Expression of basic fibroblast growth factor isoforms in postmitotic sympathetic neurons: synthesis, intracellular localization and involvement in karyokinesis

Dual Role of Fibroblast Growth Factor Pathways in Sleep Regulation

Sleep plays an important function in neuro-immuno-endocrine homeostasis. Sleep disorders have been associated with an increased risk of metabolic and cognitive impairments. Among different factors that have an effect on sleep metabolism, a growing body of literature has investigated growth factors in the course of sleep quality and disorders. A good example of growth factors is fibroblast growth factors (FGFs), which are a large family of polypeptide growth factors. Evidence has shown that FGFs are involved in the modulation of sleep-wake behavior by their receptor subtypes and ligands, e.g., FFG1 plays an important role in the quality of sleep through somnogenic effects, while the high level of FGF23 is associated with secondary disorders in shift workers. Therefore, a controversial effect of FGFs can be seen in the course of sleep in physiologic and pathologic conditions. Further investigation on this topic would help us to understand the role of FGFs in sleep disorders as a therapeutic option and biomarker.

Fibroblast Growth Factors as Tools in the Management of Neuropathic Pain Disorders

Neuropathic pain is caused by a damage to or dysfunction of the somatosensory nervous system. The main mechanisms underlying neuropathic pain include ectopic activity in nociceptive nerves, peripheral and central sensitization, impaired inhibitory modulation, and microglial activation. Fibroblast growth factors (FGFs) make up a large family of growth factors that mediate neural development, metabolism, and function through three main key signaling pathways, including RAS/MAP kinase pathway, PI3 kinase/Akt pathway, and PLCγ. An association between the members of the FGF system and the improvement of neuropathic pain has become evident, recently. These signaling molecules may be expected to provide new drug targets for the treatment of neuropathic pain. To the best of our knowledge, it is the first study that reviews the relationship between some members of the FGF system and neuropathic pain.

Fibroblast Growth Factor: Promising Target for Schizophrenia

Schizophrenia is one of the most debilitating mental disorders around the world. It is characterized by neuroanatomical or biochemical changes. The role of the fibroblast growth factors (FGFs) system in schizophrenia has received considerable attention in recent years. Various changes in the gene expression and/or level of FGFs have been implicated in the etiology, symptoms and progression of schizophrenia. For example, studies have substantiated an interaction between FGFs and the signaling pathway of dopamine receptors. To understand the role of this system in schizophrenia, the databases of Open Access Journals, Web of Science, PubMed (NLM), LISTA (EBSCO), and Google Scholar with keywords including fibroblast growth factors, dopamine, schizophrenia, psychosis, along with neurotrophic were searched. In conclusion, the FGF family represent molecular candidates as new drug targets and treatment targets for schizophrenia.

Effect of FGF-2 and sciatic nerve grafting on ChAT expression in dorsal root ganglia neurons of spinal cord transected rats

Neurotrophic factors and peripheral nerves are known to be good substrates for bridging CNS trauma. The involvement of fibroblast growth factor-2 (FGF-2) activation in the dorsal root ganglion (DRG) was examined following spinal cord injury in the rat. We evaluated whether FGF-2 increases the ability of a sciatic nerve graft to enhance neuronal plasticity, in a gap promoted by complete transection of the spinal cord. The rats were subjected to a 4mm-long gap at low thoracic level and were repaired with saline (Saline or control group, n=10), or fragment of the sciatic nerve (Nerve group, n=10), or fragment of the sciatic nerve to which FGF-2 (Nerve+FGF-2 group, n=10) had been added immediately after lesion. The effects of the FGF-2 and fragment of the sciatic nerve grafts on neuronal plasticity were investigated using choline acetyl transferase (ChAT)-immunoreactivity of neurons in the dorsal root ganglion after 8 weeks. Preservation of the area and diameter of neuronal cell bodies in dorsal root ganglion (DRG) was seen in animals treated with the sciatic nerve, an effect enhanced by the addition of FGF-2. Thus, the addition of exogenous FGF-2 to a sciatic nerve fragment grafted in a gap of the rat spinal cord submitted to complete transection was able to improve neuroprotection in the DRG. The results emphasized that the manipulation of the microenvironment in the wound might amplify the regenerative capacity of peripheral neurons.

Loss of the transcription factor Meis1 prevents sympathetic neurons target-field innervation and increases susceptibility to sudden cardiac death

Although cardio-vascular incidents and sudden cardiac death (SCD) are among the leading causes of premature death in the general population, the origins remain unidentified in many cases. Genome-wide association studies have identified Meis1 as a risk factor for SCD. We report that Meis1 inactivation in the mouse neural crest leads to an altered sympatho-vagal regulation of cardiac rhythmicity in adults characterized by a chronotropic incompetence and cardiac conduction defects, thus increasing the susceptibility to SCD. We demonstrated that Meis1 is a major regulator of sympathetic target-field innervation and that Meis1 deficient sympathetic neurons die by apoptosis from early embryonic stages to perinatal stages. In addition, we showed that Meis1 regulates the transcription of key molecules necessary for the endosomal machinery. Accordingly, the traffic of Rab5⁺ endosomes is severely altered in Meis1-inactivated sympathetic neurons. These results suggest that Meis1 interacts with various trophic factors signaling pathways during postmitotic neurons differentiation.

DOI:http://dx.doi.org/10.7554/eLife.11627.001

Nerve cells called sympathetic neurons can control the activity of almost all of our organs without any conscious thought on our part. For example, these nerve cells are responsible for accelerating the heart rate during exercise.

In a developing embryo, there are initially more of these neurons than are needed, and only those that develop correctly and form a connection with a target cell will survive. This is because the target cells provide the growing neurons with vital molecules called neurotrophins, which are trafficked back along the nerve fiber and into the main body of the nerve cell to ensure its survival. However, it is largely unknown which proteins or genes are also involved in this developmental process.

Now, Bouilloux, Thireau et al. show that if a gene called Meis1 is inactivated in mice, the sympathetic neurons start to develop and grow nerve fibers, but then fail to establish connections with their target cells and finally die. The Meis1 gene encodes a transcription factor, which is a protein that regulates gene activity. Therefore, Bouilloux, Thireau et al. looked for the genes that are regulated by this transcription factor in sympathetic neurons. This search uncovered several genes that are involved in the packaging and trafficking of molecules within cells.

Other experiments then revealed that the trafficking of molecules back along the nerve fiber was altered in mutant neurons in which the Meis1 gene had been inactivated. Furthermore, Meis1 mutant mice had problems with their heart rate, especially during exercise, and an increased risk of dying from a sudden cardiac arrest.

These findings reveal a transcription factor that helps to establish a connection between a neuron and its target, and that activates a pattern of gene expression that works alongside the neurotrophin-based signals. Since all neurons undergo similar processes during development, future work could ask if comparable patterns of gene expression exist in other types of neurons, and if problems with such processes contribute to some neurodegenerative diseases.

DOI:http://dx.doi.org/10.7554/eLife.11627.002

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.

Signaling molecules and transcription factors involved in the development of the sympathetic nervous system, with special emphasis on the superior cervical ganglion

The cells that constitute the sympathetic nervous system originate from the neural crest. This review addresses the current understanding of sympathetic ganglion development viewed from molecular and morphological perspectives. Development of the sympathetic nervous system is categorized into three main steps, as follows: (1) differentiation and migration of cells in the neural crest lineage for formation of the primary sympathetic chain, (2) differentiation of sympathetic progenitors, and (3) growth and survival of sympathetic ganglia. The signaling molecules and transcription factors involved in each of these developmental stages are elaborated mostly on the basis of the results of targeted mutation of respective genes. Analyses in mutant mice revealed differences between the superior cervical ganglion (SCG) and the other posterior sympathetic ganglia. This review provides a summary of the similarities and differences in the development of the SCG and other posterior sympathetic ganglia. Relevant to the development of sympathetic ganglia is the demonstration that neuroendocrine cells, such as adrenal chromaffin cells and carotid body glomus cells, share a common origin with the sympathetic ganglia. Neural crest cells at the trunk level give rise to common sympathoadrenal progenitors of sympathetic neurons and chromaffin cells, while progenitors segregated from the SCG give rise to glomus cells. After separation from the sympathetic primordium, the progenitors of both chromaffin cells and glomus cells colonize the anlage of the adrenal gland and carotid body, respectively. This review highlights the biological properties of chromaffin cells and glomus cells, because, although both cell types are derivatives of sympathetic primordium, they are distinct in many respects.

High molecular weight FGF2: the biology of a nuclear growth factor

Fibroblast growth factor 2 (FGF2) is one of the most studied growth factors to date. Most attention has been dedicated to the smallest, 18 kDa FGF2 variant that is released by cells and acts through activation of cell-surface FGF-receptor tyrosine kinases. There are, however, several higher molecular weight (HMW) variants of FGF2 that rarely leave their producing cells, are retained in the nucleus and act independently of FGF-receptors (FGFR). Despite significant evidence documenting the expression and intracellular trafficking of HMW FGF2, many important questions remain about the physiological roles and mechanisms of action of HMW FGF2. In this review, we summarize the current knowledge about the biology of HMW FGF2, its role in disease and areas for future investigation.

Expression of vascular endothelial growth factor and basic fibroblast growth factor in sporadic vestibular schwannomas correlates to growth characteristics

HYPOTHESIS

Expression of vascular endothelial growth factor (VEGF) and basic fibroblast growth factor (bFGF) may have an impact on the growth characteristics of sporadic vestibular schwannomas (VSs).

BACKGROUND

Vestibular schwannoma is a benign, slow-growing neoplasm that accounts for 6% of all intracranial tumors. The biological backgrounds for neoplastic growth and especially for the various growth patterns of VS remain largely unknown. Because several angiogenic and cytotrophic factors have been described to be involved in the growth of malignant tumors, we initiated this study to examine 2 major representatives of such growth factors in VS and their possible correlation to the growth characteristics of sporadic VSs.

METHODS

Surgical specimens from 17 patients with sporadic VS were examined, and the expression of 2 major angiogenic and neurotrophic factors, bFGF and VEGF, was quantitatively analyzed at the mRNA and protein levels. The microvessel density (MVD) was defined by CD31 staining.

RESULTS

All tumors showed expression of bFGF and VEGF at both the mRNA and protein levels. The mRNA expression and the protein expression of both growth factors correlated positive to tumor volume, to tumor growth index, and to MVD.

CONCLUSION

The bFGF and VEGF mRNA expression and the bFGF and VEGF protein expression in sporadic VS correlates to the tumour volume, to the tumor growth index, and to the MVD. This might indicate an angiogenic and neurotrophic influence of these factors and a possible involvement in the growth of sporadic VS.

Up-regulation of platelet-derived growth factor by peripheral-blood leukocytes during experimental allergic encephalomyelitis

In multiple sclerosis (MS) and its animal model, experimental allergic encephalomyelitis (EAE), clinical disease is associated with infiltration of the central nervous system (CNS) by immune cells. Subsequent remission with remyelination has been linked to an increased occurrence of oligodendrocyte progenitor (O2A) cells. Platelet-derived growth factor (PDGF) and fibroblast growth factor-2 (FGF-2) are key growth factors for O2A cells, yet little is known about their relevance in EAE and MS. We analyzed the expression of PDGF, FGF-2, and their receptors by peripheral-blood leukocytes (PBLs) and lymphocyte subsets during MBP-induced EAE. Strong up-regulation of PDGF, but not FGF-2, was observed in PBLs, with the highest expression after the disease maximum. T, NK, and NKT cells expressed PDGF, which is a novel observation because thus far only monocytes/macrophages have been reported to express PDGF. These results extend the idea that growth factors may contribute to improved CNS tissue repair, including PDGF, which is secreted by lesion-homing immune cells. The production of PDGF by lymphocytes may have potential therapeutic value when activating or modulating T-cell responses in demyelinating diseases.

SAFB re-distribution marks steps of the apoptotic process

We have found novel functions of scaffold attachment factor-B1 (SAFB) during apoptosis. The experiments showed that SAFB moved into the nucleolus 15 min after the induction of apoptosis and before the release of cytochrome c into the cytoplasm. Two hours later SAFB formed a peri-nucleolar ring-like structure and this occurred after cytochrome c release and before PARP cleavage. Digestion with RNase suggested that the peri-nucleolar ring structure was dependent on RNA integrity and a RNA moiety formed part of this structure. Studies using SAFB deletion mutants showed that the formation of the peri-nucleolar structure was not mediated by the DNA binding (SAP) or the RNA binding (RRM) domain of SAFB but was instead dependent on the S/K and R/E coiled-coil regions: a result suggesting that the structure is formed via protein interactions. In addition, SAFB cleavage was shown to be mediated by caspase-3 and occurred after the formation of the peri-nucleolar ring and after cleavage of PARP (characteristic of proteins having a direct role in apoptosis). A determinant for this cleavage is located in the DNA binding domain and we hypothesize that SAFB may direct the reorganization and segregation of nuclear RNA and DNA prior to endonuclease-mediated DNA cleavage.

Activation of fibroblast growth factor receptor by axotomy, through downstream p38 in dorsal root ganglion, contributes to neuropathic pain

The possible involvement of fibroblast growth factor receptor (FGFR) activation in the dorsal root ganglion (DRG) was examined following peripheral nerve injury in the rat. Ligation of the sciatic nerve down-regulated FGFR2, -3 and -4 mRNA; however, the expression of FGFR1 mRNA showed no change. Activation of FGFR was examined by immunohistochemistry using an antibody of the phosphorylated form of FGFR1-4. Ligation of the sciatic nerve produced phosphorylation of FGFR in the L4 and 5 DRG ipsilateral to the injury, starting at 3 days after the lesion and persisting for more than 30 days. Substantial activation of FGFR was observed, mainly in unmyelinated small DRG neurons that co-expressed phosphorylated p38 mitogen-activated protein kinase (MAPK). Continuous intrathecal infusion of the FGFR1 inhibitor, 3-[3-(2-carboxyethyl)-4-methylpyrrol-2-methylidenyl]-2-indolinone, reduced p38 MAPK phosphorylation in the DRG and pain-related behaviors in the partial sciatic nerve model rat without affecting on the activation of spinal glia cells (microglia and astrocyte). In the injured small DRG neurons, activation of FGFR1 may contribute to the generation of neuropathic pain by activating p38 MAPK.

Nuclear trafficking of secreted factors and cell-surface receptors: new pathways to regulate cell proliferation and differentiation, and involvement in cancers

Secreted factors and cell surface receptors can be internalized by endocytosis and translocated to the cytoplasm. Instead of being recycled or proteolysed, they sometimes translocate to the nucleus. Nuclear import generally involves a nuclear localization signal contained either in the secreted factor or its transmembrane receptor, that is recognized by the importins machinery. In the nucleus, these molecules regulate transcription of specific target genes by direct binding to transcription factors or general coregulators. In addition to the transcription regulation, nuclear secreted proteins and receptors seem to be involved in other important processes for cell life and cellular integrity such as DNA replication, DNA repair and RNA metabolism.

Nuclear secreted proteins and transmembrane receptors now appear to induce new signaling pathways to regulate cell proliferation and differentiation. Their nuclear localization is often transient, appearing only during certain phases of the cell cycle. Nuclear secreted and transmembrane molecules regulate the proliferation and differentiation of a large panel of cell types during embryogenesis and adulthood and are also potentially involved in wound healing. Secreted factors such as CCN proteins, EGF, FGFs and their receptors are often detected in the nucleus of cancer cells. Nuclear localization of these molecules has been correlated with tumor progression and poor prognosis for patient survival. Nuclear growth factors and receptors may be responsible for resistance to radiotherapy.

Functional diversity of FGF-2 isoforms by intracellular sorting

Regulation of the subcellular localization of certain proteins is a mechanism for the regulation of their biological activities. FGF-2 can be produced as distinct isoforms by alternative initiation of translation on a single mRNA and the isoforms are differently sorted in cells. High molecular weight FGF-2 isoforms are not secreted from the cell, but are transported to the nucleus where they regulate cell growth or behavior in an intracrine fashion. 18 kDa FGF-2 can be secreted to the extracellular medium where it acts as a conventional growth factor by binding to and activation of cell-surface receptors. Furthermore, following receptor-mediated endocytosis, the exogenous FGF-2 can be transported to the nuclei of target cells, and this is of importance for the transmittance of a mitogenic signal. The growth factor is able to interact with several intracellular proteins. Here, the mode of action and biological role of intracellular FGF-2 are discussed.

Constitutively expressed catalytic proteasomal subunits are up-regulated during neuronal differentiation and required for axon initiation, elongation and maintenance

Inhibition of the proteasome by lactacystin, a specific blocker of the catalytic beta-subunits, results in transient neurite outgrowth by neuronal cell lines. Vice versa, as demonstrated in this study, treatment of pheochromocytoma (PC12) cells with nerve growth factor (NGF) or other differentiating agents reduces proteasomal activity. This is accompanied by an increase in mRNA and protein levels of the catalytically active subunits beta1, beta2 and beta5, but not of their inducible counterparts, indicating changes in subunit composition of the proteasome during neuronal differentiation. In contrast to neuronal cell lines, however, pre-treatment of primary neurons with proteasome inhibitors completely prevents axon formation, and lower concentrations of lactacystin (0.5-5 microm) significantly reduce axonal elongation and branching in vitro. Furthermore, established axonal networks degenerate rapidly and long-term survival of peripheral neurons is impaired in the presence of proteasome inhibitors. Axonal pathology is reminiscent of the morphological changes observed in neurodegenerative disorders and supports a crucial role of the constitutive catalytic subunits in axon initiation, maintenance and regeneration.

NGF and IL-1beta are co-localized in the developing nervous system of the frog, Xenopus laevis

NGF, a neurotrophic factor best known for its role in promoting cell survival, regulates many neurodevelopmental processes, including synaptic plasticity, neurite outgrowth and programmed cell death. Although there is a large amount of data regarding NGF in the developing nervous system of many species, there is little known about its regulation and role in the frog, Xenopus laevis. In this report, immunocytochemistry was used to characterize NGF protein expression in developing tadpoles. Protein expression was analyzed in tadpoles from stage 44/45 through stage 50, a period of development characterized by extensive neurite outgrowth, neuronal differentiation and an initial period of programmed cell death. Similar to other species, NGF was expressed in sensory cells and tissues, including the inner ear, eye, olfactory system, lateral line organs, papillae in the oral cavity, and gills tufts. In addition, NGF was expressed in specific cells in the central nervous system, cranial and dorsal root ganglia, spinal sensory and motoneurons, and muscle tissues in the tail and body cavity. In the mammalian nervous system, the cytokine, interleukin-1beta (IL-1beta) induces expression of NGF. In this report, double-label immunocytochemistry was used to determine the relationship between NGF and IL-1beta. Results showed most cell types and/or tissues that expressed NGF also expressed IL-1beta. However, NGF was typically associated with cellular and nuclear membranes, whereas IL-1beta appeared in the cytoplasm and nucleolus. The nuclear localization of IL-1beta supports the idea that it regulates gene transcription in the frog. The appearance of NGF and IL-1beta in the same cells suggests they may interact to influence neural development.

Differentially promoted peripheral nerve regeneration by grafted Schwann cells over-expressing different FGF-2 isoforms

Artificial nerve grafts are needed to reconstruct massive defects in the peripheral nervous system when autologous nerve grafts are not available in sufficient amounts. Nerve grafts containing Schwann cells display a suitable substrate for long-distance regeneration. We present here a comprehensive analysis of the in vivo effects of different isoforms of fibroblast growth factor-2 (FGF-2) on peripheral nerve regeneration across long gaps. FGF-2 isoforms were provided by grafted, genetically modified Schwann cells over-expressing 18-kDa-FGF-2 and 21-/23-kDa-FGF-2, respectively. Functional tests evaluated motor and sensory recovery. Additionally, morphometrical analyses of regenerated nerves were performed 3 and 6 months after grafting. Distinct regeneration promoting effects of the different FGF-2 isoforms were found. 18-kDa-FGF-2 mediated inhibitory effects on the grade of myelination of regenerating axons, whereas 21-/23-kDa-FGF-2 mediated early recovery of sensory functions and stimulation of long-distance myelination of regenerating axons. The results contribute to the development of new therapeutic strategies in peripheral nerve repair.

Gene profiling of cells expressing different FGF-2 forms

Fibroblast Growth Factor-2 (FGF-2) induces cell proliferation, cell migration, embryonic development, cell differentiation, angiogenesis and malignant transformation. The four forms of FGF-2 (Low Molecular Weight) and (High Molecular Weights) are alternative translation products, and have a different subcellular localization: the high molecular weight (HMWFGF-2) forms are nuclear while the low molecular weight form, (LMWFGF-2) is mainly cytoplasmic. Our previous work demonstrated NIH 3T3 cells expressing different FGF-2 forms, displayed a different phenotype, suggesting that nuclear and cytoplasmic forms of FGF-2 may have different functions. Here we report a cDNA microarray-based study in NIH 3T3 fibroblasts expressing different FGF-2 forms. Several candidate genes that affect cell-cycle, tumor suppression, adhesion and transcription were identified as possible mediators of the HMWFGF-2 phenotype and signaling pattern. These results demonstrated that HMWFGF-2 and LMWFGF-2 target the expression of different genes. Particularly, our data suggest that HMWFGF-2 forms may function as inducers of growth inhibition and tumor suppression activities.

PDGF-BB induces vascular smooth muscle cell expression of high molecular weight FGF-2, which accumulates in the nucleus

Basic fibroblast growth factor (FGF-2) and platelet-derived growth factor (PDGF) are implicated in vascular remodeling secondary to injury. Both growth factors control vascular endothelial and smooth muscle cell proliferation, migration, and survival through overlapping intracellular signaling pathways. In vascular smooth muscle cells PDGF-BB induces FGF-2 expression. However, the effect of PDGF on the different forms of FGF-2 has not been elucidated. Here, we report that treatment of vascular aortic smooth muscle cells with PDGF-BB rapidly induces expression of 20.5 and 21 kDa, high molecular weight (HMW) FGF-2 that accumulates in the nucleus and nucleolus. Conversely, PDGF treatment has little or no effect on 18 kDa, low-molecular weight FGF-2 expression. PDGF-BB-induced upregulation of HMW FGF-2 expression is controlled by sustained activation of extracellular signal-regulated kinase (ERK)-1/2 and is abolished by actinomycin D. These data describe a novel interaction between PDGF-BB and FGF-2, and indicate that the nuclear forms of FGF-2 may mediate the effect of PDGF activity on vascular smooth muscle cells.

Basic fibroblast growth factor isoforms promote axonal elongation and branching of adult sensory neurons in vitro

Synthesis of the multifunctional cytokine basic fibroblast growth factor (FGF-2) is up-regulated after sciatic nerve lesion. In this study, the effects of low and high molecular weight FGF-2 isoforms on axonal elongation and branching of dissociated rat sensory neurons derived from adult lumbar dorsal root ganglia were investigated. These neurons express FGF receptor (FGFR) type I in the cytoplasmic/membrane compartment and in nuclear speckles. FGF-2 isoforms increase the number of axonal branches in cultures obtained from control rats, but do not promote axonal elongation. In response to a preconditioning lesion, i.e. transection of the sciatic nerve 1 week before culture, the axonal length of ipsilateral lumbar sensory neurons increases two-fold when compared with non-lesioned control rats, and this response is significantly enhanced by FGF-2 isoforms but not by nerve growth factor (NGF). Neurons dissociated from ganglia located contralaterally to the lesion exhibit a smaller increase in axon elongation (30%). The stimulating effects of FGF-2 isoforms on axon growth are fully blocked, and the enhanced regeneration of prelesioned neurons is reduced by the FGFR inhibitor SU5402 suggesting an involvement of endogenous FGF signaling in response to a lesion. The present data support a direct neurotrophic role of the 18 kD and 23 kD FGF-2 isoforms on adult axonal regeneration which may be of therapeutic value in the treatment of peripheral nerve lesions. Furthermore, evidence is provided for an enhanced regenerative capacity not only of preaxotomized neurons but also of homonymous non-axotomized neurons.