A tiny baby intubation team improves endotracheal intubation success rate but decreases residents' training opportunities.

OBJECTIVE: To assess the educational and clinical impact of a tiny baby intubation team (TBIT). STUDY DESIGN: Retrospective study comparing endotracheal intubation (ETI) performed: pre-implementation of a TBIT (T1), 6 months post-implementation (T2), and 4 years post-implementation (T3). RESULTS: Post-implementation (T2), first-attempt success rate in tiny babies increased (44% T1; 59% T2, p = 0.04; 56% T3, p = NS) and the proportion of ETIs performed by residents decreased (53% T1; 37% T2, p = 0.001; 45% T3, p = NS). After an educational quality improvement intervention (prioritizing non-tiny baby ETIs to residents, systematic simulation training and ETI using videolaryngoscopy), in T3 residents' overall (67% T1; 60% T2, p = NS; 79% T3, p = 0.02) and non-tiny baby ETI success rate improved (72% T1; 60% T2, p = NS; 82% T3, p = 0.02). CONCLUSION: A TBIT improves success rate of ETIs in ELBW infants but decreases educational exposure of residents. Educational strategies may help maintain resident procedural competency without impacting on quality of care.

The immobilization of human spermatozoa by STAT3 inhibitory compound V results from an excessive intracellular amount of reactive oxygen species.

We previously showed that Stattic V (Stat3 inhibitory compound V) reduces human sperm motility and cellular ATP levels, increases intracellular Ca(2+) concentration, and promotes mitochondrial membrane depolarization resulting in increased levels of extracellular reactive oxygen species (ROS). As these alterations in cellular function are highly similar to what is observed in a cell undergoing apoptosis, our goal was to determine if the immobilizing effect of Stattic V on spermatozoa results from apoptosis or was because of an oxidative stress. To address this question, spermatozoa were incubated with Stattic V in combination with a caspase inhibitor, a proteasome inhibitor or a cell permeant ROS scavenger. Following incubation in different conditions, sperm motility was evaluated by CASA, acrosomal integrity by FITC conjugated Pisum sativum agglutinin (PSA-FITC) labeling, intracellular pH, and mitochondrial superoxide production by flow cytometry using BCECF and MitoSoxRed dye, respectively. Levels of reduced thiols were assessed by iodoacetamidofluorescein staining on total and on sperm surface proteins, and protein tyrosine phosphorylation was evaluated by western blot. The loss in sperm motility induced by Stattic V was associated with a slight intracellular acidification and an important increase in intracellular superoxide anion. Unlike caspase and proteasome inhibitors, low molecular weight thiols, such as N-acetyl-L-cysteine (NAC), prevented Stattic V-induced sperm immobilization and increase responsiveness to acrosome reaction inducers. NAC also efficiently prevented the production of superoxide anion, mitochondrial membrane depolarization, intracellular acidification and the oxidation of protein free thiols caused by Stattic V. These results show that the deleterious effects of Stattic V on sperm functions are caused directly or indirectly by excessive intracellular ROS production without causing sperm apoptosis or necrosis.

[Adverse effects and hemodynamic effects of nifedipine as a tocolytic]. / Effets indésirables et effets hémodynamiques de la nifédipine utilisée comme tocolytique.

OBJECTIVES: To describe maternal and fetal adverse effects, in particular cardiorespiratory, of nifedipine as tocolytic, as well as effects on hemodynamic parameters. MATERIALS AND METHODS: A retrospective evaluative study describing the use of nifedipine as tocolytic at CHU Sainte-Justine in Montreal. Demographic data as well as maternal blood pressure and adverse effects, and maternal and fetal heart rate were collected from medical records of women treated with nifedipine following our tocolysis protocol between January 1st 2004 and March 1st 2007. RESULTS: The medical records of 213 pregnant women were included in the study. Cardiorespiratory adverse effects were noted in 69 (32.4%); of these, 19 (8.9%) had serious cardiorespiratory adverse events, including 6 acute pulmonary edema or overload. Mean maternal systolic and diastolic blood pressures were significantly decreased and mean maternal and fetal heart rates were significantly increased after the bolus dose. Other adverse effects were reported for 100 (46.9%) women. CONCLUSION: Nifedipine may cause cardiorespiratory adverse effects warranting a close monitoring.

Implication of the human Binder of SPerm Homolog 1 (BSPH1) protein in capacitation.

Binder of SPerm (BSP) proteins are a family of proteins expressed exclusively in the male reproductive tract (seminal vesicles or epididymis) of several mammalian species. They are known to promote capacitation, a sperm maturation step essential for fertilization. Our recent studies have shown that in human, the Binder of SPerm Homolog 1 (BSPH1) is expressed solely in epididymal tissues. The goal of the current study was to characterize BSPH1 and evaluate its effect on different sperm functions. A human recombinant BSPH1 (rec-BSPH1) was produced, purified and refolded. Rec-BSPH1 was found to share many characteristics with other members of the BSP superfamily, as it was able to bind gelatin and heparin as well as capacitate sperm. Rec-BSPH1 had no effect on sperm acrosome reaction or any sperm motility parameters. Native BSPH1 was localized on the equatorial segment, post-acrosomal segment and neck of ejaculated human sperm. Rec-BSPH1, following incubation with washed ejaculated human sperm, exhibited binding patterns similar to the native protein. These results show that the human epididymal BSPH1 shares many biochemical and functional characteristics with BSP proteins secreted by seminal vesicles of ungulates, and behaves similarly to its murine epididymal orthologue BSPH1. This study of human BSPH1 brings us one step closer to understanding the importance of this protein in male fertility.

Age differences in genetic knowledge, health literacy and causal beliefs for health conditions.

OBJECTIVES: This study examined the levels of genetic knowledge, health literacy and beliefs about causation of health conditions among individuals in different age groups. METHODS: Individuals (n = 971) recruited through 8 community health centers in Suffolk County, New York, completed a one-time survey. RESULTS: Levels of genetic knowledge were lower among individuals in older age groups (26-35, p = 0.011; 36-49, p = 0.002; 50 years and older, p<0.001) compared to those in the youngest age group (18-25). Participants in the oldest age group also had lower health literacy than those in the youngest group (p <0.001). Those in the oldest group were more likely to endorse genetic (OR = 1.87, p = 0.008) and less likely to endorse behavioral factors like diet, exercise and smoking (OR = 0.55, p = 0.010) as causes of a person's body weight than those in the youngest group. Higher levels of genetic knowledge were associated with higher likelihood of behavioral attribution for body weight (OR = 1.25, p <0.001). CONCLUSIONS: Providing additional information that compensates for their lower genetic knowledge may help individuals in older age groups benefit from rapidly emerging genetic health information more fully. Increasing the levels of genetic knowledge about common complex diseases may help motivate individuals to engage in health promoting behaviors to maintain healthy weight through increases in behavioral causal attributions.

Educating underserved Latino communities about family health history using lay health advisors.

BACKGROUND: Family health history (FHH) is a tool used to inform individuals about inherited disease risk. Due to their disproportionate morbidity and mortality from some common chronic diseases, U.S. Latinos are an important audience for FHH information. This study examined the effects of a culturally-tailored intervention led by lay health advisors (LHAs) in delivering information about FHH on participants' intentions, self-efficacy, and conceptual knowledge. METHODS: 474 Spanish-speaking Latino participants were enrolled in the study. Individuals in the intervention group participated in a single group educational session using discussion and interactive activities to build skills for discussing FHH with one's family members and doctor, while individuals in the comparison group had a brochure read aloud to them. Pre- and post-test questionnaires were verbally administered. RESULTS: Primary dependent variables were intentions and self-efficacy to discuss FHH with family members and doctors; these increased in both groups. Multivariate analyses demonstrated that the intervention led to a significantly greater increase in self-efficacy to discuss FHH with family members (p = 0.03). LHA participants were also more than twice as likely (OR = 2.6, 95% CI = 1.3-5.0) to correctly understand the purpose of a FHH and found FHH information more useful (p < 0.0001). CONCLUSIONS: A communication intervention delivered by LHAs shows promise as an effective means of educating underserved Spanish-speaking Latinos about the importance of FHH for disease prevention. Such community-based approaches can help to close knowledge and skills gaps about FHH and increase confidence in using this information to improve the health of those most at risk.

Relevance of measuring diastolic time intervals in the ductus venosus during the early stages of twin-twin transfusion syndrome.

OBJECTIVE: To determine if the discrete myocardial diastolic dysfunction documented previously in the recipient twin during the early stages of twin-twin transfusion syndrome (TTTS) has any repercussion on flow velocities through the ductus venosus (DV) and to investigate if this could allow early differentiation between TTTS and selective intrauterine growth restriction (IUGR). METHODS: Two groups of monochorionic twin pregnancies with growth discordance between twins were reviewed retrospectively. Group I was composed of fetuses in Stages I and II of TTTS; laser or amnioreduction was not performed in any instance. Group II twin pairs each included one fetus with IUGR due to placental circulatory insufficiency. Intertwin differences (smaller minus larger fetus) were analyzed for myocardial performance index of the right ventricle (MPI-RV) and for time variables in the DV. RESULTS: There were 38 pairs of monochorionic twins (24 TTTS and 14 IUGR) in this study. In the TTTS group, the donors had a significantly lower MPI-RV (0.419 +/- 0.18 vs. 0.596 +/- 0.17, F(1,19df) = 24.017, P < 0.001), a significantly longer total ventricular filling time (150.9 +/- 25.6 ms vs. 124.0 +/- 22.6 ms; F(1,21df) = 19.631, P < 0.001) and a significantly longer early filling time (118.9 +/- 22.9 ms vs. 92.6 +/- 18.9 ms, F(1,21df) = 28.419, P < 0.001) than had the recipient. None of these three differences was present in the IUGR group. Probability studies revealed that cut-off values of 12.75 for intertwin differences in total filling time and 8.5 for intertwin differences in early filling time had sensitivities of 71% and 92%, respectively. The false-positive rates were 23% and 15%, respectively, for the early diagnosis of TTTS. CONCLUSION: In monochorionic twin pregnancies, shortening of the ventricular filling time in the recipient twin indicates diastolic myocardial dysfunction occurring early in the pathophysiology of TTTS. This early interwin difference in myocardial function is not found in pregnancies with IUGR in one twin due to placental circulatory insufficiency, allowing early differentiation between TTTS and selective IUGR.

Localization of the chaperone proteins GRP78 and HSP60 on the luminal surface of bovine oviduct epithelial cells and their association with spermatozoa.

Upon their transit through the female genital tract, bovine spermatozoa bind to oviduct epithelial cells, where they are maintained alive for long periods of time until fertilization. Although carbohydrate components of the oviduct epithelial cell membrane are involved in these sperm/oviduct interactions, no protein candidate has been identified to play this role. To identify the oviduct factors involved in their survival, sperm cells were preincubated for 30 min with apical membranes isolated from oviduct epithelial cells, washed extensively, and further incubated for up to 12 h in the absence of apical membranes. During this incubation, sperm viability, motility, and acrosomal integrity were improved compared with cells preincubated in the absence of apical membranes. This suggests that, during the 30-min preincubation with apical membrane extracts, either an oviductal factor triggered intracellular events resulting in positive effects on spermatozoa or that such a factor strongly attached to sperm cells to promote a positive action. Similarly, spermatozoa were incubated with apical membranes isolated from oviduct epithelial cells labeled with [35S]-methionine and, upon extensive washes, proteins were separated by two-dimensional (2-D) gel electrophoresis to identify the factors suspected to have beneficial effects on spermatozoa. The six major proteins, according to their signal intensity on the autoradiographic film, were extracted from a 2-D gel of oviduct epithelial cell proteins run in parallel and processed for N-terminal sequencing of the first 15 amino acids. Of these, one was identical to heat shock protein 60 (HSP60) and one to the glucose-regulated protein 78 (GRP78). Their identities and association with spermatozoa were confirmed using an antibody directed against these proteins. This paper reports the localization of both GRP78 and HSP60 on the luminal/apical surface of oviduct epithelial cells, their binding to spermatozoa, and the presence of endogenous HSP60 in the sperm midpiece.

Clearance of infection with Mycobacterium bovis BCG in mice is enhanced by treatment with S28463 (R-848), and its efficiency depends on expression of wild-type Nramp1 (resistance allele).

The mouse bcg host resistance gene is known to control the activation of host macrophages for killing of intracellular parasites like Leishmania donovani as well as intracellular bacteria, including Mycobacterium bovis BCG and Salmonella enterica serovar Typhimurium. The Nramp1 gene has been mapped to this locus and affects the efficiency of macrophage activation. It has been shown that imidazoquinoline compounds, including S28463, are able to improve the clearance of a number of intracellular pathogens such as herpes simplex virus 2, human papillomavirus, and Leishmania. The goal of this study was to determine whether S28463 is efficient against infection with another intracellular pathogen, M. bovis BCG, and to determine the molecular basis underlying this effect. To achieve this, B10A.Nramp1(r) and B10A.Nramp1(-/-) mice were infected with M. bovis BCG and treated with S28463. The bacterial content in the spleen from these mice was assayed by a colony-forming assay. In addition, in vitro experiments were performed using bone marrow-derived macrophage cell lines from these mice. These cells were treated with S28463 and/or gamma interferon (IFN-gamma), and nitric oxide (NO) production was measured. Our study was able to show that S28463 acts in synergy with IFN-gamma to increase the production of NO in vitro. We were also able to demonstrate that mice that carried the resistant allele of the Nramp1 gene and were infected with M. bovis BCG responded to treatment with S28463, resulting in a decreased bacterial load after 2 weeks of treatment. Mice that do not express the Nramp1 gene responded only to a very large dose of S28463, and the response was not as efficient as that observed in mice carrying a wild-type Nramp1 allele. Our data provide evidence for the potential of S28463 as an immunomodulator that may be helpful in designing efficient strategies to improve host defense against mycobacterial infection.

Polymorphism in the 3'-untranslated region of TNFalpha mRNA impairs binding of the post-transcriptional regulatory protein HuR to TNFalpha mRNA.

Tumor necrosis factor alpha (TNFalpha) acts as a beneficial mediator in the process of host defence. In recent years major interest has focused on the AU-rich elements (AREs) present in the 3'-untranslated region (3'-UTR) of TNFalpha mRNA as this region plays a pivotal role in post-transcriptional control of TNFalpha production. Certain stimuli, such as lipopolysaccharides, a component of the Gram-negative bacterial cell wall, have the ability to relinquish the translational suppression of TNFalpha mRNA imposed by these AREs in macrophages, thereby enabling the efficient production of the TNFalpha. In this study we show that the polymorphism (GAU trinucleotide insertional mutation) present in the regulatory 3'-UTR of TNFalpha mRNA of NZW mice results in the hindered binding of RNA-binding proteins, thereby leading to a significantly reduced production of TNFalpha protein. We also show that the binding of macrophage proteins to the main ARE is also decreased by another trinucleotide (CAU) insertion in the TNFalpha 3'-UTR. One of the proteins affected by the GAU trinucleotide insertional mutation was identified as HuR, a nucleo-cytoplasmic shuttling protein previously shown to play a prominent role in the stability and translatability of mRNA containing AREs. Since binding of this protein most likely modulates the stability, translational efficiency and transport of TNFalpha mRNA, these results suggest that mutations in the ARE of TNFalpha mRNA decrease the production of TNFalpha protein in macrophages by hindering the binding of HuR to the ARE.

The p75 neurotrophin receptor (p75NTR) alters tumor necrosis factor-mediated NF-kappaB activity under physiological conditions, but direct p75NTR-mediated NF-kappaB activation requires cell stress.

The p75 neurotrophin receptor (p75NTR) has been linked to activation of the NF-kappaB transcriptional complex in oligodendrocytes, Schwann cells, and PCNA cells. In this report, tumor necrosis factor (TNF)- and neurotrophin-mediated NF (nuclear factor)-kappaB activation were compared in several cell lines. All cell types showed TNF-mediated activation of NF-kappaB, but direct neurotrophin-dependent activation of NF-kappaB was never observed under normal growth conditions. In PCNA cells, a modest nerve growth factor (NGF)-dependent induction of NF-kappaB was detected but only after cells were subjected to severe stress. Although NGF binding did not directly activate NF-kappaB under normal conditions, NGF consistently altered TNF-dependent NF-kappaB activation in each cell type examined, and extended exposure to NGF and TNF always increased NF-kappaB activation over that achieved with TNF alone. The increase in NF-kappaB activity mediated by NGF correlated with reduced levels of IkappaBalpha; NGF added alone had no effect on IkappaBalpha levels, but when added with TNF, NGF treatment significantly reduced IkappaBalpha levels. We propose that modulation of cytokine receptor signaling is a significant physiological function of the p75 neurotrophin receptor and that previous reports of direct NF-kappaB activation through p75NTR reflect this modulatory activity.

Persistent infection of human oligodendrocytic and neuroglial cell lines by human coronavirus 229E.

Human coronaviruses (HuCV) cause common colds. Previous reports suggest that these infectious agents may be neurotropic in humans, as they are for some mammals. With the long-term aim of providing experimental evidence for the neurotropism of HuCV and the establishment of persistent infections in the nervous system, we have evaluated the susceptibility of various human neural cell lines to acute and persistent infection by HuCV-229E. Viral antigen, infectious virus progeny and viral RNA were monitored during both acute and persistent infections. The astrocytoma cell lines U-87 MG, U-373 MG, and GL-15, as well as neuroblastoma SK-N-SH, neuroglioma H4, and oligodendrocytic MO3.13 cell lines, were all susceptible to an acute infection by HuCV-229E. The CHME-5 immortalized fetal microglial cell line was not susceptible to infection by this virus. The MO3.13 and H4 cell lines also sustained a persistent viral infection, as monitored by detection of viral antigen and infectious virus progeny. Sequencing of the S1 gene from viral RNA after approximately 130 days of infection showed two point mutations, suggesting amino acid changes during persistent infection of MO3.13 cells but none for H4 cells. Thus, persistent in vitro infection did not generate important changes in the S1 portion of the viral spike protein, which was shown for murine coronaviruses to bear hypervariable domains and to interact with cellular receptor. These results are consistent with the potential persistence of HuCV-229E in cells of the human nervous system, such as oligodendrocytes and possibly neurons, and the virus's apparent genomic stability.

Acute and persistent infection of human neural cell lines by human coronavirus OC43.

Human coronaviruses (HuCV) are recognized respiratory pathogens. Data accumulated by different laboratories suggest their neurotropic potential. For example, primary cultures of human astrocytes and microglia were shown to be susceptible to an infection by the OC43 strain of HuCV (A. Bonavia, N. Arbour, V. W. Yong, and P. J. Talbot, J. Virol. 71:800-806, 1997). We speculate that the neurotropism of HuCV will lead to persistence within the central nervous system, as was observed for murine coronaviruses. As a first step in the verification of our hypothesis, we have characterized the susceptibility of various human neural cell lines to infection by HuCV-OC43. Viral antigen, infectious virus progeny, and viral RNA were monitored during both acute and persistent infections. The astrocytoma cell lines U-87 MG, U-373 MG, and GL-15, as well as neuroblastoma SK-N-SH, neuroglioma H4, oligodendrocytic MO3.13, and the CHME-5 immortalized fetal microglial cell lines, were all susceptible to an acute infection by HuCV-OC43. Viral antigen and RNA and release of infectious virions were observed during persistent HuCV-OC43 infections ( approximately 130 days of culture) of U-87 MG, U-373 MG, MO3.13, and H4 cell lines. Nucleotide sequences of RNA encoding the putatively hypervariable viral S1 gene fragment obtained after 130 days of culture were compared to that of initial virus input. Point mutations leading to amino acid changes were observed in all persistently infected cell lines. Moreover, an in-frame deletion was also observed in persistently infected H4 cells. Some point mutations were observed in some molecular clones but not all, suggesting evolution of the viral population and the emergence of viral quasispecies during persistent infection of H4, U-87 MG, and MO3.13 cell lines. These results are consistent with the potential persistence of HuCV-OC43 in cells of the human nervous system, accompanied by the production of infectious virions and molecular variation of viral genomic RNA.

Involvement of aminopeptidase N (CD13) in infection of human neural cells by human coronavirus 229E.

Attachment to a cell surface receptor can be a major determinant of virus tropism. Previous studies have shown that human respiratory coronavirus HCV-229E uses human aminopeptidase N (hAPN [CD13]) as its cellular receptor for infection of lung fibroblasts. Although human coronaviruses are recognized respiratory pathogens, occasional reports have suggested their possible neurotropism. We have previously shown that human neural cells, including glial cells in primary cultures, are susceptible to human coronavirus infection in vitro (A. Bonavia, N. Arbour, V. W. Yong, and P. J. Talbot, J. Virol. 71:800-806, 1997). However, the only reported expression of hAPN in the nervous system is at the level of nerve synapses. Therefore, we asked whether hAPN is utilized as a cellular receptor for infection of these human neural cell lines. Using flow cytometry, we were able to show the expression of hAPN on the surfaces of various human neuronal and glial cell lines that are susceptible to HCV-229E infection. An hAPN-specific monoclonal antibody (WM15), but not control antibody, inhibited the attachment of radiolabeled HCV-229E to astrocytic, neuronal, and oligodendrocytic cell lines. A correlation between the apparent amount of cell surface hAPN and the level of virus attachment was observed. Furthermore, the presence of WM15 inhibited virus infection of these cell lines, as detected by indirect immunofluorescence. These results indicate that hAPN (CD13) is expressed on neuronal and glial cell lines in vitro and serves as the receptor for infection by HCV-229E. This further strengthens the neurotropic potential of this human respiratory virus.

p75 neurotrophin receptor expression on adult human oligodendrocytes: signaling without cell death in response to NGF.

Oligodendrocytes (OLs) are the primary targets in the autoimmune disease multiple sclerosis (MS). Cell receptors belonging to the tumor necrosis factor receptor (TNF-R) superfamily, such as TNF receptors and fas, are implicated in signaling the injury response of OLs. The p75 neurotrophin receptor (p75(NTR)), another member of the TNF-R superfamily, has been reported to mediate nerve growth factor (NGF)-induced apoptosis in some neural systems. To address the potential relationship between p75(NTR) signaling and OL injury, we assayed adult human OLs cultured under several different conditions for p75(NTR) and tyrosine kinase receptor trkA expression, for NGF-mediated apoptosis, and for NGF-mediated jun kinase (JNK) or nuclear factor (NF) kappaB activation. In the current study, we have found expression of p75(NTR) on cultured adult CNS-derived human OLs but not on other glial cells. TrkA was not detected on these OLs in any of the culture conditions tested. Treatment of the OLs with varying concentrations of NGF over a range of time periods resulted in no significant increase in numbers of terminal transferase (TdT)-mediated d-uridine triphosphate (UTP)-biotin nick-end labeling positive OLs, whereas significant cell death was observed using TNF-alpha. Furthermore, unlike TNF-alpha treatment, NGF treatment did not significantly activate JNK, although both TNF-alpha and NGF induced nuclear translocation of NF-kappaB. These findings contrast with the recent report of NGF-mediated apoptosis in the OLs of neonatal rats matured in vitro, which express p75(NTR) but not trkA (), and suggest that, at least in humans, p75(NTR) signaling may mediate responses other than apoptosis of OLs.

Characterization of the expression and immunogenicity of the ns4b protein of human coronavirus 229E.

Sequencing of complementary DNAs prepared from various coronaviruses has revealed open reading frames encoding putative proteins that are yet to be characterized and are so far only described as nonstructural (ns). As a first step in the elucidation of its function, we characterized the expression and immunogenicity of the ns4b gene product from strain 229E of human coronavirus (HCV-229E), a respiratory virus with a neurotropic potential. The gene was cloned and expressed in bacteria. A fusion protein of ns4b with maltose-binding protein was injected into rabbits to generate specific antibodies that were used to demonstrate the expression of ns4b in HCV-229E-infected cells using flow cytometry. Given a previously reported contiguous five amino acid shared region between ns4b and myelin basic protein, a purified recombinant histidine-tagged ns4b protein and (or) human myelin basic protein were injected into mice to evaluate whether myelin-viral protein cross-reactive antibody responses could be generated. Each immunogen induced specific but not cross-reactive antibodies. We conclude that ns4b is expressed in infected cells and is immunogenic, although this does not involve amino acids shared with a self protein, at least in the experimental conditions used.

Blocking nerve growth factor binding to the p75 neurotrophin receptor on sympathetic neurons transiently reduces trkA activation but does not affect neuronal survival.

Nerve growth factor interacts with the trkA tyrosine kinase receptor and with the p75 neurotrophin receptor. It is clear that trkA mediates most, if not all, of the stereotypical responses of sympathetic neurons to nerve growth factor but the role of the p75 neurotrophin receptor is unclear. In this study, we have asked whether a functional interaction between p75 neurotrophin receptor and trkA exists in primary sympathetic neurons by disrupting nerve growth factor binding to p75 neurotrophin receptor. Acute assays reveal that blocking antibodies directed against p75 neurotrophin receptor reduce nerve growth factor-mediated trkA tyrosine phosphorylation and reduce the amount of nerve growth factor which binds the trkA receptor. This reduction in trkA activity is relatively short-lived in vitro and blocking antibodies to p75 neurotrophin receptor do not inhibit long-term survival of nerve growth factor-dependent primary neurons. Together, these data indicate that p75 neurotrophin receptor and trkA interact within primary neurons to enhance nerve growth factor binding to the trkA receptor under conditions of acute but not chronic nerve growth factor exposure.

Transgenic mice expressing the intracellular domain of the p75 neurotrophin receptor undergo neuronal apoptosis.

We have asked whether p75(NTR) may play a role in neuronal apoptosis by producing transgenic mice that express the p75(NTR) intracellular domain within peripheral and central neurons. These animals showed profound reductions in numbers of sympathetic and peripheral sensory neurons as well as cell loss in the neocortex, where there is normally little or no p75(NTR) expression. Developmental loss of facial motor neurons was not observed, but induced expression of the p75(NTR) intracellular domain within adult animals led to increased motor neuron death after axotomy. Biochemical analyses suggest that these effects were not attributable to a p75(NTR)-dependent reduction in trk activation but instead indicate that the p75(NTR) intracellular domain may act as a constitutive activator of signaling cascades that regulate apoptosis in both peripheral and central neurons.