Regulation of nerve growth factor biosynthesis by beta-adrenergic receptor activation in astrocytoma cells: a potential role of c-Fos protein

Locus Coeruleus and neurovascular unit: From its role in physiology to its potential role in Alzheimer's disease pathogenesis

Locus coeruleus (LC) is the main noradrenergic (NA) nucleus of the central nervous system. LC degenerates early during Alzheimer's disease (AD) and NA loss might concur to AD pathogenesis. Aside from neurons, LC terminals provide dense innervation of brain intraparenchymal arterioles/capillaries, and NA modulates astrocyte functions. The term neurovascular unit (NVU) defines the strict anatomical/functional interaction occurring between neurons, glial cells, and brain vessels. NVU plays a fundamental role in coupling the energy demand of activated brain regions with regional cerebral blood flow, it includes the blood-brain barrier (BBB), plays an active role in neuroinflammation, and participates also to the glymphatic system. NVU alteration is involved in AD pathophysiology through several mechanisms, mainly related to a relative oligoemia in activated brain regions and impairment of structural and functional BBB integrity, which contributes also to the intracerebral accumulation of insoluble amyloid. We review the existing data on the morphological features of LC-NA innervation of the NVU, as well as its contribution to neurovascular coupling and BBB proper functioning. After introducing the main experimental data linking LC with AD, which have repeatedly shown a key role of neuroinflammation and increased amyloid plaque formation, we discuss the potential mechanisms by which the loss of NVU modulation by LC might contribute to AD pathogenesis. Surprisingly, thus far not so many studies have tested directly these mechanisms in models of AD in which LC has been lesioned experimentally. Clarifying the interaction of LC with NVU in AD pathogenesis may disclose potential therapeutic targets for AD.

Noradrenergic pathways of locus coeruleus in Parkinson's and Alzheimer's pathology

Noradrenergic system of brain supplies the neurotransmitter noradrenalin throughout the brain through widespread efferent projections and play pivotal role in cognitive activities and could be involve in motor and non-motor symptoms of Parkinson's disease (PD) pathology. Profound loss of noradrenergic pathways has been reported in both Parkinson's and Alzheimer's disease (AD) pathology however their employment in therapeutics is still scarce. Therefore the present review is providing the various aspects for involvement on noradrenergic pathways in PD and AD pathology as well as the imaging of locus coeruleus as indicative diagnostic marker for disease. The present review is describing about the role of tiny nucleus locus coeruleus located noradrenergic pathways in said pathologies and discussing the past research as well as lacunas in this regard.

Nerve Growth Factor Is Regulated by Toll-Like Receptor 2 in Human Intervertebral Discs

Nerve growth factor (NGF) contributes to the development of chronic pain associated with degenerative connective tissue pathologies, such as intervertebral disc degeneration and osteoarthritis. However, surprisingly little is known about the regulation of NGF in these conditions. Toll-like receptors (TLR) are pattern recognition receptors classically associated with innate immunity but more recently were found to be activated by endogenous alarmins such as fragmented extracellular matrix proteins found in degenerating discs or cartilage. In this study we investigated if TLR activation regulates NGF and which signaling mechanisms control this response in intervertebral discs. TLR2 agonists, TLR4 agonists, or IL-1β (control) treatment increased NGF, brain-derived neurotrophic factor (BDNF), and IL-1β gene expression in human disc cells isolated from healthy, pain-free organ donors. However, only TLR2 activation or IL-1β treatment increased NGF protein secretion. TLR2 activation increased p38, ERK1/2, and p65 activity and increased p65 translocation to the cell nucleus. JNK activity was not affected by TLR2 activation. Inhibition of NF-κB, and to a lesser extent p38, but not ERK1/2 activity, blocked TLR2-driven NGF up-regulation at both the transcript and protein levels. These results provide a novel mechanism of NGF regulation in the intervertebral disc and potentially other pathogenic connective tissues. TLR2 and NF-κB signaling are known to increase cytokines and proteases, which accelerate matrix degradation. Therefore, TLR2 or NF-κB inhibition may both attenuate chronic pain and slow the degenerative progress in vivo.

Pharmacological regulation of gene expression

Pharmacological regulation of gene expression was one of the top professional interests of Dr. Costa. He promoted the idea that drugs can improve the endogenous mechanisms of synaptic plasticity by modulating gene expression. In this article I reflect upon Dr. Costa's leadership in projects undertaken at FGIN that were aimed at elucidating how neurotransmitter receptor activation could affect brain function by modulating genes and their products. I will be presenting examples of how pharmacological tools can change gene expression. These include the ability of drugs of abuse to alter the synthesis of opioid peptides or an endogenous ligand for GABAA receptor. I will conclude with a brief summary of intriguing discoveries about the regulation of nerve growth factor (NGF) and its receptors by beta-receptor agonists, adrenal steroids and cytokines.

Upregulation of the glutamine transporter through transactivation mediated by cAMP/protein kinase A signals toward exacerbation of vulnerability to oxidative stress in rat neocortical astrocytes

In the present study, we have evaluated the possible functionality in astrocytes of the glutamine (Gln) transporter (GlnT) known to predominate in neurons for the neurotransmitter pool of glutamate. Sustained exposure to the adenylyl cyclase activator forskolin for 24 h led to a significant increase in mRNA expression of GlnT among different membrane transporters capable of transporting Gln, with an increase in [(3)H]Gln accumulation sensitive to a system A transporter inhibitor, in cultured rat neocortical astrocytes, but not neurons. Forskolin drastically stimulated GlnT promoter activity in a manner sensitive to a protein kinase A (PKA) inhibitor in rat astrocytic C6 glioma cells, while deletion mutation analysis revealed that the stimulation was mediated by a cAMP responsive element (CRE)/activator protein-1 (AP-1) like site located on GlnT gene promoter. Forskolin drastically stimulated the promoter activity in a fashion sensitive to a PKA inhibitor in C6 glioma cells transfected with a CRE or AP-1 reporter plasmid, in association with the phosphorylation of CRE binding protein on serine133. Transient overexpression of GlnT significantly exacerbated the cytotoxicity of hydrogen peroxide in cultured astrocytes. These results suggest that GlnT expression is upregulated by cAMP/PKA signals for subsequent exacerbation of the vulnerability to oxidative stress in astrocytes.

Mechanism of isoproterenol-induced RGS2 up-regulation in astrocytes

Regulators of G protein signaling (RGSs) are inducibly expressed in response to various stimuli and the up-regulation of RGSs leads to significant decreases in GPCR responsiveness. Isoproterenol, an adrenergic receptor agonist, stimulated RGS2 mRNA in C6 rat astrocytoma cells. The up-regulation of RGS2 mRNA was abrogated by genistein, a protein tyrosine kinase inhibitor (PTK), and by broad-spectrum protein kinase C (PKC) inhibitors (staurosporine and GF109203X). alpha-Adrenergic antagonist (prazocin), beta-adrenergic antagonist (prazocin), and pertussis toxin only partially blocked the RGS2 up-regulation, suggesting that the RGS2 up-regulation is concomitantly mediated by Galphai, Galphas, and Galphaq. It is interesting to note that SB203580, a potent p38 mitogen-activated protein kinase (MAPK) inhibitor, completely inhibited the isoproterenol-mediated RGS2 expression. In addition, isoproterenol also markedly stimulated RGS2 mRNA in rat primary astrocytes, which were sensitive to SB203580 and staurosporine. Therefore, our data suggest that adrenergic receptor-mediated signaling (induced by isoproterenol) may be involved in the regulation of RGS2 expression in astrocytes via activating PTK, PKC, and p38 MAPK.

CAAT/enhancer-binding protein delta and cAMP-response element-binding protein mediate inducible expression of the nerve growth factor gene in the central nervous system

Nerve growth factor (NGF) synthesis in the rat cerebral cortex is induced by the beta2-adrenergic receptor agonist clenbuterol (CLE). Because NGF is a crucial neurotrophic factor for basal forebrain cholinergic neurons, defining the mechanisms that regulate its transcription is important for developing therapeutic strategies to treat pathologies of these neurons. We previously showed that the transcription factor CCAAT/enhancer-binding protein delta (C/EBPdelta) contributes to NGF gene regulation. Here we have further defined the function of C/EBPdelta and identified a role for cAMP response element-binding protein (CREB) in NGF transcription. Inhibition of protein kinase A in C6-2B glioma cells suppressed CLE induction of an NGF promoter-reporter construct, whereas overexpression of protein kinase A increased NGF promoter activity, particularly in combination with C/EBPdelta. A CRE-like site that binds CREB was identified in the proximal NGF promoter, and C/EBPdelta and CREB were found to associate with the NGF promoter in vivo. Deletion of the CRE and/or C/EBP sites reduced CLE responsiveness of the promoter. In addition, ectopic expression of C/EBPdelta in combination with CLE treatment increased endogenous NGF mRNA levels in C6-2B cells. C/EBPdelta null mice showed complete loss of NGF induction in the cerebral cortex following CLE treatment, demonstrating a critical role for C/EBPdelta in regulating beta2-adrenergic receptor-mediated NGF expression in vivo. Thus, our findings demonstrate a critical role for C/EBPdelta in regional expression of NGF in the brain and implicate CREB in CLE-induced NGF gene transcription.

A review of the neuroprotective properties of the 5-HT1A receptor agonist repinotan HCl (BAYx3702) in ischemic stroke

Repinotan HCl (repinotan, BAYx3702), a highly selective 5-HT1A receptor agonist with a good record of safety was found to have pronounced neuroprotective effects in experimental models that mimic various aspects of brain injury. Repinotan caused strong, dose-dependent infarct reductions in permanent middle cerebral artery occlusion, transient middle cerebral artery occlusion, and traumatic brain injury paradigms. The specific 5-HT1A receptor antagonist WAY 100635 blocked these effects, indicating that the neuroprotective properties of repinotan are mediated through the 5-HT1A receptor. The proposed neuroprotective mechanisms of repinotan are thought to be the result of neuronal hyperpolarization via the activation of G protein-coupled inwardly rectifying K+ channels upon binding to both pre- and post-synaptic 5-HT1A receptors. Hyperpolarization results in inhibition of neuron firing and reduction of glutamate release. These mechanisms, leading to protection of neurons against overexcitation, could explain the neuroprotective efficacy of repinotan per se, but not necessarily the efficacy by delayed administration. The therapeutic time window of repinotan appeared to be at least 5 h in in vivo animal models, but may be even longer at higher doses of the drug. Experimental studies indicate that repinotan affects various mechanisms involved in the pathogenesis of brain injury. In addition to the direct effect of repinotan on neuronal hyperpolarization and suppression of glutamate release this compound affects the death-inhibiting protein Bcl-2, serotonergic glial growth factor S-100beta and Nerve Growth Factor. It also suppresses the activity of caspase-3 through MAPK and PKCalpha; this effect may contribute to its neuroprotective efficacy. The dose- and time-dependent neuroprotective efficacy of repinotan indicates that the drug is a promising candidate for prevention of secondary brain damage in brain-injured patients suffering from acute ischemic stroke. Unfortunately, however, the first, randomized, double blind, placebo-controlled clinical trial did not demonstrate the efficacy of repinotan in acute ischemic stroke.

In vivo upregulation of endogenous NGF in the rat brain by the alpha2-adrenoreceptor antagonist dexefaroxan: potential role in the protection of the basalocortical cholinergic system during neurodegeneration

We have previously reported that the alpha2-adrenoceptor antagonist dexefaroxan protects against the degeneration of nucleus basalis magnocellularis (NbM) cholinergic neurons following cortical devascularization in the adult rat. Since nerve growth factor (NGF) is critical to the survival of NbM cholinergic neurons in the adult brain and its synthesis is known to be regulated by noradrenergic mechanisms, we examined whether the protective effect of dexefaroxan in the devascularization model was associated with regional induction of NGF biosynthesis. Dexefaroxan or vehicle was administered to rats via subcutaneous minipumps for 28 days following devascularization or sham operation procedures. In vehicle-treated devascularized rats, NGF protein levels in the cortex were increased at 5 days but had normalized by 2 weeks postoperation; NGF levels in NbM remained unchanged during this time. In dexefaroxan-treated devascularized rats, increases in NGF protein levels (2-fold) and immunoreactivity were maintained in both the cortex and NbM over the entire 28-day postoperation period; these increases were coincident with changes in functional markers characteristic of NGF's actions, including increases in choline acetyltransferase (ChAT), p75 and TrkA immunoreactivities, and a preservation of NbM cholinergic cell numbers. Dexefaroxan also increased NGF protein levels in sham-operated rats, but without any significant consequence to the otherwise normal NbM cholinergic phenotype in these animals. Results indicate that activation of endogenous NGF systems could contribute to the cholinergic protective effect of dexefaroxan in the cortical devascularization model, and provide further support for a potential therapeutic utility of dexefaroxan in neurodegenerative diseases where central cholinergic function is progressively compromised.

Synergistic effect of dexamethasone and beta-adrenergic receptor agonists on the nerve growth factor gene transcription

Activation of beta-adrenergic receptor (betaAR) increases the synthesis of nerve growth factor (NGF) in the brain and in C6-2B glioma cells. However, in the brain, the betaAR-mediated increase in NGF expression appears to require the presence of glucocorticoids, suggesting that NGF promoter may be sensitive to cAMP and glucocorticoid-dependent transcription factors. We tested this hypothesis by exposing C6-2B glioma cells to dexamethasone (DEX) in combination with agents that increase cAMP levels and examining the DNA binding activity of two cAMP-dependent transcription factors that regulate NGF expression: cAMP responsive element binding protein (CREB) and CCAAT/enhancer binding protein delta (C/EBPdelta). Electrophoretic mobility shift assays revealed that the beta(2)AR agonist clenbuterol (CLE) or high levels of cAMP elicited a time-dependent increase in C/EBPdelta binding activity as well as phosphorylated CREB (P-CREB). When DEX, which per se showed little effect on these transcription factors, was combined with CLE, dibutyryl cAMP or isoproterenol, enhanced induction of P-CREB and C/EBP binding activity as well as NGF mRNA was observed. Moreover, the increase in NGF mRNA in the presence of DEX was prolonged compared to that obtained by CLE or other cAMP inducing agents alone. In fact, NGF mRNA levels remained significantly elevated at least for 24 h. These studies suggest that the synergistic effect of DEX on the induction of NGF mRNA may include the ability of this glucocorticoid to potentiate the betaAR-mediated induction of transcription factors.

Endothelin-1 regulates cardiac sympathetic innervation in the rodent heart by controlling nerve growth factor expression

The cardiac sympathetic nerve plays an important role in regulating cardiac function, and nerve growth factor (NGF) contributes to its development and maintenance. However, little is known about the molecular mechanisms that regulate NGF expression and sympathetic innervation of the heart. In an effort to identify regulators of NGF in cardiomyocytes, we found that endothelin-1 specifically upregulated NGF expression in primary cultured cardiomyocytes. Endothelin-1-induced NGF augmentation was mediated by the endothelin-A receptor, Gibetagamma, PKC, the Src family, EGFR, extracellular signal-regulated kinase, p38MAPK, activator protein-1, and the CCAAT/enhancer-binding protein delta element. Either conditioned medium or coculture with endothelin-1-stimulated cardiomyocytes caused NGF-mediated PC12 cell differentiation. NGF expression, cardiac sympathetic innervation, and norepinephrine concentration were specifically reduced in endothelin-1-deficient mouse hearts, but not in angiotensinogen-deficient mice. In endothelin-1-deficient mice the sympathetic stellate ganglia exhibited excess apoptosis and displayed loss of neurons at the late embryonic stage. Furthermore, cardiac-specific overexpression of NGF in endothelin-1-deficient mice overcame the reduced sympathetic innervation and loss of stellate ganglia neurons. These findings indicate that endothelin-1 regulates NGF expression in cardiomyocytes and plays a critical role in sympathetic innervation of the heart.

Consolidation of transient ionotropic glutamate signals through nuclear transcription factors in the brain

Long-lasting alterations of neuronal functions could involve mechanisms associated with consolidation of transient extracellular signals through modulation of de novo synthesis of particular functional proteins in the brain. In eukaryotes, protein de novo synthesis is mainly under the control at the level of gene transcription by transcription factors in the cell nucleus. Transcription factors are nuclear proteins with an ability to recognize particular core nucleotides at the upstream and/or downstream of target genes, and thereby to modulate the activity of RNA polymerase II that is responsible for the formation of mRNA from double stranded DNA. Gel retardation electrophoresis is widely employed for conventional detection of DNA binding activities of a variety of transcription factors with different protein motifs. Extracellular ionotropic glutamate (Glu) signals lead to rapid and selective potentiation of DNA binding of the nuclear transcription factor activator protein-1 (AP1) that is a homo- and heterodimeric complex between Jun and Fos family members, in addition to inducing expression of the corresponding proteins, in a manner unique to each Glu signal in murine hippocampus. Therefore, extracellular Glu signals may be differentially transduced into the nucleus to express AP1 with different assemblies between Jun and Fos family members, and thereby to modulate de novo synthesis of the individual target proteins at the level of gene transcription in the hippocampus. Such mechanisms may be operative on synaptic plasticity as well as delayed neuronal death through consolidation of alterations of a variety of cellular functions induced by transient extracellular signals in the brain.

Pharmacological modulation of nerve growth factor synthesis: a mechanistic comparison of vitamin D receptor and beta(2)-adrenoceptor agonists

Increasing nerve growth factor (NGF) in the PNS is a rational strategy for treating certain neurodegenerative disorders. The present studies were undertaken to compare two compounds, a vitamin D(3) analogue (CB1093) with minimal calcaemic effects, and clenbuterol, a long-acting beta(2)-adrenoceptor agonist, both of which induce NGF synthesis in vivo. Clenbuterol caused significant increases in both NGF mRNA and protein in 3T3 cells; with maxima at 10 nM and at 8-12 h exposure. Effects of clenbuterol on NGF mRNA were antagonized by propranolol. Mobility shift assays on whole cell extracts showed that clenbuterol increased AP1 binding in 3T3 cells prior to increasing NGF synthesis. Clenbuterol was without effect on NGF mRNA levels in L929 cells, whereas CB1093 caused significant increases in both NGF mRNA and protein levels in both 3T3 and L929 cells. Stimulation was almost maximal at 24 h exposure and was sustained for at least 72 h. The magnitude of the increase was much greater in L929 (700% increase) than in 3T3 cells (80%). Binding to the vitamin D nuclear receptor (VDR), which acts as a transcription factor itself, was increased as early as 30 min after exposure to of CB1093 and maintained up to 24 h. Increased VDR binding preceded increased NGF mRNA. A 150% increase in AP-1 binding was also evident. This study demonstrates that CB1093 and clenbuterol stimulate NGF levels in vitro and that AP-1 binding could be a commonality between the mechanism of NGF induction of these two compounds.

Reduced myocardial nerve growth factor expression in human and experimental heart failure

Maintenance of cardiac performance is tightly controlled by the autonomic nervous system. In congestive heart failure (CHF), although the adverse pathophysiological effects of cardiac sympathetic overactivity are increasingly recognized, the paradoxical finding of reduced sympathetic innervation density in the failing heart remains unexplained. Given these observations, we tested the hypothesis that a reduction in the myocardial production of nerve growth factor (NGF), which is important for the maintenance of sympathetic neuronal survival, could explain the conflicting neurochemical and neuroanatomical profile of CHF. In healthy humans (n=11), there was a significantly greater transcardiac venoarterial plasma NGF gradient than in CHF patients (n=11, P<0.05). In a rat model of CHF, a 40% reduction (P<0.05) NGF mRNA expression was apparent in association with a 24% reduction in tissue NGF content (P<0.05). In conjunction, evidence of reduced sympathetic innervation in the failing heart was apparent, as measured histologically by catecholamine fluorescence and by expression of the neuronal NGF receptor trkA. Norepinephrine (10 micromol/L) exposure reduced both NGF mRNA and protein expression in isolated cardiomyocytes, suggesting that myocardial NGF downregulation may represent an adaptive response to sympathetic overactivity. These data indicate that NGF expression in the heart is dynamic and may be altered in cardiovascular disease states. In CHF, reduced NGF expression may account for alterations in sympathetic neuronal function and neuroanatomy. The full text of this article is available at http://www.circresaha.org.

Ciliary neurotrophic factor enhances the expression of NGF and p75 low-affinity NGF receptor in astrocytes

A functional interactions between ciliary neurotrophic factor (CNTF) and NGF has recently been demonstrated. We found that the exposure of rat cortical astrocytes to human recombinant CNTF for 3 h increased the level of mRNA for NGF as determined by reverse transcription-polymerase chain reaction (RT-PCR). The increase in NGF message was followed by corresponding increase in NGF protein secreted from the astrocytes into the culture medium as determined 6 h later. C-fos seemed to be involved in the mechanism of NGF induction since the expression of c-fos gene preceded NGF mRNA elevation. Furthermore, we found that in cultured astrocytes exogenous CNTF increased the level of mRNA coding for p75(NTR), the low affinity receptor for NGF and other neurotrophins. CNTF is highly expressed in the lesioned brain and CNTF-induced upregulation of NGF synthesis could be involved in the endogenous repair mechanisms.

Neuroprotection mediated via neurotrophic factors and induction of neurotrophic factors

Neurotrophins and other neurotrophic factors have been shown to support the survival and differentiation of many neuronal populations of the central and peripheral nervous system. Therefore, administering neurotrophic factors could represent an alternative strategy for the treatment of acute and chronic brain disorders. However, the delivery of neurotrophic factors to the brain is one of the largest obstacles in the development of effective therapy for neurodegenerative disorders, because these proteins are not able to cross the blood-brain barrier. The induction of growth factor synthesis in the brain tissue by systemically administered lipophilic drugs, such as beta-adrenoceptor agonists, shown to increase endogenous nerve growth factor (NGF) synthesis in the brain, would be an elegant way to overcome these problems of application. Stimulation of beta-adrenoceptors with clenbuterol led to increased NGF synthesis in cultured central nervous system (CNS) cells and rat brain tissue. Clenbuterol-induced NGF expression was reduced to the control levels by coadministration of beta-adrenoceptor antagonist propranolol. Furthermore, clenbuterol protected rat hippocampal neurons subjected to excitotoxic damage. The neuroprotective effect of clenbuterol in vitro depended on increased NGF synthesis, since the neuroprotection was abolished by NGF antisense oligonucleotide as well as by antibodies directed against NGF itself. In vivo, clenbuterol protected rat hippocampus in a model of transient forebrain ischemia and reduced the infarct volume in a rat model of permanent middle cerebral artery occlusion (MCAo). The neuroprotective effect of clenbuterol in vivo was accompanied by enhanced NGF synthesis in brain tissue. These findings support our hypothesis that orally active NGF inducers may have a potential as therapeutic agents for the treatment of neurodegenerative disorders and stroke.

Maitotoxin-induced nerve growth factor production accompanied by the activation of a voltage-insensitive Ca2+ channel in C6-BU-1 glioma cells

1. The aim of the present study was to determine the effects of maitotoxin on nerve growth factor production and the Ca2+ influx in clonal rat glioma cells (C6-BU-1). 2. Maitotoxin (1 - 10 ng ml-1) induced a profound increase in 45Ca2+ influx in an extracellular Ca2+-dependent manner. However, high KCl had no effect at all. These effects were supported by the results from the analysis of intracellular Ca2+ concentration using fura 2. 3. The maitotoxin-induced 45Ca2+ influx was inhibited by inorganic Ca2+ antagonists, such as Mg2+, Mn2+ and Co2+. The inhibitory effect of Co2+ was antagonized by increasing the extracellular Ca2+ concentrations. 4. Maitotoxin (3 ng ml-1) as well as A-23187 (1microM) and dibutyryl cyclic AMP (0.5 mM) caused an acceleration of nerve growth factor (NGF) production in C6-BU-1 cells, as determined by NGF enzyme immunoassay. 5. Reverse transcription polymerase chain reaction (RT - PCR) analysis showed that maitotoxin (10 ng ml-1) enhanced the expression of NGF mRNA, which was abolished by the removal of extracellular Ca2+. A-23187 also accelerated its expression. 6. These results suggest that maitotoxin activates a voltage-insensitive Ca2+ channel and accelerates NGF production mediated through a Ca2+ signalling pathway in C6-BU-1 glioma cells.

The beta2-adrenoceptor agonist clenbuterol modulates Bcl-2, Bcl-xl and Bax protein expression following transient forebrain ischemia

It is well known that proteins encoded by the Bcl-2 gene family play a major role in the regulation of apoptosis. We have demonstrated previously that neuronal apoptosis can be induced in the hippocampus and striatum after global ischemia. Clenbuterol, a beta2-adrenoceptor agonist, showed considerable activity against neuronal apoptosis. In the present study, we attempted to find out whether the members of the Bcl-2 family are induced after ischemia, and whether expression of these genes could be altered by clenbuterol. Transient forebrain ischemia was performed in male Wistar rats by clamping both common carotid arteries and reducing the blood pressure to 40 mmHg for 10 min. Clenbuterol (0.5 mg/kg, i.p.) or vehicle were injected 3 h before onset of ischemia or in non-ischemic rats. The hippocampus and striatum were taken from non-ischemic rats 3, 6 and 24 h after injection of clenbuterol, as well as from drug-treated and untreated rats 6 and 24 h after ischemia. Eighty micrograms/lane total protein were loaded on a 15% sodium dodecyl sulfate-polyacrylamide gel for western blotting. Bcl-2, Bax and Bcl-xl proteins were detectable in the non-ischemic hippocampus and the striatum. Clenbuterol up-regulated the expression of Bcl-2 protein at 3, 6 and 24 h after administration. Enhanced Bcl-xl signals were found in the non-ischemic striatum 3, 6 and 24 h after clenbuterol treatment, but no change of Bcl-xl expression by clenbuterol was seen in the non-ischemic hippocampus. Bax expression was not altered by clenbuterol in the non-ischemic hippocampus and striatum. Bcl-2 was up-regulated in both detected regions at 24 h after ischemia, while the increase in Bax and Bcl-xl protein expression had appeared already at 6 h and also 24 h after ischemia. Clenbuterol further increased the expression of Bcl-2 at 6 and 24 h after ischemia. In contrast, Bax protein level was down-regulated by clenbuterol at 6 and 24 h after ischemia. Clenbuterol also increased Bcl-xl level in the ischemic striatum. The results suggest that global ischemia induces proto-oncogenes which are associated with apoptosis. Clenbuterol not only increased Bcl-2 expression in the non-ischemic hippocampus and striatum, but also up-regulated Bcl-2 and down-regulated Bax expression in the ischemic hippocampus and striatum. The increase in the ratio of Bcl-2 and Bax may contribute to the anti-apoptotic effect of clenbuterol. The present study indicates that pharmacological modulation of Bcl-2 family member expression could become a new strategy to interfere with neuronal damage.

The 5-HT1A receptor agonist Bay x 3702 inhibits apoptosis induced by serum deprivation in cultured neurons

We examined whether the highly selective 5-HT1A receptor agonist (-)-(R)-2-[4-[[(3,4-dihydro-2H-1-benzopyran-2-yl)methyl]-amino]butyl]-11 ,2-benz-isothiazol-3(2H)-one 1,1-dioxide monohydrochloride (Bay x 3702) could inhibit neuronal apoptosis induced by serum deprivation. In primary cultures of chick embryonic neurons and in mixed neuronal/glial cultures from neonatal rat hippocampus, Bay x 3702 (1 microM) rescued serum-deprived neurons from apoptosis. The antiapoptotic effect of Bay x 3702 (1 microM) was blocked in chick neurons by the selective 5-HT1A receptor antagonists 4-iodo-N-[2-[4-(methoxyphenyl)-1-piperazin]ethyl]-N-2-pyridinyl-be nzamide hydrochloride (p-MPPI, 10 microM) and 4-[3-benzotriazol-1-propyl]-1-(2-methoxyphenyl)-piperazine (BPMP, 10 microM) as well as by anti-nerve growth factor (anti-NGF) antibodies and in rat neurons by N-[2-4-(2-methoxy)-1-piperazinyl]ethyl]-N-(2-pyridinyl)cyclohexane-carbo xamide trihydrochloride (WAY 100635, 10 microM). We found only under control conditions (medium with serum), but not in serum-deprived cultures, that NGF secretion was 6-fold increased by Bay x 3702 (1 microM) compared to untreated cultures. Additionally, Bay x 3702 (4 microg/kg i.v.), infused within a period of 4 h, significantly increased the NGF content of the rat hippocampus, but not of the striatum. In summary, our data suggest that Bay x 3702 inhibited growth factor withdrawal-induced apoptosis by the stimulation of 5-HT1A receptors and that the NGF signalling pathway is involved in the mechanism of action.

Stimulation of neurotrophic factor secretion from 1321N1 human astrocytoma cells by novel diterpenoids, scabronines A and G

Glial cells release neurotrophic factors that maintain neurons functionally. When rat pheochromocytoma cells (PC-12) were cultivated with the conditioned medium of human astrocytoma cells (1321N1) incubated with the new diterpenoids, scabronines A and G, isolated from Sarcodon scabrosus, they changed their morphology and there was neurite outgrowth. The scabronines increased the expression of mRNA for nerve growth factor (NGF), and the secretion of NGF from 1321N1 cells in a concentration-dependent manner. However, the enhanced neurite outgrowth produced by the conditioned media was slightly inhibited by NGF neutralizing antibody, and the concentration of NGF released in response to the scabronines was insufficient to cause differentiation. These results suggest that scabronines cause the secretion of other factors together with NGF from 1321N1 cells. The diterpenoids are useful drugs to clarify the mechanism of synthesis and secretion of neurotrophic factors.

Comparison of the effects of dopamine D1 and D2 receptor antagonists on nerve growth factor mRNA expression

Regulation of the expression of the nerve growth factor (NGF) gene has been reported previously to be mediated by the interaction of c-fos with an activator protein-1 (AP-1) binding site present in the first intron on the NGF gene. Using an RNase protection assay and in situ hybridization, we examined the effects of dopamine D1 and D2 receptor antagonists on NGF mRNA. Haloperidol (0.1-8 mg/kg) and (-)-sulpiride (10-100 mg/kg), induced NGF mRNA in a dose-dependent fashion in the hippocampus, piriform cortex, striatum and nucleus accumbens. The haloperidol (1 mg/kg)- and (-)-sulpiride (20 mg/kg)-induced NGF mRNA expression attained a maximum level 120 min after injection and returned to control levels 24 h later. Prior administration of the protein synthesis inhibitor cycloheximide blocked the haloperidol- and (-)-sulpiride-mediated induction of NGF mRNA. In contrast, R-(-)-8-chloro-2,3,4,5-tetrahydro-3,1-methyl-5-phenyl-11-3-benzyoepin e-7-ol (SCH23390) did not induce NGF mRNA expression in either a dose-dependent or time-dependent manner. Our previous studies have shown that haloperidol and (-)-sulpiride induce the expression of c-fos and c-jun mRNAs and increase their AP-1 DNA binding activities. Thus, the data suggest that neuroleptics induce NGF gene expression by increasing AP-1 DNA binding activity.

Differentiation and growth inhibition of glioma cells induced by transfer of trk A proto-oncogene

The induction of growth inhibition and differentiation of a glioma cell line by transfection of trk A cDNA was examined, and production of endogenous nerve growth factor (NGF) also was studied in these cells. When human trk A cDNA was transfected into a human glioma cell line, U-251MG, which lacks expression of both endogenous trk A and low-affinity NGF receptor, the transfectant expressed the exogenous trk A mRNA and a functional high-affinity NGF receptor. Transfection of trk A cDNA caused a partial induction of cell differentiation, G1 arrest, growth inhibition, tyrosine phosphorylation of the trk A proto-oncogene product, and activation of MAP kinase. Exogenous NGF treatment induced further terminal differentiation and growth inhibition. In summary, our data suggest that endogenous NGF secreted by glioma cells has an important role in the induction of glioma-cell differentiation occuring with transfer of exogenous trk A cDNA.

Possible involvement of activator protein-1 DNA binding in mechanisms underlying ischemic tolerance in the CA1 subfield of gerbil hippocampus

Transcription factors are nuclear proteins with an ability to recognize particular nucleotide sequences on double stranded genomic DNAs and thereby modulate the activity of RNA polymerase II which is responsible for the formation of messenger RNAs in cell nuclei. Gel retardation electrophoresis revealed that transient forebrain ischemia for 5 min led to drastic potentiation of binding of a radiolabelled double-stranded oligonucleotide probe for the transcription factor activator protein-1, in the thalamus as well as the CA1 and CA3 subfields and the dentate gyrus of the hippocampus of the gerbils previously given ischemia for 2 min two days before, which is known to induce tolerance to subsequent severe ischemia in the CA1 subfield. By contrast, ischemia for 5 min resulted in prolonged potentiation of activator protein-1 binding in the vulnerable CA1 subfield of the gerbils with prior ischemia for 5 min 14 days before, which is shown to induce delayed death of the pyramidal neurons exclusively in this subfield. Similar prolongation was seen with activator protein-1 binding in the vulnerable thalamus but not in the resistant CA3 subfield and dentate gyrus of the gerbils with such repeated ischemia for 5 min. Limited proteolysis by Staphylococcus aureus V8 protease as well as supershift assays using antibodies against c-Fos and c-Jun proteins demonstrated the possible difference in constructive partner proteins of activator protein-1 among nuclear extracts of the CA1 subfield obtained from gerbils with single, tolerated and repeated ischemia. These results suggest that de novo protein synthesis may underlie molecular mechanisms associated with acquisition of the ischemic tolerance through modulation at the level of gene transcription by activator protein-1 composed of different constructive partner proteins in the CA1 subfield. Possible participation of glial cells in the modulation is also suggested in particular situations.

beta-adrenergic receptor-induced activation of nerve growth factor gene transcription in rat cerebral cortex involves CCAAT/enhancer-binding protein delta

Stimulation of beta-adrenergic receptors (BAR) by clenbuterol (CLE) increases nerve growth factor (NGF) biosynthesis in the rat cerebral cortex but not in other regions of the brain. We have explored the transcription mechanisms that may account for the cortex-specific activation of the NGF gene. Although the NGF promoter contains an AP-1 element, AP-1-binding activity in the cerebral cortex was not induced by CLE, suggesting that other transcription factors govern the brain area-specific induction of NGF. Because BAR activation increases cAMP levels, we examined the role of CCAAT/enhancer-binding proteins (C/EBP), some of which are known to be cAMP-inducible. In C6-2B glioma cells, whose NGF expression is induced by BAR agonists, (i) CLE increased C/EBPdelta-binding activity, (ii) NGF mRNA levels were increased by overexpressing C/EBPdelta, and (iii) C/EBPdelta increased the activity of an NGF promoter-reporter construct. Moreover, DNase footprinting and deletion analyses identified a C/EBPdelta site in the proximal region of the NGF promoter. C/EBPdelta appears to be responsible for the BAR-mediated activation of the NGF gene in vivo, since CLE elicited a time-dependent increase in C/EBPdelta-binding activity in the cerebral cortex only. Our data suggest that, while AP-1 may regulate basal levels of NGF expression, C/EBPdelta is a critical component determining the area-specific expression of NGF in response to BAR stimulation.

Noradrenergic influences on the cerebellar cortex: effects on vestibular reflexes under basic and adaptive conditions

Experiments performed either in decerebrate cats or in intact rabbits have shown that functional inactivation of the cerebellar anterior vermis or the flocculus decreased the basic gain of the vestibulospinal or the vestibulo-ocular reflex, respectively. These findings were attributed to the fact that a proportion of the vermal or floccular Purkinje cells, which are inhibitory in function, discharge out of phase with respect to the vestibulospinal or the vestibulo-ocular neurons during sinusoidal animal rotation, thus exerting a facilitatory influence on the gain of the vestibular reflexes. Intravermal injection of a beta-noradrenergic agonist slightly increased the gain of the vestibulospinal reflex, whereas the opposite result was obtained after injection of beta-antagonists. Similarly, intrafloccular injection of a beta-noradrenergic agonist slightly facilitated the gain of the vestibulo-ocular reflex in darkness (but not in light), whereas a small decrease of the reflex occurred after injection of a beta-antagonist. It was postulated that the noradrenergic system acts on Purkinje cells by enhancing their amplitude of modulation to a given labyrinth signal, thus increasing the basic gain of the vestibular reflexes. The Purkinje cells of the cerebellar anterior vermis and the flocculus also exert a prominent role on the adaptation of vestibulospinal and vestibulo-ocular reflexes, respectively. In particular, intravermal or intrafloccular injection of beta-noradrenergic antagonists decreased or suppressed the adaptive capacity of the vestibulospinal and vestibulo-ocular reflexes that always occurred during sustained out-of-phase neck-vestibular or visual-vestibular stimulation, whereas the opposite result was obtained after local injection of a beta-noradrenergic agonist. The noradrenergic innervation of the cerebellar cortex originates from the locus coeruleus complex, whose neurons respond to vestibular, neck, and visual signals. It was postulated that this structure acts through beta-adrenoceptors to increase the expression of immediate-early genes, such as c-fos and Jun-B, in the Purkinje cells during vestibular adaptation. Induction of immediate-early genes could then represent a mechanism by which impulses elicited by sustained neck-vestibular or visuovestibular stimulation are transduced into long-term biochemical changes that are required for cerebellar long-term plasticity.

TrkA receptors delay C6-2B glioma cell growth in rat striatum

Nerve growth factor (NGF) acts as an anti-mitogenic factor in C6-2B glioma cells stably expressing TrkA (C6trk+). To study the effect of TrkA on cell growth in vivo, we grafted mock and C6trk+ cells into the striatum of ACI nude rats. Thy 1.1 and p75NTR immunohistochemistry revealed that wild type C6-2B cells formed a tumor mass in the striatum by 14 days. In contrast, C6trk+ transplanted rats did not show the presence of a significant tumor mass until 71 days. Analysis of this tumor showed that expression of TrkA was retained, but the synthesis of NGF was abolished. Our data encourage the speculation that expression of TrkA in glioblastoma in vivo will attenuate tumor progression.

Gene expression of neurotrophins and their receptors in cultured rat vascular smooth muscle cells

Most previous researches on neurotrophins including nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), and neurotrophin-3 (NT-3) have focused on the nervous system, because their receptors are widely distributed in neuronal tissues. Recently, however, the participation of neurotrophins in inflammation and atherosclerosis has been proposed. Therefore, the gene expression of neurotrophins is now an urgent issue is to be investigated in nonneuronal tissues. Here, we evaluated the gene expression of neurotrophins and their receptors in rat cultured vascular smooth muscle cells (VSMCs) by the reverse transcriptase-polymerase chain reaction method. The transcripts of NGF, NT-3, and TrkC (high-affinity receptor for NT-3), and two BDNF alternative spliced transcript variants with exons 3 and 4 were clearly detected in VSMCs cultured under conventional culture conditions. The upregulation of mRNA levels for NGF, two BDNF variants with exons 1 and 2, low-affinity neurotrophin receptor, and high-affinity receptors, TrkA (for NGF) and TrkB (for BDNF), was observed in response to the treatment with serum and phorbol-ester following the serum-starvation. In contrast, the expression of NT-3 and TrkC genes was downregulated under these conditions. Co-expression of these factors and their receptors and the characteristic regulation of their gene transcriptions suggest that these factors play crucial roles in the function of VSMCs through an autocrine mechanism.

Analysis of c-Fos and glial fibrillary acidic protein (GFAP) expression following topical application of potassium chloride (KCl) to the brain surface

Application of high K+ concentrations to a limited area of the brain surface is known to trigger spreading depression. We used this model to observe the response of cortical areas, distant to the exposed site, at the cellular level. Immunostaining of glial fibrillary acidic protein (GFAP) and of the proto-oncogene c-Fos was analyzed in brain sections at different times after K+ application. Piriform and parietal cortices, as observed in coronal sections located 3 mm rostrally from the center of the stimulated area and ipsilateral to it, showed a dramatic increase in immunostaining for both markers. However, the time course for such increments was different. c-Fos protein(s) expression was high at 1.5 h and decreased at 24 h after K+ exposure and c-fos mRNA expression correlated with the immunohistochemical results. At these initial times GFAP immunoreactivity was still low but began to rise between 2 and 7 days after treatment in exactly the same areas where c-Fos expression had been up-regulated. No significant effect, for either marker, was evident in the contralateral piriform or parietal cortices. In addition, we studied the effects of the NMDA antagonist MK-801 (4 mg/kg i.p.) on the expression of mRNA for GFAP and c-fos and demonstrated a marked reduction in the upregulation of these genes.

Astrocytes are the major source of nerve growth factor upregulation following traumatic brain injury in the rat

Previous studies from our group have demonstrated an upregulation in nerve growth factor (NGF) RNA and protein in the cortex 24 h following traumatic brain injury (TBI) in a rat model. This increase in NGF is suppressed if rats are subjected to 4 h of whole-body hypothermia following TBI. In the present study we used in situ hybridization to extend our initial RNA gel-blot (Northern) hybridization findings by demonstrating that NGF RNA is increased in the cortex following TBI and that hypothermia diminishes this response. Further, by combining in situ hybridization with immunocytochemistry for glial fibrillary acidic protein we demonstrate that astrocytes are the major cellular source for the upregulation in NGF and that this upregulation can be observed in the hippocampus as early as 3 h posttrauma. The predominantly astrocytic origin suggests that the NGF upregulation is not related primarily to cholinotrophic activities. We hypothesize that its function is to stimulate upregulation of antioxidant enzymes, as part of an injury-induced cascade, and that supplementation of NGF or antioxidants may be warranted in hypothermic therapies for head injury.

Identification of c-fos related genes and their induction by neural activation in rainbow trout brain

A number of studies have shown that the induction of c-fos gene is an indicator of the responses of cells and tissues to the environmental stimuli. In the present study, using RT-PCR-based strategy, we isolated, from the brain of the rainbow trout, two partial cDNA clones (RT-fos1 and RT-fos2) that code proteins homologous to c-Fos proteins of higher vertebrates. Sequence analysis of the two clones indicated that the two rainbow trout clones are very similar to each other over the entire cloned region (88% amino acid identity) and showed moderate similarity to c-Fos proteins of higher vertebrates (40% amino acid identity with human c-Fos). Two functionally important domains (i.e. the leucine zipper and zinc finger) are highly conserved among all the vertebrate species analyzed, although the region between the two domains was highly variable between different species. Intraperitoneal administration of kainic acid, a stable agonist of glutamate receptors, transiently induced the mRNAs for both RT-fos1 and RT-fos2 in the rainbow trout brain. These results indicate that the expression pattern of the two clones can be utilized as a suitable anatomical marker for the increased neural activities in salmonid fish brain to investigate the higher order behavior such as the learning and imprinting of odors of the home river.

Differential induction of nerve growth factor and basic fibroblast growth factor mRNA in neonatal and aged rat brain

Stimulation of glucocorticoid or beta-adrenergic receptors (BAR) has been shown to increase nerve growth factor (NGF) biosynthesis in adult rat brain. Little is known about the role of these receptors in the regulation of NGF expression in neonatal and aged brain. We have examined the effect of the synthetic glucocorticoid dexamethasone (DEX) and the BAR agonist clenbuterol (CLE) on the levels of NGF mRNA in neonatal (8 day old), adult (3 month old) and aged (24 month old) rats. By 3 h, DEX (0.5 mg/kg, s.c.) evoked a comparable increase in NGF mRNA in the cerebral cortex and hippocampus in both 8-day and 3-month-old rats. In contrast, CLE (10 mg/kg, i.p.) failed to change NGF mRNA levels in neonatal rats, while increasing (2-3-fold) NGF mRNA levels in the cerebral cortex of adult rats. In 24-month-old rats, both DEX and CLE elicited only a modest increase in NGF mRNA. This increase was, however, anatomically and temporally similar to that observed in adult animals. The weak effect of DEX or CLE was not related to a down-regulation of receptor function because both DEX and CLE were able to elicit a comparable increase in the mRNA levels for basic fibroblast growth factor (FGF2) in neonatal, adult and aged rat brain. Our data demonstrate that induction of NGF expression by neurotransmitter/hormone receptor activation varies throughout life and suggest that pharmacological agents might be useful tools to enhance trophic support in aging.

Signals that regulate astroglial gene expression: induction of GFAP mRNA following seizures or injury is blocked by protein synthesis inhibitors

Previous studies have revealed that a single electroconvulsive seizure (ECS) strongly induces glial fibrillary acidic protein (GFAP) expression in astrocytes in the hippocampal dentate gyrus. The signals that trigger this induction are not known, but circumstantial evidence suggests the hypothesis that GFAP expression may be induced as a result of the induction of growth factor expression by dentate granule cells that also occurs as a result of the ECS and other types of seizures. The present study tests one prediction of this hypothesis by evaluating whether increases in GFAP mRNA levels after ECS are blocked by inhibiting protein synthesis at various times after the ECS. We report that the upregulation of GFAP expression following ECS is blocked by protein synthesis inhibitors given 5 min before or up to 12 h after a single ECS. This temporal gradient suggests an intermediate step involving the increased expression of a protein growth factor.

Nerve growth factor mRNA stability is controlled by a cis-acting instability determinant in the 3'-untranslated region

Nerve growth factor (NGF) mRNA is rapidly degraded in many non-neuronal cell types with a half-life of between 30 and 60 min. Similar to other short-lived mRNAs the 3'-untranslated region (3'-UTR) of the NGF mRNA contains a short AU nucleotide-rich sequence. To implicate this region as a cis-acting determinant of NGF mRNA instability, expression vectors containing NGF cDNA with and without the 3'-UTR, and vectors containing only the 3'-UTR were constructed and used in cell transfection experiments. Transfection of HEK293 or NIH3T3 cells with these expression vectors followed by measurement of NGF mRNA half-life indicated that NGF mRNA without the AU-rich 3'-UTR was approximately 3-fold more stable than NGF mRNA containing the 3'-UTR. Similar results were seen in a polysome-based cell-free RNA decay assay using NGF mRNA with and without the 3'-UTR prepared from transfected cells. Addition of a short RNA containing the AU-rich 3'-UTR to the cell-free RNA decay system prolonged the half-life of the full-length NGF mRNA, suggesting competition between these two RNA species for polysome-associated factors which degrade the NGF mRNA. Moreover, transfection of HEK293 or astroglial cells with vectors designed to express only the AU-rich region of the 3'-UTR resulted in enhanced expression of NGF mRNA. The results indicate that the 3'-UTR of the NGF mRNA contains a cis-acting instability determinant which, perhaps by interacting with trans-acting RNA-binding proteins, controls the rate of NGF mRNA turnover.

Evaluation of human astrocytoma and glioblastoma cell lines for nerve growth factor release

Nerve growth factor (NGF) prevents degeneration of cholinergic neurons in the central nervous system (CNS), and has potential as a therapeutic treatment for Alzheimer's disease. The inability of NGF to cross the blood-brain barrier has prompted pharmacological approaches investigating peripherally administered compounds that stimulate release of endogenous NGF. This study describes the NGF-releasing properties of six human astrocytoma and glioblastoma cell lines (SW 1088, SW 1783 and CRL 1718 astrocytomas, and U-138, U-373, and T98G glioblastomas). Using a highly specific two-site ELISA for human NGF, basal NGF release could be detected in all cell lines, with the lowest level in the T98G line (approximately 80 pg NGF/ml). Cell lines tested with a variety of compounds for 24 h in serum-free media demonstrated stimulation of NGF release by distinct mechanisms. NGF levels were markedly elevated (up to 8-fold above vehicle-treated cells) when stimulated with the cytokine interleukin-1 beta (IL-1 beta). Phorbol ester stimulated NGF release 4-fold. Clenbuterol, 4-methyl catechol, and propentofylline had little activity, while 6-(4-hydroxybutyl)-2,3,5,-trimethyl-1,4,benzoquinone (TMQ), dexamethasone and 1,25-dihydroxyvitamin D3 elevated NGF levels 3-fold. These data indicate differences in the ability of human astrocytoma and glioblastoma cells to release NGF when stimulated with mechanistically distinct compounds.

At least three neurotransmitter systems mediate a stress-induced increase in c-fos mRNA in different rat brain areas

1. Protooncogene c-fos mRNA levels were determined in the rat cerebral cortex, hippocampus, and cerebellum after exposure to a combined forced swimming and confinement stress. The stress resulted in an increase in c-fos mRNA levels in all three brain areas. 2. In an effort to elucidate the neurotransmitter systems involved in this stress-induced increase, animals were injected, prior to exposure to the stress, with either diazepam, MK-801, or propranolol. 3. In both the cerebral cortex and the hippocampus the stress-induced increase in c-fos mRNA was inhibited by MK-801, suggesting that it is mediated via NMDA receptors. In the hippocampus, propranolol had a similar effect, indicating that beta-adrenergic receptors are also involved in the stress-induced increase in c-fos mRNA. 4. On the other hand, the increase in c-fos mRNA produced by the stress of the injection was inhibited in the cerebral cortex by diazepam or propranolol and in the hippocampus only by diazepam. Furthermore, administration of MK-801 resulted in an increase in c-fos mRNA in the hippocampus of the nonstressed animals. In the cerebellum no one of the three drugs employed affected c-fos mRNA levels in either stressed or nonstressed animals. 5. Our results thus show that various forms of stress activate, in different brain areas, neurons with either NMDA, beta-adrenergic, and/or GABA-A receptors.

Effects of 1,25-dihydroxyvitamin D3 on growth of mouse neuroblastoma cells

Epitopes of the 1,25-dihydroxyvitamin D(1,25(OH)2D3) receptor have been shown in developing dorsal root ganglia in fetal mice, as well as in cells maintained in culture [Johnson, J.A., Grande, J.P., Windebank, A.J. and Kumar, R., 1,25-Dihydroxyvitamin D3 receptors in developing dorsal root ganglia of fetal rats, Dev. Brain Res., 92 (1996) 120-124]. To investigate a possible role for 1,25(OH)2D3 in neural cell growth and development, a murine neuroblastoma cell line that expresses 1,25(OH)2D3 receptors, was treated with 1,25(OH)2D3. Treatment with 1,25(OH)2D3 resulted in a decrease in cell proliferation, a change in cell morphology, and the expression of protein markers of mature neuronal cells. The decrease in cell proliferation was accompanied by an increase in the expression of nerve growth factor (NGF). Anti-NGF monoclonal antibody added to the growth medium blocked the decrease in cell proliferation caused by 1,25(OH)2D3 treatment. Our results show that the sterol hormone 1,25(OH)2D3, causes a decrease in the proliferation of mouse neuroblastoma cells through alterations in the expression of NGF.

Differential effects of protein synthesis inhibition on the activity-dependent expression of BDNF transcripts: evidence for immediate-early gene responses from specific promoters

In the adult rat forebrain, brain-derived neurotrophic factor (BDNF) expression is very rapidly induced by neuronal activity, suggesting that this might occur without intervening protein synthesis. The rat BDNF gene has four differentially regulated promoter regions; each gives rise to an mRNA containing a unique 5' exon (I-IV) and a common 3' exon (V) that codes for mature BDNF protein. The present study used exon-specific in situ hybridization and both in vivo and in vitro preparations to determine whether activity induces BDNF as an "immediate-early gene" (IEG) from specific promoter regions and to compare the regulation of BDNF and nerve growth factor (NGF). In cultured hippocampal slices, kainic acid markedly increased pan-BDNF (exon V) and NGF mRNA content; cycloheximide attenuated the effect of kainic acid on both. In vivo stimulation of a paroxysmal afterdischarge increased both pan-BDNF and NGF mRNA levels in the dentate gyrus granule cells; pretreatment with anisomycin modestly attenuated the paroxysmal afterdischarge-induced increase of both transcripts. To determine whether partial drug effects on BDNF expression reflect the differential regulation of transcript species, levels of mRNAs containing exons I-IV were evaluated. A single afterdischarge increased exon I-IV-containing mRNA levels; anisomycin significantly attenuated the increase in exon I- and II-containing mRNAs but had no effect on the increase in exon III- and IV-containing mRNAs. These data show that for mature forebrain neurons, activity induces the expression of BDNF exon III- and IV-containing transcripts as IEG responses.

Differential effects of protein synthesis inhibition on the activity-dependent expression of BDNF transcripts: evidence for immediate-early gene responses from specific promoters

In the adult rat forebrain, brain-derived neurotrophic factor (BDNF) expression is very rapidly induced by neuronal activity, suggesting that this might occur without intervening protein synthesis. The rat BDNF gene has four differentially regulated promoter regions; each gives rise to an mRNA containing a unique 5' exon (I-IV) and a common 3' exon (V) that codes for mature BDNF protein. The present study used exon-specific in situ hybridization and both in vivo and in vitro preparations to determine whether activity induces BDNF as an "immediate-early gene" (IEG) from specific promoter regions and to compare the regulation of BDNF and nerve growth factor (NGF). In cultured hippocampal slices, kainic acid markedly increased pan-BDNF (exon V) and NGF mRNA content; cycloheximide attenuated the effect of kainic acid on both. In vivo stimulation of a paroxysmal afterdischarge increased both pan-BDNF and NGF mRNA levels in the dentate gyrus granule cells; pretreatment with anisomycin modestly attenuated the paroxysmal afterdischarge-induced increase of both transcripts. To determine whether partial drug effects on BDNF expression reflect the differential regulation of transcript species, levels of mRNAs containing exons I-IV were evaluated. A single afterdischarge increased exon I-IV-containing mRNA levels; anisomycin significantly attenuated the increase in exon I- and II-containing mRNAs but had no effect on the increase in exon III- and IV-containing mRNAs. These data show that for mature forebrain neurons, activity induces the expression of BDNF exon III- and IV-containing transcripts as IEG responses.

Effects of phencyclidine on immediate early gene expression in the brain

The N-methyl-D-aspartate receptor antagonist phencyclidine (PCP) is a psychotomimetic drug which produces schizophrenia-like psychosis. In animal studies it is toxic to neurons in the posterior cingulate and retrosplenial cortex and to cerebellar Purkinje cells. To find clues about the mechanism and pathways of PCP action, we studied the effect of systemic PCP administration (10 and 50 mg/kg, intraperitoneal) on the expression of immediate-early genes (IEGs) (c-fos, c-jun, egr-2, egr-3, NGFI-A, NGFI-B, NGFI-C, and Nurr1) using in situ hybridization histochemistry. PCP, 50 mg/kg, produced a biphasic IEG induction: an early induction in the hippocampus, cerebral cortex, and cerebellar granule cell layer, and a delayed induction in the posterior cingulate cortex and cerebellar Purkinje cell layer. The early induction of all eight IEGs was observed 30 min after drug treatment in the cerebral cortex and in the hippocampus. c-fos, NGFI-A, and NGFI-B were also induced in thalamic nuclei, and c-fos was also induced in the cerebellar granule cell layer. In contrast, a delayed induction of c-fos, c-jun, NGFI-A, NGFI-B, NGFI-C, and Nurr1 in the posterior cingulate cortex was observed 2-6 hr after PCP, 50 mg/kg. egr-2 and egr-3 were not induced in the posterior cingulate cortex. c-fos induction in the cerebellar Purkinje cell layer peaked 2 hr after PCP, 50 mg/kg. In addition, PCP induced c-fos, egr-3, NGFI-A, NGFI-B, NGFI-C, and Nurr1 in the inferior olivary nucleus. PCP-induced IEG expression returned to baseline by 24 hr. A lower PCP dose, 10 mg/kg, induced lower levels of IEG expression, with similar anatomical and biphasic temporal pattern as with the higher PCP dose of 50 mg/kg. However, no IEG induction was observed in the hippocampus following 10 mg/kg PCP. These results demonstrate that PCP produces neural activation not only in the cingulate and retrosplenial cortex, but also in many other regions of forebrain and cerebellum. Moreover, prolonged IEG expression in the posterior cingulate cortex and cerebellar Purkinje cells, the sites of PCP toxicity, suggests that IEGs could mediate neurotoxic/neuroprotective effects in these brain regions.

Neurotrophins and peripheral neuropathy

The most common form of peripheral neuropathy is that associated with diabetes mellitus. In rodent models of diabetes there are expression deficits in nerve growth factor (NGF) and in its high-affinity receptor, trkA, leading to decreased retrograde axonal transport of NGF and decreased support of NGF-dependent sensory neurons, with reduced expression of their neuropeptides, substance P and calcitonin gene-related peptide (CGRP). Treatment of diabetic rats with intensive insulin normalized these deficits and treatment with exogenous NGF caused dose-related increases, giving levels of NGF and neuropeptides which were greater than those of controls. Neurotrophin-3 (NT-3) mRNA was also deficient in leg muscle from diabetic rats and administration of recombinant NT-3 to diabetic rats increased the conduction velocity of sensory nerves without affecting motor conduction velocity. These findings implicate deficient neurotrophic support in diabetic neuropathy and suggest that its correction should be a paramount therapeutic target.

Regional and temporal profiles of c-fos and nerve growth factor mRNA expression in rat brain after lateral cortical impact injury

Lesion-induced increases in NGF mRNA are thought to be mediated by c-fos gene expression. Conversely, NGF induction of c-fos expression has been reported following administration of exogenous NGF. However, the relationship between c-fos and NGF gene expression after traumatic injury to the intact brain is not known. Thus, we applied in situ hybridization and semiquantitative reverse transcription-polymerase chain reaction (RT-PCR) methods to determine temporal profiles of c-fos and NGF mRNA expression in rat brains after controlled impact to the exposed cortex. Using alternate sections from the same rat brains, in situ hybridization studies showed that in neocortex, c-fos mRNA transiently increased at 30 min, 1 hr, and 3 hr after injury, while there were no increases of NGF mRNA at these postinjury time points. In the hippocampus, in situ hybridization showed that c-fos mRNA increased at 30 min, 1 hr and 3 hr postinjury, while NGF mRNA increased at 1 hr, 3 hr but not at 30 min after injury. RT-PCR studies in hippocampus confirmed that c-fos mRNA increased as early as 5 min after injury, peaked at 30 min postinjury, and remained elevated 5 hr postinjury. Levels of hippocampal NGF mRNA expression increased by 1 hr after injury and plateaued until 3 and 5 hr postinjury. These data are consistent with the possible regulatory role of endogenous c-fos on NGF expression following traumatic brain injury.

Neurotrophic factors in central nervous system trauma

Although regeneration of injured neurons does not occur after trauma in the central nervous system (CNS), there is often significant recovery of functional capacity with time. Little is currently known about the molecular basis for such recovery, but the increased trophic activity in injured CNS tissue and the known properties of neurotrophic factors in neuronal growth and maintenance suggest that these polypeptides are probably involved in recovery of function. Members of the neurotrophin family, including nerve growth factor (NGF), brain-derived neurotrophic factors (BDNF), and neurotrophin 3 (NT-3), are capable of supporting survival of injured CNS neurons both in vitro and in vivo. They also stimulate neurite outgrowth, needed for reorganization of the injured CNS, and the expression of key enzymes for neurotransmitter synthesis that may need to be upregulated to compensate for reduced innervation. The effects of the neurotrophins are mediated through specific high affinity trk receptors (trk A, B, C) as well as a common low affinity receptor designated p75NGFR. Another class of neurotrophic polypeptides also provides candidate recovery-promoting molecules, the heparin-binding growth factors' acidic and basic fibroblast growth factor (aFGF, bFGF). FGFs not only sustain survival of injured neurons but also stimulate revascularization and certain glial responses to injury. Both the neurotrophins and the FGFs, as well as their respective receptors, have been shown to be upregulated after experimental CNS injury. Further, administration of neurotrophins or FGF has been shown to reduce the effects of experimental injury induced by axotomy, excitotoxins, and certain other neurotoxins. The cellular basis for the potential therapeutic use of neurotrophic molecules is discussed as well as new strategies to increase neurotrophic activity after CNS trauma based on the recently obtained information on pharmacological and molecular control of the expression of these genes.

Changes in gene expression following traumatic brain injury in the rat

This paper reviews changes in gene expression produced by two rodent models of traumatic brain injury: cortical impact injury and fluid-percussion injury. Cortical impact injury produces transient increases in c-fos mRNA expression, which begin as early as 5 min after injury and subsides by 1 day after injury in the cerebral cortex ipsilateral to injury. In addition, AP-1 transcription factor binding is greatly increased in the injured cerebral cortex at 1, 3, and 5 h post-injury. AP-1 binding remains increased for at least 1 day after injury, while SP-1 transcription factor binding activity does not increase. Additional studies have confirmed increases in c-fos mRNA expression in the hippocampus at 30 min, 1 h, and 3 h after injury. These increases in c-fos mRNA in the hippocampus preceded increased levels of NGF mRNA that were detected at 1 and 3 h but not at 30 min following injury. Following fluid-percussion injury, increases in c-fos mRNA can be detected as early as 2 h following injury in the cortex ipsilateral to the site of injury as well as in the hippocampus. Heat-shock protein (hsp72) mRNA is also increased in the ipsilateral cortex and hippocampus following fluid percussion injury. By 24 h post-injury, both c-fos and hsp72 gene expression return to control levels. Severe but not moderate fluid percussion injury produces increased gene expression for glucose-regulated proteins (grp78, grp94) 12 h following injury. Fluid-percussion injury also produces significant increases in expression of both interleukin-1 beta and tumor necrosis factor-alpha in the injured cortex and ipsilateral hippocampus as early as 1 h post-injury, that remains elevated up to 6 h in the injured cortex and hippocampus.

Okadaic acid increases nerve growth factor secretion, mRNA stability, and gene transcription in primary cultures of cortical astrocytes

Neonatal rat cortical astrocytes in primary culture synthesize and secrete nerve growth factor (NGF) in response to cytokines, growth factors, and activators of protein kinases. To further implicate a protein phosphorylation mechanism in the regulation of NGF expression, astrocytes were treated with okadaic acid and calyculin A, inhibitors of phosphoprotein phosphatases 1 and 2A. Okadaic acid dramatically increased both NGF mRNA content (50-fold) and NGF secretion (100-fold) in astrocytes, while calyculin A, which has a spectrum of phosphatase inhibitory activity different from okadaic acid, failed to augment NGF expression. The increased mRNA accumulation was due mainly to an increase (4-fold) in the half-life of the NGF mRNA following 9 or 24 h of treatment. Nuclear run-on assays indicated that okadaic acid also activated NGF gene transcription, which was preceded by an induction of c-fos and c-jun gene transcription. The induction of NGF expression by okadaic acid appeared independent from protein kinase C activity because down-regulating protein kinase C activity failed to decrease the okadaic acid stimulation. In contrast, interleukin-1 beta acted synergistically with okadaic acid to stimulate NGF secretion. The results indicate that okadaic acid profoundly stimulates NGF expression in astrocytes mainly by enhancing NGF mRNA stability and suggest important roles for phosphoprotein phosphatases in regulating NGF production.

Brain transcription factor gene expression, neurotransmitter levels, and novelty response behaviors: alterations during rat amphetamine withdrawal and following chronic injection stress

Transcription factors are known to act as gene expression regulators, possibly linking extracellular stimuli to long-term modifications at the neuronal level. Such modifications may potentially underlie chronic psychostimulant- and stress-induced behavioral alterations. This study illustrates how a 2 week, twice daily 7.5 mg/kg d-amphetamine or saline regimen alters rat brain regional expression of transcription factor genes, including c-fos, fos-B, jun-B, c-jun, and zif 268, and seeks potential correlations between those changes and alterations in neurotransmitter levels and behavioral novelty responses. Amphetamine withdrawal-induced decreases in transcription factor mRNA levels, assessed using Northern blot analysis, appear most prominent in prefrontal cortex, begin approximately 12 h after the last injection, and largely recover to control levels by 54 h. Prefrontal cortical and striatal dopamine content, assessed using HPLC, decrease and recover over a similar time course. Behavioral "stereotypy time" manifest by animals exposed to a novel environment, a measure sensitive to psychostimulant withdrawal, also decreases beginning 12 h after the last injection, is still significantly reduced at 54 h, and recovers at 72 h. Chronic saline injections are followed by a consistent decrease in transcription factor gene expression, observed 6 h after the last injection, followed by a "rebound" increase at 12 h. These changes are accompanied by dramatic, mostly biphasic alterations in prefrontal cortical biogenic amines and by a short-lived increase in striatal dopamine turnover. At the same time, rats display much longer-lasting decreases in locomotor responses when exposed to a novel environment, with recovery occurring only 54 h after the last injection. The delayed recovery of behavioral responses to novelty is consistent with potential involvement of changes in transcription factor-mediated gene expression in neurochemical mechanisms underlying psychostimulant withdrawal and chronic injection stress-induced behavioral alterations.

Prolonged alkylcatechol-induced expression of c-jun proto-oncogene followed by elevation of NGF mRNA in cultured astroglial cells

We have already shown that alkylcatechol markedly enhances synthesis/secretion of nerve growth factor (NGF) in cultured mouse fibroblasts and astroglial cells through immediate accumulation of NGF mRNA and that the stimulatory effect of alkylcatechol on NGF synthesis/secretion is synergistically enhanced by the coadministration of phorbol 12-myristate 13-acetate (PMA). The stimulatory effect on NGF mRNA expression of astroglial cells in culture by 4-methylcatechol (MC), an alkylcatechol, and/or PMA was blocked by treatment of the cells with cycloheximide, suggesting de novo synthesis of some cellular protein(s) is essential for the observed increase in the NGF mRNA level. The exposure to MC and/or PMA caused a rapid increase in c-fos mRNA content, which was immediately followed by an increase in c-jun mRNA, prior to NGF mRNA elevation. The expression of c-fos mRNA was transiently enhanced in all cases of the treatment with MC and/or PMA. The c-jun mRNA expression was also observed transiently when the cells were treated with PMA alone, while the expression of c-jun mRNA was pronounced and long-lasting after the treatment with MC, which was much further enhanced by the coadministration of PMA. The result that the profile of the change in c-jun mRNA expression resembled that in NGF mRNA expression suggests that the increase in c-jun mRNA is responsible for the subsequent increase in NGF mRNA after MC treatment. The contransfection of mouse astroglial cells with expression plasmids of c-fos and/or c-jun and NGF promoter gene showed that simultaneous expression of both c-fos and c-jun genes was necessary to enhance NGF promoter activity.(ABSTRACT TRUNCATED AT 250 WORDS)