 at 24 hours. The reduction of regional coronary flow initially produced acute myocardial ischemia, as evidenced by reduced regional wall thickening (from 37.2 +/- 6.9% at baseline to 11.5 +/- 6.8%), regional lactate production (-0.34 +/- 0.28 mumol.g-1.min-1), and a decrease in regional coronary venous pH (from 7.41 +/- 0.035 at baseline to 7.30 +/- 0.030). At 24 hours, the reductions in coronary flow and wall thickening were maintained relatively constant and the rate-pressure product was relatively unchanged, but lactate production ceased and regional H+ concentration normalized, with a tendency toward a further reduction in regional oxygen consumption, from 3.10 +/- 0.90 mL.min-1.100 g-1 at 15 minutes after stenosis to 2.52 +/- 0.95 mL.min-1.100 g-1 at 24 hours (P = .06), indicating metabolic adaptation of the hypoperfused regions. Of 11 pigs, 6 were free of myocardial infarction; 3 had patchy necrosis involving 4%, 5%, and 6% of the area at risk; and 2 other pigs had a few scattered myocytes with necrosis, detected only by light and electron microscopy. Ultrastructural changes consisted of a partial loss of myofibrils and an increase in mitochondria and glycogen deposition. Regional wall thickening recovered 1 week after reperfusion in most pigs, and the ultrastructural changes reverted to normal.

CONCLUSIONS

In this pig model, moderately ischemic myocardium undergoes metabolic and structural adaptations but preserves the capacity to recover both functionally and ultrastructurally after reperfusion.

Inhibition of growth of human tumor cell lines in nude mice by an antisense of oligonucleotide inhibitor of protein kinase C-alpha expression

A 20-mer phosphorothioate oligodeoxynucleotide (ISIS 3521) designed to hybridize sequences in the 3'-untranslated region of human protein kinase C-alpha (PKC-alpha) mRNA has been shown to inhibit the expression of PKC-alpha in multiple human cell lines. In human bladder carcinoma (T-24) cells, inhibition of PKC-alpha was both concentration dependent and oligonucleotide sequence specific. ISIS 3521 had a IC50 of 50-100 nM for PKC-alpha mRNA reduction and was without effect on the expression of other members of the PKC family of genes (PKC-eta and zeta). Toxicity studies in mice revealed that the oligodeoxynucleotide was well tolerated at repeat doses of 100 mg/kg i.v. for up to 14 days, with no acute toxicity apparent. The oligodeoxynucleotide was found to also inhibit the growth of three different human tumor cell lines, the T-24 bladder, human lung carcinoma (A549), and Colo 205 colon carcinoma grown in nude mice. The inhibition was dose dependent with ID50 values for the growth inhibition between 0.06 and 0.6 mg/kg daily when given i.v., depending on the cell line examined. Three control phosphorothioate oligodeoxynucleotides not targeting human PKC-alpha were without effect on the growth of the tumors at doses as high as 6 mg/kg. Recovery of ISIS 3521 from tumor tissue and resolution by capillary gel electrophoresis revealed that 24 It after the final dose of oligodeoxynucleotide, intact, full-length 20-mer material was present as well as some apparent exonuclease degradation products (e.g., n-1 and n-2 mers). These studies demonstrate the in vivo antitumor effects of an antisense oligodeoxynucleotide targeting PKC-alpha and suggest that this compound may be of value as a chemotherapeutic agent in the treatment of human cancers.

The coronary arteries in hearts with discordant atrioventricular connections

Gross morphologic study of 14 hearts with congenitally corrected transposition or discordant atrioventricular connections and double-outlet right ventricle or pulmonary atresia disclosed consistently the origins of the coronary arteries from two aortic sinuses. With usual atrial arrangement, the artery arising in sinus 1 (right-hand facing), as seen from the noncoronary aortic sinus, supplied the morphologically right ventricle. Coronary blood supply to the morphologically left ventricle usually came from sinus 2 (left-hand facing), although in two hearts the circumflex branch was a continuation of the artery from sinus 1. The sinus nodal artery arose from the circumflex coronary artery, and histologic studies of two hearts demonstrated that blood supply to the anterior atrioventricular node also came from this vessel. Early branching and entrapment in fat or right ventricular muscle, as well as malalignment of aortic and pulmonary sinuses, occurred frequently. These findings may have implications for coronary arterial transfer in the double switch operation in hearts with discordant atrioventricular connections.

Dopaminergic microtransplants into the substantia nigra of neonatal rats with bilateral 6-OHDA lesions. II. Transplant-induced behavioral recovery

Transplants of fetal ventral mesencephalic (VM) dopamine neurons implanted into the substantia nigra in 6-hydroxy-dopamine (6-OHDA)-lesioned neonatal pups establish axonal connections with the denervated caudate putamen (Nikkhah et al., 1995). In the present study, we have explored the functional capabilities of these animals after they reached adulthood on a battery of spontaneous and drug-induced behavioral tasks. The results demonstrate that unilateral intranigral VM grafts in bilaterally lesioned neonates induce a marked bias in spontaneous- and stress-induced rotation contralateral to the implant not present in the lesion-only controls. Amphetamine and apomorphine induced vigorous contra- and ipsilateral rotation, respectively. Moreover, grafted animals achieved 75% of the performance level in contralateral skilled forelimb use when compared to normal controls, which was significantly above lesion-only animals (50% of normal). Spontaneous nocturnal locomotor activity was elevated 2.2-fold in the grafted animals. Sensorimotor orientation and disengage behavior was spared by the neonatal dopamine lesion and unaffected by the grafts. The level of functional restoration seen in the present study was more extensive than reported previously in neonatally 6-OHDA-lesioned rats where the VM grafts were implanted ectopically into the striatum. However, functional recovery remained incomplete also after intranigral graft placement compared to normal intact animals. The present approach should provide a new promising avenue for the continued exploration of the mechanisms involved in functional recovery and structural repair in the damaged nigrostriatal system.

Identification of target genes regulated by homeotic proteins in Drosophila melanogaster through genetic selection of Ultrabithorax protein-binding sites in yeast

A method based on the transcriptional activation of a selectable reporter in yeast cells was used to identify genes regulated by the Ultrabithorax homeoproteins in Drosophila melanogaster. Fifty-three DNA fragments that can mediate activation by UBX isoform Ia in this test were recovered after screening 15% of the Drosophila genome. Half of these fragments represent single-copy sequences in the genome. Six single-copy fragments were investigated in detail, and each was found to reside near a transcription unit whose expression in the embryo is segmentally modulated as expected for targets of homoeotic genes. Four of these putative target genes are expressed in patterns that suggest roles in the development of regional specializations within mesoderm derivatives; in three cases these expression patterns depend on Ultrabithorax function. Extrapolation from this pilot study indicates that 85-170 candidate target genes can be identified by screening the entire Drosophila genome with UBX isoform Ia. With appropriate modifications, this approach should be applicable to other transcriptional regulators in diverse organisms.

Nerve growth factor amplifies cyclic AMP production in the HT4 neuronal cell line

There has been considerable interest and controversy in the relationship between nerve growth factor (NGF) and the cyclic AMP (cAMP) second messenger system. We have used a novel, neuronal cell line (HT4) to investigate the effect of NGF on the adenylyl cyclase signaling system. Treatment of cells with NGF (100 ng/ml, 15 min) amplified cAMP accumulation (approximately 75%) in response to activation of adenosine A2 receptors (5 min) with 5'-N-ethylcarboxamidoadenosine or activation of adenylyl cyclase directly with forskolin. Basal cAMP accumulation was not altered by NGF. This amplification appears to be mediated by activation of protein kinase C (PKC) because (1) it was mimicked by activators (phorbol esters and a diacylglycerol analogue) of PKC, (2) the effects of NGF and phorbol ester on cAMP accumulation were not additive, (3) NGF amplification of cAMP accumulation was abolished by down-regulation of PKC, (4) NGF increased cytosolic PKC activity, and (5) inhibitors of PKC blocked the NGF-induced amplification of cAMP accumulation. Although NGF-induced amplification of cAMP accumulation was dependent upon PKC, mechanisms other than the classic activation pathway (i.e., hydrolysis of inositol phospholipids or the production of diacylglycerol) appeared to mediate PKC activation by NGF. The tyrosine kinase inhibitor, lavendustin A, blocked NGF-mediated amplification of cAMP accumulation, suggesting a novel interaction between a tyrosine kinase and protein kinase C.

Transplantation strategies for the analysis of brain development and repair

Fetal tissue provides the best functional restoration in transplantation therapies for neurodegenerative diseases. Lineage analysis using in vivo cell marking methods shows that a multipotential cell gives rise to different neuronal types in the mammalian central nervous system. Culture methods that allow this cell to be expanded in vitro would provide important additional tools in the development of brain transplant therapies. The stem cells of the mammalian central nervous system express nestin, an intermediate filament protein that is abundant in neuronal and glial precursors but not present in the normal adult brain. Primary and immortal cultures of nestin-positive cells have been established and the differentiation of these cells analyzed both in vitro and by transplantation into the developing central nervous system. We have expanded neuronal precursor cells in vitro as both primary and immortal cells. Following implantation into the hippocampus, neurons derived from cultured stem cells are integrated into the host tissue. These findings encourage re-examination of the use of cultured cells in therapeutic transplants to the adult brain. In addition to increasing cell number, the period of culture may also permit genetic manipulation to define mechanisms of neuronal function and to enhance the therapeutic utility of transplanted cells.

Inhibition of protein kinase C-alpha expression in mice after systemic administration of phosphorothioate antisense oligodeoxynucleotides

A 20-mer phosphorothioate oligodeoxynucleotide designed to hybridize to the AUG translation initiation codon of mRNA encoding murine protein kinase C-alpha (PKC-alpha) inhibits the expression of PKC-alpha both in vitro and in vivo. In mouse C127 mammary epithelial cells, the reduction in PKC-alpha mRNA expression was both dose and time dependent. The oligodeoxynucleotide exhibited an IC50 value of 100-200 nM and reduced PKC-alpha mRNA expression for up to 48 hr. This reduction was specific for PKC-alpha versus other PKC isozymes (delta, epsilon, and zeta) and completely dependent upon oligodeoxynucleotide sequence. When administered intraperitoneally in mice, the same oligodeoxynucleotide caused a dose-dependent, oligodeoxynucleotide sequence-dependent reduction of PKC-alpha mRNA in liver, with an IC50 value of 30-50 mg/kg of body weight. Inhibition of expression was 64 +/- 11% after a single 50-mg/kg dose. The expression of PKC-delta, epsilon, and zeta mRNA was unaffected by this treatment. The oligodeoxynucleotide activity in vivo did not require the presence of cationic liposomes or any other delivery systems, although in vitro, the oligodeoxynucleotide required cationic liposomes for inhibition of PKC-alpha expression. This study demonstrates the utility of phosphorothioate oligodeoxynucleotides as specific inhibitors of gene expression in vivo after systemic administration.

Inhibition of protein kinase C-alpha expression in human A549 cells by antisense oligonucleotides inhibits induction of intercellular adhesion molecule 1 (ICAM-1) mRNA by phorbol esters

We have identified 20-mer phosphorothioate oligodeoxynucleotides which potently (IC50 values of 100-200 nM) and specifically inhibit protein kinase C (PKC)-alpha mRNA and protein expression in human lung carcinoma (A549) cells. These oligonucleotides target multiple, diverse sites on PKC-alpha mRNA including the AUG translation codon and 3'-untranslated sequences. 2'-O-Methyl phosphorothioate analogs of these oligonucleotides were without effect on PKC-alpha mRNA levels, suggesting that the reduction in targeted PKC-alpha mRNA is through RNase H-mediated cleavage. One oligonucleotide, however, was effective at inhibiting PKC-alpha protein levels as a 2'-O-methyl phosphorothioate at concentrations 2-3-fold greater than its phosphorothioate/deoxy homolog. These results suggest that the ability to serve as an RNase H substrate, although not required for all oligonucleotides, certainly increases their potency. These oligonucleotides have been used to examine the role played by PKC-alpha in mediating the phorbol ester-induced changes in mRNA levels of the cell adhesion molecule ICAM-1. In A549 cells, ICAM-1 mRNA is increased 10-20-fold by treatment of cells with the phorbol ester phorbol 12-myristate 13-acetate. When PKC-alpha protein levels are depleted by oligonucleotide treatment of A549 cells, the increase in ICAM-1 expression in response to phorbol 12-myristate 13-acetate is greatly reduced, demonstrating that PKC-alpha plays a major role in this process.

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.