Acidic fibroblast growth factor prevents post-axotomy neuronal death of the newborn rat facial nerve

Central Facial Nervous System Biomolecules Involved in Peripheral Facial Nerve Injury Responses and Potential Therapeutic Strategies

Peripheral facial nerve injury leads to changes in the expression of various neuroactive substances that affect nerve cell damage, survival, growth, and regeneration. In the case of peripheral facial nerve damage, the injury directly affects the peripheral nerves and induces changes in the central nervous system (CNS) through various factors, but the substances involved in these changes in the CNS are not well understood. The objective of this review is to investigate the biomolecules involved in peripheral facial nerve damage so as to gain insight into the mechanisms and limitations of targeting the CNS after such damage and identify potential facial nerve treatment strategies. To this end, we searched PubMed using keywords and exclusion criteria and selected 29 eligible experimental studies. Our analysis summarizes basic experimental studies on changes in the CNS following peripheral facial nerve damage, focusing on biomolecules that increase or decrease in the CNS and/or those involved in the damage, and reviews various approaches for treating facial nerve injury. By establishing the biomolecules in the CNS that change after peripheral nerve damage, we can expect to identify factors that play an important role in functional recovery from facial nerve damage. Accordingly, this review could represent a significant step toward developing treatment strategies for peripheral facial palsy.

Roles of growth factors in eye development and ophthalmic diseases

Growth factors are active substances secreted by a variety of cells, which act as messengers to regulate cell migration, proliferation and differentiation. Many growth factors are involved in the eye development or the pathophysiological processes of eye diseases. Growth factors such as vascular endothelial growth factor and basic fibroblast growth factor mediate the occurrence and development of diabetic retinopathy, choroidal neovascularization, cataract, diabetic macular edema, and other retinal diseases. On the other hand, growth factors like nerve growth factor, ciliary neurotrophic factor, glial cell line-derived neurotrophic factor, pigment epithelial-derived factor and granulocyte colony-stimulating factor are known to promote optic nerve injury repair. Growth factors are also related to the pathogenesis of myopia. Fibroblast growth factor, transforming growth factor-β, and insulin-like growth factor regulate scleral thickness and influence the occurrence and development of myopia. This article reviews growth factors involved in ocular development and ocular pathophysiology, discusses the relationship between growth factors and ocular diseases, to provide reference for the application of growth factors in ophthalmology.

Events Occurring in the Axotomized Facial Nucleus

Transection of the rat facial nerve leads to a variety of alterations not only in motoneurons, but also in glial cells and inhibitory neurons in the ipsilateral facial nucleus. In injured motoneurons, the levels of energy metabolism-related molecules are elevated, while those of neurofunction-related molecules are decreased. In tandem with these motoneuron changes, microglia are activated and start to proliferate around injured motoneurons, and astrocytes become activated for a long period without mitosis. Inhibitory GABAergic neurons reduce the levels of neurofunction-related molecules. These facts indicate that injured motoneurons somehow closely interact with glial cells and inhibitory neurons. At the same time, these events allow us to predict the occurrence of tissue remodeling in the axotomized facial nucleus. This review summarizes the events occurring in the axotomized facial nucleus and the cellular and molecular mechanisms associated with each event.

Human Adipose-Derived Stem Cells Combined with Nano-Hydrogel Promote Functional Recovery after Spinal Cord Injury in Rats

Simple Summary

Nerve regeneration and functional recovery after spinal cord injury (SCI) are worldwide problems. Scientists have achieved encouraging results in the repair of spinal cord injuries using natural or synthetic materials. In this paper, we report that nano-hydrogel combined with human adipose-derived stem cells regulate the inflammatory microenvironment, protect neurons and axons, and promote motor function recovery. In addition, three proteins related to neuronal and axonal growth were screened by Liquid chromatography-mass spectrometry. These results provide evidence for clinical treatment of spinal cord injury.

Abstract

The treatment of spinal cord injury aims to reconstruct the fiber connection and restore the interrupted neural pathways. Adipose mesenchymal stem cells (ADSCs) can promote the recovery of motor functions in spinal cord injury. However, poor survival of ADSCs and leakage outside of the injury site after local transplantation reduce the number of cells, which seriously attenuates the cumulative effect. We performed heterotopic transplantation on rats with severe spinal cord injury using human ADSCs loaded within self-assembly hydrogel RADA16-RGD (R: arginine; A: alanine; D: aspartic acid; G: glycine). Our results indicate that the combined transplantation of human ADSCs with RADA16-RGD improved the survival of ADSCs at the injured site. The inflammatory reaction was inhibited, with improved survival of the neurons and increased residual area of nerve fibers and myelin protein. The functional behaviors were promoted, as determined by the Basso, Beattie, and Bresnahan (BBB) locomotor rating scale score and electrophysiological measurements. ADSCs can promote the repair of spinal cord injury. This study provides new ideas for the treatment of spinal cord injury.

Acidic fibroblast growth factor attenuates type 2 diabetes-induced demyelination via suppressing oxidative stress damage

Prolonged type 2 diabetes mellitus (T2DM) produces a common complication, peripheral neuropathy, which is accompanied by nerve fiber disorder, axon atrophy, and demyelination. Growing evidence has characterized the beneficial effects of acidic fibroblast growth factor (aFGF) and shown that it relieves hyperglycemia, increases insulin sensitivity, and ameliorates neuropathic impairment. However, there is scarce evidence on the role of aFGF on remodeling of aberrant myelin under hyperglycemia condition. Presently, we observed that the expression of aFGF was rapidly decreased in a db/db T2DM mouse model. Administration of exogenous aFGF was sufficient to block acute demyelination and nerve fiber disorganization. Furthermore, this strong anti-demyelinating effect was most likely dominated by an aFGF-mediated increase of Schwann cell (SC) proliferation and migration as well as suppression of its apoptosis. Mechanistically, the beneficial biological effects of aFGF on SC behavior and abnormal myelin morphology were likely due to the inhibition of hyperglycemia-induced oxidative stress activation, which was most likely activated by kelch-like ECH-associated protein 1 (Keap1)/nuclear factor erythroid-derived-like 2 (Nrf2) signaling. Thus, this evidence indicates that aFGF is a promising protective agent for relieving myelin pathology through countering oxidative stress signaling cascades under diabetic conditions.

FGF binding proteins (FGFBPs): Modulators of FGF signaling in the developing, adult, and stressed nervous system

Members of the fibroblast growth factor (FGF) family are involved in a variety of cellular processes. In the nervous system, they affect the differentiation and migration of neurons, the formation and maturation of synapses, and the repair of neuronal circuits following insults. Because of the varied yet critical functions of FGF ligands, their availability and activity must be tightly regulated for the nervous system, as well as other tissues, to properly develop and function in adulthood. In this regard, FGF binding proteins (FGFBPs) have emerged as strong candidates for modulating the actions of secreted FGFs in neural and non-neural tissues. Here, we will review the roles of FGFBPs in the peripheral and central nervous systems.

Putative roles of soluble trophic factors in facial nerve regeneration, target reinnervation, and recovery of vibrissal whisking

It is well-known that, after nerve transection and surgical repair, misdirected regrowth of regenerating motor axons may occur in three ways. The first way is that the axons enter into endoneurial tubes that they did not previously occupy, regenerate through incorrect fascicles and reinnervate muscles that they did not formerly supply. Consequently the activation of these muscles results in inappropriate movements. The second way is that, in contrast with the precise target-directed pathfinding by elongating motor nerves during embryonic development, several axons rather than a single axon grow out from each transected nerve fiber. The third way of misdirection occurs by the intramuscular terminal branching (sprouting) of each regenerating axon to culminate in some polyinnervation of neuromuscular junctions, i.e. reinnervation of junctions by more than a single axon. Presently, "fascicular" or "topographic specificity" cannot be achieved and hence target-directed nerve regeneration is, as yet, unattainable. Nonetheless, motor and sensory reinnervation of appropriate endoneurial tubes does occur and can be promoted by brief nerve electrical stimulation. This review considers the expression of neurotrophic factors in the neuromuscular system and how this expression can promote functional recovery, with emphasis on the whisking of vibrissae on the rat face in relationship to the expression of the factors. Evidence is reviewed for a role of neurotrophic factors as short-range diffusible sprouting stimuli in promoting complete functional recovery of vibrissal whisking in blind Sprague Dawley (SD)/RCS rats but not in SD rats with normal vision, after facial nerve transection and surgical repair. Briefly, a complicated time course of growth factor expression in the nerves and denervated muscles include (1) an early increase in FGF2 and IGF2, (2) reduced NGF between 2 and 14days after nerve transection and surgical repair, (3) a late rise in BDNF and (4) reduced IGF1 protein in the denervated muscles at 28days. These findings suggest that recovery of motor function after peripheral nerve injury is due, at least in part, to a complex regulation of nerve injury-associated neurotrophic factors and cytokines at the neuromuscular junctions of denervated muscles. In particular, the increase of FGF2 and concomittant decrease of NGF during the first week after facial nerve-nerve anastomosis in SD/RCS blind rats may prevent intramuscular axon sprouting and, in turn, reduce poly-innervation of the neuromuscular junction.

FGF1 protects neuroblastoma SH-SY5Y cells from p53-dependent apoptosis through an intracrine pathway regulated by FGF1 phosphorylation

Neuroblastoma, a sympathetic nervous system tumor, accounts for 15% of cancer deaths in children. In contrast to most human tumors, p53 is rarely mutated in human primary neuroblastoma, suggesting impaired p53 activation in neuroblastoma. Various studies have shown correlations between fgf1 expression levels and both prognosis severity and tumor chemoresistance. As we previously showed that fibroblast growth factor 1 (FGF1) inhibited p53-dependent apoptosis in neuron-like PC12 cells, we initiated the study of the interaction between the FGF1 and p53 pathways in neuroblastoma. We focused on the activity of either extracellular FGF1 by adding recombinant rFGF1 in media, or of intracellular FGF1 by overexpression in human SH-SY5Y and mouse N2a neuroblastoma cell lines. In both cell lines, the genotoxic drug etoposide induced a classical mitochondrial p53-dependent apoptosis. FGF1 was able to inhibit p53-dependent apoptosis upstream of mitochondrial events in SH-SY5Y cells by both extracellular and intracellular pathways. Both rFGF1 addition and etoposide treatment increased fgf1 expression in SH-SY5Y cells. Conversely, rFGF1 or overexpressed FGF1 had no effect on p53-dependent apoptosis and fgf1 expression in neuroblastoma N2a cells. Using different FGF1 mutants (that is, FGF1^K132E, FGF1^S130A and FGF1^S130D), we further showed that the C-terminal domain and phosphorylation of FGF1 regulate its intracrine anti-apoptotic activity in neuroblastoma SH-SY5Y cells. This study provides the first evidence for a role of an intracrine growth factor pathway on p53-dependent apoptosis in neuroblastoma, and could lead to the identification of key regulators involved in neuroblastoma tumor progression and chemoresistance.

FGF1 C-terminal domain and phosphorylation regulate intracrine FGF1 signaling for its neurotrophic and anti-apoptotic activities

Fibroblast growth factor 1 (FGF1) is a prototypic member of the FGFs family overexpressed in various tumors. Contrarily to most FGFs, FGF1 lacks a secretion peptide signal and acts mainly in an intracellular and nuclear manner. Intracellular FGF1 induces cell proliferation, differentiation and survival. We previously showed that intracellular FGF1 induces neuronal differentiation and inhibits both p53- and serum-free-medium-induced apoptosis in PC12 cells. FGF1 nuclear localization is required for these intracellular activities, suggesting that FGF1 regulates p53-dependent apoptosis and neuronal differentiation by new nuclear pathways. To better characterize intracellular FGF1 pathways, we studied the effect of three mutations localized in the C-terminal domain of FGF1 (i.e., FGF1^K132E, FGF1^S130A and FGF1^S130D) on FGF1 neurotrophic and anti-apoptotic activities in PC12 cells. The change of the serine 130 to alanine precludes FGF1 phosphorylation, while its mutation to aspartic acid mimics phosphorylation. These FGF1 mutants kept both a nuclear and cytosolic localization in PC12 cells. Our study highlights for the first time the role of FGF1 phosphorylation and the implication of FGF1 C-terminal domain on its intracellular activities. Indeed, we show that the K132E mutation inhibits both the neurotrophic and anti-apoptotic activities of FGF1, suggesting a regulatory activity for FGF1 C terminus. Furthermore, we observed that both FGF1^S130A and FGF1^S130D mutant forms induced PC12 cells neuronal differentiation. Therefore, FGF1 phosphorylation does not regulate FGF1-induced differentiation of PC12 cells. Then, we showed that only FGF1^S130A protects PC12 cells against p53-dependent apoptosis, thus phosphorylation appears to inhibit FGF1 anti-apoptotic activity in PC12 cells. Altogether, our results show that phosphorylation does not regulate FGF1 neurotrophic activity but inhibits its anti-apoptotic activity after p53-dependent apoptosis induction, giving new insight into the poorly described FGF1 intracrine/nuclear pathway. The study of nuclear pathways could be crucial to identify key regulators involved in neuronal differentiation, tumor progression and resistances to radio- and chemo-therapy.

Gene expression changes in spinal motoneurons of the SOD1(G93A) transgenic model for ALS after treatment with G-CSF

Background: Amyotrophic lateral sclerosis (ALS) is an incurable fatal motoneuron disease with a lifetime risk of approximately 1:400. It is characterized by progressive weakness, muscle wasting, and death ensuing 3–5 years after diagnosis. Granulocyte-colony stimulating factor (G-CSF) is a drug candidate for ALS, with evidence for efficacy from animal studies and interesting data from pilot clinical trials. To gain insight into the disease mechanisms and mode of action of G-CSF, we performed gene expression profiling on isolated lumbar motoneurons from SOD1^G93A mice, the most frequently studied animal model for ALS, with and without G-CSF treatment.

Results: Motoneurons from SOD1^G93A mice present a distinct gene expression profile in comparison to controls already at an early disease stage (11 weeks of age), when treatment was initiated. The degree of deregulation increases at a time where motor symptoms are obvious (15 weeks of age). Upon G-CSF treatment, transcriptomic deregulations of SOD1^G93A motoneurons were notably restored. Discriminant analysis revealed that SOD1 mice treated with G-CSF has a transcriptom close to presymptomatic SOD1 mice or wild type mice. Some interesting genes modulated by G-CSF treatment relate to neuromuscular function such as CCR4-NOT or Prss12.

Conclusions: Our data suggest that G-CSF is able to re-adjust gene expression in symptomatic SOD1^G93A motoneurons. This provides further arguments for G-CSF as a promising drug candidate for ALS.

Neurotrophic growth factors for the treatment of amyotrophic lateral sclerosis: where do we stand?

Amyotrophic lateral sclerosis (ALS) is a devastating neurodegenerative disease that results in progressive loss of motoneurons, motor weakness and death within 3–5 years after disease onset. Therapeutic options remain limited despite substantial number of approaches that have been tested clinically. Many neurotrophic growth factors are known to promote the survival of neurons and foster regeneration in the central nervous system. Various neurotrophic factors have been investigated pre-clinically and clinically for the treatment of ALS. Although pre-clinical data appeared promising, no neurotrophic factors succeeded yet in a clinical phase III trial. In this review we discuss the rationale behind those factors, possible reasons for clinical failures, and argue for a renewal of hope in this powerful class of drugs for the treatment of ALS.

Adult rat spinal cord culture on an organosilane surface in a novel serum-free medium

In this study, we have documented by morphological analysis, immunocytochemistry, and electrophysiology, the development of a culture system that promotes the growth and long-term survival of dissociated adult rat spinal cord neurons. This system comprises a patternable, nonbiological, cell growth-promoting organosilane substrate coated on a glass surface and an empirically derived novel serum-free medium, supplemented with specific growth factors (acidic fibroblast growth factor, heparin sulfate, neurotrophin-3, brain-derived neurotrophic factor, glial-derived neurotrophic factor, cardiotrophin-1, and vitronectin). Neurons were characterized by immunoreactivity for neurofilament 150, neuron-specific enolase, Islet-1 antibodies, electrophysiology, and the cultures were maintained for 4-6 wk. This culture system could be a useful tool for the study of adult mammalian spinal neurons in a functional in vitro system.

Neurotrophic factors and amyotrophic lateral sclerosis

The cause of motor neuron death in amyotrophic lateral sclerosis (ALS) remains a mystery. Initial implications of neurotrophic factor impairment involved in disease progression causing selective motor neuron death were brought forward in the late 1980s. These implications were based on several in vitro studies of motor neuron cultures in which a near to complete rescue of axotomized neonatal motor neurons in the presence of supplementary neurotrophic factors were revealed. These findings pawed the way for extensive investigations in experimental animal models of ALS. Neurotrophic factor administration in rodent ALS models demonstrated a remarkable effect on survival of degenerating motor neurons and rescue of axotomized motor neurons, both in vivo and in vitro. In the absence of efficient therapy for ALS, some of these promising neurotrophic factors have been administered to groups of ALS patients, as they appeared available for clinical trials. Up to date, none of tested factors has lived up to expectations, altering the outcome of the disease. This review summarizes current findings on neurotrophic factor expression in ALS tissue and these factors' potential/debatable clinical relevance to ALS and the treatment of ALS. It also discusses possible interventions improving clinical trial design to obtain efficacy of neurotrophic factor treatment in patients suffering from ALS.

Localization of Fibroblast Growth Factor-1 in Cholinergic Neurons Innervating the Rat Larynx

Cholinergic neurons in the dorsal motor nucleus of the vagus (DMNV) are particularly vulnerable to laryngeal nerve damage, possibly because they lack fibroblast growth factor-1 (FGF1). To test this hypothesis, we investigated the localization of FGF1 in cholinergic neurons innervating the rat larynx by immunohistochemistry using central-type antibodies to choline acetyltransferase (cChAT) and peripheral type (pChAT) antibodies, as well as tracer experiments. In the DMNV, only 9% of cChAT-positive neurons contained FGF1, and 71% of FGF1-positive neurons colocalized with cChAT. In the nucleus ambiguus, 100% of cChAT-positive neurons were FGF1 positive. In the intralaryngeal ganglia, all ganglionic neurons contained both pChAT and FGF1. In the nodose ganglia, 66% of pChAT-positive neurons were also positive for FGF1, and 90% of FGF1-positive ganglionic cells displayed pChAT immunoreactivity. Neuronal tracing using cholera toxin B subunit (CTb) demonstrated that cholinergic neurons sending their axons from the DMNV and nucleus ambiguus to the superior laryngeal nerve were FGF1 negative and FGF1 positive, respectively. In the nodose ganglia, some FGF1-positive cells were labeled with CTb. The results indicate that for innervation of the rat larynx, FGF1 is localized to motor neurons, postganglionic parasympathetic neurons, and sensory neurons, but expression is very low in preganglionic parasympathetic cholinergic neurons.

Angiogenic capacity of human omental stem cells

OBJECTIVES

The goals of the present study are to obtain, expand and characterize a stem cell population from human omentum and to evaluate its in vivo angiogenic capacities.

METHODS

Human omental CD34+ cells were obtained from samples of human omentum by density gradient centrifugation in Ficoll. Proliferative pattern, marker expression (by flow cytometry) and angiogenic growth factor synthesis by omental cell cultures were determined. In vivo angiogenic capacity of the cells was evaluated in rats.

RESULTS

Omental stem cells showed a high rate of proliferation (Ki67 staining), expressed CD34 marker and synthesized bFGF and VEGF. When implanted in rats, omental cells promoted neovascularization. Human omental cells were localized in rat tissue, mainly forming the endothelium of neo-vessels. Implantation of omental cells also facilitated angiogenesis of rat origin.

CONCLUSION

CD34+ cell population of human omentum could be responsible for the clinical benefit of omental transplantation by promoting angiogenesis and synthesizing angiogenic growth factors to facilitate revascularization of injured tissue.

The facial nerve axotomy model

Experimental models such as the facial nerve axotomy paradigm in rodents allow the systematic and detailed study of the response of neurones and their microenvironment to various types of challenges. Well-studied experimental examples include peripheral nerve trauma, the retrograde axonal transport of neurotoxins and locally enhanced inflammation following the induction of experimental autoimmune encephalomyelitis in combination with axotomy. These studies have led to novel insights into the regeneration programme of the motoneurone, the role of microglia and astrocytes in synaptic plasticity and the biology of glial cells. Importantly, many of the findings obtained have proven to be valid in other functional systems and even across species barriers. In particular, microglial expression of major histocompatibility complex molecules has been found to occur in response to various types of neuronal damage and is now regarded as a characteristic component of "glial inflammation". It is found in the context of numerous neurodegenerative disorders including Parkinson's and Alzheimer's disease. The detachment of afferent axonal endings from the surface membrane of regenerating motoneurones and their subsequent displacement by microglia ("synaptic stripping") and long-lasting insulation by astrocytes have also been confirmed in humans. The medical implications of these findings are significant. Also, the facial nerve system of rats and mice has become the best studied and most widely used test system for the evaluation of neurotrophic factors.

Growth factor enhancement of peripheral nerve regeneration through a novel synthetic hydrogel tube

OBJECT

The authors' long-term goal is repair of peripheral nerve injuries by using synthetic nerve guidance devices that improve both regeneration and functional outcome relative to an autograft. They report the in vitro processing and in vivo application of synthetic hydrogel tubes that are filled with collagen gel impregnated with growth factors.

METHODS

Poly(2-hydroxyethyl methacrylate-co-methyl methacrylate) (PHEMA-MMA) porous 12-mm-long tubes with an inner diameter of 1.3 mm and an outer diameter of 1.8 mm were used to repair surgically created 10-mm gaps in the rat sciatic nerve. The inner lumen of the tubes was filled with collagen matrix alone or matrix supplemented with either neurotropin-3 at 1 microg/ml, brain-derived neurotrophic factor at 1 microg/ml, or acidic fibroblast growth factor (FGF-1) at 1 or 10 microg/ml. Nerve regeneration through the growth factor-enhanced tubes was assessed at 8 weeks after repair by histomorphometric analysis at the midgraft level and in the nerve distal to the tube repair. The tubes were biostable and biocompatible, and supported nerve regeneration in more than 90% of cases. Nerve regeneration was improved in tubes in which growth factors were added, compared with empty tubes and those containing collagen gel alone (negative controls). Tubes filled with 10 microg/ml of FGF-1 dispersed in collagen demonstrated regeneration comparable to autografts (positive controls) and showed significantly better regeneration than the other groups.

CONCLUSIONS

The PHEMA-MMA tubes augmented with FGF-1 in their lumens appear to be a promising alternative to autografts for repair of nerve injuries. Studies are in progress to assess the long-term biocompatibility of these implants and to enhance regeneration further.

Acidic fibroblast growth factor (FGF-1) in the anterior horn cells of ALS and control cases

The expression and localization of acidic fibroblast growth factor (aFGF; FGF-1) were examined in the spinal cord of patients with amyotrophic lateral sclerosis (ALS) and controls by reverse transcription-polymerase chain reaction (RT-PCR) method and immunohistochemistry. The RT-PCR experiments demonstrated that aFGF amplification products were clearly detected in all control cases but could be scarcely seen in ALS patients. aFGF immunoreactivity was detected in the anterior horn cells of the spinal cord. Double immunostaining for aFGF and choline acetyltransferase revealed that the majority (95.9%) of cholinergic neurons expressed aFGF. In ALS cases, the number and the staining intensity of aFGF-positive neurons were markedly decreased. These results suggest that aFGF is involved in ALS pathology.

Macrophage stimulating protein is a novel neurotrophic factor

Macrophage stimulating protein (MSP), also known as hepatocyte growth factor-like, is a soluble cytokine that belongs to the family of the plasminogen-related growth factors (PRGFs). PRGFs are alpha/beta heterodimers that bind to transmembrane tyrosine kinase receptors. MSP was originally isolated as a chemotactic factor for peritoneal macrophages. Through binding to its receptor, encoded by the RON gene, it stimulates dissociation of epithelia and works as an inflammatory mediator by repressing the production of nitric oxide (NO). Here, we identify a novel role for MSP in the central nervous system. As a paradigm to analyze this function we chose the hypoglossal system of adult mice. We demonstrate in vivo that either administration of exogenous MSP or transplantation of MSP-producing cells at the proximal stump of the resected nerve is sufficient to prevent motoneuron atrophy upon axotomy. We also show that the MSP gene is expressed in the tongue, the target of the hypoglossal nerve, and that MSP induces biosynthesis of Ron receptor in the motoneuron somata. Finally, we show that MSP suppresses NO production in the injured hypoglossal nuclei. Together, these data suggest that MSP is a novel neurotrophic factor for cranial motoneurons and, by regulating the production of NO, may have a role in brain plasticity and regeneration.

Molecular mechanisms regulating motor neuron development and degeneration

Motor neurons are a well-defined, although heterogeneous group of cells responsible for transmitting information from the central nervous system to the locomotor system. Spinal motor neurons are specified by soluble factors produced by structures adjacent to the primordial spinal cord, signaling through homeodomain proteins. Axonal pathfinding is regulated by cell-surface receptors that interact with extracellular ligands and once synaptic connections have formed, the survival of the somatic motor neuron is dependent on the provision of target-derived growth factors, although nontarget-derived factors, produced by either astrocytes or Schwann cells, are also potentially implicated. Somatic motor neuron degeneration leads to profound disability, and multiple pathogenetic mechanisms including aberrant growth factor signaling, abnormal neurofilament accumulation, excitotoxicity, and autoimmunity have been postulated to be responsible. Even when specific deficits have been identified, for example, mutations of the superoxide dismutase-1 gene in familial amyotrophic sclerosis and polyglutamine expansion of the androgen receptor in spinal and bulbar muscular atrophy, the mechanisms by which somatic motor neuronal degeneration occurs remain unclear. In order to treat motor system degeneration effectively, we will need to understand these mechanisms more thoroughly.

Time course and age dependence of motor neuron death following facial nerve crush injury: role of fibroblast growth factor

Peripheral nerve crush injury (PNCI) has been used for many years in adult animals to study central and peripheral changes related to regeneration across the injury site. While these adult animals experience full recovery with no neuronal cell loss following PNCI, it has been noted that the injury in perinatal animals is followed by retrograde neuronal cell death. The present study determines, in mice of different postnatal ages, the degree to which motor neurons are vulnerable to PNCI induced cell death and examines the rate of neuronal loss. Animals of 4 days of age and younger were found to be significantly more vulnerable to motor neuron cell death following PNCI. There also was a proportional relationship between age at injury and final motor neuronal survival and an inverse relationship between age at injury and rate of neuronal cell death following injury. In addition a proportional relationship was observed between the expression level of acidic fibroblast growth factor within motor neurons and the resistance to PNCI induced neuronal death. It was also found that PNCI in an environment that contained higher levels of FGFs (either in mice treated with acidic FGF or in transgenic mice that overexpress basic FGF) significantly decreases neuronal cell death following early postnatal injury.

The microglia/macrophage response in the neonatal rat facial nucleus following axotomy

Microglia represent a population of brain macrophage precursor cells which are intrinsic to the CNS parenchyma. Transection of the facial nerve in the newborn rat causes death of the affected motor neurons which is accompanied by massive activation of local microglia. Many of these cells develop into macrophages as can be shown by immunocytochemistry for OX-42 and ED1. Using the new polyclonal microglial marker ionized calcium binding adapter molecule 1, iba1, in combination with immunocytochemical double-labeling for the proliferating cell nuclear antigen (PCNA), or [3H]thymidine autoradiography, and confocal microscopy, qualitative as well as quantitative differences can be demonstrated between the newborn and the adult axotomized rat facial nucleus. While microglial cells are the only cell population which responds to axotomy by cell division in the adult facial nucleus, GFAP positive reactive astrocytes can be shown to undergo mitosis following axotomy in the newborn rat. Furthermore, ED1 immunoreactivity, early expression of MHC class II molecules and morphological transformation of microglia into macrophages can only be observed under conditions of neuronal degeneration, i.e., in the neonatal rat facial nucleus. Thus, the combination of cellular markers described here should be useful for studies employing the neonatal rat facial nucleus as an in vivo assay system to test the efficacy of neurotrophic factors.

Regulation of expression of the sensory neuron-specific sodium channel SNS in inflammatory and neuropathic pain

Increased voltage-gated sodium channel activity may contribute to the hyperexcitability of sensory neurons in inflammatory and neuropathic pain states. We examined the levels of the transcript encoding the tetrodotoxin-resistant sodium channel SNS in dorsal root ganglion neurons in a range of inflammatory and neuropathic pain models in the rat. Local Freund's adjuvant or systemic nerve growth factor-induced inflammation did not substantially alter the total levels of SNS mRNA. When NGF-treated adult rat DRG neurons in vitro were compared with NGF-depleted control neurons, SNS total mRNA levels and the levels of membrane-associated immunoreactive SNS showed a small increase (17 and 25%, respectively), while CGRP levels increased fourfold. SNS expression is thus little dependent on NGF even though SNS transcript levels dropped by more than 60% 7-14 days after axotomy. In the streptozotocin diabetic rat SNS levels fell 25%, while in several manipulations of the L5/6 tight nerve ligation rat neuropathic pain model, SNS levels fell 40-80% in rat strains that are either susceptible or relatively resistant to the development of allodynia. Increased expression of SNS mRNA is thus unlikely to underlie sensory neuron hyperexcitability associated with inflammation, while lowered SNS transcript levels are associated with peripheral nerve damage.

Acute neuronal and vascular changes following unilateral cerebellar pedunculotomy in the neonatal rat

During development of the central nervous system (CNS) both deafferentation and axotomy induce increased neuronal death and result in a smaller brain with diminished function at maturity. Unilateral cerebellar pedunculotomy has been used as a model to study the relative importance of these 2 types of lesion on the survival of developing CNS neurons. Within the cerebellum, unilateral pedunculotomy causes deafferentation of the hemicerebellum and axotomy in the efferent pathway from the ipsilateral deep cerebellar nuclei. This results in a smaller hemicerebellum with normal cortical laminae but no extracerebellar outflow. In order to identify the sequence of events which leads to this altered structure and therefore to understand the relative importance of afferent versus target-derived trophic support, unilateral cerebellar pedunculotomy was performed on neonatal rat pups, aged between 1 and 3 days. The cerebella were analysed for histological and vascular changes after survival times of 0, 3, 6, 9, 12, 18, 21, 24 and 48 h. The results show that the effects of axotomy on the deep cerebellar nuclear neurons begin within 3 h of the lesion and apoptotic neuronal degeneration occurs within 48 h. However, the cerebellar cortical neurons continue to undergo normal histological development for at least 48 h after deafferentation. In addition, since ischaemia induces similar effects, a study of the vascular tree was made. The results indicate that the pedunculotomy does not alter the blood supply to the cerebellum, nor induce ischaemia of the cerebellar neurons. From this it may be hypothesised that target-derived trophic support is more crucial for the survival of immature neurons than is the trophic effect of afferent input.

Osteopromotion for cranioplasty: an experimental study in rats using acidic fibroblast growth factor

BACKGROUND

Many growth factors influence the bone healing cascade. Furthermore, the occasional failure of bone repair may in part be due to perturbation in the activation of local growth factors. Local activation of fibroblast growth factors (FGFs) at the fracture site may serve to increase neovascularization, and induce early granulation formation that can affect bone healing.

METHODS

We have performed a rat parietal (6 x 3 mm) critical size defect (CSD). Human recombinant acidic fibroblast growth factor (hraFGF) imbided in agarose was topically administered at the craniectomy site. Control animals received agarose alone in the same manner. Three weeks after surgery, osteopromotion was histologically evaluated.

RESULTS

hraFGF-treated animals show a continuous bridge of regenerated bone extending from one edge of the defect to the other. None of the parietal defects that had been treated with agarose contained new bone in the central portion.

CONCLUSION

Our results suggest an important role of FGFs to promote large cranioplasty repair and support the use of these proteins as an alternative choice for bone grafts and bone substitutes.