Prominent expression of acidic fibroblast growth factor in motor and sensory neurons

Multiple controlling mechanisms of FGF1 gene expression through multiple tissue-specific promoters

We now know that fibroblast growth factor-1 (FGF1) transcription is controlled by at least four distinct promoters in a tissue-specific manner. Thus, promoter 1.A is active in the kidney, 1.B in the brain, and 1.C and 1.D in a variety of cultured cells including vascular smooth muscle cells. These promoters are separated from each other by up to 70 kbp. Multiple FGF1 transcripts arise from alternate promoter usage and alternative splicing of different 5'-untranslated exons. The 1.A and 1.B promoters are constitutively active in their respective cell types. In contrast, different biological response modifiers, including serum and transforming growth factor beta, can induce the 1.C and 1.D promoters. The 540-bp sequence upstream of the 1B transcription initiation site is sufficient to drive the expression of a heterologous luciferase reporter in cultured cells, and an 18-bp sequence within this region is important for the regulation of brain-specific gene expression. Furthermore, regulation occurs through the binding of the 18-bp sequence to a brain-specific 37-kDa protein and a ubiquitous basic helix-loop-helix protein, E2-2. We have produced transgenic mice bearing the brain-specific promoter of the human FGF1 gene joined to the SV40 immediate-early gene, which encodes the large T antigen. The resulting mice developed brain tumors that originated in the pontine gray, just rostral to the fourth ventricle. We have also identified a serum response element, comprising a CarG box and an Ets-binding site, in the 1.D promoter. Continued characterization of the mechanistic events that control the tissue-specific activation of FGF1 promoters will help us to understand the role of FGF1 in cancer, atherosclerosis, and neural development.

The role of acidic fibroblast growth factor in recovery of acoustic trauma

We administered acidic fibroblast growth factor (aFGF) to the perilymph of the guinea pig cochlea after exposure to intense sound to investigate its effect on the process of recovery after acoustic trauma. We assessed auditory brain stem response (ABR) thresholds to evaluate cochlear function and observed the sensory epithelium using confocal laser-scanning microscopy. After noise exposure (120 dB SPL, 5 h), the ABR threshold showed an increase of approximately 50 dB SPL that recovered after 14 days. Cochlear function in aFGF treated ears recovered more quickly than that in control ears. These results suggest that aFGF may play an important role in cochlear recovery after acoustic injury.

Transforming growth factor alpha: a promoter of motoneuron survival of potential biological relevance

Expression of transforming growth factor alpha (TGFalpha), a member of the epidermal growth factor (EGF) family, is a general response of adult murine motoneurons to genetic and experimental lesions, TGFalpha appearing as an inducer of astrogliosis in these situations. Here we address the possibility that TGFalpha expression is not specific to pathological situations but may participate to the embryonic development of motoneurons. mRNA of TGFalpha and its receptor, the EGF receptor (EGFR), were detected by ribonuclease protection assay in the ventral part of the cervical spinal cord from embryonic day 12 (E12) until adult ages. Reverse transcription-PCR amplification of their transcripts from immunopurified E15 motoneurons, associated with in situ double-immunohistological assays, identified embryonic motoneurons as cellular sources of the TGFalpha-EGFR couple. In vitro, TGFalpha promoted the survival of immunopurified E15 motoneurons in a dose-dependent manner, with a magnitude similar to BDNF neuroprotective effects at equivalent concentrations. In a transgenic mouse expressing a human TGFalpha transgene under the control of the metallothionein 1 promoter, axotomy of the facial nerve provoked significantly less degeneration in the relevant motor pool of 1-week-old mice than in wild-type animals. No protection was observed in neonates, when the transgene exhibits only weak expression levels in the brainstem. In conclusion, our results point to TGFalpha as a physiologically relevant candidate for a neurotrophic role on developing motoneurons. Its expression by the embryonic motoneurons, which also synthesize its receptor, suggests that this chemokine is endowed with the capability to promote motoneuron survival in an autocrine-paracrine manner.

Effects of locomotor training on hindlimb regeneration in the urodele amphibian Pleurodeles waltlii

1. The effects of locomotor training on hindlimb regeneration were studied in the urodele amphibian Pleurodeles waltlii. 2. After amputation of one hindlimb at mid-femur, adult animals were subjected to regular training sessions (1 h daily, 5 days a week, over 8 months) of terrestrial stepping. 3. Eight months post-amputation, trained animals exhibited regenerated limbs of reduced size as compared to animals kept in their aquaria. Histological data showed an abnormal regeneration of both the femur and distal structures (e.g. digit muscles, metatarsi and phalanges) while medial structures (e.g. tibia and fibula) were totally re-formed. The study of the electromyographical activity in regenerated limbs during stepping and that of their reflex responsiveness to electrical stimulation showed that both motor and sensory innervations were functional in the limb stump of trained animals. 4. The regenerative capacity of the abnormal stumps was preserved since following a second amputation a quite normal hindlimb was regenerated in 3 months, provided the re-amputated animals were not trained to terrestrial stepping. 5. The stress due to handling, change in locomotor medium (aquatic vs. terrestrial) and the friction of the wound epidermis with the ground were not involved in the disruption of limb regeneration. 6. The locomotor pattern, the reflex responsiveness and the muscle fibre composition were similar in supernumerary forelimbs grafted on the back and in normal forelimbs. However, the supernumerary forelimbs regenerated normally even in animals subjected to locomotor training while the hindlimb did not. It is concluded that the disrupting effects of locomotor training on limb regeneration were localized to the the limb directly involved in locomotion. 7. The mechanisms underlying abnormal limb regeneration in animals subjected to locomotor training are discussed.

Fibroblast growth factors in the developing central nervous system

1. It is now clear that members of the fibroblast growth factor (FGF) family have multiple roles during the formation of the central nervous system (CNS). 2. There are at least 23 members of the FGF family and, of these, 10 are expressed in the developing CNS, along with four FGF receptors (FGFR-1-4). 3. The present review discusses the roles of these FGFs, with emphasis on FGF-2, FGF-8, FGF-15 and FGF-17. Fibroblast growth factors-2 and -15 are generally expressed throughout the developing CNS, whereas FGF-8 and FGF-17 are tightly localized to specific regions of the developing brain and are only expressed in the embryo during the early phases of proliferation and neurogenesis. 4. Expression studies on FGFRs in the chick and mouse indicate that FGFR-1 is most generally expressed, whereas FGFR-2 and FGFR-3 show highly localized but changing patterns of expression throughout CNS development. The FGFR-4 has been localized to the developing CNS in fish but not at a detailed level, as yet, in chick or mouse. 5. A picture is emerging from these studies that particular FGFs signal through specific receptors in a highly localized manner to regulate the development of different regions of the brain. 6. This picture has been demonstrated so far for the developing cortex (FGF-2-/- mice), the forebrain and midbrain (FGF-8 hypomorphs) and the cerebellum (FGF-17/FGF-8 mutant mice). In addition, generation of mutant animals deleted for FGFR-1 and FGFR-2b IIIb demonstrate their importance in FGF signalling. 7. However, there are significant gaps in our knowledge of the localization of members of the FGF family and their receptors. More detailed information on the spatio-temporal mapping of FGFs and FGFR isoforms is required in order to understand the molecular mechanisms through which FGFs signal.

Nerve-independence of limb regeneration in larval Xenopus laevis is correlated to the level of fgf-2 mRNA expression in limb tissues

In both larval and adult urodele amphibians, limb blastema formation requires the presence of an adequate nerve supply. In previous research, we demonstrated that the hindlimb of early Xenopus laevis larvae formed a regeneration blastema even when denervated, while the denervated limb of late larvae did not. We hypothesized that the nerve-independence was due to the autonomous synthesis of a mitogenic neurotrophic-like factor by undifferentiated limb bud cells. In this paper, we demonstrate that fgf-2 mRNA is present in larval limb tissues and that its level is correlated to the extent of mesenchymal cells populating the limb: in early limbs, fgf-2 mRNA is present at high levels all over the limb, while, in late limbs, the fgf-2 expression is low and detectable only in the distal autopodium. After denervation, fgf-2 mRNA synthesis increases in amputated early limbs but not in amputated late limbs. The implantation of anti-FGF-2 beads into amputated early limbs hardly lowers the mitotic activity of blastema cells. However, FGF-2 beads implanted into the blastema of late limbs prevent the denervation-induced inhibition of mitosis and oppose blastema regression. Our data indicate that FGF-2 is a good candidate for the endogenous mitogenic factor responsible for blastema formation and growth in amputated and denervated early limbs. However, in amputated late limbs, the very limited fgf-2 expression is not sufficient to promote blastema formation in the absence of nerves.

Differential patterns of ERK and STAT3 phosphorylation after sciatic nerve transection in the rat

Peripheral nerve injury induces a specific pattern of expression of growth factors and cytokines, which regulate injury responses and regeneration. Distinct classes of growth factors and cytokines signal through specific intracellular phosphorylation cascades. For example, the ERK phosphorylation cascade mediates signaling through transmembrane tyrosine kinase receptors and the JAK/STAT cascade mediates signaling through the GP130 receptor complex. We tested whether specific phosphorylation patterns of ERK and STAT3 result from nerve injury and whether such phosphorylation correlates with the expression of specific growth factors and cytokines. At sites adjacent to a nerve transection, we observed that ERK phosphorylation peaked early, persisted throughout 16 days, and was equally intense at proximal and distal sites. In contrast, STAT3 phosphorylation peaked later than ERK but did not persist as long and was stronger in the proximal than in the distal segment adjacent to the injury. In addition, in distal segments further away from the injury site, ERK became phosphorylated with a delayed time course, while STAT3 remained unphosphorylated. These patterns of phosphorylation correlated well with the expression of neurotrophin and interleukin-6 mRNAs in the distal stump. In addition, we found that the pattern of SAPK phosphorylation is similar to the pattern observed for STAT3, while the pattern of macrophage infiltration into the transected nerve was distinct from all the phosphorylation patterns observed. Together, these observations suggest that ERK activation is important in the establishment of a regeneration-promoting extracellular environment in the far distal stump of transected nerves and that STAT3 activation is important in the control of cellular responses close to the site of injury.

FGF-20, a novel neurotrophic factor, preferentially expressed in the substantia nigra pars compacta of rat brain

We have isolated cDNA encoding a novel FGF (212 amino acids) from rat brain. Because this is the 20th documented member of the FGF family, we tentatively term it FGF-20. Among FGF family members, FGF-20 is most similar to FGF-9 and FGF-16 (70 and 62% amino acid identity, respectively). Human FGF-20 gene was found in the human genomic sequence mapped to the 8p21.3-p22 region. Human FGF-20 is highly identical to rat FGF-20 (95% amino acid identity). FGF-20 mRNA was preferentially expressed in rat brain among the adult major tissues examined. The localization of FGF-20 mRNA in rat brain was also examined by in situ hybridization. FGF-20 mRNA was preferentially expressed in the substantia nigra pars compacta. To examine the biological activity of FGF-20, recombinant rat FGF-20 was produced by insect cells infected with recombinant baculovirus containing rat FGF-20 cDNA. Recombinant rat FGF-20 enhanced the survival of midbrain dopaminergic neurons. The present results indicate that FGF-20 is a novel neurotrophic factor preferentially expressed in the substantia nigra pars compacta of rat brain.

Self-secretion of fibroblast growth factor-9 supports basal forebrain cholinergic neurons in an autocrine/paracrine manner

We examined the effect of fibroblast growth factor (FGF)-9 on primary cultures of rat basal forebrain cholinergic neurons (BFCN) obtained at embryonic day 17. FGF-9 enhanced survival of AChE-positive neurons, increased their mean soma size, and up-regulated their choline acetyltransferase (ChAT) activity. The ChAT-promoting effect of FGF-9 was approximately as potent as that of nerve growth factor (NGF) and was greater than those of basic fibroblast growth factor (bFGF), ciliary neurotrophic factor (CNTF), or glia-derived neurotrophic factor (GDNF). Simultaneous addition of FGF-9 and NGF induced extremely high ChAT levels, suggesting that FGF-9 and NGF may enhance cholinergic properties in BFCN via different pathways that can act synergistically. In immunocytochemical and in situ hybridization studies in cultured cells and also in sections of adult rat brain, BFCN showed cytoplasmic immunostaining for FGF-9 and expressed FGF-9 messenger RNA; thus, we concluded that FGF-9 acts on BFCN in an autocrine and/or paracrine manner. Although effective delivery of exogenous FGF-9 into the central nervous system remains a problem to be solved, FGF-9 may be a promising candidate for therapeutic trials in Alzheimer disease.

Effect of NGF, BDNF, bFGF, aFGF and cell density on NPY expression in cultured rat dorsal root ganglion neurones

The effect of neurotrophic factors on neuropeptide Y (NPY) expression was studied in adult rat dispersed dorsal root ganglion (DRG) cultures. Nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), acidic fibroblast growth factor (aFGF) or basic FGF was included in the culture medium during incubation for 72 h. In untreated cultures, around 18% of all neurones (visualized by antibodies to PGP 9.5) expressed NPY-like immunoreactivity (LI). In contrast, in vivo uninjured neurones do not contain detectable levels of NPY-LI. In the immunohistochemical analysis aFGF increased the percentage of NPY-immunoreactive (-IR) neurones 1.8-fold, while NGF, BDNF or bFGF had no significant effect on NPY expression. When the effect of these growth factors was monitored with non-radioactive in situ hybridization, both aFGF and bFGF caused a significant increase (2.25- and 1.8-fold, respectively), whereas, again, NGF and BDNF had no effect. The results also showed an effect of cell density on NPY expression, whereby fewer neurones expressed NPY in high than in low density cultures. This difference was seen in untreated as well as growth factor-treated cultures. The present results support the hypothesis that DRG neurones in culture are in an axotomized state, since they express NPY to about the same extent as axotomized DRG neurones in vivo. Surprisingly, two growth factors of the FGF family enhance NPY expression in DRG neurones, which is in apparent contrast to a published in vivo study [Ji, R.-R., Zhang, Q., Pettersson, R.F., Hökfelt, T., 1996. aFGF, bFGF and NGF differentially regulate neuropeptide expression in dorsal root ganglia after axotomy and induce autotomy. Reg. Pept. 66, 179-189.]. Finally, NPY expression was also influenced by cell density.

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.

Acidic fibroblast growth factor is present in the enteric nervous system of the large intestine

Acidic fibroblast growth factor (aFGF) is a heparin binding protein that displays pleiotropic activity. The purpose of this study was to document the presence of the translated aFGF product, its mRNA, and its location in the colon. mRNA was extracted from bovine large intestine and reverse transcribed to cDNA. Nested-primer PCR was used to determine the presence of mRNA using primers homologous to the previously published bovine aFGF cDNA. Purification of translated aFGF was performed using an established HPLC protocol. Western blot analysis of the HPLC fractions was performed using two epitope-independent antibodies against aFGF. Immunohistochemistry employed these antibodies to determine the locus of aFGF expression. The nested-primer PCR product of predicted size was homologous to the published bovine aFGF mRNA sequence, as determined by DNA sequencing. Intestinal aFGF had a mass similar to bovine aFGF isolated from other tissues, and immunocrossreacted with two peptide-based, epitope-independent anti-aFGF antisera on Western blotting. Immunohistochemical analysis of large intestine using these two independent antisera localized aFGF within the myenteric plexus. These data demonstrate that aFGF is present within the myenteric plexus of the enteric nervous system.

Enkephalin and aFGF are differentially regulated in rat spinal motoneurons after chemodenervation with botulinum toxin

Botulinum toxin is used to induce transient graded paresis by chemodenervation in the treatment of focal hyperkinetic movement disorders. While the molecular events occurring in motoneurons after mechanical nerve lesioning leading to muscle paresis are well known, they have been investigated to a lesser extent after chemodenervation. We therefore examined the expression of enkephalin (ENK), acidic fibroblast growth factor (aFGF), neurotensin (NT), galanin (GAL), substance P (SP), vasoactive intestinal polypeptide (VIP), and neuropeptide Y (NPY) in rat spinal motoneurons after chemodenervation of the gastrocnemius. In order to precisely localize the motoneurons targeting the injection site, retrograde tracing was performed in additional rats by using Fluorogold injections. ENK expression was upregulated in the region corresponding to the Fluorogold positive motoneurons, but also on the contralateral side and in more distant parts of the spinal cord. The highest upregulation occurred 7 to 14 days after injections and decreased over a period of three months. At 8 days, aFGF was slightly downregulated in all regions studied, single motoneurons showed NT expression, while expression of GAL, SP, VIP, and NPY could be detected neither in controls nor in toxin-treated animals. These alterations in gene expression were strikingly different from those described after axotomy. Our present findings give additional demonstration of the considerable plasticity of the adult spinal cord after botulinum toxin treatment.

Fibroblast growth factor-1 improves the survival and regeneration of rat vagal preganglionic neurones following axon injury

Adult rat neurones of the dorsal motor nucleus of the vagus (DMNV) react more severely to axon injury than most other peripherally projecting neurones. Following axon injury, DMNV neurones atrophy and die such that after 18 months only 25% remain. In contrast, the majority of somatic motor neurones (e.g. in the hypoglossal nerve) survive axon injury. The reasons for this difference are unknown. We administered a brief pulse of fibroblast growth factor-1 (FGF-1 or acidic FGF) to the vagus nerve trunk immediately after applying a standardized crush injury to the nerve. FGF-1 increased the number of axons regenerating in the injured vagal nerve and the number of neurones surviving in the DMNV 9 weeks after injury. This is to our knowledge the first demonstration of a peptide growth factor that ameliorates this distinct degeneration of DMNV neurones in vivo.

Restoration of walking in paraplegia by transferring the ulnar nerve to the hip: A report on the first patient

There is no known way to make paraplegics walk when their spinal cord is completely transected. Many researchers worldwide have been developing different methods to solve this problem. We believe that transferring a sound nerve from the upper limb to the main muscles of the hip could help paraplegics to walk, although light orthotic devices would still be needed. We chose to transfer the ulnar nerve because it is the longest in the upper limb and can reach the glutei without grafts. In addition, palsy of the ulnar nerve can be repaired by classical reconstructive surgery. After many years of research in animals and after obtaining permission from the Ethical Committee of the National Health Surgery, we operated on three human beings bilaterally. The first patient is walking. Two are still recovering.

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

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

Novel receptor protein tyrosine phosphatase (RPTPrho) and acidic fibroblast growth factor (FGF-1) transcripts delineate a rostrocaudal boundary in the granule cell layer of the murine cerebellar cortex

We have identified a novel receptor-like protein tyrosine phosphatase (RPTPrho) transcript whose expression in the cerebellar cortex is restricted to the granule cell layer of lobules 1-6. Acidic fibroblast growth factor (FGF-1) mRNA follows a similar cerebellar expression pattern. Together, the two markers define a sharp boundary in lobule 6, slightly caudal to the primary fissure. Anterior and posterior compartments became discernible only during postnatal weeks two and six, for RPTPrho and FGF-1, respectively. A rostrocaudal boundary in lobule 6 of the murine cerebellar cortex has also been identified morphologically by the effects of the meander tail mutation. The position of the RPTPrho and FGF-1 boundary on the rostrocaudal axis of the cerebellar cortex was close to, but not coincident with, the caudal extent of the disorganized anterior lobe of meander tail and the rostral extent of Otx-2 expression. The restricted pattern of FGF-1 and RPTPrho implies that these molecules may have specific signaling roles in the tyrosine phosphorylation/dephosphorylation pathway in the anterior compartment of the adult cerebellar cortex.

Neuronal localization of fibroblast growth factor-9 immunoreactivity in human and rat brain

Fibroblast growth factor-9 (FGF-9) is a relatively new member of the FGF family isolated from the conditioned medium of a human glioblastoma cell line as a secreting-type factor that exhibits a growth-stimulating effect on cultured glial cells. In order to elucidate the roles of FGF-9 in the central nervous system, we investigated in detail the distribution of FGF-9 proteins in the normal human and rat brains by immunohistochemistry using two different antibodies specific to FGF-9. In both human and rat, a strong expression of FGF-9 immunoreactivity was localized mainly in neurons throughout the normal brain. Immunoreactive glial cells were rarely encountered. In the human brain, strong and uniform immunoreactivity was observed in neurons of cerebral cortex, hippocampus, substantia nigra, motor nuclei of the brainstem, and Purkinje cell layer. A detailed mapping in the rat brain showed a distribution of FGF-9 immunoreactivity in a widespread population of neurons, though the intensity varied between different locations and even among the same nucleus. The most prominent expression in rat was observed in neurons of the mitral cell layer of the olfactory bulb, red nucleus, mesencephalic trigeminal nucleus, motor trigeminal nucleus, facial nucleus, reticular nucleus and Purkinje cell layer. These findings suggest that FGF-9 plays an important role in the central nervous system and may have a potential function closely connected to neurons in the normal brain.

Transient expression of FGF-5 mRNA in the rat cerebellar cortex during post-natal development

Previously, we showed that fibroblast growth factor (FGF) receptor-4 mRNA was transiently expressed in proliferative granule cells of the external granule layer of the rat cerebellar cortex during early post-natal development (A. Miyake et al., Mol. Brain Res., 31 (1995) 95-100). In this study, we examined the expression of FGF-5 mRNA in the rat brain during post-natal development by in situ hybridization. FGF-5 mRNA was transiently expressed in granule cells of the internal granule layer of the cerebellar cortex during early post-natal development. The temporal sequence of FGF-5 mRNA expression was similar to that of FGFR-4 mRNA expression. As the proliferation of granule cells in the external granule layer and their migration through the molecular layer into the internal granule layer actively occur during these periods, the present findings suggest that FGF-5 as well as FGFR-4 might play important roles in the proliferation and/or migration of granule cells during the post-natal development of the cerebellar cortex.

Spatially restricted expression of fibroblast growth factor-10 mRNA in the rat brain

Fibroblast growth factor (FGF)-10 is a novel member of the FGF family. Although FGF-10 mRNA was preferentially expressed in the lung, the mRNA was also expressed, although at low levels, in the brain. We examined the localization of FGF-10 mRNA along with FGF-7 mRNA in the rat brain by in situ hybridization. FGF-10 mRNA showed spatially restricted expression in some regions of the brain, including the hippocampus, thalamus, midbrain and brainstem, although FGF-7 mRNA was not expressed in any of the brain regions examined. FGF-10 mRNA was strongly expressed in several restricted nuclei, especially in motor nuclei, including the oculomotor nucleus, dorsal motor nucleus of vagus, motor trigeminal nucleus, facial nucleus and hypoglossal nucleus. This localization pattern was distinct from those of aFGF, bFGF FGF-5 and FGF-9 mRNAs reported previously. The cellular localization of FGF-10 mRNA showed that the mRNA in the brain was preferentially expressed in neurons but not in glial cells. The present findings indicate that FGF-10, an additional member of the FGF family expressed in the brain, has a distinct role in the brain.

The effect of NGF, BDNF and bFGF on expression of galanin in cultured rat dorsal root ganglia

Peripheral nerve injury causes a marked change in expression of the neuropeptide galanin in dorsal root ganglion (DRG) neurons. We have used DRG cell cultures to study whether growth factors, especially nerve growth factor (NGF), play a role in this regulation. Adult rat DRG cultures seem to represent a suitable model for this study, since the neurons are axotomized during culture preparation and are known to survive independently of added neurotrophic factors. The effect of NGF, brain derived neurotrophic factor (BDNF) and basic fibroblast growth factor (bFGF) was studied on the expression of galanin and galanin message-associated peptide (GMAP)-like immunoreactivities using immunohistochemistry, as well as of prepro-galanin (ppGAL) mRNA levels using radioactive and non-radioactive in situ hybridization. The results show that 100, but not 20 or 50 ng/ml NGF, as well as 10 ng/ml BDNF cause a 40% decrease in the number of GMAP expressing neurons in 72 h cell cultures. A 50% decrease was observed after treatment with 10 ng/ml bFGF. The high dose needed and the modest effect suggest that NGF is not a major factor involved in galanin regulation, whereas BDNF and bFGF may have a role. Moreover, the strong upregulation of galanin/GMAP and ppGAL mRNA levels in the untreated cultures indicates that DRG neurons in vitro have a phenotype similar to DRG neurons after axotomy, i.e. a phenotype distinctly different from normal DRG neurons.

Nitric oxide and fibroblast growth factor in autonomic nervous system: short- and long-term messengers in autonomic pathway and target-organ control

The freely diffusible messenger nitric oxide (NO), generated by NO synthase (NOS)-containing "nitroxergic" (NO-ergic) neurons, is unique among classical synaptic chemical transmitters because of its "non-specificity", molecular "NO-receptors" (e.g. guanylyl cyclase, iron complexes, nitrosylated proteins or DNA) in target cells, intracellular targeting, regulated biosynthesis, and growth factor/cytokine-dependence. In the nervous system, expression of NOS is particularly intriguing in central and peripheral autonomic pathways and their targets. Here, anatomical and functional links appear to exist between NOS, its associated catalytic NADPH-diaphorase enzyme activity (NOSaD) and fibroblast growth factor-2 (FGF-2), a pleiotropic cytokine with mitogenic actions, suggesting mutual "short- and long-term" actions. Several recent studies performed in the rat sympathoadrenal system, an anatomically and neurochemically well-defined autonomic pathway with target-specific functional units of sympathetic preganglionic neurons (SPNs) in the spinal cord, provide evidence for this hypothesis. The NO and cytokine signals may interact at the level of gene expression, transcription factors, post-transcriptional control or second messenger cross-talk. Thus, unique biological roles of FGF-2 and the NO system are likely to exist in neuroendocrine actions, vasomotory perfusion control as well as in neurotrophic actions in sympathetic innervation of the adrenal gland. In view of their anatomical co-existence, functional interplay and synchronizing effects on neuronal networks, multiple roles are suggested for both "short- and long-term" signalling molecules in neuroendocrine functions and integrated autonomic target organ control.

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.

Glial lineages and myelination in the central nervous system

Oligodendrocytes, derived from stem cell precursors which arise in subventricular zones of the developing central nervous system, have as their specialist role the synthesis and maintenance of myelin. Astrocytes contribute to the cellular architecture of the central nervous system and act as a source of growth factors and cytokines; microglia are bone-marrow derived macrophages which function as primary immunocompetent cells in the central nervous system. Myelination depends on the establishment of stable relationships between each differentiated oligodendrocyte and short segments of several neighbouring axons. There is growing evidence, especially from studies of glial cell implantation, that oligodendrocyte precursors persist in the adult nervous system and provide a limited capacity for the restoration of structure and function in myelinated pathways damaged by injury or disease.

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.

Expression of fibroblast growth factor-2 and fibroblast growth factor receptor 1 messenger RNAs in spinal ganglia and sciatic nerve: regulation after peripheral nerve lesion

In order to determine functional roles of basic fibroblast growth factor (FGF-2) in the peripheral nervous system we have analysed the expression of FGF-2 and FGF receptor 1 (FGFR1) in spinal ganglia and the sciatic nerve under normal conditions and after nerve crush using RNAse protection assay and in situ hybridization. In intact spinal ganglia, both FGF-2 and FGFR1 messenger RNAs are expressed, albeit at different levels. In situ hybridization identifies satellite cells as the source of FGF-2 and sensory neurons as the source of FGFR1 suggesting a paracrine mode of action of FGF-2 on sensory neurons. One day after crush lesion FGF-2 is significantly up-regulated in sensory ganglia L4-L6. Highest levels are found at day 7; control levels are approached after 28 days. FGFR1 messenger RNA, which is strongly expressed in intact spinal ganglia, displays no significant change after lesion. In the intact sciatic nerve, FGFR1 messenger RNA is detected at higher levels than FGF-2 messenger RNA. After injury, both transcripts display a time-dependent up-regulation in both the proximal and distal nerve stump. Schwann cells, as a putative source of the sciatic nerve-derived FGF-2, express both FGF-2 and FGFR1 messenger RNAs in vitro. The FGFR1 transcript level is increased in the presence of forskolin. FGF-2 does not affect expression of FGFR1 messenger RNA but stimulates its own expression. These results show that during peripheral nerve regeneration FGF-2 is up-regulated in both the crushed nerve and the respective spinal ganglia suggesting a possible physiological function of FGF-2 during the regeneration process.

Characterization of the 1B promoter of fibroblast growth factor 1 and its expression in the adult and developing mouse brain

The present study elucidates the molecular structure of a murine fibroblast growth factor 1 (FGF-1) promoter and describes its distribution in the adult and developing mouse brain. A cDNA clone coding for FGF-1 was isolated from a mouse brain cDNA library. Nucleotide sequence analysis revealed that the clone contained, in addition to the protein coding region, an untranslated exon (FGF-1B) 34 base pairs upstream of the translation start codon ATG. The mouse cDNA clone corresponded to the sole FGF-1 transcript in the brain. An RNase protection assay was used to map the transcription start site of the 1B promoter. The sequences upstream from the major transcription initiation site lacked consensus TATA or CAAT boxes. In situ hybridization with cRNA probes specific for the 1B transcript showed the message to be restricted largely to sensory and motor nuclei in the brainstem, and to the ventral spinal cord and cerebellum. Although occasional brainstem nuclei were labeled at low levels by embryonic day 18, the majority of nuclei became detectable autoradiographically during postnatal weeks 1 and 2, and adult levels of grain density were reached during the 3rd and 4th postnatal weeks. FGF-1B mRNA was expressed in phylogenetically older brain regions, which are involved primarily in processing information from exteroceptive sensory mechanoreceptors and in motor control. The relatively late developmental expression suggests a role for FGF-1 in neuronal maturation, rather than in neurogenesis.

Basic fibroblast growth factor (FGF-2) affects development of acoustico-vestibular neurons in the chick embryo brain in vitro

The effects of basic fibroblast growth factor (FGF-2) on presumptive auditory and vestibular neurons from the medulla were studied in primary cell cultures. The part of the rhombic lip that forms nucleus magnocellularis (homologue of the mammalian anteroventral cochlear nucleus) was explanted from white leghorn chicken embryos at Hamburger-Hamilton stage 28 (E5.5), the time when precursors of the magnocellularis bushy cells migrate and begin to differentiate in situ. In vitro the neuroblasts migrated onto 2-D substrates of purified collagen, differentiated, and expressed neuronal markers. One-half of the cultures were supplemented with human recombinant FGF-2 (10 ng/ml daily) for 5-7 days; the others, with fetal bovine serum. FGF-2 more than doubled the length of neurite outgrowth during the first 3 day treatment compared to serum, but the number of migrating neuroblasts was unaffected. Although neurites attained greater lengths in FGF-2, they usually degenerated after 4-5 days; in serum their growth continued for several weeks. Differentiation of neuronal structure, including axons and dendrites, began within 1-2 days in bFGF but required at least 5-7 days in serum. Histochemical observations in vitro and in situ with antibodies to FGF receptor demonstrated immunopositive patches on acoustico-vestibular neuroblasts at stage 28, when they are migrating and first forming their axons. The findings suggest that FGF-2 stimulates neurite outgrowth in the cochlear and vestibular nuclei. FGF-2 may accelerate cell death by overstimulating neuroblasts, but other factors are needed to sustain their further development.

Nerve dependency of regeneration: the role of Distal-less and FGF signaling in amphibian limb regeneration

Dlx-3, a homolog of Drosophila Dll, has been isolated from an axolotl blastema cDNA library, and its expression in developing and regenerating limbs characterized. The normal expression pattern, and the changes that occur during experimental treatments, indicate a correlation between Dlx-3 expression and the establishment of the outgrowth-permitting epidermis. Dlx-3 is expressed at high levels in a distal-to-proximal gradient in the epidermis of developing limb buds, and is upregulated in the apical ectodermal cap (AEC) during limb regeneration. Expression is maximal at the late bud stage of regeneration, coincident with the transition from the early phase of nerve dependency to the later phase of nerve independence. Dlx-3 expression in the epidermis is rapidly downregulated by denervation during the nerve-dependent phase and is unaffected by denervation during the nerve-independent phase. We investigated this relationship between nerves and Dlx-3 expression by implanting FGF-2 beads into regenerates that had been denervated at a nerve-dependent stage. Dlx-3 expression was maintained by FGF-2 after denervation, and regeneration progressed to completion. In addition, we detected FGF-2 protein in the AEC and in nerves, and observed that the level of expression in both tissues decreases dramatically in response to denervation. We conclude that both limb development and regeneration require a permissive epidermis, characterized by Dlx-3 and FGF expression, both of which are maintained by FGF through an autocrine loop. The transformation of the limb epidermis into a functional AEC that produces and responds to FGF autocatalytically, is presumed to be induced by FGF. Since nerves appear to be a source of this priming FGF, it is possible that a member of the FGF family of growth factors is the elusive neurotrophic factor of limb regeneration.

aFGF, bFGF and NGF differentially regulate neuropeptide expression in dorsal root ganglia after axotomy and induce autotomy

Using immunohistochemistry and in situ hybridization the in vivo effects of acidic and basic fibroblast growth factor (aFGF, bFGF), and of nerve growth factor (NGF) on the expression of galanin, neuropeptide Y (NPY) and substance P in axotomized dorsal root ganglia (DRGs) were examined. Self-mutilation (autotomy), a supposed pain-related behavior, was investigated after growth factor treatment. One microgram of aFGF, bFGF or NGF was applied directly to the transected sciatic nerve via a capsule. In normal rats 3.2%, 0% and 17.5% of the neuron profiles in the DRGs contained galanin-, NPY- and substance P-like immunoreactivity (LI), respectively. Sciatic nerve transection induced a distinct increase in galanin- and NPY-LIs, but a downregulation of substance P-LI. Thus three days after axotomy 23.5%, 26.9% and 9.8% of the DRG neuron profiles showed immunoreactivity for galanin-, NPY- and substance P-LI, respectively. In vivo administration of aFGF counteracted the axotomy-induced increase in galanin and NPY, whereas bFGF only suppressed NPY upregulation. NGF reversed in the injury-induced decrease in substance P-LI, but had no significant effect on galanin- and NPY-LIs. These results were confirmed by monitoring the mRNA levels for these neuropeptides. Moreover, aFGF was found to induce autotomy in 60% of the rats 3 days after axotomy. NGF produced autotomy in about 30% of the rats. Taken together, the present results suggest (1) that aFGF, bFGF and NGF differentially regulate neuropeptide expression in vivo; (2) that FGFs can inhibit neuropeptide upregulation of some peptides after nerve injury; and (3) that aFGF and NGF may induce pain-related behavior.

Spinal cord repair in adult paraplegic rats: partial restoration of hind limb function

Complete spinal cord gaps in adult rats were bridged with multiple intercostal nerve grafts that redirected specific pathways from white to gray matter. The grafted area was stabilized with fibrin glue containing acidic fibroblast growth factor and by compressive wiring of posterior spinal processes. Hind limb function improved progressively during the first 6 months, as assessed by two scoring systems. The corticospinal tract regenerated through the grafted area to the lumbar enlargement, as did several bulbospinal pathways. These data suggest a possible repair strategy for spinal cord injury.

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.

Analgesic effects of fibroblast growth factor in the rat

Intraperitoneal (i.p.) injection of acidic fibroblast growth factor (aFGF) to Sprague-Dawley rats induced short-lasting analgesia as measured by tail-flick latency (TFL) test. The maximum effect, a 26% increase in tail-flick latency, was obtained 15 min following 1 microgram i.p. aFGF. By 30 min the effect was considerably reduced, and was no longer present by 45 min after treatment. Administration of heat-inactivated aFGF or a hybrid form of aFGF (CLYT/aFGF) that, although active, is unable to cross the blood-brain barrier (BBB), caused no analgesia. Furthermore, the analgesic effects of aFGF were prevented by pretreatment with the nitric oxide synthase inhibitor, L-NG-nitroarginine methyl ester (L-NAME). Our findings demonstrate an analgesic effect of FGF, which requires crossing of BBB and implicates the nitric oxide pathway.

Basic fibroblast growth factor (FGF-2) affects development of acoustico-vestibular neurons in the chick embryo brain in vitro

The effects of basic fibroblast growth factor (FGF-2) on presumptive auditory and vestibular neurons from the medulla were studied in primary cell cultures. The part of the rhombic lip that forms nucleus magnocellularis (homologue of the mammalian anteroventral cochlear nucleus) was explanted from white leghorn chicken embryos at Hamburger-Hamilton stage 28 (E5.5), the time when precursors of the magnocellularis bushy cells migrate and begin to differentiate in situ. In vitro the neuroblasts migrated onto 2-D substrates of purified collagen, differentiated, and expressed neuronal markers. One-half of the cultures were supplemented with human recombinant FGF-2 (10 ng/ml daily) for 5-7 days; the others, with fetal bovine serum. FGF-2 more than doubled the length of neurite outgrowth during the first 3 day treatment compared to serum, but the number of migrating neuroblasts was unaffected. Although neurites attained greater lengths in FGF-2, they usually degenerated after 4-5 days; in serum their growth continued for several weeks. Differentiation of neuronal structure, including axons and dendrites, began within 1-2 days in bFGF but required at least 5-7 days in serum. Histochemical observations in vitro and in situ with antibodies to FGF receptor demonstrated immunopositive patches on acoustico-vestibular neuroblasts at stage 28, when they are migrating and first forming their axons. The findings suggest that FGF-2 stimulates neurite outgrowth in the cochlear and vestibular nuclei. FGF-2 may accelerate cell death by overstimulating neuroblasts, but other factors are needed to sustain their further development.

Acidic fibroblast growth factor mRNA is expressed by basal forebrain and striatal cholinergic neurons

Evidence for the importance of the basal forebrain cholinergic system in the maintenance of cognitive function has stimulated efforts to identify trophic mechanisms that protect this cell population from atrophy and dysfunction associated with aging and disease. Acidic fibroblast growth factor (aFGF) has been reported to support cholinergic neuronal survival and has been localized in basal forebrain with the use of immunohistochemical techniques. Although these data indicate that aFGF is present in regions containing cholinergic cell bodies, the actual site of synthesis of this factor has yet to be determined. In the present study, in situ hybridization techniques were used to evaluate the distribution and possible colocalization of mRNAs for aFGF and the cholinergic neuron marker choline acetyltransferase (ChAT) in basal forebrain and striatum. In single-labeling preparations, aFGF mRNA-containing neurons were found to be codistributed with ChAT mRNA+ cells throughout all fields of basal forebrain, including the medial septum/diagonal band complex and striatum. By using a double-labeling (colormetric and isotopic) technique, high levels of colocalization (over 85%) of aFGF and ChAT mRNAs were observed in the medial septum, the diagonal bands of Broca, the magnocellular preoptic area, and the nucleus basalis of Meynert. The degree of colocalization was lower in the striatum, with 64% of the cholinergic cells in the caudate and 33% in the ventral striatum and olfactory tubercle labeled by the aFGF cRNA. These data demonstrate substantial regionally specific patterns of colocalization and support the hypothesis that, via an autocrine mechanism, aFGF provides local trophic support for cholinergic neurons in the basal forebrain and the striatum.

Expression and localization of FGF-1 in the developing rat olfactory system

Primary olfactory axons project from the nasal olfactory neuroepithelium to glomeruli in the olfactory bulb where they synapse with mitral cells, the second-order olfactory neurons. We have shown that the heparin-binding growth factor FGF-1 is expressed by olfactory nerve ensheathing cells which surround fascicles of primary olfactory axons en route to the olfactory bulb. These cells are believed to modulate olfactory axon growth between the olfactory neuroepithelium and the olfactory bulb. During late embryogenesis, FGF-1 expression is turned on in the mitral cells, and the FGF-1 peptide becomes confined to layers of synaptic neuropil in the postnatal olfactory bulb. FGF-1 is selectively present in glomeruli and the external plexiform layer. In cultures of olfactory neuroepithelial cells, complexes between FGF-1 and an appropriate activating heparan sulfate proteoglycan stimulated morphological differentiation of both olfactory nerve ensheathing cells and primary sensory olfactory neurons. Thus, the spatiotemporal expression and the functional properties of FGF-1 in this system suggest that this molecule plays an important regulatory role in the formation of the olfactory pathway.

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

Developing chick motoneurons depend on as yet unidentified factors from the periphery and the central nervous system for their survival. Using cultures of purified embryonic motoneurons, we show that basic fibroblast growth factor (FGF-2) or transforming growth factor-beta 3 (TGF beta 3) each have only low survival-promoting activity when tested alone, but act synergistically to keep motoneurons alive for at least 3 days. Glial cell line-derived neurotrophic factor (GDNF), another member of the TGF beta family, was itself sufficient to maintain a population of motoneurons. However, its effect was not significantly increased by the addition of FGF-2. These results suggest that FGF-2, TGF beta 3, and GDNF, which are all present in the environment of developing motoneurons, may act different mechanisms as physiological survival factors for this population of central neurons.

The neurotrophic activity of fibroblast growth factor 1 (FGF1) depends on endogenous FGF1 expression and is independent of the mitogen-activated protein kinase cascade pathway

The expression of fibroblast growth factor (FGF) 1, a potent neurotrophic factor, increases during differentiation and remains high in adult neuronal tissues. To examine the importance of this expression on the neuronal phenotype, we have used PC12 cells, a model to study FGF-induced neuronal differentiation. After demonstrating that FGF1 and FGF2 are synthesized by PC12 cells, we investigated if FGF1 expression could be a key element in differentiation. Using the cell signaling pathway to determine the effects of FGF1 alone, FGF1 plus heparin, or a mutated FGF1, we showed an activation to the same extent of mitogen-activated protein (MAP) kinase kinase and MAP kinase (extracellular regulated kinase 1). However, only FGF1 plus heparin could promote PC12 cell differentiation. Thus, the MAP kinase pathway is insufficient to promote differentiation. Analysis of the PC12 cells after the addition of FGF1 plus heparin or FGF2 demonstrated a significant increase in the level of FGF1 expression with the same time course as the appearance of the neuritic extensions. Transfection experiments were performed to enhance constitutivly or after dexamethasone induction the level of FGF1 expression. The degree of differentiation achieved by the cells correlated directly with the amount of FGF1 expressed. The MAP kinase pathway did not appear to be involved. Interestingly, a 5-fold increase in FGF1 in constitutive transfected cells extended dramatically their survival in serum-free medium, suggesting that the rise of FGF1 synthesis during neuronal differentiation is probably linked to their ability to survive in the adult. All of these data demonstrate that, in contrast to the MAP kinase cascade. FGF1 expression is sufficient to induce in PC12 cells both differentiation and survival. It also shows that auto- and trans-activation of FGF1 expression is involved in the differentiation process stimulated by exogenous FGFs through a new pathway which remains to be characterized.

Distribution of acidic fibroblast growth factor-like immunoreactivity in rat skeletal muscle fibers

Acidic fibroblast growth factor (aFGF) is a mitogenic, angiogenic and neurotrophic growth factor which promotes proliferation, but delays differentiation of cultured myoblasts. Its mRNA is expressed in the skeletal muscle, however, the distribution of aFGF in the postnatal skeletal muscle is poorly characterized. In the present study, the distribution of aFGF-like immunoreactivity (LI) was examined in developing and adult rat skeletal muscle fibers. In addition, the effect of the transection of the sciatic nerve on aFGF-LI in calf muscle fibers was examined. From the first postnatal day on, aFGF-immunoreactive (IR) muscle fibers were observed in different calf muscles. From the 7th postnatal day on a large number of muscle fibers exhibited aFGF-LI in the soleus muscle, some in plantaris and only few in gastrocnemius and extraocular muscles. Double-labelling with fast-myosin antibody showed that aFGF-LI was restricted to the slow oxidative muscle fibers. aFGF-IR intrafusal muscle fibers were seen in developing and mature muscle spindles. In addition, aFGF-IR nerve fibers and myoneural junctions were observed in different muscles. Transection of the sciatic nerve did not noticeably alter the expression pattern of aFGF-LI in calf muscles during two-week period. The present study demonstrates aFGF-LI in the rat slow oxidative muscle fibers where it may have fiber-type specific functions in addition to its known trophic effects.

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.

Prominent expression of bFGF in dorsal root ganglia after axotomy

Using quantitative in situ hybridization and immunohistochemistry the expression of acidic and basic fibroblast growth factors (aFGF, bFGF) in dorsal root ganglia (DRGs) was examined. Around 5% of the small neurons expressed bFGF mRNA in normal DRGs. Nerve injury induced a very dramatic and rapid up-regulation in bFGF mRNA levels, and around 80% of all DRG neurons expressed bFGF mRNA 3 days after axotomy. A distinct increase in bFGF-like immunoreactivity (LI) was also detected as early as 15 h after axotomy. The elevation of bFGF mRNA and protein levels declined after 1 week. bFGF mRNA was also up-regulated in non-neuronal cells following axotomy. Normally bFGF-LI was mainly localized in the nuclei of DRG neurons and in some non-neuronal cells. After nerve section, bFGF-LI was in addition found in the cytoplasm, and many more bFGF-positive non-neuronal cells were observed. By means of confocal microscopy analysis of axotomized DRGs, some bFGF-LI could be detected in vesicle-like structures in the cytoplasm as well as in the nucleoli, in addition to the nuclear location. Application of leukaemia inhibitory factor to the transected sciatic nerve significantly increased the number of bFGF-positive neurons, whereas the bFGF-LI in non-neuronal cells was strongly suppressed. About 70% of the normal DRG neurons expressed aFGF mRNA and aFGF-LI. Axotomy produced a moderate increase in aFGF mRNA levels, but no detectable effect on protein levels. Taken together, the results show that bFGF may be involved in the neuronal response to injury and suggest a role in neuronal survival and regeneration in axotomized DRG neurons.

Characterization of the signaling interactions that promote the survival and growth of developing retinal ganglion cells in culture

The signaling mechanisms that control the survival of CNS neurons are poorly understood. Here we show that, in contrast to PNS neurons, the survival of purified postnatal rat retinal ganglion cells (RGCs) in vitro is not promoted by peptide trophic factors unless their intracellular cAMP is increased pharmacologically or they are depolarized by K+ or glutamate agonists. Long-term survival of most RGCs in culture can be promoted by a combination of trophic factors normally produced along the visual pathway, including BDNF, CNTF, IGF1, an oligodendrocyte-derived protein, and forskolin. These results suggest that neurotransmitter stimulation and electrical activity enhance the survival of developing RGCs and raise the question of whether the survival control mechanisms of PNS and CNS neurons are different.