Basic fibroblast growth factor in the hypoglossal system: specific retrograde transport, trophic, and lesion-related responses

Characterizing the multiple roles of FGF-2 in SOD1G93A ALS mice in vivo and in vitro

We have previously shown that knockout of fibroblast growth factor-2 (FGF-2) and potential compensatory effects of other growth factors result in amelioration of disease symptoms in a transgenic mouse model of amyotrophic lateral sclerosis (ALS). ALS is a rapidly progressive neurological disorder leading to degeneration of cortical, brain stem, and spinal motor neurons followed by subsequent denervation and muscle wasting. Mutations in the superoxide dismutase 1 (SOD1) gene are responsible for approximately 20% of familial ALS cases and SOD1 mutant mice still are among the models best mimicking clinical and neuropathological characteristics of ALS. The aim of the present study was a thorough characterization of FGF-2 and other growth factors and signaling effectors in vivo in the SOD1^G93A mouse model. We observed tissue-specific opposing gene regulation of FGF-2 and overall dysregulation of other growth factors, which in the gastrocnemius muscle was associated with reduced downstream extracellular-signal-regulated kinases (ERK) and protein kinase B (AKT) activation. To further investigate whether the effects of FGF-2 on motor neuron death are mediated by glial cells, astrocytes lacking FGF-2 were cocultured together with mutant SOD1 ^G93A motor neurons. FGF-2 had an impact on motor neuron maturation indicating that astrocytic FGF-2 affects motor neurons at a developmental stage. Moreover, neuronal gene expression patterns showed FGF-2- and SOD1 ^G93A -dependent changes in ciliary neurotrophic factor, glial-cell-line-derived neurotrophic factor, and ERK2, implying a potential involvement in ALS pathogenesis before the onset of clinical symptoms.

A nuclear odyssey: fibroblast growth factor-2 (FGF-2) as a regulator of nuclear homeostasis in the nervous system

Nuclear localization of classical growth factors is a well-known phenomenon but still remains a molecular and cellular conundrum. Fibroblast growth factor-2 (FGF-2) is an excellent example of a protein which functions as an extracellular molecule involved in canonical receptor tyrosine kinase signaling as well as displaying intracellular functions. Paracrine and nuclear functions are two important sides of the same protein. FGF-2 is expressed in isoforms with different molecular weights from one mRNA species. In rodents, all of these isoforms become imported to the nucleus. In this review, we discuss structural and functional aspects of FGF-2 isoforms in the nervous system. The nuclear odyssey of FGF-2 is reflected by nuclear dynamics, localization to nuclear bodies such as nucleoli, binding to chromatin and engagement in various protein interactions. Recently discovered molecular partnerships of the isoforms shed light on their nuclear functions, thereby greatly extending our knowledge of the multifaceted functions of FGF-2.

Specificity of peripheral nerve regeneration: interactions at the axon level

Peripheral nerves injuries result in paralysis, anesthesia and lack of autonomic control of the affected body areas. After injury, axons distal to the lesion are disconnected from the neuronal body and degenerate, leading to denervation of the peripheral organs. Wallerian degeneration creates a microenvironment distal to the injury site that supports axonal regrowth, while the neuron body changes in phenotype to promote axonal regeneration. The significance of axonal regeneration is to replace the degenerated distal nerve segment, and achieve reinnervation of target organs and restitution of their functions. However, axonal regeneration does not always allows for adequate functional recovery, so that after a peripheral nerve injury, patients do not recover normal motor control and fine sensibility. The lack of specificity of nerve regeneration, in terms of motor and sensory axons regrowth, pathfinding and target reinnervation, is one the main shortcomings for recovery. Key factors for successful axonal regeneration include the intrinsic changes that neurons suffer to switch their transmitter state to a pro-regenerative state and the environment that the axons find distal to the lesion site. The molecular mechanisms implicated in axonal regeneration and pathfinding after injury are complex, and take into account the cross-talk between axons and glial cells, neurotrophic factors, extracellular matrix molecules and their receptors. The aim of this review is to look at those interactions, trying to understand if some of these molecular factors are specific for motor and sensory neuron growth, and provide the basic knowledge for potential strategies to enhance and guide axonal regeneration and reinnervation of adequate target organs.

Prolonged survival and milder impairment of motor function in the SOD1 ALS mouse model devoid of fibroblast growth factor 2

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease characterized by selective motoneuron loss in brain and spinal cord. Mutations in the superoxide dismutase (SOD) 1 gene account for 10-20% of familial ALS patients. The ALS-mouse model over-expressing a mutant human SOD1 (G93A) gene closely mimics human ALS disease. The cause for the selective death of motoneurons is still unclear, but among several pathomechanisms discussed, loss of neurotrophic factors is one possibility. Basic fibroblast growth factor 2 (FGF-2) plays a prominent role in the motor system. In order to evaluate a role of FGF-2 in ALS pathogenesis, double mouse mutants transgenic for the human SOD1 mutation and lacking the endogenous FGF-2 gene were generated. Both heterozygous and homozygous FGF-2 deficient mutant SOD1 mice showed a significant delay in disease onset and less impaired motor performance in comparison to mutant SOD1 mice with normal FGF-2 levels. Survival of the double mouse mutants was significantly prolonged for two weeks. Motoneuron numbers were significantly higher in the double mutants and astrocytosis was diminished at disease endstage. While one would initially have expected that FGF-2 deficiency deteriorates the phenotype of mutant SOD1 animals, our results revealed a protective effect of FGF-2 reduction. In search of the underlying mechanisms, we could show up-regulation of other neurotrophic factors with proven protective effects in the ALS mouse model, ciliary neurotrophic factor (CNTF) and glial derived neurotrophic factor (GDNF) in muscle and spinal cord tissue of double mutant animals.

Analysis of the fibroblast growth factor system reveals alterations in a mouse model of spinal muscular atrophy

The monogenetic disease Spinal Muscular Atrophy (SMA) is characterized by a progressive loss of motoneurons leading to muscle weakness and atrophy due to severe reduction of the Survival of Motoneuron (SMN) protein. Several models of SMA show deficits in neurite outgrowth and maintenance of neuromuscular junction (NMJ) structure. Survival of motoneurons, axonal outgrowth and formation of NMJ is controlled by neurotrophic factors such as the Fibroblast Growth Factor (FGF) system. Besides their classical role as extracellular ligands, some FGFs exert also intracellular functions controlling neuronal differentiation. We have previously shown that intracellular FGF-2 binds to SMN and regulates the number of a subtype of nuclear bodies which are reduced in SMA patients. In the light of these findings, we systematically analyzed the FGF-system comprising five canonical receptors and 22 ligands in a severe mouse model of SMA. In this study, we demonstrate widespread alterations of the FGF-system in both muscle and spinal cord. Importantly, FGF-receptor 1 is upregulated in spinal cord at a pre-symptomatic stage as well as in a mouse motoneuron-like cell-line NSC34 based model of SMA. Consistent with that, phosphorylations of FGFR-downstream targets Akt and ERK are increased. Moreover, ERK hyper-phosphorylation is functionally linked to FGFR-1 as revealed by receptor inhibition experiments. Our study shows that the FGF system is dysregulated at an early stage in SMA and may contribute to the SMA pathogenesis.

Differential cellular FGF-2 upregulation in the rat facial nucleus following axotomy, functional electrical stimulation and corticosterone: a possible therapeutic target to Bell's palsy

BACKGROUND

The etiology of Bell's palsy can vary but anterograde axonal degeneration may delay spontaneous functional recovery leading the necessity of therapeutic interventions. Corticotherapy and/or complementary rehabilitation interventions have been employed. Thus the natural history of the disease reports to a neurotrophic resistance of adult facial motoneurons leading a favorable evolution however the related molecular mechanisms that might be therapeutically addressed in the resistant cases are not known. Fibroblast growth factor-2 (FGF-2) pathway signaling is a potential candidate for therapeutic development because its role on wound repair and autocrine/paracrine trophic mechanisms in the lesioned nervous system.

METHODS

Adult rats received unilateral facial nerve crush, transection with amputation of nerve branches, or sham operation. Other group of unlesioned rats received a daily functional electrical stimulation in the levator labii superioris muscle (1 mA, 30 Hz, square wave) or systemic corticosterone (10 mgkg-1). Animals were sacrificed seven days later.

RESULTS

Crush and transection lesions promoted no changes in the number of neurons but increased the neurofilament in the neuronal neuropil of axotomized facial nuclei. Axotomy also elevated the number of GFAP astrocytes (143% after crush; 277% after transection) and nuclear FGF-2 (57% after transection) in astrocytes (confirmed by two-color immunoperoxidase) in the ipsilateral facial nucleus. Image analysis reveled that a seven days functional electrical stimulation or corticosterone led to elevations of FGF-2 in the cytoplasm of neurons and in the nucleus of reactive astrocytes, respectively, without astrocytic reaction.

CONCLUSION

FGF-2 may exert paracrine/autocrine trophic actions in the facial nucleus and may be relevant as a therapeutic target to Bell's palsy.

Differential regulation of FGF-2 in neurons and reactive astrocytes of axotomized rat hypoglossal nucleus. A possible therapeutic target for neuroprotection in peripheral nerve pathology

Despite the favorable treatment of cranial nerve neuropathology in adulthood, some cases are resistant to therapy leading to permanent functional impairments. In many cases, suitable treatment is problematic as the therapeutic target remains unknown. Basic fibroblast growth factor (bFGF, FGF-2) is involved in neuronal maintenance and wound repair following nervous system lesions. It is one of few neurotrophic molecules acting in autocrine, paracrine and intracrine fashions depending upon specific circumstances. Peripheral cranial somatic motor neurons, i.e. hypoglossal (XII) neurons, may offer a unique opportunity to study cellular FGF-2 mechanisms as the molecule is present in the cytoplasm of neurons and in the nuclei of astrocytes of the central nervous system. FGF-2 may trigger differential actions during development, maintenance and lesion of XII neurons because axotomy of those cells leads to cell death during neonatal ages, but not in adult life. Moreover, the modulatory effects of astroglial FGF-2 and the Ca+2-binding protein S100β have been postulated in paracrine mechanisms after neuronal lesions. In our study, adult Wistar rats received a unilateral crush or transection (with amputation of stumps) of XII nerve, and were sacrificed after 72h or 11 days. Brains were processed for immunohistochemical localization of neurofilaments (NF), with or without counterstaining for Nissl substance, glial fibrillary acidic protein (GFAP, as a marker of astrocytes), S100β and FGF-2. The number of Nissl-positive neurons of axotomized XII nucleus did not differ from controls. The NF immunoreactivity increased in the perikarya and decreased in the neuropil of axotomized XII neurons 11 days after nerve crush or transection. An astrocytic reaction was seen in the ipsilateral XII nucleus of the crushed or transected animals 72h and 11 days after the surgery. The nerve lesions did not change the number of FGF-2 neurons in the ipsilateral XII nucleus; however, the nerve transection increased the number of FGF-2 glial profiles by 72h and 11 days. Microdensitometric image analysis revealed a short lasting decrease in the intensity of FGF-2 immunoreactivity in axotomized XII neurons by 72h after nerve crush or transection and also an elevation of FGF-2 in the ipsilateral of glial nuclei by 72h and 11 days after the two lesions. S100β decreased in astrocytes of 11-day-transected XII nucleus. The two-color immunoperoxidase for the simultaneous detection of the GFAP/FGF-2 indicated FGF-2 upregulation in the nuclei of reactive astrocytes of the lesioned XII nucleus. Astroglial FGF-2 may exert paracrine trophic actions in mature axotomized XII neurons and might represent a therapeutic target for neuroprotection in peripheral nerve pathology.

Neurotrophic factors in neurodegenerative disorders : potential for therapy

Finding an effective therapy to treat chronic neurodegenerative disorders still represents an unmet and elusive goal, mainly because so many pathogenic variables come into play in these diseases. Recent emphasis has been placed on the role of neurotrophic factors in the aetiology of such disorders because of their role in the survival of different cell phenotypes under various adverse conditions, including neurodegeneration.This review summarizes the current status and the efforts to treat neurodegenerative disorders by the exogenous administration of neurotrophic factors in an attempt to replenish trophic supply, the paucity of which may contribute to the development of the illness. Although promising results have been seen in animal models, this approach still meets disparate and often insurmountable problems in clinical settings, presumably related to the unique nature of the human being.

The physiological and pharmacological role of basic fibroblast growth factor in the dopaminergic nigrostriatal system

Basic fibroblast growth factor (FGF-2) is a physiological relevant neurotrophic factor in the nigrostriatal system and hence a promising candidate for the establishment of alternative therapeutic strategies in Parkinson's disease. FGF-2 and its high-affinity receptors (FGFR) display an expression in the developing, postnatal, and adult substantia nigra (SN) and in the striatum. Exogenous application promoted survival, neurite outgrowth and protection from neurotoxin-induced death of dopaminergic (DA) neurons both in vitro and in vivo. In animal models of Parkinson's disease, co-transplantation of fetal DA cells with FGF-2 expressing cells increased survival and functional integration of the grafted DA neurons resulting in improved behavioral performance. Analyzing the physiological function of the endogenous FGF-2 system during development and after neurotoxin-induced lesion revealed for the DA neurons of the SNpc a dependence on FGFR3 signaling during development. In addition, in the absence of FGF-2 an increased number of DA neurons was found, whereas enhanced levels of FGF-2 resulted in a reduced DA cell density. Following neurotoxin-induced lesion of DA neurons, FGF-2-deleted mice displayed a higher extent of DA neuron death whereas in FGF-2 overexpressing mice more DA neurons were protected. According to the data, FGF-2 seems to promote DA neuron survival via FGFR3 during development, whereas absence of this ligand could be compensated by other members of the FGF family. In contrast, in the adult organism, FGF-2 cannot be compensated by other factors under lesion conditions suggesting a central role for this molecule in the nigrostriatal system.

The spinal muscular atrophy gene product regulates neurite outgrowth: importance of the C terminus

Spinal muscular atrophy is a neurodegenerative disease accompanied by a loss of motoneurons. Either mutations or deletions in the survival of motoneuron (SMN) gene are responsible for this defect. SMN is an assembly protein for RNA-protein complexes in the nucleus and is also found in axons of neurons. However, it is unclear which dysfunctions of SMN are important for disease progression. In this study we analyzed the contributions of different SMN regions for localization and neuronal differentiation associated with outgrowth of neurites. Suppression of endogenous SMN protein levels significantly decreased the growth of neurites. Down-regulation of the interacting protein gemin2 had the opposite effect. Surprisingly, selective overexpression of the SMN C-terminal domain promoted neurite outgrowth similar to full-length protein and could rescue the SMN knock-down effects. The knock-down led to a significant change in the G-/F-actin ratio, indicating a role for SMN in actin dynamics. Therefore, our data suggest a functional role for SMN in microfilament metabolism in axons of motoneurons.

Possible joint origin of restless leg syndrome (RLS) and migraine

Sleep disorders have been described in migraine patients. Among sleep disorders RLS has been reported in up to one-third of migraineurs. Adverse effects of anti migraine therapy by dopamine antagonists can not fully explain this association. Therefore we present the hypothesis that RLS and migraine may have a joint origin. The hypothesis is supported by: (1) the same genetic origin for migraine without aura and RLS in single Italian family on chromosome 14q21; this gene codes survival motor neuron-interacting protein 1 (SIP1) which can play role in both diseases. (2) Correlation of both RLS and migraine with fibromyalgia. (3) Alteration of cortical excitability in both migraine and RLS.

Relevance of motoneuron specification and programmed cell death in embryos to therapy of ALS

The molecular cues that generate spinal motoneurons in early embryonic development are well defined. Motoneurons are generated in excess and consequently undergo a natural period of programmed cell death. Although it is not known exactly how motoneurons compete for survival in embryonic development, it is hypothesized that they rely on the ability to access limited amounts of trophic factors from peripheral tissues, a process that is tightly regulated by skeletal muscle activity. Attempts to elucidate the molecular mechanisms that underlie motoneuron generation and programmed cell death in embryos have led to various effective strategies for treating injury and disease in animal models. Such studies provide great hope for the amelioration of human amyotrophic lateral sclerosis (ALS), a devastating progressive motoneuron degenerative disease. Here we review the clinical relevance of studying motoneuron specification and death during embryonic development.

Synaptic targeting of retrogradely transported trophic factors in motoneurons: comparison of glial cell line-derived neurotrophic factor, brain-derived neurotrophic factor, and cardiotrophin-1 with tetanus toxin

Glial cell line-derived neurotrophic factor (GDNF), brain-derived neurotrophic factor (BDNF), and cardiotrophin-1 (CT-1) are the most potent neurotrophic factors for motoneurons, but their fate after retrograde axonal transport is not known. Internalized trophic factors may be degraded, or they may be recycled and transferred to other neurons, similar to the known route of tetanus toxin. We tested whether neonatal rat hypoglossal motoneurons target retrogradely transported trophic factors to synaptic sites on their dendrites within the brainstem and subsequently transfer these trophins across the synaptic cleft to afferent synapses (transsynaptic transcytosis). Motoneurons retrogradely transport from the tongue radiolabeled GDNF, BDNF, and CT-1 as well as tetanus toxin. Quantitative autoradiographic electron microscopy showed that GDNF and BDNF were transported into motoneuron dendrites with labeling densities similar to those of tetanus toxin. Although tetanus toxin accumulated rapidly (within 8 h) at presynaptic sites, GDNF accumulated at synapses more slowly (within 15 h), and CT-1 never associated with synapses. Thus, some retrogradely transported neurotrophic factors are trafficked similarly but not identically to tetanus toxin. Both GDNF and BDNF accumulate at the external (limiting) membrane of multivesicular bodies within proximal dendrites. We conclude that tetanus toxin, GDNF, and BDNF are released from postsynaptic sites and are internalized by afferent presynaptic terminals, thus demonstrating transsynaptic transcytosis. CT-1, however, follows a strict degradation pathway after retrograde transport to the soma. Synaptic and transcytotic trafficking thus are restricted to particular neurotrophic factors such as GDNF and BDNF.

Neural adhesion molecules L1 and CHL1 are survival factors for motoneurons

Many neurotrophic factors with survival activity for motoneurons in vivo were first identified using cultures of purified embryonic motoneurons. The L1 neural cell adhesion molecule has multiple roles in brain development. We showed by in situ hybridization and RT-PCR that L1 mRNA was expressed at significant levels in motoneurons of embryonic and postnatal spinal cord. We therefore cultured purified motoneurons from E14 rat embryos in the absence of trophic factors but with L1-Fc and CHL1-Fc fusion proteins. L1-Fc prevented the death of approximately half of the motoneurons that were saved by BDNF in a dose-dependent manner (EC50 = 10 pM). CHL1-Fc saved the same number of motoneurons as did L1-Fc, whereas P0-Fc had little neurotrophic activity at the same concentrations. Survival induced by L1 and CHL1 was completely inhibited by 20 microM LY294002 and PD98059, indicating that both MEK and PI3K pathways are required for signaling by these molecules. L1 can signal in other cell types through the FGF receptor FGFR1. In cultures of motoneurons, effects of suboptimal concentrations of L1 and suboptimal concentrations of FGF-2 were additive, but the effects of optimal concentrations of FGF-2 (50 ng/ml) were not further increased in the presence of L1-Fc. Thus, in this system, too, FGF and L1 may use similar signaling pathways.

Fibroblast growth factor-2(23) binds directly to the survival of motoneuron protein and is associated with small nuclear RNAs

The SMN (survival of motoneuron) protein is mutated in patients with the neurodegenerative disease spinal muscular atrophy. We have shown previously that a high-molecular-mass isoform of FGF (fibroblast growth factor) 2 (FGF-2(23)) is in a complex with SMN [Claus, Doring, Gringel, Muller-Ostermeyer, Fuhlrott, Kraft and Grothe (2003) J. Biol. Chem. 278, 479-485]. FGF-2 is a neurotrophic factor for motoneurons, and is known not only as a classical extracellular growth factor, but also as a nuclear protein. In the present study, we demonstrate that SMN binds to the arginine-rich N-terminus of FGF-2(23). In turn, FGF-2(23) interacts with amino acid residues 1-90 of the human SMN protein. This sequence displays nucleic-acid-binding capacity and overlaps partially with known binding sites for Gemin2/SIP1 (SMN-interacting protein 1) and p53. Finally, as a functional consequence of FGF-2(23) binding to SMN, FGF-2(23) is in a complex with the small nuclear RNAs U2 and U4. Since SMN functions as an assembly factor for snRNPs (small nuclear ribonucleoprotein particles), these results suggest binding of FGF-2(23) to snRNPs.

Regulation of neuronal death and calcitonin gene-related peptide by fibroblast growth factor-2 and FGFR3 after peripheral nerve injury: Evidence from mouse mutants

The presence and regulation of basic fibroblast growth factor and its high-affinity tyrosine kinase receptor FGFR3 in sensory neurons during development and after peripheral nerve injury suggest a physiological role of the fibroblast growth factor-2 system for survival and maintenance of sensory neurons. Here we investigated L5 spinal ganglia of intact and lesioned fibroblast growth factor-2 knock-out and FGFR3 knock-out mice. Quantification of sensory neurons in intact L5 spinal ganglia revealed no differences between wild-types and mutant mice. After sciatic nerve axotomy, the normally occurring neuron loss in wild-type mice was significantly reduced in both knock-out strains suggesting that fibroblast growth factor-2 is involved in neuronal death mediated via FGFR3. In addition, the number of chromatolytic and eccentric cells was significantly increased in fibroblast growth factor-2 knock-out mice indicating a transient protection of injured spinal ganglia neurons in the absence of fibroblast growth factor-2. The expression of the neuropeptide calcitonin gene-related peptide in sensory neurons of intact fibroblast growth factor-2 knock-out and FGFR3 knock-out mice was not changed in comparison to adequate wild-types. Fibroblast growth factor-2 wild-type and FGFR3 wild-type mice showed a lesion-induced decrease of calcitonin gene-related peptide-positive neurons in ipsilateral L5 spinal ganglia whereas the loss of calcitonin gene-related peptide-immunoreactive sensory neurons is reduced in the absence of fibroblast growth factor-2 or FGFR3, respectively. In addition, FGFR3 wild-type and knock-out mice displayed a contralateral reduction of the neuropeptide after axotomy. These results suggest that endogenous fibroblast growth factor-2 and FGFR3 are crucially involved in the regulation of survival and calcitonin gene-related peptide expression of lumbar sensory neurons after lesion, but not during development.

Fibroblast growth factors as regulators of central nervous system development and function

Fibroblast growth factors (FGFs) are multifunctional signaling proteins that regulate developmental processes and adult physiology. Over the last few years, important progress has been made in understanding the function of FGFs in the embryonic and adult central nervous system. In this review, I will first discuss studies showing that FGF signaling is already required during formation of the neural plate. Next, I will describe how FGF signaling centers control growth and patterning of specific brain structures. Finally, I will focus on the function of FGF signaling in the adult brain and in regulating maintenance and repair of damaged neural tissues.

Differential intranuclear localization of fibroblast growth factor-2 isoforms and specific interaction with the survival of motoneuron protein

Fibroblast growth factor 2 (FGF-2) is an important modulator of cell growth and differentiation and a neurotrophic factor. FGF-2 occurs in isoforms, at a low molecular weight of 18,000 and at least two high molecular weight forms (21,000 and 23,000), representing alternative translation products from a single mRNA. In addition to its role as an extracellular ligand, FGF-2 localizes to the nuclei of cells. Here we show differential localization of the 18- and 23-kDa isoforms in the nuclei of rat Schwann cells. Whereas the 18-kDa isoform was found in the nucleoli, nucleoplasm, and Cajal bodies, the 23-kDa isoform localized in a punctuate pattern and associates with mitotic chromosomes suggesting different functional roles of the isoforms. Moreover, we show here that the 23-kDa FGF-2 isoform co-immunoprecipitates specifically with the survival of motor neuron protein (SMN). SMN is an assembly and recycling factor of the splicing machinery and locates to the cytoplasm, the nucleoplasm, and nuclear gems, where it co-localizes with 23-kDa FGF-2. Patients with spinal muscular atrophy suffer from fatal degeneration of motoneurons because of mutations and deletions of the gene for the SMN protein.

Promoting axonal regeneration in the central nervous system by enhancing the cell body response to axotomy

Neurons projecting into the peripheral nervous system (PNS) regenerate their axons after injury, in contrast to those confined to the central nervous system (CNS). Both neuronal and nonneuronal factors contribute to the lack of CNS regeneration. In this review we concentrate on the differential gene expression response to axotomy in PNS vs. CNS neurons. In general CNS neurons fail to up-regulate or sustain the expression of regeneration-associated proteins (RAGs), including trophic factors and their receptors. The presumed lack of trophic support of axotomized CNS neurons provided the rationale for the exogenous application of trophic factors, either to the lesion site or to the cell bodies. Here, we review our data on the application of trophic factors to rubrospinal and corticospinal neurons. Cell body treatment of axotomized rubrospinal neurons with brain-derived neurotrophic factor (BDNF) reversed atrophy, increased GAP-43 and Talpha-1 tubulin mRNA expression, and promoted axonal regeneration into peripheral nerve grafts. Importantly, BDNF cell body treatment was still effective in the chronic setting, i.e., when initiated 1 year after injury, but BDNF had no effect when applied to the chronic spinal cord injury site. The ability to promote regeneration in chronically injured neurons will hopefully contribute to the development of treatment strategies for chronic spinal injuries.

Neuroprotective actions of selegiline

Selegiline, a selective inhibitor of monoamine oxidase-B (MAO-B), was one of the first adjunct therapies in clinical neurology. A retrospective analysis of data from patients with Parkinson's disease found a significant increase in survival in those treated with selegiline plus L-dopa compared with L-dopa alone. The mechanism of action of selegiline is complex and cannot be explained solely by its MAO-B inhibitory action. Pretreatment with selegiline can protect neurons against a variety of neurotoxins, such as 1-methyl-4-phenyl-1,2,3,6 tetrahydropyridine (MPTP), 6-hydroxydopamine, N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine (DSP-4), methyl-beta-acetoxyethyl-2-chloroethylamine (AF64A), and 5,6-dihydroxyserotonin, which damage dopaminergic, adrenergic, cholinergic, and sertoninergic neurons, respectively. Selegiline produces an amphetamine-like effect, enhances the release of dopamine, and blocks the reuptake of dopamine. It stimulates gene expression of L-aromatic amino acid decarboxylase, increases striatal phenylethylamine levels, and activates dopamine receptors. Selegiline reduces the production of oxidative radicals, up-regulates superoxide dismutase and catalase, and suppresses nonenzymatic and iron-catalyzed autooxidation of dopamine. Selegiline compensates for loss of target-derived trophic support, delays apoptosis in serum-deprived cells, and blocks apoptosis-related fall in the mitochondrial membrane potential. Most of the aforementioned properties occur independently of selegiline's efficacy to inhibit MAO-B.

Fibroblast growth factor-5 is expressed in Schwann cells and is not essential for motoneurone survival

Fibroblast growth factor-5 (FGF-5) is a putative target-derived survival factor for motoneurones as it is concentrated in the synaptic portions of skeletal muscles and because it promotes the survival of embryonic motoneurones in vitro. A variety of experimental approaches have been used to examine this possibility. The expression of FGF-5 in the neuromuscular system was analysed using the reverse transcription-polymerase chain reaction (RT-PCR). Both splice variants of FGF-5 were detected in adult rat skeletal muscle, sciatic nerve, and spinal cord. The expression of FGF-5 in skeletal muscle was up-regulated after denervation. At first sight this appears to be consistent with FGF-5 being a target-derived factor. However, FGF-5 protein was detected in Schwann cells, macrophages, vascular smooth muscle and endothelial cells, but not in muscle fibres. The absence of FGF-5 in muscle fibres was confirmed by RT-PCR examination of isolated muscle fibres. Furthermore, FGF-5 protein was also not detected in denervated fibres, as would be expected for a neuronal survival factor. Denervation did however lead to up-regulation of FGF-5 in the Schwann cells of the distal nerve trunk. This may indicate that FGF-5 is either an autocrine regulator of Schwann cells or a Schwann cell-derived neurotrophic factor. The latter appears not to be the case for two reasons. First, the double-ligation technique was used to show that endogenous FGF-5 is not transported in motor axons. Second, stereological estimates of the number of motoneurones in an FGF-5 null mutant (Angora) mouse failed to reveal any loss of motoneurones. Collectively these experiments suggest that FGF-5 is not a physiological regulator of motoneurones, and therefore raise the possibility that it is an autocrine regulator of Schwann cells.

Fibroblast growth factor-2 and transforming growth factor-beta1 immunostaining in rat brain after cerebral postischemic reperfusion

Several trophic factors are known to regulate the survival and growth of neurons in brain and peripheral tissues. Several findings suggest that basic fibroblast growth factor-2 (FGF-2) plays an important role in the "self-repair" responses that follow injuries such as trauma and brain ischemia and that FGF-2 contributes to the repair of damaged tissue. Transforming growth factor-beta (TGF-beta) is a potent growth-regulatory protein secreted by virtually all cells. In the present study, we used immunohistochemical techniques to investigate whether FGF-2 and TGF-beta1 participate in the healing of damaged tissue following partial brain ischemia. The profile of the observed immunoreactivities indicated that TGF-beta1 and FGF-2 release varies between the different cerebral areas subjected to ischemic insult. Moreover, the sectorial heterogeneity of immunocytochemical response suggests that, during postischemic reperfusion, neuronal recovery may be due not only to neuron-glia interaction but also to neurochemical conditions involving inhibitory interneurons.

Expression of interleukin-6 and its receptor in the sciatic nerve and cultured Schwann cells: relation to 18-kD fibroblast growth factor-2

Expression of interleukin-6 (IL-6) and fibroblast growth factor-2 (FGF-2) in Schwann cells is modulated by external stimuli. To study possible interactions of both factors we have analyzed mutual effects of exogenous IL-6 and FGF-2 on the expression of each other and the corresponding receptor (R) molecules IL-6R and FGFR1 after peripheral nerve lesion in vivo and in vitro using cultured Schwann cells. Using rat Schwann cells we found that IL-6 did not exert any effects on the expression of FGF-2 and FGF receptor type 1 (R1) whereas exogenously applied 18-kD FGF-2 strongly increased the expression of the mRNAs of IL-6 and its receptor. In addition, immortalized Schwann cells over-expressing the 18-kD FGF-2 isoform showed elevated levels of IL-6 and IL-6R whereas immortalized Schwann cells over-expressing the high-molecular-weight isoforms (21 kD and 23 kD) displayed unaltered IL-6 and IL-6R expression levels. According to in situ hybridization studies of intact and crushed sciatic nerves in vivo, Schwann cells seems to be the main source of IL-6 and IL-6R. Following sciatic nerve crush, the FGF-2 and the IL-6 system are upregulated after the first hours. Furthermore, we showed that the early increase of the FGF-2 protein is mainly confined to the 18-kD isoform. These results are consistent with the idea of a functional coupling of FGF-2 and the IL-6 system in the early reaction of Schwann cells to nerve injury.

Fibroblast growth factor 2 (FGF2) and FGF receptor expression in an experimental demyelinating disease with extensive remyelination

Fibroblast growth factor 2 (FGF2) is an excellent candidate to regulate remyelination based on its proposed actions in oligodendrocyte lineage cell development in conjunction with its involvement in CNS regeneration. To assess the potential for FGF2 to play a role in remyelination, we examined the expression pattern of FGF2 and FGF receptors (FGFRs) in an experimental demyelinating disease with extensive remyelination. Adult mice were intracranially injected with murine hepatitis virus strain A-59 (MHV-A59) to induce focally demyelinated spinal cord lesions that spontaneously remyelinate, with corresponding recovery of motor function. Using kinetic RT-PCR analysis of spinal cord RNA, we found significantly increased levels of FGF2 mRNA transcripts, which peaked during the initial stage of remyelination. Analysis of tissue sections demonstrated that increased levels of FGF2 mRNA and protein were localized within demyelinated regions of white matter, including high FGF2 expression associated with astrocytes. The expression of corresponding FGF receptors was significantly increased in lesion areas during the initial stage of remyelination. In normal and lesioned white matter, oligodendrocyte lineage cells, including progenitors and mature cells, were found to express multiple FGFR types (FGFR1, FGFR2, and/or FGFR3). In addition, in lesion areas, astrocytes expressed FGFR1, FGFR2, and FGFR3. These findings indicate that, during remyelination, FGF2 may play a role in directly regulating oligodendrocyte lineage cell responses and may also act through paracrine or autocrine effects on astrocytes, which are known to synthesize other growth factors and immunoregulatory molecules that influence oligodendrocyte lineage cells.

Induction of reactive astrocytosis and prevention of motoneuron cell death by the I(2)-imidazoline receptor ligand LSL 60101

I(2)-imidazoline receptors are mainly expressed on glial cells in the rat brain. This study was designed to test the effect of treatment with the I(2)-imidazoline selective receptor ligand LSL 60101 [2-(2-benzofuranyl)imidazole] on the morphology of astrocytes in the neonate and adult rat brain, and to explore the putative neuroprotective effects of this glial response. Short-term (3 days) or chronic (7-10 days) treatment with LSL 60101 (1 mg kg(-1), i.p. every 12 h) enhanced the area covered by astroglial cells in sections of facial motor nucleus from neonate rats processed for glial fibrillary acidic protein (GFAP) immunostaining. Facial motoneurons surrounded by positive glial cell processes were frequently observed in sections of LSL 60101-treated rats. A similar glial response was observed in the parietal cortex of adult rats after chronic (10 days) treatment with LSL 60101 (10 mg kg(-1), i.p. every 12 h). Western-blot detection of the specific astroglial glutamate transporter GLT-1, indicated increased immunoreactivity after LSL 60101 treatment in the pons of neonate and in the parietoccipital cortex of adult rats. In the facial motor nucleus of neonate rats, the glial response after LSL 60101 treatment was associated to a redistribution of the immunofluorescence of the basic fibroblast growth factor (FGF-2) from the perinuclear area of motoneurons to cover most of their cytoplasm, suggesting a translocation of this mitogenic and neurotrophic factor towards secretion pathways. The neuroprotective potential of the above effects of LSL 60101 treatment was tested after neonatal axotomy of facial motor nucleus. Treatment with LSL 60101 (1 mg kg(-1), i.p. every 12 h from day 0 to day 10 after birth) significantly reduced (38%) motoneuron death rate 7 days after facial nerve axotomy performed on day 3 after birth. It is concluded that treatment with the I(2)-imidazoline selective receptor ligand LSL 60101 provokes morphological/biochemical changes in astroglia that are neuroprotective after neonatal axotomy.

FGF9: a motoneuron survival factor expressed by medial thoracic and sacral motoneurons

In the nervous system, fibroblast growth factor-9 (FGF9) is produced mainly by neurons. By whole-mount in situ hybridization, on embryonic rat spinal cord, we observed Fgf9 expression in a subpopulation of motoneurons located in the thoracic and sacral regions of the median motor column that innervate the axial muscles. Furthermore, FGF9 prevented death of purified rat and chicken motoneurons in culture in the same concentration range as FGF2. The targets of FGF9 are more restricted than that of the other FGFs, however, because conversely to FGF1 or FGF2, FGF9 had only weak or inexistent survival effects on chicken ciliary neurons or rat DRG. FGF9 may therefore play a role as an autocrine/paracrine survival factor for motoneurons.

FGF-9 is an autocrine/paracrine neurotrophic substance for spinal motoneurons

Motoneurons need muscle-derived neurotrophic substances for their survival during the initial phase of their development, but after maturation they lose this requirement and can survive after axotomy. This suggests that some neurotrophic substances other than target-derived ones control the survival of motoneurons in adults. Because spinal motoneurons express fibroblast growth factor-9 (FGF-9) messenger RNA, we hypothesized that FGF-9 might be an autocrine or paracrine survival factor for motoneurons. FGF-9 promoted the survival of motoneurons and upregulated the choline acetyl-transferase (ChAT) activity in the dissociated cultures of ventral half of rat E13 spinal cord. Externally added FGF-9 was more effective in low density cultures, and polyclonal blocking antibody against FGF-9 significantly lowered the ChAT activity. Our results support an autocrine or paracrine role for FGF-9 in mediating the survival of spinal motoneurons. Non-target-derived neurotrophic substances for motoneurons including FGF-9 should be important in the pathogenesis of motor neuron disorders in the adults, especially amyotrophic lateral sclerosis.

Glial cell line-derived neurotrophic factor rescues target-deprived sympathetic spinal cord neurons but requires transforming growth factor-beta as cofactor in vivo

Glial cell line-derived neurotrophic factor (GDNF) is a potent neurotrophic factor for several populations of CNS and peripheral neurons. Synthesis and storage of GDNF by the neuron-like adrenal medullary cells suggest roles in adrenal functions and/or in the maintenance of spinal cord neurons that innervate the adrenal medulla. We show that unilateral adrenomedullectomy causes degeneration of all sympathetic preganglionic neurons within the intermediolateral column (IML) of spinal cord segments T7-T10 that project to the adrenal medulla. In situ hybridization revealed that IML neurons express the glycosylphosphatidylinositol-linked alpha receptor 1 and c-Ret receptors, which are essential for GDNF signaling. IML neurons also display immunoreactivity for transforming growth factor-beta (TGF-beta) receptor II. Administration of GDNF (recombinant human, 1 microg) in Gelfoam implanted into the medullectomized adrenal gland rescued all Fluoro-Gold-labeled preganglionic neurons projecting to the adrenal medulla after four weeks. Cytochrome c applied as a control protein was not effective. The protective effect of GDNF was prevented by co-administration to the Gelfoam of neutralizing antibodies recognizing all three TGF-beta isoforms but not GDNF. This suggests that the presence of endogenous TGF-beta was essential for permitting a neurotrophic effect of GDNF. Our data indicate that GDNF has a capacity to protect a population of autonomic spinal cord neurons from target-deprived cell death. Furthermore, our results demonstrate for the first time that the previously reported requirement of TGF-beta for permitting trophic actions of GDNF in vitro (Kreiglstein et al., 1998) also applies to the in vivo situation.

Localization and regulation of basic fibroblast growth factor (FGF-2) and FGF receptor-1 in rat superior cervical ganglion after axotomy

In response to peripheral nerve lesion, synthesis of basic fibroblast growth factor (FGF-2) increases in sensory ganglia and motoneurons. Here, we investigated the axotomy-induced regulation of FGF-2 and FGF receptor-1 (FGFR-1) expression in the autonomic nervous system using the sympathetic superior cervical ganglion of the adult rat as a model. Transcripts for both proteins were detected by ribonuclease protection assay. Western blotting indicated the presence of all three FGF-2 isoforms (18, 21, and 23 kD) in the superior cervical ganglion. Immunohistochemical analysis revealed FGF-2 localization in nuclei of satellite cells surrounding postganglionic perikarya. After transection of the carotid nerves, the number of FGF-2-immunoreactive glial cells increased. FGF-2 mRNA was up-regulated within 6 h and remained elevated for 3 weeks. The 18-, 21-, and 23-kD isoforms were all increased 7 days after axotomy. FGFR-1 immunoreactivity was observed in neuronal and nonneuronal nuclei in the normal rat superior cervical ganglion. In contrast to FGF-2, expression of FGFR-1 was unchanged in ganglia after axotomy. Taken together, the present results suggest that FGF-2 participates in neuron-glial interactions of sympathetic ganglia and may be involved in sympathetic neuron survival or nerve regeneration after nerve lesion.

TrkB and neurotrophin-4 are important for development and maintenance of sympathetic preganglionic neurons innervating the adrenal medulla

The adrenal medulla receives its major presynaptic input from sympathetic preganglionic neurons that are located in the intermediolateral (IML) column of the thoracic spinal cord. The neurotrophic factor concept would predict that these IML neurons receive trophic support from chromaffin cells in the adrenal medulla. We show here that adrenal chromaffin cells in the adult rat store neurotrophin (NT)-4, but do not synthesize or store detectable levels of BDNF or NT-3, respectively. Preganglionic neurons to the adrenal medulla identified by retrograde tracing with fast blue or Fluoro-Gold (FG) express TrkB mRNA. After unilateral destruction of the adrenal medulla, 24% of IML neurons, i.e., all neurons that are preganglionic to the adrenal medulla in spinal cord segments T7-T10, disappear. Administration of NT-4 in gelfoams (6 microgram) implanted into the medullectomized adrenal gland rescued all preganglionic neurons as evidenced by their presence after 4 weeks. NT-3 and cytochrome C were not effective. The action of NT-4 is accompanied by massive sprouting of axons in the vicinity of the NT-4 source as monitored by staining for acetylcholinesterase and synaptophysin immunoreactivity, suggesting that NT-4 may enlarge the terminal field of preganglionic nerves and enhance their access to trophic factors. Analysis of TrkB-deficient mice revealed degenerative changes in axon terminals on chromaffin cells. Furthermore, numbers of FG-labeled IML neurons in spinal cord segments T7-T10 of NT-4-deficient adult mice were significantly reduced. These data are consistent with the notion that NT-4 from chromaffin cells operates through TrkB receptors to regulate development and maintenance of the preganglionic innervation of the adrenal medulla.

Neuroprotective fibroblast growth factor type-2 down-regulates the c-Jun transcription factor in axotomized sympathetic preganglionic neurons of adult rat

The immediate-early gene encoded transcription factor c-Jun is highly inducible following axotomy and therefore serves as a valuable marker in neuronal de- and regeneration. As the signals that may trigger c-Jun expression are still obscure, molecules derived from lesioned neurons and/or their targets such as growth factors or cytokines have been proposed as candidates for interneuronal transcriptional regulation in vivo. We therefore tested whether local administration of the neuroprotective cytokine fibroblast growth factor type-2 in vivo has an effect on the axotomy-induced nuclear expression patterns of the activator protein-1 transcription factors c-Fos and JunB, or c-Jun in the spinal cord-intermedolateral nucleus-adrenal axis lesion paradigm in the rat. Partial axotomy of preganglionic nerve fibres by selective unilateral removal of the adrenal medulla resulted in strong staining patterns of c-Jun in the nuclei of preganglionic cell bodies located in the spinal intermediolateral cell column identified by in vivo retrograde prelabelling with the fluorescent tracer Fast Blue prior to lesion. Axotomy-induced nuclear c-Jun expression was highly increased when compared with the moderate baseline expression in normal or sham-operated animals. In animals treated with fibroblast growth factor-2 gelfoams implanted to the lesioned adrenal gland the nuclear c-Jun staining pattern is reduced or even absent from these neurons. By contrast, c-Fos and JunB induction did not occur in the intermediolateral nucleus in the lesion paradigm investigated. These results support the idea of functional links between neurotrophic cytokines such as fibroblast growth factor-2 and transcriptional effectors such as c-Jun. The target derived fibroblast growth factor-2 thus may signal the intactness of the neuron-target axis resulting in suppression of central extrinsic neurons and promotion of neuroprotective gene activation. Neuronal survival in absence of c-Jun indicates that c-Jun exerts negative actions in vulnerated neurons.

Heparan sulfate modifies the effects of basic fibroblast growth factor on glial reactivity

Our previous studies have shown that injection of basic fibroblast growth factor (bFGF) into a brain wound enhances astrocyte hypertrophy and macrophage-microglia proliferation in areas adjacent to the lesion. In the present study, designed to test the effects of co-administration of bFGF and heparan sulfate (HS), rats received injections of 200 ng bFGF, 200 ng bFGF with 50 microg HS, or 50 microg HS into a brain wound. Glial proliferation and astrocyte hypertrophy were evaluated in seven non-overlapping subfields in the mid-cortex including the wound edge. Our results show that bFGF-HS, compared to bFGF or HS alone, enhanced the total area of GFAP staining in all subfields except the one nearest to the wound edge. The combination of bFGF and HS did not increase total glial or astrocyte proliferation. We propose that the observed effects resulted from a greater diffusion of bFGF-HS complex into the brain parenchyma, where it bypassed low-affinity binding sites that would otherwise sequester free bFGF. Our results suggest that bFGF-HS complex, compared to bFGF alone, may gain entry into the brain more readily, reach higher concentrations and be more effective as a neurotrophic agent.

Changes occur in the ability to promote axonal regeneration as the post-injury period increases

This study tested whether adult rat brain stem neurons could respond to growth or trophic factors provided after an extended post-injury period. The number of neurons that regenerated their axon into a peripheral nerve graft following exposure to ciliary neurotrophic factor (CNTF) 8 weeks after a cervical lesion was comparable to the number regenerating after exposure to CNTF 4 weeks after injury. In contrast, there was a significant decrease of 50% in the number of regenerating neurons following exposure to basic fibroblast growth factor (bFGF) 8 weeks after injury compared with the number regenerating after treatment with bFGF 4 weeks after injury. These results indicate that some factors are effective promoters of regeneration only if provided within a defined post-injury period.

Localization, differential expression and retrograde axonal transport suggest physiological role of FGF-2 in spinal autonomic neurons of the rat

Fibroblast growth factor-2 (FGF-2) has marked pharmacological neurotrophic effects on lesioned spinal autonomic neurons following target removal of the adrenal medulla, yet expression and axonal transport in autonomic neurons remain to be shown. We show here FGF-2 and FGF receptor type 1 (FGFR1) protein and mRNA expression in preganglionic intermediolateral neurons of the rat thoracic spinal cord. While immunoreactivity of both FGF-2 and FGFR1 co-localize to intermediolateral neurons, mRNA transcripts of FGFR1, but not of FGF-2, are detectable in intermediolateral preparations by RNase protection analysis, suggesting protein translocation in vivo. Unilateral microinjection of 125iodinated FGF-2 into the adrenal medulla (a major target of intermediolateral neurons) results in significant accumulation of specific radioactivity in thoracic spinal cord tissue, including the intermediolateral neurons, and the ipsilateral splanchnic nerve. Emulsion autoradiography demonstrated labelling over ipsilateral intermediolateral neurons only. Neuronal co-localization of FGF-2/FGFR1 protein, differential mRNA expression, specific retrograde axonal transport and the known neurotrophic actions in vivo, strongly suggest unique physiological roles of FGF-2 in the autonomic nervous system.

The cellular and molecular basis of peripheral nerve regeneration

Functional recovery from peripheral nerve injury and repair depends on a multitude of factors, both intrinsic and extrinsic to neurons. Neuronal survival after axotomy is a prerequisite for regeneration and is facilitated by an array of trophic factors from multiple sources, including neurotrophins, neuropoietic cytokines, insulin-like growth factors (IGFs), and glial-cell-line-derived neurotrophic factors (GDNFs). Axotomized neurons must switch from a transmitting mode to a growth mode and express growth-associated proteins, such as GAP-43, tubulin, and actin, as well as an array of novel neuropeptides and cytokines, all of which have the potential to promote axonal regeneration. Axonal sprouts must reach the distal nerve stump at a time when its growth support is optimal. Schwann cells in the distal stump undergo proliferation and phenotypical changes to prepare the local environment to be favorable for axonal regeneration. Schwann cells play an indispensable role in promoting regeneration by increasing their synthesis of surface cell adhesion molecules (CAMs), such as N-CAM, Ng-CAM/L1, N-cadherin, and L2/HNK-1, by elaborating basement membrane that contains many extracellular matrix proteins, such as laminin, fibronectin, and tenascin, and by producing many neurotrophic factors and their receptors. However, the growth support provided by the distal nerve stump and the capacity of the axotomized neurons to regenerate axons may not be sustained indefinitely. Axonal regenerations may be facilitated by new strategies that enhance the growth potential of neurons and optimize the growth support of the distal nerve stump in combination with prompt nerve repair.

Motor neurons in human and rat spinal cord synthesize fibroblast growth factor-9

Fibroblast growth factor (FGF)-9, initially referred to as a glia-activating factor, is a recently identified member of the FGF family. In the present study we demonstrated that spinal cord motor neurons and dorsal root ganglion neurons were strongly immunostained with specific antibodies to FGF-9 in human and rat tissues. By in situ hybridization using digoxigenin-labeled antisense probe to FGF-9 mRNA, we found specific signals in these neurons in rat. By immunoblotting analysis, we detected a 30/29 kDa doublet band in human spinal cord proteins, which corresponded to the doublet band of originally isolated FGF-9 from culture media. Our results indicate that these neurons synthesize FGF-9.

Selegiline enhances NGF synthesis and protects central nervous system neurons from excitotoxic and ischemic damage

It has been previously demonstrated that selegiline, an irreversible monoamine oxidase B (MAO-B) inhibitor, potentiates glial reaction to injury and possesses some 'trophic-like' activities which do not depend on the inhibition of MAO-B and which are probably associated with the induction of astrocyte-derived neurotrophic substances. Based on these findings, we tried to find out whether selegiline is able to modify the expression of nerve growth factor (NGF) and to protect central nervous system (CNS) neurons from excitotoxic and ischemic damage. Selegiline (10 pM-1 nM) induced NGF messenger RNA (mRNA) expression in cultured rat cortical astrocytes as determined by reverse transcription-polymerase chain reaction (RT-PCR) followed by a corresponding increase in NGF protein content measured by two-site NGF-enzyme-linked immunosorbent assay (ELISA) in astrocyte-conditioned medium. Additionally, exposure of hippocampal cultures containing neuronal and glial cells to this drug at the same concentrations enhanced significantly the content of NGF measured in the culture medium after 6 h of incubation. We hypothesize that selegiline could rescue hippocampal neurons from injury by induction of astrocyte-derived NGF in this cell culture system. To test this hypothesis, an excitotoxic damage was induced in the same type of cells by exposure to 0.5 mM L-glutamate for 1 h. Selegiline (10 pM-1 nM) present in the growth medium 6 h before until 18 h after induction of injury (the point of glutamate-toxicity measurement) protected hippocampal neurons from excitotoxic death. Furthermore, administered intraperitoneally (i.p.) (8 x 15 mg/kg per day) this drug enhanced the expression of NGF message in intact rat cerebral cortex and protected rat cortical tissue from ischemic insult due to permanent occlusion of the middle cerebral artery (MCA). The neuroprotective activity of selegiline (5 x 10 mg/kg per day i.p.) was also demonstrated in a mouse model of focal cerebral ischemia. The present data show that selegiline induced NGF expression in cultured rat cortical astrocytes. In mixed primary cultures of hippocampal neuronal and glial cells, selegiline increased NGF protein content and protected hippocampal neurons from excitotoxic degeneration. In vivo, this drug induced NGF gene expression in cerebral cortex from intact rats and protected rat and mouse cortical tissue from ischemic insult after occlusion of the MCA. Our results indicate that the induction of astrocyte-derived NGF could contribute to the neuroprotective activity of selegiline demonstrated both in vivo and in vitro and can explain, in part, the 'trophic-like' properties of this compound which has been observed by others.

Computer-assisted mapping of basic fibroblast growth factor immunoreactive nerve cell populations in the rat brain

We have performed a mapping of basic fibroblast growth factor (bFGF) immunoreactive (ir) glial and nerve cell populations in the male rat brain using a rabbit antibody raised against a synthetic peptide of bovine bFGF. Regional morphometric and microdensitometric analysis of the bFGF ir neuronal profiles in coronal brain sections was carried out by means of an automatic image analyser. The density and intensity of the bFGF ir glial profiles were subjectively evaluated. The bFGF immunoreactivity (IR) was detected within the cytoplasm of neurons, except within the pyramidal neurons of hippocampal CA2 region, the fasciola cinerea and the indusium griseum, where bFGF IR was present in the nucleus. In contrast, in glial cells bFGF IR was always found in the nucleus. Neuronal and glial IR was no longer observed after absorption of the bFGF antiserum with recombinant bFGF. Basic FGF IR was found in neuronal and glial cell populations throughout the brain as well as in the choroid plexus and in the ependymal cells lining the ventricles. Basic FGF ir nerve cells were found in all layers of both the neocortex and allocortex. Within the caudate putamen and the nucleus accumbens a low density of weak bFGF ir neuronal profiles was detected. The majority of the thalamic nuclei showed medium to high densities of moderate to strong bFGF ir neuronal profiles. All the hypothalamic nuclei, with the exception of the anterior and lateral hypothalamic area and of the ventral hypothalamic nucleus, contained a high density of bFGF ir profiles. The pons and the medulla oblongata were characterized by the presence of a large number of nuclei containing moderate to high densities of strong bFGF ir profiles. The Purkinje cell layer of the cerebellar cortex contained a high density of moderately bFGF ir profiles. A moderate density of strong bFGF ir nerve cell profiles was observed within all the laminae of the spinal cord, except within the II and III laminae where a high density of strongly ir profiles was found. Histogram analysis of total immunoreactivity showed that the distribution of bFGF ir profiles within the telencephalon and mesencephalon tend to be similar with regard to the central tendency and spread. Using Kendall's tau, a significant correlation between intensity and density values was obtained only in the diencephalon. The cytoplasmic bFGF IR found in distinct nerve cell populations all over the rat brain and spinal cord may represent forms of bFGF which can be released from the nerve cells via non-exocytotic mechanisms in view of the absence of an intracellular signal peptide in bFGF. The presence of nuclear bFGF IR within the glial cells all over the central nervous system (CNS) suggests an intracellular function of bFGF, such as the promotion of mitogenesis and/or participation in the transcriptional regulation of various genes.

Fibroblast growth factor receptor 1 in skeletal and heart muscle cells: expression during early avian development and regulation after notochord transplantation

Basic fibroblast growth factor (bFGF, FGF-2) mediates several biological functions during embryonic development. With regard to skeletal muscle formation, it has been suggested that FGF-2 is involved in the growth and differentiation of myogenic precursor cells. To identify the FGF-responsive cells we studied the expression of FGF receptor type I (FGFR-1) during early embryonic development of the chick. FGFR-1 immunoreactivity is present at all stages examined (embryonic day [E] 2-E5). Expression of FGFR-1 is found in the somite myotome, limb bud muscle cells, eye and tongue muscle cells, and myocardium. Transplantation of an additional notochord into the paraxial mesoderm, which prevents the formation of a myotome, reveals the absence of FGFR-1 immunoreactivity on the operated side. The distinct expression pattern of FGFR-1 in migrating and differentiating muscle cells indicates that in addition to the stimulation of proliferation of myoblasts, FGF-2 exerts other (nonmitogenic) effects on postmitotic myocytes.

Cytokine-induced selective increase of high-molecular-weight bFGF isoforms and their subcellular kinetics in cultured rat hippocampal astrocytes

Cytokines such as interleukin-1 beta (IL-1 beta), tumor necrosis factor-alpha (TNF-alpha) and epidermal growth factor (EGF) are probable factors responsible for up-regulation of basic fibroblast growth factor (bFGF) expression in reactive astrocytes following brain damage, however the effect of these cytokines on the expression of each bFGF-isoform has not been elucidated. Western blot analysis revealed the expression of 18, 22 and 24-kD bFGF isoforms in cultured rat hippocampal astrocytes, and the expression of high molecular weight (HMW)-isoforms (22 and 24-kD isoforms) but not of 18-kD isoform was selectively increased by cytokines. Immunofluorescent analysis demonstrated that bFGF content in the cytoplasm of astrocytes is initially increased by cytokines followed by nuclear targeting and localization in agreement with the previous evidence that HMW-isoforms possess a nuclear targeting signal. The present results suggest the important role of HMW-bFGF isoforms in the response of nervous tissue to injury.

Basic fibroblast growth factor (FGF-2) protects rat cochlear hair cells in organotypical culture from aminoglycoside injury

Given the evidence that basic fibroblast growth factor (FGF-2) can protect neural and retinal cells from degeneration, we evaluated the potential of this growth factor to protect sensory cells in the inner ear. When sensory cells of the organ of Corti are exposed to aminoglycoside antibiotics such as neomycin either in vivo or in vitro, significant ototoxicity is observed. The in vitro cytotoxic effects of neomycin are dose and time dependent. In neonatal rat organ of Corti cultures, complete inner and outer hair cell destruction is observed at high (mM) concentrations of neomycin while inner hair cell survival and severely damaged outer hair cells are noted at moderate (microM) concentrations, with a maximal effect observed after 2 days of culture. Approximately 50% of cochlear outer hair cells are lost at a dose of 35 microM neomycin, and most surviving cells show disorganized stereocilia. Inner hair cells show primarily disorganization of their stereocilia. A significant protective effect is observed when the organ of Corti is pre-treated with FGF-2 (500 ng/ml) for 48 hours, and then FGF-2 is included with neomycin in the culture medium. A greater extent of outer hair cell survival and a significant decrease in stereociliary damage are noted with FGF-2. However, disorganization of inner hair cell stereocilia is unaffected by FGF-2. The protective effect of FGF-2 is specific, since interleukin-1B, nerve growth factor, tumor necrosis factor, and epidermal growth factor are ineffective, while retinoic acid and transforming growth factor alpha show only a moderate protective effect. These results confirm the potential of molecules like FGF-2 for preventing cell death due to a variety of causes.

Prevention by lamotrigine, MK-801 and N omega-nitro-L-arginine methyl ester of motoneuron cell death after neonatal axotomy

Motoneuron cell death was analysed in the rat facial motor nucleus after neonatal facial nerve transection. In situ DNA fragmentation labelling showed that axotomized motoneurons die by an apoptotic mechanism. In order to investigate the existence of excitotoxic mechanisms in this type of neuronal death, rats were treated with several agents known to possess neuroprotective action through a variety of mechanisms. The Na+ channel inhibitor lamotrigine and the antagonist for the N-methyl-D-aspartate-type glutamate receptor, dizocilpine maleate (MK-801) were found to be able to rescue motoneurons from cell death induced by axotomy. The nitric oxide synthase inhibitor N omega-nitro-L-arginine methyl ester was also able to protect motoneurons from death, but to a lesser extent. The distribution of constitutive and inducible isoforms of nitric oxide synthase was investigated by immunocytochemistry in the facial motor nucleus. No changes were detected in constitutive nitric oxide synthase immunoreactivity in the facial motor nucleus after axotomy. However, in the axotomized facial motor nucleus, inducible nitric oxide synthase showed a positive immunolabelling specifically located in activated astrocytes, but not in microglia. Nitric oxide derived from activated astrocytes may have a role in promoting excitotoxic mechanisms in axotomized motoneurons. We conclude that excitotoxic mechanisms involving apoptotic cell death are present when immature motoneurons die as a consequence of target disconnection.

Fibroblast growth factor receptor 1 in the adrenal gland and PC12 cells: developmental expression and regulation by extrinsic molecules

In the present study we have analyzed the expression of fibroblast growth factor receptor 1 (FGFR-1) mRNA in the developing and adult rat adrenal gland and in PC12 cells under different culture conditions. For this purpose a sensitive ribonuclease protection assay using 33P-labelled riboprobes was established. 33P-labelled riboprobes show a high resolution and are relatively easy to handle. FGFR-1 mRNA was found to be present in the postnatal and adult adrenal gland. In the cortex high levels of FGFR-1 mRNA were detected at postnatal day (P) 1 and P8, during the third week the mRNA levels declined, and reached low levels during adulthood. PC12 cells also contained detectable amounts of FGFR-1 mRNA. With the exception of NGF, however, the different treatment procedures did not affect FGFR-1 mRNA levels. The expression pattern of the FGFR-1 transcript matches that of the expression of FGF-2 and of the mitotic activity in the developing and adult cortex. This supports the idea that FGF-2 might act as an autocrine mitogen for adrenocortical cells. In the medulla FGFR-1 mRNA levels were low at the first 3 postnatal weeks and increased towards the adult. In accordance with the developing expression pattern of FGF-2 in the medulla and in vitro effects of this protein on chromaffin and PC12 cells an autocrine/paracrine role as a maintenance and differentiation factor for chromaffin cells is conceivable.

TGF-beta rescues target-deprived preganglionic sympathetic neurons in the spinal cord

Transforming growth factors beta (TGF-beta), a family of pleiotropic cytokines, are widely distributed in the developing and adult nervous system. In order to further determine the neural functions of TGF-beta, we have localized the TGF-beta isoforms 1, 2 and 3 in the adult rat adrenal medulla and studied the neuroprotective capacity of one representative family member, TGF-beta 2, for those spinal cord neurons which innervate adrenal chromaffin cells and which die after destruction of the adrenal medulla. Unilateral electrothermal destruction of the adrenal medulla led to the disappearance of 25% of sympathetic preganglionic neurons, which are located in the intermediolateral (IML) column of thoracic spinal cord segments 7-10 and can be selectively marked by NADPH-diaphorase. The neurons which disappeared following adrenomedullectomy constitute the full set of neurons that innervate the adrenal medulla. Implantation of gelfoam soaked with 0.5 micrograms TGF-beta 2 into the adrenal wound cavity rescued all spinal cord neurons in the IML ipsilaterally to the lesioned side. Cytochrome c was not effective. Injections of [125I]TGF-beta 2 into the adrenal medulla did not result in retrograde transport and subsequent labelling of spinal cord neurons, suggesting that TGF-beta may exert its neuroprotective actions by indirect mechanisms. TGF-beta applied to cultured adrenocortical cells did not overtly increase the amount of mRNA for fibroblast growth factor-2, an established trophic molecule for sympathetic preganglionic spinal cord neurons. The mechanisms by which TGF-beta exerts its neurotrophic effect are therefore unclear. Even so, our data provide the first evidence that TGF-beta may play an important role in vivo in the control of maintenance of a population of spinal cord neurons.

Co-existence of NADPH-diaphorase, fibroblast growth factor-2 and fibroblast growth factor receptor in spinal autonomic system suggests target-specific actions

In the rat spinal cord, we found substantial co-existence of fibroblast growth factor-2, fibroblast growth factor receptor (type-1 or flg) immunoreactivity and reduced nicotinamide adenine dinucleotide phosphate (NADPH)-diaphorase activity (a histochemical marker for neuronal nitric oxide synthase) in preganglionic autonomic cell groups of intermediate layers VI, VII and X. Anti-fibroblast growth factor-2 and anti-nitric oxide synthase binding sites were confined to the cytoplasm of reactive neurons as judged by immunogold electron microscopy. Within the major autonomic nucleus, i.e. intermediolateral column, three different populations were identified: (i) fibroblast growth factor and fibroblast growth factor receptor, (ii) fibroblast growth factor/NADPH-diaphorase and (iii) NADPH-diaphorase-only stained cell groups. Sympathoadrenal neurons were prelabelled with fluorescent tracer Fast Blue and co-stained for fibroblast growth factor-like protein and NADPH-diaphorase, suggesting heterologous diversification of neuronal phenotypes and functional organization in the spinal autonomic system. Our findings suggest intriguing roles for nitric oxide and fibroblast growth factor-2 cytokine in the preganglionic sympathetic spinal cord system: The "short-term" diffusible messenger nitric oxide may act as "tonic" and/or "phasic" signal within rostrocaudally oriented function-specific preganglionic units necessary for integrated target control. The "long-term" messenger fibroblast growth factor-2 may be involved in, for example, cytokine-dependent regulation of neuronal NADPH-diaphorase/nitric oxide synthase. Furthermore, co-existence of NADPH-diaphorase, fibroblast growth factor-2 and receptor in sympathoadrenal neurons suggest mutual target-specific regulatory functions, e.g. hormone release and blood perfusion or maintenance of phenotype and plasticity responsiveness of adrenal medullary tissue.