Nerve growth factor (NGF) stimulation of cholinergic telencephalic neurons in aggregating cell cultures

The Nerve Growth Factor Metabolic Pathway Dysregulation as Cause of Alzheimer's Cholinergic Atrophy

The cause of the loss of basal forebrain cholinergic neurons (BFCNs) and their terminal synapses in the cerebral cortex and hippocampus in Alzheimer's disease (AD) has provoked a decades-long controversy. The cholinergic phenotype of this neuronal system, involved in numerous cognitive mechanisms, is tightly dependent on the target-derived nerve growth factor (NGF). Consequently, the loss of BFCNs cholinergic phenotype in AD was initially suspected to be due to an NGF trophic failure. However, in AD there is a normal NGF synthesis and abundance of the NGF precursor (proNGF), therefore the NGF trophic failure hypothesis for the atrophy of BCNs was abandoned. In this review, we discuss the history of NGF-dependency of BFCNs and the atrophy of these neurons in Alzheimer's disease (AD). Further to it, we propose that trophic factor failure explains the BFCNs atrophy in AD. We discuss evidence of the occurrence of a brain NGF metabolic pathway, the dysregulation of which, in AD explains the severe deficiency of NGF trophic support for the maintenance of BFCNs cholinergic phenotype. Finally, we revise recent evidence that the NGF metabolic dysregulation in AD pathology starts at preclinical stages. We also propose that the alteration of NGF metabolism-related markers in body fluids might assist in the AD preclinical diagnosis.

Pharmacology of nerve growth factor and discovery of tanezumab, an anti-nerve growth factor antibody and pain therapeutic

The pharmacology of Nerve Growth Factor (NGF) and the discovery and development of tanezumab, a monoclonal anti-NGF antibody for the treatment of pain illustrate the complex and unpredictable nature of modern drug development. Initial efforts attempted to use NGF agonistically for Alzheimer's disease and neuropathies. Most unexpectedly, clinical studies unmasked hyperalgesic effects. These observations together with new data emerging from molecular and animal model studies stimulated the idea of using an NGF antagonist for chronic pain. These events also reflect the advances of neuropharmacology from classical small molecule efforts directed at neurotransmitter receptors to modern biotechnology with significant integration in molecular biology, biochemistry, and protein engineering.

Impaired NGF/TrkA Signaling Causes Early AD-Linked Presynaptic Dysfunction in Cholinergic Primary Neurons

Alterations in NGF/TrkA signaling have been suggested to underlie the selective degeneration of the cholinergic basal forebrain neurons occurring in vivo in AD (Counts and Mufson, 2005; Mufson et al., 2008; Niewiadomska et al., 2011) and significant reduction of cognitive decline along with an improvement of cholinergic hypofunction have been found in phase I clinical trial in humans affected from mild AD following therapeutic NGF gene therapy (Tuszynski et al., 2005, 2015). Here, we show that the chronic (10–12 D.I.V.) in vitro treatment with NGF (100 ng/ml) under conditions of low supplementation (0.2%) with the culturing serum-substitute B27 selectively enriches the basal forebrain cholinergic neurons (+36.36%) at the expense of other non-cholinergic, mainly GABAergic (−38.45%) and glutamatergic (−56.25%), populations. By taking advantage of this newly-developed septo-hippocampal neuronal cultures, our biochemical and electrophysiological investigations demonstrate that the early failure in excitatory neurotransmission following NGF withdrawal is paralleled by concomitant and progressive loss in selected presynaptic and vesicles trafficking proteins including synapsin I, SNAP-25 and α-synuclein. This rapid presynaptic dysfunction: (i) precedes the commitment to cell death and is reversible in a time-dependent manner, being suppressed by de novo external administration of NGF within 6 hr from its initial withdrawal; (ii) is specific because it is not accompanied by contextual changes in expression levels of non-synaptic proteins from other subcellular compartments; (ii) is not secondary to axonal degeneration because it is insensible to pharmacological treatment with known microtubule-stabilizing drug such paclitaxel; (iv) involves TrkA-dependent mechanisms because the effects of NGF reapplication are blocked by acute exposure to specific and cell-permeable inhibitor of its high-affinity receptor. Taken together, this study may have important clinical implications in the field of AD neurodegeneration because it: (i) provides new insights on the earliest molecular mechanisms underlying the loss of synaptic/trafficking proteins and, then, of synapes integrity which occurs in vulnerable basal forebrain population at preclinical stages of neuropathology; (ii) offers prime presynaptic-based molecular target to extend the therapeutic time-window of NGF action in the strategy of improving its neuroprotective in vivo intervention in affected patients.

Organotypic brain slice cultures: A review

In vitro cell cultures are an important tool for obtaining insights into cellular processes in an isolated system and a supplement to in vivo animal experiments. While primary dissociated cultures permit a single homogeneous cell population to be studied, there is a clear need to explore the function of brain cells in a three-dimensional system where the main architecture of the cells is preserved. Thus, organotypic brain slice cultures have proven to be very useful in investigating cellular and molecular processes of the brain in vitro. This review summarizes (1) the historical development of organotypic brain slices focusing on the membrane technology, (2) methodological aspects regarding culturing procedures, age of donors or media, (3) whether the cholinergic neurons serve as a model of neurodegeneration in Alzheimer’s disease, (4) or the nigrostriatal dopaminergic neurons as a model of Parkinson’s disease and (5) how the vascular network can be studied, especially with regard to a synthetic blood–brain barrier. This review will also highlight some limits of the model and give an outlook on future applications.

Transplantation of NSC-derived cholinergic neuron-like cells improves cognitive function in APP/PS1 transgenic mice

The ability to selectively control the differentiation of neural stem cells (NSCs) into cholinergic neurons in vivo would be an important step toward cell replacement therapy. First, green fluorescent protein (GFP)-NSCs were induced to differentiate into cholinergic neuron-like cells (CNLs) with retinoic acid (RA) pre-induction followed by nerve growth factor (NGF) induction. Then, these CNLs were transplanted into bilateral hippocampus of APP/PS1 transgenic mice. Behavioral parameters showed by Morris water maze (MWM) tests and the percentages of GFP-labeled cholinergic neurons of CNL transplanted mice were compared with those of controls. Brain levels of choline acetyltransferase (ChAT) mRNA and proteins were analyzed by quantitative real-time PCR and Western blotting, ChAT activity and acetylcholine (ACh) concentration were also evaluated by ChAT activity and ACh concentration assay kits. Immunofluorescence analysis showed that 80.3±1.5% NSCs differentiated into CNLs after RA pre-induction followed by NGF induction in vitro. Three months after transplantation, 82.4±6.3% CNLs differentiated into cholinergic neurons in vivo. APP/PS1 mice transplanted with CNLs showed a significant improvement in learning and memory ability compared with control groups at different time points. Furthermore, CNLs transplantation dramatically increased in the expressions of ChAT mRNA and protein, as well ChAT activity and ACh concentration in APP/PS1 mice. Our findings support the prospect of using NSC-derived CNLs in developing therapies for Alzheimer's disease (AD).

Changes in CSF cholinergic biomarkers in response to cell therapy with NGF in patients with Alzheimer's disease

INTRODUCTION

The extensive loss of central cholinergic functions in Alzheimer's disease (AD) brain is linked to impaired nerve growth factor (NGF) signaling. The cardinal cholinergic biomarker is the acetylcholine synthesizing enzyme, choline acetyltransferase (ChAT), which has recently been found in cerebrospinal fluid (CSF). The purpose of this study was to see if EC-NGF therapy will alter CSF levels of cholinergic biomarkers, ChAT, and acetylcholinesterase.

METHOD

Encapsulated cell implants releasing NGF (EC-NGF) were surgically implanted bilaterally in the basal forebrain of six AD patients for 12 months and cholinergic markers in CSF were analyzed.

RESULTS

Activities of both enzymes were altered after 12 months. In particular, the activity of soluble ChAT showed high correlation with cognition, CSF tau and amyloid-β, in vivo cerebral glucose utilization and nicotinic binding sites, and morphometric and volumetric magnetic resonance imaging measures.

DISCUSSION

A clear pattern of association is demonstrated showing a proof-of-principle effect on CSF cholinergic markers, suggestive of a beneficial EC-NGF implant therapy.

GABAergic terminals are a source of galanin to modulate cholinergic neuron development in the neonatal forebrain

The distribution and (patho-)physiological role of neuropeptides in the adult and aging brain have been extensively studied. Galanin is an inhibitory neuropeptide that can coexist with γ-aminobutyric acid (GABA) in the adult forebrain. However, galanin's expression sites, mode of signaling, impact on neuronal morphology, and colocalization with amino acid neurotransmitters during brain development are less well understood. Here, we show that galaninergic innervation of cholinergic projection neurons, which preferentially express galanin receptor 2 (GalR2) in the neonatal mouse basal forebrain, develops by birth. Nerve growth factor (NGF), known to modulate cholinergic morphogenesis, increases GalR2 expression. GalR2 antagonism (M871) in neonates reduces the in vivo expression and axonal targeting of the vesicular acetylcholine transporter (VAChT), indispensable for cholinergic neurotransmission. During cholinergic neuritogenesis in vitro, GalR2 can recruit Rho-family GTPases to induce the extension of a VAChT-containing primary neurite, the prospective axon. In doing so, GalR2 signaling dose-dependently modulates directional filopodial growth and antagonizes NGF-induced growth cone differentiation. Galanin accumulates in GABA-containing nerve terminals in the neonatal basal forebrain, suggesting its contribution to activity-driven cholinergic development during the perinatal period. Overall, our data define the cellular specificity and molecular complexity of galanin action in the developing basal forebrain.

TrkA gene ablation in basal forebrain results in dysfunction of the cholinergic circuitry

Dysfunction of basal forebrain cholinergic neurons (BFCNs) is an early pathological hallmark of Alzheimer's disease (AD). Numerous studies have indicated that nerve growth factor (NGF) supports survival and phenotypic differentiation of BFCNs. Consistent with a potential link to AD pathogenesis, TrkA, a NGF receptor, is expressed in cholinergic forebrain neuronal populations including those in BF and striatum, and is markedly reduced in individuals with mild cognitive impairment (MCI) without dementia and early-stage AD. To investigate the role of TrkA in the development, connectivity, and function of the BF cholinergic system and its contribution to AD pathology, we have generated a forebrain-specific conditional TrkA knock-out mouse line. Our findings show a key role for TrkA signaling in establishing the BF cholinergic circuitry through the ERK pathway, and demonstrate that the normal developmental increase of choline acetyltransferase expression becomes critically dependent on TrkA signaling before neuronal connections are established. Moreover, the anatomical and physiological deficits caused by lack of TrkA signaling in BFCNs have selective impact on cognitive activity. These data demonstrate that TrkA loss results in cholinergic BF dysfunction and cognitive decline that is reminiscent of MCI and early AD.

Effects of Low-dose X-irradiation on Mouse-brain Aggregation Cultures

Biochemical and morphological differentiation in reaggregating mouse-brain cell cultures after low-dose radiation (0.5 Gy) in vitro was studied. Cells were irradiated on culture day 2, corresponding to embryonic day 15-16, and different glial and neuronal markers were followed through development to postnatal day 40. The shape and size of irradiated aggregates were more irregular and smaller compared with controls. Total amounts of DNA and protein were significantly lower in irradiated aggregates than in controls between days 8 and 20. After 30 days in culture activities of the glial markers glutamine synthetase (GS) and 2',3'-cyclic nucleotide 3'-phosphodiesterase (CNP) were lower in X-irradiated aggregates than in controls. However, after 40 days the CNP activity in irradiated aggregates increased to levels above those of the controls. Irradiated and control aggregates did not differ significantly in neuronal marker enzyme activities, i.e. choline acetyltransferase (ChAT), acetylcholine esterase (AChE) and glutamic acid decarboxylase (GAD) measured on a per mg protein basis. On days 20 and 30 the amount of nerve growth factor (NGF) was two-fold higher in irradiated aggregates compared with non-irradiated ones, suggesting that, after irradiation, surviving cells in culture were induced to produce more NGF. After 40 days the amount of NGF in irradiated aggregates had decreased to the level found in the control aggregates.

Induction of NGF synthesis in astrocytes by onjisaponins of Polygala tenuifolia, constituents of kampo (Japanese herbal) medicine, Ninjin-yoei-to

The effect of a kampo medicine, Ninjin-yoei-to (NYT; Ren-shen-yang-rong-tang in Chinese) on nerve growth factor (NGF) secretion from the cultured rat astrocytes was examined in vitro. When rat embryo astrocytes were cultured in the presence of NYT for 24 h, the amount of NGF in the medium was significantly increased in a dose dependent manner. Among 14 kinds of component herbs in NYT, the roots of Polygala tenuifolia and roots of Panax ginseng extracts increased NGF levels from the astrocytes. Saponin fraction from the roots of P. tenuifolia enhanced the production of NGF, however phenolic glycoside fraction showed no effect. Onjisaponins A, B, E, F and G as major saponins of the root of P. tenuifolia strongly increased the NGF level, whereas ginsenosides Rb1 and Rg1 did not affect the NGF level. Onjisaponin F also induced ChAT mRNA level in rat basal forebrain cells. These results indicate the possibility that NYT and/or onjisaponins in P. tenuifolia may have potential therapeutic effects for the treatment of Alzheimer disease patients.

Developmentally Regulated Expression of HDNF/NT-3 mRNA in Rat Spinal Cord Motoneurons and Expression of BDNF mRNA in Embryonic Dorsal Root Ganglion

Northern blot analysis was used to demonstrate high levels of hippocampus-derived neurotrophic factor/neurotrophin-3 (HDNF/NT-3) mRNA in the embryonic day (E) 13 - 14 and 15 - 16 spinal cord. The level decreased at E18 - 19 and remained the same until postnatal day (P) 1, after which it decreased further to a level below the detection limit in the adult. In situ hybridization revealed that the NT-3 mRNA detected in the developing spinal cord was derived from motoneurons and the decrease seen at E18 - 19 was caused by a reduction in the number of motoneurons expressing NT-3 mRNA. The distribution of NT-3 mRNA-expressing cells in the E15 spinal cord was very similar to the distribution of cells expressing choline acetyltransferase or nerve growth factor receptor (NGFR) mRNA. Moreover, a striking similarity between the developmentally regulated expression of NT-3 and NGFR mRNA was noted in spinal cord motoneurons. A subpopulation of all neurons in the dorsal root ganglia expressed brain-derived neurotrophic factor (BDNF) mRNA from E13, the earliest time examined, to adulthood. These results are consistent with a trophic role of NT-3 for proprioceptive sensory neurons innervating the ventral horn, and imply a local action of BDNF for developing sensory neurons within the dorsal root ganglia.

Localization of Sequences Determining Cell Type Specificity and NGF Responsiveness in the Promoter Region of the Rat Choline Acetyltransferase Gene

A genomic clone containing 7 kb of 5' flanking sequences from the rat choline acetyltransferase (ChAT) gene was isolated and shown to contain a TATA box-like sequence and several consensus binding sites for the transcription factor AP1. Two constructs containing 450 and 1450 base pairs (bp), respectively, of 5' flanking sequences promoted expression of a fused chloramphenicol acetyltransfersase (CAT) gene when transfected into fibroblast FR3T3, Sertoli TM4, phaeochromocytoma PC12 and cholinergic neuronal SN6 cell lines. In contrast, a longer construct containing 3850 bp of 5' flanking sequence allowed CAT activity only in the cholinergic cell line SN6. CAT activity with this construct was suppressed in the three other cell lines, indicating that the distal region of the ChAT promoter contains a cell type-specific silencer-like element that restricts ChAT gene expression to cholinergic cells. Treatment of PC12 cells with nerve growth factor (NGF) increased the promoter activity of the -450 and -1450 constructs approximately four-fold and allowed promoter activity from the -3850 construct, indicating that elements involved in NGF responsiveness of the ChAT promoter are contained in the first 450 bp of upstream sequence. These results support a model in which gene transcription controlled by cell-type specific regulatory elements contribute to the establishment, maintenance and plasticity of the cholinergic transmitter phenotype in the nervous system.

Neurotrophic factor strategies for the treatment of Alzheimer disease

Cholinergic neurons in the nucleus basalis of Meynert are reduced early in the course of Alzheimer disease, and the dysfunction of cholinergic neurons is believed to be primarily responsible for cognitive deficits in the disease. Nerve growth factor has a trophic effect on cholinergic neurons and therefore may have some beneficial effects on the cognitive impairment observed in patients with Alzheimer disease. Experimental studies demonstrated that a continuous infusion of nerve growth factor into the cerebroventricle prevents cholinergic neuron atrophy after axotomy or associated with normal aging and ameliorates cognition impairment in these animals. A clinical study in three patients with Alzheimer disease revealed, however, that a long-term intracerebroventricular infusion of nerve growth factor may have certain potentially beneficial effects, but the continuous intracerebroventricular route of administration is also associated with negative side effects that appear to outweigh the positive effects. Several other strategies have been suggested to provide neurotrophic support to cholinergic neurons. In this article, we review the neurotrophic factor strategies for the treatment of Alzheimer disease.

Nerve growth factor treatment in dementia

Millions of people are affected by Alzheimer disease. As longevity increases, so will the number of patients with dementia. This has led to an intense search for successful treatment strategies. One area of interest is neurotrophic factors. Brain development and neuronal maintenance, as well as protective efforts, are mediated by a large number of different neurotrophic factors acting on specific receptors. In neurodegenerative disorders, there may be a possibility of rescuing degenerating neurons and stimulating terminal outgrowth with use of neurotrophic factors. The first neurotrophic factor discovered was nerve growth factor (NGF). A wealth of animal studies have shown that cholinergic neurons are NGF sensitive and NGF dependent, which is especially interesting in cognitive disorders, in which central cholinergic projections are important for cognitive function. In Alzheimer disease, cholinergic neurons have been shown to degenerate. This suggests that NGF may be used to pharmacologically counteract cholinergic degeneration and/or induce terminal sprouting in Alzheimer disease. Data from animal studies, as well as from the author's recent clinical trial, in which NGF was infused to the lateral ventricle in patients with Alzheimer disease, will be presented. Effects of NGF on cognition, as well as issues regarding dosage, side effects, and alternative ways of administering NGF, will be discussed.

Non-linear cortico-cortical interactions modulated by cholinergic afferences from the rat basal forebrain

In the adult rat most of basal forebrain cholinergic neurons (BFCN) express the low-affinity p75 nerve growth factor recceptor (NGFr). The immunotoxin 192 IgG-saporin (SAP) provokes a selective loss of NGFr-positive BFCN, somewhat similar to the loss of integrity of BFCN associated with human senile dementia of Alzheimer's type, whereas NGF exerts a trophic action on BFCN. Cortico-cortical interactions are modulated by cholinergic projections of BFCN and it is proposed that alterations of these projections by SAP and by NGF produce opposite effects. This hypothesis was tested by recording multiple local field potentials (LFPs) in the rat temporal cortex and applying bispectral analysis to measure phase-coupled frequencies, somewhat analogous to frequencies of resonance. Choline acetyltransferase (ChAT) activity was measured in the septal area in order to assess the effects of the treatments. NGF-treatment increased ChAT activity by 45% and frequencies of non-linear coupling were shifted towards frequencies higher than 70 Hz, thus suggesting the presence of increased functional interactions in the short range. By contrast, SAP provoked a decrease of nearly 40% in ChAT activity and an increase of phase-coupling in the low frequencies (< 50 Hz), being interpreted as a decreased functional cortico-cortical interaction. Bispectral analysis revealed features of the effect of BFCN on cortical activity that could not be observed by other means and offers as a valuable tool of study that could be extended to the EEG of Alzheimer's patients.

Cholinergic differentiation triggered by blocking cell proliferation and treatment with all-trans-retinoic acid

This study determined whether the effect of all-trans-retinoic acid (t-RA) on markers of cholinergic differentiation in a murine septal cell line, SN56.B5.G4, differed depending upon the cell's proliferative status. To develop a model of non-proliferating cells, aphidicolin, a DNA alpha-polymerase inhibitor, was used. Cessation of proliferation by aphidicolin increased intracellular choline and acetylcholine (ACh) levels in the absence of change to choline acetyltransferase (ChAT) activity and mRNA and vesicular ACh transporter (VAChT) mRNA. Importantly, the response to t-RA differed depending upon proliferative status. Consistent with previous reports, t-RA increased ChAT and VAChT mRNA, ChAT activity and intracellular ACh levels in proliferating SN56 cells with no effect on intracellular choline levels. When cells were treated with t-RA while undergoing proliferative arrest, an additive effect of combined treatment was observed on ACh levels; nevertheless, this was only accompanied by an increase in choline levels, VAChT and ChAT mRNAs, but not ChAT activity. Indeed, aphidicolin treatment completely suppressed the t-RA-induced increase in ChAT activity observed in proliferating cells. To explore the response to t-RA in post-mitotic cells, a sequential treatment of aphidicolin and t-RA was employed. t-RA treatment was ineffective in increasing ACh and choline levels, over and above that observed with the aphidicolin treatment alone. Comparable to the combined treatment, sequential treatment lead to an increase in ChAT mRNA without any increase in ChAT activity. In conclusion, both the magnitude and the mechanism(s) of action whereby t-RA enhances the cholinergic phenotype of SN56 cells is dependent upon the cell's proliferative status.

A non-invasive system for delivering neural growth factors across the blood-brain barrier: a review

Intraventricular administration of nerve growth factor (NGF) in rats has been shown to reduce age-related atrophy of central cholinergic neurons and the accompanying memory impairment, as well as protect these neurons against a variety of perturbations. Since neurotrophins do not pass the blood-brain barrier (BBB) in significant amounts, a non-invasive delivery system for this group of therapeutic molecules needs to be developed. We have utilized a carrier system, consisting of NGF covalently linked to an anti-transferrin receptor antibody (OX-26), to transport biologically active NGF across the BBB. The biological activity of this carrier system was tested using in vitro bioassays and intraocular transplants; we were able to demonstrate that cholinergic markers in both developing and aged intraocular septal grafts were enhanced by intravenous delivery of the OX-26-NGF conjugate. In subsequent experiments, aged (24 months old) Fischer 344 rats received intravenous injections of the OX-26-NGF conjugate for 6 weeks, resulting in a significant improvement in spatial learning in previously impaired rats, but disrupting the learning ability of previously unimpaired rats. Neuroanatomical analyses showed that OX-26-NGF conjugate treatment resulted in a significant increase in cholinergic cell size as well as an upregulation of both low and high affinity NGF receptors in the medial septal region of rats initially impaired in spatial learning. Finally, OX-26-NGF was able to protect striatal cholinergic neurons against excitotoxicity and basal forebrain cholinergic neurons from degeneration associated with chemically-induced loss of target neurons. These results indicate the potential utility of the transferrin receptor antibody delivery system for treatment of neurodegenerative disorders with neurotrophic substances.

Propentofylline improves learning and memory deficits in rats induced by beta-amyloid protein-(1-40)

We have reported that continuous infusion of beta-amyloid protein-(1-40) into the cerebral ventricle produces learning and memory deficits in rats. Propentofylline has potent stimulatory effects on nerve growth factor (NGF) synthesis/secretion in mouse astrocytes in vitro and increases cerebral NGF content in aged rats. In the present study, we examined the effects of propentofylline on learning and memory deficits in beta-amyloid protein-infused rats. The rats were given propentofylline orally once a day throughout the period of behavioral examination. In the beta-amyloid protein-infused rats, spontaneous alternation behavior in a Y-maze, and performance in water maze and passive avoidance tasks were significantly impaired compared to sham-operated rats. Propentofylline prevented these behavioral deficits, but did not change the reduction of the activity of choline acetyltransferase in the hippocampus in the beta-amyloid protein-infused rats. These results suggest that propentofylline is useful for the treatment of patients with Alzheimer's disease.

The novel compound TDN-345 induces synthesis/secretion of nerve growth factor in C6-10A glioma cells

A novel compound, TDN-345, not bearing catechol moiety, induced NGF synthesis/secretion in C6-10A glioma cells. Both intracellular and extracellular nerve growth factor (NGF) protein levels increased within 3 h and reached a maximum around 12 h after the addition of TDN-345. The induction of NGF synthesis/secretion by TDN-345 occurred in a concentration-dependent manner, beginning with about 0.1 microM and reaching a maximum at 10 microM. The ED50 was 0.88 microM. The induction was accompanied by an increase in NGF mRNA but not beta-actin mRNA. In a time-course study, the NGF mRNA level was found to reach a maximum 2-3 h after the addition of TDN-345 and then to return to control levels. The induction occurred dose-dependently. The catecholaminergic compound epinephrine, which induces NGF synthesis/secretion, increased the intracellular cyclic AMP content by more than 1000-times at 10 microM. In contrast, TDN-345 did not cause such a prominent increase in cAMP even at 100 microM. These results indicate that TDN-345 induces NGF synthesis/secretion by increasing NGF mRNA expression, and the action of TDN-345 clearly differs from that of epinephrine, as it does not seem to involve cAMP as a second messenger. The results of the present study suggest the existence of a signal transduction pathway for NGF synthesis/secretion which is not mediated by cAMP.

Morphological alterations in the peripheral and central nervous systems of mice lacking glial cell line-derived neurotrophic factor (GDNF): immunohistochemical studies

Glial cell line-derived neurotrophic factor (GDNF) is a member of the TGF-beta superfamily of growth factors with neurotrophic activity on midbrain dopaminergic neurons and on developing and mature motoneurons of the brainstem and spinal cord. To investigate the extent of GDNF dependency of central and peripheral nervous structures during development, we have performed an immunohistochemical analysis of sections from the whole head including brain, peripheral ganglia, developing teeth and tongue, as well as intestines, in mutant mice lacking a part of the third exon that encodes the GDNF protein. As described previously, these null-mutated mice lack most of the enteric nerve plexus and are subject to agenesis or severe dysgenesis of the kidneys. In the present communication, we examined the development of vibrissae and incisor and molar teeth, as well as the innervation of these structures, and found no differences between null-mutated and control mice. A decrease in the immunohistochemical labeling intensity with tyrosine hydroxylase was observed in the superior cervical ganglion (SCG), as well as in the pontine nucleus locus coeruleus, and the sympathetic innervation of blood vessels and glands in the head was significantly decreased. None of the brain nuclei studied exhibited any significant decreases in the total number of neurons, but the packing density of neurons in the nucleus locus coeruleus was decreased. These data indicate that GDNF might be one neurotrophic factor that contributes to the development of central and peripheral noradrenergic neurons.

Orally active NGF synthesis stimulators: potential therapeutic agents in Alzheimer's disease

The degeneration of cholinergic neurons may be responsible for cognitive impairment in patients with Alzheimer's disease (AD). Since nerve growth factor (NGF) plays an important role in the survival and maintenance of cholinergic neurons in the central nervous system, this factor may have some beneficial effects on the cognitive impairment observed in patients with AD. However, since NGF does not cross the blood-brain barrier and is easily metabolized when administered peripherally, it can only be used when directly injected into the brain. In this review, we show that repeated oral administration of the NGF synthesis stimulators, idebenone and propentofylline, partially restored the age-associated decrease of NGF in the frontal and parietal cortices. Furthermore, this treatment attenuated the impairment of performance in the water maze, passive avoidance, and habituation tasks in rats with bilateral forebrain lesions, and in rats which had received continuous infusion of anti-NGF antibody into the septum. The behavioral improvement induced by idebenone and propentofylline was accompanied by recovery of both the reduced activity of choline acetyltransferase and the changes in [3H]QNB binding. These results suggest that the use of NGF synthesis stimulators may provide a novel therapeutic approach to cholinergic dysfunction.

Oral administration of propentofylline, a stimulator of nerve growth factor (NGF) synthesis, recovers cholinergic neuronal dysfunction induced by the infusion of anti-NGF antibody into the rat septum

We have reported that the continuous infusion of anti-nerve growth factor (NGF) monoclonal antibody into the septum of rats produces an impairment of memory and a decrease in choline acetyltransferase (ChAT) and cholinesterase (ChE) activities in the hippocampus. Propentofylline, a xanthine derivative, has potent stimulatory effects on NGF synthesis/secretion in mouse astrocytes in vitro. To investigate the pharmacological effects of propentofylline in vivo, we induced amnesia in rats by infusing anti-NGF antibody into the septum for 16 days. One group of rats was given no further treatment, while the other group was treated with propentofylline orally once a day for 19 days, commencing 3 days before the implantation of the mini-osmotic pump, and continuing throughout the period during which the animals performed the behavioral tasks. In the treated amnesic rats, learning and memory in the 3 tasks and ChAT and ChE activity were reduced compared to values in control rats. The administration of propentofylline recovered the decreased learning capacity and the deficit in cholinergic marker enzyme activity. These results suggest that the use of NGF stimulators may provide a new approach to the treatment of dementia.

NGF prevents further atrophy of cholinergic cells of the nucleus basalis due to cortical infarction in adult post-hypothyroid rats but does not restore cell size compared to euthyroid [correction of euthroid] rats

We have tested the hypotheses that nerve growth factor treatment in adult post-hypothyroid rats can: (1) restore cross-sectional area of cholinergic cells of the nucleus basalis and (2) prevent further atrophy of these neurons following cortical infarction. In addition, we assessed the expression of p75NGFR and p140trkA mRNAs in the nucleus basalis cells of post-hypothyroid rats. Rats were rendered hypothyroid by the addition of propylthiouracil to their diet beginning on embryonic day 19 until the age of 1 month. At this time both the pups and their dams continued to receive 0.05% propylthiouracil in their diet and the pups were thyroidectomized. At 60 days, propylthiouracil treatment was interrupted and thyroxine levels were restored to normal by daily subcutaneous administration of physiological levels of thyroxine. Morphometric analysis identified atrophied nucleus basalis magnocellularis cholinergic cells at two ages, days 75 and 105, identified by in situ hybridization for p75NGFR and p140trkA mRNAs in methylene blue stained cells (day 75) and choline acetyltransferase immunostaining (day 105). The mean number of silver grains (pixels) per microns2 (mean +/- S.E.M.) of cell body cross-sectional area for p75NGFR mRNA in the nucleus basalis magnocellularis of euthyroid rats was 3.43 +/- 0.89, which was not statistically different from post-hypothyroid animals (4.02 +/- 1.07). A similar finding was noted for p140trkA mRNA: mean number of grains in the euthyroid group was 5.54 +/- 0.96 and was not statistically different from the post-hypothyroid group (6.32 +/- 1.45). Nerve growth factor treatment in adulthood (between days 75 and 82) did not restore cross-sectional area from early thyroid deprivation. However, it prevented further atrophy of nucleus basalis magnocellularis neurons following cortical devascularization inflicted in adulthood (day 75).

Propentofylline prevents neuronal dysfunction induced by infusion of anti-nerve growth factor antibody into the rat septum

We have reported that the continuous infusion of anti-nerve growth factor (NGF) monoclonal antibody into the septum of rats produces neuronal dysfunction in the cholinergic system. Propentofylline has potent stimulatory effects on NGF synthesis/secretion in mouse astrocytes in vitro. To investigate the pharmacological effects of propentofylline, we used an animal model of dementia in which anti-NGF antibody was infused into the septum for 16 days via a mini-osmotic pump. The rats were treated with propentofylline orally once a day throughout the period during which performance in learning and memory tasks was observed. In the vehicle-treated dementia rats, learning and memory ability and choline acetyltransferase and cholinesterase activity were reduced compared to values in the control rats. The administration of propentofylline prevented the decreased learning capacity and the deficit in cholinergic marker enzyme activities. These results suggest that the use of NGF stimulators may provide a new approach to the treatment of dementia.

Induction of calmodulin kinase IV by the thyroid hormone during the development of rat brain

This communication reports the specific induction of calmodulin kinase IV by the thyroid hormone 3,3',5-triiodo-L-thyronine (T3) in a time- and concentration-dependent manner at a very early stage of brain differentiation using a fetal rat telencephalon primary cell culture system, which can grow and differentiate under chemically defined conditions. The induction of the enzyme that can be observed both on the mRNA and on the protein level is T3-specific, i.e. it cannot be induced by retinoic acid or reverse T3, and can be inhibited on both the transcriptional and the translational level by adding to the culture medium actinomycin D or cycloheximide, respectively. The earliest detection of calmodulin kinase IV in the fetal brain tissue of the rat is at days E16/E17, both on the mRNA as well as on the protein level. This is the first report in which a second messenger-dependent kinase involved in the control of cell regulatory processes is itself controlled by a primary messenger, the thyroid hormone.

NGF regulatory role in stress and coping of rodents and humans

Nerve growth factor (NGF) is a polypeptide growth factor which exerts trophic and differentiative effects on specific peripheral and central populations of neurons. Recent data showing that various cellular types of the endocrine and immune systems are able to synthesize and release NGF have suggested that this neurotrophic factor may also play an important role in vertebrate physiologic homeostasis. Previous studies using a mouse model of aggressive behavior have shown that NGF levels increase in both plasma and the CNS following intermale agonistic encounters. More recently, we have extended this research area to include other species: in particular, humans. The data now available indicate that labour and lactation, or the occurrence of a stressful event such as the very first jump with a parachute causes in NGF plasma levels as well as changes in the distribution of NGF receptors on lymphocytes. This review aimed to outline the current understanding of NGF role in vertebrates in stress-related events.

Nerve growth factor modulates information processing in the auditory thalamus

The spatio-temporal organization of spike discharges was studied in rat auditory thalamus (i.e., medial geniculate body and auditory sector of thalamic reticular nucleus) following a 2-week continuous intracerebroventricular administration of nerve growth factor (NGF). Recording of extracellular single-unit activity indicated that, in medial geniculate body, NGF induced a significant increase of the mean firing rate. In thalamic reticular nucleus, where units tend to discharge in bursts, NGF increased the average burst size (number of spikes) and the intraburst frequency without affecting the firing rate. Following white noise acoustical stimulation, in medial geniculate body, more onset excitation and a lower signal-to-noise ratio were observed in NGF-treated rats than in controls. Conversely, in thalamic reticular nucleus, NGF-treated animals showed more inhibitory responses than controls. In addition, within the medial geniculate body, functional interactions between pairs of units simultaneously recorded from different electrodes were greatly increased by the nerve growth factor treatment. These data indicate that modifications of temporal pattern of discharges in selected brain regions are among the effects induced by the intracerebroventricular administration of nerve growth factor.

Differential expression of p140trk, p75NGFR and growth-associated phosphoprotein-43 genes in nucleus basalis magnocellularis, thalamus and adjacent cortex following neocortical infarction and nerve growth factor treatment

A loss of target-derived neurotrophic factors is hypothesized to be one of the major determinants of central nervous system neuronal degeneration. In order to obtain further insight into early neuronal responses to injury, lesion-induced alterations in the expression of high- and low-affinity nerve growth factor receptors, as well as growth-associated phosphoprotein-43 genes in nucleus basalis magnocellularis, thalamic and neocortical neurons were studied. For this purpose, unilateral cortical devascularization operations were conducted on adult rats. Animals received i.c.v. infusions of vehicle or nerve growth factor (12 micrograms/day) and were killed at one, three, seven and 15 days post-lesion. In situ hybridization studies using 35S-labelled oligonucleotide probes for p75NGFR, p140trk and growth-associated phosphoprotein-43 messenger RNAs reveals that these genes were differentially regulated following the lesion. In the nucleus basalis magnocellularis ipsilateral to the lesion, p140trk gene expression significantly decreased on days 3 and 7, while p75NGFR messenger RNA initially increased on day 3 and decreased on days 7 and 15 after lesion. GAP-43 messenger RNA levels were significantly increased in the nucleus basalis magnocellularis on post-lesion days 3 and 7. Moreover, in contrast to p75NGFR or 140trk, growth-associated phosphoprotein-43 messenger RNA levels were significantly increased in pyramidal neurons located in the remaining cortex adjacent to the cortical lesion at all time points. In the lateral and ventroposterior nuclei of the thalamus, growth-associated phosphoprotein-43 messenger RNA level was slightly increased on days 1 and 3 and was dramatically decreased, significantly below the levels in sham-operated controls, on post-lesion days 7 and 15. During nerve growth factor application, the level of p140trk messenger RNA in the lesioned nucleus basalis magnocellularis returned to values observed in the contralateral nucleus basalis magnocellularis while p75NGFR messenger RNA was increased above values noted in all animals not treated with nerve growth factor. Nerve growth factor treatment did not affect the expression of growth-associated phosphoprotein-43 messenger RNA in any of the areas studied. p140trk messenger RNA was not up-regulated during the time that nerve growth factor was applied, as observed for p75NGFR, but only eight days after interrupting nerve growth factor treatment. Three cell types, nucleus basalis magnocellularis, cortical pyramidal and thalamic neurons, were probably affected in different ways by the devascularization with respect to lesion extent. Consequently, the remaining number of synaptic contacts in each of these brain areas is most likely different which may lead to a differential regulation of growth-associated phosphoprotein-43 messenger RNA.(ABSTRACT TRUNCATED AT 400 WORDS)

Regulatory region in choline acetyltransferase gene directs developmental and tissue-specific expression in transgenic mice

Acetylcholine, one of the main neurotransmitters in the nervous system, is synthesized by the enzyme choline acetyltransferase (ChAT; acetyl-CoA:choline O-acetyltransferase, EC 2.3.1.6). The molecular mechanisms controlling the establishment, maintenance, and plasticity of the cholinergic phenotype in vivo are largely unknown. A previous report showed that a 3800-bp, but not a 1450-bp, 5' flanking segment from the rat ChAT gene promoter directed cell type-specific expression of a reporter gene in cholinergic cells in vitro. Now we have characterized a distal regulatory region of the ChAT gene that confers cholinergic specificity on a heterologous downstream promoter in a cholinergic cell line and in transgenic mice. A 2342-bp segment from the 5' flanking region of the ChAT gene behaved as an enhancer in cholinergic cells but as a repressor in noncholinergic cells in an orientation-independent manner. Combined with a heterologous basal promoter, this fragment targeted transgene expression to several cholinergic regions of the central nervous system of transgenic mice, including basal forebrain, cortex, pons, and spinal cord. In eight independent transgenic lines, the pattern of transgene expression paralleled qualitatively and quantitatively that displayed by endogenous ChAT mRNA in various regions of the rat central nervous system. In the lumbar enlargement of the spinal cord, 85-90% of the transgene expression was targeted to the ventral part of the cord, where cholinergic alpha-motor neurons are located. Transgene expression in the spinal cord was developmentally regulated and responded to nerve injury in a similar way as the endogenous ChAT gene, indicating that the 2342-bp regulatory sequence contains elements controlling the plasticity of the cholinergic phenotype in developing and injured neurons.

Degeneration of rat cholinergic basal forebrain neurons and reactive changes in nerve growth factor expression after chronic neurotoxic injury--II. Reactive expression of the nerve growth factor gene in astrocytes

Long-term consumption of ethanol both in human and rodent induces a process of chronic degeneration of cholinergic basal forebrain neurons which results in a cholinergic deafferentation of the cortical mantle. We have used quantitative northern blot analysis and in situ hybridization to demonstrate that these degenerative events in rat evoke an increase in the expression of the nerve growth factor gene in a number of brain areas, including the cholinergic basal forebrain nuclei and their cortical target regions. By combining non-radioactive in situ hybridization and immunohistochemistry activated astrocytes were identified as the major source of altered nerve growth factor gene expression. This increased nerve growth factor expression is paralleled by a dendritic remodelling of basal forebrain neurons, while the expression of choline acetyltransferase in surviving neurons remains the same. This failure of nerve growth factor to rescue the expression of choline acetyltransferase differs from the effects of exogenously administered nerve growth factor in acutely lesioned systems. The results indicate that under certain conditions of chronic neurodegeneration, the utilization of nerve growth factor might be impaired, which could be due to a defective nerve growth factor signalling mechanism.

Neurochemical effects of a 20 kHz magnetic field on the central nervous system in prenatally exposed mice

C57/B1 mice were exposed during pregnancy (gestation days 0-19) to a 20 kHz magnetic field (MF). The asymmetric sawtooth-waveform magnetic field in the exposed racks had a flux density of 15 microT (peak to peak). After 19 days, the exposure was terminated, and the mice were housed individually under normal laboratory conditions. On postnatal day (PD) 1, PD21, and PD308, various neurochemical markers in the brains of the offspring were investigated and the brains weighed. No significant difference was found in the whole brain weight at PD1 or PD21 between exposed offspring and control animals. However, on PD308, a significant decrease in weight of the whole brain was detected in exposed animals. No significant differences were found in the weight of cortex, hippocampus, septum, or cerebellum on any of the sampling occasions, nor were any significant differences detected in protein-, DNA-level, nerve growth factor (NGF), acetylcholine esterase- (AChE), or 2',3'-cyclic nucleotide 3'-phosphodiesterase- (CNP; marker for oligodendrocytes) activities on PD21 in cerebellum. Cortex showed a more complex pattern of response to MF: MF treatment resulted in a decrease in DNA level and increases in the activities of CNP, AChE, and NGF protein. On PD308, the amount of DNA was significantly reduced in MF-treated cerebellum and CNP activity was still enhanced in MF-treated cortex compared to controls. Most of the effects of MF treatment during the embryonic period were similar to those induced by ionizing radiation but much weaker. However, the duration of the exposure required to elucidate the response of different markers to MF seems to be greater and effects appear later during development compared to responses to ionizing radiation.

Expression of nerve growth factor, p75, and trk in the somatosensory and motor cortices of mature rats: evidence for local trophic support circuits

Neurotrophins such as nerve growth factor (NGF) are critical for the maintenance of CNS neurons. We determined the expression of NGF and the neurotrophin receptors p75 and trk in the somatosensory and motor cortices of mature rats with immunohistochemical techniques. Sections of mature rat cortex were processed immunohistochemically with primary antibodies directed against NGF, p75, or trk. The distribution of immunoreactive elements was examined, and stereological techniques were used to determine the density and size of immunoreactive cell bodies. Some sections processed for trk immunoreactivity were examined with an electron microscope. From the size and morphology of the labeled cells, it appeared that only neurons in the gray matter were NGF-positive. NGF was detected in one-third of the neurons in layers II-III, V, and VI of both somatosensory cortex and motor cortex; however, fewer than 1 in 12 of the layer IV neurons was NGF-positive. With the notable exception of layer V, few cell bodies (2-10% of the total population) were p75- or trk-immunoreactive. Layer Vb was replete with receptor-positive cell bodies; more than one-third of the layer Vb neurons were p75- or trk-positive. All labeled cells appeared to be pyramidal neurons. The distribution of p75 labeling with the two anti-p75 antibodies was indistinguishable. In addition, the neuropil in the supragranular laminae was p75- or trk-positive. Electron microscopy showed that trk immunoreactivity was also expressed by dendrites. Only rarely were immunoreactive axons detected. In summary, NGF is expressed by cortical neurons throughout cortex, and neurotrophin receptors are widely produced by postsynaptic targets. Thus, NGF appears to participate in an intracortical autoregulatory system. The strong expression of neurotrophin receptors by pyramidal neurons in layer Vb (the origin of brainstem and spinal cord projections) suggests that the neurotrophins are especially critical for the regulation of corticofugal projection systems.

Decreased choline acetyltransferase activity in nerve growth factor-transgenic mice during brain development

Activity of the synthetic enzyme for acetylcholine, choline acetyltransferase was investigated during development and in adult nerve growth factor-transgenic mice. A conspicuous reduction of choline acetyltransferase activity was observed in the anterior brain of nerve growth factor-transgenic embryos from embryonic days 13 to 16 (E13 to E16). Choline acetyltransferase activity levels subsequently resumed to normal levels, with the exception of a 15% increase in the adult hippocampus. Nerve growth factor contents followed a similar time-course and regional distribution in normal and nerve growth factor-transgenic animals and displayed significantly higher values from E14 to the early postnatal period. Nerve growth factor contents were normal in the adult brain. In vitro experiments confirmed the involvement of nerve growth factor in the decrease of choline acetyltransferase activity levels observed in transgenic neurons during development. These results suggest a role for nerve growth factor in the initial phase of the phenotypic differentiation of cholinergic neurons. They show that nerve growth factor may, under specific development conditions, lead to a paradoxical down-regulation of choline acetyltransferase activity.

Phorbol ester stimulates acetylcholine synthesis in cultured endothelial cells isolated from porcine cerebral microvessels

Acetylcholine (ACh) is one of the factor which induces vasodilation through the release of endothelium-derived relaxing factor. The aim of this study was to clarify whether endothelial cells can synthesize ACh and the types of substance which regulate the synthesis of ACh in endothelial cells. We determined the ACh content of endothelial cells isolated from porcine cerebral microvessels and of the culture medium. ACh was detected in the medium after 12 h incubation in the presence of diisopropylfluorophosphate, a non-specific cholinesterase inhibitor, and increased linearly up to 24 h. Phorbol 12-myristate 13-acetate (PMA, 10(-7) M) increased the ACh content of the medium in a dose-dependent manner. The effect of PMA was most apparent between 12 and 24 h after treatment, and was inhibited by cycloheximide. Calphostin C, a specific inhibitor of protein kinase C (PKC), did not inhibit the effect of PMA. Dioctanoyl glycerol, a specific activator of PKC, did not increase the intracellular ACh content or the amount released into the culture medium. ACh synthesis was not inhibited by bromoacetylcholine, a specific inhibitor of choline acetyltransferase (ChAT). PMA treatment did not affect the specific activity of ACh synthesis in endothelial cells. These data show that endothelial cells are able to synthesize ACh, and that ACh synthesis is up-regulated by PMA through the PKC independent mechanism via protein induction. The enzyme which synthesizes ACh in endothelial cells is not ChAT. The increase in ACh synthesis induced by PMA may not be due to induction of the ACh synthetic enzyme.

Nerve growth factor and Alzheimer's disease

Nerve growth factor (NGF) is a well-characterized protein that exerts pharmacological effects on a group of cholinergic neurons known to atrophy in Alzheimer's disease (AD). Considerable evidence from animal studies suggests that NGF may be useful in reversing, halting, or at least slowing the progression of AD-related cholinergic basal forebrain atrophy, perhaps even attenuating the cognitive deficit associated with the disorder. However, many questions remain concerning the role of NGF in AD. Levels of the low-affinity receptor for NGF appear to be at least stable in AD basal forebrain, and the recent finding of AD-related increases in cortical NGF brings into question whether endogenous NGF levels are related to the observed cholinergic atrophy and whether additional NGF will be useful in treating this disorder. Evidence regarding the localization of NGF within the central nervous system and its presumed role in maintaining basal forebrain cholinergic neurons is summarized, followed by a synopsis of the relevant aspects of AD neuropathology. The available data regarding levels of NGF and its receptor in the AD brain, as well as potential roles for NGF in the pathogenesis and treatment of AD, are also reviewed. NGF and its low affinity receptor are abundantly present within the AD brain, although this does not rule out an NGF-related mechanism in the degeneration of basal forebrain neurons, nor does it eliminate the possibility that exogenous NGF may be successfully used to treat AD. Further studies of the degree and distribution of NGF within the human brain in normal aging and in AD, and of the possible relationship between target NGF levels and the status of basal forebrain neurons in vivo, are necessary before engaging in clinical trials.

Changes in the response of cultured septal cholinergic neurons to nerve growth factor exposure and deprivation during the first postnatal month

The effects of nerve growth factor (NGF) and a blocking anti-NGF antibody were studied in cultures plated from postnatal day 1-28 (P1-P28) rat septum and maintained 3 weeks in vitro. 7S NGF (100 ng/ml = 0.75 nM) increased choline acetyltransferase (ChAT) activity in P7-P21 cultures. The largest increase was measured in P7-P14 cultures, where NGF addition produced ChAT activities 5-12 times higher than those measured in cultures grown in anti-NGF antibody. NGF also increased the number of acetylcholinesterase (AChE)-positive neurons in P7-P14 cultures. To determine whether this increase was due to enhanced survival of cholinergic neurons or simply to enhanced AChE expression, we examined cultures to which NGF was added only after an initial 1-2-week exposure to anti-NGF antibody. This delayed addition of NGF also increased ChAT activity and the number of AChE-positive neurons, indicating that cholinergic neurons survived the initial exposure to anti-NGF antibody. Thus even during a period when ChAT activity was most sensitive to NGF, postnatal septal cholinergic neurons did not require NGF for survival in vitro.

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)

Oral administration of idebenone induces nerve growth factor in the brain and improves learning and memory in basal forebrain-lesioned rats

Nerve growth factor plays an important role in the survival and maintenance of cholinergic neurons in the central neuronal system. In senile dementia of the Alzheimer type, learning and memory are impaired by the loss of neurons in the magnocellular cholinergic neuronal system. It is therefore, of interest to investigate the role of nerve growth factor in this degenerative disorder. Since nerve growth factor does not cross the blood-brain barrier and is easily metabolized by peptidases when administered peripherally, it can be used for medical treatment only when directly injected into the brain. We demonstrate here that the oral administration of idebenone, a potent in vitro nerve growth factors synthesis stimulator, induced an increase in nerve growth factor protein and mRNA, and in choline acetyltransferase activity, in basal forebrain lesioned rats, but not in intact rats. Idebenone also ameliorated the behavioral deficits in habituation, water maze, and passive avoidance tasks in these animals. These results suggest that idebenone stimulated nerve growth factor synthesis in vivo and ameliorates the behavioral deficits which were accompanied with the recovery of the reduced choline acetyltransferase activity in the basal forebrain-lesioned rats.

An aggregate brain cell culture model for studying neuronal degeneration and regeneration

Rotation-mediated aggregating cell cultures from fetal rat telencephalons containing glial and neuronal cells mature in a fashion comparable to that known to occur in brain in vivo. Large aggregates of 300-500 microM diameters can now reproducibly be cultivated and maintained for more than 40 days in a well defined serum free medium. Validity of the use of such cultures for in vitro studies of various physiological, pharmacological and toxicological phenomenon has already been demonstrated. In this communication some observations suggesting the usefulness of such cultures for pharmacological studies clarifying the possible effects of drugs and other agents on excitatory amino acid induced pathological processes will be presented. The advantages and limitations of the use of aggregated brain cell culture based models for the development of agents potentially useful for the treatment of aging and dementia will also be discussed.

Oral administration of idebenone, a stimulator of NGF synthesis, recovers reduced NGF content in aged rat brain

The relationship between nerve growth factor (NGF) and senile dementia of the Alzheimer type is of interest. We demonstrate here that the oral administration of idebenone, a stimulator of NGF synthesis in vitro, produced recovery of reduced NGF content in aged rat brain. Twenty-one-day successive administration of idebenone produced significant recovery of reduced NGF content in the frontal cortex and parietal cortex of aged rats. These results suggest that NGF content in the brain is low in aged rats and that oral administration of idebenone leads to a recovery of this reduction.

Effects of nerve growth factor on X-irradiated reaggregation cultures of rat brain cells

The effects of exogenously added nerve growth factor (NGF) on reaggregation cultures of foetal rat brain cells after X-irradiation with 2 Gy were studied. Irradiation caused decreased protein and DNA levels, which was not prevented by NGF. The activities of the cholinergic marker enzymes choline acetyl transferase and acetylcholine esterase were increased in irradiated cultures. However, no difference in the activities of these enzymes was found between irradiated and unirradiated NGF-treated cultures. Irradiation did not affect the activity of the marker enzyme for oligodendrocytes (2',3'-cyclic nucleotide 3'-phosphodiesterase), but caused an increase in the astrocyte marker (glutamine synthetase) activity. This effect on astrocytes was prevented by NGF.

Regulation of expression of cholinergic neuronal phenotypic markers in neuroblastoma LA-N-2

Cholinergic neurons in PNS and CNS are identified by the presence of choline acetyltransferase and the accumulation of choline by a high-affinity, sodium-coupled choline transporter to be used for acetylcholine synthesis. It appears that expression of choline acetyltransferase can be altered by several physiological conditions, including hormones and trophic factors, but little is known about control of expression of the sodium-coupled choline carrier or whether these two phenotypic markers are regulated similarly. In the present study, the cholinergic human neuroblastoma LA-N-2 was used to investigate regulation of expression of choline acetyltransferase and choline uptake activity associated with differentiation and neurite extension. Cells grown in serum-containing basal medium maintained a relatively undifferentiated morphology, expressed low levels of choline acetyltransferase activity, and accumulated choline by a sodium-dependent process followed by conversion to acetylcholine. Transfer of cells to an enriched, serum-free defined medium resulted in morphological and neurochemical differentiation, with an enhancement of cholinergic phenotype. Hemicholinium-sensitive choline uptake activity was increased about sixfold over a 4-day period, with no change in choline acetyltransferase or acetylcholinesterase specific activity. Acetylcholine synthesis was increased in parallel with the changes in choline accumulation; choline metabolism in the differentiated cells differed significantly from that observed in the undifferentiated cells, with proportionally less converted to phosphorylcholine and proportionally more remaining as unmetabolized choline and converted to acetylcholine. The enhanced choline accumulation appeared to be mediated by an increased number of choline carriers, demonstrated by increased binding of the affinity ligand [3H]-choline mustard to the transporter and by an increased Vmax for the uptake process. The increased expression of the transport function appeared to be under transcriptional control, as the enhancement of uptake was blocked by the RNA polymerase II inhibitor alpha-amanitin as well as by the protein synthesis inhibitor cycloheximide. These results show that expression of sodium-coupled choline carriers and choline acetyltransferase may be regulated separately in the differentiating neuroblastoma LA-N-2 and that neurotransmitter synthesis is controlled by provision of precursor rather than at the level of the biosynthetic enzyme.

Neurotrophin-4 is a target-derived neurotrophic factor for neurons of the trigeminal ganglion

The cellular localization of mRNA for neurotrophin-4 (NT-4), a novel neurotrophic factor, in the developing whisker follicles and skin of the embryonic rat is demonstrated by in situ hybridization. Levels of NT-4 mRNA in the whisker pad decrease between embryonic day 13 (E13) and E20, correlating in time with the onset of naturally occurring neuronal death in the innervating trigeminal ganglion. In addition to NT-4, brain-derived neuotrophic factor (BDNF) mRNA is also shown to be expressed in the rat embryonic whisker follicles although in a different cellular localization, which combined with previous data on the expression of NGF and NT-3 mRNAs, shows that all four neurotrophins are expressed during development of this structure. NT-4 protein is shown to elicit neurite outgrowth from explanted embryonic trigeminal ganglia and to promote neuronal survival of dissociated trigeminal ganglion neurons when cultured during the phase of cell death. NT-4 and NT-3 mainly support different neuronal subpopulations, whereas some NT-4-responsive cells appear to respond also to NGF and BDNF. Analysis of mRNAs for members of the Trk family of neurotrophin receptors in neurons rescued by different neurotrophins demonstrates the presence of distinct neuronal subpopulations that respond to specific combinations of these factors. Based on these results we propose that NT-4, together with the other three neurotrophins, orchestrate the innervation of the different structures of the developing whisker pad by the trigeminal ganglion, acting as target-derived neurotrophic factors for different subpopulations of trigeminal ganglion neurons.

Detailed characterization of the biological activities of recombinant human nerve growth factor expressed in Chinese hamster ovary cells

The biological activities of recombinant human nerve growth factor (rhNGF) produced by Chinese hamster ovary (CHO) cells that were transfected with human NGF gene were investigated in vitro and in vivo. rhNGF showed the same immunoreactivity as mouse NGF (mNGF) in a highly sensitive two-site enzyme immunoassay system employing mouse monoclonal antibody against mouse beta-NGF (MAb 27/21) for both the primary and the secondary antibodies. In PC12 cells, rhNGF promoted neurite extension and induced acetylcholinesterase (AChE) with the same potency as mNGF, showing an ED50 of 10-20 ng/mL. In fetal rat septal neurons cultured on a feeder layer of astroglial cells, rhNGF promoted survival and neurite extension as well as an increase in choline acetyltransferase (ChAT) activity and acetylcholine (ACh) content. At a maximal effective concentration of 30 ng/mL, rhNGF promoted a 1.4-, 2.8-, and 4-fold increase in surviving cell number, ACh content, and ChAT activity, respectively. rhNGF was five times more potent than mNGF for the increase in ChAT activity and ACh content showing an ED50 of 0.5 ng/mL, although the maximal response was the same for the two NGFs. Transection of the fimbria-fornix resulted in a loss of AChE-positive cells in the medial septum (MS) and vertical limb of the diagonal band of Broca (VDB). The administration of rhNGF or mNGF (3 or 30 micrograms in gel form) attenuated the loss of AChE-positive cells; rhNGF was as potent as or even more potent than mNGF. Radio frequency lesion of the basal forebrain (BF) including the nucleus basalis magnocellularis (NBM) resulted in severe impairment of memory and/or learning in passive avoidance and Morris' water maze tasks. Repeated injection of rhNGF (5 micrograms x 5 over 2 wk) into the lateral ventricle ameliorated the behavioral impairment in the water maze task but not in passive avoidance. rhNGF treatment increased ChAT activity in the frontal cortex and even in other subregions of the cerebral cortex where ChAT activity was not decreased by BF lesion. These results indicate that human NGF can be measured in an enzyme immunoassay system using monoclonal antibody against mNGF (MAb 27/21) and that rhNGF has potent biological activity, comparable to or greater than mNGF, both in vitro and in vivo.