Promote Motoneuron Survival Research Articles

Influence of FK506, Cyclosporin A, Testosterone and Nimodipine on Motoneuron Survival Following Axotomy

Injury to immature motoneurons results in extensive nerve cell death. Avulsion injury in adult animals has a similar effect. Rescuing injured neurons from degeneration and death is a prerequisite for succesful functional recovery. Here, we have explored the possible survival promoting effect of the immunosuppressant agents FK506 and cyclosporin A, the calcium channel blocker nimodipine as well testosterone on axotomized neonatal facial motoneurons. In addition, we examined the effect of cyclosporin A and Nimodipine, a calcium channel blocker, on survival of adult motoneurons following hypoglossal nerve avulsion. FK506 and cyclosporin A were administered intraperitoneally, testosterone intramuscularly and Nimodipine via the food. After the appropriate postoperative survival periods, the number of surviving facial or hypoglossal motoneurons respectively was calculated. FK506 and Cyclosporin A were found to enhance facial motoneuron survival following neonatal axotomy. Cyclosporin A and Nimodipine were found to promote motoneuron survival in adult rats after hypoglossal nerve avulsion. Nimodipine possibly also reduced motoneuron death in neonatal rats twenty-one days after facial nerve transsection, but failed to rescue motoneurons in neonatal rats during the first seven days after nerve injury. Treatment with testosterone was ineffective in preventing neonatal facial motoneurons from axotomy-induced death at seven days postaxotomy. The restults indicate that motoneuron degeneration can be counteracted to a large extent by immunosuppressant agents as well as by calcium channel blockers. Taken together with findings form previous studies, we conclude that motoneuron survival following axotomy can be promoted by a variety of endogenous and exogenous molecules acting on different cellular mechanisms.

Effect of transforming growth factor β1 on spinal motor neurons after axotomy

Glial cell line-derived neurotrophic factor (GDNF), a member of the transforming growth factor β (TGF-β) family, has potent effects on developing motor neurons. TGF are pluripotent cytokines that exert biological effects on a variety of neurons. TGF β 1, on the other hand, promotes motor neuron survival in vitro and saves motor neurons from naturally occurring cell death. Here we investigate the neurotrophic effects of TGF β 1, for axotomized motor neuron death. The sciatic nerve was cut in newborn rats and TGF β 1, was injected, either by intraperitoneally or by lesion site, for 14 days after transection. Two or six weeks postlesion, the number and the diameter of motor neurons was assessed. TGF β 1, significantly attenuated axotomy induced motor neuron death by intraperitoneal administration or by lesion site administration at 2 weeks after neonatal axotomy in a similar way. However, no effect was observed at 6 weeks after nerve lesion, despite continuous application of TGF β 1, daily for 14 days. These results indicate that TGF β 1, can prevent the death of motor neurons in vivo, but it cannot permanently rescue lesioned motor neurons.

Hepatocyte Growth Factor Promotes Motor Neuron Survival and Synergizes with Ciliary Neurotrophic Factor

Hepatocyte growth factor (HGF) has been shown to function as a potent mitogen for a variety of cells, transducing its signal through the c-met tyrosine kinase receptor. Ciliary neurotrophic factor (CNTF) is a cytokine that has been shown to promote survival of motor neurons. We show here that c-met mRNA is present in the embryonic rat spinal cord. Peak expression of c-met (at E14) coincides with the period of naturally occurring cell death in motor neurons, suggesting a possible role of HGF in the regulation of this process. Utilizing a neuron-enriched culture system, we established that HGF, like CNTF, stimulates choline acetyltransferase (CAT) activity in motor neurons. When co-administered to motor neuron cultures, saturating concentrations of HGF and CNTF produced a synergistic increase in CAT levels. We show that this synergy reflects enhanced motor neuron survival. Exposure of motor neuron cultures to the cytostatic agent vincristine markedly decreased CAT levels; co-treatment with HGF and CNTF (but not either factor alone) restored CAT activity to control levels. Our findings indicate that HGF is a survival factor for motor neurons, that it acts synergistically with CNTF, and that HGF and CNTF can together be neuroprotective in the face of vincristine toxicity.

Transforming growth factor‐beta 3, glial cell line‐derived neurotrophic factor, and fibroblast growth factor‐2, act in different manners to promote motoneuron survival in vitro

Transforming growth factor‐beta 3, glial cell line‐derived neurotrophic factor, and fibroblast growth factor‐2, act in different manners to promote motoneuron survival in vitro

Insulin-like growth factors: putative muscle-derived trophic agents that promote motoneuron survival.

Treatment of chick embryos in ovo with IGF-I during the period of normal, developmentally regulated neuronal death (embryonic days 5-10) resulted in a dose-dependent rescue of a significant number of lumbar motoneurons from degeneration and death. IGF-II and two variants of IGF-I with reduced affinity for IGF binding proteins, des(1-3) IGF-I and long R3 IGF-I, also elicited enhanced survival of motoneurons equal to that seen in IGF-I-treated embryos. IGF-I did not enhance mitogenic activity in motoneuronal populations when applied to embryos during the period of normal neuronal proliferation (E2-5). Treatment of embryos with IGF-I also reduced two types of injury-induced neuronal death. Following either deafferentation or axotomy, treatment of embryos with IGF-I rescued approximately 75% and 50%, respectively, of the motoneurons that die in control embryos as a result of these procedures. Consistent with the survival-promoting activity on motoneurons in ovo, IGF-I, -II, and des(1-3) IGF-I elevated choline acetyltransferase activity in embryonic rat spinal cord cultures, with des(1-3) IGF-I demonstrating 2.5 times greater potency than did IGF-I. A single addition of IGF-I at culture initiation resulted in the maintenance of 80% of the initial ChAT activity for up to 5 days, during which time ChAT activity in untreated control cultures fell to 9%. In summary, these results demonstrate clear motoneuronal trophic activity for the IGFs. These findings, together with previous reports that IGFs are synthesized in muscle and may participate in motoneuron axonal regeneration and sprouting, indicate that these growth factors may have an important role in motoneuron development, maintenance, and recovery from injury.

Biological studies of a putative avian muscle-derived neurotrophic factor that prevents naturally occurring motoneuron death in vivo.

A series of in vivo studies have been carried out using the chick embryo to address several critical questions concerning the biological, and to a lesser extent, the biochemical characteristics of a putative avian muscle-derived trophic agent that promotes motoneuron survival in vivo. A partially purified fraction of muscle extract was shown to be heat and trypsin sensitive and rescued motoneurons from naturally occurring cell death in a dose-dependent fashion. Muscle extract had no effect on mitotic activity in the spinal cord and did not alter cell number when administered either before or after the normal cell death period. The survival promoting activity in the muscle extract appears to be developmentally regulated. Treatment with muscle extract during the cell death period did not permanently rescue motoneurons. The motoneuron survival-promoting activity found in skeletal muscle was not present in extracts from a variety of other tissues, including liver, kidney, lung, heart, and smooth muscle. Survival activity was also found in extracts from fetal mouse, rat, and human skeletal muscle. Conditioned medium derived from avian myotube cultures also prevented motoneuron death when administered in vivo to chick embryos. Treatment of embryos in ovo with muscle extract had no effect on several properties of developing muscles. With the exception of cranial motoneurons, treatment with muscle extract did not promote the survival of several other populations of neurons in the central and peripheral nervous system that also exhibit naturally occurring cell death. Initial biochemical characterization suggests that the activity in skeletal muscle is an acidic protein between 10 and 30 kD. Examination of a number of previously characterized growth and trophic agents in our in vivo assay have identified several molecules that promote motoneuron survival to one degree or another. These include S100 beta, brain-derived neurotrophic factor (BDNF), neurotrophin 4/5 (NT-4/5), ciliary neurotrophic factor (CNTF), transforming growth factor beta (TGF beta), platelet-derived growth factor-AB (PDGF-AB), leukemia inhibitory factor (CDF/LIF), and insulin-like growth factors I and II (IGF). By contrast, the following agents were ineffective: nerve growth factor (NGF), neurotrophin-3 (NT3), epidermal growth factor (EGF), acidic and basic fibroblast growth factors (aFGF, bFGF), and the heparin-binding growth-associated molecule (HB-GAM).(ABSTRACT TRUNCATED AT 400 WORDS)

Neurotrophins promote motor neuron survival and are present in embryonic limb bud.

Embryonic spinal motor neurons are thought to depend for survival on unidentified factors secreted both by their peripheral targets and by cells within the central nervous system. The neurotrophins are a family of polypeptides required for survival of discrete central and peripheral neuronal populations in vivo and in vitro. In spite of their ability to reduce motor neuron death in vivo, the known neurotrophins have been thought to be without direct effect on motor neurons. Here we show that picomolar concentrations of three of them, brain-derived neurotrophic factor, neurotrophin-3 and neurotrophin-5, can prevent the death of cultured embryonic rat spinal motor neurons. Furthermore, messenger RNA coding for neurotrophins is present at appropriate stages in spinal cord and limb bud, and mRNA for their receptors is found in motor neurons. These neurotrophins may therefore be physiological motor neuron growth factors.

Motoneuron survival factors: Biological roles and therapeutic potential

The existence of factors that promote motoneuron survival in the spinal cord at critical stages of development was first deduced 50 yr ago. The large amount of work that has been put into characterizing such factors reflects both their biological importance and the hope that such molecules may be used therapeutically to slow motoneuron death in pathologies such as the spinal muscular atrophies and amyotrophic lateral sclerosis. Since 1990, several factors have been shown to have in vitro and/or in vivo activities that suggest they play a role in regulating motoneuron survival. Their physiological functions during motoneuron development are probably different and complementary. Several of them seem reasonable candidates for preclinical development, but many crucial experiments remain to be done.

Brain-derived neurotrophic factor rescues spinal motor neurons from axotomy-induced cell death.

Current ideas about the dependence of neurons on target-derived growth factors were formulated on the basis of experiments involving neurons with projections to the periphery. Nerve growth factor (NGF) and recently identified members of the NGF family of neuronal growth factors, known as neurotrophins, are thought to regulate survival of sympathetic and certain populations of sensory ganglion cells during development. Far less is known about factors that regulate the survival of spinal and cranial motor neurons, which also project to peripheral targets. NGF has not been shown to influence motor neuron survival, and whether the newly identified neurotrophins promote motor neuron survival is unknown. We show here that brain-derived neurotrophic factor (BDNF) is retrogradely transported by motor neurons in neonatal rats and that local application of BDNF to transected sciatic nerve prevents the massive death of motor neurons that normally follows axotomy in the neonatal period. These results show that BDNF has survival-promoting effects on motor neurons in vivo and suggest that BDNF may influence motor neuron survival during development.

Brain-derived neurotrophic factor prevents the death of motoneurons in newborn rats after nerve section.

Motoneurons innervating the skeletal musculature were among the first neurons shown to require the presence of their target cells to develop appropriately. But the characterization of molecules allowing motoneuron survival has been difficult. Ciliary neurotrophic factor prevents the death of motoneurons, but its gene is not expressed during development. Although the presence of a neurotrophin receptor on developing motoneurons has suggested a role for neurotrophins, none could be shown to promote motoneuron survival in vitro. We report here that brain-derived neurotrophic factor can prevent the death of axotomized motoneurons in newborn rats, suggesting a role for this neurotrophin for motoneuron survival in vivo.

S100 is present in developing chicken neurons and Schwann cells and promotes motor neuron survival in vivo.

We used polyclonal antisera recognizing S100, a small acidic protein highly enriched in nervous tissue, to stain sections of embryonic chicken lumbosacral spinal cord and hindlimb. S100 immunoreactivity was detected in developing sensory neurons of the dorsal root ganglia (DRG) and motor neurons of the ventral spinal cord as early as embryonic day (E) 5, and staining persisted through hatching. In contrast, expression of S100 first became apparent in Schwann cells at E13, just before myelination, and was not detected in developing skin or muscle. Since S100 beta was present in motor and sensory neurons and is known to promote neuronal survival and neurite extension in vitro (Winningham-Major, Staecker, Barger, Coats, and Van Eldik, 1989), we tested the ability of S100 to promote neuron survival in an in ovo survival assay. Addition of S100 to chick embryos in ovo during the period of naturally occurring motor neuron cell death resulted in a significant increase in motor neuron survival, but had no effect on the in vivo survival of sensory neurons in the DRG. The findings that S100 is present in spinal motor neurons and that the addition of S100 enhances the survival of these cells in vivo are consistent with the possibility that S100 may act as a naturally occurring neuron survival factor during development.