摘要:

To understand limb abnormalities it is necessary to understand how the limb develops. The limb is the organ whose development is probably best understood. The limbs develop from small protrusions (the limb buds) that arise from the body wall of the embryo. Positioning and patterning the limb involves cellular interactions both between the ectoderm surrounding the limb bud and between the mesenchymal cells that form the core of the limb bud. As the limb grows out the cells acquire a positional value that relates to their position in the bud with respect to all three axes, proximo-distal, antero-posterior, and dorso-ventral. These positional values largely determine how the cells will develop such as what sort of cartilaginous elements they will form. The positional value of the cells is acquired in the progress zone at the tip of the growing bud. The time spent in the progress zone may determine the positional values along the proximo-distal axis, that is the formation of, for example the humerus, then the radius and ulna. Loss of the progress zone due to damage to the overlying apical ridge leads to truncations, and this progress zone model can also account for the effects of thalidomide. Position along the antero-posterior axis such as the character of the digits is by a signal from the polarizing region at the posterior margin of the limb and involves the signaling protein Sonic hedgehog. A signal from the dorsal ectoderm specifies the dorso-ventral axis. Hox genes that are transcription factors are expressed both along the body axis and in a complex pattern in the limb and may record positional value. Human mutations in these genes lead to limb abnormalities. Muscle cells have a separate origin from the cartilaginous cells and those that form connective tissue and tendons, and they migrate into the bud from the somites and are patterned by the connective tissue. Cell death separates the digits.

ISSN:0031-3998    

出版商:OVID    

年代:1999

数据来源: OVID

摘要:

The N-myconcogene directs organogenesis, and gene amplification is associated with aggressive forms of neuroblastoma, a common malignant tumor in children. N-mycis expressed in fetal epithelium, and expression decreases markedly postnatally. To localize sequences responsible for directing expression, we have analyzed the human N-mycpromoter. We noted previously that N-mycpromoter regions 5′ to exon 1 directed reporter gene expression in all cell lines, including those without detectable N-myctranscripts. However, when promoter constructs included 3′ exon 1 and the 5′ portion of intron 1, reporter activity was detected only when there was expression of the endogenous gene. To determine the role of this "tissue-specific region" in directing expression during development, we generated transgenic mice carrying N-mycpromoterlacZminigenes that contained 5′ N-mycpromoter elements alone or the promoter linked to the 3′ axon 1/5′ intron 1 tissue-specific region. Animals lacking the tissue-specific exon 1/intron 1 region showed β-galactosidase expression in the CNS, but expression was not observed in other organs in which endogenously derived N-myctranscripts were seen. Within the CNS, transgene expression was seen mainly in the olfactory system and was not observed in other areas in which expression of the murine gene has been noted. In contrast, no transgene expression was observed in any of the animals carrying the tissue-specific exon 1/intron 1 region. Thus, sequences that direct expression within the olfactory system were contained within our 5′ promoter transgene, whereas sequences that guide the ubiquitous expression of N-mycduring organogenesis lie outside the regions studied here. Finally, the exon 1/intron 1 region seems to act in a dominant fashion to repress expression in the CNS from the immediate 5′ N-mycpromoter.

ISSN:0031-3998    

出版商:OVID    

年代:1999

数据来源: OVID

摘要:

Erythropoietin receptors (Epo-R) are expressed on cells in the small bowel of human fetuses, but their function has not been defined. We hypothesized that intestinal Epo-R are present postnatally, and that recombinant erythropoietin (rEpo) would increase enterocyte migration and decrease cytokine-induced apoptosis. We used reverse transcriptase-polymerase chain reaction and immunohistochemistry to evaluate the presence of Epo-R mRNA and protein in rat intestinal epithelial cells (IEC-6), and in postnatal human and rat bowel. The effect of rEpo on rates of cell migration and proliferation were established in IEC-6 cells by using cell counting and incorporation of bromodeoxyuridine. To determine whether rEpo affects response to injury, cells were pretreated with rEpo, then were damaged with 25 or 50 ng/mL tumor necrosis factor-α plus 2.5 µg/mL cycloheximide. Cell death was determined by colorimetric bioassay. We found that Epo-R mRNA and protein were expressed by IEC-6 cells and by enterocytes of postnatal rat and human small bowel. Cells that had been exposed to 0.05 or 5.00 U/mL rEpo migrated faster than did the controls (p< 0.05), but no difference was noted in cell proliferation. Treatment of IEC-6 cells with rEpo before or at the time of injury resulted in a lower percentage of cell death, and this effect was neutralized by anti-Epo antibody. We conclude that Epo-R is expressed in enterocytes postnatally in rats and humans. Recombinant Epo increases the rate of migration of IEC-6 cells and decreases cytokine-induced apoptosis. These studies suggest that Epo within human milk has actions on neonate's intestinal function.

ISSN:0031-3998    

出版商:OVID    

年代:1999

数据来源: OVID

摘要:

Sex steroids accelerate bone maturation, but it is believed that estrogen action is needed for terminal epiphyseal fusion. In this study, we investigated the effects of a new estrogen-blocking agent, Faslodex (ICI 182,780), on estrogen-accelerated skeletal maturation in immature mice. On day-of-life 2 through 8, mice pups received either estradiol (5 µg/100 g body weight), Faslodex (100 µg/100 g body weight), a combination of Faslodex + estradiol, or vehicle alone. Skeletal maturation was assessed with a scoring system based on the size and appearance of epiphyseal plates in the forepaw and the lumbar spine. Estradiol caused acceleration of bone maturation in our mouse model (p< 0.05). Faslodex blocked the effect of estrogen, such that the mice receiving Faslodex + estradiol did not vary significantly from controls. Faslodex may prove useful in the treatment of patients with diseases causing rapid skeletal maturation, such as precocious puberty.

ISSN:0031-3998    

出版商:OVID    

年代:1999

数据来源: OVID

摘要:

Prolonged cerebral hypothermia is neuroprotective if started within a few hours of hypoxia-ischemia. However, delayed seizure activity is one of the major clinical indicators of an adverse prognosis after perinatal asphyxia. The aim of this study was to determine whether head cooling delayed until after the onset of postasphyxial seizures may still be neuroprotective. Unanesthetized near-term fetal sheepin uteroreceived 30 min of cerebral ischemia induced by bilateral carotid artery occlusion. Eight and one-half hours later, they received either cooling (n= 5) or sham cooling (n= 13) until 72 h after the insult. Intrauterine cooling, induced by circulating cold water through a coil around the fetal head, was titrated to reduce fetal extradural temperature from 39.4 ± 0.1°C to between 30 and 33°C. Cerebral ischemia led to the delayed development of intense epileptiform activity from 6 to 8 h postinsult, followed by a marked secondary rise in cortical impedance (a measure of cytotoxic edema) and in carotid blood flow. Cerebral cooling markedly attenuated the secondary rise in impedance and reduced carotid blood flow (p< 0.001). After 5 d recovery, there was no significant difference in loss of parietal EEG activity relative to baseline in the hypothermia compared with the control group (- 12.5 ± 1.4versus- 15.2 ± 1.2 dB, mean ± SEM, NS) or in parasagittal cortical neuronal loss (82 ± 9versus90 ± 5%, NS). In conclusion, delayed prolonged head cooling begun after the onset of postischemic seizures was not neuroprotective. These data highlight the importance of intervention in the latent phase, after reperfusion but before the onset of secondary injury.

ISSN:0031-3998    

出版商:OVID    

年代:1999

数据来源: OVID

摘要:

Magnesium is a potential neuroprotective agent in the treatment of head injury and ischemia whose efficacy is likely determined by increases in brain extracellular fluid (ECF) magnesium, which in turn depends on its concentration in plasma. The objectives of this study were to:1) examine the effects of increasing plasma magnesium concentration ([Mg]plasma) to 4-6 mM on brain ECF magnesium concentration ([Mg]ECF) and2) determine whether maturational changes occur in the transfer of magnesium into brain ECF for newborn and more mature (approximately 1 month old) miniswine. Increases in [Mg]plasmaby systemic administration of MgSO4resulted in similar maximal elevations in brain [Mg]ECFfor both age groups (193 ± 76%versus253 ± 106% of control for newborn and 1-month-old miniswine, respectively). Calculations of half-lives (t1/2) for the increase and decrease in magnesium concentration (t1/2uptake and t1/2clearance) were used to characterize magnesium kinetics in plasma and brain ECF. Plasma magnesium uptake was shorter in 1-month-old (t1/2= 11.1 ± 0.9 min) compared with newborns (12.9 ± 1.7 min,p< 0.05). The faster increase in [Mg]plasmaprobably contributed to a faster uptake of brain [Mg]ECFin 1-month-old compared with newborn swine (t1/2uptake = 27.9 ± 12.8versus46.0 ± 20.9 min, respectively,p< 0.05). Although plasma magnesium clearance was shorter in 1-month-old swine compared with newborn (t1/2= 34.3 ± 7.0versus74.7 ± 33.7 min, respectively,p< 0.05), the clearance of magnesium from the brain ECF was similar for each age group. Reductions in blood pressure and heart rate occurred during hypermagnesemia and were similar in each age group. This study shows that acute elevations in [Mg]plasmato 4-6 mM result in similar relative increases in brain [Mg]ECFfor both newborn and 1-month-old miniswine. However, there are maturational differences, as demonstrated by the faster rate of magnesium uptake into the ECF observed in the older miniswine.

ISSN:0031-3998    

出版商:OVID    

年代:1999

数据来源: OVID

摘要:

We have found that cerebral lactate can be detected later than 1 month of age after neonatal encephalopathy (NE) in infants with severe neurodevelopmental impairment at 1 y. Our hypothesis was that persisting lactate after NE is associated with alkalosis and a decreased cell phosphorylation potential. Forty-three infants with NE underwent proton and phosphorus-31 magnetic resonance spectroscopy at 0.2-56 wk postnatal age. Seventy-seven examinations were obtained: 25 aged <2 wk, 16 aged ≥ 2 to ≤ 4 wk, 25 aged >4 to ≤ 30 wk, and 11 aged >30 wk. Neurodevelopmental outcome was assessed at 1 y of age: 17 infants had a normal outcome and 26 infants had an abnormal outcome. Using univariate linear regression, we determined that increased lactate/creatine plus phosphocreatine (Cr) was associated with an alkaline intracellular pH (pHi) (p< 0.001) and increased inorganic phosphate/phosphocreatine (Pi/PCr) (p< 0.001). This relationship was significant, irrespective of outcome group or age at time of study. Between outcome groups, there were significant differences for lactate/Cr measured at <2 wk (p= 0.005) and >4 to ≤ 30 wk (p= 0.01); Pi/PCr measured at <2 wk (p< 0.001); pHimeasured at <2 wk (p< 0.001), ≥ 2 to ≤ 4 wk (p= 0.02) and >4 to ≤ 30 wk (p= 0.03); and forN-acetylaspartate/Cr measured at ≥ 2 to ≤ 4 wk (p= 0.03) and >4 to ≤ 30 wk (p= 0.01). Possible mechanisms leading to this persisting cerebral lactic alkalosis are a prolonged change in redox state within neuronal cells, the presence of phagocytic cells, the proliferation of glial cells, or altered buffering mechanisms. These findings may have implications for therapeutic intervention.

ISSN:0031-3998    

出版商:OVID    

年代:1999

数据来源: OVID

摘要:

Magnetic resonance imaging with diffusion- and T2-weighted imaging and31P magnetic resonance spectroscopy was used to investigate the relationship between development of brain edema and alterations of the brain energy metabolism after hypoxia-ischemia (HI) brain injury in 7-d-old rats. The results were correlated with histologic examinations at various times during recovery up to 5 d. Moderate HI, induced by right common carotid artery ligation and subsequent exposure to 8% O2for 90 min, produced a cytotoxic edema of 52 ± 9% brain volume and depressed the ratio of phosphocreatine to inorganic phosphate from 1.43 ± 0.21 to 0.11 ± 0.09. Within 1 h of reoxygenation, the edema decreased to 4 ± 2% of brain volume, demarcating the core of the lesion. At 5 h of recovery, a secondary cytotoxic edema together with a newly developing vasogenic edema expanded again, reaching its maximal extent of 45 ± 10% brain volume at around 24 h. The ratio of phosphocreatine to inorganic phosphate recovered slowly, reaching 1.12 ± 0.27 around 13 h. Thereafter it declined again in a manner analogous to the observations made in human newborns after severe perinatal asphyxia, reaching trough values of 0.48 ± 0.22 around 24 h after HI. At the cellular level, the vast majority of neuronal death occurred before 15 h. Subsequently, strong glial activation lasted 2-3 d after HI. At 5 d, a cystic infarction of 35 ± 12% brain volume was found. We conclude that the biphasic evolution of brain edema and energy metabolism reflects early neuronal and late glial damage in response to moderate HI injury. Therefore, the secondary energy breakdown reflects glial activation and subsequent glial death.

ISSN:0031-3998    

出版商:OVID    

年代:1999

数据来源: OVID

摘要:

The imbalance between high oxidant loads and immature antioxidant defenses is associated with long-term complications of prematurity. Glutathione is a central element among the antioxidants. Depletion of pulmonary glutathione accelerates the development of oxygen-induced lung injury in neonatal animal models. After the observation that newborn infants exposed to oxygen have low glutathione levels, a study was designed to test the hypothesis that in neonates from a species susceptible to oxygen toxicity, the lethal effect of hyperoxia is related to a low availability of substances for glutathione production rather than an impairment in synthetic activity. One-day-old guinea pigs, randomly assigned to room air or oxygen (>95%), were fed by their mothers (n= 16) or i.v. by dextrose (n= 14) or by total parenteral nutrition (TPN,n= 20). After 3 d, glutathione and activities of enzymes involved in maintaining intracellular glutathione levels were determined in lungs and liver. The lethal effect of oxygen (p< 0.05) observed in animals without TPN was not related to glutathione depletion, as oxygen induced a 33% increase in lung glutathione, positively correlated (r2= 0.35) with enhanced synthesis. With TPN, the animals were protected against the lethal effects of hyperoxia and lung glutathione increased by 67% in oxygen. The results suggest that the glutathione demand by the lungs in the presence of an oxidant stimulus was met by the increased (p< 0.001) hepatic production supported by TPN. Under hyperoxic conditions, early nutritional support is of vital importance.

ISSN:0031-3998    

出版商:OVID    

年代:1999

数据来源: OVID

摘要:

Prostaglandin E is a major dilator of the fetal ductus arteriosus (DA), but the role of nitric in fetal ductal dilation has not been established. We studied the effects of a potent nitric oxide synthase inhibitor.Nω-nitro-L-arginine methyl ester (L-NAME), on the fetal DA in rats. L-NAME was injected into the dorsum of pregnant rats, and fetal DA was studied 4 h later with a rapid whole body freezing method. The inner diameters of the DA and the main pulmonary artery were measured on a freezing microtome. The inner diameter ratio of DA to main pulmonary artery (DA/PA) was 1.02 ± 0.03 (mean ± SEM; number of fetuses [n], 21) in normal near-term fetuses. The effect of prostaglandin synthesis inhibition was studied after orogastric administration of indomethacin to pregnant rats. In near-term rats on the 21st day of gestation (term, 21.5 d), a large dose of L-NAME (100 mg/kg) caused only mild ductal constriction, with DA/PA reduced to 0.83 ± 0.05 (n= 20). Indomethacin (1 mg/kg) caused moderate ductal constriction, and DA/PA was decreased to 0.65 ± 0.05 (n= 21). Combined administration of L-NAME (10 mg/kg) and indomethacin (1 mg/kg) caused severe ductal constriction, with DA/PA of 0.26 ± 0.03 (n= 16). In preterm rats on the 19th day of gestation, a moderate dose of L-NAME (10 mg/kg) caused severe ductal constriction, with a DA/PA of 0.32 ± 0.05 (n= 24). Indomethacin (1 mg/kg) alone caused only mild ductal constriction, with DA/PA 0.86 ± 0.02 (n= 16). In conclusion, prostaglandin has a major role and nitric oxide has a minor role in dilating the DA in the near-term fetal rat. In contrast, nitric oxide has a major role and prostaglandin has a minor role in dilating the DA in preterm fetal rats.

ISSN:0031-3998    

出版商:OVID    

年代:1999

数据来源: OVID