Basic fibroblast growth factor prevents death of lesioned cholinergic neurons in vivo

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.

Basic fibroblast growth factor is highly neuroprotective against seizure-induced long-term behavioural deficits

Basic fibroblast growth factor has been reported to protect neurons of various structures from excitotoxic damage. To study the effects of basic fibroblast growth factor on seizure-induced brain damage we infused the growth factor into the lateral ventricles of 35-day-old rats receiving convulsant dosages of kainic acid. Artificial cerebrospinal fluid or basic fibroblast growth factor at dosages of 0.5 ng/h or 2.5 ng/h was infused into the lateral ventricle continuously for seven days starting two days before and continuing for five days after the animals had kainic acid-induced status epilepticus. At age 80 days the animals underwent behavioural testing using the water maze, open field, and handling tests and at age 95 days were tested for seizure threshold using flurothyl inhalation. Neither artificial cerebrospinal fluid or basic fibroblast growth factor modified the latency or duration of the acute seizures following kainic acid. However, rats infused with 2.5 ng/h, but not 0.5 ng/h of basic fibroblast growth factor, had fewer spontaneous recurrent seizures, a higher seizure threshold, better performance in the handling, open field and water maze test, and less cell loss in the hippocampus when compared to rats receiving artificial cerebrospinal fluid or 0.5 ng/h of basic fibroblast growth factor. These results show that basic fibroblast growth factor has a dose-related neuroprotective effect against seizure-induced long-term behavioural deficits when administered by osmotic pump prior to seizure onset. This neuroprotective effect is not related to an anticonvulsant effect.

The control of cell death in the early chick embryo wing bud

Developmentally programmed cell death occurs in several regions of the chick wing bud. We have studied the nature and control of this cell death in vitro in tissues from two of these regions, the posterior necrotic zone (PNZ) and the opaque patch (OP). When tissue from these regions is excised prior to normal cell death and placed into organ culture, cell death ensues. Under these conditions, cell death in tissue from both of these regions is inhibited by fibroblast growth factor-2 (FGF-2). The only other growth factor we have found to have this function is insulin-like growth factor-II. Cell death in tissue from the OP and PNZ occurs by apoptosis, as indicated by the internucleosomal degradation of DNA and the inhibition of cell death by cycloheximide, an inhibitor of protein synthesis. If cell death is inhibited by FGF-2 and then the growth factor is washed away, a compensatory burst of cell death occurs in the PNZ tissue but not the OP tissue. This finding may indicate that in the PNZ, a death program progresses in the face of FGF-2 inhibition, resulting in more cells on the brink of death when the growth factor is removed.

Models to study the role of neurotrophic factors in neurodegeneration

The physiological functions of neurotrophic factors, such as nerve growth factor (NGF), in supporting the survival and differentiation of specific neurons during early development has in many cases been well established. Recent studies have shown that neurotrophic factors can also protect vulnerable neurons against a variety of mechanical and chemical injuries. The role and the effects of neurotrophic factors in various neurological diseases are however less known. Neurodegenerative diseases such as Parkinson and Alzheimer's diseases as well as amyotrophic lateral sclerosis (ALS) are characterized by an impaired function and ultimate loss of specific populations of neurons. The study of the ethiology and molecular biology of these diseases has for a long time been hampered by the lack of good animal models mimicked part of the human disease in experimental animals. Here we will discuss some of the current approaches taken in these studies as well as address the important question of the possible beneficial effect of neurotrophic factors in alleviating the symptoms and possibly retarding the course of neurodegenerative diseases.

Elevated basic fibroblast growth factor levels in stroke-prone spontaneously hypertensive rats

Basic fibroblast growth factor is a biologically active polypeptide with mitogenic, angiogenic and neurotrophic properties. In the present study, the temporal and spatial expressions of basic fibroblast growth factor in stroke-prone spontaneously hypertensive rats were compared to two related strains of rat: spontaneously hypertensive rats and normotensive Wistar Kyoto rats. Higher levels of total RNA concentration were found in cerebral cortex of four-week-old stroke-prone rats compared to spontaneously hypertensive rats and Wistar Kyoto rats. Northern blot analysis showed no changes in levels of basic fibroblast growth factor messenger RNA with increasing age in cerebral cortex of Wistar Kyoto and spontaneously hypertensive rats. However, significant increases were found in 26- and 38-week-old stroke-prone rats compared to four-week-old stroke-prone rats. Although messenger RNA increases were also found in subcortical and cerebellar regions, a significant difference in levels of basic fibroblast growth factor messenger RNA was observed only in cerebral cortices among these three strains. This age-related increase in basic fibroblast growth factor messenger RNA correlated with the increase incidence of stroke in stroke-prone rats. Immunohistochemical study further revealed a dramatic increase in levels of basic fibroblast growth factor immunoreactivity in cerebral cortex of 30-week-old stroke-prone rats as compared to young stroke-prone rats, as well as age-matched Wistar Kyoto and spontaneously hypertensive rats. This increase in basic fibroblast growth factor immunoreactivity therefore appears very specific to aged stroke-prone rats. However, immunoreactivity decreased once severe tissue damages were observed in the cerebral cortex. Basic fibroblast growth factor-positive cells were diffusely expressed in cerebral cortex; double staining with glial fibrillary acidic protein showed the majority of these basic fibroblast growth factor-positive cells to be astrocytes. In summary, although young stroke-prone spontaneously hypertensive rats showed significantly higher RNA concentration, significant increases in levels of basic fibroblast growth factor, including both messenger RNA and protein expression, were observed in aged stroke-prone rats with a high incidence of stroke. These findings suggest the possibility that basic fibroblast growth factor may play a role in the developmental sequelae of cerebral lesions in stroke-prone spontaneously hypertensive rats.

Heparan sulfate potentiates the autocrine action of basic fibroblast growth factor in astrocytes: an in vivo and in vitro study

Increasing evidence indicates that heparan sulfate proteoglycans have a critical role in the regulation of the activity of basic fibroblast growth factor by interacting with it or its receptor. In this study we examined the possibility that heparan sulfate can modulate the basic fibroblast growth factor system at a more fundamental level than activity regulation, by influencing the synthesis of basic fibroblast growth factor and its receptor messenger RNAs. Previous studies in vitro indicate that basic fibroblast growth factor promotes proliferation and differentiation of astrocytes. Accordingly, we examined the possibility that the action of heparan sulfate on the basic fibroblast growth factor system could have a critical role in the modulation of reactivity and/or proliferation of astrocytes in vitro and in vivo. We report that basic fibroblast growth factor applied to pure astrocyte cultures or rat neocortex promoted an increase in the messenger RNA for basic fibroblast growth factor itself and for its receptor. Furthermore, basic fibroblast growth factor applied directly into the brain elicited an increase in messenger RNA for the astrocytic marker glial fibrillary acidic protein. All of these actions, both in vitro and in vivo, were highly potentiated when heparan sulfate was applied in combination with basic fibroblast growth factor. These results suggest that basic fibroblast growth factor regulates astrocytic proliferation or reactivity via an autocrine cascade that involves induction of its own receptor and that this action is modulated by heparan sulfate.

Effect of basic fibroblast growth factor on experimental focal ischemia studied by diffusion-weighted and perfusion imaging

BACKGROUND AND PURPOSE

Basic fibroblast growth factor (bFGF) has documented neuroprotective properties. This study was performed to evaluate the effects of bFGF on infarct size when administered 30 minutes after induction of focal cerebral ischemia in rats. Diffusion-weighted and perfusion MRI were used during the drug infusion.

METHODS

We blindly randomized 20 Sprague-Dawley rats to receive either drug (n = 10) or vehicle (n = 10). The animals underwent middle cerebral artery (MCA) occlusion using the suture model. Diffusion-weighted MRI was initiated 30 minutes after induction of ischemia and repeated frequently for 3.5 hours. Drug (45 micrograms/kg per hour) or vehicle (saline) infusion began 30 minutes after MCA occlusion and continued for 3 hours. Perfusion images were made at 25, 90, and 150 minutes after MCA occlusion. The animals were killed after 24 hours of permanent MCA occlusion, and brains were stained with 2,3,5-triphenyltetrazolium chloride (TTC).

RESULTS

The TTC-derived, corrected infarct volume postmortem in the bFGF-treated group was significantly smaller than that in controls (126.6 +/- 51.9 versus 180.2 +/- 54.9 mm3, mean +/- SD, P = .038). Diffusion imaging showed essentially equal lesion volumes 3 hours after MCA occlusion (195.4 +/- 61 mm3 in the drug-treated group and 194.4 +/- 65 mm3 in controls). At 4 hours, ischemic lesion size was 182.1 +/- 56.9 mm3 in treated animals and 222.9 +/- 88.7 mm3 in the controls (P = .24, NS). Perfusion imaging did not show a change of cerebral perfusion within ischemic brain regions in the bFGF group during the infusion. No behavioral or physiological side effects were observed.

CONCLUSIONS

bFGF is a safe and effective treatment for focal cerebral ischemia in rats. We observed a modest delayed difference of ischemic lesion size in vivo with diffusion MRI. The diffusion-weighted MRI findings suggest a potential delayed therapeutic effect of bFGF, and the perfusion imaging findings imply that the effect is not due to increased blood flow to the ischemic region.

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.

The fibroblast growth factor receptor-1 is necessary for the induction of neurite outgrowth in PC12 cells by aFGF

The PC12 subclone, fnr-PC12 cells, is defective in neurite outgrowth in response to acidic fibroblast growth factor (aFGF); however, its response to nerve growth factor (NGF) is normal. Examination of the expression of FGF receptors (FGFRs) revealed that although PC12 cells express FGFR-1, -3, and -4, fnr-PC12 cells have a reduced level of expression of FGFR-1 but not FGFR-3 and -4. Transfection of FGFR-1 into fnr-PC12 cells efficiently restored aFGF-induced neurite outgrowth, whereas transfection of FGFR-3 was much less efficient. Transfection of a chimeric receptor consisting of the extracellular domain of FGFR-3 fused to the transmembrane and intracellular domain of FGFR-1, termed FR31b, efficiently restored aFGF-induced neurite outgrowth. This demonstrates that the difference between these two receptors in their ability to induce neurite outgrowth is attributable to differences in the signaling capacity of their cytoplasmic domains. Activation of the chimeric receptor by aFGF induced a stronger and more persistent increase in the tyrosine phosphorylation of cellular proteins than did activation of FGFR-3 alone. In particular, the activation of MAP kinase by FR31b was more persistent than when activated by FGFR-3. This difference in signaling potential of FGFR-1 and -3 in fnr-PC12 cells may account for the difference in the potential for induction of neurite outgrowth. These results demonstrate that FGF-induced neurite outgrowth in PC12 cells occurs mainly via FGFR-1 and not via the other FGFRs expressed in these cells.

Reduction in myocardial infarct size by basic fibroblast growth factor after temporary coronary occlusion in a canine model

BACKGROUND

Basic fibroblast growth factor (bFGF) has been shown to reduce infarct size in canine acute myocardial infarction; however, the mechanism of tissue salvage remains uncertain. We evaluated the effect of bFGF on infarct size in a model of acute infarction in which coronary occlusion was followed by prolonged reperfusion and sought to determine whether reperfusion attenuates the stimulus for myocardial neovascularization.

METHODS AND RESULTS

Anesthetized dogs undergoing 4-hour balloon occlusion of the left anterior descending coronary artery were treated with intracoronary bFGF (n = 8) or vehicle (n = 6). Ten-microgram doses of bFGF were administered 10 minutes after occlusion and again immediately before reperfusion. Left ventriculograms were obtained before occlusion, after reperfusion, and preceding euthanasia on day 7. Infarct size, expressed as a percentage of the area at risk, was reduced in bFGF-treated dogs (13.7 +/- 2.1% versus 28 +/- 3.4%; P = .002). Changes in left ventricular ejection fraction, capillary density, and cellular proliferation-assessed immunohistochemically with factor VIII and proliferating cell nuclear antigen antibodies-were similar in both groups. To assess coronary vasomotor responses to bFGF, a separate hemodynamic study was performed in five anesthetized nonischemic dogs in which incremental bFGF doses up to 100 micrograms induced no vasodilator response.

CONCLUSIONS

Treatment with bFGF was associated with a reduction in infarct size without hemodynamic effects or evidence of neovascularization. These data suggest that bFGF mediates myocardial salvage independently of angiogenesis and that reperfusion after infarction may attenuate the stimulus for neovascularization.

Cultured basal forebrain cholinergic neurons in contact with cortical cells display synapses, enhanced morphological features, and decreased dependence on nerve growth factor

Prior studies examining the dependence of basal forebrain cholinergic neurons (BFCNs) on nerve growth factor (NGF) for survival have reached differing conclusions depending on the experimental paradigm employed, suggesting the importance of environmental and developmental variables. The present study examined the NGF dependence of BFCNs and modulatory effects of target (cortical) neurons under the controlled conditions of dissociated cell cultures. Initial experiments found BFCNs (identified by using choline acetyltransferase immunocytochemistry) in pure basal forebrain (BF) cultures to be dependent on NGF between the 2nd and 4th week in vitro. During that developmental period, NGF deprivation for 3 days, induced by application of anti-NGF antibody, resulted in degeneration of over 80% of BFCNs, whereas at earlier or later times, BFCNs were largely resistant to NGF deprivation. When BF neurons were plated together with cortical neurons (as dissociated co-cultures), the BFCNs grew neuritic processes (labeled with acetylcholinesterase histochemistry) that appeared to specifically target cortical neurons; electron microscopy revealed that synapses formed between these cells. BFCNs in co-cultures were more resistant to NGF deprivation, were larger, and had much more extensive neuritic growth than BFCNs in pure BF cultures. The resistance of BFCNs to NGF deprivation provided by cortical neurons could be largely reproduced by addition of other trophic factors (brain-derived neurotrophic factor, BDNF; neurotrophin 3, NT3; neurotrophin 4/5, NT4/5; or glial-derived neurotrophic factor, GDNF) during NGF deprivation in pure BF cultures. These results suggest that developing BFCNs undergo a critical period requiring trophic influences that may be provided by NGF or other trophic factors, as well as unknown factors derived from cortical neurons.

Selective induction of fibroblast growth factor receptor-1 mRNA after transient focal ischemia in the cerebral cortex of rats

The expression of the mRNA of four members of the fibroblast growth factor (FGF) receptor family, was examined in rats subjected to temporal middle cerebral artery occlusion using an in situ hybridization technique. Fibroblast growth factor receptor-1 (FGFR-1) mRNA was strongly expressed in neurons of the cerebral cortex, whereas mRNAs of the other 3 subtypes of FGFRs (FGFR-2, -3, and -4) were not expressed. After temporal occlusion of the middle cerebral artery, expression of FGFR-1 mRNA in cerebral cortical neurons markedly increased in association with the progressive neuronal death; this increase was evident for at least 5 days after the focal ischemia. In view of the neuroprotective activity of basic FGF reported so far, the present results suggest that FGFR-1 induction may subserve to self-protect neurons in the ischemic penumbral field of the cerebral cortex.

Increased expression of basic fibroblast growth factor (bFGF) following focal cerebral infarction in the rat

Basic fibroblast growth factor (bFGF) is a polypeptide with potent trophic effects on brain neurons, glia, and endothelial cells. In the current study, we used Northern blotting, in situ hybridization, and immunohistochemical techniques to examine bFGF expression in brain following focal infarction due to permanent occlusion of the proximal middle cerebral artery in mature Sprague-Dawley rats. We found a four-fold increase in bFGF mRNA in tissue surrounding focal infarcts at 1 day after ischemia. In situ hybridization showed that this increase was found throughout several structures in the ipsilateral hemisphere, including frontoparietal, temporal, and cingulate cortex, as well as in caudoputamen, globus pallidus, septal nuclei, nucleus accumbens, and olfactory tubercle. Increased bFGF mRNA expression was associated with cells having the distinct morphological appearance of astroglia in these structures. Immunohistochemistry showed an increase in the size and number of bFGF-immunoreactive (IR) nuclei in these same structures, as well as a shift from nuclear to nuclear plus cytoplasmic localization of immunoreactivity, beginning at 1 day, and peaking at 3 days after ischemia. Double immunostaining identified bFGF-IR cells as astroglia in these structures. (An exception was the piriform cortex, in which both increased bFGF mRNA levels and increased bFGF-IR was found in neurons at 1 day after ischemia). Overall, the peak of increased bFGF expression preceded the peak in expression of the astroglial marker GFAP within the ipsilateral hemisphere. Increased bFGF expression may play an important role in the glial, neuronal, and vascular changes occurring after focal infarction.

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

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

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

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

Posttreatment with intravenous basic fibroblast growth factor reduces histopathological damage following fluid-percussion brain injury in rats

The purpose of this study was to determine whether treatment with intravenous basic fibroblast growth factor (bFGF) would protect histopathologically in a rat model of traumatic brain injury (TBI). Twenty-four hours prior to TBI, the fluid-percussion interface was positioned parasagittally over the right cerebral cortex. On the second day, fasted rats were anesthetized with 70% nitrous oxide, 1% halothane, and 30% oxygen. Under controlled physiological conditions and normothermic brain temperature (37-37.5 degrees C), rats were injured with a fluid-percussion pulse ranging from 1.6 to 1.9 atm. Rats were randomized into two groups where either bFGF (45 micrograms/kg/h) in vehicle (n = 7) or vehicle alone (n = 7) was infused intravenously for 3 h, beginning 30 min after TBI. Three days later, brains were perfusion-fixed for histopathological assessment and quantitative analysis of contusion volume and numbers of necrotic cortical neurons. In vehicle-treated animals, necrotic neurons were observed throughout the lateral cerebral cortex remote from the impact site. In addition, an intracerebral contusion was present in all rats at the gray-white interface underlying the injured cortical areas. Posttraumatic administration of bFGF significantly reduced the numbers of damaged cortical neuron profiles at several coronal levels and reduced the total number of damaged neurons (696 +/- 148 vs. 1,248 +/- 198, means +/- SEM), p < 0.05, ANOVA). In addition, contusion ares at several coronal levels as well as total contusion volume was significantly reduced (1.13 +/- 0.39 mm(3) vs. 3.18 +/- 0.81 mm(3), p < 0.05). These data demonstrate neuroprotection with intravenous bFGF infusion in the posttraumatic setting.

Influence of the postsynaptic target on the functional properties of neurons in the adult mammalian central nervous system

In this review we have attempted to summarize present knowledge concerning the regulatory role of target cells on the expression and maintenance of the neuronal phenotype during adulthood. It is well known that in early developmental stages the survival of neurons is maintained by specific neurotrophic factors derived from their target tissues. Neuronal survival is not the only phenotype that is regulated by target-derived neurotrophic factors since the expression of electrophysiological and cytochemical properties of neurons is also affected. However, a good deal of evidence indicates that the survival of neurons becomes less dependent on their targets in the adult stage. The question is to what extent are target cells still required for the maintenance of the pre-existing or programmed state of the neuron; i.e., what is the functional significance of target-derived factors during maturity? Studies addressing this question comprise a variety of neuronal systems and technical approaches and they indicate that trophic interactions, although less apparent, persist in maturity and are most easily revealed by experimental manipulation. In this respect, research has been directed to analyzing the consequences of disconnecting a group of neurons from their target-by either axotomy or selective target removal using different neurotoxins-and followed (or not) by the implant of a novel target, usually a piece of embryonic tissue. Numerous alterations have been described as taking place in neurons following axotomy, affecting their morphology, physiology and metabolism. All these neuronal properties return to normal values when regeneration is successful and reinnervation of the target is achieved. Nevertheless, most of the changes persist if reinnervation is prevented by any procedure. Although axotomy may represent, besides target disconnection, a cellular lesion, alternative approaches (e.g., blockade of either the axoplasmic transport or the conduction of action potentials) have been used yielding similar results. Moreover, in the adult mammalian central nervous system, neurotoxins have been used to eliminate a particular target selectively and to study the consequences on the intact but target-deprived presynaptic neurons. Target depletion performed by excitotoxic lesions is not followed by retrograde cell death, but targetless neurons exhibit several modifications such as reduction in soma size and in the staining intensity for neurotransmitter-synthesizing enzymes. Recently, the oculomotor system has been used as an experimental model for evaluating the functional effects of target removal on the premotor abducens internuclear neurons whose motoneuronal target is destroyed following the injection of toxic ricin into the extraocular medial rectus muscle. The functional characteristics of these abducens neurons recorded under alert conditions simultaneously with eye movements show noticeable changes after target loss, such as a general reduction in firing frequency and a loss of the discharge signals related to eye position and velocity. Nevertheless, the firing pattern of these targetless abducens internuclear neurons recovers in parallel with the establishment of synaptic contacts on a presumptive new target: the small oculomotor internuclear neurons located in proximity to the disappeared target motoneurons. The possibility that a new target may restore neuronal properties towards a normal state has been observed in other systems after axotomy and is also evident from experiments of transplantation of immature neurons into the lesioned central nervous system of adult mammals. It can be concluded that although target-derived factors may not control neuronal survival in the adult nervous system, they are required for the maintenance of the functional state of neurons, regulating numerous aspects of neuronal structure, chemistry and electro-physiology.(ABSTRUCT TRUNCATED)

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.

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.

Infusion of glial maturation factor-beta reduces behavioral deficits after caudate nucleus injury in rats

Adult rats with bilateral thermal lesions of the caudate nuclei (CN) show severe learning and memory deficits. The present study was designed to test the effects of an astroglial stimulating growth factor in this behavioral model. Immediately after receiving lesions of the CN, experimental subjects received an injection of one of three doses of glial maturation factor-beta (GMF-beta) directly in the lesion site. All subjects were then tested for twenty days on an active avoidance spatial alternation task. The behavioral recovery of the three groups of experimental animals was compared to that of animals having received the same brain damage and administration of a control substance (lesion controls), and to that of animals receiving a sham operation and no treatment (shams). The beneficial effects of administration were evident in the group of experimental animals receiving the lowest dose of GMF-beta. The performance of animals in this group was indistinguishable from that of the shams, and was significantly better than that of the lesion controls. The results suggest a behavioral role of GMF-beta which, in an in vitro system, is known to be a growth regulator of astroglial cells.

Effects of basic fibroblast growth factor and ganglioside GM1 on neuronal survival in primary cultures and on eight-arm radial maze task in adult rats following partial fimbria transections

The effects of basic fibroblast growth factor (bFGF) and ganglioside GM1 (GM1) were evaluated alone and simultaneously in two types of experiments. First, the neuronal survival of primary culture neurons from fetal rat brain was measured. Then, performance on radial maze task in adult male rats following bilateral partial Fimbria-Fornix transections (F-F lesion) was tested. In primary culture neurons, bFGF (1-10 ng/ml) supported the neuronal survival from three regions (hippocampus, cortex and septum) of embryonic rat brain. However, GM1 (0.1-10 micrograms/ml) did not support the neuronal survival from any regions. Survival of cultured neurons was not supported by addition of 0.1 ng/ml bFGF, but when bFGF (0.1 ng/ml) and GM1 (0.1, 1 microgram/ml) were given to the cultured neurons simultaneously, the number of surviving neurons increased significantly. In the eight-arm radial maze task, where only the same four arms were baited, F-F lesion produced substantial memory impairment. In this task, administration of bFGF (10 micrograms/ml) or GM1 (1 mg/ml) alone did not produce any effects. However, when they were given simultaneously, the number of working memory errors decreased significantly, in spite of no amelioration for hippocampal choline acetyl transferase (ChAT) depletion. These findings indicate that actions of bFGF may be potentiated by the addition of GM1 in both primary neuronal cultures and radial maze task performance. These results suggest that the combination of bFGF and GM1 may synergistically improve spatial memory deficits.

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

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

The effect of basic fibroblast growth factor on glutamate-injured neuroarchitecture and arachidonic acid release in adult hippocampal neurons

During development in culture, basic fibroblast growth factor (bFGF) protected immature primary hippocampal neurons against glutamate-induced neurotoxicity. We investigated the effects of bFGF on mature, differentiated rat hippocampal neurons cultured for 10-12 days after an 8-min exposure to 500 microM glutamate. Seven days post-injury, hippocampal cells demonstrated severe reductions in cellular viability and axonal and dendritic outgrowth, which were accompanied by a marked increase in [3H]arachidonic acid (ARA) release from prelabelled neurons. bFGF applied post-injury attenuated cell death and cytoarchitectural destruction at all concentrations used (500 pg/ml, 1, 10, 20 ng/ml). However, neurite elongation and branching processes were only significantly protected by 10 ng/ml bFGF. [3H]ARA release decreased in a dose-related fashion within a concentration range of 1-10 ng/ml bFGF. 20 ng/ml bFGF was not superior to 10 ng/ml bFGF. Therefore, bFGF's neurotropic actions appear to be concentration-dependent. Our data suggest that bFGF applied post-injury may have a neuroprotective potential for mature, differentiated, completely polarized hippocampal neurons.

Involvement of wound-associated factors in rat brain astrocyte migratory response to axonal injury: in vitro simulation

The poor ability of mammalian central nervous system (CNS) axons to regenerate has been attributed, in part, to astrocyte behavior after axonal injury. This behavior is manifested by the limited ability of astrocytes to migrate and thus repopulate the injury site. Here, the migratory behavior of astrocytes in response to injury of CNS axons in vivo was simulated in vitro using a scratch-wounded astrocytic monolayer and soluble substances derived from injured rat optic nerves. The soluble substances, applied to the scratch-wounded astrocytes, blocked their migration whereas some known wound-associated factors such as transforming growth factor-beta 1 (TGF-beta 1), basic fibroblast growth factor (bFGF), epidermal growth factor (EGF), transforming growth factor-alpha (TGF-alpha), and heparin-binding epidermal growth factor in combination with insulin-like growth factor-1 (HB-EGF + IGF-1) stimulated intensive migration with consequent closure of the wound. Migration was not dominated by proliferating cells. Both bFGF and HB-EGF + IGF-1, but not TGF-beta 1, could overcome the blocking effect of the optic nerve-derived substances on astrocyte migration. The induced migration appeared to involve proteoglycans. It is suggestive that appropriate choice of growth factors at the appropriate postinjury period may compensate for the endogenous deficiency in glial supportive factors and/or presence of glial inhibitory factors in the CNS.

Adrenalectomy reduces FGF-1 and FGF-2 gene expression in specific rat brain regions and differently affects their induction by seizures

We have previously reported that limbic seizures regulate the gene expression of fibroblast growth factor-2 (basic, FGF-2) according to a specific spatio-temporal pattern. In the present paper we have investigated the role of adrenal hormones on seizure-induced elevation of fibroblast growth factor-1 (acidic, FGF-1) and FGF-2 gene expression. Adrenalectomy reduces FGF-2 mRNA expression in specific brain regions, such as frontal cortex, hippocampus and striatum, whereas FGF-1 mRNA levels were decreased only in the frontal cortex. The injection of kainic acid in adrenalectomized rats produced a widespread increase of FGF-2 mRNA with a pattern similar to sham animals as indicated by in situ hybridization. In contrast, although kainate-induced elevation of FGF-1 mRNA in the hippocampus was not influenced by adrenalectomy, its induction in frontal cortex was prevented by this surgery procedure. Taken together, these data indicate that adrenal hormones play a role in the regulation of the gene expression for fibroblast growth factors, but different mechanisms are operative in their induction following seizure activity.

Role of nerve growth factor in the expression of trkA mRNA in cultured embryonic rat basal forebrain cholinergic neurons

Using a quantitative reverse transcription-polymerase chain reaction (RT-PCR), we studied the regulation of trkA mRNA expression in serum-free, cultured basal forebrain neurons from 17-day fetal rats. Besides increasing choline acetyltransferase (ChAT) activities, nerve growth factor (NGF) strikingly induced trkA gene expression in a time- and NGF concentration-dependent manner. Therefore, NGF might play a critical role in trkA gene expression during the development of basal forebrain cholinergic neurons. Furthermore, to investigate whether this up-regulation is connected with the trophic effects on basal forebrain cholinergic neurons, we examined the effects of some other neurotrophic agents (BDNF, NT-3, bFGF, CNTF, and 40 mM KCI) upon ChAT activity and trkA gene expression. Some neurotrophic factors increased ChAT activities to the same degree as NGF, whereas they did not stimulate trkA mRNA expression so potently. NT-3 plus K252b promotes the tyrosine phosphorylation of TrkA in PC12 cells and increases ChAT activity in cultured basal forebrain cholinergic neurons like NGF (Knusel et al., J Neurochem 59: 715-722, 1992). We found that NT-3 plus K252b upregulated the level of trkA mRNA. These results suggested that the expression of trkA mRNA is regulated directly by its specific ligand NGF, rather than neurotrophic effects upon basal forebrain cholinergic neurons and that the up-regulation is connected to a molecular event initiated by the binding of NGF to the TrkA receptor.

A comprehensive analysis of the distribution of FGF-2 and FGFR1 in the rat brain

We have examined the cellular distribution of both FGF-2 and FGFR1 immunoreactivity and their mRNAs throughout the normal adult rat brain in order to reconcile numerous disparate findings in the published literature. The results confirm a widespread distribution of FGF-2 and FGFR1 in the rat brain, and different regions express distinct patterns of FGF-2 and FGFR1 mRNA and protein: neuronal and non-neuronal cells show different subcellular distributions that vary according to the area where they are located. The intensity of the staining and hybridization also varies according to the loci examined and the cell type involved. Astrocytes contain the highest levels of FGF-2 and FGFR1 mRNAs, and characteristically, possess high levels of immunoreactive FGF-2 within the nucleus. Amongst non-neuronal cells, oligodendrocytes do not synthesize or contain significant levels of FGF-2 immunoreactivity however, they do express FGFR1 mRNA. In these cells, immunoreactive FGFR1 is mainly associated with the myelin sheaths of neuronal fibers. In ventricular systems, ependymal cells synthesize and contain immunoreactive FGFR1. In contrast, only cells lining the lateral wall of the IIIrd ventricle express FGF-2 mRNA. Subependymal cells contain high levels of both FGF-2 and FGFR1 immunoreactivity. Neurons express low levels of FGF-2 mRNA and immunoreactive FGF-2 is localized predominantly to the perikaryon. However, selected populations of neurons, such as CA2 field of the hippocampus, show high levels of FGF-2 mRNA, in which the nucleus is strongly immunopositive. Similarly, high levels of FGFR1 mRNA are localized to select populations of neurons (e.g. amygdala). FGFR1 immunoreactivity is mainly associated with myelinated fiber tracts (e.g. striatum), and some neurons show immunoreactivity in the perikaryon (e.g. hippocampus), the nucleus (e.g. mesencephalic trigeminal nucleus), or in axonal projections (e.g. hypothalamus). Remarkably, in many of the areas studied, FGF-2 and FGFR1 mRNA and/or their translated protein do not co-localize in neurons (e.g. neo-cortices) or even in the same regions of the brain (e.g. substantia nigra). In other instances, mRNAs for both FGF-2 and FGFR1 colocalize (e.g. supraoptic nucleus). The brain, in contrast to peripheral tissues, contains high levels of FGF-2 and actively expresses its gene under normal physiological conditions. The highly specific anatomical distribution of immunoreactive FGF-2 in neuronal and non-neuronal brain cells, supports the notion that it plays a multifunctional role in the CNS under normal physiology. By correlating the localization and the synthesis of FGF-2 and one of its high affinity receptors, FGFR1, in the CNS, it should be possible to obtain a better understanding of the roles of FGF-2 in normal and pathological conditions.

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.

Increased immunoreactivities for the basic fibroblast growth factor and its receptor in astrocytes at the site of cerebral lesions and oedematous change in SHR

1. To obtain information about changes of basic fibroblast growth factor (bFGF) in the brain in chronic hypertension, we immunohistochemically studied the distribution and level of bFGF and its receptor in the brain of stroke-prone spontaneously hypertensive rats (SHRSP). 2. In the control normotensive rats, immunoreactivity for bFGF was demonstrated in nerve cells, while there was almost no reactivity in astrocytes. 3. In SHRSP, there was a marked immunoreactivity in the densely accumulated reactive cells, particularly astrocytes, in and around cerebral cortical lesions. Slightly increased reaction for bFGF was found in the nerve cells around lesions. Astrocytes in the subcortical white matter on both ipsi- and contralateral sides of the cortical lesion also showed immunoreactivity for bFGF. The location of increased bFGF expression in SHRSP corresponded very well with the site of extravasated plasma fluid demonstrated by anti-fibrinogen antibody. Electron microscopically, bFGF was shown in astrocytes along the rough endoplasmic reticulum suggesting the growth factor to be produced in the cells and not to be taken up from the surroundings. Expression of FGF-receptor was also demonstrated in reactive astrocytes in the oedematous cortical portion around lesion and in the oedematous subcortical white matter. 4. These findings indicate the possibility that oedema and the simultaneously generated free radicals or some extravasated plasma components express bFGF in astrocytes and probably in nerve cells as well as FGF-receptor in astrocytes, and that the thus expressed bFGF and its receptor play some role in the sequence of developmental events of hypertensive cerebral lesions.

Delayed treatment with intravenous basic fibroblast growth factor reduces infarct size following permanent focal cerebral ischemia in rats

Basic fibroblast growth factor (bFGF) is a polypeptide that supports the survival of brain cells (including neurons, glia, and endothelia) and protects neurons against a number of toxins and insults in vitro. This factor is also a potent dilator of cerebral pial arterioles in vivo. In previous studies, we found that intraventricularly administered bFGF reduced infarct volume in a model of focal cerebral ischemia in rats. In the current study, bFGF (45 micrograms/kg/h) in vehicle, or vehicle alone, was infused intravenously for 3 h, beginning at 30 min after permanent middle cerebral artery occlusion by intraluminal suture in mature Sprague-Dawley rats. After 24 h, neurological deficit (as assessed by a 0- to 5-point scale, with 5 = most severe) was 2.6 +/- 1.0 in vehicle-treated and 1.5 +/- 1.3 in bFGF-treated rats (mean +/- SD; N = 12 vs. 11; p = 0.009). Infarct volume was 297 +/- 65 mm3 in vehicle- and 143 +/- 135 mm3 in bFGF-treated animals (p = 0.002). During infusion, there was a modest decrease in mean arterial blood pressure but no changes in arterial blood gases or core or brain temperature in bFGF-treated rats. Autoradiography following intravenous administration of 111In-labeled bFGF showed that labeled bFGF crossed the damaged blood-brain barrier to enter the ischemic (but not the nonischemic) hemisphere. Whether the infarct-reducing effects of bFGF depend on intraparenchymal or intravascular mechanisms requires further study.

FGF inhibits neurite outgrowth over monolayers of astrocytes and fibroblasts expressing transfected cell adhesion molecules

We have cultured cerebellar neurons on monolayers of cortical astrocytes in control medium or medium containing recombinant basic fibroblast growth factor (FGF). FGF was found to inhibit neurite outgrowth, with a significant effect seen at 0.5 ng/ml and a maximal effect at 10 ng/ml. FGF increased the production of arachidonic acid (AA) in cerebellar neurons, and when added directly to cultures or generated endogenously via activation of phospholipase A2 using melittin, this second messenger could mimic the inhibitory effect of FGF. FGF and AA could also specifically inhibit neurite outgrowth stimulated by three cell adhesion molecules (NCAM, N-cadherin and L1) expressed in transfected fibroblasts, or in the case of L1 bound to a tissue culture substratum. These data demonstrate that, in certain cellular contexts, FGF can act as an inhibitory cue for axonal growth and that arachidonic acid is the second messenger responsible for this activity. We discuss the possibility that arachidonic acid inhibits neurite outgrowth by desensitising the second messenger pathway underlying neuronal responsiveness to cell adhesion molecules.

Role of basic fibroblast growth factor in the regulation of rat basilar artery tone in vivo

Using the cranial window method, we investigated the effect of basic fibroblast growth factor (bFGF) on the diameter of the rat basilar artery in vivo. bFGF (5-200 ng/ml) caused significant vasodilation in a dose-dependent manner with the maximal effect (119% of baseline diameter) at 200 ng/ml. Vasodilation was not observed when the basilar artery was treated with heat-inactivated bFGF or bFGF preincubated with bFGF-neutralizing monoclonal antibody. Moreover, bFGF-induced vasodilation was suppressed significantly by coadministration of the nitric oxide (NO) synthase inhibitor, NG-nitro-L-arginine methyl ester (L-NAME). In contrast, NG-nitro-D-arginine methyl ester (D-NAME), which is the isomer of L-NAME, exerted no influence on bFGF-induced vasodilation. These findings suggest that the dilatation by bFGF of the rat basilar artery is mediated by NO, and that bFGF plays an important role in the regulation not only of the anterior circulation as previously described but also of the posterior circulation in the brain.

Neurotrophic factors in central nervous system trauma

Although regeneration of injured neurons does not occur after trauma in the central nervous system (CNS), there is often significant recovery of functional capacity with time. Little is currently known about the molecular basis for such recovery, but the increased trophic activity in injured CNS tissue and the known properties of neurotrophic factors in neuronal growth and maintenance suggest that these polypeptides are probably involved in recovery of function. Members of the neurotrophin family, including nerve growth factor (NGF), brain-derived neurotrophic factors (BDNF), and neurotrophin 3 (NT-3), are capable of supporting survival of injured CNS neurons both in vitro and in vivo. They also stimulate neurite outgrowth, needed for reorganization of the injured CNS, and the expression of key enzymes for neurotransmitter synthesis that may need to be upregulated to compensate for reduced innervation. The effects of the neurotrophins are mediated through specific high affinity trk receptors (trk A, B, C) as well as a common low affinity receptor designated p75NGFR. Another class of neurotrophic polypeptides also provides candidate recovery-promoting molecules, the heparin-binding growth factors' acidic and basic fibroblast growth factor (aFGF, bFGF). FGFs not only sustain survival of injured neurons but also stimulate revascularization and certain glial responses to injury. Both the neurotrophins and the FGFs, as well as their respective receptors, have been shown to be upregulated after experimental CNS injury. Further, administration of neurotrophins or FGF has been shown to reduce the effects of experimental injury induced by axotomy, excitotoxins, and certain other neurotoxins. The cellular basis for the potential therapeutic use of neurotrophic molecules is discussed as well as new strategies to increase neurotrophic activity after CNS trauma based on the recently obtained information on pharmacological and molecular control of the expression of these genes.

Acidic FGF induces NGF and its mRNA in the injured neocortex of adult animals

Recently we reported that human recombinant acidic fibroblast growth factor (aFGF) is capable of preventing degeneration of nucleus basalis magnocellularis neurons in vivo and inducing growth of astrocytes in vitro. In the present study, the effects of aFGF on the concentration of nerve growth factor (NGF) and its messenger RNA were investigated in the rat cerebral cortex following unilateral cortical infarction. Lesioned animals exhibited a significant increase of NGF in the remaining cortex ipsilateral to the lesion. After combining cortical lesion with intracerebroventricular application of aFGF (12 micrograms/day for 7 days), we observed an 8-fold increase in the NGF concentration and a marked increase in the level of steady state NGF mRNA relative to controls ipsilaterally, and a less pronounced aFGF effect in the contralateral cerebral cortex. These results support the hypothesis that the neurotrophic effects previously shown for aFGF and basic FGF (bFGF) in neurotrophin-sensitive neurons is mediated by inducing increased production of NGF within the injured central nervous system (CNS) of adult animals.

Neurodegeneration mediated by glutamate and beta-amyloid peptide: a comparison and possible interaction

In Alzheimer's disease, abnormal extracellular accumulations of beta-amyloid (a major component of the senile plaques) and of the excitatory amino acid glutamate are both thought to be associated with degeneration of nerve cells. In the present study, using cultured cortical or hippocampal neurons as an in vitro model, we compared the effects of various factors influencing neurodegeneration mediated by glutamate or by beta-amyloid peptide (A beta). We also asked the question: does long-term treatment with sublethal doses of A beta-(25-35) potentiate glutamate-mediated excitotoxicity? Neuronal cell death was quantified using the lactate dehydrogenase (LDH) method. Since extracellular LDH remains stable for days, the magnitude of relative afflux of LDH correlates in a linear fashion with the number of damaged neurons in cultures. When applied singly, both glutamate (for 15 min) and A beta-(25-35) or its parent peptide A beta-(1-40) (continuously) produced a dose-dependent neuronal degeneration. In the case of glutamate, the half-maximal effects were observed at about 0.08 mM glutamate for both cerebral cortical and hippocampal neurons (cultured for 13 days in vitro, DIV). The effect of A beta-(25-35) was also time-dependent, while neurons grown in a chemically defined medium showed relatively greater susceptibility to A beta-(25-35) than those cultured in a serum-containing medium. These differential effects were not related to the presence of different numbers of glial cells in the cultures. Treatment with different doses of the antimitotic inhibitor, cytosine arabinoside, for 24 h (6-7 DIV) produced at 13 DIV cortical neuronal cultures with varying numbers of astrocytes, as determined by the astrocyte-specific enzyme glutamine synthetase. The presence of astrocytes decreased the toxicity of glutamate for neurons. The modulation was due to uptake of glutamate by astrocytes, thereby reducing its effective concentration, as the effect was seen at 0.1 mM and not at 10 mM glutamate. Incorporation of an NMDA receptor mediated Ca2+ ion channel blocker, MK-801, together with glutamate completely inhibited degeneration of cortical neurons, and pretreatment of cultures with basic fibroblast growth factor for 2 days did so partially. However, these compounds had no effect on neurotoxicity mediated by A beta-(25-35). Lastly, the effect of glutamate interacted with that of A beta-(25-35). Pretreatment of cortical neurons for 2 days with 10 microM A beta-(25-35) by itself had no appreciable effect, but it potentiated significantly the degeneration of these neurons mediated by glutamate.(ABSTRACT TRUNCATED AT 400 WORDS)

Chronic ethanol administration decreases brain-derived neurotrophic factor gene expression in the rat hippocampus

We have previously demonstrated that chronic ethanol consumption decreases neurotrophic activity in hippocampal extracts, as assessed by a chick dorsal root ganglia bioassay, but has no effect on hippocampal NGF mRNA or NGF protein levels. We presently report that hippocampal mRNAs encoding neurotrophin-3 and basic fibroblast growth factor are also unaffected. However, in contrast, brain-derived neurotrophic factor mRNA is reliably decreased, thereby suggesting that ethanol-induced damage of the septohippocampal system may at least partially result from an ethanol-induced decrease in hippocampal brain-derived neurotrophic factor expression.

Promoter activity of the gene encoding the beta-amyloid precursor protein is up-regulated by growth factors, phorbol ester, retinoic acid and interleukin-1

Abnormalities in gene regulation of the beta-amyloid precursor protein (beta APP) might be an important factor in the neuropathology of Alzheimer's disease. We analyzed the effects of nerve growth factor (NGF), basic fibroblast growth factor (bFGF), phorbol 12-myristate 13-acetate (PMA), interleukin-1 (IL-1) and retinoic acid (RA) on promoter activity of the beta APP gene. To investigate the effect of these factors on promoter activity, we used two fusion plasmids which contain sequences of -489 and -415 base pairs (bp), respectively, from the transcription start site of the beta APP gene. The truncated regions of the promoter wer linked upstream to a reporter gene, chloramphenicol acetyl transferase (CAT). Promoter activity was tested by transient transfection of fusion plasmids in PC12 cells using the electroporation method (960 microF at 350 V). We report that the treatment of PC12 cells with either NGF, bFGF, PMA, IL-1 or RA stimulated the activity of the beta APP promoter. The treatment of cells with either NGF or bFGF resulted in a higher degree of stimulation in the basal level of promoter activity than when cells were treated with either PMA, IL-1 or RA. The deletion of sequences between -489 to -416 bp had no significant effect on promoter activity. The treatment of cells with these factors for a duration of 4 days prior to transfection with the plasmids is necessary for the stimulatory effect. The cells that were only treated with any of these factors after transfection showed no significant change in the basal level of promoter activity. We conclude that certain growth factors and a cytokine could enhance the basal level of promoter activity of the beta APP gene, suggesting a possible participation of a growth-factor(s)-mediated transcription element in the control of gene expression of beta APP.

GABAergic deafferentation hypothesis of brain aging and Alzheimer's disease; pharmacologic profile of the benzodiazepine antagonist, flumazenil

Recent experiments have shown that: 1) A chronic 10 month daily administration to rats of the benzodiazepine (BDZ) receptor antagonist, flumazenil (FL; 4 mg/kg in drinking water), from the age of 13 through 22 months, significantly retarded the age-related loss of cognitive functions, as ascertained by the radial arm maze tests conducted two months after FL withdrawal. 2) An equal number of 8 rats died in the control and FL-treated group before the behavioral tests were completed and the animals were sacrificed; the life span of the FL-treated 8 rats equaled 24.0 (+/- 0.6 SEM) months, while that of the control 8 rats equaled 22.3 months (+/- 0.7 SEM), and the group difference was marginally significant (p = 0.04 Mann-Whitney test). 3) In rats sacrificed 3 months after FL withdrawal and behavioral testing, the protective action of FL, relative to age-matched controls, was revealed by a significant reduction in the age-related loss of neurons in the hippocampal formation. 4) In the time period of 3 months between the drug withdrawal and sacrificing of the animals, stress experienced by the aging rats during behavioral testing, related to excessive daily handling of the animals and partial food deprivation to motivate them to perform in the radial arm maze, apparently had excitotoxic effects on the hippocampal neurons, as indexed by the presence of 30% neurons in a state of moderate pyknosis found both in the FL group and the age-matched controls. In the 6 months "young" control group, the number of pyknotic neurons equaled only 3.5%. It was concluded that the drug withdrawal and stress of behavioral testing unleashed the previously FL-controlled age-related degeneration. On the basis of these results and the literature, showing that the tone of the GABAergic system increases with age, and particularly in Alzheimer's disease (AD), the hypothesis of brain aging was formulated. It postulates that in mammals, with growing age, and prematurely in humans with AD, the increasing tone of the BDZ/GABAergic system interferes with antero- and retrograde axonal transport through a chronic depolarizing block of preterminal axon varicosities of the ascending aminergic and cholinergic/peptidergic systems, which are indispensable for normal metabolic/trophic glial-neuronal relationships. Such a state leads to discrete anatomic deafferentation of forebrain systems, and particularly of the neocortex, where block of the anterograde axonal transport results in induction of the cortical mRNA responsible for synthesis of the beta-amyloid precursor protein (beta APP). The simultaneous block of retrograde transport from chronically depolarized preterminal axon varicosities may account for toxic accumulation in cortex of the nerve growth factor (NGF) and other trophins, without which the basal forebrain cholinergic neurons degenerate. The general pharmacologic profile of FL has been discussed on the basis of FL administration to animals and healthy and diseased humans. This profile shows that FL: 1) increases brain metabolic functions; 2) reduces emotional responses, thereby stabilizing the functions of the autonomic system in both humans and animals challenged by adverse environmental stimuli; 3) improves cognitive and coordinated motor functions in both humans and animals; 4) uniquely combines anxiolytic, vigilance and cognitive enhancing, i.e. nootropic, properties, which may, in part, stem from FL-induced emotional imperturbability (ataraxy); 5) facilitates habituation of healthy humans and animals to novel but inconsequential environmental stimuli, and promotes non-aggressive interactions among animals; 6) in single i.v. doses, and administered chronically to humans, FL has antiepileptic actions in the Lennox-Gastaut syndrome and other forms of epilepsy characterized by "spike-and-dome" EEG patterns; these actions are likely to depend on FL's disinhibition of the serotonin system; 7) administered in single i.v...

Localization of fibroblast growth factor-9 mRNA in the rat brain

We examined the localization of fibroblast growth factor-9 (FGF-9) mRNA in the rat brain by in situ hybridization. FGF-9 mRNA was moderately or weakly expressed in widespread regions including the olfactory bulb, caudate putamen, cerebral cortex, hippocampus, thalamus, hypothalamus, midbrain, brainstem and cerebellum. However, FGF-9 mRNA was also strongly expressed in several specific nuclei including the red nucleus and oculomotor nucleus in the midbrain, the vestibular nucleus and facial nucleus in the brainstem and the medial cerebellar nucleus, interposed cerebellar nucleus and lateral cerebellar nucleus in the cerebellum. The cellular localization of FGF-9 mRNA indicated that the mRNA in the rat brain was expressed preferentially in neurons, although FGF-9 was originally isolated from human glioma cells. The localization profile of FGF-9 mRNA is different from those of aFGF, bFGF and FGF-5 mRNAs reported previously. The present findings indicate that FGF-9 has a unique role in the brain.

Ciliary neurotrophic factor supports p75NGFR-immunoreactive non-cholinergic, but not cholinergic, developing septal neurons in vitro

Ciliary neurotrophic factor is known to exert both survival and differentiative actions on a number of neuronal populations of the peripheral and central nervous systems. In this study we have compared the trophic effects of ciliary neurotrophic factor and nerve growth factor on developing septal neurons of the rat in vitro. Fetal septal neurons were grown in vitro under glass coverslips in sandwich culture. Septal cultures grown for 14 days in the continual presence of nerve growth factor contain a population of cholinergic neurons that stain intensely for the low-affinity nerve growth factor receptor (p75NGFR), choline acetyltransferase and acetylcholinesterase. Without added nerve growth factor, few neurons stain for these markers. Ciliary neurotrophic factor addition for 14 days from plating in the absence of exogenous nerve growth factor results in the appearance of a population of neurons that stains for p75NGFR. This population is similar in number to that seen in nerve growth factor-treated cultures but is not immunoreactive for choline acetyltransferase and is significantly smaller in mean cross-sectional area. Delayed addition of nerve growth factor to ciliary neurotrophic factor-supported cultures at 14 days for a further seven days fails to induce choline acetyltransferase immunoreactivity in these p75NGFR-positive septal neurons. In cultures grown in the continual presence of nerve growth factor from plating, removal of nerve growth factor and addition of nerve growth factor antibodies at 14 days results in the death of over 80% of the cholinergic neurons after a further four days. Addition of ciliary neurotrophic factor during the period of nerve growth factor withdrawal appears to preserve a p75NGFR-positive, choline acetyltransferase-negative neuronal population. However, seven day re-addition of nerve growth factor to ciliary neurotrophic factor-treated, nerve growth factor-withdrawn cultures fails to induce choline acetyltransferase immunoreactivity in the ciliary neurotrophic factor-supported p75NGFR-positive septal neurons. Simultaneous treatment of cultures with both ciliary neurotrophic factor and nerve growth factor for 14 days from plating approximately doubles the number of p75NGFR-positive neurons relative to cultures treated with either ciliary neurotrophic factor or nerve growth factor alone, but the number of choline acetyltransferase-positive neurons in these cultures is not significantly greater than that found in cultures treated solely with nerve growth factor. These results suggest that ciliary neurotrophic factor does not support the survival and differentiation of developing septal cholinergic neurons in vitro, but can support the development of a p75NGFR-immunoreactive population of non-cholinergic septal neurons.

Central action of basic fibroblast growth factor on ingestive behaviour in mice

Intracerebroventricular (ICV) infusion of basic fibroblast growth factor (FGF-2) at 50 ng/h for 5 days in male BALB/c mice suppressed the daily intakes of water and food (n = 4). Intakes were reduced on the second day, and were suppressed until the second day after stopping the infusion. The same infusion for 4 days had little effect on the high intakes of 0.3 M NaCl solution and water induced by prolonged ICV infusion of angiotensin II, or the daily food intake in these experiments (n = 7). However, the same infusion for 3-4 days reduced the increased intake of NaCl solution in Na-depleted mice (n = 8), reduced the increased water intake of water-restricted mice (n = 6 or n = 7), and reduced daily food intake in both experiments. Ventricular enlargement was noted in mice at the end of these experiments but, for reasons advanced, did not appear to account for the responses. The results indicate that FGF-2 may have an inhibitory role in these ingestive behaviours.

Dose-response comparison of recombinant human nerve growth factor and recombinant human basic fibroblast growth factor in the fimbria fornix model of acute cholinergic degeneration

Both nerve growth factor (NGF) and basic fibroblast growth factor (bFGF) have been proposed for the treatment of Alzheimer's disease. This study describes a comparative, dose-response analysis of recombinant human (rh)NGF and rhbFGF in a rat unilateral fimbria-fornix model of acute cholinergic neuronal degeneration. Doses for rhNGF were 0.6, 6, 60, 600 and 1,800 ng/rat/day and for rhbFGF were 600, 1,800, 3,000 and 6,000 ng/rat/day, delivered for 4 weeks. The number of surviving septal cholinergic neurons was evaluated using ChAT immunohistochemistry. In control animals, the number of ChAT-positive neurons remaining on the lesioned side was between 22 and 18% compared to the non-lesioned side. Infusion with either neurotrophic factor increased the number of ChAT-positive neurons on the lesioned side in a dose-dependent manner. The maximal response to rhbFGF peaked at 3,000 ng/rat/day with a cell savings of 47%. However, there was evidence of neuropathological changes associated with rhbFGF. In contrast, rhNGF produced a maximal response with an infusion of 600 ng rhNGF/rat/day and a cell savings of 70% and no evidence of neuropathology, indicating that rhNGF was better tolerated and more efficacious than rhbFGF.