bFGF promotes the survival of entorhinal layer II neurons after perforant path axotomy

Impact of continuous versus discontinuous progesterone on estradiol regulation of neuron viability and sprouting after entorhinal cortex lesion in female rats

Because the estrogen-based hormone therapy (HT) in postmenopausal women typically contains a progestogen component, understanding the interactions between estrogens and progestogens is critical for optimizing the potential neural benefits of HT. An important issue in this regard is the use of continuous vs discontinuous hormone treatments. Although sex steroid hormone levels naturally exhibit cyclic fluctuation, many HT formulations include continuous delivery of hormones. Recent findings from our laboratory and others have shown that coadministration of progesterone (P4) can either attenuate or augment beneficial actions of 17β-estradiol (E2) in experimental models depending in part upon the delivery schedule of P4. In this study, we demonstrate that the P4 delivery schedule in combined E2 and P4 treatments alters degenerative and regenerative outcomes of unilateral entorhinal cortex lesion. We assessed how lesion-induced degeneration of layer II neurons in entorhinal cortex layer and deafferentation in dentate gyrus are affected by ovariectomy and treatments with E2 alone or in combination with either continuous or discontinuous P4. Our results demonstrate the combined efficacy of E2 and P4 is dependent on the administration regimen. Importantly, the discontinuous-combined E2+P4 regimen had the greatest neuroprotective efficacy for both end points. These data extend a growing literature that indicates qualitative differences in the neuroprotective effects of E2 as a function of cotreatment with continuous versus discontinuous P4, the understanding of which has important implications for HT in postmenopausal women.

Degeneration of axotomized projection neurons in the rat dLGN: temporal progression of events and their mitigation by a single administration of FGF2

Removal of visual cortex in the rat axotomizes projection neurons in the dorsal lateral geniculate nucleus (dLGN), leading to cytological and structural changes and apoptosis. Biotinylated dextran amine was injected into the visual cortex to label dLGN projection neurons retrogradely prior to removing the cortex in order to quantify the changes in the dendritic morphology of these neurons that precede cell death. At 12 hours after axotomy we observed a loss of appendages and the formation of varicosities in the dendrites of projection neurons. During the next 7 days, the total number of dendrites and the cross-sectional areas of the dendritic arbors of projection neurons declined to about 40% and 20% of normal, respectively. The response of dLGN projection neurons to axotomy was asynchronous, but the sequence of structural changes in individual neurons was similar; namely, disruption of dendrites began within hours followed by cell soma atrophy and nuclear condensation that commenced after the loss of secondary dendrites had occurred. However, a single administration of fibroblast growth factor-2 (FGF2), which mitigates injury-induced neuronal cell death in the dLGN when given at the time of axotomy, markedly reduced the dendritic degeneration of projection neurons. At 3 and 7 days after axotomy the number of surviving dendrites of dLGN projection neurons in FGF-2 treated rats was approximately 50% greater than in untreated rats, and the cross-sectional areas of dendritic arbors were approximately 60% and 50% larger. Caspase-3 activity in axotomized dLGN projection neurons was determined by immunostaining for fractin (fractin-IR), an actin cleavage product produced exclusively by activated caspase-3. Fractin-IR was seen in some dLGN projection neurons at 36 hours survival, and it increased slightly by 3 days. A marked increase in reactivity was seen by 7 days, with the entire dLGN filled with dense fractin-IR in neuronal cell somas and dendrites.

Transplantation of bone marrow-derived mononuclear cells improves mechanical hyperalgesia, cold allodynia and nerve function in diabetic neuropathy

Relief from painful diabetic neuropathy is an important clinical issue. We have previously shown that the transplantation of cultured endothelial progenitor cells or mesenchymal stem cells ameliorated diabetic neuropathy in rats. In this study, we investigated whether transplantation of freshly isolated bone marrow-derived mononuclear cells (BM-MNCs) alleviates neuropathic pain in the early stage of streptozotocin-induced diabetic rats. Two weeks after STZ injection, BM-MNCs or vehicle saline were injected into the unilateral hind limb muscles. Mechanical hyperalgesia and cold allodynia in SD rats were measured as the number of foot withdrawals to von Frey hair stimulation and acetone application, respectively. Two weeks after the BM-MNC transplantation, sciatic motor nerve conduction velocity (MNCV), sensory nerve conduction velocity (SNCV), sciatic nerve blood flow (SNBF), mRNA expressions and histology were assessed. The BM-MNC transplantation significantly ameliorated mechanical hyperalgesia and cold allodynia in the BM-MNC-injected side. Furthermore, the slowed MNCV/SNCV and decreased SNBF in diabetic rats were improved in the BM-MNC-injected side. BM-MNC transplantation improved the decreased mRNA expression of NT-3 and number of microvessels in the hind limb muscles. There was no distinct effect of BM-MNC transplantation on the intraepidermal nerve fiber density. These results suggest that autologous transplantation of BM-MNCs could be a novel strategy for the treatment of painful diabetic neuropathy.

Neurotrophic effects of fibroblast growth factor-like autoantibodies in serum from three patients with breast cancer

Basic fibroblast growth factor (FGF) promotes branching neuritogenesis and survival in rat hippocampal neurons in vitro. Basic FGF is a broad spectrum mitogen which does not normally circulate, but increases in serum from a variety of cancers. In prior work, we described spontaneously-occurring fibroblast growth factor-like autoantibodies in serum from a subset of breast cancer patients with neurological complications. The FGF-like autoantibodies mimicked the potent endothelial cell growth-promoting activity of bFGF yet had remarkably increased stability (activity survived storage at 0-4 degrees C for up to 5 years). In the present study we tested whether FGF-like autoantibodies from breast cancer sera is neurotrophic or neuroprotective. We now report that FGF-like autoantibodies (2-3 microg/mL) from breast cancer sera promoted neuritogenesis in DIV 12 embryonic day 18 rat hippocampal neurons and neurite extension in undifferentiated rat pheochromocytoma PC12 cells. The FGF-like autoantibodies from a breast cancer patient with lupus were unique in protecting rat hippocampal neurons from glutamate-induced cell loss and promoting long-lasting neurite extension and survival in PC-12 cells (up to 25 days in vitro). Breast cancer sera FGF-like autoantibodies induced large sustained increases in inward cationic current associated with depolarization in hippocampal neurons that exceeded the electrophysiological effects of substantial concentrations of basic FGF. These results suggest that differences in potency or other unknown factors contribute to whether subsets of FGF-like autoantibodies from breast cancer sera exhibit long-lasting neurotrophic and neuroprotective effects or an early neurotrophic effect followed by accelerated late neuron death.

Fibroblast growth factors and neuroprotection

Several members of the FGF family, in particular FGF2, are intimately involved in neuronal protection and repair after ischemic, metabolic or traumatic brain injury. Expression of Fgf2 mRNA and protein is strongly upregulated after neuronal damage, with glial cells as the predominant source. Given its survival-promoting effects on cultured neurons, exogenous FGF2 was tested in several animal models of stroke and excitotoxic damage, in which it consistently proved protective against neuronal loss. FGF2 affords neuroprotection by interfering with a number of signaling pathways, including expression and gating of NMDA receptors, maintenance of Ca2+ homeostasis and regulation of ROS detoxifying enzymes. FGF2 prevents apoptosis by strengthening anti-apoptotic pathways and promotes neurogenesis in adult hippocampus after injury. The protective action of FGF2 has been linked to its augmenting effect on the lesion-induced upregulation of activin A, a member of the TGF-beta superfamily. Despite the well-documented benefits of FGF2 in animal models of stroke, there is currently no clinical development in stroke, after a phase II/III trial with FGF2 in acute stroke patients was discontinued because of an unfavorable risk-to-benefit ratio. As the molecular targets of FGF2 are going to be unraveled over the next years, new therapeutic strategies will hopefully emerge that enable us to influence the various protective mechanisms of FGF2 in a more specific fashion.

Experimental focal ischemic injury: behavior-brain interactions and issues of animal handling and housing

In experimental neurological models of brain injury, behavioral manipulations before and after the insult can have a major impact on molecular, anatomical, and functional outcome. Investigators using animals for preclinical research should keep in mind that people with brain injury have lived in, and will continue to live in, an environment that is far more complex than that of the typical laboratory rodent. To yield more reliable and relevant behavioral assessment, it may be appropriate in some cases to house animals in environments that allow for motor enrichment and to handle animals in ways that promote tameness. Experience can affect mechanisms of plasticity and degeneration beneficially or adversely. Behavioral interventions that have been found to modulate postinjury brain events are reviewed. The timing and interaction of biological and motor therapies and the potential contribution of experience-dependent and drug-induced trophic factor expression are discussed.

Effect of reactive cell density on net [2-14C]acetate uptake into rat brain: labeling of clusters containing GFAP+- and lectin+-immunoreactive cells

Astrocytic proliferation is a hallmark of brain injury, but the biological functions and metabolic activities of reactive astrocytes in vivo are poorly understood. [2-14C]Acetate, which is preferentially transported into and, therefore, metabolized by astrocytes, was used to assess injury- and trophic factor-induced changes in astrocyte metabolic activity. Local rates of net [2-14C]acetate uptake and glucose utilization (CMR(glc)), determined with [14C]deoxyglucose to assay overall metabolic activity of all brain cells, were assayed 7 days after a cannula placement; adjacent brain sections were immunostained to identify glial fibrillary acidic protein-positive (GFAP(+)) astrocytes and microglia plus macrophages (lectin-positive cells). GFAP(+) cells were abundant in tissue surrounding the cannula compared to the contralateral hemisphere, whereas lectin(+) cells were restricted to the wound boundary. CMR(glc) fell 25% in regions enriched in reactive astrocytes compared to the homologous contralateral hemisphere, whereas [14C]acetate uptake increased slightly (6%) but statistically significantly; metabolism of both tracers in 13 other brain structures was unchanged. Injection of basic fibroblast growth factor (b-FGF) into cerebral cortex or superior colliculus produced fiber-rich cell clusters containing both GFAP(+) and lectin(+) cells that had a 37% increase in [14C]acetate uptake; GFAP(+)-cell density rose in the nearby neuropil but the corresponding change in [14C]acetate uptake was small (6-8%). Sensory stimulation did not alter [14C]acetate uptake into the clusters. Thus, [14C]acetate uptake was relatively stable with respect to changes in the density of reactive astrocytes that are dispersed throughout the neuropil and to changes in cellular activity arising from sensory stimulation. In contrast, b-FGF-induced cell clusters that contain mixed cell types and numerous fibers accumulated higher levels of [14C]acetate, raising the possibility that increased uptake might be due to high numbers of activated astrocytes and, perhaps, acetate metabolism by other cell types.

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.

Differential expression of fibroblast growth factor-2 and fibroblast growth factor receptor 1 in a scarring and nonscarring model of CNS injury in the rat

Injury to the adult brain results in abortive axon regeneration and the deposition of a dense fibrous glial scar. Therapeutic strategies to promote postinjury axon regeneration are likely to require antiscarring strategies. In neonatal brain wounds, scar material is not laid down and axons grow across the lesion site, either by de novo growth or regeneration. To achieve the therapeutic goal of recapitulating the nonscarring neonatal response in the injured adult, an understanding of how ontogenic differences in scarring reflect developmental diversities in the trophic response to injury is required. Fibrobast growth factor-2 (FGF-2) expression is developmentally regulated and has been implicated as a regulator of the wounding response of the adult rat central nervous system. We have investigated the expression of FGF-2 and fibroblast growth factor receptor 1 (FGFR1) after penetrating lesions to the cerebral cortex of 5 days post partum (dpp) (nonscarring) and 16 dpp and adult (scarring) rats. In situ hybridization, immunohistochemistry and Western blotting showed robust and sustained increases in FGF-2 and FGFR1 mRNA and protein in reactive astrocytes around the lesion in scarring rats, a response that was attenuated substantially in the nonscarring neonate. These results demonstrate that changes in astrocyte FGF-2 and FGFR1 expression are coincident with the establishment of a mature pattern of glial scarring after injury in the maturing central nervous system, but it is premature to infer a causal relationship without further experiments.

Fibroblast growth factor treatment produces differential effects on survival and neurite outgrowth from identified bulbospinal neurons in vitro

The in vivo application of appropriate trophic factors may enhance regeneration of bulbospinal projections after spinal cord injury. Currently, little is known about the sensitivities of specific bulbospinal neuron populations to the many identified trophic factors. We devised novel in vitro assays to study trophic effects on the survival and neurite outgrowth of identified bulbospinal neurons. Carbocyanine dye crystals implanted into the cervical spinal cord of embryonic day (E)5 chick embryos retrogradely labeled developing bulbospinal neurons. On E8, dissociated cultures containing labeled bulbospinal neurons were prepared. Fibroblast growth factor (FGF)-2 (but not FGF-1) promoted the survival of bulbospinal neurons. FGF receptor expression was widespread in the E8 brainstem, but not detected in young bulbospinal neurons, suggesting that nonneuronal cells mediated the FGF-stimulated survival response. Astrocytes synthesize a variety of trophic factors, and astrocyte-conditioned medium (ACM) also promoted the survival of bulbospinal neurons. As might be expected, FGF-2 function blocking antibodies did not suppress ACM-promoted survival, nor did an ELISA detect FGF-2 in ACM. This suggests that nonneuronal cells synthesize other factors in response to exogenous FGF-2 which promote the survival of bulbospinal neurons. Focusing on vestibulospinal neurons, dissociated (survival assay) or explant (neurite outgrowth assay) cultures were prepared. FGF-2 promoted both survival and neurite outgrowth of identified vestibulospinal neurons. Interestingly, FGF-1 promoted neurite outgrowth but not survival; the converse was true of FGF-9. Thus, differential effects of specific growth factors on survival or neurite outgrowth of bulbospinal neurons were distinguished.

Ovariectomy of adult rats leads to increased expression of astrocytic basic fibroblast growth factor in the ventral tegmental area and in dopaminergic projection regions of the entorhinal and prefrontal cortex

Changes in astrocytic function may underlie the neurochemical and morphological alterations in limbic and cortical areas after estrogen loss in adult females. We assessed whether increased expression of basic fibroblast growth factor (bFGF), an astrocytic response involved in injury-induced neuronal plasticity, occurs after ovariectomy. We examined bFGF immunoreactivity (IR) in ovariectomized rats with oil or estradiol benzoate (5 microgram every 4 d; Experiment 1) and in ovariectomized and intact animals (Experiment 2). In the ventral tegmental area (VTA), bFGF-IR and glial fibrillary acidic protein (GFAP)-IR were greater in ovariectomized animals than in animals with estrogen replacement. bFGF-IR in the VTA was greater in ovariectomized than in intact females. In the dorsal raphe, no differences between groups were found in GFAP-IR or bFGF-IR. In mesolimbic dopaminergic target areas within entorhinal cortex (Ent), prefrontal cortex, and nucleus accumbens, bFGF-IR was higher in Ent of ovariectomized animals 4 weeks after surgery in both experiments, but no differences were seen in nucleus accumbens or in an occipital cortical, control, area in either study. In Experiment 2, small increases in bFGF-IR were seen in the prefrontal cortex after ovariectomy. In the VTA and Ent, changes in bFGF-IR developed gradually, peaking at 4 weeks and waning at 40 weeks. Furthermore, increased dendritic arbor of Ent layer II/III pyramidal cells was found in ovariectomized females with the use of a modified Golgi-Cox staining procedure. These findings suggest that, within specific regions, ovariectomy induces astrocytic responses similar to those observed after injury that may affect neuronal chemistry and morphology.

Death of transcallosal neurons after close axotomy

The extent of cell death after axotomy may limit potential recovery after brain injury. We wished to determine the effect of axotomizing lesions on survival of transcallosally projecting cortical neurons. Transcallosal neurons were prelabeled by retrograde transport of the fluorescent dyes Fluoro-Gold and True Blue. A transcortical stab wound divided the field of labeled cortical cells into axotomized and unaxotomized groups. Little difference in labeled cell density was seen over the first few days after injury. Animals surviving at least 2 weeks after injury had clear loss of axotomized neurons. By 1 month after injury, the vast majority of axotomized labeled cells appeared to have died. Quantitative evaluation of labeled cells showed that the region of cortex within 1 mm of the axotomizing injury had less than 10% of the expected neuronal density in animals surviving at least 4 weeks after injury. Close axotomy appears to cause dramatic loss of transcallosal neurons even in adult animals.

Influence of IN-1 antibody and acidic FGF-fibrin glue on the response of injured corticospinal tract axons to human Schwann cell grafts

Two strategies have been shown by others to improve CST regeneration following thoracic spinal cord injury: 1) the administration of a monoclonal antibody, IN-1, raised against a myelin-associated, neurite growth inhibitory protein, and 2) the delivery of acidic fibroblast growth factor (aFGF) in fibrin glue in association with peripheral nerve grafts. Because autologous transplantation of human Schwann cells (SCs) is a potential strategy for CNS repair, we evaluated the ability of these two molecular agents to induce CST regeneration into human SC grafts placed to span a midthoracic spinal cord transection in the adult nude rat, a xenograft tolerant strain. IN-1 or control (HRP) antibodies were delivered to the injury/graft region by encapsulated hybridoma cells ("IN-1 ravioli") or daily infusion of hybridoma culture supernatant; aFGF-fibrin glue was placed in the same region in other animals. Anterograde tracing from the motor cortex using the dextran amine tracers, Fluororuby (FR) and biotinylated dextran amine (BDA), was performed. Thirty-five days after grafting, the CST response was evaluated qualitatively by looking for regenerated CST fibers in or beyond grafts and quantitatively by constructing camera lucida composites to determine the sprouting index (SI), the position of the maximum termination density (MTD) rostral to the GFAP-defined host/graft interface, and the longitudinal spread (LS) of bulbous end terminals. The latter two measures provided information about axonal die-back. In control animals (graft only), the CST did not enter the SC graft and underwent axonal die-back [SI = 1.4 +/- 0.1, MTD = 2.0 +/- 0.2, LS = 1.3 +/- 0.3, (n = 3)]. Results of IN-1 delivery from ravioli did not differ from controls, but injections of IN-1-containing supernatant resulted in a significant degree of sprouting but did not prevent axonal die-back [SI = 1.9 +/- 0.1, MTD = 1.5 +/- 0.2, LS = 1.1 +/- 0.1, (n = 7)] and traced fibers did not enter grafts. Acidic FGF dramatically reduced axonal die-back and caused sprouting [SI = 2.0 +/- 0.1 (n = 5), MTD = 0.5 +/- 0.04 (n = 6), LS = 0.4 +/- 0.1 (n = 6)]. Some traced fibers entered SC grafts and in 2/6 cases entered the distal interface. We conclude that 1) human SC grafts alone do not support the regeneration of injured CST fibers and do not prevent die-back, 2) grafts plus IN-1 antibody-containing supernatant support some sprouting but die-back continues, and 3) grafts plus aFGF-fibrin glue support regeneration of some fibers into the grafts and reduce die-back.

Blockade of basic fibroblast growth factor retards recovery from motor cortex injury in rats

The endogenous expression of basic fibroblast growth factor (bFGF) was blocked by neutralizing antibodies following unilateral suction lesions of the motor cortex. Rats with control treatment (saline, goat IgG) after motor cortex lesions showed slow recovery of forelimb manipulatory abilities. Rats with blockade of bFGF expression showed little recovery. Anatomically, the control-treated lesioned rats showed an acute increase in bFGF and glial fibrillary acidic protein (GFAP) reactivity, and chronically they had normal dendritic arborization and spine density in layer V pyramidal cells in the remaining motor cortex. In contrast, rats treated with antibodies to bFGF showed little bFGF reactivity, normal GFAP reactivity, and atrophy of dendritic arbor and decreased spine density in layer V pyramidal cells. These results demonstrate the importance of endogenous bFGF release in processes related to functional recovery after cortical injury.

Deafferentation causes apoptosis in cortical sensory neurons in the adult rat

The present study provides an experimental model of the apoptotic death of pyramidal neurons in rat olfactory cortex after total bulbectomy. Terminal transferase (TdT)-mediated deoxyuridine triphosphate (d-UTP)-biotin nick end labeling (TUNEL), DNA electrophoresis, and neuronal ultrastructure were used to provide evidence of apoptosis; neurons in olfactory cortex were counted by stereology. Maximal TUNEL staining occurred in the piriform cortex between 18 and 26 hr postbulbectomy. Within the survival times used in the present study (up to 48 hr postlesion), cell death was observed exclusively in the piriform cortex; there was no evidence of cell death in any other areas connected with the olfactory bulb. Neurons undergoing apoptosis were pyramidal cells receiving inputs from, but not projecting to, the olfactory bulb. The apical dendrites of these neurons were contacted by large numbers of degenerating axonal terminals. Gel electrophoresis of DNA purified from lesioned olfactory cortex showed a ladder pattern of fragmentation. Inflammatory cells or phagocytes were absent in the environment of degenerating neurons in the early stages of the apoptotic process. The present model suggests that deafferentation injury in sensory systems can cause apoptosis. In addition, olfactory bulbectomy can be used for investigating molecular mechanisms that underlie apoptosis in mature mammalian cortical neurons and for evaluating strategies to prevent the degeneration of cortical neurons.

Pharmacology of neurotrophic factors

The field of neurotrophic factor pharmacology emerged during the past decade with the discovery that these proteins can counteract neuronal atrophy and death in the adult nervous system. These concepts are being tested in clinical trials. Therapeutic use of neurotrophic proteins seems practical for diseases of the peripheral nervous system (PNS), where they can be given by systemic administration. For diseases of the CNS, special administration strategies will have to be developed to deliver the neurotrophic factors into the brain. The development of small molecule mimetics represents an alternative approach that is actively pursued to provide brain-penetrant neurotrophics.

Alpha 2-adrenergic agonists induce basic fibroblast growth factor expression in photoreceptors in vivo and ameliorate light damage

We observed an induction of basic fibroblast growth factor (bFGF) mRNA in the rat retina after systemic administration of the alpha 2-adrenergic agonists xylazine and clonidine. A single injection of xylazine or clonidine transiently increased bFGF mRNA. Preinjection of yohimbine, an alpha 2-adrenergic antagonist, completely inhibited this increase. Higher dosage of yohimbine inhibited the baseline expression of bFGF. Of particular interest is the finding that the induced bFGF expression occurred almost exclusively in the inner segment region of photoreceptors. No increase in bFGF mRNA was found in the brain after either xylazine or clonidine injection. Xylazine or clonidine given systemically before and during constant light exposure also reduces photoreceptor degeneration in albino rats. These results indicate that regulation of bFGF expression in photoreceptors is unique in the CNS and suggest that endogenous bFGF promotes photoreceptor survival.

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.

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.

Mesencephalic dopaminergic neurons protected by GDNF from axotomy-induced degeneration in the adult brain

Glial-cell-line-derived neurotrophic factor (GDNF) promotes survival of embryonic dopaminergic neurons in culture, and its expression pattern suggests a role as a transient target-derived trophic factor for dopaminergic neurons of the substantia nigra. These neurons participate in the control of motor activity, emotional status and cognition, and they degenerate in Parkinson's disease for unknown reasons. To test whether GDNF has a trophic effect on dopaminergic neurons in the adult brain, we used a rat model in which these neurons are induced to degenerate by transecting their axons within the medial forebrain bundle. We report here that axotomy resulted in loss of half the tyrosine hydroxylase-expressing neurons in the substantia nigra. This loss was largely prevented by repeated injections of GDNF adjacent to the substantia nigra. Our findings suggest that GDNF or related molecules may be useful for the treatment of Parkinson's disease.

Beta-amyloid-induced changes in cultured astrocytes parallel reactive astrocytosis associated with senile plaques in Alzheimer's disease

One neuropathological characteristic of Alzheimer's disease is an abundance of reactive astrocytes, particularly in association with senile plaques. Neither the factor(s) responsible for initiating the reactive astrocytosis nor the effects of this event on disease progression are known. We investigated the possibility that beta-amyloid protein, the primary constituent of plaques, contributes to reactive astrocytosis by comparing results derived from both culture studies and immunohistochemical analyses of Alzheimer brain tissue. We report that beta-amyloid peptides, in an aggregation-dependent manner, rapidly induce a reactive phenotype in cultured rat astrocytes. Reactive morphological changes are accompanied by increased immunoreactivities for glial fibrillary acidic protein and basic fibroblast growth factor. Although toxic to other types of central nervous system cells, aggregated beta-amyloid peptides do not significantly decrease astrocyte viability. Rather, the processes of cultured astrocytes envelop aggregated deposits of beta-amyloid peptide. In Alzheimer brain, the processes of reactive astrocytes were also observed to engulf beta-amyloid deposits. Similar to the in vitro findings, the astrocytic response was associated only with beta-amyloid plaques exhibiting an aggregated structure. Further, the plaque-associated reactive astrocytes showed enhanced immunoreactivities for glial fibrillary acidic protein and basic fibroblast growth factor. These data suggest that beta-amyloid which has assembled into beta-sheet fibrils significantly contributes to the reactive astrocytosis characteristic of Alzheimer's disease. Thus, in addition to its hypothesized direct effects on neuronal viability, beta-amyloid may also influence disease progression indirectly via reactive astrocytosis.

Neurotrophic factor therapy for nervous system degenerative diseases

The ability of neurotrophic factors to regulate developmental neuronal survival and adult nervous system plasticity suggests the use of these molecules to treat neurodegeneration associated with human diseases. Solid rationales exist for the use of NGF and neurotrophin-3 in the treatment of neuropathies of the peripheral sensory system, insulin-like growth factor and ciliary neurotrophic factor in motor neuron atrophy, and NGF in Alzheimer's disease. Growth factors have been identified for neurons affected in Parkinson's disease, Huntington's disease, and acute brain and spinal cord injury. Various strategies are actively pursued to deliver neurotrophic factors to the brain, and develop therapeutically useful molecules that mimic neurotrophic factor actions or stimulate their production or receptor mechanisms.

Temporal and spatial increase of astroglial basic fibroblast growth factor synthesis after 6-hydroxydopamine-induced degeneration of the nigrostriatal dopamine neurons

The present study investigates the temporal and spatial changes of the cellular expression of basic fibroblast growth factor messenger RNA and immunoreactivity after a 6-hydroxydopamine-induced lesion in the nigrostriatal dopamine system. In situ hybridization revealed a sustained (from 4 h to two weeks) and strong (300-400% of control, at the peak intervals) increase of basic fibroblast growth factor messenger RNA in the pars compacta of the substantia nigra and the ventral tegmental area ipsilateral to the lesion. A short-lasting increase of basic fibroblast growth factor messenger RNA was observed in he ipsilateral pars reticulata of the substantia nigra (from 4-24 h, 300% of control) and neostriatum (24 h, 180% of control) as well as in the ipsilateral and contralateral hippocampus and neocortex (by 4 h, 200% of control). Brightfield microscopy showed an increased number of putative glial cells expressing the basic fibroblast growth factor messenger RNA signal. Basic fibroblast growth factor immunohistochemistry revealed on control brains the protein in the nuclei of glial cells throughout the forebrain and the midbrain and in the nuclei of neurons of the layer II of the retrosplenial granular cortex, the CA2 region of the hippocampus and the fasciola cinereum as well as in the nuclei of ependymal cells. The injection of 6-hydroxydopamine increased basic fibroblast growth factor immunoreactivity in the nuclei of astrocytes only within the ipsilateral substantia nigra and ventral tegmental area. By 2 h after the drug injection, the density of glial basic fibroblast growth factor-immunoreactive profiles was increased in the pars compacta of the substantia nigra and the ventral tegmental area. The density, size and intensity of the astroglial basic fibroblast growth factor immunoreactive nuclei were increased in the entire substantia nigra and the ventral tegmental area at 72 h, and peaked one week after the 6-hydroxydopamine injection. The saline injection promoted a time-dependent increase in the density of the glial basic fibroblast growth factor immunoreactivity but only in the ipsilateral pars compacta of the substantia nigra. In conclusion, the dopamine cell degeneration may give rise to extracellular signals activating the surrounding astroglia, leading to a sustained increased synthesis of astroglial basic fibroblast growth factor, which may exert neuroprotective action and increase repair on the nigrostriatal dopamine system.

Dynamics of synapsin I gene expression during the establishment and restoration of functional synapses in the rat hippocampus

Synapse development and injury-induced reorganization have been extensively characterized morphologically, yet relatively little is known about the underlying molecular and biochemical events. To examine molecular mechanisms of synaptic development and rearrangement, we looked at the developmental pattern of expression of the neuron-specific gene synapsin I in granule cell neurons of the dentate gyrus and their accompanying mossy fibers during the main period of synaptogenic differentiation in the rat hippocampus. We found a significant difference between the temporal expression of synapsin I messenger RNA in dentate granule somata and the appearance of protein in their mossy fiber terminals during the postnatal development of these neurons. Next, to investigate the regulation of neuron-specific gene expression during the restoration of synaptic contacts in the central nervous system, we examined the expression of the synapsin I gene following lesions of hippocampal circuitry. These studies show marked changes in the pattern and intensity of synapsin I immunoreactivity in the dendritic fields of dentate granule cell neurons following perforant pathway transection. In contrast, changes in synapsin I messenger RNA expression in target neurons, and in those neurons responsible for the reinnervation of this region of the hippocampus, were not found to accompany new synapse formation. On a molecular level, both developmental and lesion data suggest that the expression of the synapsin I gene is tightly regulated in the central nervous system, and that considerable changes in synapsin I protein may occur in neurons without concomitant changes in the levels of its messenger RNA. Finally, our results suggest that the appearance of detectable levels of synapsin I protein in in developing and sprouting synapses coincides with the acquisition of function by those central synapses.

Fibroblast growth factors: activities and significance of non-neurotrophin neurotrophic growth factors

Although first characterized by virtue of their ability to stimulate endothelial cell proliferation in vitro and angiogenesis in vivo, the fibroblast growth factors are now also well recognized for their neurotrophic activities. Understanding the physiological significance of these multifunctional, virtually ubiquitous and pluripotential molecules, however, remains enigmatic. Recent advances describing their molecular, biochemical and biological characteristics has led to a better understanding of their role in the central nervous system.

Endogenous neuroprotection factors and traumatic brain injury: mechanisms of action and implications for therapy

Throughout evolution the brain has acquired elegant strategies to protect itself against a variety of environmental insults. Prominent among these are signals released from injured cells that are capable of initiating a cascade of events in neurons and glia designed to prevent further damage. Recent research has identified a remarkably large number of neuroprotection factors (NPFs), whose expression is increased in response to brain injury. Examples include the neurotrophins (NGF, NT-3, NT-5, and BDNF), bFGF, IGFs, TGFs, TNFs and secreted forms of the beta-amyloid precursor protein. Animal and cell culture studies have shown that NPFs can attenuate neuronal injury initiated by insults believed to be relevant to the pathophysiology of traumatic brain injury (TBI) including excitotoxins, ischemia, and free radicals. Studies of the mechanism of action of these NPFs indicate that they enhance cellular systems involved in maintenance of Ca2+ homeostasis and free radical metabolism. Recent work has identified several low-molecular-weight lipophilic compounds that appear to mimic the action of NPFs by activating signal transduction cascades involving tyrosine phosphorylation. Such compounds, alone or in combination with antioxidants and calcium-stabilizing agents, have proved beneficial in animal studies of ischemic brain injury and provide opportunities for development of preventative/therapeutic approaches for TBI.

CCK-A and CCK-B receptors enhance olfactory recognition via distinct neuronal pathways

We have previously reported that CCK-A receptor agonists and CCK-B receptor antagonists both enhance memory in an olfactory recognition test. Here, we report that the memory-enhancing effect of the CCK-B receptor antagonist L-365,260 (1 mg/kg i.p.), but not that of the CCK-A receptor agonist caerulein (0.03 mg/kg i.p.), was dramatically decreased following a bilateral transection of the perforant path, a principal source of input to the hippocampal formation. We further confirmed that a significant memory deficit occurred subsequent to this deafferentation of the hippocampus in untreated animals. In contrast, the effect of caerulein, but not that of L-365,260, was abolished following a bilateral subdiaphragmatic vagotomy. These results demonstrate that the hippocampal system plays a role in olfactory recognition and indicate that distinct neuronal pathways underlie the memory-enhancing effects of CCK-A and CCK-B drugs observed in the olfactory recognition test. The former effects (CCK-A) appear to involve a peripheral relay to the brain via the vagus nerve, whereas the latter (CCK-B) are directly central and involve, at least in part, the hippocampal system.

Growth factors in CNS repair and regeneration

Traumatic central nervous system (CNS) injury is a significant clinical problem in the developed world. After injuries that penetrate into either the mature brain or spinal cord, damaged neurons initially begin to regrow, but this regeneration is aborted as a fibrotic scar is laid down within the wound. Reconnection of several neuronal pathways does not occur. Functional recovery from such injuries is therefore poor and morbidity severe, particularly for those patients with spinal cord damage. Although palliative measures are available to improve the quality of life, there is no accepted treatment to restore impaired sensory or motor function, so patients remain significantly and permanently debilitated. However, the rapid recent advances that have been made in our understanding of the underlying cellular and trophic pathology of such injuries offer the potential for development of novel therapies to control scarring, enhance neuron survival and stimulate axon regeneration, thereby promoting functional recovery.