Choline acetyltransferase activity in striatum of neonatal rats increased by nerve growth factor

Nerve growth factor-induced increase in calcium uptake by PC12 cells

Treatment of PC12 cells with nerve growth factor (NGF) produces a rapid and transient increase in calcium uptake into the cells. The increased uptake is maximal after 5 minutes of NGF treatment, but after 15 minutes of NGF treatment, no such increase can be observed. The effect of NGF is partially inhibited by blockers of L-type calcium channels. K-252a, an alkaloid-like kinase inhibitor that usually is found to inhibit the actions of NGF on PC12 cells, produces an increase in calcium uptake similar to, but smaller than, that seen with NGF. NGF had no effect on calcium release under these conditions.

1,25-Dihydroxyvitamin D3 is a potent inducer of nerve growth factor synthesis

1,25-Dihydroxyvitamin D3 (1,25-(OH)2D3), a metabolically active form of vitamin D, is shown to increase in a dose-dependent manner the cellular pool of NGF mRNA in murine L-929 fibroblasts cultured in a serum-free medium. This effect can be detected as early as 3 hours after 1,25-(OH)2D3 addition and persists for at least 28 hours. It is accompanied by an enhancement of the amount of NGF protein secreted in the culture medium. Since the proto-oncogene c-fos appears involved in the regulation of the NGF gene (Mocchetti et al.: Proceedings of the National Academy of Sciences of the United States of America 86: 3871-895, 1989; Hengerer et al: Proceedings of the National Academy of Sciences of the United States of America 87:3899-3903, 1990), the effect of 1,25-(OH)2D3 on c-fos expression was analysed and compared to that elicited by other inducers of the NGF gene, serum (Wion et al: FEBS Letters 189:37-41, 1985) and phorbol 12-myristate 13-acetate (PMA) (Wion et al: FEBS Letters 262:42-44, 1990). Addition of serum or PMA to L-929 cells was rapidly followed by a transient activation of the c-fos gene. In contrast, c-fos transcripts remained undetected in the presence of 1,25-(OH)2D3. The failure to find any evidence of c-fos expression suggests that 1,25-(OH)2D3 could enhance the pool of NGF mRNA by a mechanism independent of the c-fos pathway.(ABSTRACT TRUNCATED AT 250 WORDS)

The nerve growth factor receptor gene is expressed in both neuronal and non-neuronal tissues in the human fetus

In situ hybridization was used to study expression of beta-nerve growth factor receptor (NGF-R) mRNA in the early human fetus. In 8- to 12-week old fetuses, high labelling was found over motoneurons along the entire length of the lateral motor column. High levels of NGF-R mRNA were also seen over most developing nerve cell bodies in both the dorsomedial and ventrolateral part of the dorsal root ganglia. Lower, but clearly specific labelling was detected over a subpopulation of cells in Auerbach's plexus in the intestines. Evidence for a non-neuronal expression of NGF-R mRNA came from labelling over a subpopulation of cells in glomeruli of the kidney in a 12-week old human embryo. Myoblasts in skeletal muscle anlagen were labelled as well as cells along peripheral nerve. The widespread expression of NGF-R mRNA in the human fetus suggests that the NGF-R is important for development of a variety of different tissues of both neuronal and non-neuronal origin.

Interleukin-6 improves the survival of mesencephalic catecholaminergic and septal cholinergic neurons from postnatal, two-week-old rats in cultures

Interleukin-6 (human recombinant) supported the survival of cultured mesencephalic, catecholaminergic and septal cholinergic neurons from postnatal, two-week-old (P13-P15) rats. Significantly, more catecholaminergic neurons, stained by monoclonal anti-tyrosine hydroxylase antibody, were found in cultures supplemented with interleukin-6 at a concentration of 5 ng/ml than in cultures not treated with interleukin-6. The optimal dose used was 50 ng/ml. The survival effect of interleukin-6 on postnatal rat, tyrosine hydroxylase-positive neurons was observed both in cultures using serum-containing and serum-free medium. Contents of dopamine and noradrenaline in cultures with interleukin-6 were also larger than in control cultures. Interleukin-6 also increased the survival of cultured embryonic (E17) rat midbrain tyrosine hydroxylase-positive neurons. The effect on these neurons was, however, smaller, and the optimal dose of interleukin-6 was nearly 5 ng/ml. Interleukin-6 also supported the survival of cultured postnatal (P13) rat septal cholinergic neurons, visualized by acetylcholinesterase staining. The concomitant addition of mouse nerve growth factor (100 ng/ml) and interleukin-6 (50 ng/ml) had a synergetic effect on the survival of acetylcholinesterase-positive neurons in culture. Our data suggest that the survival of cultured tyrosine hydroxylase-positive, mesencephalic, and acetylcholinesterase-positive, septal neurons from postnatal two-week-old rats was supported by interleukin-6, just as there was a different dose dependency of interleukin-6 on the cultured postnatal neurons compared with embryonic neurons.

In vitro cell cultures as a model of the basal forebrain

The basal forebrain has attracted considerable attention because of its putative role in complex functions such as learning, memory and behavioral state control as well as its vulnerability in neurological disorders such as Alzheimer's Disease (AD). The finding that nerve growth factor provides trophic support for the cholinergic basal forebrain neurons has stimulated further interest in understanding trophic interactions of basal forebrain neurons as well as in possible trophic factor therapeutic strategies for disease states. Our laboratory has utilized primary cell cultures and developed immortalized central nervous system cell lines to study the trophic interactions that establish and maintain the septohippocampal pathway, a basal forebrain component which plays an essential role in cognitive function and is prominently affected in AD. The results of our primary cell culture studies have demonstrated the importance of trophic signals elaborated by the hippocampus in mediating the development of septal cholinergic neurons. Nerve growth factor plays an important role in this process, but it cannot account for all of the trophic signals elaborated by authentic hippocampal target cells. The development by this laboratory of clonal cell lines of septal and hippocampal lineage offers the prospect of investigating both the response to and elaboration of neural trophic signals at a more precise level of resolution than can be achieved with primary cultures. The technology and information that is generated from the engineering of such cell lines will also serve as a strategy to study trophic interactions in other brain circuits in future years, and to investigate possible changes or dysfunctions that occur neurological diseases.

Nerve growth factor and the neostriatum

1. The present review summarizes evidence describing the expression, immunoreactivity, binding, transport, development, aging, and functions of NGF in the mammalian neostriatum. 2. Neostriatal NGF binding sites and intrinsic cholinergic neurons are co-localized, increase at a similar rate during ontogeny, and are lost to an equal extent following age- or injury-induced loss of neostriatal neurons. 3. Exogenously administered NGF augments ChAT activity in the intact caudate-putamen, nucleus accumbens, and following mechanical or excitotoxin-induced cholinergic injury. NGF antibodies lower ChAT in the intact caudate-putamen. 4. Neostriatal cholinergic interneurons are lost in the aged rat but also in Alzheimer's disease, Parkinson's disease, supranuclear palsy, and Huntington's chorea. Future studies need to address the extent to which these losses result from an abbreviation of NGF production, binding, or transport and whether rhNGF administration may retard or reverse these cholinergic losses.

Exogenous nerve growth factor stimulates choline acetyltransferase activity in aging Fischer 344 male rats

The effect of age and exogenous nerve growth factor (NGF) infusion on choline acetyltransferase (ChAT) specific activity is examined in microdissections of cerebral and hippocampal cortices, and the cholinergic nuclei of the medial septum and diagonal band of Broca (MS/DB), the nucleus basalis magnocellularis (NBM), and striatum of Fischer 344 male rats. Significant, 20% losses in ChAT activity are found in the MS/DB and striatum of 24-month-old rats (n = 21) compared to 4-month-old animals, but there is no apparent loss of enzyme activity in the NBM. Loss of ChAT activity in the MS/DB is only observed in animals older than 19 months of age, while a striatal deficit is found in animals older than 7 months. Treatment for 2 weeks with NGF at 1.2 micrograms/day results in significant 70% increases of ChAT activity in the MS/DB and striatum of 24-month-old rats compared to untreated and vehicle-treated 4-month-old rats, but does not stimulate activity in the NBM. Sensitivity of ChAT activity in the MS/DB and striatum to exogenous NGF increases with age. These experiments indicate that in the MS/DB, NBM, and striatum of Fischer 344 male rat there is an age-associated, differential regulation of ChAT enzyme activity and sensitivity to exogenous NGF.

Nerve growth factor levels and choline acetyltransferase activity in the brain of aged rats with spatial memory impairments

Nerve growth factor (NGF) and choline acetyltransferase (ChAT) activity levels were measured in 7 different brain regions in young (3-month-old) and aged (2-years-old) female Sprague-Dawley rats. Prior to analysis the spatial learning ability of the aged rats was assessed in the Morris' water maze test. In the aged rats a significant, 15-30%, increase in NGF levels was observed in 4 regions (septum, cortex, olfactory bulb and cerebellum), whereas the levels in hippocampus, striatum and the brainstem were similar to those of the young rats. The NGF changes did not correlate with the behavioral performance within the aged group. Minor 15-30%, changes in ChAT activity were observed in striatum, brainstem and cerebellum, but these changes did not correlate with the changes in NGF levels in any region. The results indicate that brain NGF levels are maintained at normal or supranormal levels in rats with severe learning and memory impairments. The results, therefore, do not support the view that the marked atrophy and cell loss in the forebrain cholinergic system that is known to occur in the behaviorally impaired aged rats is caused by a reduced availability of NGF in the cholinergic target areas. The results also indicate that the slightly increased levels of NGF are not sufficient to prevent the age-dependent atrophy of cholinergic neurons, although they might be important for the stimulation of compensatory functional changes in a situation where the system is undergoing progressive degeneration.

Trophic actions of recombinant human nerve growth factor on cultured rat embryonic CNS cells

NGF is a neurotrophic factor for basal forebrain cholinergic neurons and may serve to counteract the cholinergic deficits that are observed in Alzheimer's disease. Prior to the introduction of clinical trials, it is essential that recombinant human NGF (rhNGF) be produced and that its actions on target cells in the CNS be demonstrated. We prepared rhNGF and examined its actions on fetal rat brain neurons in culture including, in particular, the cholinergic neurons of the basal forebrain. rhNGF was more potent in increasing choline acetyltransferase (ChAT) activity in septal cultures than NGF purified from mouse salivary glands (mNGF). ED50s of the beta-NGF dimers were 4.9 pM for rhNGF and 12.4 pM for mNGF. The maximal ChAT activity response was achieved at approximately 35 pM with both NGFs and their efficacies were not significantly different. The two NGFs were not additive in effect. Identical to the results with mNGF, rhNGF strongly enhanced the intensity of ChAT immunostaining in septal cultures. Neither rhNGF nor mNGF affected the appearance of the cultures under phase-contrast illumination. Survival of cells at very low plating density on polyornithine/laminin-coated culture dishes was not affected by rhNGF or mNGF. Protein content and the uptake of GABA were also unaffected. At concentrations of up to 10 micrograms/ml, rhNGF did not significantly increase uptake of dopamine into cultures of ventral mesencephalon. We conclude that rhNGF produces potent and selective actions on cholinergic neurons of the basal forebrain as previously shown for mNGF.

Identification of high- and low-affinity NGF receptors during development of the chicken central nervous system

In order to study regulation of the nerve growth factor (NGF) receptor during embryogenesis in chick brain, we have used affinity crosslinking of tissues with 125I-NGF. NGF interacts with high- and low-affinity receptors; high-affinity receptors are required for the majority of NGF's actions. Most measurements of receptor levels do not distinguish between high- and low-affinity forms of the receptor. We have used the lipophilic crosslinking agent HSAB to identify the high-affinity, functional receptor during development of the chicken central nervous system. A peak of expression during Embryonic Days 5-10 was detected in all regions of the chicken central nervous system, but, shortly after birth, only the cerebellar region displays significant levels of NGF receptor protein. The time course of expression confirms the dramatic regulation of the NGF receptor gene during defined embryonic periods. The detection of high-affinity NGF receptors in brain and neural retina provides strong evidence that NGF is involved in essential ontogenetic events in the development of the chicken central nervous system.

Regulation of beta-nerve growth factor expression by inflammatory mediators in hippocampal cultures

Substances which regulate expression of nerve growth factor (NGF) were examined in embryonic rat hippocampal cultures containing both neurons and glial cells. Both cell types expressed NGF mRNA when cultivated in vitro. Lipopolysaccharide, an activator of macrophages, elicited a significant increase in NGF mRNA. Interleukin-1 beta evoked a similar increase in NGF mRNA which was accompanied by a rise in NGF protein. The Il-1-induced increase was partially blocked by indomethacin, suggesting that prostaglandins might mediate this effect. Treatment of the cultures directly with prostaglandin E2 resulted in elevated levels of both NGF mRNA and protein. Thus, agents which promote inflammatory activity appear to increase NGF expression. Moreover, a suppressor of inflammation, dexamethasone, decreased NGF expression. Our observations indicate that a variety of immunomodulators regulate NGF expression in the hippocampus.

Identification of cells in rat brain and peripheral tissues expressing mRNA for members of the nerve growth factor family

Cells expressing mRNA for hippocampus-derived neurotrophic factor (HDNF/NT-3) or brain-derived neurotrophic factor (BDNF) were identified by in situ hybridization. In the rat brain, HDNF mRNA was predominantly found in pyramidal neurons in CA1 and CA2 of the hippocampus. Lower levels of HDNF mRNA were found in granular neurons of the dentate gyrus and in neurons of the taenia tecta and induseum griseum. BDNF mRNA-expressing cells were more widely distributed in the rat brain, with high levels in neurons of CA2, CA3, and the hilar region of the dentate gyrus, in the external and internal pyramidal layers of the cerebral cortex, in the claustrum, and in one brainstem structure. Lower levels were seen in CA1 and in the granular layer of the hippocampus, in the taenia tecta, and in the mammillary complex. In peripheral tissues, HDNF mRNA was found in glomerular cells in the kidney, secretory cells in the male rat submandibular gland, and epithelial cells in secondary and tertiary follicles in the ovary. Cells expressing BDNF mRNA were found in the dorsal root ganglia, where neurons of various sizes were labeled.

Long-term administration of mouse nerve growth factor to adult rats with partial lesions of the cholinergic septohippocampal pathway

Nerve growth factor (NGF), a neurotrophic factor acting on cholinergic neurons of the basal forebrain, has been proposed as a treatment for Alzheimer's disease. Experimental support for its pharmacological use is derived from short-term studies showing that intraventricular administration of NGF during 2-4 weeks protects cholinergic cell bodies from lesion-induced degeneration, stimulates synthesis of choline acetyltransferase, and improves various behavioral impairments. To investigate the consequences of long-term NGF administration, we tested whether cholinergic cell bodies are protected from lesion-induced degeneration and whether cholinergic axons are stimulated to regrow into the denervated hippocampus following fimbrial transections. We found that intraventricular injections of NGF twice a week for 5 months to adult rats resulted in extended protection of cholinergic cell bodies from lesion-induced degeneration and did not produce obvious detrimental effects on the animals. NGF treatment mildly stimulated growth of cholinergic neurites within the 2-mm area directly adjacent to the fimbrial lesion but it failed to induce significant homotypic growth of cholinergic neurites into the deafferented hippocampus.

Environmental influence on behaviour and nerve growth factor in the brain

The influence of the environment on the endogenous levels of nerve growth factor (NGF) in the cortex, hippocampus and septum was examined in adult (82 days old) and juvenile (51 days old) rats. Animals were reared/housed for 30 days in an enriched, standard or isolated environment prior to analysis. In addition, another group of rats were given behavioural tests (4 days) after differential rearing/housing before measurements of NGF. We found complex variations in the level of NGF both in juvenile and adult hippocampus after differential environmental rearing/housing. Rearing/housing in an enriched environment improved performance in the Morris maze and decreased spontaneous motor activity. Exposure to behavioural tests caused alterations in adult hippocampus and septum NGF levels. The results show that testing in a novel environment causes small but significant changes in the hippocampal and septal NGF levels depending upon the environmental history of the animal. In view of the purported involvement of the septohippocampal pathway and NGF in the pathophysiology of Alzheimer's disease, our finding suggests that lack of adequate environmental stimulation might be of importance in age-related behavioural and neurochemical deficits.

Exogenous nerve growth factor increases the activity of high-affinity choline uptake and choline acetyltransferase in brain of Fisher 344 male rats

The objective of this study was to determine the effect of age and chronic intracerebral administration of nerve growth factor (NGF) on the activity of the presynaptic cholinergic neuronal markers hemicholinium-sensitive high-affinity choline uptake (HACU) and choline acetyltransferase (ChAT) in the brain of Fisher 344 male rats. In 24-month-old rats, a substantial decrease in ChAT activity (30%) was measured in striatum, and decreases in HACU were found in frontal cortex (28%) and hippocampus (23%) compared with 4-month-old controls. Cholinergic neurons in brain of both young adult and aged rats responded to administration of exogenous NGF by increased expression of both phenotypes. In 4-month-old animals, NGF treatment at 1.2 micron/day resulted in increased activities of both ChAT and HACU in striatum (175 and 170%, respectively), frontal cortex (133 and 125%), and hippocampus (137 and 125%) compared with untreated and vehicle-treated 4-month-old animals; vehicle treatment had no effect on the activity of either marker. In 24-month-old animals treated with NGF for 2 weeks, ChAT activity was increased in striatum (179%), frontal cortex (134%), and hippocampus (119%) compared with 24-month-old control animals. Synaptosomal HACU in 24-month-old rats was increased in striatum (151%) and frontal cortex (128%) after 2 weeks of NGF treatment, but hippocampal HACU was not significantly different from control values.(ABSTRACT TRUNCATED AT 250 WORDS)

Beta-adrenergic receptor regulation, through cyclic AMP, of nerve growth factor expression in rat cortical and cerebellar astrocytes

1. Type 1 astrocytes prepared from 3-day rat cortex and cerebellum express the 1.3-kb nerve growth factor (NGF) mRNA and synthesize and release beta-NGF. 2. Isoproterenol (IP), a beta-adrenergic agonist, stimulates NGF mRNA content in cortical astrocytes; this increase is blocked by the beta-adrenergic antagonist propranolol but not the alpha-antagonist phenoxybenzamine. The EC50 for the effect of IP is 5 nM. 3. IP increases astrocyte cyclic AMP as does forskolin, which directly activates adenylate cyclase and also increases NGF mRNA content. Cerebellar astrocytes contain about one-third as much NGF mRNA, which can also be increased by forskolin and cyclic AMP. 4. These results suggest that CNS astrocytes can serve as a source of NGF and that the NGF gene is one of the class of cyclic AMP regulated genes.

Basic fibroblast growth factor suppressed the enhancement of choline acetyltransferase activity induced by nerve growth factor

We investigated change of choline acetyltransferase (ChAT) activities in rat embryonic (16 days) septal neuron culture in treatment with basic fibroblast growth factor (bFGF) and nerve growth factor (NGF). Total ChAT activity increased by addition of bFGF, NGF, and bFGF plus NGF with dose-dependent manner. NGF showed much enhancement of specific ChAT activities per mg protein, but bFGF or bFGF plus NGF, respectively showed little or slightly enhanced ChAT activities. In histochemical studies with anti-ChAT antibody staining, cholinergic neurons in NGF-treated culture were stained more strongly than those in other conditioned cultures such as control, bFGF-treated, and bFGF plus NGF-treated cultures. These results suggest that bFGF enhances total ChAT activity but not cellular ChAT activity and further suppresses the enhancement of cellular ChAT activity induced by NGF in septal neuron culture.

Effect of basic fibroblast growth factor on neurons cultured from various regions of postnatal rat brain

Neurons from various brain regions of postnatal (15 days after birth) and fetal (16 days gestation) rats were cultured in the presence of basic fibroblast growth factor (bFGF). bFGF increased the survival of neurons from postnatal septum, striatum, midbrain, and hippocampus. Fetal neurons derived from cerebral cortex, septum, striatum, midbrain, thalamus, and colliculus were far more dependent on bFGF for survival in comparison with postnatal neurons. In contrast, cerebellum neurons of postnatal and fetal rat brain did not respond to bFGF. The increase of postnatal and fetal neuronal survival with bFGF treatment (0.01-10 ng/ml) was dose-dependent and reached 2-4-fold and 5-10-fold more than the control, respectively. Fetal cortical neurons showed almost complete dependence on bFGF since almost all neurons died in control cultures. Nerve growth factor was slightly effective only on postnatal septal and striatal neurons, being ineffective on the other neurons tested. These results indicate that bFGF can function as a neurotrophic factor not only on fetal but also on postnatal neurons of the central nervous system, and that bFGF has great potential for application in vivo.

Detection of beta-nerve growth factor mRNA in the human fetal brain

Nerve growth factor (NGF) is a trophic molecule recently demonstrated to interact with different structures in the central nervous system. The expression of the beta-NGF mRNA from human fetal cortices at the 15-16th week of gestational age has been demonstrated and quantitated by polymerase chain reaction amplification of the specific cDNA. beta-NGF mRNA expression in the human brain coincides with the period of active differentiation and synaptogenesis, suggesting that the trophic agent plays a role in the cerebral development.

Nerve growth factor receptor in neural lobe of rat pituitary gland: immunohistochemical localization, biochemical characterization and regulation

Nerve growth factor-receptor immunoreactivity was detected in the neural lobe of the pituitary gland in developing and adult rats of both sexes. The presence of nerve growth factor receptor in the neural lobe was further verified by a quantitative 125I-nerve growth factor/crosslink/immunoprecipitation assay and subsequent visualization by SDS-PAGE autoradiography. Nerve growth factor-receptor immunoreactivity was detected in the neural lobe of postnatal 5-day-old rats, had increased by 2 months and was much higher in 1-year-old rats. In 2-month-old rats, no immunoreactivity was observed in anterior or intermediate lobes. Pituitary stalk transection in young adult rats greatly increased the expression of nerve growth factor-receptor immunoreactivity in the neural lobe, although the staining pattern remained the same. This increase began 3 days after surgery, and reached peak levels at approximately 15 days. Other physiological or non-physiological changes did not alter the nerve growth factor-receptor immunoreactivity in the neural lobe; these changes included dehydration, pregnancy and lactation, castration of male rats, bilateral superior cervical ganglionectomy and intraventricular injection of colchicine. Intravenously injected 125I-nerve growth factor was specifically accumulated in both normal and denervated neural lobe. Nerve growth factor-receptor immunohistochemical electron microscopy showed that the receptor-positive cells are fusiform and found both inside and outside the basal lamina that delimits the neural lobe parenchyma. Based upon the anatomical localization, morphology and response to axotomy, we identify, at least the perivascular component, as microglia. These data suggest a role for nerve growth factor and/or nerve growth factor receptor in microglial function.

Selective expression of factors preventing cholinergic dedifferentiation

Chicken retina neurons from 8-9-day-old embryos developed prominent cholinergic properties after several days in stationary dispersed cell (monolayer) culture. These cells accumulated [3H]choline by a high-affinity, hemicholinium-sensitive transport system, converted [3H]choline to [3H]-acetylcholine [( 3H]ACh), released [3H]ACh in response to depolarization stimuli, and developed choline acetyltransferase (ChAT) activity to levels comparable to those of the intact retina. The cholinergic state, however, was not permanent. After 7 days in culture, the capacity for [3H]ACh release decreased drastically and continued to diminish with longer culture periods. Loss of this capacity seemed not to be due to loss of cholinergic neurons, because high-affinity choline uptake was unchanged. However, a substantial decrease of ChAT activity was observed as a function of culture age, and probably accounted for the low level of ACh synthesis in long-lasting cultures. The loss of ChAT activity could be prevented in at least two different ways: (a) Maintaining the neurons in rotary (aggregate) rather than stationary culture completely blocked the loss of enzyme activity and gave a developmental profile identical to the known "in situ" pattern of differentiation; and (b) Conditioned medium from aggregate cultures significantly reduced the drop in ChAT activity of neurons maintained in stationary, dispersed cell cultures. Activity that stabilized cholinergic differentiation was nondialyzable, heat-sensitive, and not mimicked by functional nerve growth factor. Production of activity by aggregates was developmentally regulated; medium obtained from aggregates after 3 days in culture had no effect on cholinergic differentiation, whereas medium obtained from aggregates between 6 and 10 days in culture produced a fivefold increase of ChAT in monolayers.(ABSTRACT TRUNCATED AT 250 WORDS)

Specific neuronal expression of human NGF receptors in the basal forebrain and cerebellum of transgenic mice

Transgenic mice carrying multiple copies of the human NGF receptor gene have been generated. Using a monoclonal antibody specific for the human receptor, we have detected specific expression in cholinergic neurons in the basal forebrain and Purkinje cells in the cerebellum during the postnatal period. Expression in the PNS was exemplified by immunostaining of sympathetic and sensory neurons during an early embryonic age. Transection of the sciatic nerve in transgenic animals resulted in induction of human NGF receptors, indicating that the inserted gene can be appropriately regulated. These transgenic mice will provide an opportunity to study the elements regulating the NGF receptor. Furthermore, the ability to obtain specific expression in transgenic mice will permit directed expression of heterologous genes in discrete cells important in the cholinergic septal-hippocampal pathway and the PNS.

Localization of nerve growth factor receptor mRNA in the rat basal forebrain with in situ hybridization histochemistry

1. In situ hybridization histochemistry was used to localize nerve growth factor receptor (NGFR) mRNA in the adult rat basal forebrain. 2. In emulsion-dipped sections 35S-labeled RNA antisense probes produced a high density of silver grains over cells located in the medial septum, vertical and horizontal limbs of the diagonal band of Broca, and nucleus basalis. 3. This distribution of NGFR mRNA overlaps with the distribution of NGFR protein localized using immunocytochemical techniques. 4. No hybridization signal was detected when sections were hybridized with a 35S-labeled RNA sense (control) probe. 5. We suggest that NGFRs are synthesized in these basal forebrain nuclei and transported to terminal areas where NGF is thought to be bound and internalized, an initial step in the many actions of this neurotrophic factor.

Multiple pathways of N-kinase activation in PC12 cells

Past work established a cell-free assay for a nerve growth factor (NGF)-activated protein kinase activity (designated N-kinase) that utilizes tyrosine hydroxylase and histone H1 as substrates and that is distinct from a variety of well-characterized kinases. This study explores the specificity and mechanistic pathway(s) by which N-kinase activity is regulated in PC12 rat pheochromocytoma cells. N-kinase is rapidly activated in these cells by treatment with NGF, epidermal growth factor (EGF), basic fibroblast growth factor (bFGF), phorbol ester, or dibutyryl cyclic AMP. Our data indicate that the stimulated activity is the same for each agent by several criteria: It exhibits the same characteristic biphasic elution pattern by Mono S fast protein liquid chromatography (FPLC), except for the case of dibutyryl cyclic AMP in which one of the activity peaks is somewhat shifted; it shows the same elution pattern by FPLC on a Superose 12 column; it possesses identical substrate specificity; and, except in the case of dibutyryl cyclic AMP, it does not show additivity when each agent is added simultaneously with NGF. The multiple forms of N-kinase are interconvertible in that rechromatography on a Mono S column yields a single peak of activity. Also, when NGF and dibutyryl cyclic AMP are simultaneously presented to cells, the chromatographic profile resembles that with NGF alone. Activation occurs through several independent initial pathways. Down-regulation of protein kinase C by phorbol ester pretreatment prevents N-kinase activation by phorbol ester, but not by the other agents. A PC12 cell-derived line deficient in cyclic AMP-dependent protein kinase II activity exhibits N-kinase activation by all treatments except dibutyryl cyclic AMP. The properties of N-kinase suggests that it is similar or identical to the ribosomal S6 protein kinase described by Blenis and Erikson. Additional experiments revealed that N-kinase activity can be stimulated in several cell lines in addition to PC12 cells. These findings indicate that the N-kinase can be activated via multiple second-messenger pathways and that it could therefore potentially play a significant role in mediating shared intracellular responses to various extracellular signals.

Gene therapy in the CNS: intracerebral grafting of genetically modified cells

Grafting cells to the CNS has been suggested and applied as a potential approach to CNS therapy through the selective replacement of cells lost as a result of disease or damage. Independently, studies aimed at direct genetic therapy in model systems have recently begun to suggest conceptually new approaches to the treatment of several kinds of human genetic disease, especially those caused by single gene enzyme deficiencies. We suggest that a combination of these two approaches, namely the graftment into the CNS of genetically modified cells, may provide a new approach toward the restoration of some functions in the damaged or diseased CNS. We present evidence for the feasibility of this approach, including a description of some current techniques for mammalian cell gene transfer and CNS grafting, and several possible approaches to clinical applications. Specifically, we report that fibroblasts, genetically modified to secrete NGF by infection with a retroviral vector and implanted into the brains of rats with a surgical lesion of the fimbria-fornix, prevented the degeneration of cholinergic neurons that would die without treatment.

Neuronal localization of the nerve growth factor precursor-like immunoreactivity in the rat brain

The distribution of the nerve growth factor precursor(proNGF)-like immunoreactivity was examined in the adult rat brain with affinity-purified antisera directed against synthetic peptides that reproduce sequences of the precursor protein. Immunoreactivity was localized in defined areas of the neocortex, hippocampal formation, thalamus/hypothalamus, striatum, olfactory bulb, pons and spinal cord, which are regions previously reported to contain NGF mRNA. Interestingly, immunoreactivity was also observed in the septum and diagonal band of Broca known to contain very low NGF mRNA levels. Using immunohistochemical methods combined with the retrograde transport of a protein gold complex we demonstrate that proNGF-like immunoreactivity is localized within neuronal cell bodies, in the cortex, hippocampus and septum. These results suggest that the immunological approach may not only identify NGF-synthesizing cells, but also cells which may accumulate proNGF or some cleavage products by an uptake mechanism.

Nerve growth factor induces functional nicotinic acetylcholine receptors on rat sensory neurons in culture

Neonatal sensory neurons from rat nodose ganglia express nicotinic acetylcholine receptors when grown in tissue culture without other cell types. The present study investigates the role of nerve growth factor in inducing these receptors. Nerve growth factor has little effect on the growth and survival of nodose neurons in culture, although most neurons were found by quantitative radioautography to have high-affinity nerve growth factor receptors. Nerve growth factor strongly influenced the expression of nicotinic receptors on these neurons: the proportion of acetylcholine-sensitive neurons was approximately 60% in cultures with nerve growth factor compared with 15% in cultures grown without nerve growth factor. The proportion of acetylcholine-sensitive neurons increased over the first week, plateaued by day 12 and remained high for at least three weeks. In contrast, without NGF, the proportion of acetylcholine-sensitive neurons was low throughout the three-week period. The results indicate that nerve growth factor is an important factor in promoting nicotinic receptors on these neurons in culture.

Intracerebral NGF infusion induces hyperinnervation of cerebral blood vessels

The use of intracerebral NGF (nerve growth factor) infusions as a therapeutic tool to prevent the degeneration of cholinergic neurons in humans suffering from Alzheimer's disease has recently been suggested. In the present study, intracerebroventricular infusion of nerve growth factor into the adult rat brain was found to induce axonal sprouting of mature, uninjured axons associated with the intradural segment of the internal carotid artery. Following NGF infusion, a three-fold increase in the total number of axons associated with the vessel wall was observed when compared with vehicle-infused animals. This vascular hyperinnervation might also occur in humans. Before NGF infusion therapy is initiated, more research is necessary concerning the specificity, mechanisms, and functional significance of the sprouting response observed in this study.

NGF-dependent sprouting and regeneration in the hippocampus

While a variety of sprouting and regenerative responses have been investigated in the hippocampus, the cellular and molecular events responsible for these plastic responses have not been determined. One transmitter system, the cholinergic system, shows several distinct responses to damage in the septohippocampal circuit. Present evidence strongly supports a role for nerve growth factor (NGF) in these responses. NGF is not only important for the survival of the adult cholinergic neurons, but can also induce regrowth of the damaged fibers given an appropriate substratum for growth. These reparative effects of NGF can manifest themselves in functional recovery in the aged rat and the young rat with fimbria-fornix lesions. Finally, a role for glia cells is proposed to clarify how NGF availability may be regulated during the degenerative and regenerative events. While all plasticity events certainly cannot be explained by the coincidence of NGF and the cholinergic system, their interaction may provide a template for other transmitter/trophic factor interactions.

Seizures, neuropeptide regulation, and mRNA expression in the hippocampus

Recent studies have demonstrated that the regulation of neuropeptide expression in forebrain neurons is responsive to external influences including changes in physiological activity. This has been demonstrated most clearly in studies of hippocampus where the synthesis and resting levels of several neuropeptides, localized within well-characterized components of hippocampal circuitry, have been shown to be selectively influenced by seizure activity. In studies described here, we examined the influence of recurrent limbic seizures on the expression of enkephalin, dynorphin, cholecystokinin, and neuropeptide Y (NPY) in rat and mouse hippocampus using immunohistochemical, in situ hybridization and blot hybridization techniques. The data demonstrate that seizures differentially influence the expression of each peptide as a part of a broader cascade of changes in genomic expression within individual hippocampal neurons. In particular, seizures increase preproenkephalin mRNA and enkephalin peptide but decrease dynorphin peptide in the dentate gyrus granule cell/mossy fiber system. Seizure-induced decreases in the concentration of preprodynorphin mRNA in the granule cells have been reported by others. Immunoreactivity for CCK, which is codistributed with the opioid peptides in the mossy fiber system of mouse, is also dramatically reduced in the granule cell axons by seizure. Recurrent seizures induce two temporally distinct changes in NPY expression in hippocampus. First, there is an increase in hybridization to preproNPY mRNA within scattered, probable local circuit neurons in all subfields. This is followed by the seemingly novel appearance of preproNPY mRNA within the dentate gyrus granule cells and pyramidal cells of field CA1. Clues about mechanisms of neuropeptide regulation have come from observations of other, more rapid, transcriptional events induced by seizure. Most notably, our results and those of others demonstrate that seizures increase the expression of messenger RNAs from immediate-early genes (c-fos, c-jun, and NGFI-A) which encode proteins that may mediate neuropeptide gene regulation. In addition, mRNA for nerve growth factor is dramatically increased in the dentate gyrus granule cells by seizure; increased production of this trophic factor might mediate the more delayed changes in genomic expression and growth responses observed to occur in hippocampus and other forebrain areas following seizure activity.

Nerve growth factor in the primate central nervous system: regional distribution and ontogeny

An enzyme immunoassay for nerve growth factor was developed to determine the regional distribution and ontogenic change in the macaque (Macaca fascicularis) CNS. The standard curve of mouse nerve growth factor paralleled the dilution curves of extracts from the primate CNS at the adult and pre-natal stages. Furthermore, the nerve growth factor immunoreactive material comigrated with mouse nerve growth factor by means of carboxy methyl cellulose chromatography. These findings suggest that the immunoreactive material extracted from the primate CNS is mouse nerve growth factor-like molecules. At the adult stage, the highest level of nerve growth factor was in the hippocampus, with relatively high levels also in the hypothalamus, the cerebral cortex, the amygdala, the basal nucleus of Meynert, the septal nucleus, the cerebellum and the caudate nucleus. No detectable amounts were observed in the spinal cord, the substantia nigra or the dentate nucleus. In addition to the CNS, the pituitary gland contained about four times the level found in the hippocampus. At embryonic day 120, a high level of nerve growth factor already existed in the occipital cortex (80% of the level at the adult stage) and in the hippocampus (70% of the level at the adult stage). Between embryonic day 120 and the newborn stage in the occipital cortex and between embryonic day 120 and postnatal day 60 in the hippocampus, nerve growth factor levels increased about 1.7-fold, and after that, they gradually decreased until the adult stage was reached. In contrast, in the cerebellum, the level was quite high during the pre-natal period and declined to one-third at postnatal day 60. The developmental changes in nerve growth factor and choline acetyltransferase activity in the hippocampus were well correlated (r = 0.963) between embryonic day 120 and postnatal day 60. Our studies reveal that nerve growth factor is present in the primate CNS. The high level of nerve growth factor during embryonic stages and the good correlation with choline acetyltransferase activity suggest a physiological role for nerve growth factor in the development of the primate CNS.

Distribution of nerve growth factor receptor-like immunoreactivity in the adult rat central nervous system. Effect of colchicine and correlation with the cholinergic system--I. Forebrain

Nerve growth factor receptor, as recognized by the monoclonal antibody 192-IgG, was localized to multiple regions of the adult rat forebrain. Immunoreactive cell bodies and fibers were seen in both sensory and motor regions which are known to contain cholinergic and non-cholinergic neurons. Specifically, nerve growth factor receptor immunoreactivity was present in cells lining the olfactory ventricle, rostral portion of the lateral ventricle, in basal forebrain nuclei, caudate putamen, globus pallidus, zona incerta and hypothalamus. Immunoreactive cells which were situated subpially along the olfactory ventricle and anterior portions of the lateral ventricle, and in the arcuate nucleus resembled neuroglia but could not definitively identified at the light microscopic level. Animals pretreated with intracerebroventricular colchicine displayed significantly increased nerve growth factor receptor immunoreactivity in all previously positive neurons and particularly in the medial preoptic area and ventral premammillary nucleus of the hypothalamus. In such animals, receptor immunoreactivity also appeared in previously non-immunoreactive cells of the hippocampal CA3 region and polymorph layer of the dentate gyrus as well as in the mitral cell layer of the olfactory bulb. Nerve growth factor receptor-immunoreactive fibers and varicosities were seen in the olfactory bulb, piriform cortex, neocortex, amygdala, hippocampus, thalamus, olivary pretectal nucleus and hypothalamus. In most regions, such fiber-like immunoreactive structures likely represented axon terminals, although in some areas, neuroglial or extracellular localizations could not be excluded. In this context, diffuse, non-fibrillar receptor immunoreactivity occurred in the lateral habenular nucleus and medial terminal nucleus of the accessory optic tract. Furthermore, intense nerve growth factor receptor immunoreactivity occurred along certain regions of the pial surface on the ventral surface of the brain. The distribution of nerve growth factor receptor-immunoreactive cell bodies and fibers in multiple sensory and motor nuclei suggests wide-spread influences of nerve growth factor throughout the adult rat forebrain. There is a high degree of overlap with regions containing choline acetyltransferase immunoreactivity. However, significant disparities exist suggesting that certain nerve growth factor receptor-containing non-cholinergic neurons of the rat forebrain may also be affected by nerve growth factor.

Immunohistochemical localization and biochemical characterization of nerve growth factor receptor in adult rat brain

The expression of nerve growth factor (NGF) receptor in adult rat brain was studied by immunohistochemistry with a specific anti-rat NGF receptor monoclonal antibody, 192-IgG. Intense NGF receptor immunoreactivity (NGFRI) was found in structures known to be NGF responsive, including forebrain cholinergic neurons in medial septum, diagonal band of Broca, and basal nucleus of Meynert; central processes of neural-crest-derived sensory ganglion neurons and their innervated nucleus also contained such immunoreactivity. Distinct NGFRI staining was also found in many brain areas and cell types not known to be NGF responsive, including some hypothalamic regions, circumventricular organs, some areas related to the optic system, olfactory glomeruli, ependymal and subependymal cells in some locations, mesencephalic nucleus of the trigeminal nerve, cerebellar molecular layer, central linear nucleus, solitary tract and its nucleus, and inferior olive. The NGFRI in the circumventricular organs was further studied by in vivo labeling of 125I-ligands. Intravenously injected 125I-NGF, but not 125I-cytochrome c, was specifically accumulated in the area postrema. Biochemical study of the NGF receptor showed a major band of molecular weight of approximately 90 KDa in the area postrema, choroid plexus, median eminence, and medial septum with the relative content consistent with that seen by immunohistochemistry. No evidence of a truncated NGF receptor was observed. The results of this study suggest that NGF and its receptor have broader roles in adult mammalian brain than previously thought.

Correlative decrease of large neurons in the neostriatum and basal nucleus of Meynert in Alzheimer's disease

A quantitative investigation was performed on the large neurons in the neostriatum and basal nucleus of Meynert (bnM) in patients with Alzheimer's disease (AD) and progressive supranuclear palsy (PSP). The degree of decrease of the large neurons in the neostriatum was quite similar to that in the bnM; these decreases were significantly correlative in AD, but not in PSP. These findings indicate that the large neurons in the neostriatum and bnM, which are considered to be cholinergic and to exclusively possess nerve growth factor receptors in the cerebrum, degenerate simultaneously in an equal ratio in AD.

Expression of NGF receptor in the rat forebrain detected with in situ hybridization and immunohistochemistry

The expression of nerve growth factor (NGF) receptor mRNA and NGF receptor protein was examined in the adult rat basal forebrain using in situ hybridization and immunohistochemical techniques. NGF receptor mRNA and protein were detected within cells in the medial septum, diagonal band of Broca, and nucleus basalis of Meynert. Controls showed that the hybridization signal was not due to nonspecific binding of the probe to heterologous RNAs or other molecules. As expected, the distribution of NGF receptor mRNA-containing cells correlated nicely with the distribution of NGF receptor immunoreactive cells in each of these areas. These data extend previous work which suggests that neurons in these areas express the NGF receptor mRNA and manufacture functional NGF receptors. NGF receptor immunoreactivity was also detected in the arcuate nucleus of the hypothalamus, in the leptomeninges at the base of the brain and overlying the tectum, and within ependymal regions along the lateral walls of the cerebral ventricles. A few weakly stained neurons in the lateral hypothalamus and ventrolateral striatum were also consistently observed. In contrast, NGF receptor mRNA was not detected within any meningial, ependymal, or hypothalamic tissues using in situ hybridization. A cross-linking/immunoprecipitation assay demonstrated normal, membrane-bound NGF receptors within extracts of dorsal superior colliculus, ventromedial hypothalamic, and overlying meningial tissues, proving that the staining observed in these areas was not a non-specific artifact associated with the immunohistochemistry. The lack of hybridization in these areas may reflect levels of NGF receptor mRNA which are too low to be detected by the in situ hybridization methods being used. Alternatively, the staining may represent innervation of these areas by afferents whose cell bodies are located elsewhere, and whose terminals contain the NGF receptor protein.

Distribution of beta-nerve growth factor receptors in the human basal forebrain

The distribution of neurons expressing the receptor for beta-nerve growth factor has been examined immunohistochemically in serial coronal sections of basal forebrain from aged normal human subjects. Neurons expressing the receptor were observed in the nucleus of the diagonal band of Broca and in the anterior, the intermediate, and the posterior portions of the nucleus basalis of Meynert. Neurons could also be seen in the medial septal nucleus and embedded in myelinated fibre tracts such as those of the external capsule, cingulum, medullary laminae of the globus pallidus, ansa penduncularis, ansa lenticularis, and anterior commissure. In situ hybridization with a 35S cDNA probe to the human beta-nerve growth factor receptor confirms a neuronal location as the site of synthesis of beta-nerve growth factor receptors in the nucleus basalis of Meynert in a fifth brain. A high percentage of Nissl-stained hyperchromic magnocellular neurons expressed the receptor for beta-nerve growth factor, suggesting that most neurons in the human cholinergic magnocellular basal forebrain system express these receptors. Recent data suggest that beta-nerve growth factor functions as a neurotrophic factor in basal forebrain cholinergic neurons. In Alzheimer's disease there is known to be a reduction in cholinergic function and an apparent loss of neurons in the cholinergic nucleus basalis of Meynert. For this reason we have examined the distribution of receptors for beta-nerve growth factor in the normal human basal forebrain in order to form a basis for comparison to those with Alzheimer's disease.

Differential inhibition of nerve growth factor responses by purine analogues: correlation with inhibition of a nerve growth factor-activated protein kinase

Purine analogues were used in this study to dissect specific steps in the mechanism of action of nerve growth factor (NGF). Protein kinase N (PKN) is an NGF-activated serine protein kinase that is active in the presence of Mn++. The activity of PKN was inhibited in vitro by purine analogues, the most effective of which was 6-thioguanine (apparent Ki = 6 microM). Several different criteria indicated that 6-thioguanine is not a general inhibitor of protein kinases and that it is relatively specific for PKN. For instance, it did not affect protein kinases A or C and was without effect on the overall level and pattern of protein phosphorylation by either intact or broken PC12 cells. Since purine analogues rapidly and effectively enter cells, they were also assessed for their actions on both transcription-dependent and -independent responses of PC12 cells to NGF. NGF-promoted neurite regeneration was reversibly suppressed by the analogues and at concentrations very similar to those that inhibit PKN. Comparable concentrations of the analogues also blocked NGF-stimulated induction of ornithine decarboxylase activity. In contrast to its inhibition of neurite regeneration and ornithine decarboxylase induction, 6-thioguanine did not suppress NGF-dependent induction of c-fos mRNA expression. Thus, purine analogues such as 6-thioguanine appear capable of differentially suppressing some, but not other actions of NGF. These findings suggest the presence of multiple pathways in the NGF mechanism and that these can be dissected with purine analogues. Moreover, these data are compatible with a role for protein kinase N in certain of these pathways.

Developmental regulation of nerve growth factor and its receptor in the rat caudate-putamen

In prior studies, nerve growth factor (NGF) administration induced a robust, selective increase in the neurochemical differentiation of caudate-putamen cholinergic neurons. In this study, expression of NGF and its receptor was examined to determine whether endogenous NGF might serve as a neurotrophic factor for these neurons. The temporal pattern of NGF gene expression and the levels of NGF mRNA and protein were distinct from those found in other brain regions. NGF and high-affinity NGF binding were present during cholinergic neurochemical differentiation and persisted into adult-hood. An increase in NGF binding during the third postnatal week was correlated with increasing choline acetyltransferase activity. The data are consistent with a role for endogenous NGF in the development and, possibly, the maintenance of caudate-putamen cholinergic neurons.

Interleukin-6 as a neurotrophic factor for promoting the survival of cultured basal forebrain cholinergic neurons from postnatal rats

Human recombinant interleukin-6 (IL-6, B-cell stimulating factor-2) was capable of supporting neuronal survival in cholinergic neuron culture, prepared from 10-day-old rat brain septal region. Cell survival of the cultured cholinergic neurons was estimated by measuring the remaining choline acetyltransferase (ChAT) activities after 6 days of culture. IL-6 at a concentration of 5 ng/ml maintained a more than 3-fold higher ChAT activity in the culture as compared with that in cultures without IL-6. The maximal dose of IL-6 was near 50 ng/ml. The concomitant addition of mouse nerve growth factor (NGF) and IL-6, both at maximal doses, had a synergistic effect on cholinergic cell survival. These results indicate that IL-6 can act as a neurotrophic agent, independent of the action of NGF, supporting neuronal survival of cultured postnatal rat septal cholinergic neurons. On the other hand, IL-6 did not affect the differentiation of the cultured embryonic rat septal cholinergic neurons, differently from the differentiation action by NGF.

Axotomy-dependent stimulation of choline acetyltransferase activity by exogenous mouse nerve growth factor in adult rat basal forebrain

Transection of the adult rat dorsal fornix and fimbria (F-F) induced a sensitivity of the cholinergic neurons in the medial septum and diagonal band (MS/DB) to exogenous mouse nerve growth factor (mNGF). Continuous infusion of mNGF for two weeks after complete unilateral F-F aspiration resulted in a stimulation of choline acetyltransferase (ChAT)-specific activity in precise micro-dissections of the MS/DB ipsilateral to the transection to a level that was 200% higher than that measured in normal adult animals. This supranormal stimulation of ChAT activity reached plateau levels after 10 days of NGF infusion and was dose-dependent with an E.D.50 equal to 120 ng/day. Administration of mNGF had no effect on the ChAT activity in the MS/DB of normal animals or animals with a unilateral transection of only the supracallosal dorsal septo-hippocampal pathway. Partial transection experiments indicated that a predominent pathway for cholinergic neurons potentially sensitive to exogenous mNGF runs in the paramedian F-F. Administration of mNGF also induced a stimulation of ChAT activity in dissections of the caudate-putamen both ipsi- and contralateral to the infusion cannula. This indicates that unlike the cholinergic projection neurons of the MS/DB, adult cholinergic striatal interneurons are sensitive to exogenous NGF without prior axotomy.