Differential effects of acidic and basic fibroblast growth factors on spinal cord cholinergic, GABAergic, and glutamatergic neurons

Bi-functional effects of ATP/P2 receptor activation on tumor necrosis factor-alpha release in lipopolysaccharide-stimulated astrocytes

Neuroinflammation is associated with a variety of CNS pathologies. Levels of tumor necrosis factor-alpha (TNF-alpha), a major proinflammatory cytokine, as well as extracellular ATP, are increased following various CNS insults. Here we report on the relationship between ATP/P2 purinergic receptor activation and lipopolysaccharide (LPS)-induced TNF-alpha release from primary cultures of rat cortical astrocytes. Using ELISA, we confirmed that treatment with LPS stimulated the release of TNF-alpha in a concentration and time dependent manner. ATP treatment alone had no effect on TNF-alpha release. LPS-induced TNF-alpha release was attenuated by 1 mm ATP, a concentration known to activate P2X7 receptors. Consistent with this, 3'-O-(4-Benzoyl)benzoyl-ATP (BzATP), a P2X7 receptor agonist, also attenuated LPS-induced TNF-alpha release. This reduction in TNF-alpha release was not due to loss of cell viability. Adenosine and 2-chloroadenosine were ineffective, suggesting that attenuation of LPS-induced TNF-alpha release by ATP was not due to ATP breakdown and subsequent activation of adenosine/P1 receptors. Interestingly, treatment of astrocyte cultures with 10 microm or 100 microm ATP potentiated TNF-alpha release induced by a submaximal concentration of LPS. UTP and 2methylthioADP (2-MeSADP), P2Y receptor agonists, also enhanced this LPS-induced TNF-alpha release. Our observations demonstrate opposing effects of ATP/P2 receptor activation on TNF-alpha release, i.e. P2X receptor activation attenuates, whereas P2Y receptor activation potentiates TNF-alpha release in LPS-stimulated astrocytes. These observations suggest a mechanism whereby astrocytes can sense the severity of damage in the CNS via ATP release from damaged cells and can modulate the TNF-alpha mediated inflammatory response depending on the extracellular ATP concentration and corresponding type of astrocyte ATP/P2 receptor activated.

Regeneration neurohormones and growth factors in echinoderms

There has been much recent interest in the presence and biological functions of growth regulators in invertebrates. In spite of the different distribution patterns of these molecules in different phyla (from molluscs, insects, and annelids to echinoderms and tunicates), they seem always to be extensively involved in developmental processes, both embryonic and regenerative. Echinoderms are well known for their striking regenerative potential and many can completely regenerate arms that, for example, are lost following self-induced or traumatic amputation. Thus, they provide a valuable experimental model for the study of regenerative processes from the macroscopic to the molecular level. In crinoids as well as probably all ophiuroids, regeneration is rapid and occurs by means of a mechanism that involves blastema formation, known as epimorphosis, where the new tissues arise from undifferentiated cells. In asteroids, morphallaxis is the mechanism employed, replacement cells being derived from existing tissues following differentiation and (or) transdifferentiation. This paper focuses on the possible contribution of neurohormones and growth factors during both repair and regenerative processes. Three different classes of regulatory molecules are proposed as plausible candidates for growth-promoting factors in regeneration: neurotransmitters (monoamines), neuropeptides (substance P, SALMFamides 1 and 2), and growth-factor-like molecules (TGF-β (transforming growth factor β), NGF (nerve growth factor), RGF-2 (basic fibroblast growth factor)).

Gap junctions modulate survival-promoting effects of fibroblast growth factor-2 on cultured midbrain dopaminergic neurons

Fibroblast growth factor 2 (FGF-2) and glial cell line-derived neurotrophic factor (GDNF) support survival of dopaminergic midbrain neurons. Neurons are coupled by gap junctions, propagating metabolites and intracellular second messengers possibly mediating growth factor effects. We asked, therefore, whether gap junctions influence the survival-promoting effects of FGF-2 and GDNF. RT-PCR, Western blotting, and immunocytochemistry demonstrate that FGF-2 but not GDNF upregulates cx43 mRNA and immunoreactivity in rat embryonic day 14 midbrain cultures, whereas cx26, cx32, and cx45 were unchanged. In addition, functional coupling as assayed by the spread of neurobiotin was increased by FGF-2. Furthermore, the gap junction blocker oleamide abolished survival-promoting effects of FGF-2 on dopaminergic midbrain neurons. Together, these results support a direct role of gap junction communication for survival-promoting effects of FGF-2 on dopaminergic midbrain neurons, making gap junction communication a substantial parameter for neuron survival.

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 hippocampus: anatomy, pathophysiology, and regenerative capacity

Cognitive deficits following insults to the central nervous system-particularly those involving the hippocampus and related structures-are often persistent and severely debilitating. Progress has been made in establishing the role of the hippocampus in integrating information in the formation of memory necessary for subsequent recollection of information. The present article will review anatomic, physiological, and functional aspects of the hippocampus in reference to learning and memory. Both animal and human hippocampal pathophysiological processes will be explored. Adaptive and maladaptive central nervous system responses will be reviewed, with a special emphasis on neurogenesis. Ideally, physiological and cellular compensatory responses ought to parallel clinical observation. However, this association is not clearly established. Finally, the current understanding of neuromodulatory mechanisms (although quite preliminary) will also be discussed.

Mitogen and substrate differentially affect the lineage restriction of adult rat subventricular zone neural precursor cell populations

The effects of specific mitogens and substrates on the proliferative capacity and the differentiated phenotypic plasticity of neural precursor cell populations isolated from the adult rat subventricular zone (SVZ) were examined. SVZ cells were grown on uncoated tissue culture plastic, extracellular matrix, or poly-D-ornithine with either laminin or fibronectin. SVZ neural precursor cells could not be generated with platelet-derived growth factor (PDGF), granulocyte macrophage colony stimulating factor, stem cell factor, heparin-binding epidermal growth factor (HB-EGF), granulocyte colony stimulating factor, or ciliary neurotrophic factor (CNTF), but could be with EGF, fibroblast growth factor 2 (FGF2), and FGF2 plus heparin. Varying combinations of substrate and mitogen resulted in very different expansion rates and/or lineage potential. Neurons, oligodendrocytes, and astrocytes differentiated from all cultures, but EGF-generated neural precursor cells were more restricted to an astrocytic lineage and FGF2-generated neural precursor cells had a greater capacity for neuronal differentiation. In both EGF- and FGF2-generated cell populations, CNTF increased the number of differentiated astrocytes, triiodothyronine oligodendrocytes, PDGF neurons, and brain-derived neurotrophic factor neurons only from EGF cells. Electrophysiological analysis of differentiated cells showed three distinct phenotypes, glial, neuronal, and presumed precursor cells, although the neuronal properties were immature. Collectively, these data indicate that CNS neural precursor cell populations isolated with different mitogens and substrates are intrinsically different and their characteristics cannot be directly compared.

Potentiation of glutamatergic agonist-induced inositol phosphate formation by basic fibroblast growth factor is related to developmental features in hippocampal cultures: neuronal survival and glial cell proliferation

We investigated the modulation by growth factors of phospholipase C (PLC)-linked glutamate receptors during in vitro development of hippocampal cultures. In defined medium, glial cells represent between 3 and 14% of total cell number. When we added basic fibroblast growth factor (bFGF) 2 h after plating, we found: (i) a neuroprotection from naturally occurring death for up to 5 days; (ii) a proliferation of glial cells from day 3; and (iii) a potentiation of quisqualate (QA)-induced inositol phosphate (IP) formation from 1 to 10 days in vitro (DIV) and 1S, 3R-amino-cyclopentane-1,3-dicarboxylate (ACPD) response from 3 to 10 DIV. The antimitotic cytosine-beta,D-arabinofuranoside (AraC) blocked glial cell proliferation induced by bFGF, but not neuroprotection. Under these conditions, the early potentiation of the QA response (1-3 DIV) was not changed, while the ACPD and late QA response potentiations were prevented (5-10 DIV). Epidermal growth factor was not neuroprotective but it induced both glial cell proliferation and late QA or ACPD potentiation. Surprisingly, the early bFGF-potentiated QA-induced IP response was blocked by 6, 7-dinitro-quinoxaline-2,3-dione (DNQX), suggesting the participation of ionotropic (RS)-alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA)/kainate (KA) receptors. The delayed bFGF-potentiated ACPD-induced IP response is inhibited by (S)-alpha-methyl-4-carboxyphenylglycine (MCPG), indicating possible activation of glial metabotropic receptors. These results suggest that, in hippocampal cultures, bFGF modulates AMPA and metabotropic glutamate receptors linked to the IP cascade, possibly in relation to the regulation of neuronal survival and glial cell proliferation, respectively.

Effects of an acidic fibroblast growth factor fragment analog on learning and memory and on medial septum cholinergic neurons in senescence-accelerated mice

We examined the effects of repeated subcutaneous injections of an acidic fibroblast growth factor fragment analog, [Ala16] acidic fibroblast growth factor (1-29), on learning and memory and on the choline acetyltransferase immunoreactivity of forebrain neurons in senescence-accelerated mice. One group of accelerated senescence-prone mice (accelerated senescence-prone-8) received [Ala16] acidic fibroblast growth factor (1-29), whereas the other group of accelerated senescence-prone-8 mice and a group of accelerated senescence-resistant mice (control) received vehicle solution. Injections began at three weeks after birth and were given weekly for 10 months. In a passive avoidance test, the mean retention latency at three, six and nine months of age was significantly longer in controls (vehicle-treated accelerated senescence-resistant-1) and acidic fibroblast growth factor fragment-treated accelerated senescence-prone-8 than in vehicle-treated accelerated senescence-prone-8 mice, and the latency in acidic fibroblast growth factor fragment-treated accelerated senescence-prone-8 mice was significantly shorter than that in controls only at nine months of age. In the Morris water maze task, the mean latency to climb onto the platform was significantly longer in acidic fibroblast growth factor fragment- and vehicle-treated accelerated senescence-prone-8 mice than in controls. However, the mean latency in the third and fourth trial blocks was significantly shorter for acidic fibroblast growth factor fragment-treated accelerated senescence-prone-8 than for vehicle-treated accelerated senescence-prone-8 mice. In the probe trials, controls and acidic fibroblast growth factor fragment-treated accelerated senescence-prone-8 mice spent significantly more time in the quadrant in which the platform had previously been located than in the other three quadrants. In acidic fibroblast growth factor fragment-treated accelerated senescence-prone-8 mice, the density of medial septum neurons intensely stained for choline acetyltransferase was significantly greater than that in vehicle-treated accelerated senescence-prone-8 mice, but significantly less than that in controls. The results indicate that the beneficial effect of [Ala16] acidic fibroblast growth factor (1-29) on learning and memory function in accelerated senescence-prone-8 mice may be related to a preservation of function in medial septum cholinergic neurons.

Protein kinase C and cAMP-dependent protein kinase regulate the neuronal differentiation of immortalized raphe neurons

These studies examined the extent to which protein kinase C (PKC) and cAMP-dependent protein kinase (PKA) regulate the neuronal differentiation of the raphe-derived neuronal cell line, RN33B. A differentiation-specific 2.25-fold increase in soluble PKA activity was observed. Neither membrane-associated-PKA, -PKC, or soluble PKC activities changed concomitant with differentiation. The PKC activity was derived from PKC alpha, gamma, epsilon, and theta isoenzymes. Activation of PKC inhibited the immunocytochemical expression of low and medium molecular weight neurofilament proteins, an effect due at least in part to decreased steady-state levels of protein. PKC activation also decreased glutamate immunoreactivity and increased cell number, protein synthesis, and bromodeoxyuridine uptake by 2.4-fold, 25%, and 32%, respectively. Coupled with the decrease in mature neuronal antigen expression, these data suggest that PKC activation inhibits neuronal differentiation by inducing proliferation. Inhibition of PKC markedly upregulated glutamate immunoreactivity. PKA activation potentiated the glutamatergic phenotype of RN33B cells, but inhibition of PKA was without effect on the expression of all neuronal antigens examined. Thus, both PKC and PKA regulate the differentiation of RN33B cells, although neither is absolutely necessary for expression of the differentiated neuronal phenotype. These results suggest the existence of parallel pathways regulating raphe neuronal differentiation.

Heparin, but not other proteoglycans potentiates the mitogenic effects of FGF-2 on mesencephalic precursor cells

There is increasing evidence that the proteoglycan heparin plays a critical role in the regulation of the activity of FGF-2 by either interacting with its receptor or modifying its stability and functioning. In this study precursor cells were isolated from the rat E14 ventral mesencephalon and cultured as free floating spheres in FGF-2 alone or in combination with heparin or other related proteoglycans, including chondroitin sulfate, keratin sulfate, dermatan sulfate, or hyaluronic acid. Our results show the mitogenic effects of FGF-2 could be potentiated by heparin but not the other four proteoglycans. Sodium chlorate, which blocks the cells ability to sulfate its proteoglycans, was shown to reduce the mitogenic effects of FGF-2 alone to below that of control levels, suggesting that endogenous sulfated molecules are required for the FGF-2 effects on mesencephalic precursors. Cells expanded for 7 days with either FGF-2 or FGF-2 + heparin were plated onto a substrate and allowed to differentiate for a further 7 days in the absence of growth factors. Approximately 6% of the precursors developed into neurons whether grown with or without heparin and none were positive for TH, a marker for dopamine neurons. However, there was a significant decrease in the number of astrocytes developing from cultures grown in FGF-2 + heparin when compared to FGF-2 alone. Interestingly we could not find an EGF responsive cell in the mesencephalon at this embryonic age in the absence or presence of heparin. However, there was a synergistic effect of combining EGF + FGF-2, which could be potentiated by heparin. We conclude that heparin, but not other closely related proteoglycans, is vital for the growth of FGF-2-responsive mesencephalic neural precursors.

Heparan sulfate modifies the effects of basic fibroblast growth factor on glial reactivity

Our previous studies have shown that injection of basic fibroblast growth factor (bFGF) into a brain wound enhances astrocyte hypertrophy and macrophage-microglia proliferation in areas adjacent to the lesion. In the present study, designed to test the effects of co-administration of bFGF and heparan sulfate (HS), rats received injections of 200 ng bFGF, 200 ng bFGF with 50 microg HS, or 50 microg HS into a brain wound. Glial proliferation and astrocyte hypertrophy were evaluated in seven non-overlapping subfields in the mid-cortex including the wound edge. Our results show that bFGF-HS, compared to bFGF or HS alone, enhanced the total area of GFAP staining in all subfields except the one nearest to the wound edge. The combination of bFGF and HS did not increase total glial or astrocyte proliferation. We propose that the observed effects resulted from a greater diffusion of bFGF-HS complex into the brain parenchyma, where it bypassed low-affinity binding sites that would otherwise sequester free bFGF. Our results suggest that bFGF-HS complex, compared to bFGF alone, may gain entry into the brain more readily, reach higher concentrations and be more effective as a neurotrophic agent.

A simple technique to efficiently dissociate primary auditory neurons from 5 day-old rat cochleas

The aim of this work was to develop a simple and reproducible method of dissociation of cochlear spiral ganglion neurons in the rat. This technique, wich was developed in 5 day-old rat pups, was based on the use of a single enzyme, thermolysin. It is easy to set up and allows the collection of a large amount of neurons. These isolated neurons were kept in a definite, serum free culture medium up to 7 days. Neurons were characterized both by standard morphological criteria and by using a specific neuronal marker (anti-neurofilament 200 kD) after 2 h and 7 days in culture. Cell viability, assessed by fluorescent dyes indicated that all isolated cells were healthy even after 7 days in vitro. The dissociation and culture methods were found very satisfactory and can be easily adapted to any kind of experiment requiring isolated spiral ganglion neurons.

Delayed administration of basic fibroblast growth factor (bFGF) attenuates cognitive dysfunction following parasagittal fluid percussion brain injury in the rat

The present study evaluates the therapeutic effects of delayed administration of bFGF on cognitive dysfunction and histopathological damage following lateral fluid-percussion (FP) brain injury. Male Sprague-Dawley rats were trained to learn a visuospatial task in a Morris Water Maze (MWM) paradigm and then were anesthetized and subjected to either FP brain injury of moderate severity (2.5-2.8 atm, n = 32) or surgery without brain injury (n = 10). Twenty-four hours postinjury, an infusion cannula connected to a mini-osmotic pump was implanted into the area of maximal cortical injury to continuously infuse either bFGF (2.0 g) or vehicle for 7 days. Treatment with bFGF significantly attenuated posttraumatic memory dysfunction in the MWM at 8 days postinjury when compared to vehicle treatment (p < 0.05). The cortical lesion and significant cell loss in the ipsilateral CA3 region of the hippocampus, produced by FP injury, was not affected by bFGF treatment. However, immunohistochemical evaluation of glial fibrillary acidic protein revealed a trend toward increased astrocytosis in the injured cortex of bFGF-treated animals compared to vehicle-treated animals (p < 0.1). These results indicate that bFGF may be efficacious in attenuating cognitive dysfunction associated with traumatic brain injury.

Substance P and enkephalin immunoreactivities in axonal boutons presynaptic to physiologically identified dorsal horn neurons. An ultrastructural multiple-labelling study in the cat

A combination of intracellular electrophysiological recording and injection of horseradish peroxidase with ultrastructural immunocytochemistry was used to investigate the synaptic interplay between substance P- and enkephalin-immunoreactive axonal boutons and three types of functionally characterized dorsal horn neurons in the cat spinal cord. The dorsal horn neurons were classified as nociceptive specific, wide dynamic range and non-nociceptive based on their responses to innocuous and noxious stimuli. Most of the nociceptive neurons (either nociceptive specific or wide dynamic range) contained enkephalin immunoreactivity, but none of the non-nociceptive neurons were positive for enkephalin. Three types of immunoreactive boutons were found in contact with the functionally characterized dorsal horn neurons. These boutons were positive for either substance P, enkephalin, or substance P+enkephalin. Quantitative analysis revealed that the percentages of substance P-immunoreactive boutons apposed to the cell bodies, proximal dendrites and distal dendrites of nociceptive neurons were significantly higher than those of non-nociceptive neurons. Furthermore, the percentages of substance P+enkephalin-immunoreactive axonal boutons apposed to the distal dendrites of nociceptive neurons were significantly higher than those of non-nociceptive neurons and the percentages of enkephalin-immunoreactive boutons apposed to the cell bodies and proximal dendrites of nociceptive neurons were significantly higher than in non-nociceptive neurons. Finally, neither enkephalin-immunoreactive nor substance P+enkephalin-immunoreactive boutons were ever seen presynaptic to substance P-immunoreactive boutons. These results provide evidence of an anatomical substrate within the dorsal horn for the interaction of substance P-mediated with enkephalin-mediated mechanisms. The data support the idea that the modulation of nociceptive input in the dorsal horn by enkephalinergic neurons occurs mainly via a postsynaptic mechanism, and thus suggest that dorsal horn enkephalinergic neurons participate in a local inhibitory feedback loop in a distinct pathway from the previously postulated opioid-mediated depression of substance P release from primary afferent terminals.

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

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

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

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

Quantitative analysis of vascularization and cytochrome oxidase following fetal transplantation in the contused rat spinal cord

In the normal adult central nervous system, a coupling between energy consumption and vascular density is well established. Likewise, the survival of fetal neural tissue grafts is highly dependent on the establishment of functional vascular integration with the host. However, to what degree graft vascularization and tissue metabolism influence the normal host response to traumatic injury has not been extensively studied. In the present report, embryonic day 14 fetal spinal cord suspension grafts were made into the lesion epicenter of subchronic (10 days) contusion-injured rats. Three months later, intraspinal transplants were analyzed using correlative cytochrome oxidase histochemistry and vascular morphometric analysis. The same approaches were applied to the host spinal cord and injured, non-transplanted animals in order to determine the ability of a graft to alter the level of post-injury vascularization and/or metabolism. In general, graft vascular density was increased over that measured in normal or injured gray matter. Vascular density in gray matter near the host/graft interface was markedly increased when compared to either gray matter of the same spinal level in injured non-grafted animals or normal control spinal gray matter. Vascular changes were not noted in gray matter 3 mm distal to the lesion epicenter (rostral or caudal) in all groups analyzed. Cytochrome oxidase was up-regulated at this time in the graft and gray matter at the host/graft interfaces when compared to either gray matter of the same spinal level in injured, non-grafted animals or that of uninjured controls. These data indicate that an intraspinal transplant placed into the contused adult rat spinal cord reaches a metabolic capacity that is likely to be associated with high levels of oxidative metabolism in the well-vascularized graft neuropil. In addition, transplantation chronically alters vascularization and metabolic patterns of adjacent spinal gray matter following contusion injury.

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

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

Expression of acidic FGF mRNA in rat auditory brainstem during postnatal maturation

In situ hybridization was used to investigate the mRNA distribution of acidic and basic fibroblast growth factor (aFGF and bFGF) in the auditory brainstem of neonatal and adult rats. bFGF mRNA was not detected at any age. In adult rats, aFGF mRNA was strongly expressed in the principal neurons of the anteroventral and posteroventral cochlear nuclei, but not in the octopus cells. In the dorsal cochlear nucleus, aFGF mRNA was seen only in scattered smaller vertical cells. aFGF was strongly expressed in the nucleus of the trapezoid body and in all periolivary cell groups, but not in the medial and lateral olivary nuclei. No expression was observed in the lemniscal nuclei or in the central nucleus of the inferior colliculus, but large neurons in the external zone of the colliculus were labeled. Developmentally, low levels of aFGF expression appeared in the cochlear nuclei and olivary nuclei between P0 and P6. This expression increased rapidly during the onset of hearing, between P10 and P14, and reached adult level by P14-P17. Labeling in collicular neurons appeared slightly later. The results suggest that the appearance of strong aFGF mRNA expression is related to the onset of function.

Acidic FGF and FGF receptors are specifically expressed in neurons of developing and adult rat dorsal root ganglia

Employing complementary technical approaches, we have studied the expression of acidic fibroblast growth factor (aFGF) and FGF receptors in rat dorsal root ganglia. The results clearly showed that within spinal nerves aFGF and two high-affinity FGF receptors, FGFR-1 and FGFR-2, were prominently expressed in neurons, while expression in Schwann cells was undetectable. FGFR-3 and FGFR-4 were not expressed in dorsal root ganglia. Acidic FGF mRNA was detected in the majority of dorsal root ganglion neurons, including all size classes: FGFR-1 and FGFR-2 transcripts were only detected in subpopulations of mainly large and medium size neurons. In subcellular fractionation studies on dorsal root ganglion and spinal root tissue, aFGF was recovered in the soluble fraction and was thus not tightly associated with neuronal membranes. During development FGFR-1 and FGFR-2 mRNAs were found to be present at all stages examined (embryonic days 15-21 and postnatal days 1-120). Acidic FGF mRNA and protein were first detected at embryonic day 18, and their expression then increased progressively up to postnatal levels. In cultures of dorsal root ganglion neurons derived from day 15 embryos, aFGF expression was first detected 3 days after plating. The resulting neuron cultures continued to express aFGF in a Schwann cell-independent manner. In combination, these results indicate that aFGF expression in dorsal root ganglia is initiated and maintained in postmitotic neurons. Furthermore, the data suggest that the physiological function of aFGF in the peripheral nervous system is connected to processes specific to the mature sensory (and motor) system, such as the maintenance and survival of peripheral nerve neurons.

Fibroblast growth factor-2-like immunoreactivity in auditory brainstem nuclei of the developing and adult rat: correlation with onset and loss of hearing

Fibroblast growth factor-2 (FGF-2; basic FGF) is widely distributed in the developing and adult brain and has numerous effects on cultured and lesioned neural cells. The physiological role of FGF-2 in the unlesioned nervous system, however, is still not understood. We have studied the distribution of FGF-2 in the developing, adult, and functionally impaired central auditory system of the rat using specific antibodies and peroxidase-antiperoxidase immunocytochemistry. FGF-2-like immunoreactivity (FGF-2-IR) occurred in neuronal cell bodies and/or nerve fibers but was very rarely observed in glial cells. Several auditory brainstem nuclei, including the superior paraolivary nucleus, the medial superior olive, the lateral and ventral trapezoid nuclei, and the central nucleus, as well as the external cortex of the inferior colliculus, were entirely devoid of FGF-2-IR. In the dorsal cochlear nucleus, the lateral superior olive, and the nuclei of the lateral lemniscus, FGF-2-IR was not detectable in nerve cell bodies prior to adult age. Neurons in the medial geniculate body exhibited FGF-2-IR only transiently, from postnatal day (P) 5 until P16. Neurons in the medial nucleus of the trapezoid body were immunoreactive from P8 onwards. FGF-2-IR in anteroventral and posteroventral cochlear neurons disappeared at P14, i.e., at the onset of hearing, but immunoreactivity returned after P21. A transient expression of FGF-2 around the time when hearing function commences was observed in the dorsal cortex of the inferior colliculus.(ABSTRACT TRUNCATED AT 250 WORDS)

Cytokines in sleep regulation

The central thesis of this essay is that the cytokine network in brain is a key element in the humoral regulation of sleep responses to infection and in the physiological regulation of sleep. We hypothesize that many cytokines, their cellular receptors, soluble receptors, and endogenous antagonists are involved in physiological sleep regulation. The expressions of some cytokines are greatly amplified by microbial challenge. This excess cytokine production during infection induces sleep responses. The excessive sleep and wakefulness that occur at different times during the course of the infectious process results from dynamic changes in various cytokines that occur during the host's response to infectious challenge. Removal of any one somnogenic cytokine inhibits normal sleep, alters the cytokine network by changing the cytokine mix, but does not completely disrupt sleep due to the redundant nature of the cytokine network. The cytokine network operates in a paracrine/autocrine fashion and is responsive to neuronal use. Finally, cytokines elicit their somnogenic actions via endocrine and neurotransmitter systems as well as having direct effects neurons and glia. Evidence in support of these postulates is reviewed in this essay.

Comparative effect of alpha-MSH and b-FGF on neurite extension of fetal rat spinal cord neurons in culture

Basic fibroblast growth factor (b-FGF) and alpha melanocyte stimulating hormone (alpha-MSH) were tested for their ability to promote axonal elongation on E14 fetal rat spinal cord cell culture, and to support cell survival. A similar development of neurite was observed in alpha-MSH treated cultures or in control cultures, with an axonal length ranging from 87.50 microns to 195.60 microns on day 3. Complete cell death occurred after 6 days of incubation. Whatever the concentration of b-FGF used (0.312-2.5 ng/ml), a significant increase (1.2- to 1.4-fold) in neurite length was observed, with neuronal survival up to 9 days.

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.

Septal neuron cholinergic and GABAergic functions: differential regulation by basic fibroblast growth factor and epidermal growth factor

Numerous studies suggest that growth and trophic factors play roles in the development and mature function of brain neurons. Recently, growth factors whose actions were previously characterized on non-neuronal cells have been localized to the brain. We sought to determine whether these factors influence septal cholinergic function. Initially, we defined the effects of basic fibroblast growth factor (bFGF) and epidermal growth factor (EGF) on septal cholinergic cells in dissociated neuronal culture. Both factors elevated activity of the acetylcholine synthetic enzyme, choline acetyltransferase (CAT). To determine whether the factors acted directly on neurons or whether glia mediated the effects, a mitotic inhibitor, 5-fluorodeoxyuridine (FDUR), was added to the cultures to eliminate dividing glia. The action of EGF was completely blocked by the addition of FDUR. However, bFGF elevated CAT activity even in the presence of FDUR. Consequently, bFGF may regulate septal cholinergic function directly, whereas EGF may affect cholinergic cells indirectly through glia. To determine whether increases in CAT activity reflect increased enzyme activity per neuron or an increase in the number of cholinergic cells, bFGF-treated cultures were stained for acetylcholinesterase (AChE) to determine numbers of cholinergic cells. No differences in AChE-positive cells were noted, suggesting that bFGF increased CAT activity per cholinergic neuron. To determine whether bFGF regulates other populations in the septum, we examined GABAergic neurons by monitoring the activity of glutamic acid decarboxylase (GAD), a GABA synthetic enzyme. Basic FGF significantly increased GAD activity; however, the effect was completely abolished by addition of FDUR. Thus, bFGF may act directly on cholinergic neurons and indirectly on GABA cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Isolation and characterization of conditionally immortalized astrocyte cell lines derived from adult human spinal cord

As an approach to develop both oligodendrocytic and astrocytic cell lines from adult human spinal cord, a cellular preparation of highly enriched oligodendrocytes and their precursors was infected with a replication-deficient retrovirus containing DNA sequences encoding the temperature-sensitive mutant of SV40 large T antigen. Six immortal cell lines were obtained. At both permissive (33 degrees C) and non-permissive (38.5 degrees C) temperatures, all cell lines were positive for vimentin, two demonstrated glial fibrillary acidic protein (GFAP) immunoreactivity, and none expressed oligodendrocyte or microglial markers. The 2 GFAP-positive cell lines [human spinal cord (HSC)2 and HSC6] were further characterized. Karyotype analysis revealed that both HSC2 and HSC6 cells showed gain of chromosomal material and structural chromosomal abnormalities. However, at non-permissive temperature both cell lines were indistinguishable from primary human astrocytes by a number of criteria. These properties included glutamine synthetase activity, Na(+)-dependent glutamate uptake, K+ flux, purine-evoked Ca2+ mobilization and entry, and the ability to support neurite outgrowth from embryonic rat retinal explants. The HSC2 and HSC6 cell lines may prove to be valuable models for studying the physiological properties of adult human astrocytes.

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.

Differentiation of an immortalized CNS neuronal cell line decreases their susceptibility to cytotoxic T cell lysis in vitro

RN33B cells are a temperature-sensitive neuronal cell line derived from rat E12 medullary raphe nucleus (Whittemore and White (1993) Brain Research 615, 27-40). Undifferentiated RN33B cells express class I but not class II antigens of the major histocompatibility complex (MHC), and intercellular adhesion molecule-1 (ICAM-1), a ligand for lymphocyte function associated antigen-1 (LFA-1), expressed on cytotoxic T lymphocytes (CTLs). Treatment of undifferentiated RN33B cells with interferon-gamma (IFN-gamma) upregulated both class I MHC and ICAM-1. After neuronal differentiation, expression of class I MHC antigens or ICAM-1 was undetected, even after IFN-gamma treatment. The neuronally differentiated RN33B cells were also markedly less susceptible to lysis by alloantigen-specific CTLs. These data suggest that intrinsic to the differentiation of CNS neurons is a mechanism to escape CTL-mediated cell lysis.

Concurrent isolation and characterization of oligodendrocytes, microglia and astrocytes from adult human spinal cord

A cellular preparation of highly enriched oligodendrocytes was obtained from adult human spinal cord by Percoll gradient centrifugation followed by either differential adhesion or fluorescence-activated cell sorting after immunostaining with an antibody against galactocerebroside (O1). The adherent and O1-negative cell fractions were > 96% microglia. The non-adherent and O1-positive fractions were > 96% positive for the oligodendrocyte markers O4 and O1, 0-2% positive for glial fibrillary acidic protein, and were devoid of neuronal or microglial markers. If the oligodendrocyte fraction was co-cultured with purified dissociated rat dorsal root ganglion neurons, the oligodendrocytes adhered to the axons and their numbers increased over a 4 week period. However, myelin sheaths were not produced around axons in these cultures. In contrast, if the oligodendrocyte cell fraction was grown alone in culture for > 3 weeks, the number of oligodendrocytes decreased and a layer of astrocytes developed underneath the oligodendrocytes. The oligodendrocytes could be eliminated from these cultures by subsequent passaging, thus producing cultures of pure astrocytes. The astrocytes accumulated both K+ and glutamate with kinetic properties similar to those reported for rodent astrocytes. We suggest that these astrocytes arose in part from an O4/O1-positive precursor which did not initially express glial fibrillary acidic protein. These results define a relatively simple method by which highly enriched populations of oligodendrocytes, astrocytes and microglia can be obtained from adult human spinal cord.

Effects of acidic fibroblast growth factor on cholinergic neurons of nucleus basalis magnocellularis and in a spatial memory task following cortical devascularization

The ability of acidic fibroblast growth factor to elicit a trophic response in the nervous system of the rat was tested in vitro and in vivo. Treatment of cultured septal cells with acidic fibroblast growth factor resulted in an elongation of glial processes as assessed by immunostaining for glial fibrillary acidic protein. Increased choline acetyltransferase was also observed. The responses to acidic fibroblast growth factor in vivo were studied in rats trained in a spatial memory task, using the Morris water maze. Randomly selected animals were subjected to unilateral cortical devascularization. This lesion results in partial unilateral infarction of the neocortex, and in retrograde degeneration of the nucleus basalis magnocellularis. Animals were tested post-lesion for memory retention and were then killed for morphological studies. Intracerebroventricular administration of acidic fibroblast growth factor (0.6 microgram/h for seven days starting at surgery) prevented the lesion-induced impairment in this test, and reduced the nucleus basalis magnocellularis cholinergic degeneration, as assessed by morphometric choline acetyltransferase-like immunoreactivity and radioenzymatic assay for choline acetyltransferase activity. The preservation of the phenotype of injured cholinergic neurons of the nucleus basalis magnocellularis by acidic fibroblast growth factor was indicated by the maintenance of the cross-sectional area of cell bodies and mean length of neuritic processes one month after surgery. The effect of acidic fibroblast growth factor in non-cholinergic cells remains to be investigated. It is suggested that acidic fibroblast growth factor may alleviate the lesion-induced deficit in the memory retention task by preventing disruption of functional connections between nucleus basalis magnocellularis and intact cortical areas.(ABSTRACT TRUNCATED AT 250 WORDS)

Acidic and basic FGF mRNA expression in the adult and developing rat cochlea

In situ hybridization was used to document the distribution of mRNA encoding acidic and basic fibroblast growth factor (aFGF and bFGF) in the rat cochlea from embryonic day (E) 16 to postnatal day (P) > 60. bFGF mRNA was not detected in the cochlea at any age. In the adult, aFGF mRNA was strongly expressed in spiral ganglion (SG) neurons, and this expression increased from base to apex. The stria vascularis (SV) and spiral prominence (SP) showed lesser expression which was equal in all turns. Developmentally, low level expression of aFGF mRNA was first seen in the SG at E-20, and remained low until P-4. Expression increased from P-6 to P-14, when adult levels were reached. aFGF mRNA was also observed in the developing hair cells of all turns at E-20. This expression increased after birth but disappeared after P-6. Expression in the SV and SP was first noted at E-20 and reached adult levels by P-16 and P-10, respectively. High levels of aFGF mRNA in the adult SG suggest that aFGF is important for the maintenance of SG neuron function and structure. aFGF in hair cells during the first postnatal week may be involved in the establishment of cochlear innervation.

Target regulation of neuronal differentiation in a temperature-sensitive cell line derived from medullary raphe

Following infection of dissociated embryonic day 13 rat medullary raphe cells with a retrovirus encoding the temperature-sensitive mutant of SV40 large T antigen, a clonal cell line, RN33B, was isolated by serial dilution. At 33 degrees C, RN33B cells divide with a doubling time of 48 h and show T antigen, vimentin, nestin, diffuse neuron-specific enolase, and low and medium molecular weight neurofilament immunoreactivities. RN33B cells are immortal, but not transformed, as they will not grow in soft agar. At non-permissive temperature (38.5 degrees C), T antigen expression is markedly decreased and RN33B cells cease mitotic activity and differentiate with phase bright cell bodies and 'neuritic-like' processes. Differentiated RN33B cells express enhanced neuronal-specific protein expression but do not synthesize astrocytic or oligodendrocytic-specific proteins. Moreover, differentiated RN33B cells returned to 33 degrees C re-express T antigen, but do not de-differentiate or begin dividing. Co-culture with embryonic hippocampus and cerebral cortex, but not medullary raphe or spinal cord, resulted in significantly greater survival, more complex neuronal morphology, and enhanced expression of neuronal-specific antigens. Immunohistochemical and Northern blot analysis revealed high levels of low affinity NGF receptor protein and mRNA in differentiated RN33B cells. PCR analysis demonstrated the presence of trkB, but not trkA or trkC, mRNA in both undifferentiated and differentiated RN33B cells. These data suggest that the observed target regulation of RN33B cell neuronal differentiation in co-culture may be mediated by neurotrophin(s).

In vitro labeling strategies for identifying primary neural tissue and a neuronal cell line after transplantation in the CNS

Potential labels for identifying embryonic raphe neurons and a clonal, neuronally differentiating, raphe-derived cell line, RN33B, in CNS transplantation studies were tested by first characterizing the labels in vitro. The labels that were tested included 4',6-diamidino-2-phenylindole hydrochloride, 1,1'-dioctadecyl-3,3,3'-tetramethylindocarbocyanine perchlorate, the Escherichia coli lacZ gene, Fast Blue, Fluoro-Gold, fluorescein-conjugated latex microspheres, fluorescein isothiocyanate-conjugated or nonconjugated Phaseolus vulgaris leucoagglutinin, methyl o-(6-amino-3'-imino-3H-xanthen-9-yl) benzoate monohydrochloride, or tetanus toxin C fragment. Subsequently, the optimal in vitro labels for embryonic raphe neurons and for RN33B cells were characterized in vivo after CNS transplantation. In vitro, 1,1'-dioctadecyl-3,3,3'-tetramethylindocarbocyanine perchlorate (DiI) optimally labeled embryonic neurons. The Escherichia coli lacZ gene optimally labeled RN33B cells. Most labels were rapidly diluted in cultures of embryonic astrocytes and proliferating RN33B cells. Some labels were toxic and were often retained in cellular debris. In vivo, DiI was visualized in transplanted, DiI-labeled raphe neurons, but not in astrocytes up to 1 mo posttransplant. DiI-labeled host cells were seen after transplantation of lysed, DiI-labeled cells. beta-Galactosidase was visualized in transplanted, Escherichia coli lacZ gene-labeled RN33B cells after 15 days in vivo. No beta-galactosidase was seen in host cells after transplantation of lysed, lacZ-labeled RN33B cells. The results demonstrate that labels for use in CNS transplantation studies should be optimized for the specific population of donor cells under study, with the initial step being characterization in vitro followed by in vivo analysis. Appropriate controls for false-positive labeling of host cells should always be assessed.

Role of the cell recognition molecule, cognin, in GABAergic differentiation in chick retina

Previous work showed that GABAergic differentiation in developing chick retina depends on insulin and cell interactions. Here, we investigated whether it depended on cell signaling mediated by retina cognin, a 50 kDa cell recognition molecule. Cognin mediates cell adhesion in vitro and occurs on retinal neurons that become both GABAergic and cholinergic. We investigated two markers of GABAergic differentiation: glutamate decarboxylase (GAD) activity and high-affinity GABA uptake. Both increase during differentiation of retinal neurons in culture and can be easily measured. We blocked cognin-mediated cell signaling with cognin antibody and found a reduction of the developmental increase in GAD activity in cultures of retinal neurons from 7 and 11 day chick embryos. There was no reduction of high-affinity GABA uptake. This suggested that cognin-mediated signaling was necessary for the normal developmental increase in GAD but not for high-affinity GABA uptake. These results contrasted with our previous observations on cholinergic differentiation in cultured retinal neurons. We found that cognin antibody blocked the normal developmental increase in choline acetyltransferase (ChAT) only if the cells were exposed before embryonic day 7. Thus, while both GAD and ChAT activity appear to be controlled by cell signaling involving cognin, the periods of developmental sensitivity for the two differentiation markers are different. Antibodies to other adhesion molecules, Ng-CAM, and N-cadherin, did not similarly affect GAD activity. Antibodies to laminin at a 10-fold higher concentration inhibited GAD activity only in early embryonic retina. Tests for protein synthesis and "housekeeping" enzyme activity demonstrated that the cognin antibody effect was selective for neuronal differentiation pathways.(ABSTRACT TRUNCATED AT 250 WORDS)

Interleukin-6 and leukemia inhibitory factor promote the survival of acetylcholinesterase-positive neurons in culture from embryonic rat spinal cord

Interleukin-6 (IL-6) and leukemia inhibitory factor (LIF) promoted the survival of acetylcholinesterase (AChE)-positive neurons in culture from embryonic E15 rat spinal cord. Half of the AChE-positive neurons died during 3-7 days in culture in the absence of IL-6 and LIF. However, IL-6 at a concentration of 5 ng/ml completely prevented the death of AChE-positive neurons. LIF at a concentration of 5 U/ml also stimulated the survival of neurons, although to a lesser extent than IL-6. IL-6 and LIF also increased the numbers of process-bearing neuron-like cells in culture. The dose-dependencies of IL-6 and LIF with regard to the survival of total neuron-like cells were different from those for AChE-positive neurons.

Characterization of a neurotrophic factor produced by cultured astrocytes involved in the regulation of subcortical cholinergic neurons

When dissociated subcortical cells were cultured in the presence of conditioned medium of relatively differentiated astrocytes (ACM), a marked increase was observed in the expression of choline acetyltransferase (ChAT), an enzyme required for the synthesis of the neurotransmitter acetylcholine. Astrocytes from the target regions of subcortical neurons, the hippocampus and the cerebral cortex, produced neurotrophic factor consistently more than those derived from the nontarget region, the cerebellum. The production of cholinergic trophic activity was increased with the maturation of astrocytes. Even though, nerve growth factor (NGF) and ciliary neurotrophic factor (CNTF) are known cholinergic trophic compounds produced by astrocytes in vitro, a large part of the neurotrophic activity in our ACM was not related to either of these 2 factors. This is because (i) ACM and NGF produced an additive effect on ChAT activity, (ii) only a small proportion of the cholinergic trophic activity in ACM was abolished by anti-NGF antibody, and (iii) treatment with CNTF had no effect on ChAT activity of basal forebrain cholinergic neurons. On the other hand, when cholinergic neurons are cultured on a preformed layer of astrocytes, addition of basal fibroblast growth factor (bFGF) failed to increase further the ChAT activity. Similarly the effects of ACM and bFGF were not additive. A large proportion of the cholinergic trophic activity in ACM was neutralized by anti-bFGF antibody. These findings would suggest that the trophic activity on septal cholinergic neurons in our ACM was due to bFGF or a bFGF-like compound.

Acidic and basic fibroblast growth factor levels in spinal cord cultures are not regulated by alterations in heparan sulfate proteoglycan expression

The present study was undertaken to assess both the levels of acidic and basic fibroblast growth factors in spinal cord cultures and to determine how they were presented to responsive cells. Western blots detected a single acidic fibroblast growth factor-like protein (17 kDa) and two (18 kDa, 24 kDa) basic fibroblast growth factor-immunoreactive proteins, the levels of which varied with the antibody used. Levels of all three proteins were unaltered in cultures grown in the presence of a mitotic inhibitor, which greatly reduced the number of astrocytes. Cell blots showed increased survival of spinal cord neurons at Mr that corresponded with the three proteins detected immunologically. Solubilized cultures separated on a P100 column showed mitogenic activity for NIH3T3 cells from 17-18 and 24 kDa fractions. Treatment of the cultures with heparitinase did not decrease the levels of acidic and basic fibroblast growth factors detected by Western blots, suggesting that these proteins were not associated with extracellular membrane heparan sulfate proteoglycans. The major fraction of both proteins appeared to be intracellular with a minor amount complexed with extracellular matrix proteins. An inhibitor of xylose-linked proteoglycan synthesis significantly altered heparan sulfate proteoglycan deposition into extracellular matrix, but did not alter the levels of acidic or basic fibroblast growth factors detected by Western blots, or the levels of choline acetyltransferase, glutamic acid decarboxylase, or aspartate aminotransferase activities. These results indicate that both acidic and basic fibroblast growth factors are stored predominantly intracellularly, with only a minor fraction complexed with extracellular proteins. We suggest that these intracellular proteins may be released following injury in the CNS and mediate a cascade of neuroprotective events.