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S Wyatt

Publications and source records attributed to S Wyatt.

53 records · Page 3Linked to original sources
PubMed1995

Role of Bcl-2 in the brain-derived neurotrophic factor survival response.

Developing neurons die if they fail to obtain an adequate supply of neurotrophins from their targets but how neurotrophins suppress cell death is not known. Although over-expression of exogenous Bcl-2 can prevent the death of cultured neurons deprived of members of the nerve growth factor family of neurotrophins it is not known if this effect is physiologically relevant. To determine if Bcl-2 participates in the neurotrophin survival response we used antisense bcl-2 RNA to inhibit endogenous Bcl-2 expression. Here we show that brain-derived neurotrophic factor (BDNF)-dependent neurons are killed by antisense bcl-2 RNA in the presence of BDNF. However, when these neurons were supported with ciliary neurotrophic factor (CNTF) their survival was not affected by antisense bcl-2 RNA. Likewise, the survival of CNTF-dependent ciliary neurons was not affected by antisense bcl-2 RNA. Our findings suggest that Bcl-2 is required for the BDNF survival response and that alternative, Bcl-2-independent survival mechanisms operate in sensory and parasympathetic neurons exposed to CNTF.

Animals↗
PubMed1995

NGF receptor expression in sensory neurons develops normally in embryos lacking NGF.

Numerous in vivo and in vitro studies have shown that NGF increases the expression of its receptors, p75 and TrkA, in NGF-responsive cell lines and in NGF-responsive neurons of the developing and mature nervous system. To determine if endogenous NGF is required for the normal developmental increase in p75 and TrkA expression that occurs in sensory neurons shortly after they innervate their targets, we used quantitative RT/PCR to compare the levels of p75 and trkA mRNAs in the trigeminal ganglia of normal mouse embryos and embryos that are homozygous for a null mutation in the NGF gene. We show that the marked increase in p75 and trkA mRNA expression that occurs between E11 and E13 in normal embryos takes place on time and to the same extent in NGF-/- embryos. We also show that trigeminal neurons from E13 NGF+/+ and NGF-/- embryos have very similar dose responses for survival induced by NGF. These findings clearly show that the expression of both p75 and TrkA and the sensitivity of developing sensory neurons to NGF do not require and are not modulated by target-derived NGF during the early stages of target field innervation.

Animals↗
PubMed1995

Regulation of nerve growth factor receptor gene expression in sympathetic neurons during development.

We used quantitative reverse transcription (RT)/PCR to study the regulation of p75 mRNA and trkA mRNA expression in the developing sympathetic neurons of the mouse superior cervical sympathetic ganglion (SCG) in vivo and in vitro. At E13, the SCG contains proliferating cells that express many features of differentiated neurons. These immature neurons survived in culture without NGF, and NGF did not induce c-fos expression. Low levels of p75 and trkA mRNAs were expressed at this stage in vivo. There was no significant increase in the level of either trkA mRNA or p75 mRNA in E13 control cultures up to 72 h in vitro, and neither NGF nor depolarizing levels of K+ ions (40 mM KC1) affected the expression of trkA mRNA. In E14 cultures, NGF induced c-fos expression in 10-15% of the neurons and enhanced the survival of a similar percentage of neurons. The proportion of neurons responding to NGF increased with age, reaching 90% in E18 cultures. The in vivo level of trkA mRNA increased markedly from E14 onward, but in contrast to sensory neurons (in which p75 and trkA mRNA levels increase in parallel), the level of trkA mRNA initially increased far more rapidly than that of p75 mRNA. After E17, the level of p75 mRNA increased rapidly and approached that of trkA mRNA postnatally, but at no stage did this exceed the level of trkA mRNA. In E14 cultures, the level of trkA mRNA increased in the absence of neurotrophins or 40 mM KC1. The level of p75 mRNA in E14 cultures was enhanced by NGF but was unaffected by 40 mM KC1. Our findings show that NGF receptor expression during the earliest stages of sympathetic neuron development is not affected by depolarization but indicate that by an early developmental stage (between E13 and E14 in vivo), sympathetic neurons become specified to upregulate trkA mRNA in culture independently of added factors. In addition, our findings reveal several distinctive features of p75 mRNA and trkA mRNA expression in sympathetic neurons compared with sensory neurons and provide a plausible explanation for previously observed differences in the effects of a p75 null mutation on the response of sensory and sympathetic neurons during embryonic and postnatal development.

Animals↗
PubMed1994

TrkA mediates an NGF survival response in NGF-independent sensory neurons but not in parasympathetic neurons.

We have investigated the role of trkA, the tyrosine kinase NGF receptor in mediating the survival response of embryonic chicken neurons to NGF. Embryonic trigeminal mesencephalic (TMN) neurons, which normally survive in the presence of BDNF but not NGF, become NGF-responsive when microinjected with an expression vector containing rat trkA cDNA. In contrast, microinjection of CNTF-dependent embryonic ciliary neurons with the same construct does not result in the acquisition of NGF-responsiveness. RT-PCR shows that injected TMN and ciliary neurons do not differ in their ability to express rat trkA mRNA or protein. The failure of injected ciliary neurons to show an NGF-promoted survival response is not due to absence of the low-affinity NGF receptor, p75, in these neurons. Quantitative PCR and immunocytochemistry shows that TMN and ciliary neurons both express p75 mRNA and protein. These findings not only provide the first direct experimental demonstration of trkA mediating a physiological response in an appropriate cell type, i.e. NGF-promoted survival of embryonic neurons, but indicate that not all neurons are able to respond to a trkA-mediated signal transduction event.

Animals↗
PubMed1993

The proto-oncogene bcl-2 can selectively rescue neurotrophic factor-dependent neurons from apoptosis.

Apoptosis plays an important role in regulating cell numbers in a wide variety of tissues during development. The product of the bcl-2 gene inhibits apoptosis in certain cells of the myeloid and lymphoid lineages and is expressed in many cells that have an extended life span. To assess the role of bcl-2 in neuronal apoptosis, we microinjected a bcl-2 expression vector into neurotrophic factor-deprived embryonic neurons. Sensory neurons that depend for survival on one or more members of the nerve growth factor family of neurotrophic factors (nerve growth factor, brain-derived neurotrophic factor, and neurotrophin-3) were rescued by bcl-2, whereas ciliary neurotrophic factor (CNTF)-dependent ciliary neurons were not. Sensory neurons, however, became refractory to bcl-2 after exposure to CNTF. These findings indicate that at least two death pathways operate in neurons that are distinguished by their susceptibility to bcl-2. Neurons may die by either pathway, depending on the factors to which they have been exposed.

Animals↗
PubMed1993

Ectopic trkA expression mediates a NGF survival response in NGF-independent sensory neurons but not in parasympathetic neurons.

We have investigated the role of trkA, the tyrosine kinase NGF receptor, in mediating the survival response of embryonic neurons to NGF. Embryonic trigeminal mesencephalic (TMN) neurons, which normally survive in the presence of brain-derived neurotrophic factor (BDNF) but not NGF, become NGF-responsive when microinjected with an expression vector containing trkA cDNA. In contrast, microinjection of ciliary neurotrophic factor (CNTF)-dependent embryonic ciliary neurons with the same construct does not result in the acquisition of NGF responsiveness by these neurons despite de novo expression of trkA mRNA and protein. The failure of trkA to result in an NGF-promoted survival response in ciliary neurons is not due to absence of the low-affinity NGF receptor, p75, in these neurons. Quantitative RT/PCR and immunocytochemistry showed that TMN and ciliary neurons both express p75 mRNA and protein. These findings not only provide the first direct experimental demonstration of trkA mediating a physiological response in an appropriate cell type, namely NGF-promoted survival of embryonic neurons, but indicate that not all neurons are able to respond to a trkA-mediated signal transduction event.

Animals↗
PubMed1993

Regulation of expression of mRNAs encoding the nerve growth factor receptors p75 and trkA in developing sensory neurons.

We have used a quantitative reverse transcription/polymerase chain reaction amplification technique to study the regulation of p75 mRNA and trkA mRNA expression in developing NGF-dependent trigeminal neurons. Before becoming NGF dependent, these neurons express low levels of p75 and trkA mRNAs in vivo. At this stage in vitro, the level of p75 mRNA is maintained and up-regulated by BDNF, whereas the level of trkA mRNA is sustained independently of neurotrophins and is down-regulated by BDNF. With the acquisition of NGF dependence, p75 and trkA mRNA levels increase markedly in vivo. At this stage in vitro, the level of p75 mRNA is up-regulated by NGF, but this response is lost at later stages. The level of trkA mRNA is sustained in neurons grown with NGF but is not up-regulated by concentrations of NGF above those required to support survival. At no stage during the early development of trigeminal neurons do depolarising levels of potassium ions affect the expression of either p75 mRNA or trkA mRNA. These findings suggest that the expression of p75 and trkA mRNAs are differentially regulated by BDNF and NGF at successive early stages of neuronal development.

Animals↗
PubMed1990

Expression of the NGF receptor gene in sensory neurons and their cutaneous targets prior to and during innervation.

We have studied the expression of NGF receptor (NGFR) mRNA in the mouse trigeminal system at closely staged intervals throughout development. The level of NGFR mRNA per neuron is at a constant low level before the earliest axons reach the target field and increases 5-fold to plateau shortly after the arrival of the last axons. NGFR mRNA expression in developing target skin is restricted to mesenchyme, precedes the arrival of the earliest axons, and increases throughout the phase of target field innervation. These findings suggest that NGFR expression on sensory neurons occurs at a low level prior to target field innervation and is up-regulated with this event, and they raise the possibility that NGFRs on mesenchymal cells restrict the distribution of NGF in the target field.

Animals↗
PubMed1986

Glycerol-3-phosphate excretion in fructose-1,6-diphosphatase deficiency.

A patient aged 23 months with fructose-1,6-diphosphatase deficiency is reported. This infant demonstrated an increased urine excretion of glycerol-3-phosphate during episodes of hypoglycaemia. The excretion of this compound has not previously been described in this disease or in those disorders associated with a deficiency in one of the other three gluconeogenic enzymes associated with hypoglycaemia. Its presence in the urine from patients may be useful in diagnosis.

Carbohydrate Metabolism, Inborn Errors↗
PubMedDate not supplied

Quantitative assessment of dietary adherence in patients with insulin-dependent diabetes mellitus.

Research on the education of diabetic patients in diet management suffers from lack of an adequate method for describing patients' dietary behavior. In this report, a method is proposed for the quantitative assessment of dietary adherence in patients with IDDM. The method relies on comparisons between individualized diet plans and actual consumption as reflected by 24-h diet recalls. Data are presented that suggest this method has reliability and validity. In a sample of 97 patients with IDDM, nearly two-thirds adhered to the number and timing of planned feedings, while only about 10% of patients adhered to planned exchanges, 90% of the time. The average patient added or deleted one exchange for every four exchanges in the diet plan.

Adolescent↗