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

Multimodal Optical Imaging to Investigate Spatiotemporal Changes in Cerebrovascular Function in AUDA Treatment of Acute Ischemic Stroke

Administration of 12-(3-adamantan-1-yl-ureido)-dodecanoic acid (AUDA) has been demonstrated to alleviate infarction following ischemic stroke. Reportedly, the main effect of AUDA is exerting anti-inflammation and neovascularization via the inhibition of soluble epoxide hydrolase. However, the major contribution of this anti-inflammation and neovascularization effect in the acute phase of stroke is not completely elucidated. To investigate the neuroprotective effects of AUDA in acute ischemic stroke, we combined laser speckle contrast imaging and optical intrinsic signal imaging techniques with the implantation of a lab-designed cranial window. Forepaw stimulation was applied to assess the functional changes via measuring cerebral metabolic rate of oxygen (CMRO₂) that accompany neural activity. The rats that received AUDA in the acute phase of photothrombotic ischemia stroke showed a 30.5 ± 8.1% reduction in the ischemic core, 42.3 ± 15.1% reduction in the ischemic penumbra (p < 0.05), and 42.1 ± 4.6% increase of CMRO₂ in response to forepaw stimulation at post-stroke day 1 (p < 0.05) compared with the control group (N = 10 for each group). Moreover, at post-stroke day 3, increased functional vascular density was observed in AUDA-treated rats (35.9 ± 1.9% higher than that in the control group, p < 0.05). At post-stroke day 7, a 105.4% ± 16.4% increase of astrocytes (p < 0.01), 30.0 ± 10.9% increase of neurons (p < 0.01), and 65.5 ± 15.0% decrease of microglia (p < 0.01) were observed in the penumbra region in AUDA-treated rats (N = 5 for each group). These results suggested that AUDA affects the anti-inflammation at the beginning of ischemic injury and restores neuronal metabolic rate of O₂ and tissue viability. The neovascularization triggered by AUDA restored CBF and may contribute to ischemic infarction reduction at post-stroke day 3. Moreover, for long-term neuroprotection, astrocytes in the penumbra region may play an important role in protecting neurons from apoptotic injury.

Protecting axons in multiple sclerosis

Typically patients with multiple sclerosis (MS) experience acute episodes of neurological dysfunction, which recover followed, at a later stage, by slow and insidious accumulation of disability (disease progression). Disease progression reflects axon damage and loss within the central nervous system. However, the precise mechanism of axon injury in MS is not clear. Inflammation occurring during acute relapses undoubtedly causes some degree of acute axon damage, but epidemiological data and treatment studies have suggested that inflammation alone is not the sole cause of axonopathy. Indeed, there appears to be dissociation between inflammation and disease progression once a certain level of clinical disability has been reached because immune suppression in patients who have established disease progression does not halt the slow decrease of function. The slow and insidious loss of neurological function that occurs during the progressive phase of the disease implies a degenerative process. Whether axon drop-out occurs at these later stages because of previous inflammatory damage to axons; because of low grade inflammation causing damage to already vulnerable demyelinated axons; because of loss of trophic environment for axons to survive; or as part of a completely independent neurodegenerative process is not clear. Understanding disease mechanisms involved in the axonopathy of MS allows for the development of rational therapies for disease progression.

Astrocytes enhance long-term survival of cholinergic neurons differentiated from human fetal neural stem cells

Establishment of an in vitro model of human cholinergic neurons would be highly desirable for understanding and developing treatment for Alzheimer's and motoneuron diseases. Previously we reported that the combination of basic fibroblast growth factor (bFGF), heparin, and laminin directs human fetal neural stem cells to form cholinergic neurons. One problem, however, is that long-term in vitro survival of these cells is low. Our goal for this study was to determine whether astrocytes or their secreted factors enhance differentiation and survival of cholinergic neurons under long-term differentiation conditions. We demonstrate here that astrocytes or astrocyte conditioned media did not enhance cholinergic differentiation but did increase the long-term survival of differentiated human neural stem cells, particularly cholinergic neurons. We further show that astrocytes protected long-term-differentiated cells from apoptotic cell death, which is at least partially mediated by astrocyte-secreted bFGF. Our findings indicate that long-term survival of human stem cell-derived cholinergic neurons requires trophic factors from nonneuronal cells. This data may provide insights into the development of an in vitro model of long-term cultured human cholinergic neurons useful for understanding of the mechanisms of cholinergic differentiation and developing treatments for neurological diseases.

Glial-derived neurotrophic factor (GDNF) prevents ethanol (EtOH) induced B92 glial cell death by both PI3K/AKT and MEK/ERK signaling pathways

We investigated the neuroprotective effect of glial-derived neurotrophic factor (GDNF) upon alcohol-exposed B92 cultures, as well as the role of the cytoskeleton and mitogen-activated protein kinase (MAPK) pathways in this effect. Ethanol (EtOH) was added to cultures, either alone or in combination with 30 ng/ml GDNF. Exposure to EtOH (86 and 172 mM; 60 and 120 min) increased the frequency of apoptotic cells identified by nuclear DNA staining with 4,6-diamidino-2-phenylindole (DAPI). Cultures treated with GDNF showed a decrease in ethanol-induced apoptosis. A jun N-terminal kinase (JNK) pathway is activated by EtOH and their pharmacological inhibition (by SP600125) neutralized ethanol-induced apoptosis, suggesting a role for JNK in EtOH neurotoxicity. Immunocytochemically detected phospho-JNK (p-JNK) showed an unusual filamental expression, and localized together with actin stress fibers. Examination of the cytoskeleton showed that EtOH depolymerized actin filaments, inducing p-JNK dissociation and translocation to the nucleus, which suggests that released p-JNK may contribute to glial cell death after EtOH exposure. Treatment with GDNF, in turn, may neutralize the ethanol-induced cell death pathway. Either a phosphatidylinositol 3-kinase (PI3K)/AKT pathway inhibitor (LY294002) or an inhibitor of the extracellular signal-regulated kinase (ERK) 1, 2 pathways (UO126) failed to neutralize GDNF protective effects. However, the simultaneous use of both inhibitors blocked the protective effect of GDNF, suggesting a role for both signaling cascades in the GDNF protection. These findings provide further insight into the mechanism involved in ethanol-induced apoptosis and the neurotrophic protection of glial cells.

Tyrosine kinase activity of nerve growth factor and estrogen in embryonic septal neurons cultured from the rat

Alzheimer's disease (AD) is a neurodegenerative disease characterized by dementia, senile plaques, fibrillary tangles, and a reduction of cholinergic neurons in the septal nucleus of the brain. Nerve growth factor (NGF) and estrogen were studied to observe effects on tyrosine kinase activity in septal neurons. The time course of tyrosine kinase activation and number of cells in which tyrosine kinase was activated were measured. Tissue from embryonic day 16 rats was microdissected and the septal neurons obtained were treated with estrogen (10 microM) or NGF (100 ng/mL) at intervals of 1, 2, 3, 4, 5, or 10 min. Immunostaining for phosphotyrosine revealed that cells treated with NGF showed an increase in phosphotyrosine activity within 2-4 min followed by a decline to control levels of enzyme activity. Treatment with estrogen led to an increase in phosphotyrosine immunostaining within 2-3 min followed by a decline to control levels. This time course suggests a mechanism for estrogen activity other than the traditional method involving binding to nuclear receptors followed by protein synthesis.

The modulations of NCAM polysialylation state that follow transient global ischemia are brief on neurons but enduring on glia

To investigate the role of polysialylated neural cell adhesion molecule (NCAM PSA)-mediated plasticity after injury, we examined the temporal and spatial expression of NCAM PSA immunoreactivity in the medial temporal lobe following global ischemia. Male Mongolian gerbils were subjected to bilateral common carotid artery occlusion for 5 min and killed at increasing times post-occlusion. The well-characterized delayed CAl pyramidal cell death was observed 5-7 days post-occlusion. At post-occlusion days 1-2 there was a small but significant increase of NCAM PSA-positive hippocampal granule cells followed by an equally significant decrease at post-occlusion day 5. In contrast, a substantial increase in glial PSA expression was observed in all hippocampal regions at 1-7 days post-occlusion that was associated generally with stellate astroglia and specifically with the radial processes of glia traversing the granule cell layer of the dentate gyrus. Administration of the glutamate antagonist 2,3-dihydroxy-6-nitro-7-sulfamoyl-ben-zo(F)quinoxaline significantly blocked the ischemia-induced modulation of neuronal and glial NCAM PSA expression. Astroglial NCAM polysialylation became attenuated by 35 days post-occlusion except in the CAI area of cell death. The temporal and regional pattern of polysialylated NCAM expression in the ischemic gerbil hippocampus implicates this neuroplastic marker in mechanisms of neurotrophic-dependent repair/remodeling that ensue following transient interruption of blood flow.

Growth factor effects on survival and development of calbindin immunopositive cultured septal neurons

Alzheimer's disease (AD) is a neurodegenerative disease characterized by dementia, senile plaques, fibrillary tangles, and a reduction of cholinergic neurons in areas of the brain, including the septal nucleus. Certain growth factors may promote the long-term survival of this subpopulation of neurons at risk. This study was undertaken to characterize growth factors' long-term effects on survival and development of neurons expressing the calcium-binding protein calbindin. In order to accomplish this, embryonic day 16 rat septal neurons were grown in bilaminar culture with astrocytes and in the absence of serum. These cultures were chronically treated with estrogen (Es), insulin-like growth factors I/II (IGF-I, IGF-II), basic fibroblast growth factor (bFGF), and nerve growth factor (NGF). Insulin-like growth factor II significantly increased the number of neurons immunoreactive for calbindin by 155%, suggesting either an increase in the survival of this subpopulation or an increase in the percentage of cells expressing calbindin. Chronic treatment with NGF, IGF-II, and Es significantly increased the number of primary neuritic processes on calbindin-positive neurons, whereas NGF and Es caused significant increases in the number of secondary processes and in the total lengths of the neuritic processes. Thus, effects of IGF-II, estrogen, and NGF on survival and maintenance of this neuronal subpopulation may be dependent on alterations in neurons which are immunopositive for calbindin.

Neuregulin is a mitogen and survival factor for olfactory bulb ensheathing cells and an isoform is produced by astrocytes

The rat olfactory bulb is an exceptional CNS tissue. Unlike other areas of the brain, growing axons are able to enter the olfactory bulb and extend within this CNS environment throughout adult life. It appears that the glial cells of the olfactory system, known as olfactory bulb ensheathing cells (OBECs), may have an important role in this remarkable process of CNS neural regeneration. OBECs are unusual glial cells, possessing properties of both astrocytes and Schwann cells. In this study we show that astrocytes (in the form of astrocyte-conditioned medium; ACM) produce two critical regulatory functions for OBECs: mitogenic activity and a survival factor. Interestingly, the ACM-derived activity for OBECs appears to reside in a signalling protein(s) belonging to the neuregulin (NRG) family of growth factors, and specifically appears to coincide with one or more products of the nrg-1 gene. Our observations provide evidence for the following: recombinant human neu differentiation factors (NDFbeta1, -2 and -3) are mitogenic to OBECs; the activity in ACM can be neutralized by NDF antibodies; these same antibodies detect a 50-kDa, non-heparin binding protein in concentrated ACM; astrocytes express detectable nrg-1 transcripts; and OBECs express functional NRG receptors erbB2 and erbB4.

An immortalized, type-1 astrocyte of mesencephalic origin source of a dopaminergic neurotrophic factor

Rat embryonic d 14 (E14) mesencephalic cells, 2.5% of which are glioblasts, were incubated in medium containing 10% of fetal bovine serum for 12 h and subsequently expanded in a serum-free medium using basic fibroblast growth factor (bFGF) as the mitogen. On a single occasion, after more than 15 d in culture, several islets of proliferating, glial-like cells were observed in one dish. The cells, when isolated and passaged, proliferated rapidly in either a serum-free or serum-containing growth medium. Subsequent immunocytochemical analysis showed that they stained positive for GFAP and vimentin, and negative for A2B5, O4, GalC, and MAP2. Serum-free conditioned medium (CM) prepared from these cells caused a fivefold increase in survival and promoted neuritic expansion of E14 mesencephalic dopaminergic neurons in culture. These actions are similar to those exerted by CM derived from primary, mesencephalic type-1 astrocytes. The pattern of expression of the region-selective genes; wnt-1, en-1, sis showed that 70% of the cells were heteroploid, and of these, 50% were tetraploid. No apparent decline in proliferative capacity has been observed after 25 passages. The properties of this cell line, named ventral mesencephalic cell line one (VMCL1), are consistent with those of an immortalized, type-1 astrocyte. The mesencephalic origin of the cell line, and the pattern and potency of the neurotrophic activity exerted by the CM, strongly suggest that the neurotrophic factor(s) identified are novel, and will likely be strong candidates with clinical utility for the treatment of Parkinson's disease.

Effects of growth factors and estrogen on the development of septal cholinergic neurons from the rat

Cholinergic neurons of the septum are preferentially subject to degeneration in Alzheimer's disease. There is evidence that nerve growth factor, basic fibroblast growth factor, insulin-like growth factors, and estrogen all have effects on survival of this specific population of neurons at risk. We used a bilaminar culturing method to grow embryonic septal neurons from the rat in the presence of a separate glial plane but in the absence of serum. These neurons were treated with a number of factors, and neurite development of cholinergic neurons was assessed. Basic fibroblast growth factor and estrogen altered the number of primary neurites, number of secondary neurites, and mean total neurite lengths, while none of the other factors affected these end points. This would suggest a mechanism for the effects of these factors on memory.

The pharmacology of amino-acid responses in septal neurons

Septal cholinergic neurons are known to play an important role in cognitive processes including learning and memory through afferent innervation of the hippocampal formation and cerebral cortex. The septum contains not only cholinergic neurons but also various types of neurons including GABA (gamma-aminobutyric acid)-ergic neurons. Although synaptic transmission in the septum is mediated primarily by the activation of excitatory and inhibitory amino-acid receptors, it is possible that a distinct phenotype of neuron is endowed with a different type for each of the amino-acid receptors and thus they play different roles from each other, since it has been demonstrated within the septum that there is a regional distribution of various types of amino-acid receptor subunits, their expression as different combinations within a specific cell may produce receptor channels with disparate functional properties. As a first step towards knowing the various functions of septal cholinergic neurons, we characterized the functional properties of glutamate, GABA (type A; GABAA) and glycine receptor channels on cultured rat septal neurons which were histologically identified to be cholinergic. These were similar to those of receptor channels on other types of neurons, except for the actions of some neuromodulators. The septal N-methyl-D-aspartate receptor channel was distinct in being less sensitive to Mg2+ and in a voltage-dependent action of Zn2+. The septal GABAA receptor channel exhibited a lanthanide site whose activation resulted in a positive allosteric interaction with a binding site of pentobarbital. The septal glycine receptor channel was only positively modulated by Zn2+; this action of Zn2+ was not accompanied by an inhibitory effect. Our data suggest that the amino-acid receptors on septal cholinergic neurons may play a distinct role compared to other types of neurons; this difference depends on the actions of neuromodulators and metal cations. It would be interesting to compare these effects recorded in tissue culture to those observed with septal cholinergic neurons in slice preparations.

Catecholamine enzymes and neuropeptides are expressed in fibres and somata in the intermediate gray matter in chronic spinal rats

Spinal cord injury disrupts control of sympathetic preganglionic neurons because bulbospinal input has been lost and the remaining regulation is accomplished by spinal circuits consisting of dorsal root afferent and spinal neurons. Moreover, an initial retraction and regrowth of dendrites of preganglionic neurons in response to deafferentation creates the potential for remodelling of spinal circuits that control them. Although catecholamines and neuropeptide Y are found in descending inputs to the preganglionic neurons, their presence in spinal circuits has not been established. Spinal circuits controlling preganglionic neurons contain substance P but participation of these peptidergic neurons in remodelling responses has not been examined. Therefore, we compared immunoreactivity for the catecholamine-synthesizing enzyme dopamine beta-hydroxylase, for neuropeptide Y and for substance P in the intermediate gray matter of the spinal cord in control rats and in rats seven or fourteen days after transection at the fourth thoracic cord segment. Sympathetic preganglionic neurons were retrogradely labelled by intraperitoneal injection of the tracer FluoroGold. These experiments yielded three original findings. 1) At one and two weeks after cord transection, fibres and terminals immunoreactive for dopamine beta-hydroxylase and neuropeptide Y were consistently found in the intermediolateral cell column in segments caudal to the transection. The area of fibres and terminals containing these immunoreactivities was markedly reduced compared to control rats or to segments rostral to the transection in the spinal rats. 2) Immunoreactivity for substance P was increased after cord transection and the distribution of fibres immunoreactive for this peptide in segments caudal to the transection extended more widely through the intermediate gray matter. These reactions demonstrated a plastic reaction to cord transection by spinal neurons expressing substance P. 3) Dopamine beta-hydroxylase expression was up-regulated in somata within the intermediate gray matter of spinal segments caudal to the transection. The numbers of somata immunoreactive for this enzyme increased six-fold by 14 days after cord transection, compared to the few somata counted in control rats. In conclusion, the presence of a catecholamine synthesizing enzyme and neuropeptides in fibres surrounding sympathetic preganglionic neurons caudal to a cord transection suggests a source of catecholamines and these peptides within spinal circuits in the chronic spinal rat. The presence of dopamine beta-hydroxylase in a markedly greater number of neuronal somata after cord transection reflects significant up-regulation of gene expression and may indicate a switch by these neurons to an adrenergic phenotype, revealing a plastic response to injury within the spinal cord.

Deficiency of essential neurotrophic factors in conditioned media produced by ethanol-exposed cortical astrocytes

Prior research in this laboratory has shown that in utero ethanol exposure adversely affects the development of serotonergic neurons. The current study investigated the hypothesis that cortical astrocytes produce trophic factors which are essential for the development of the fetal precursors of serotonergic and other raphe neurons (e.g. rhombencephalic neurons), and that ethanol exposure impairs the production of these factors by astrocytes. The results of these experiments demonstrated that cultured cortical astrocytes produce trophic factors which are necessary for the development of rhombencephalic neurons. Conditioned media obtained from control astrocytes promoted both general neuronal development (increased cell number, cell survival, DNA content, protein content, and neurite outgrowth) and serotonergic neuronal development (increased number of serotonin (5-HT) immunopositive cells and [3H]5-HT uptake). However, the conditioned media produced by ethanol-treated astrocytes (ECM) lacked essential neurotrophic factors. Neuronal cultures maintained in ECM had reduced DNA and neuronal survival, and altered neurite outgrowth. 5-HT immunopositive neurons and [3H]5-HT uptake were also decreased in ECM cultures. Thus, the damaging effects of in utero ethanol exposure on developing serotonergic neurons may be due to impaired production of astroglial neurotrophic factors.

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

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

Basal magnocellular and pontine cholinergic neurons coexpress FGF receptor mRNA

By in situ hybridization histochemistry, fibroblast growth factor receptor gene (flg)-expressing neurons were newly identified in the basal magnocellular nuclei (the vertical and horizontal limbs of the diagonal band, and Meynert's nucleus). The present study also confirmed flg localization in the laterodorsal tegmental nucleus and the pedunculopontine tegmental nucleus of the pons. Immuno- and in situ hybridization histochemistry on the same sections demonstrated that choline acetyltransferase and flg were colocalized in single neurons of the diagonal band, Meynert's nucleus and the pontine tegmental areas. The results suggest that a significant number of the basal magnocellular and a majority of the mesopontine cholinergic neurons are directly affected by fibroblast growth factors (FGF) via FGF receptor gene.

Interferon-gamma promotes cholinergic differentiation of embryonic septal nuclei and adjacent basal forebrain

In cultured rat embryonic septal nuclei with adjacent basal forebrain, murine interferon-gamma (IFN gamma) produces a striking increase in choline acetyltransferase (ChAT) activity and mRNA. The effect of IFN gamma on cholinergic differentiation is more potent in E14 cultures than in older cultures. IFN gamma does not cause a change in the affinity of ChAT for choline, nor does it affect cell proliferation. Whereas IFN gamma doubles neuronal cell number, the cholinergic cell number increases more than 7-fold. Ameboid microglia respond to IFN gamma with the translocation of p91 to the nucleus. The action of IFN gamma is not mediated by NGF or bFGF. The enhancement of cholinergic expression that occurs with increased cell density may be partly attributable to an endogenous IFN gamma-like molecule, since antibodies to IFN gamma offset the effects of increased cell density.

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)

Regulation of beta-amyloid precursor protein isoform mRNAs by transforming growth factor-beta 1 and interleukin-1 beta in astrocytes

In cultured astrocytes, all three major transcripts of beta-amyloid precursor protein (APP) were expressed with the ratio for APP695, APP751 and APP770 isoform mRNAs being 1:4:2. In comparison with controls, treatment of astrocytes with transforming growth factor-beta 1 (TGF-beta 1) produced about 6 fold increase in total APP mRNA, while elevation in the interleukin-1 beta (IL-1 beta) treated group was small and may relate to the mitogenic effect of IL-1 beta on astrocytes. Treatment of astrocytes with cytokines also produced marked changes in the upregulation in expression of different APP isoforms. The net increase in mRNAs of KPI-containing isoforms APP751 and APP770 was relatively more than for the APP695 isoform. This phenomenon was mainly related to the differences in the expression of KPI-containing APP isoforms and APP695 isoform in the controls. The present findings provide further evidence for the involvement of astrocytes in a cascade of events leading to the development of senile plaques in Alzheimer's disease and Down's syndrome.

Immunohistochemical localization of basic fibroblast growth factor in cultured rat astrocytes and oligodendrocytes

The distribution of basic fibroblast growth factor in cultured astrocytes and oligodendrocytes was examined using immunocytochemistry. The results demonstrate a localization of basic fibroblast growth factor immunoreactivity predominantly in astrocyte nuclei at all stages of differentiation. Cytoplasmic and process staining was best detected during early stages of differentiation, under normal growth conditions or as a result of treatment with dibutyryl cyclic adenosine monophosphate. Astrocytes at all stages of differentiation bound antibody-complexed bFGF, suggesting the presence of cell-associated low affinity binding sites for the growth factor. Our studies also show the presence of immunoreactivity for basic fibroblast growth factor in process-bearing oligodendrocytes. These results suggest a role for endogenous basic fibroblast growth factor in astrocyte and oligodendrocyte growth and function.

Development of the cholinergic fibres innervating the cerebral cortex of the rat

The ontogeny of innervation of the cholinergic fibres from the basal forebrain into the cingulate, frontal, parietal and piriform cortices of the rat has been examined using a modified histochemical method of acetylcholinesterase (AChE). The method produced crisp fibre staining with enhanced visibility and a clear back-ground, and a pattern of the distribution of these fibres was comparable to that achieved by choline acetyltransferase (ChAT) immunocytochemistry. In the rat, the AChE-stained fibres developed progressively from the deep cortical white matter towards the cortex itself. In general, a few AChE-positive fibres were seen in the subcortical white matter and the cingulum bundle, entering into the cerebral cortex by about 5 postnatal days. The number of these AChE-positive processes increased dramatically during the following two weeks. Thereafter, the general appearance of the overall pattern of distribution of the AChE fibres changed little, but the staining density became gradually more intense and by about 28 days after birth it was virtually indistinguishable from that in the adult. The onset and the development of the AChE-positive fibre network varied considerably between individual cortical regions, and indicated, in general, an anterior to posterior gradient. Within the dispersed AChE fibre network in the cerebral cortex, three bands of relatively enriched cholinergic processes, namely the deep cortical, mid-cortical and superficial layers, developed in an 'inside-out' fashion. The exact position of some of these AChE-rich bands varied from one cortical region to another and during development. A striking correlation during ontogeny was observed in the cerebral cortex between the changing patterns of AChE fibre network and the activity of ChAT, the enzyme synthesizing acetylcholine. The present findings can also provide an important anatomical baseline for future studies related to the factors controlling the expression of ChAT activity and the development of cholinergic neurotransmitter system in the rat.