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Biomedical subjects

M Sendtner

Publications and source records attributed to M Sendtner.

At least 37 records · Page 2Linked to original sources
PubMed2000

Developmental motoneuron cell death and neurotrophic factors.

During the development of higher vertebrates, motoneurons are generated in excess. In the lumbar spinal cord of the developing rat, about 6000 motoneurons are present at embryonic day 14. These neurons grow out axons which make contact with their target tissue, the skeletal muscle, and about 50% of the motoneurons are lost during a critical period from embryonic day 14 until postnatal day 3. This process, which is called physiological motoneuron cell death, has been the focus of research aiming to identify neurotrophic factors which regulate motoneuron survival during this developmental period. Motoneuron cell death can also be observed in vitro when the motoneurons are isolated from the embryonic avian or rodent spinal cord. These isolated motoneurons and other types of primary neurons have been a useful tool for studying basic mechanisms underlying neuronal degeneration during development and under pathophysiological conditions in neurodegenerative disorders. Accumulating evidence from such studies suggests that some specific requirements of motoneurons for survival and proper function may change during development. The focus of this review is a synopsis of recent data on such specific mechanisms.

Animals↗
PubMed2000

Reg-2 is a motoneuron neurotrophic factor and a signalling intermediate in the CNTF survival pathway.

Cytokines that are related to ciliary neurotrophic factor (CNTF) are physiologically important survival factors for motoneurons, but the mechanisms by which they prevent neuronal cell death remain unknown. Reg-2/PAP I (pancreatitis-associated protein I), referred to here as Reg-2, is a secreted protein whose expression in motoneurons during development is dependent on cytokines. Here we show that CNTF-related cytokines induce Reg-2 expression in cultured motoneurons. Purified Reg-2 can itself act as an autocrine/paracrine neurotrophic factor for a subpopulation of motoneurons, by stimulating a survival pathway involving phosphatidylinositol-3-kinase, Akt kinase and NF-kappaB. Blocking Reg-2 expression in motoneurons using Reg-2 antisense adenovirus specifically abrogates the survival effect of CNTF on cultured motoneurons, indicating that Reg-2 expression is a necessary step in the CNTF survival pathway. Reg-2 shows a unique pattern of expression in late embryonic spinal cord: it is progressively upregulated in individual motoneurons on a cell-by-cell basis, indicating that only a fraction of motoneurons in a given motor pool may be exposed to cytokines. Thus, Reg-2 is a neurotrophic factor for motoneurons, and is itself an obligatory intermediate in the survival signalling pathway of CNTF-related cytokines.

Animals↗
PubMed2000

A phase I/II trial of recombinant methionyl human brain derived neurotrophic factor administered by intrathecal infusion to patients with amyotrophic lateral sclerosis.

BACKGROUND: Brain derived neurotrophic factor (BDNF) is a potent survival factor for motoneurons. This study investigated the safety and tolerability of recombinant methionyl human BDNF (r-metHuBDNF) infused intrathecally by means of an implanted pump in patients with ALS. METHODS: Twenty-five patients with probable or definite ALS were treated with either r-metHuBDNF (25, 60, 150, 400 or 1000 microg/day) or placebo in a 12-week, randomized, double-blinded, sequential, dose-escalation study. Test treatment was interrupted by a washout period from days 11 to 25 to allow the evaluation of laboratory safety measures. In each dose cohort four patients received r-metHuBDNF and one received placebo. On completion of the double-blind period of the study all patients continued to receive r-metHuBDNF in an open-label extension for up to 60 weeks. Lumbar cerebrospinal fluid (CSF) samples were taken periodically from all patients for the measurement of r-metHuBDNF levels and in a minority of patients these were supplemented by cistemal samples. RESULTS: Within days after the initiation of infusion the majority of patients receiving r-metHuBDNF reported mild sensory symptoms, including paraesthesias or a sense of warmth, which were usually confined to the lower limbs and were frequently exacerbated by neck flexion. In most instances these symptoms decreased or even disappeared over several weeks. Sleep disturbance, dry mouth, agitation and other behavioural effects were encountered at higher doses (>150 microg/day) and necessitated dose reductions. The spinal CSF levels of r-metHuBDNF were directly related to dose, with a lumbar to cervical ratio of approximately 4:1. CONCLUSIONS: The intrathecal delivery of r-metHuBDNF in doses of up to 150 microg/day was well tolerated and appears feasible. The reversible CNS effects with higher dose indicate that BDNF can be delivered cranially against CSF flow. The small number of patients and the design of the study did not permit conclusions to be drawn about the efficacy of the treatment.

Adult↗
PubMed2000

Contribution of Ca(2+)-permeable AMPA/KA receptors to glutamate-induced Ca(2+) rise in embryonic lumbar motoneurons in situ.

Intracellular Ca(2+) ([Ca(2+)](i)) was fluorometrically measured with fura-2 in lumbar motoneurons of acutely isolated spinal cord slices from embryonic rats. In ester-loaded cells, bath-applied glutamate (3 microM to 1 mM) evoked a [Ca(2+)](i) increase by up to 250 nM that was abolished by 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) plus 2-amino-5-phosphonovalerate (APV). CNQX or APV alone reduced the response by 82 and 25%, respectively. The glutamatergic agonists kainate (KA), quisqualate (QUI), and S-alpha-amino-3-hydroxy-5-methyl-4-isoxalone (S-AMPA) evoked a similar [Ca(2+)](i) transient as glutamate. N-methyl-D-aspartate (NMDA) was only effective to increase [Ca(2+)](i) in Mg(2+)-free saline, whereas [1S,3R]-1-aminocyclopentane-1,3-dicarboxylic acid ([1S,3R]-ACPD) had no effect. The glutamate-induced [Ca(2+)](i) rise was suppressed in Ca(2+)-free superfusate. Depletion of Ca(2+) stores with cyclopiazonic acid (CPA) did not affect the response. Thirty-six percent of the [Ca(2+)](i) increase in response to membrane depolarization induced by a 50 mM K(+) solution persisted on combined application of the voltage-gated Ca(2+) channel blockers nifedipine, omega-conotoxin-GVIA and omega-agatoxin-IVA. In fura-2 dialyzed motoneurons, the glutamate-induced [Ca(2+)](i) increase was attenuated by approximately 70% after changing from current to voltage clamp. Forty percent of the remaining [Ca(2+)](i) transient and 20% of the concomitant inward current of 0.3 nA were blocked by Joro spider toxin-3 (JSTX). The results show that voltage-gated Ca(2+) channels, including a major portion of R-type channels, constitute the predominant component of glutamate-induced [Ca(2+)](i) rises. NMDA and Ca(2+)-permeable KA/AMPA receptors contribute about equally to the remaining component of the Ca(2+) rise. The results substantiate previous assumptions that Ca(2+) influx through JSTX-sensitive KA/AMPA receptors is involved in (trophic) signaling in developing motoneurons.

2-Amino-5-phosphonovalerate↗
PubMed1999

Comparative analysis of motoneuron loss and functional deficits in PMN mice: implications for human motoneuron disease.

We have investigated the correlation between functional and morphological deficits in PMN mice, an animal model of human motoneuron disease. Electrophysiologic investigations showed first abnormalities, i.e. reduction of M-response amplitudes, already at postnatal d 13 when the disease was not yet phenotypically apparent, and when motoneuron and motor axon numbers were still normal. After d 27, a loss of more than 30% of motoneuron axons and cell bodies was detectable in the phrenic nerve and facial nucleus, respectively. At that stage, PMN mice showed severe functional and electrophysiological deficits. At later stages of the disease when still more than 50% of motor axons and at least 60% of motoneuron cell bodies were present, the distal compound muscle action potential amplitude decreased by more than 95% in small foot muscles after sciatic nerve stimulation. We conclude that functional deficits precede structural deficits in this animal model of human motoneuron disease. Our findings are in agreement with the concept of the 'sick motoneuron' in this animal model of motoneuron disease rather than the idea of progressive loss of motoneurons resulting in disease only after a significant number of motoneurons has degenerated.

Action Potentials↗
PubMed1999

Developmental requirement of gp130 signaling in neuronal survival and astrocyte differentiation.

gp130 is a signal-transducing receptor component used in common by the interleukin-6 (IL-6) family of hematopoietic and neurotrophic cytokines, including IL-6, IL-11, leukemia-inhibitory factor, ciliary neurotrophic factor, oncostatin-M, and cardiotrophin-1. We have examined in this study a role of gp130 in the nervous system by analyzing developmental cell death of several neuronal populations and the differentiation of astrocytes in gp130-deficient mice. A significant reduction was observed in the number of sensory neurons in L5 dorsal root ganglia and motoneurons in the facial nucleus, the nucleus ambiguus, and the lumbar spinal cord in gp130 -/- mice on embryonic day 18.5. On the other hand, no significant neuronal loss was detectable on day 14.5, suggesting a physiological role of gp130 in supporting newly generated neurons during the late phase of development when naturally occurring cell death takes place. Moreover, expression of an astrocyte marker, GFAP, was severely reduced in the brain of gp130 -/- mice. Our data demonstrate that gp130 expression is essential for survival of subgroups of differentiated motor and sensory neurons and for the differentiation of major populations of astrocytes in vivo.

Animals↗
PubMed1999

Toxoplasma gondii in primary rat CNS cells: differential contribution of neurons, astrocytes, and microglial cells for the intracerebral development and stage differentiation.

The central nervous system (CNS) of the intermediate host plays a central role in the lifelong persistence of Toxoplasma gondii as well as in the pathogenesis of congenital toxoplasmosis and reactivated infection in immunocompromised patients. In order to analyze the parasite-host interaction within the CNS, the host cell invasion, the intracellular replication, and the stage conversion from tachyzoites to bradyzoites was investigated in mixed cultures of dissociated CNS cells from cortices of Wistar rat embryos. Two days post infection (p.i.) with T. gondii tachyzoites, intracellular parasites were detected within neurons, astrocytes, and microglial cells as assessed by double immunofluorescence and confocal microscopy. Quantitative analyses revealed that approximately 10% of neurons and astrocytes were infected with T. gondii, while 30% of the microglial cells harbored intracellular parasites. However, the replication of T. gondii within microglial cells was considerably diminished, since 93% of the parasitophorous vacuoles (PV) contained only one to two parasites which often appeared degenerated. This toxoplasmacidal activity was not abrogated after treatment with NO synthase inhibitors or neutralization of IFN-gamma production. In contrast, 30% of the PV in neurons and astrocytes harbored clearly proliferating parasites with at least four to eight parasites per vacuole. Four days p.i. with tachyzoites of T. gondii, bradyzoites were detected within neurons, astrocytes, and microglial cells of untreated cell cultures. However, the majority of bradyzoite-containing vacuoles were located in neurons. Spontaneous differentiation to the bradyzoite stage was not inhibited after addition of NO synthase inhibitors or neutralization of IFN-gamma. In conclusion, our results indicate that intracerebral replication of T. gondii as well as spontaneous conversion from the tachyzoite to the bradyzoite stage is sustained predominantly by neurons and astrocytes, whereas microglial cells may effectively inhibit parasitic growth within the CNS.

Animals↗
PubMed1999

Mechanical and excitotoxic lesion of motoneurons: effects of neurotrophins and ciliary neurotrophic factor on survival and regeneration.

Mechanical lesion of peripheral nerves leads to extensive death of corresponding motoneurons in newborn rodents. The extent of cell death can be significantly reduced by neurotrophic factors. These molecules are produced by glial and neuronal cells and play an important role in supporting survival and regeneration of various neuronal populations in the central nervous system, in particular after mechanical, excitotoxic and ischemic insults. In addition, factors such as ciliary neurotrophic factor and neurotrophin-3 influence glial cell proliferation and survival. We have investigated the role of neurotrophic factors on motoneurons, both in cell culture and after axotomy in vivo. Moreover, the role of excitatory neurotransmission in modulating dendritic architecture of these cells was analyzed. Our data suggest that motoneurons are a suitable model for investigating the complex functional and morphological changes after brain lesion and for the identification of new therapeutic strategies to influence survival and functional recovery under such circumstances.

Animals↗
PubMed1999

The anti-apoptotic protein ITA is essential for NGF-mediated survival of embryonic chick neurons.

The avian ITA is homologous to the baculoviral and mammalian inhibitor of apoptosis (IAP) proteins, which can prevent apoptosis by inhibition of specific caspases. We investigated the role of ITA in embryonic chick sympathetic and dorsal root ganglionic neurons, which depend on nerve growth factor (NGF) for their survival. Within 6 hours, NGF upregulated ITA protein production more than 25-fold in sensory and sympathetic neurons. Overexpression of ITA in primary neurons supported survival of these cells in the absence of NGF, and ita antisense constructs inhibited NGF-mediated survival. Thus the induction of ITA expression seems to be an essential signaling event for survival of sympathetic and dorsal root ganglionic sensory neurons in response to NGF.

Animals↗
PubMed1999

The role of p75NTR in modulating neurotrophin survival effects in developing motoneurons.

Neurotrophins exert their biological functions on neuronal cells through two types of receptors, the trk tyrosine kinases and the low-affinity neurotrophin receptor (p75NTR), which can bind all neurotrophins with similar affinity. The p75NTR is highly expressed in developing motoneurons and in adult motoneurons after axotomy, suggestive of a physiological role in mediating neurotrophin responses under such conditions. In order to characterize this specific function of p75NTR, we have tested the effects of nerve growth factor (NGF) on embryonic motoneurons from control and p75NTR-deficient mice. NGF antagonizes brain-derived neurotrophic factor (BDNF)- and neurotrophin-3 (NT-3)-mediated survival in control but not p75NTR-deficient motoneurons. Survival of cultured motoneurons in the presence of 0.5 ng/mL of either ciliary neurotrophic factor (CNTF) or glial-derived neurotrophic factor (GDNF) was not reduced by 20 ng/mL NGF. Dose-response investigations revealed that five times higher concentrations of BDNF are required for half-maximal survival of p75NTR-deficient motoneurons in comparison to motoneurons from wild-type controls. After facial nerve lesion in newborn wild-type mice, local administration of NGF reduced survival of corresponding motoneurons to less than 2% compared to the unlesioned control side. In p75NTR-deficient mice, the same treatment did not enhance facial motoneuron death on the lesioned side. In the facial nucleus of 1-week-old p75NTR -/- mice, a significant reduction of motoneurons was observed at the unlesioned side in comparison to p75NTR +/+ mice. The observation that motoneuron cell numbers are reduced in the facial nucleus of newborn p75NTR-deficient mice suggests that p75NTR might not function as a physiological cell death receptor in developing motoneurons.

Animals↗
PubMed1999

Leukaemia inhibitory factor gene mutations in infertile women.

The glycoprotein leukaemia inhibitory factor (LIF) is produced by the endometrium and is involved in the control of implantation. In women with unexplained infertility reduced uterine concentrations of LIF have been reported. Studies with mice lacking a functional LIF gene have shown that the LIF protein is essential for implantation of the embryo. We have developed a method for screening of gene mutations in the coding region and critical regulatory regions of the LIF gene. Thus we could screen nulligravid infertile women (n = 74), fertile controls (n = 75) and as a second unrelated control group, neurological patients (n = 131) for LIF gene mutations. In infertile women, three heterozygous point mutations have been identified: one in close proximity to the start codon of exon 1 and two mutations in exon 3. These correspond to regions of the LIF protein which are thought to be highly important for interaction with the LIF receptor and thus lead to reduced biological activity of the LIF protein. Only one point mutation/polymorphism in the non-coding region between exon 2 and 3 was found in the control groups. Our results suggest that heterozygosity for a LIF gene mutation could give rise to decreased availability or biological activity of LIF in the uterus and cause implantation failure. Thus the mutations identified in our study could be responsible for infertility in a subgroup of nulligravid women.

Adolescent↗
PubMed1998

Intraocular gene transfer of ciliary neurotrophic factor prevents death and increases responsiveness of rod photoreceptors in the retinal degeneration slow mouse.

Several mutations causing both photoreceptor degeneration and malfunction have been identified in humans and animals. Although intraocular injection of trophic factors has been shown to reduce photoreceptor death in a few conditions of rapid photoreceptor loss, it is unclear whether long-term beneficial changes in functional properties of affected photoreceptors can be obtained by treatment with these factors. The rds/rds mouse is a spontaneous mutant bearing a null mutation in the rds/peripherin gene, which is linked to many forms of dominant retinal degenerations in humans. Here, we report that intraocular adenovirus-mediated gene transfer of ciliary neurotrophic factor (CNTF) in this mutant reduces photoreceptor loss, causes a significant increase in the length of photoreceptor segments, and results in a redistribution and an increase in the retinal content of the photopigment rhodopsin. These effects are accompanied by a significant increase in the amplitude of the a- and b-waves of the scotopic electroretinogram. These results suggest that continuous administration of CNTF could potentially be useful for the treatment of some forms of retinal degeneration.

Adenoviridae↗
PubMed1998

Effect of glutamate on dendritic growth in embryonic rat motoneurons.

Glutamate is a major excitatory neurotransmitter for spinal motoneurons. We have investigated its effect on survival and neurite formation in cultures of highly enriched motoneurons from 15-d-old rat embryos. Whereas the survival of these neurons was not reduced by this treatment, a distinct and specific effect on dendrite outgrowth could be observed. Axon outgrowth was not affected by glutamate. Our data suggest that calcium influx via ionotropic AMPA/kainate (AMPA/KA) receptors is responsible for the regulation of dendrite outgrowth by excitatory neurotransmission. This was shown by the use of specific inhibitors for the different classes of glutamate receptors. The effect was reduced by continuous depolarization at 35 mM KCl and by treatment with joro spider toxin (JSTX-3, 3 microM), a blocker of Ca2+-conducting AMPA receptors. Removal of glutamate after 5 d of culture led to increased dendrite growth during the following culture period, and delayed addition resulted in a reduction in the length of already existing dendrites. Our observation that the effect is dose-dependent and reversible reflects a potential physiological function of excitatory neurotransmission on dendrite growth and morphology during a developmental period when synaptic contacts from afferent neurons to motoneurons are made in the spinal cord.

Animals↗
PubMed1998

Potential implications of a ciliary neurotrophic factor gene mutation in a German population of patients with motor neuron disease.

The frequency of a recently described point mutation of the ciliary neurotrophic factor (CNTF) gene was investigated in a population of 154 German patients with motor neuron disease (MND). Twenty-two percent of the patients were heterozygous, 2% homozygous for the CNTF mutation. Since the gene defect is per se not linked to MND, the identification of additional gene defects occurring simultaneously with this mutation could be informative for the understanding of pathogenic mechanisms of MND.

Adolescent↗
PubMed1998

Neurotrophic factors: effects in modulating properties of the neuromuscular endplate.

Besides their function in supporting neuronal survival, neurotrophic factors influence various functional properties of responsive neurons. In particular the role of these molecules in activity-mediated synaptic modulation has attracted great interest. Motoneurons and their specific synapses with muscle cells, the neuromuscular endplates, are well-characterized structures which have been known for long to depend on trophic support, at least during development. This review summarizes recent findings about the role of neurotrophic factors in modulating synaptic efficacy of neuromuscular synapses, both in an activity-dependent and -independent fashion.

Animals↗
PubMed1997

Endogenous ciliary neurotrophic factor is a lesion factor for axotomized motoneurons in adult mice.

Ciliary neurotrophic factor (CNTF) is an abundant cytosolic molecule in myelinating Schwann cells of adult rodents. In newborn animals in which CNTF is not yet expressed, exogenous CNTF that is locally administered very effectively protects motoneurons from degeneration by axotomy. To evaluate whether endogenous CNTF, released after nerve injury from the cytosol of Schwann cells, supports motoneuron survival, we transected the facial nerve in 4-week-old pmn mice. In this mouse mutant a rapidly progressing degenerative disease of motoneurons starts by the third postnatal week at the hindlimbs and progresses to the anterior parts of the body, leading to death by the seventh to eighth week. Apoptotic death of motoneurons can be observed during this period, as revealed by TUNEL staining. In 6-week-old unlesioned pmn mice approximately 40% of facial motoneurons have degenerated. Facial nerve lesion dramatically increased the number of surviving motoneurons in pmn mice. This protective effect was absent in pmn mice lacking endogenous CNTF. Quantitative analysis of leukemia inhibitory factor (LIF) mRNA expression revealed that the dramatic upregulation seen in wild-type mice after peripheral nerve lesion did not occur in pmn mice. Therefore, endogenous LIF cannot compensate for the lack of CNTF in pmn crossbred with CNTF knock-out mice. Thus, endogenous CNTF released from lesioned Schwann cells supports the survival of axotomized motoneurons under conditions in which motoneurons are in the process of rapid degeneration.

Animals↗
PubMed1997

Inactivation of the survival motor neuron gene, a candidate gene for human spinal muscular atrophy, leads to massive cell death in early mouse embryos.

Proximal spinal muscular atrophy is an autosomal recessive human disease of spinal motor neurons leading to muscular weakness with onset predominantly in infancy and childhood. With an estimated heterozygote frequency of 1/40 it is the most common monogenic disorder lethal to infants; milder forms represent the second most common pediatric neuromuscular disorder. Two candidate genes-survival motor neuron (SMN) and neuronal apoptosis inhibitory protein have been identified on chromosome 5q13 by positional cloning. However, the functional impact of these genes and the mechanism leading to a degeneration of motor neurons remain to be defined. To analyze the role of the SMN gene product in vivo we generated SMN-deficient mice. In contrast to the human genome, which contains two copies, the mouse genome contains only one SMN gene. Mice with homozygous SMN disruption display massive cell death during early embryonic development, indicating that the SMN gene product is necessary for cellular survival and function.

Amino Acid Sequence↗