Transforming growth factor-β mediates the neurotrophic effect of fibroblast growth factor-2 on midbrain dopaminergic neurons

Fibroblast growth factor (FGF)-2 is an established neurotrophic factor for dopaminergic (DAergic) neurons in the ventral midbrain. Its survival and differentiation-promoting effects on DAergic neurons in vitro and in vivo are crucially dependent on the presence, numerical expansion and maturation of astroglial cells. We show now that transforming growth factor (TGF)-β, an established trophic factor for DAergic neurons and product of astroglial cells, mediates the trophic effect of FGF-2 on DAergic neurons cultured from the embryonic rat midbrain floor. Antibodies to TGF-β that neutralize the isoforms -β1, -β2 and -β3 abolish the trophic effect of FGF-2. FGF-2 increases TGF-β3 mRNA and amounts of biologically active TGF-β determined in a mink lung epithelial cell assay in a time-dependent manner. FGF-2 also induces levels of active TGF-β in neonatal rat astrocytes cultured from midbrain, striatum and cortex. We conclude that TGF-β is required for mediating the survival promoting effect of FGF-2 on DAergic and, possibly, cortical and striatal neurons grown in the presence of glial cells.     

Basic Fibroblast Growth Factor in the Adrenal Gland

The importance of trophic agents for the development and maintenance of neurons and their presence in mesenchyme-derived neuronal target organs such as muscle is well exemplified by the protein nerve growth factor (NGF) and its synthesis in target areas of sympathetic and sensory nerves. Stringent conceptualization of target organ-regulated neuronal maintenance would imply that neurons were able to provide trophic support to their presynaptic counterparts. We present data suggesting that basic fibroblast growth factor (bFGF), a mitogen and trophic factor for several neuron populations in vitro, may be such a protein involved in retrograde trophic neuron - neuron interaction. Basic FGF or a closely related protein is present in the adrenal medulla and its sympathetic neuron-like chromaffin cells. A polyclonal antibody specific for bFGF recognizes an 18 kD band in Western blots of bFGF-enriched bovine adrenal medulla extracts and immunostains isolated bovine chromaffin cells. This antibody also blocks the bFGF-like activity present in adrenal medullary extracts and chromaffin granule extracts that both promote in vitro survival of embryonic chick ciliary ganglionic neurons. Furthermore, like bFGF, the soluble proteins of bovine chromaffin granules are mitogenic for cultured bovine aorta endothelial cells. Electrothermal unilateral destruction of the adrenal medulla causes the disappearance of 25% of Nissl-stained neurons in the ipsilateral intermediolateral column (IML) of the spinal cord between levels Th7 and L1, which contains the preganglionic neurons projecting to the adrenal medulla. Substitution of the adrenal medulla by gel foams soaked with bFGF prevents neuron losses in the IML. The effects are specific in that NGF and cytochrome C are ineffective. Our results suggest that bFGF is located in chromaffin cells and maintains target-deprived autonomic spinal cord neurons, thus possibly acting as an interneuronal trophic messenger in vivo.     

Glial cell line-derived neurotrophic factor prevents death,but not reductions in tyrosine hydroxylase,of injured nigrostriatal neurons in adult rats

Glial cell line-derived neurotrophic factor (GDNF) promotes survival of mesencephalic dopaminergic neurons in vitro and when injected locally into the brains of lesioned adult animals. Here, we show that GDNF (3 μg per day and higher) can promote the survival of all (retrogradely labeled) axotomized nigrostriatal dopaminergic neurons of adult rats when continuously infused for 2 weeks close to the substantia nigra, compared to only ∼30% survival with control infusions. Based on our previous observations, GDNF was as potent as ciliary neurotrophic factor and neurotrophin-4 and approximately five to ten times more potent than brain-derived neurotrophic factor and was most effective in promoting survival. GDNF prevented neuronal death induced by 6-hydroxydopamine to a lesser extent than after axotomy. GDNF treatments begun 1 week after axotomy could maintain those neurons that had not yet died. When a 2 week GDNF treatment was interrupted, most of the GDNF-rescued neurons died over the following 2 weeks. This suggests that longer trophic factor treatments or nigrostriatal connections are needed to achieve permanent survival. Measurements of tyrosine hydroxylase (TH) immunoreactivity of the rescued neuronal cell bodies suggest that GDNF cannot prevent the lesion-induced loss of this rate-limiting enzyme for dopamine synthesis. In fact, GDNF induced a decrease in TH in normal animals, suggesting an active down-regulation of TH synthesis. Levels of TH immunoreactivity were recovered between 7 and 14 days after withdrawal of a 2 week GDNF infusion, in the neurons that survived axotomy. These results may have implications for developing new treatment strategies for Parkinson's disease. J. Comp. Neurol. 388:484–494, 1997. © 1997 Wiley-Liss, Inc.     

Apomorphine induces trophic factors that support fetal rat mesencephalic dopaminergic neurons in cultures

Apomorphine, the catechol-derived dopamine D1/D2 receptor agonist, is currently in use as an antiparkinsonian drug. It has previously been reported that apomorphine was able to elicit expression of the enzyme tyrosine hydroxylase, a marker for DA neurons, in the fetal rat cerebrocortical cultures whilst in the presence of brain-derived neurotrophic factor. The present study demonstrated that treatment of fetal rat ventral mesencephalic cultures with apomorphine caused a marked increase in the number of dopaminergic neurons. The action of apomorphine can be mimicked by dopamine receptor (D1 and D2) agonists or blocked by preincubation with D1/D2 receptor antagonists. Incubation of recipient mesencephalic cultures with the conditioned medium derived from apomorphine-stimulated donor mesencephalic cultures elicited a 3.72-fold increase in the number of TH-positive neurons. Increased mRNA expression levels of brain-derived neurotrophic factor and glial cell line-derived neurotrophic factor were also found in the apomorphine-treated mesencephalic cells along with concomitant protein expression increases in the conditioned medium. Moreover, the trophic activity observed could be partially neutralized by antibodies against either brain-derived neurotrophic factor or glial cell line-derived neurotrophic factor. Cultured fetal striatal cells, but not hippocampal cells, also responded to apomorphine treatment. The membrane filtration studies revealed that both <30 kDa and >50 kDa fractions contained trophic activities. The latter characterization distinguishes them from most known neurotrophic factors. These results suggest that the apomorphine-modulated development of dopaminergic neurons may be mediated by activation of the dopamine receptor subtypes D1 and D2 thereby increasing the production of multiple growth factors.     

Basic FGF reverses chemical and morphological deficits in the nigrostriatal system of MPTP-treated mice

The specific mechanisms underlying the restorative effects of adrenal chromaffin grafts in experimental parkinsonism are still obscure. Recent findings indicated an involvement of graft-induced trophic interactions in the course of recovery-related events. Evidence that basic fibroblast growth factor (bFGF), a potent trophic protein for neurons, (1) is present in chromaffin cells (Blottner et al., 1989) and (2) exerts trophic activities on embryonic mesencephalic neurons in vitro (Ferrari et al., 1989) provided the rationale for administering bFGF in gel foam implants unilaterally to the striatum of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) lesioned mice. Simultaneous bFGF/MPTP treatment diminished bilaterally the reduction of striatal dopamine (DA) levels observed in cytochrome c/MPTP-treated mice and led to an ipsilateral reappearance of tyrosine hydroxylase (TH)-like immunoreactive fibers, most notably adjacent to the implant, 2 weeks after the surgery. Determinations of TH activities and TH immunoblotting demonstrated that bFGF almost fully reversed the loss of TH activity on either side but restored TH protein more on the ipsilateral than on the contralateral side. Furthermore, differences in dihydroxyphenylacetic acid levels, which were about twice as high on the contralateral side yet still reduced with respect to untreated mice, supported our assumption that the molar TH activity was increased on the untreated side, possibly due to an intrinsic compensatory up-regulation. Delayed administration of bFGF starting 8 d after the MPTP treatment was equally effective with regard to morphological parameters. Our results suggest that bFGF partially prevents the deleterious chemical and morphological consequences of an MPTP-mediated nigrostriatal lesion. Thus, bFGF mimics at least the morphological effects of chromaffin cell grafts to the MPTP-lesioned brain.     

Regulation of connexin-43, GFAP,and FGF-2 is not accompanied by changes in astroglial coupling in MPTP-lesioned,FGF-2-treated Parkisonian mice

Basic fibroblast growth factor (bFGF; FGF-2) has potent trophic effects on developing and toxically impaired midbrain dopaminergic (DAergic) neurons which are crucially affected in Parkinson's disease. The trophic effects of FGF-2 are largely indirect, both in vitro and in vivo, and possibly involve intermediate actions of astrocytes and other glial cells. To further investigate the cellular and molecular mechanisms underlying the restorative actions of FGF-2, and to analyse in more detail the changes within astroglial cells in the MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine)-lesioned striatum, we have studied striatal expression and regulation of connexin-43 (cx43), the principal gap junction protein of astroglial cells, along with the expression of glial fibrillary acidic protein (GFAP), FGF-2, and functional coupling. Our results show an immediate, yet transient increase in cx43 mRNA, and a sustained increase in FGF-2 mRNA, GFAP-positive cells, and cx43-immunoreactive punctata following the MPTP lesion, without any induction of functional coupling between astrocytes and other glial cells as revealed by dye coupling of patched cells. Unilateral administration of FGF-2 in a piece of gelfoam caused a further increase in cx43-positive punctata immediately adjacent to the implant, which was more pronounced than after application of a gelfoam containing the non-trophic control protein in cytochrome C. These changes were parallelled by a small increase in cx43 protein determined by Western blot, but not by alterations in the coupling state of cells in the vicinity of the gelfoam implant. Although our data indicate that MPTP and exogenous FGF-2 may alter expression and protein levels of cx43, they do not support the notion that increases in cellular coupling may underly the trophic and widespread actions of FGF-2 in the MPTP-model of Parkinson's disease. © 1996 Wiley-Liss, Inc.     

Selective and nonselective stimulation of central cholinergic and dopaminergic development in vitro by nerve growth factor, basic fibroblast growth factor, epidermal growth factor, insulin and the insulin-like growth factors I and II

To study the selectivity of neurotrophic actions in the brain, we analyzed the actions of several known growth factors on septal cholinergic, pontine cholinergic, and mesencephalic dopaminergic neurons in culture. Similar to nerve growth factor (NGF), basic fibroblast growth factor (bFGF) stimulated choline acetyltransferase activity in septal cultures. In contrast to NGF, bFGF also enhanced dopamine uptake in mesencephalic cultures and stimulated cell proliferation in all 3 culture types. Insulin and the insulin-like growth factors I and II stimulated transmitter-specific differentiation and cell proliferation in all culture types. Epidermal growth factor (EGF) produced a small increase in dopamine uptake by mesencephalic cells and stimulated cell proliferation in all culture types. In septal cultures, bFGF was most effective when given at early culture times, NGF at later times. The stimulatory actions of bFGF and insulin did not require the presence of glial cells and were not mediated by NGF. In mesencephalic cultures, the stimulation of dopamine uptake by bFGF and EGF was dependent on glial proliferation. The results suggest different degrees of selectivity of the neurotrophic molecules. NGF and, very similarly, bFGF seem to influence septal cholinergic neurons directly and rather selectively, whereas the neurotrophic actions of insulin and the insulin-like growth factors appear to be more general.     

GDNF is a major component of trophic activity in DA-depleted striatum for survival and neurite extension of DAergic neurons

Extracts from dopamine (DA)-depleted striatal tissue (lesion extract) and from intact striatal tissue (intact extract) were prepared, and trophic activities in these extracts were evaluated using survival and neurite extension of DAergic neurons as indices. Levels of brain-derived neurotrophic factor (BDNF), basic fibroblast growth factor (bFGF), glial cell-line derived neurotrophic factor (GDNF) and neurotrophin-3 (NT-3) in extracts were measured using enzyme-linked immunosorbent assay (ELISA). The lesion extract exhibited a stronger trophic activity on survival and neurite extension of DAergic neurons than intact extract. In lesion extract, bFGF was slightly and GDNF was significantly increased, while BDNF and NT-3 were the same level in each extract. The peak increase of bFGF and GDNF was during 2 to 3 weeks after DA depletion. Trophic activity of extract was strongly attenuated after immunoprecipitation of GDNF and partly attenuated after immunoprecipitation of bFGF. In parallel immunohistological study, no significant variations were found for striatal microtubule-associated protein-2 (MAP-2)- nor OX-41-immunoreactive cells, while the number of strongly labeled glial fibrillary acidic protein (GFAP)-immunoreactive cells were increased in DA-depleted striatum, suggesting reactive gliosis. Data suggest that bFGF is a minor, while GDNF is a major component of trophic activity for DAergic neurons in DA-depleted striatum, and increased bFGF and GDNF levels may be mediated partly by reactive gliosis.     

Screening of adrenal medullary neuropeptides for putative neurotrophic effects.

Chromaffin granules, the secretory organelles of the neuron-like adrenal medullary chromaffin cells, have previously been shown to store and liberate neurotrophic activities that support in vitro survival of several neuron populations including those innervating the adrenal medulla. Molecules resembling fibroblast growth factor and ciliary neurotrophic factor have been identified among these activities. Since chromaffin granules store a variety of neuropeptides and many neuropeptides can have pleiotropic effects on neuronal growth and maintenance we have tested 24 different neuropeptides for their capacities to promote survival of embryonic chick ciliary, dorsal root and sympathetic ganglionic neurons. Peptides tested included several derivatives of proenkephalin (Leu- and met-enkephalin, fragments BAM 22, B, F and E), somatostatin, substance P, neuropeptide Y, neurotensin, VIP, bombesin, secretin, pancreastatin, dynorphin B, dynorphin 1-13, beta-endorphin, alpha-, beta-, and gamma-MSH. Control cultures received saturating concentrations of ciliary neurotrophic or nerve growth factor (CNTF; NGF), or no trophic supplements. At 1 x 10(-5) M leu- and met-enkephalin as well as somatostatin supported sympathetic neurons to the same extent as NGF. At the same concentrations, leu-enkephalin, the proenkephalin fragments BAM 22 and E, and somatostatin maintained about half of the dorsal root ganglionic neurons supported by NGF, but were not effective on ciliary neurons. VIP promoted the survival of approximately 50% of the ciliary and embryonic day 10 dorsal root ganglionic neurons as compared to saturating amounts of CNTF, but required the presence of non-neuronal cells in the cultures to be effective. Neurotensin (1 x 10(-5) M had a small effect on ciliary neurons.(ABSTRACT TRUNCATED AT 250 WORDS)     

Survival and differentiation of dopaminergic mesencephalic neurons are promoted by dopamine-mediated induction of FGF-2 in striatal astroglial cells

Survival of dopaminergic (DAergic) midbrain neurons during development and after lesioning depends, in part, on the presence of astroglia-derived growth factors, as, e.g., fibroblast growth factor (FGF)-2. Astrocytes express DA receptors in a brain-region-specific manner. We show here that DA (10(-3) to 10(-6) mol/liter) applied continuously for 12 h or as a 10-min pulse significantly upregulates FGF-2 immunoreactivity quantified by Western blot and densitometry in astrocytes cultured from two target areas of DAergic neurons, striatum and cortex, but not in mesencephalic astroglia. Semiquantitative competitive RT-PCR confirmed the increase in FGF-2 on the mRNA level. The effects were specific in that glutamate, which can also activate receptors on astroglial cells, did not influence FGF-2 synthesis. In addition to the DA-mediated increase in FGF-2 synthesis the capability of conditioned medium (CM) from DA-stimulated striatal and cortical astrocytes to promote survival and process formation of cultured rat DAergic neurons was significantly enhanced. These effects could be fully blocked by preincubation of the CM with an FGF-2-specific polyclonal antiserum. Our results suggest that DA released from DAergic axon terminals in target regions of DAergic neurons and astroglial FGF-2 production are interdependent in that DA triggers synthesis of FGF-2, which, in turn enhances survival and differentiation of DAergic neurons.     

The TrkC receptor is transiently localized to Purkinje cell dendrites during outgrowth and maturation in the rat

In vivo studies of granule cell gene expression during corticocerebellar development and in vitro studies of Purkinje cell neurite outgrowth suggest that neurotrophin-3 may influence growth of Purkinje cell dendrites. To determine whether neurotrophic substances affect the growth of specific neuronal processes (i.e. axons and dendrites) or nonspecifically cause process development by exerting a trophic influence upon neuronal physiology we performed an immunohistochemical examination of trkC protein expression during early postnatal development of the rat cerebellum. Our findings indicate that Purkinje cells begin to synthesize trkC protein coincident with the onset of dendritic outgrowth. Robust immunostaining was evident throughout the entire somatodendritic domain of Purkinje cells during dendritic development but became faint and restricted to the cell body subsequent to the completion of dendritogenesis. These results suggest that growth and maturation of the Purkinje cell dendritic arbor may be influenced by neurotrophin-3 activation of trkC receptors distributed within developing dendrites. J. Neurosci. Res. 50: 649–656, 1997. © 1997 Wiley-Liss, Inc.     

Astroglial ciliary neurotrophic factor mRNA expression is increased in fields of axonal sprouting in deafferented hippocampus

Evidence that ciliary neurotrophic factor promotes axonal sprouting and regeneration in the periphery raises the possibility that this factor is involved in reactive axonal growth in the brain. In situ hybridization was used in the present study to determine whether ciliary neurotrophic factor mRNA expression is increased in association with axonal sprouting in deafferented adult rat hippocampus. In untreated rats, ciliary neurotrophic factor cRNA labeling density was high in the olfactory nerve, pia mater, and aspects of the ventricular ependyma and was relatively low within areas of white matter (fimbria, internal capsule) and select neuronal fields (hippocampal cell layers, habenula). After an entorhinal cortex lesion, hybridization was markedly increased in fields of anterograde degeneration, including most prominently the ipsilateral dentate gyrus outer molecular layer and hippocampal stratum lacunosum moleculare. Labeling in these fields was increased by 3 days postlesion, was maximal at 5 days, and returned to normal levels by 14 days. Double labeling demonstrated that, in both control and experimental tissue, ciliary neurotrophic factor mRNA was colocalized with glial fibrillary acidic protein immunoreactivity in astroglia, but it was not colocalized with markers for oligodendrocytes or microglia. These results demonstrate that astroglial ciliary neurotrophic factor expression is increased in fields of axonal and terminal degeneration and that increased expression is coincident with 1) increased insulin-like growth factor-1 and basic fibroblast growth factor expression and 2) the onset of reactive axonal growth. The synchronous expression of these glial factors in fields of deafferentation suggests the possibility of additive or synergistic interactions in the coordination of central axonal growth. J. Comp. Neurol. 386:137–148, 1997. © 1997 Wiley-Liss, Inc.     

Fibroblast growth factor 2 (FGF-2) differentially regulates connexin (cx) 43 expression and function in astroglial cells from distinct brain regions

Fibroblast growth factor (FGF)-2 is a peptide growth factor that promotes the generation, differentiation, and survival of neurons and glial cells. In the CNS, astroglial cells are coupled in a region-specific manner by gap junctions consisting of connexin 43 (cx43). In the present study we have investigated effects of FGF-2 and of other growth factors on the expression and function of cx43 in astroglial cells cultured from telencephalic cortex, striatum, and mesencephalon of newborn rats. Confluent cultures were maintained for two days in low serum, and then exposed to FGF-2 (10 ng/ml) for 48 h. FGF-2 caused a reduction of cx43-protein, -mRNA, and intercellular communication revealed by dye spreading. These changes occurred in cortical and striatal cells, but not in mesencephalic astroglial cells. Effects of FGF-2 were time- and concentration-dependent, with a minimal effective dose of 1 ng/ml FGF-2, and an onset of effects after 6 h of incubation. The reduction of coupling by FGF-2 was transient, since in cortical and striatal cultures coupling recovered to control levels 48 h after removal of the growth factor. Like FGF-2, transforming growth factor-β3 (TGF-β3) decreased coupling of cortical and striatal, but not mesencephalic astroglial cells. Astroglial cells from all brain regions showed a slight FGF-mediated increase in 5-bromo-2′-desoxy-uridine (BrdU) incorporation, which was abolished upon co-treatment with TGF-β3. However, TGF-β3 did not interfere with the repression of cx43-function by FGF-2. Epidermal growth factor (EGF) that has been demonstrated to influence coupling in other cell types had no effect on dye spreading but significantly increased BrdU incorporation. Our results reveal a novel function of FGF-2 on cultured astroglial cells which may be relevant to the regulation of astroglial cell connectivity in vivo. GLIA 22:19–30, 1998. © 1998 Wiley-Liss, Inc.     

Epidermal growth factor receptor expression is related to post-mitotic events in cerebellar development: regulation by thyroid hormone

It has been established that thyroid hormone and neurotrophic factors both orchestrate developmental events in the brain. However, it is not clear how these two influences are related. In this study, we investigated the effects of thyroid hormone on cerebellar development and the coincident expression of transforming growth factor-alpha (TGF-alpha), a ligand in the epidermal growth factor (EGF) family, and the epidermal growth factor receptor (EGFR). Profiles of thyroid hormone expression were measured in postnatal animals and were found to peak at postnatal day 15 (P15). These levels dropped below detectable levels when mice were made hypothyroid with propylthiouracil (PTU). TGF-alpha and EGFR expression, as determined by RNAse protection assay, was maximal at P6 in normal animals, but remained low in hypothyroid animals, suggesting that thyroid hormone was responsible for their induction. In situ hybridization and immunohistochemical analysis of EGFR expression revealed that this receptor was present on granule cells within the inner zone of the external granule cell layer (EGL), suggesting that EGFR-ligands were not inducing granule cell proliferation. The persistence of EGFR expression on migrating granule cells and subsequent down-regulation of expression in the internal granule cell layer (IGL) implicates a role for EGFR-ligands in differentiation and/or migration. In hypothyroid animals, we observed a delayed progression of granule cell migration, consistent with the persistence of EGFR labeling in the EGL, and in the 'pile-up' of labeled cells at the interface between the molecular layer and the Purkinje cell layer. Taken together, these results implicate thyroid hormone in the coordinated expression of TGF-alpha and EGFR, which are positioned to play a role in post-mitotic developmental events in the cerebellum.     

Bone Morphogenetic Proteins: Neurotrophic Roles for Midbrain Dopaminergic Neurons and Implications of Astroglial Cells

Bone morphogenetic proteins (BMPs) are members of the transforming growth factor β (TGF-β) superfamily that have been implicated in tissue growth and remodelling. Recent evidence suggests that several BMPs are expressed in the developing and adult brain. Specifically, we show that BMP 2 and BMP 6 are expressed in the developing midbrain floor of the rat. We studied potential neurotrophic effects of BMPs on the in vitro survival, transmitter uptake and protection against MPP+ toxicity of mesencephalic dopaminergic neurons cultured from the embryonic midbrain floor at embryonic day (E) 14. At 10 ng/ml and under serum-free conditions, most BMPs promoted the survival of dopaminergic neurons visualized by tyrosine hydroxylase immunocytochemistry during an 8-day culture period, but to varying extents (relative potencies: BMP 6 = 12 > 2, 4, 7). BMPs 6 and 12 were as effective as fibroblast growth factor-2 (FGF-2) and glial cell line-derived neurotrophic factor, promoting survival 1.7-fold compared with controls. BMPs 9 and 11 were not effective. Dose-response curves revealed an EC₅₀ for BMPs 2, 6 and 12 of 2 ng/ml. BMPs 2, 4, 6, 7, 9 and 12 also promoted DNA synthesis and astroglial cell differentiation, visualized by 5-bromodeoxyuridine (BrdU) incorporation and glial fibrillary acidic protein (GFAP) immunocytochemistry respectively. Suppression of cell proliferation and subsequent maturation of GFAP-positive cells by 5-fluorodeoxyuridine or aminoadipic acid abolished the neuron survival-promoting effect of BMP 2. This suggests that BMPs, like other non-TGF-β factors affecting dopaminergic neuron survival, act indirectly, probably by stimulating the synthesis and/or release of glial-derived trophic factors. BMP 6 and BMP 7 also increased the uptake of [³H]dopamine without affecting the uptake of [³H]5-hydroxytryptamine and [³H]GABA, underscoring the specificity of the trophic effect. We conclude that several BMPs share a neurotrophic capacity for dopaminergic midbrain neurons with other members of the TGF-β superfamily, but act indirectly, possibly through glial cells.     

Forebrain and midbrain astrocytes promote neuritogenesis in cultured chromaffin cells

Adrenal chromaffin cells from immature or adult rats were grown in one of the following 'in vitro' conditions: (1) on coverslips placed on top of confluent, fetal, regional glia cultures; (2) in conditioned media from similar confluent cultures; (3) after direct seeding on top of such confluent cultures. Astroglia was obtained from cerebral cortex, septum, striatum and ventral mesen-cephalon from El6-17 pregnant-dated rats. All regions succesfully generated conditions for the early (less than 24 h) expression of neuritogenesis in about 15% of cells, which was more apparent in immature adrenal cell dissociates than in adult ones. The former grew long neurites compared with their adult counterparts. In addition to the known effects of glioma conditioned medium and isolated trophic factors described by other authors, it is concluded that adrenal chromaffin cells are responsive to the neuritogenic activity of (central) astroglial diffusible factor(s) in non-supplemented, defined culture media conditioned by astrocytes from various brain regions. Additionally, evidence is offered that adult chromaffin cells show a reduced responsiveness towards such astroglial factor(s). Possible implications for cell trasplantation chimeras are discussed.     

Leukemia inhibitory factor augments neurotrophin expression and corticospinal axon growth after adult CNS injury.

The cytokine leukemia inhibitory factor (LIF) modulates glial and neuronal function in development and after peripheral nerve injury, but little is known regarding its role in the injured adult CNS. To further understand the biological role of LIF and its potential mechanisms of action after CNS injury, effects of cellularly delivered LIF on axonal growth, glial activation, and expression of trophic factors were examined after adult mammalian spinal cord injury. Fibroblasts genetically modified to produce high amounts of LIF were grafted to the injured spinal cords of adult Fischer 344 rats. Two weeks after injury, animals with LIF-secreting cells showed a specific and significant increase in corticospinal axon growth compared with control animals. Furthermore, expression of neurotrophin-3, but not nerve growth factor, brain-derived neurotrophic factor, glia cell line-derived neurotrophic factor, or ciliary neurotrophic factor, was increased at the lesion site in LIF-grafted but not in control subjects. No differences in astroglial and microglial/macrophage activation were observed. Thus, LIF can directly or indirectly modulate molecular and cellular responses of the adult CNS to injury. These findings also demonstrate that neurotrophic molecules can augment expression of other trophic factors in vivo after traumatic injury in the adult CNS.     

Role of trophic factors on neuroimmunity in neurodegenerative infectious diseases

Viral infection of the central nervous system elicits a myriad of cellular, vascular, and neuroimmune factors that contribute to acute, subacute, and chronic damage to the brain. In response to cellular damage, the host is capable of producing trophic factors that may protect neuronal, glial, and endothelial cell populations. Both neurotrophic and angiotrophic factors can also operate by modulating the neuroimmune response, which plays a central role in the pathogenesis of the neurodegenerative process. In this regard, crosstalk signaling among host cells, components of the neuroimmune response, and virus could influence cell fate by production of trophic factors that protect or rescue neurons vulnerable to viral damage. In this context, the main objective of this review is to provide an overview of evidence in support of the role of trophic factors in regulating the neuroimmune response in chronic viral infections of the central nervous system. Special emphasis is placed on the interaction of the human immunodeficiency virus (HIV) Tat protein with endothelial, astroglial, microglial, and neuronal cells, resulting in altered expression of vascular endothelial growth factor, fibroblast growth factor, interleukin-8, and regulation of calcium flux via CXCR2, which directly influences neuronal cell fitness.     

Adrenal medullary graft induces recovery of the host nigrostriatal dopaminergic system in MPTP-induced mouse model of Parkinson's disease

C57BL/6 mice show decreased dopaminergic fibers and dopamine concentration in the striatum following systemic injection of 1-methyl-4-phenyl-1, 2, 3, 6-tetrahydropyridine (MPTP). We have investigated the effect of adrenal medullary grafts into the striatum of young mice treated with MPTP. Enhanced recovery of the host nigrostriatal dopaminergic system was observed in those adrenal medullary grafted mice. However, this recovery was influenced by the survivability of grafted chromaffin cells and adrenal chromaffin cells from younger donors survived better than those from older donors. Since adrenal chromaffin cells contain several kinds of neurotrophic factors such as basic fibroblast growth factor and gangliosides, survivability of those grafted chromaffin cells may play an important role concerning recovery of the host intrinsic dopaminergic fibers. Adrenal medullary grafts to the patients with Parkinson's disease are currently under way in a large number of hospitals and we suggest more consideration be given to methods which lead to enhance the grafted chromaffin cell survival, since those survivability might be closely related to the functional recovery of these patients.