Endogenous FGF-2 is important for cholinergic sprouting in the denervated hippocampus

Basal forebrain cholinergic signalling: development, connectivity and roles in cognition

Acetylcholine plays an essential role in fundamental aspects of cognition. Studies that have mapped the activity and functional connectivity of cholinergic neurons have shown that the axons of basal forebrain cholinergic neurons innervate the pallium with far more topographical and functional organization than was historically appreciated. Together with the results of studies using new probes that allow release of acetylcholine to be detected with high spatial and temporal resolution, these findings have implicated cholinergic networks in 'binding' diverse behaviours that contribute to cognition. Here, we review recent findings on the developmental origins, connectivity and function of cholinergic neurons, and explore the participation of cholinergic signalling in the encoding of cognition-related behaviours.

Gold nanoparticle-enhanced X-ray microtomography of the rodent reveals region-specific cerebrospinal fluid circulation in the brain

Cerebrospinal fluid (CSF) is essential for the development and function of the central nervous system (CNS). However, the brain and its interstitium have largely been thought of as a single entity through which CSF circulates, and it is not known whether specific cell populations within the CNS preferentially interact with the CSF. Here, we develop a technique for CSF tracking, gold nanoparticle-enhanced X-ray microtomography, to achieve micrometer-scale resolution visualization of CSF circulation patterns during development. Using this method and subsequent histological analysis in rodents, we identify previously uncharacterized CSF pathways from the subarachnoid space (particularly the basal cisterns) that mediate CSF-parenchymal interactions involving 24 functional-anatomic cell groupings in the brain and spinal cord. CSF distribution to these areas is largely restricted to early development and is altered in posthemorrhagic hydrocephalus. Our study also presents particle size-dependent CSF circulation patterns through the CNS including interaction between neurons and small CSF tracers, but not large CSF tracers. These findings have implications for understanding the biological basis of normal brain development and the pathogenesis of a broad range of disease states, including hydrocephalus.

FGF-2 Attenuates Neuronal Apoptosis via FGFR3/PI3k/Akt Signaling Pathway After Subarachnoid Hemorrhage

Neuronal apoptosis is a common and critical pathology following subarachnoid hemorrhage (SAH). We investigated the anti-apoptotic property of fibroblast growth factor (FGF)-2 after SAH in rats. A total of 289 rats underwent endovascular perforation to induce SAH or sham operation. Three dosages (3, 9, or 27 μg) of recombinant FGF-2 (rFGF-2) or vehicle was administered intranasally to rats 30 min after SAH induction. The pan-FGF receptor (FGFR) inhibitor PD173074 or vehicle was administered intracerebroventricularly (i.c.v.) 1 h before modeling, in addition to rFGF-2 treatment. Small interfering ribonucleic acid (siRNA) for FGFR1 and FGFR3 or scrambled siRNA was administered i.c.v. 48 h before SAH induction in addition to rFGF-2 treatment. Anti-FGF-2 neutralizing antibody or normal mouse immunoglobulin G (IgG) was administered i.c.v. 1 h before SAH model. Neurobehavioral tests, SAH severity, brain water content, immunofluorescence, Fluoro-Jade C, TUNEL staining, and western blot were evaluated. The expression of FGF-2, FGFR1, and FGFR3 increased after SAH. FGFR1 and FGFR3 were expressed in the neurons. Nine micrograms of FGF-2 alleviated neurological impairments, brain edema, and neuronal apoptosis following SAH. A rFGF-2 treatment improved motor skill learning and spatial memory and increased the number of surviving neurons postinjury to 28 days after SAH. PD173074 abolished the anti-apoptotic effects of rFGF-2 via suppression of the expression of PI3k, phosphorylated Akt (p-Akt), and Bcl-2 leading to enhancement of the expression of Bax. FGFR3 siRNA worsened neurobehavioral function and suppressed the expression of PI3k, p-Akt, and Bcl-2 rather than FGFR1 siRNA in SAH rats treated with rFGF-2. Anti-FGF-2 neutralizing antibody suppressed the expression of PI3k and p-Akt after SAH. FGF-2 may be a promising therapy to reduce post-SAH neuronal apoptosis via activation of the FGFR3/PI3k/Akt signaling pathway.

Fibroblast growth factors in the management of spinal cord injury

Spinal cord injury (SCI) possesses a significant health and economic burden worldwide. Traumatic SCI is a devastating condition that evolves through two successive stages. Throughout each of these stages, disturbances in ionic homeostasis, local oedema, ischaemia, focal haemorrhage, free radicals stress and inflammatory response were observed. Although there are no fully restorative cures available for SCI patients, various molecular, cellular and rehabilitative therapies, such as limiting local inflammation, preventing secondary cell death and enhancing the plasticity of local circuits in the spinal cord, were described. Current preclinical studies have showed that fibroblast growth factors (FGFs) alone or combination therapies utilizing cell transplantation and biomaterial scaffolds are proven effective for treating SCI in animal models. More importantly, some studies further demonstrated a paucity of clinical transfer usage to promote functional recovery of numerous patients with SCI. In this review, we focus on the therapeutic capacity and pitfalls of the FGF family and its clinical application for treating SCI, including the signalling component of the FGF pathway and the role in the central nervous system, the pathophysiology of SCI and the targets for FGF treatment. We also discuss the challenges and potential for the clinical translation of FGF-based approaches into treatments for SCI.

FGF1 - a new weapon to control type 2 diabetes mellitus

A hypercaloric diet combined with a sedentary lifestyle is a major risk factor for the development of insulin resistance, type 2 diabetes mellitus (T2DM) and associated comorbidities. Standard treatment for T2DM begins with lifestyle modification, and includes oral medications and insulin therapy to compensate for progressive β-cell failure. However, current pharmaceutical options for T2DM are limited in that they do not maintain stable, durable glucose control without the need for treatment intensification. Furthermore, each medication is associated with adverse effects, which range from hypoglycaemia to weight gain or bone loss. Unexpectedly, fibroblast growth factor 1 (FGF1) and its low mitogenic variants have emerged as potentially safe candidates for restoring euglycaemia, without causing overt adverse effects. In particular, a single peripheral injection of FGF1 can lower glucose to normal levels within hours, without the risk of hypoglycaemia. Similarly, a single intracerebroventricular injection of FGF1 can induce long-lasting remission of the diabetic phenotype. This Review discusses potential mechanisms by which centrally administered FGF1 improves central glucose-sensing and peripheral glucose uptake in a sustained manner. Specifically, we explore the potential crosstalk between FGF1 and glucose-sensing neuronal circuits, hypothalamic neural stem cells and synaptic plasticity. Finally, we highlight therapeutic considerations of FGF1 and compare its metabolic actions with FGF15 (rodents), FGF19 (humans) and FGF21.

Expression and Functions of Fibroblast Growth Factor 2 (FGF-2) in Hippocampal Formation

Among the 23 members of the fibroblast growth factor (FGF) family, FGF-2 is the most abundant one in the central nervous system. Its impact on neural cells has been profoundly investigated by in vitro and in vivo studies as well as by gene knockout analyses during the past 2 decades. Key functions of FGF-2 in the nervous system include roles in neurogenesis, promotion of axonal growth, differentiation in development, and maintenance and plasticity in adulthood. From a clinical perspective, its prominent role for the maintenance of lesioned neurons (e.g., ischemia and following transection of fiber tracts) is of particular relevance. In the unlesioned brain, FGF-2 is involved in synaptic plasticity and processes attributed to learning and memory. The focus of this review is on the expression of FGF-2 and its receptors in the hippocampal formation and the physiological and pathophysiological roles of FGF-2 in this region during development and adulthood.

Local cell proliferation upon enucleation in Direct Retinal Brain Targets in the Visual system of the Adult Mouse

In this study we used incorporation of the DNA synthesis marker 5-bromo-2′-deoxyuridine or BrdU to visualize cell proliferation in the visual system of the adult mouse as a response to monocular enucleation. We detected new BrdU-labeled cells in different subcortical retinal target regions and we established a specific time frame in which this cell proliferation occurred. By performing immunofluorescent double stainings for BrdU and different vascular (glucose transporter type 1, collagen type IV), glial (thymosin β4, glial fibrillary acidic protein) and neuronal (Neuronal Nuclei, doublecortin) markers, we identified these proliferating cells as activated microglia. Additional immunohistochemical stainings for thymosin β4 and glial fibrillary acidic protein also revealed reactive astrocytes in the different retinorecipient nuclei and allowed us to delineate a time frame for microglial and astroglial activation. A PCR array experiment further showed increased levels of cytokines, chemokines, growth factors and enzymes that play an important role in microglial-astroglial communication during the glial activation process in response to the deafferentation.

Structural reorganization of the dentate gyrus following entorhinal denervation: species differences between rat and mouse

Deafferentation of the dentate gyrus by unilateral entorhinal cortex lesion or unilateral perforant pathway transection is a classical model to study the response of the central nervous system (CNS) to denervation. This model has been extensively characterized in the rat to clarify mechanisms underlying denervation-induced gliosis, transneuronal degeneration of denervated neurons, and collateral sprouting of surviving axons. As a result, candidate molecules have been identified which could regulate these changes, but a causal link between these molecules and the postlesional changes has not yet been demonstrated. To this end, mutant mice are currently studied by many groups. A tacit assumption is that data from the rat can be generalized to the mouse, and fundamental species differences in hippocampal architecture and the fiber systems involved in sprouting are often ignored. In this review, we will (1) provide an overview of some of the basics and technical aspects of the entorhinal denervation model, (2) identify anatomical species differences between rats and mice and will point out their relevance for the axonal reorganization process, (3) describe glial and local inflammatory changes, (4) consider transneuronal changes of denervated dentate neurons and the potential role of reactive glia in this context, and (5) summarize the differences in the reorganization of the dentate gyrus between the two species. Finally, we will discuss the use of the entorhinal denervation model in mutant mice.

Functional restoration using basic fibroblast growth factor (bFGF) infusion in Kainic acid induced cognitive dysfunction in rat: neurobehavioural and neurochemical studies

Neurogenesis occurs in dentate gyrus of adult hippocampus under the influence of various mitogenic factors. Growth factors besides instigating the proliferation of neuronal progenitor cells (NPCs) in dentate gyrus, also supports their differentiation to cholinergic neurons. In the present study, an attempt has been made to investigate the neurotrophic effect of bFGF in Kainic acid (KA) induced cognitive dysfunction in rats. Stereotaxic lesioning using (KA) was performed in hippocampal CA3 region of rat's brain. Four-weeks post lesioning rats were assessed for impairment in learning and memory using Y maze followed by bFGF infusion in dentate gyrus region. The recovery was evaluated after bFGF infusion using neurochemical, neurobehavioural and immunohistochemical approaches and compared with lesioned group. Significant impairment in learning and memory (P < 0.01) observed in lesioned animals, four weeks post lesioning exhibited significant restoration (P < 0.001) following bFGF infusion twice at one and four week post lesion. The bFGF infused animals exhibited recovery in hippocampus cholinergic (76%)/ dopaminergic (46%) receptor binding and enhanced Choline acetyltransferase (ChAT) immunoreactivity in CA3 region. The results suggest restorative potential of bFGF in cognitive dysfunctions, possibly due to mitogenic effect on dentate gyrus neurogenic area leading to generation and migration of newer cholinergic neurons.

Effects on neurite outgrowth and cell survival of a secreted fibroblast growth factor binding protein upregulated during spinal cord injury

The fibroblast growth factor binding protein (FGF-BP; GenBank accession no. NP_005121) is a secreted protein that mobilizes FGFs from the extracellular matrix, protects them from degradation, and enhances their biological activity. Several previous studies reported that FGF-BP is an early response gene upregulated during tissue repair processes including wound healing and atherogenesis. In this study we analyzed whether FGF-BP expression was impacted by spinal cord injury and could have an effect on neuronal cell viability. Immunohistochemical and in situ hybridization studies revealed a dramatic upregulation of FGF-BP protein and mRNA levels following unilateral hemisection and contusion injury of adult rat spinal cord. In spinal cord sections of laminectomized rats, increased FGF-BP expression was observed in the fibers and cell bodies ipsilateral to the lesion site but was absent in the uninjured spinal cord tissue contralateral to the lesion. Increased expression of FGF-BP was observed at all postinjury time points, examined with peak levels occurring at day 4, a time when injury-induced increased levels of FGF2 have also been reported to be maximal. Moreover, using PC12 cells as a neuronal model, we observed that exogenous FGF-BP increased the capacity of FGF2 to stimulate neurite outgrowth and to increase cell survival. At the molecular level, FGF-BP enhanced FGF2-induced protein tyrosine phosphorylation and AKT/PKB activation. Collectively, these results suggest that FGF-BP is an early response gene after spinal cord injury and that its upregulation in regenerating spinal cord tissue may provide a molecular mechanism for enhancing the initial FGF2-mediated neurotrophic effects occurring after such tissue damage.

Collateral Sprouting as a Target for Improved Function after Spinal Cord Injury

Functional recovery after spinal cord injury might be improved by enhancing the extent of innervation through stimulation of collateral sprouting, which is the growth of a new axon along the shaft of a non-injured axon. This review discusses (1) the spontaneous collateral sprouting of uninjured motor and sensory systems that has been shown after spinal cord injury in animal models, (2) experimental treatment strategies that are being developed to enhance collateral sprouting in motor systems and to reduce sensory sprouting which is associated with autonomic dysreflexia and pain, and (3) cell-surface and intracellular signaling mechanisms that are known to regulate axonal branching. The conclusion is that relatively little is known about collateral sprouting in adult mammals after spinal cord injury but that it may contribute to spontaneous functional motor recovery and causes sensory dysfunction. There is some promising data in rodents that collateral sprouting can be modulated for improved function, but the applicability to primates and relevance to human spinal cord injury remains to be determined.

Neuronal vulnerability in transgenic mice expressing an inducible dominant-negative FGF receptor

Fibroblast Growth Factors (FGFs) and their receptors (FGFRs) are widely expressed in the mature nervous system and are thought to mediate plasticity and repair. We report the generation of transgenic mice that can be induced to express a dominant-negative FGFR (dnFGFR) in select neuronal populations. We show that a modified Thy1 promoter [Vidal, M., Morris, R., Grosveld, F., and Spanopoulou, E. 1990. Tissue-specific control elements of the Thy-1 gene. EMBO J 9 833-840] can be used to drive widespread neuronal expression of the reverse tetracycline transactivator M2 (rtTA-M2 [Urlinger, S., Baron, U., Thellmann, M., Hasan, M.T., Bujard, H., and Hillen, W., 2000. Exploring the sequence space for tetracycline-dependent transcriptional activators: novel mutations yield expanded range and sensitivity. Proc. Natl. Acad. Sci. U. S. A. 97, 7963-7968]), which after stimulation with doxycycline induces co-expression of dnFGFR in mosaic subpopulations of rtTA-M2-positive forebrain neurons, but not in hindbrain and spinal cord rtTA-M2-positive neurons. Expression of dnFGFR did not cause overt neurodegeneration, but led to increased neuronal vulnerability: four days after a stab injury, cell death was marked in the hippocampus of dnFGFR-expressing animals when compared to controls. The nuclear morphology of dying CA1 pyramidal cells suggested an apoptotic mechanism of cell death. These observations demonstrate the importance of endogenous FGFs in the maintenance of the nervous system.

Vascular endothelial growth factor and its receptor Flk-1 are expressed in the hippocampus following entorhinal deafferentation

Vascular endothelial growth factor (VEGF) has been thought of as a mitogen that promotes proliferation of endothelial cells and as a neurotrophic factor that stimulates neurogenesis and axonal growth in both peripheral and central nervous systems. To investigate the potential involvement of VEGF in the lesion-induced reorganization in the brain, the expression changes of VEGF and its receptor Flk-1 were analyzed in the mouse hippocampus after transections of the entorhinal afferents. In situ hybridization and immunohistochemistry showed the time-dependent expression upregulation of VEGF mRNA and protein in the entorhinally denervated hippocampal stratum lacunosum-moleculare and dentate outer molecular layer, which initiated by 3 days postlesion, reached its maximum at 7-15 days postlesion, still persisted by 30 days postlesion for protein, and recovered to the normal levels at 30 days postlesion for mRNA and at 60 days postlesion for protein. Double labeling of VEGF and glial fibrillary acidic protein revealed that VEGF-expressing cells in the denervated areas were reactive astrocytes. Semi-quantitative RT-PCR analysis showed that VEGF receptor Flk-1 mRNA was also time-dependently upregulated in the deafferented hippocampus with its maximal elevation at 7-15 days postlesion while the Flt-1 mRNA levels remained unchanged at any time point we examined. Immunohistochemistry analysis also displayed the upregulation of Flk-1 protein in the denervated stratum lacunosum-moleculare and outer molecular layer with a time course similar to that of VEGF mRNA upregulation. Flk-1 receptors were found to be expressed not only by reactive astrocytes but also by neurites, which most likely belong to sprouting axons by 7 days postlesion and regrowing dendrites by 15-30 days postlesion. From these data we suggest that the spatiotemporal upregulation of VEGF and Flk-1 in the hippocampus is induced by entorhinal deafferentation and that VEGF may be involved in the structural reorganization in the deafferented hippocampus via directly or indirectly promoting neurite growth.

Entorhinal deafferentation induces upregulation of SPARC in the mouse hippocampus

SPARC is a matricellular protein that modulates cell-cell and cell-matrix interactions by virtue of its antiproliferative and counteradhesive properties. Here, we report the denervation-induced upregulation of SPARC mRNA and protein in the mouse hippocampus following transections of the entorhinal afferents. Northern blot analysis showed that SPARC mRNA was upregulated in a transient manner in the deafferented mouse hippocampus. In situ hybridization and immunohistochemistry confirmed the temporal upregulation of both SPARC mRNA and protein specifically in the denervated areas, which initiated at 7 days postlesion, reached the maximum at 15 as well as 30 days postlesion, and subsided towards normal levels by 60 days postlesion. Double labeling by either a combination of in situ hybridization for SPARC mRNA with immunohistochemistry for glial fibrillary acidic protein or double immunofluorescence staining for both proteins in the hippocampus revealed that SPARC-expressing cells are reactive astrocytes. In respect to the spatiotemporal alterations of SPARC expression in the denervated hippocampus, we suggest that SPARC may be involved in modulation of the denervation-induced plasticity processes such as glial cell proliferation, axonal sprouting and subsequent synaptogenesis in the hippocampus following entorhinal deafferentation.

Entorhinal cortex lesioning promotes neurogenesis in the hippocampus of adult mice

Hippocampal neurogenesis in adult mammals is influenced by many factors. Lesioning of the entorhinal cortex is a standard model used to study injury and repair in the hippocampus. Here we use bromodeoxyuridine (BrdU) labeling combined with immunohistochemical identification using cell type specific markers to follow the fate of neural progenitors in the hippocampus following entorhinal cortex lesioning in mice. We show that unilateral entorhinal cortex lesioning does not alter the rate of neural progenitor proliferation in the ipsilateral dentate gyrus during the first 3 days after lesioning. However it enhances cell survival at 42 days post-lesioning leading to an increased number of beta-III tubulin and calbindin-immunoreactive neurons being produced. By contrast, when BrdU was administered 21 days post-lesioning, the number of surviving cells 21 days later was similar on the lesioned and non-lesioned sides. Thus, acutely entorhinal cortex lesioning promotes neurogenesis by enhancing survival of either neural progenitors or their progeny. However, this stimulus to neurogenesis is not sustained into the recovery period.

Regulated transcripts in the hippocampus following transections of the entorhinal afferents

Based on the data from a cDNA microarray experiment which was carried out to screen the differential expressed genes in the rat hippocampus 10 days after removal of the entorhinal afferents, we confirmed the increase of expression of eight transcripts encoding protein osteonectin, thymosin-beta4, gelsolin, MHC I, MHC II, beta2-microglobulin, and interferon-gamma receptor using Northern blot. In situ hybridization revealed that the up-regulation of all these 8 transcripts localized specifically in the denervated target areas, the hippocampal stratum lacunosum-moleculare, and the dentate outer molecular layer. The results suggest that these molecules may have roles in the plasticity events in the hippocampus after entorhinal deafferentation.

Monocyte chemoattractant protein-1 and macrophage inflammatory protein-2 are involved in both excitotoxin-induced neurodegeneration and regeneration

Intrahippocamal injections of kainic acid (KA) significantly increase the expression of monocyte chemoattractant protein-1 (MCP-1) and macrophage inflammatory protein-2 (MIP-2) in the ipsilateral hippocampus at 2-4 h and 21-45 days post-administration, suggesting the possible involvement of these chemokines in both neurodegenerative and regenerative processes. To examine the possible role of these chemokines on neuronal cell death, hippocampal neurons were incubated with either MCP-1 or MIP-2 in vitro and examined to assess the effects on neuronal cell viability. These treatments resulted in significant neuronal apoptosis that could be abrogated by prior treatment with the caspase-1 inhibitor, Z-VAD-FMK, the caspase-3 inhibitor, Z-DEVD-FMK, the Galphai inhibitor, pertussis toxin, or the MAO-B inhibitor, (-)deprenyl. Furthermore, this chemokine apoptotic effect could also be observed in vivo as intrahippocampal injections of MCP-1 or MIP-2 resulted in the apoptosis of hippocampal neurons, thus supporting a direct role of these chemokines in neuronal death. In contrast, immunohistological analysis of kainic acid lesions on days 21-45 revealed significant expression of MCP-1 and MIP-2 associated with reactive astrocytes and macrophages, respectively, with no apoptotic populations being observed. These results suggested that these chemokines might also mediate distinct biological effects on local microenvironmental cell populations at various stages post truama and during cellular repair. To address this possibility, astrocyte were cultured in the presence or absence of these chemokines and examined by microarray analysis for effects on astrocytes gene expression. A number of genes encoding proteins associated with inflammation, cellular signaling, differentiation, and repair were directly modulated by chemokine treatment. More specifically, the RNA and protein expression of the neurotrophic factor, basic fibroblast growth factor (bFGF), was found to be significantly increased upon culture with MCP-1 and MIP-2. Conditioned media derived from chemokine-stimulated astrocytes also facilitated bFGF-dependent neuronal cell differentiation and promoted survival of H19-7 neurons in vitro, suggesting a possible role for chemokine-activated astrocytes as a source of trophic support. Taken together, these data support possible autocrine and paracrine roles for MCP-1 and MIP-2 in both the "death and life" of hippocampal neurons following CNS injury.

Stereological analysis of the reorganization of the dentate gyrus following entorhinal cortex lesion in mice

Denervation of the dentate gyrus by entorhinal cortex lesion has been widely used to study the reorganization of neuronal circuits following central nervous system lesion. Expansion of the non-denervated inner molecular layer (commissural/associational zone) of the dentate gyrus and increased acetylcholinesterase-positive fibre density in the denervated outer molecular layer have commonly been regarded as markers for sprouting following entorhinal cortex lesion. However, because this lesion extensively denervates the outer molecular layer and causes tissue shrinkage, stereological analysis is required for an accurate evaluation of sprouting. To this end we have performed unilateral entorhinal cortex lesions in adult C57BL/6J mice and have assessed atrophy and sprouting in the dentate gyrus using modern unbiased stereological techniques. Results revealed the expected increases in commissural/associational zone width and density of acetylcholinesterase-positive fibres on single brain sections. Yet, stereological analysis failed to demonstrate concomitant increases in layer volume or total acetylcholinesterase-positive fibre length. Interestingly, calretinin-positive fibres did grow beyond the border of the commissural/associational zone into the denervated layer and were regarded as sprouting axons. Thus, our data suggest that in C57BL/6J mice shrinkage of the hippocampus rather than growth of fibres underlies the two morphological phenomena most often cited as evidence of regenerative sprouting following entorhinal cortex lesion. Moreover, our data suggest that regenerative axonal sprouting in the mouse dentate gyrus following entorhinal cortex lesion may be best assessed at the single-fibre level.

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

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

Comparison of commissural sprouting in the mouse and rat fascia dentata after entorhinal cortex lesion

Reactive axonal sprouting occurs in the fascia dentata after entorhinal cortex lesion. This sprouting process has been described extensively in the rat, and plasticity-associated molecules have been identified that might be involved in its regulation. To demonstrate causal relationships between these candidate molecules and the axonal reorganization process, it is reasonable to analyze knockout and transgenic animals after entorhinal cortex lesion, and because gene knockouts are primarily generated in mice, it is necessary to characterize the sprouting response after entorhinal cortex lesion in this species. In the present study, Phaseolus vulgaris-leucoagglutinin (PHAL) tracing was used to analyze the commissural projection to the inner molecular layer in mice with longstanding entorhinal lesions. Because the commissural projection to the fascia dentata is neurochemically heterogeneous, PHAL tracing was combined with immunocytochemistry for calretinin, a marker for commissural/associational mossy cell axons. Using both techniques singly as well as in combination (double-immunofluorescence) at the light or electron microscopic level, it could be shown that in response to entorhinal lesion mossy cell axons leave the main commissural fiber plexus, invade the denervated middle molecular layer, and form asymmetric synapses within the denervated zone. Thus, the commissural sprouting response in mice has a considerable translaminar component. This is in contrast to the layer-specific commissural sprouting observed in rats, in which the overwhelming majority of mossy cell axons remain within their home territory. These data demonstrate an important species difference in the commissural/associational sprouting response between rats and mice that needs to be taken into account in future studies.

Changes in FGF-2 expression in the distal spinal cord stump after complete cord transection: a comparison between infant and adult rats

STUDY DESIGN

Expression patterns of fibroblast growth factor-2 (FGF-2) in distal transected spinal cord in infant and adult rats were determined by reverse-transcription polymerase chain reaction (RT-PCR) and immunostaining.

OBJECTIVE

To reveal the expression pattern of FGF-2 in distal transected cord of infant and adult rats.

SUMMARY OF BACKGROUND DATA

Descending fibers in the spinal cord of infant and adult rats show different regenerative capacity. One explanation is that different levels of FGF-2, an important neurotrophic factor for promoting neurite outgrowth and repair, are expressed in the distal transected cords of the rats, providing different levels of support for severed axons.

MATERIALS AND METHODS

Spinal cords of infant and adult rats were completely transected. At 12, 24, and 72 hours and at 1 week, segments of distal spinal cord tissues were removed and expression of FGF-2 mRNA was evaluated by RT-PCR. The distribution of FGF-2 and the phenotype of FGF-2-positive cells were determined by immunostaining.

RESULTS

Expression of FGF-2 mRNA was shown to be up-regulated in the distal cord of infant rats but not adult rats. Immunohistochemical analysis showed that neurons in distal cord of infant rats were rich in FGF-2 immunoreactivity (IR), whereas in adult rat neurons FGF-2 IR was hardly observed at all, although a few FGF-2-positive astrocytes were observed in the white matter.

CONCLUSION

After complete spinal cord transection, the expression of FGF-2 in the distal cord of infant rats was high compared with that of adults. This may provide neurotrophic support for axonal extension and functional recovery.

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

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

Adeno-associated virus vector expressing nerve growth factor enhances cholinergic axonal sprouting after cortical injury in rats

Nerve growth factor (NGF) is known to promote both the survival of cholinergic neurons after injury and the regeneration of damaged cholinergic axons. Recent evidence has implicated NGF in the regulation of cholinergic axonal sprouting by intact neurons projecting to the hippocampus of rats, sustaining a lesion of the entorhinal cortex. We explored the possibility that NGF may regulate this lesion-induced cholinergic sprouting by injecting recombinant adeno-associated virus (rAAV) vector expressing NGF and green fluorescent protein (GFP) into the dentate gyrus of rats that were subsequently given unilateral entorhinal lesions. Sprague Dawley rats were unilaterally injected with (1) rAAV vector expressing NGF and GFP or (2) rAAV vector expressing GFP. Fourteen days after injection, the animals received lesions of the entorhinal area ipsilateral to the virus injection. Four days after lesion, GFP expression and the septodentate sprouting response in the dentate gyrus were assessed. Optical densitometric analyses revealed a significant increase in acetylcholinesterase label (a marker for cholinergic septodentate sprouting) in the ipsilateral outer molecular layer of the dentate gyrus in rats injected with rAAV vector expressing NGF. Thus, NGF-expressing rAAV vector enhanced the sprouting response of intact cholinergic neurons after unilateral entorhinal lesions in rats.

Altered expression of CHL1 by glial cells in response to optic nerve injury and intravitreal application of fibroblast growth factor-2

The close homologue of L1 (CHL1) is a member of the L1 family of cell recognition molecules. The protein is expressed by a variety of nerve cell types and subpopulations of glial cells in vivo and promotes elongation of neurites and survival of nerve cells in vitro. Here we demonstrate that glial cells up-regulate expression of CHL1 in response to an intraorbital crush of the adult mouse optic nerve. We also demonstrate that a single intravitreal application of fibroblast growth factor-2 (FGF-2) increases expression of CHL1 in retinal astrocytes and Müller cells. Elevated expression of CHL1 by glial cells in injured optic nerves and astrocytes and Müller cells in FGF-2-treated retinas suggests a role of the protein in the lesioned central nervous system. Results also suggest that trophic factors might exert part of their biological function by modifying expression of cell recognition molecules.

D2 Dopamine receptor blockade results in sprouting of DA axons in the intact animal but prevents sprouting following nigral lesions

Recently it was demonstrated that sprouting of dopaminergic neurons and a microglial and astrocyte response follows both partial lesions of the substantia nigra pars compacta and blockade of the D2 dopamine receptor. We therefore studied the effects of the combination of these two treatments (lesioning and D2 dopamine receptor blockade). Haloperidol administration caused a 57% increase in dopaminergic terminal tree size (measured as terminal density per substantia nigra pars compacta neuron) and an increase of glia in the striatum. Following small to medium nigral lesions (less than 60%), terminal tree size increased by 51% on average and returned density of dopaminergic terminals to normal. In contrast, administration of haloperidol for 16 weeks following lesioning resulted in reduced dopaminergic terminal density and terminal tree size (13%), consistent with absent or impaired sprouting. Glial cell numbers increased but were less than with lesions alone. When haloperidol was administered after the striatum had been reinnervated through sprouting (16-32 weeks after lesioning), terminal tree size increased up to 150%, similar to the effect of haloperidol in normal animals. By examining the effect of administering haloperidol at varying times following a lesion, we concluded that a switch in the effect of D2 dopamine receptor blockade occurred after dopaminergic synapses began to form in the striatum. We postulate that when synapses are present, D2 dopamine receptor blockade results in increased terminal density, whereas prior to synapse formation D2 dopamine receptor blockade causes attenuation of a sprouting response. We speculate that D2 dopamine receptors located on growth cones 'push' neurites toward their targets, and blockade of these receptors could lead to attenuation of sprouting.

Differential regulation of fibroblast growth factor receptors in the regenerating amphibian spinal cord in vivo

Unlike mammals, adult urodele amphibians can regenerate their spinal cord and associated ganglia, but the molecular mechanisms controlling regeneration are not fully understood. We have recently shown that expression of FGF2, a member of the fibroblast growth factor family, is induced in the progenitor cells of the regenerating spinal cord and appears to play a role in their proliferation and possibly in their differentiation. In order to investigate which receptor(s) may mediate FGF2 signaling and their role in regeneration, we have studied expression of the four fibroblast growth factor receptors, FGFR1, FGFR2, FGFR3 and FGFR4, and of the spliced variants, sFGFR and KGFR, in the regenerating spinal cord of the adult urodele, Pleurodeles waltl, following tail amputation. We show that all FGFRs are expressed in normal and regenerating spinal cord, with the exception of the spliced variants that are expressed only in non-neural tissues of the tail. FGFR1 and 4 show the more interesting spatio-temporal patterns of expression. They are not detectable in the ependymal cells of normal cords, from which neural progenitors for regeneration are believed to originate, though they are expressed in some mature neurons. During regeneration, significant up-regulation of FGFR1 precedes that of FGFR4 in the ependymal tube from which the new cord will form. FGFR4 is highly expressed in these cells at later stages of regeneration, when neuronal differentiation is becoming apparent, and like FGFR1 is also expressed in some newborn neurons. In addition to the known form of FGFR1, the antibody against this receptor reacts also with a non-phosphorylated protein that appears to be present only during regeneration, and might represent a yet undescribed variant of the receptor. Altogether this study shows that fibroblast growth factor signaling is finely modulated during tail and spinal cord regeneration, and points to FGFR1 and FGFR4 as key players in this process, suggesting that FGFR1 is primarily associated with proliferation of progenitor cells and FGFR4 with early stages of neuronal differentiation.

Molecules involved in reactive sprouting in the hippocampus

Denervation of the hippocampus triggers reactive responses in neurons and glial cells in their affected strata in a temporally ordered fashion. Many of these responses have been studied extensively, focusing on the one hand on glial initiation and clearing responses during the degeneration phase and, on the other, on transneuronal reorganization and the newly adjusted physiological balance. We used the entorhinal cortex lesion (ECL) as a model system to study the cues that underlie the layer-specific sprouting response. This lesion destroys the perforant path, which is a massive excitatory projection to the dentate gyrus and hippocampus proper. In the deafferented zones of the hippocampus, sprouting of the remaining unlesioned fibers occurs, which replaces the lost afferences of the perforant path. We focus on candidate molecules which govern the layer-specific sprouting of the remaining axons and, in particular, on membrane-bound cues. The fact that layer-specific sprouting occurs even in the adult central nervous system (CNS) provides a valuable model for understanding the mechanisms of reactive neuronal growth and reorganization in the adult CNS. Isolation and analysis of the molecules involved in these mechanisms are important steps in understanding the potential and limitations of regeneration in the CNS.

Astrocytes mediate cerebral cortical neuronal axon and dendrite growth, in part, by release of fibroblast growth factor

Astrocytes occupy a central role in central nervous system (CNS) function. In particular astyrocytes can support neurite growth, in part, by release of diffusable factors. We therefore performed biochemical analysis of astrocyte conditioned medium to examine possible mechanisms of astrocyte mediated axon and dendrite growth in the mammalian CNS. Culture medium was conditioned on purified astrocyte monolayers derived from P3 rat cerebral cortex or on fibroblasts. Conditioned medium (CM) was subject to protein denaturation, molecular weight fractionation, and heparin affinity chromatography. E18 mouse cerebral cortical neurons were then cultured in the various media or directly on astrocyte monolayers and axon and dendrite growth from 50 neurons in each condition quantified after 3 DIV using double-labeled immunohistochemical techniques. Axon and dendrite growth was supported by astrocyte CM and both were significantly greater than process growth from neurons incubated in fibroblast CM. Protein denaturation significantly reduced astrocyte CM support of axon and dendrite growth. Following ultrafiltration and dialysis dendrite and axon growth was observed in the molecular weight fraction between 10 and 100 kDa. Axon growth also was observed in the CM molecular weight fraction greater than 100 kDa. Conditioned medium was eluted on a heparin column; when the bound fragment was reconstituted in chemically defined medium extensive dendrite and axon growth was observed. Since fibroblast growth factor (FGF) has these biochemical characteristics we added anti-bFGF neutralizing antibodies to astrocyte monolayers or CM; this significantly reduced astrocyte support of process growth. By contrast, the addition of heparin, which helps activate FGF receptors, to astrocyte CM further enhanced process growth. Western blot analysis confirmed that bFGF was present in astrocyte CM. We then examined axon and dendrite growth from cortical neurons after the addition of various growth factors to chemically defined medium. Axon and dendrite growth, similar to that found in astrocyte CM was observed after the addition of bFGF or aFGF. Astrocyte support of cerebral cortical neuron axon and dendrite growth in vitro may be explained, in part, by FGF release.

Functional switch between motor tracts in the presence of the mAb IN-1 in the adult rat

Fine finger and hand movements in humans, monkeys, and rats are under the direct control of the corticospinal tract (CST). CST lesions lead to severe, long-term deficits of precision movements. We transected completely both CSTs in adult rats and treated the animals for 2 weeks with an antibody that neutralized the central nervous system neurite growth inhibitory protein Nogo-A (mAb IN-1). Anatomical studies of the rubrospinal tracts showed that the number of collaterals innervating the cervical spinal cord doubled in the mAb IN-1- but not in the control antibody-treated animals. Precision movements of the forelimb and fingers were severely impaired in the controls, but almost completely recovered in the mAb IN-1-treated rats. Low threshold microstimulation of the motor cortex induced a rapid forelimb electromyography response that was mediated by the red nucleus in the mAb IN-1 animals but not in the controls. These findings demonstrate an unexpectedly high capacity of the adult central nervous system motor system to sprout and reorganize in a targeted and functionally meaningful way.

Fibroblast growth factor-2 promotes axon branching of cortical neurons by influencing morphology and behavior of the primary growth cone

Interstitial branching is an important mechanism for target innervation in the developing CNS. A previous study of cortical neurons in vitro showed that the terminal growth cone pauses and enlarges in regions from which interstitial axon branches later develop (Szebenyi et al., 1998). In the present study, we investigated how target-derived signals affect the morphology and behaviors of growth cones leading to development of axon branches. We used bath and local application of a target-derived growth factor, FGF-2, on embryonic pyramidal neurons from the sensorimotor cortex and used time-lapse digital imaging to monitor effects of FGF-2 on axon branching. Observations of developing neurons over periods of several days showed that bath-applied FGF-2 significantly increased growth cone size and slowed growth cone advance, leading to a threefold increase in axon branching. FGF-2 also had acute effects on growth cone morphology, promoting rapid growth of filopodia within minutes. Application of FGF-2-coated beads promoted local axon branching in close proximity to the beads. Branching was more likely to occur when the FGF-2 bead was on or near the growth cone, suggesting that distal regions of the axon are more responsive to FGF-2 than other regions of the axon shaft. Together, these results show that interstitial axon branches can be induced locally through the action of a target-derived growth factor that preferentially exerts effects on the growth cone. We suggest that, in target regions, growth factors such as FGF-2 and other branching factors may induce formation of collateral axon branches by enhancing the pausing and enlargement of primary growth cones that determine future branch points.

Alzheimer's disease as a disorder of mechanisms underlying structural brain self-organization

Mental function has as its cerebral basis a specific dynamic structure. In particular, cortical and limbic areas involved in "higher brain functions" such as learning, memory, perception, self-awareness and consciousness continuously need to be self-adjusted even after development is completed. By this lifelong self-optimization process, the cognitive, behavioural and emotional reactivity of an individual is stepwise remodelled to meet the environmental demands. While the presence of rigid synaptic connections ensures the stability of the principal characteristics of function, the variable configuration of the flexible synaptic connections determines the unique, non-repeatable character of an experienced mental act. With the increasing need during evolution to organize brain structures of increasing complexity, this process of selective dynamic stabilization and destabilization of synaptic connections becomes more and more important. These mechanisms of structural stabilization and labilization underlying a lifelong synaptic remodelling according to experience, are accompanied, however, by increasing inherent possibilities of failure and may, thus, not only allow for the evolutionary acquisition of "higher brain function" but at the same time provide the basis for a variety of neuropsychiatric disorders. It is the objective of the present paper to outline the hypothesis that it might be the disturbance of structural brain self-organization which, based on both genetic and epigenetic information, constantly "creates" and "re-creates" the brain throughout life, that is the defect that underlies Alzheimer's disease (AD). This hypothesis is, in particular, based on the following lines of evidence. (1) AD is a synaptic disorder. (2) AD is associated with aberrant sprouting at both the presynaptic (axonal) and postsynaptic (dendritic) site. (3) The spatial and temporal distribution of AD pathology follows the pattern of structural neuroplasticity in adulthood, which is a developmental pattern. (4) AD pathology preferentially involves molecules critical for the regulation of modifications of synaptic connections, i.e. "morphoregulatory" molecules that are developmentally controlled, such as growth-inducing and growth-associated molecules, synaptic molecules, adhesion molecules, molecules involved in membrane turnover, cytoskeletal proteins, etc. (5) Life events that place an additional burden on the plastic capacity of the brain or that require a particularly high plastic capacity of the brain might trigger the onset of the disease or might stimulate a more rapid progression of the disease. In other words, they might increase the risk for AD in the sense that they determine when, not whether, one gets AD. (6) AD is associated with a reactivation of developmental programmes that are incompatible with a differentiated cellular background and, therefore, lead to neuronal death. From this hypothesis, it can be predicted that a therapeutic intervention into these pathogenetic mechanisms is a particular challenge as it potentially interferes with those mechanisms that at the same time provide the basis for "higher brain function".

Plasticity of motor systems after incomplete spinal cord injury

Although spontaneous regeneration of lesioned fibres is limited in the adult central nervous system, many people that suffer from incomplete spinal cord injuries show significant functional recovery. This recovery process can go on for several years after the injury and probably depends on the reorganization of circuits that have been spared by the lesion. Synaptic plasticity in pre-existing pathways and the formation of new circuits through collateral sprouting of lesioned and unlesioned fibres are important components of this recovery process. These reorganization processes might occur in cortical and subcortical motor centres, in the spinal cord below the lesion, and in the spared fibre tracts that connect these centres. Functional and anatomical evidence exists that spontaneous plasticity can be potentiated by activity, as well as by specific experimental manipulations. These studies prepare the way to a better understanding of rehabilitation treatments and to the development of new approaches to treat spinal cord injury.

Effects of basic fibroblast growth factor on central nervous system functions

Basic fibroblast growth factor (bFGF), initially identified as mitogens with prominent angiogenic properties, is now recognized as multifunctional growth factors with notable actions on neuronal cells. bFGF promotes the survival and neurite growth of brain neurons in vitro and in vivo, suggesting that it functions as a neurotrophic factor. This effect of bFGF could be beneficial for improving the survival of grafted neurons in transplantation. Furthermore, bFGF acutely modulates synaptic transmission in the hippocampus, suggesting that it has a role like a neurotransmitter or neuromodulator. In this article, we make a brief review of multiple biological activities of bFGF for brain neurons and discuss its potential usefulness for the treatment of neurodegenerative disorders including Alzheimer's disease and Parkinson's disease.

Diazepam induces FGF-2 mRNA in the hippocampus and striatum

starting by 6 h following diazepam injection and returning to approximately control values by 24 h. In situ hybridization showed elevated FGF-2 mRNA labeling in the hippocampal formation, mostly in the pyramidal layer of the CA1 and CA2 subfields and in the dentate gyrus hilar region. These results indicate that diazepam treatment up-regulates FGF-2 expression in select regions of the brain and suggest that GABA may promote neuroplasticity in concert with FGF-2.

Changes in astrocytic basic fibroblast growth factor expression during and after prolonged exposure to escalating doses of amphetamine

We have shown that brief exposure to amphetamine leads to sustained glutamate-dependent increases in expression of the neurotrophic, neuroprotective factor, basic fibroblast growth factor, in astrocytes in dopaminergic cell body regions and that blockade of basic fibroblast growth factor in this region prevents the development of behavioral sensitization to amphetamine. Here we examine the effects of prolonged exposure to an escalating-dose regimen of amphetamine known to induce long-lasting sensitization to amphetamine and leading to increases in neuronal dendritic length and spine density in nucleus accumbens and prefrontal cortex and to decreases in spine density in occipital cortex. Astrocytic basic fibroblast growth factor immunoreactivity was increased in both dopaminergic cell body and terminal regions one week after termination of a two-week amphetamine treatment (1-4mg/kg). These effects were not evident one week after a five-week treatment (1-9mg/kg) and, in fact, one month later basic fibroblast growth factor levels in cell body regions were decreased. In the occipital cortex, basic fibroblast growth factor immunoreactivity was decreased one week after the two-week amphetamine treatment, but was not different from that seen in saline-treated animals after the five-week treatment. Increased astrocytic basic fibroblast growth factor expression appears to be an early, but relatively prolonged, response to amphetamine exposure and seems to parallel structural changes induced by repeated drug exposure.These findings suggest that basic fibroblast growth factor may participate in the development of structural changes brought about by amphetamine. The fact that the basic fibroblast growth factor response is not maintained after prolonged intense exposure to amphetamine suggests that the factors that initially induce basic fibroblast growth factor expression are self-regulating.

Basic fibroblast growth factor (bFGF) enhances functional recovery following severe spinal cord injury to the rat

We have recently demonstrated that following a moderate contusion spinal cord injury (SCI) to rats, subsequent administration of basic fibroblast growth factor (bFGF) significantly enhances functional recovery and tissue sparing. To further characterize the effects of bFGF, we evaluated its efficacy after a more severe contusion injury at T(10) using the NYU impactor. Immediately after SCI, osmotic minipumps were implanted into the lateral ventricle and lumbar thecal sac to deliver bFGF at 3 or 6 microg per day versus control vehicle for 1 week. Animals were behaviorally tested for 6 weeks before histological assessment of tissue sparing through the injured segment and glial reactivity distal to the lesion. Compared to moderate SCI, all rats had more prolonged and sustained functional deficits 6 weeks after severe contusion. Subjects treated with bFGF had pronounced recovery of hindlimb movements from 2 to 6 weeks compared to controls, manifested in significantly higher behavioral scores. Only marginal tissue sparing was seen rostral to the injury in bFGF-treated spinal cords versus controls. Optical density measurements of astrocyte and microglial cell immunoreactivity in bFGF-treated spinal cords showed that after 6 weeks they approximated controls, although astrocyte immunoreactivity remained higher in controls rostrally. In summary, intrathecal infusion of bFGF following severe SCI significantly restores gross hindlimb motor function that is not correlated with significant tissue sparing. In light of previous evidence that pharmacological intervention with bFGF after moderate SCI enhances tissue preservation, the current findings indicate that yet undefined mechanisms contribute to the enhanced functional recovery following bFGF treatment.

Acetylcholinesterase-positive fiber deafferentation and cell shrinkage in the septohippocampal pathway of aged amyloid precursor protein london mutant transgenic mice

Several lines of evidence implicate a cholinergic deficit in Alzheimer's disease (AD). Transgenic mice that overexpress clinical mutants of the human amyloid precursor protein (APP) have been generated that recapitulate many aspects of AD. We now analyzed the cholinergic system in aged APP/London transgenic mice. The major finding was the reorganization of acetylcholinesterase-positive fibers within the hippocampus and the reduced size of cholinergic cells in the medial septum. The reduction of acetylcholinesterase-positive fibers in the subiculum together with increased fiber density in the CA1 and in the dentate gyrus suggests a synaptic sprouting compensatory mechanism within the hippocampus. In the cortex, amyloid plaques were associated with intense acetylcholinesterase activity and surrounded by dystrophic acetylcholinesterase-positive fibers. Nevertheless, the overall pattern of cholinergic innervation was unchanged. These results demonstrate that overexpression of APP/London caused, besides amyloid plaques in aged mouse brain, also cholinergic deafferentation and cholinergic cell shrinkage.

Outgrowth-promoting molecules in the adult hippocampus after perforant path lesion

Lesion-induced neuronal plasticity in the adult central nervous system of higher vertebrates appears to be controlled by region- and layer-specific molecules. In this study we demonstrate that membrane-bound hippocampal outgrowth-promoting molecules, as present during the development of the entorhino-hippocampal system and absent or masked in the adult hippocampus, appear 10 days after transection of the perforant pathway. We used an outgrowth preference assay to analyse the outgrowth preference of axons from postnatal entorhinal explants on alternating membrane lanes obtained from hippocampus deafferented from its entorhinal input taken 4, 10, 20, 30 and 80 days post-lesion and from adult control hippocampus. Neurites from the entorhinal cortex preferred to extend axons on hippocampal membranes disconnected from their entorhinal input for 10 days in comparison with membranes obtained from unlesioned adult animals. Membranes obtained from hippocampi disconnected from their entorhinal input for 10 days were equally as attractive for growing entorhinal cortex (EC) axons as membranes from early postnatal hippocampi. Further analysis of membrane properties in an outgrowth length assay showed that entorhinal axons extended significantly longer on stripes of lesioned hippocampal membranes in comparison with unlesioned hippocampal membranes. This effect was most prominent 10 days after lesion, a time point at which axonal sprouting and reactive synaptogenesis are at their peak. Phospholipase treatment of membranes obtained from unlesioned hippocampi of adult animals strongly promoted the outgrowth length of entorhinal axons on these membranes but did not affect their outgrowth preference for deafferented hippocampal membranes. Our results indicate that membrane-bound outgrowth-promoting molecules are reactivated in the adult hippocampus following transection of the perforant pathway, and that neonatal entorhinal axons are able to respond to these molecules. These findings support the hypothesis of a temporal accessibility of membrane-bound factors governing the layer-specific sprouting of remaining axons following perforant path lesion in vivo.

Proliferation of microglia and astrocytes in the dentate gyrus following entorhinal cortex lesion: a quantitative bromodeoxyuridine-labelling study

Entorhinal cortex lesion of adult rats induces glial activation and proliferation in the deafferented dentate molecular layer. Double-labelling immunocytochemistry for the astrocyte-specific antigen glial fibrillary acidic protein or the microglial cell marker Griffonia simplicifolia isolectin B4 with bromodeoxyuridine detection revealed that microglia counts and the proliferation rate in the ipsilateral dentate gyrus reached a maximum in the molecular layer at 3 days post-lesion (dpl) and returned to control levels by 30 dpl. Astrocyte counts in the ipsilateral dentate gyrus peaked at 30 dpl, with maximum proliferation at 7 dpl. At 100 dpl the astrocyte count had reverted to control levels. Glial proliferation was not restricted to the ipsilateral molecular layer but also occurred to some degree in the granule cell layer and the contralateral dentate gyrus. Thus entorhinal cortex lesion induces a rapid microglia reaction and long-lasting astrocyte activation in the deafferented termination zone of the perforant path. We conclude that glial proliferation after entorhinal cortex lesion follows a complex temporal and spatial pattern that coincides with processes of neuronal and axonal reorganization.

Basic fibroblast growth factor (bFGF) enhances tissue sparing and functional recovery following moderate spinal cord injury

The rapid increase in basic fibroblast growth factor (bFGF) production following spinal cord injury (SCI) in rats is thought to serve a role in the cellular processes responsible for the functional recovery often observed. In this study, bFGF was intrathecally administered continuously for 1 week beginning 30 min after a moderate (12.5 mm) spinal cord contusion in adult rats using the New York University impactor device. Osmotic minipumps were implanted into the lateral ventricle and lumbar thecal sac to deliver bFGF at a rate of 3 microg or 6 microg per day versus control vehicle. Animals were behaviorally tested for 6 weeks using the Basso, Beattie, Bresnahan locomotor rating scale and histologically assessed for both tissue sparing and glial reactivity rostral and caudal to the lesion. Rats treated with bFGF regained coordinated hindlimb movements earlier than controls and demonstrated consistent coordination from 4 to 6 weeks. Vehicle-treated rats showed only modest improvements in hindlimb function. The amount of spared tissue was significantly higher in bFGF-treated rats than in controls. Astrocyte and microglial reactivity was more pronounced in bFGF-treated animals versus controls. In summary, intrathecal infusion of exogenous bFGF following SCI significantly reduces tissue damage and enhances functional recovery. Early pharmacological intervention with bFGF following SCI may serve a neuroprotective role and/or create a proregenerative environment, possibly by modulating the neuroglial response.

Basic fibroblast growth factor increases long-term survival of spinal motor neurons and improves respiratory function after experimental spinal cord injury

Acute focal injection of basic fibroblast growth factor (FGF2) protects ventral horn (VH) neurons from death after experimental contusive spinal cord injury (SCI) at T8. Because these neurons innervate respiratory muscles, we hypothesized that respiratory deficits resulting from SCI would be attenuated by FGF2 treatment. To test this hypothesis we used a head-out plethysmograph system to evaluate respiratory parameters in conscious rats before and at 24 hr and 7, 28, and 35 d after SCI. Two groups of rats (n = 8 per group) received either FGF2 (3 microg) beginning 5 min after injury or vehicle (VEH) solution alone. We found significantly increased respiratory rate and decreased tidal volume at 24 hr and 7 d after SCI in the VEH-treated group. Ventilatory response to breathing 5 or 7% CO(2) was also significantly reduced. Recovery took place over time. Respiration remained normal in the FGF2-treated group. At 35 d after injury, histological analyses were used to compare long-term neuron survival. FGF2 treatment doubled the survival of VH neurons adjacent to the injury site. Because the number of surviving VH neurons rostral to the injury epicenter was significantly correlated to the ventilatory response to CO(2), it is likely that the absence of respiratory deficits in FGF2-treated rats was caused by its neuroprotective effect. Our results demonstrate that FGF2 treatment prevents the respiratory deficits produced by thoracic SCI. Because FGF2 also reduced the loss of preganglionic sympathetic motoneurons after injury, this neurotrophic factor may have broad therapeutic potential for SCI.

Increased corticofugal plasticity after unilateral cortical lesions combined with neutralization of the IN-1 antigen in adult rats

If damage to the central nervous system (CNS) occurs early in life, extensive rearrangements of the remaining fiber systems as well as regeneration of lesioned fibers take place. In the rat or hamster, newly grown projections have been described only if the lesion occurred within the first two weeks postnatally. This decreasing growth ability correlates with CNS maturation and the progression of myelination. Myelin contains the potent neurite growth inhibitors NI-35/250 that are crucially involved in the failure of long-distance regeneration and the lack of compensatory structural plasticity after adult CNS lesions. In this study, we show that extensive remodeling occurs well after the termination of the growth permissive period in the adult rat if we neutralize the inhibitory properties of myelin with the monoclonal antibody IN-1. After ablation of one motor cortex and treatment with the antibody IN-1, we observed that the remaining corticospinal tract (CST) from the spared hemisphere sprouted into the denervated, contralateral red nucleus and pons. In the pons, these fibers terminated in a typical somatotopic pattern. For comparison with neonatal plasticity, we performed the same lesion in two-day-old rats (no antibody). This lesion led as well to sprouting of the remaining CST into denervated brainstem nuclei, resulting in a bilateral corticofugal projection. Our results show that neutralization of myelin-associated neurite-growth inhibitors after CNS lesions leads to a structural remodeling of the spared corticofugal fibers in adult rats, a process normally restricted to a short postnatal period.

Dexamethasone selectively suppresses microglial trophic responses to hippocampal deafferentation

Hippocampal deafferentation increases the expression of insulin-like growth factor-1 by microglia, and of ciliary neurotrophic factor and basic fibroblast growth factor by astroglia in fields and periods of reactive axonal growth. Glucocorticoids attenuate lesion-induced hippocampal sprouting, possibly by reducing trophic signals that stimulate growth. With an interest in this hypothesis, the present studies evaluated the influence of systemic treatment with the synthetic glucocorticoid dexamethasone on entorhinal lesion-induced increases in neurotrophic factor expression in young adult rat hippocampus. Daily dexamethasone injections almost completely blocked increases in insulin-like growth factor-1 messenger RNA content, but did not perturb increases in ciliary neurotrophic factor or basic fibroblast growth factor messenger RNA content, in the deafferented dentate gyrus molecular layer. To determine if the suppression of insulin-like growth factor-1 expression was secondary to a general inhibition of microglial responses, and to identify the time period of glucocorticoid sensitivity, additional rats were prepared to evaluate the effects of semi-chronic (i.e. daily) and single dexamethasone injections on microglial proliferation, ED-1 immunoreactivity (a marker of microglial reactivity) and insulin-like growth factor-1 messenger RNA expression. Semi-chronic dexamethasone treatment attenuated all three measures of deafferentation-induced microglial reactivity. However, a single dexamethasone injection given two (but not one or three) days postlesion inhibited deafferentation-induced increases in insulin-like growth factor-1 messenger RNA content, without having significant effects on other measures. These results demonstrate that dexamethasone treatment preferentially suppresses microglial, as opposed to astroglial, trophic responses to deafferentation, and suggest that glucocorticoids attenuate reactive axonal sprouting by inhibiting the microglial production of insulin-like growth factor-1.

Dynamic regulation of expression and phosphorylation of tau by fibroblast growth factor-2 in neural progenitor cells from adult rat hippocampus

The nature of the extracellular signals that regulate the expression and the phosphorylation of the microtubule-associated protein tau, which is aberrantly hyperphosphorylated in Alzheimer disease and other adult-onset neurodegenerative diseases, is not known. We have found that neural progenitor cells from adult rat hippocampus express adult isoforms of tau and that the expression and the phosphorylation of tau are regulated by fibroblast growth factor-2 (FGF-2). Astrocytes that are differentiated from these cells by stimulation with ciliary neurotrophic factor express phosphorylated tau similarly when cultured in the presence of FGF-2. In fetal progenitor cells that express only the fetal tau isoform, expression, but not the phosphorylation, of this protein is regulated by FGF-2 in cultures of higher passages. The FGF-2-mediated tau hyperphosphorylation is inhibited by lithium, an inhibitor of glycogen synthase kinase-3 (GSK-3), but not by inhibitors of mitogen-activated protein kinase or the cyclin-dependent kinases. Furthermore, both GSK-3 activity and the phosphorylation of tau increase when the concentration of FGF-2 is increased up to 40 ng/ml. These results demonstrate that proliferating adult rat hippocampal progenitor cells express adult isoforms of tau stably and that FGF-2 upregulates the expression and, by upregulating GSK-3 activity, the phosphorylation of tau.

Central peptidergic neurons are hyperactive during collateral sprouting and inhibition of activity suppresses sprouting

Little is known regarding the effect of chronic changes in neuronal activity on the extent of collateral sprouting by identified CNS neurons. We have investigated the relationship between activity and sprouting in oxytocin (OT) and vasopressin (VP) neurons of the hypothalamic magnocellular neurosecretory system (MNS). Uninjured MNS neurons undergo a robust collateral-sprouting response that restores the axon population of the neural lobe (NL) after a lesion of the contralateral MNS (). Simultaneously, lesioned rats develop chronic urinary hyperosmolality indicative of heightened neurosecretory activity. We therefore tested the hypothesis that sprouting MNS neurons are hyperactive by measuring changes in cell and nuclear diameters, OT and VP mRNA pools, and axonal cytochrome oxidase activity (COX). Each of these measures was significantly elevated during the period of most rapid axonal growth between 1 and 4 weeks after the lesion, confirming that both OT and VP neurons are hyperactive while undergoing collateral sprouting. In a second study the hypothesis that chronic inhibition of neuronal activity would interfere with the sprouting response was tested. Chronic hyponatremia (CH) was induced 3 d before the hypothalamic lesion and sustained for 4 weeks to suppress neurosecretory activity. CH abolished the lesion-induced increases in OT and VP mRNA pools and virtually eliminated measurable COX activity in MNS terminals. Counts of the total number of axon profiles in the NL revealed that CH also prevented axonal sprouting from occurring. These results are consistent with the hypothesis that increased neuronal activity is required for denervation-induced collateral sprouting to occur in the MNS.

Central neuronal loss and behavioral impairment in mice lacking neurotrophin receptor p75

The neurotrophin receptor p75 is a low-affinity receptor that binds neurotrophins. To investigate the role of p75 in the survival and function of central neurons, p75 null-mutant and wild type litter mate mice were tested on behavioral tasks. Null mutants showed significant performance deficits on water maze, inhibitory avoidance, motor activity, and habituation tasks that may be attributed to cognitive dysfunction or may represent a global sensorimotor impairment. The p75 null-mutant and wild type litter mate mice were assessed for central cholinergic deficit by using quantitative stereology to estimate the total neuronal number in basal forebrain and striatum and for subpopulations expressing the high-affinity tyrosine receptor kinase A (trkA) neurotrophin receptor and choline acetyltransferase (ChAT). In the adult brain, cholinergic neurons of the basal forebrain receive target-derived trophic support, whereas cholinergic striatal neurons do not. Adult p75 null-mutant mice had significant reduction of basal forebrain volume by 25% and had a corresponding significant loss of 37% of total basal forebrain neurons. The basal forebrain population of ChAT-positive neurons in p75-deficient mice declined significantly by 27%, whereas the trkA-positive population did not change significantly. There was no significant change in striatal volume or in striatal neuronal number either in total or by cholinergic subpopulation. These results demonstrate vulnerability to the lack of p75 in adult central neurons that are neurotrophin dependent. In addition, the loss of noncholinergic central neurons in mice lacking p75 suggests a role for p75 in cell survival by an as yet undetermined mechanism. Possible direct and indirect effects of p75 loss on neuronal survival are discussed.