Neurotrophin-6 is a new member of the nerve growth factor family

Neural growth, neural damage and neurotrophins in the kindling model of epilepsy

Do seizures change the brain? Studies on the kindling model--a widely used animal model of epilepsy--suggest that they do. Dr. Racine, one of the pioneers in the kindling field, describes the basic phenomena of kindling, and discusses the possible roles of cell growth and cell death in this model.

Immunohistochemical localization of BDNF-, TrkB- and TrkA-like proteins in the teleost lateral line system

The lateral line system, formed of both superficial (pit organs) and canal neuromasts, is one of the major mechanosensory systems in fish. It has always been assumed that this system depends on neurotrophins and their cognate Trk receptors for development and maintenance, as has been shown in other mechanosensitive systems of vertebrates. However, until nowthis issue has not been specifically addressed. In this study we used immunohistochemistry to investigate the occurrence and localization both of neurotrophins (NGF-, BDNF- and NT-3-like) and of Trk-like proteins (TrkA-, TrkB-, TrkC-like) in alevins of Salmo salar and S. trutta. All cells in the pit organs of S. salar displayed strong immunoreactivity for TrkB-like and BDNF-like, whereas they were restricted to the hair cells in S. trutta. The hair, supporting and mantle cells of S. salar, and the mantle cells of S. trutta, also expressed TrkA-like immunoreactivity. In the canal neuromasts BDNF-, TrkA- and TrkB-like proteins were present in all cells, without differences between species. NGF-, NT-3- and TrkC-like immunoreactivity were never detected. The present results suggest that mechanoreceptive hair cells, as well as supporting cells, in the lateral line system are under the control of the BDNF-TrkB-like complex, and probably of ligands of TrkA-like receptors.

Spatiotemporal expression of NGFR during pre-natal human tooth development

OBJECTIVES

The relation between nerve growth factor receptor (NGFR) in the human pre-natal tooth buds and the dental follicle was investigated. In particular, we sought to determine if there is a specific pattern of p75NGFR expression in developing human tooth buds and their surrounding tissue.

SETTING AND SAMPLE POPULATION

The Department of Orthodontics at Copenhagen University, Denmark. Histological sections from 11 fetuses, aged 11-21 gestational weeks.

METHOD

The sections were studied by conventional immunohistochemistry.

RESULTS

Specific spatiotemporal patterns of p75NGFR reactions were observed in the tooth buds and dental follicle: Before matrix production by the ameloblasts, the entire inner enamel epithelium and the entire dental follicle display p75NGFR immunoreactivity; after matrix production is initiated, the immunoreactivity of the matrix producing cells is lost, as is that of the dental follicle adjacent to these matrix-producing cells.

CONCLUSION

A unique spatiotemporal distribution of NGFR in the pre-eruptive human tooth bud was demonstrated.

Phosphatidylinositol kinase enzymes regulate the retrograde axonal transport of NT-3 and NT-4 in sympathetic and sensory neurons

Phosphatidylinositol 3-kinase (PI3-kinase) and phosphatidylinositol 4-kinase (PI4-kinase) enzymes are an important family of signaling molecules that have been implicated in the regulation of intracellular vesicle trafficking. It has previously been shown that PI3-kinase and PI4-kinase enzymes regulate neuronal survival and the retrograde axonal transport of nerve growth factor in sympathetic and sensory neurons. We have extended these studies to examine the role these enzymes play in the regulation of the retrograde axonal transport of neurotrophin-3 (NT-3) and neurotrophin-4 (NT-4) in sympathetic and sensory neurons in vivo. Wortmannin (0.1 nmol/eye), a PI3-kinase and PI4-kinase antagonist, reduced the amount of (125)I-NT-3 retrograde transport in sympathetic neurons by approximately 50% and (125)I-NT-4 in sympathetic neurons by approximately 40% and sensory neurons by approximately 20%. The PI3-kinase antagonist LY294002 (100 nmol/eye) reduced the retrograde axonal transport of (125)I-NT-4 in sympathetic and sensory neurons, and (125)I-NT-3 in sympathetic neurons. Phenylarsine oxide (PAO), a PI4-kinase antagonist, significantly inhibited (125)I-NT-4 retrograde axonal transport in sympathetic and sensory neurons. These results show that wortmannin-sensitive PI3-kinases and PI4-kinases may be involved in NT-3 and NT-4 retrograde axonal transport. The retrograde axonal transport of neurotrophic factors in sympathetic and sensory neurons in vivo appears to depend upon the activation of different receptors and second messenger cascades at the nerve terminal.

Additive effect of glial cell line-derived neurotrophic factor and neurotrophin-4/5 on rat fetal nigral explant cultures

Transplantation of embryonic dopaminergic neurons is an experimental therapy for Parkinson's disease, but limited tissue availability and suboptimal survival of grafted dopaminergic neurons impede more widespread clinical application. Glial cell line-derived neurotrophic factor (GDNF) and neurotrophin-4/5 (NT-4/5) exert neurotrophic effects on dopaminergic neurons via different receptor systems. In this study, we investigated possible additive or synergistic effects of combined GDNF and NT-4/5 treatment on rat embryonic (embryonic day 14) nigral explant cultures grown for 8 days. Contrary to cultures treated with GDNF alone, cultures exposed to NT-4/5 and GDNF+NT-4/5 were significantly larger than controls (1.6- and 2.0-fold, respectively) and contained significantly more protein (1.6-fold). Treatment with GDNF, NT-4/5 and GDNF+NT-4/5 significantly increased dopamine levels in the culture medium by 1.5-, 2.5- and 4.7-fold, respectively, compared to control levels, and the numbers of surviving tyrosine hydroxylase-immunoreactive neurons increased by 1.7-, 2.1-, and 3.4-fold, respectively. Tyrosine hydroxylase enzyme activity was moderately increased in all treatment groups compared to controls. Counts of nigral neurons containing the calcium-binding protein, calbindin-D28k, revealed a marked increase in these cells by combined GDNF and NT-4/5 treatment. Western blots for neuron-specific enolase suggested an enhanced neuronal content in cultures after combination treatment, whereas the expression of glial markers was unaffected. The release of lactate dehydrogenase into the culture medium was significantly reduced for GDNF+NT-4/5-treated cultures only. These results indicate that combined treatment with GDNF and NT4/5 may be beneficial for embryonic nigral donor tissue either prior to, or in conjunction with, intrastriatal transplantation in Parkinson's disease.

Delivery of neurotrophic factors to the central nervous system: pharmacokinetic considerations

Neurotrophic factors are proteins with considerable potential in the treatment of central nervous system (CNS) diseases and traumatic injuries. However, a significant challenge to their clinical use is the difficulty associated with delivering these proteins to the CNS. Neurotrophic factors are hydrophilic, typically basic, monomeric or dimeric proteins, mostly in the size range of 5 to 30 kDa. Neurotrophic factors potently support the development, growth and survival of neurons, eliciting biological effects at concentrations in the nanomolar to femtomolar range. They are not orally bioavailable and the blood-brain and blood-cerebrospinal fluid barriers severely limit their ability to enter into and act on sites in the CNS following parenteral systemic routes of administration. Most neurotrophic factors have short in vivo half-lives and poor pharmacokinetic profiles. Their access to the CNS is restricted by rapid enzymatic inactivation, multiple clearance processes, potential immunogenicity and sequestration by binding proteins and other components of the blood and peripheral tissues. The development of targeted drug delivery strategies for neurotrophic factors will probably determine their clinical effectiveness for CNS conditions. Achieving significant CNS target site concentrations while limiting systemic exposure and distribution to peripheral sites of action will lessen unwanted pleiotropic effects and toxicity. Local introduction of neurotrophic factors into the CNS intraparenchymally by direct injection/infusion or by implantation of delivery vectors such as polymer matrices or genetically modified cells yields the highest degree of targeting, but is limited by diffusion restrictions and invasiveness. Delivery of neurotrophic factors into the cerebrospinal fluid (CSF) following intracerebroventricular or intrathecal administration is less invasive and allows access to a much wider area of the CNS through CSF circulation pathways. However, diffusional and cellular barriers to penetration into surrounding CNS tissue and significant clearance of CSF into the venous and lymphatic circulation are also limiting. Unconventional delivery strategies such as intranasal administration may offer some degree of CNS targeting with minimal invasiveness. This review presents a summary of the neurotrophic factors and their indications for CNS disorders, their physicochemical characteristics and the different approaches that have been attempted or suggested for their delivery to the CNS. Future directions for further research such as the potential for CNS disease treatment utilising combinations of neurotrophic factors, displacement strategies, small molecule mimetics, chimaeric molecules and gene therapy are also discussed.

Cyclic AMP increases the survival of ganglion cells in mixed retinal cell cultures in the absence of exogenous neurotrophic molecules, an effect that involves cholinergic activity

Natural cell death is a well-known degenerative phenomenon occurring during development of the nervous system. The role of trophic molecules produced by target and afferent cells as well as by glial cells has been extensively demonstrated. Literature data demonstrate that cAMP can modulate the survival of neuronal cells. Cultures of mixed retinal cells were treated with forskolin (an activator of the enzyme adenylyl cyclase) for 48 h. The results show that 50 microM forskolin induced a two-fold increase in the survival of retinal ganglion cells (RGCs) in the absence of exogenous trophic factors. This effect was dose dependent and abolished by 1 microM H89 (an inhibitor of protein kinase A), 1.25 microM chelerythrine chloride (an inhibitor of protein kinase C), 50 microM PD 98059 (an inhibitor of MEK), 25 microM Ly 294002 (an inhibitor of phosphatidylinositol-3 kinase), 30 nM brefeldin A (an inhibitor of polypeptide release), and 10 microM genistein or 1 ng/ml herbimycin (inhibitors of tyrosine kinase enzymes). The inhibition of muscarinic receptors by 10 microM atropine or 1 microM telenzepine also blocked the effect of forskolin. When we used 25 microM BAPTA, an intracellular calcium chelator, as well as 20 microM 5-fluoro-2'-deoxyuridine, an inhibitor of cell proliferation, we also abolished the effect. Our results indicate that cAMP plays an important role controlling the survival of RGCs. This effect is directly dependent on M1 receptor activation indicating that cholinergic activity mediates the increase in RGC survival. We propose a model which involves cholinergic amacrine cells and glial cells in the increase of RGC survival elicited by forskolin treatment.

Brain-derived neurotrophic factor gene organization and transcription in the zebrafish embryo

The gene encoding zebrafish brain-derived neurotrophic factor (BDNF) was cloned from a PAC genomic DNA library. The entire transcription unit was contained in two independently isolated clones that together encompass 120 kb of genomic DNA. The intron/exon organization of the zebrafish gene was found to be identical to that of the mammalian gene but only one promoter has so far been identified. The associated 5' exon is 67% identical to exon 1c of the rat BDNF gene. A search of the 5' flank of the cloned promoter for sequence similarities with known transcription factor binding sites revealed potential AP-1, CREB, and SP1 binding sites. Fusion constructs containing the cloned promoter and 1.7 kb of 5' flank and an enhanced green fluorescent protein reporter that becomes membrane-anchored were injected into 1-8 cell stage embryos. Expression was seen in notochord, muscle, epithelial and endothelial cells of the 1-day-old embryo in consonance with the endogenous gene. These results demonstrate that the cloned promoter mediates cell-specific expression.

The role of neurotrophic factors in psychostimulant-induced behavioral and neuronal plasticity

Several neurotrophic factors influence the development, maintenance and survival of dopaminergic neurons in the mammalian central nervous system (CNS), including neurotrophin-3 (NT-3), brain derived neurotrophic factor (BDNF), ciliary neurotrophic factor (CNTF), basic fibroblast growth factor (bFGF) and glial derived neurotrophic factor (GDNF). This review focuses on the role of these neurotrophic factors in psychostimulant-induced behavioral sensitization, a form of dopamine-mediated neuronal plasticity that models aspects of paranoid schizophrenia as well as drug craving among psychostimulant addicts. Whereas NT-3, CNTF and bFGF appear to play a positive role in psychostimulant-induced behavioral sensitization, GDNF inhibits this form of behavioral plasticity. The role of BDNF in behavioral sensitization, however, remains elusive. While it has been shown that neurotrophic factors can influence the behavioral, structural and biochemical phenomena related to psychostimulant-induced neuronal plasticity, it is unclear which neurotrophic factors are important physiologically and which have purely pharmacological effects. In either case, examining the role of neurotrophic factors in behavioral sensitization may enhance our understanding of the mechanisms underlying the development of paranoid psychosis and drug craving and lead to the development of novel pharmacological treatments for these disorders.

Cholinergic activity modulates the survival of retinal ganglion cells in culture: the role of M1 muscarinic receptors

The control of natural cell death is mediated by neurotrophins released by target, afferent and glial cells. In the present work we show that treatment of retinal cells 'in vitro' for 48 h with 25 microM carbamylcholine induced a two-fold increase in retinal ganglion cells survival. This effect was dose-dependent and mediated by M1 receptors since it could be blocked by 1 microM telenzepine (a M1 receptor antagonist) and mimicked by 200 microM oxotremorine (a M1 receptor agonist). The effect of carbamylcholine was abolished by 10 microM BAPTA-AM (an intracellular Ca2+ chelator), 30 microM dantrolene (an inhibitor of ryanodinic receptors), 500 nM H-89 (an inhibitor of PKA), 1.25 microM chelerythrine chloride (an inhibitor of PKC) and 50 microM PD-98059 (a MEK inhibitor). Treatment with 10 microM genistein (an inhibitor of tyrosine kinase), 25 microM LY-294002 (a PI-3 kinase blocker), 30 nM brefeldin-A (a blocker of polypeptides release), 50 nM K-252a (a Trk receptor inhibitor) and 20 microM fluorodeoxyuridine (an inhibitor of cell proliferation) totally inhibited the effect of carbamylcholine. Taken together our results indicate that muscarinic activity controls the survival of retinal ganglion cells through a mechanism involving the release of polypeptides and activation of Irk receptors.

Brain-derived neurotrophic factor and TrkB tyrosine kinase receptor gene expression in zebrafish embryo and larva

The genes that encode the neurotrophin family of secreted polypeptides and the Trk family of high affinity neurotrophin transmembrane protein tyrosine kinase receptors are induced at the time of neurogenesis in mammals and are known to play critical roles in nervous system development. We show here that in contrast to mammals, the genes encoding the neurotrophin brain-derived neurotrophic factor (BDNF) and the neurotrophin receptor TrkB are expressed throughout embryonic development in the zebrafish. At the embryonic stages preceding transcription of endogenous genes all cells contain BDNF transcripts and immunoreactive BDNF and the trkB transcripts lack the region that encodes a kinase domain. As development proceeds, progressively fewer cells contain BDNF transcripts and by the time of neurogenesis the trkB transcripts encode a kinase-domain. In the 4-day-old larva, a small subset of specialized sensory cells on the surface and cells in deeper structures including the gill arches, fin, and cloaca express the BDNF gene at high levels in a promoter-specific fashion. This progressive restriction of BDNF gene expression must involve an extinction of BDNF gene transcription in some and induction of high levels of transcription in a promoter-specific fashion in other cells.

Nerve growth factor signaling, neuroprotection, and neural repair

Nerve growth factor (NGF) was discovered 50 years ago as a molecule that promoted the survival and differentiation of sensory and sympathetic neurons. Its roles in neural development have been characterized extensively, but recent findings point to an unexpected diversity of NGF actions and indicate that developmental effects are only one aspect of the biology of NGF. This article considers expanded roles for NGF that are associated with the dynamically regulated production of NGF and its receptors that begins in development, extends throughout adult life and aging, and involves a surprising variety of neurons, glia, and nonneural cells. Particular attention is given to a growing body of evidence that suggests that among other roles, endogenous NGF signaling subserves neuroprotective and repair functions. The analysis points to many interesting unanswered questions and to the potential for continuing research on NGF to substantially enhance our understanding of the mechanisms and treatment of neurological disorders.

TrkA and TrkB neurotrophin receptor immunoreactivity in the teleost (Scorpaena porcus) endocrine pancreas

Mammalian-like and specific neurotrophins, as well as their cognate tyrosine kinase Trk-like receptors have been identified in teleosts. They are mainly distributed in neuronal tissues, but evidence suggests that some non-neuronal tissues also express Trks. In this study we used immunohistochemistry to investigate the occurrence and cell distribution of Trks in the pancreas of teleosts (Scorpaena porcus). Immunoreactivity for TrkA and TrkB, but not for TrkC receptors, was found in the scorpionfish pancreas. TrkA-like positive cells were exclusively observed within pancreatic islets, among insulin- and glucagon-containing cells, but apparently did not co-localize with these hormones. TrkB immunostaining was found in islet cells, presumably colocalized with glucagon, as well as in some cells of the exocrine portion. These data provide a morphological basis for a role of the TrkA and TrkB ligands in the endocrine pancreas of teleosts.

Neurotrophin receptor-like proteins in the bovine (Bos taurus) lymphoid organs, with special reference to thymus and spleen

Increasing evidence suggests that neurotrophins could regulate immune functions acting directly or indirectly on immunocompetent cells. The indirect pathway involves stromal cells of the primary and secondary lymphoid organs. In the present study the occurrence of Trk proteins (TrkA, TrkB and TrkC), regarded as the high-affinity signal-transducing receptors for neurotrophins, was investigated in cow lymphoid organs using immunohistochemistry. The thymus and spleen of both fetal and adult animals, and the palatine tonsils, lymph nodes and Peyer's patches of adult animals, were analysed. Unidentified cells displaying TrkA-like immunoreactivity were found in the fetal thymus, whereas those expressing this protein in the adult gland were identified as epithelial cells. In the spleen, immunoreactive TrkA was observed in cells of the white pulp. TrkB immunoreactivity in both fetal and adult thymus and spleen was localized in monocyte/macrophage cells. As a rule, TrkC was absent from the thymus and the spleen independent of the animal's age. Different types of stromal cells, but never the lymphocytes themselves, displayed TrkA, TrkB, or TrkC immunoreactivity in the other lymphoid organs analysed. As in other vertebrate species, Trk proteins in the lymphoid organs of the cow were localized in the stromal, non-lymphoid cells, thus suggesting that neurotrophins might regulate the immune function acting indirectly on lymphocytes.

The expression profiles of neurotrophins and their receptors in rat and chicken tissues during development

Neurotrophic factors are target-derived proteins that promote the survival and differentiation of the innervating neurons. Increasing evidence indicate the involvement of these factors and receptors during the formation and maturation of the neuromuscular junction. To gain further insight on the expression pattern of these factors and receptors in developing spinal cord and skeletal muscle during the critical stages of synapse formation, a systematic study was performed with chicken and rat tissues using Northern blot analysis. The expression of all the neurotrophins was detected in skeletal muscle early in development, coincidental with the appearance of their corresponding receptors in the spinal cord. Taken together, the similar regulatory patterns observed in both rat and chicken tissues suggest that the potential roles of neurotrophins at the neuromuscular synapse are conserved throughout evolution.

Prolonged recycling of internalized neurotrophins in the nerve terminal

BACKGROUND

Neurons require contact with their target tissue in order to survive and make correct connections. The retrograde axonal transport of neurotrophins occurs after receptor-mediated endocytosis into vesicles at the nerve terminal. However, the mechanism by which the neurotrophin signal is propagated from axon terminal to cell body remains unclear.

METHODS

Retrograde axonal transport was examined using the transport of I(125)-labeled neurotrophins from the eye to sympathetic and sensory ganglia. The phenomena was further studied by adding rhodamine-labeled nerve growth factor (NGF) to cultures of dissociated sympathetic ganglia and the movement of organelles followed with the aid of video microscopy.

RESULTS

I(125)-labeled neurotrophins were transported from the eye to the sympathetic and sensory ganglia. A 100-fold excess of unlabeled neurotrophin, administered up to 4 h after the labeled material, completely prevented accumulation of labeled neurotrophin in the ganglia. The effect was specific for the labeled neurotrophin as administration of a high concentration of a different neurotrophin failed to inhibit the transport. In dissociated cultures, we found rapid binding of label, to surface membrane receptors, followed by an accumulation of labeled vesicles in the growth cone. Incubation of these cultures with unlabeled NGF led to a rapid loss of label in the growth cones.

CONCLUSIONS

These results suggest that there is a pool of internalized neurotrophin, in vesicles in the nerve terminal, which is in rapid equilibrium with the external environment. It is from this pool that a small fraction of the neurotrophin-containing vesicles is targeted for retrograde transport. Potential models for this system are presented.

Alterations in trk A, trk B and trk C receptor immunoreactivities in parietal cortex and cerebellum in Alzheimer's disease

The neurotrophins nerve growth factor, brain-derived neurotrophic factor and neurotrophin-3 bind to the tyrosine kinase (trk) receptors trk A, trk B and trk C, respectively, with high affinity. We investigated the expression of the trk receptors in the parietal cortex (PC) and cerebellum of patients with Alzheimer's disease (AD) and age-matched controls. Cortical layers II-VI displayed a distinct cellular immunoreactivity for trk A and C with an emphasis in the pyramidal neurons of layers III and V. Trk B immunoreactivity was primarily located in the deeper cortical layers with a predominance in layer V. There was a decrease in trk A and C immunoreactivity in the PC of AD cases, while trk B density appeared to be unchanged. In addition, cerebellar Purkinje cells revealed a distinct immunoreactivity for trk C both in control and AD cases, suggesting trk C may be important in the maintenance of these cells in the aged brain.

Brain-derived neurotrophic factor in the control human brain, and in Alzheimer's disease and Parkinson's disease

Brain-derived neurotrophic factor (BDNF) is a small dimeric protein, structurally related to nerve growth factor, which is abundantly and widely expressed in the adult mammalian brain. BDNF has been found to promote survival of all major neuronal types affected in Alzheimer's disease and Parkinson's disease, like hippocampal and neocortical neurons, cholinergic septal and basal forebrain neurons, and nigral dopaminergic neurons. In this article, we summarize recent work on the molecular and cellular biology of BDNF, including current ideas about its intracellular trafficking, regulated synthesis and release, and actions at the synaptic level, which have considerably expanded our conception of BDNF actions in the central nervous system. But our primary aim is to review the literature regarding BDNF distribution in the human brain, and the modifications of BDNF expression which occur in the brain of individuals with Alzheimer's disease and Parkinson's disease. Our knowledge concerning BDNF actions on the neuronal populations affected in these pathological states is also reviewed, with an aim at understanding its pathogenic and pathophysiological relevance.

Neurotrophins: roles in neuronal development and function

Neurotrophins regulate development, maintenance, and function of vertebrate nervous systems. Neurotrophins activate two different classes of receptors, the Trk family of receptor tyrosine kinases and p75NTR, a member of the TNF receptor superfamily. Through these, neurotrophins activate many signaling pathways, including those mediated by ras and members of the cdc-42/ras/rho G protein families, and the MAP kinase, PI-3 kinase, and Jun kinase cascades. During development, limiting amounts of neurotrophins function as survival factors to ensure a match between the number of surviving neurons and the requirement for appropriate target innervation. They also regulate cell fate decisions, axon growth, dendrite pruning, the patterning of innervation and the expression of proteins crucial for normal neuronal function, such as neurotransmitters and ion channels. These proteins also regulate many aspects of neural function. In the mature nervous system, they control synaptic function and synaptic plasticity, while continuing to modulate neuronal survival.

Cytokine/neurotrophin interaction in the aged central nervous system

Age-associated neurodegenerative diseases such as Alzheimer's disease are characterised by neuronal impairment that leads to cognitive deficits. As certain affected neurons depend on trophic factors such as neurotrophins (NTs), impairment in NT function has been suggested to be a component of neuronal damage associated with such disorders. Age-related neurodegenerative diseases are also characterised by high levels of proinflammatory cytokines such as tumour necrosis factor alpha (TNFalpha) in the CNS. Because TNFalpha receptors and certain NT receptors share a high degree of homology and are capable of activating similar signalling pathways, one possibility is that altered cytokine levels may affect NT function in the aged or diseased CNS. Here we wish briefly to review the evidence suggesting a role for cytokine and NT in the onset of age-associated neurodegenerative diseases. We propose that cytokine/NT interactions may alter neuronal homeostasis, thus possibly contributing to some of the neuronal degeneration occurring during such age-associated CNS diseases.

Exogenous BDNF, NT-3 and NT-4 differentially regulate neurite outgrowth in cultured hippocampal neurons

Multiple growth factors contribute to the differentiation of dendritic and axonal processes by a neuron. Cultured hippocampal cells elaborate dendritic and axonal processes following well-defined steps. We used this culture system to determine the specific effects of brain-derived neurotrophic factor (BDNF), neurotrophin-3 (NT-3) and neurotrophin-4 (NT-4) on dendritic and axonal differentiation in hippocampal pyramidal neurons. We demonstrated that each of these neurotrophins exert distinct effects on neurite outgrowth. Both BDNF and NT-3 had positive effects on the outgrowth of undifferentiated neurites, called minor neurites, and on the axonal process of hippocampal pyramidal neurons. However, the effect of NT-3 was more important than that of BDNF. On the other hand, NT-4 did not enhance axonal outgrowth but had only an effect on the outgrowth of minor neurites. Since cytoskeletal proteins play crucial roles in promoting neurite outgrowth, we examined the protein levels of some of these proteins that are associated with neurite outgrowth: beta-actin, gamma-actin, alpha-tubulin, MAP2 and tau. Surprisingly, we did not detect any change in their protein levels. Taken together, our results show that BDNF, NT-3 and NT-4 exert distinct effects on the neuritic compartments of hippocampal neurons.

Neurotrophins and neurotrophin receptors in human pulmonary arteries

The localization of neurotrophins (NTs) and NT receptors was analyzed in sections of human extra- and intrapulmonary arteries by Western blot analysis and immunohistochemistry. In extrapulmonary branches of human pulmonary artery, NT and NT receptor immunoreactivity was located in the tunica intima, within endothelium, in the tunica media, within smooth muscle and in the tunica adventitia. In different sized intrapulmonary arteries, NT and NT receptor immunoreactivity was observed primarily in the tunica adventitia. A faint NT and NT receptor immunoreactivity was observed in the tunica media of large-sized branches of intrapulmonary arteries, but not within medium- or small-sized intrapulmonary vessels or in tunica intima of different sized intrapulmonary arteries. These findings suggest that NTs may have a role in the control of vascular responses in the pulmonary system acting as local paracrine or autocrine mediators. The possible relevance of the NT system in human pulmonary vasculature identified in this study is discussed.

Molecular mechanisms regulating the retrograde axonal transport of neurotrophins

Neurotrophins are released from target tissues following neural innervation and bind to specific receptors situated on the nerve terminal plasma membrane. The neurotrophin-receptor complex undergoes retrograde axonal transport towards the cell soma, where it signals to the nucleus. This process allows neurotrophins to perform their numerous functions, which include the promotion of neuronal survival and the outgrowth of axons towards certain target tissues. The molecular events controlling each of the components of retrograde axonal transport are beginning to become defined. There is good evidence for the participation of phosphatidylinositol 3-kinase, phosphatidylinositol 4-kinase and the actin cytoskeleton in neurotrophin retrograde axonal transport in vivo. It also appears that the retrograde motor protein dynein mediates the retrograde axonal transport in vivo of neurotrophins such as nerve growth factor. This review discusses the role of the neurotrophin receptors in binding and axonal transport, the endocytic processes required for neurotrophin internalization, the targeting and trafficking of neurotrophins, and the propagation of neurotrophin-induced signals along the axon.

Signalling organelle for retrograde axonal transport of internalized neurotrophins from the nerve terminal

The retrograde axonal transport of neurotrophins occurs after receptor-mediated endocytosis into vesicles at the nerve terminal. We have been investigating the process of targeting these vesicles for retrograde transport, by examining the transport of [125I]-labelled neurotrophins from the eye to sympathetic and sensory ganglia. With the aid of confocal microscopy, we examined the phenomena further in cultures of dissociated sympathetic ganglia to which rhodamine-labelled nerve growth factor (NGF) was added. We found the label in large vesicles in the growth cone and axons. Light microscopic examination of the sympathetic nerve trunk in vivo also showed the retrogradely transported material to be sporadically located in large structures in the axons. Ultrastructural examination of the sympathetic nerve trunk after the transport of NGF bound to gold particles showed the label to be concentrated in relatively few large organelles that consisted of accumulations of multivesicular bodies. These results suggest that in vivo NGF is transported in specialized organelles that require assembly in the nerve terminal.

Transient increase of brain derived neurotrophic factor mRNA expression in substantia nigra reticulata after partial lesion of the nigrostriatal dopaminergic pathway

By using non-isostopic in situ hybridization we have demonstrated a transient increase of BDNF mRNA in the lateral subregion of the substantia nigra pars reticulata 1 week after intrastriatal application of 6-OH-DA. These changes correlate with a partial reduction of dopamine (DA) content in the striatum but with a normal tyrosine hydroxylase immunoreactivity in substantia nigra pars compacta. Our data suggest that non-DA, BDNF expressing cells in substantia nigra pars reticulata may play a role in neuronal protection after partial lesions of the DA nigrostriatal pathway.

Neurotrophic and cell-cell dependent control of early follicular development

Neurotrophins (NTs) and their receptors play an essential role in the differentiation and survival of defined neuronal populations of the central and peripheral nervous systems. Their actions, however, do not appear to be limited to the nervous system, as both NTs and their receptors have been found in non neuronal cells, including cells of the endocrine system. At least four of the five known neurotrophins, including nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), neurotrophin-3 (NT-3), and neurotrophin-4 (NT-4), and their receptors (p75 NTR, trkA, trkB and trkC) are present in the developing ovary. Using mice carrying null mutations of the genes encoding neurotrophins (NGF, NT-4, BDNF) or the receptor that mediates the actions of NT-4 and BDNF (trkB), we have obtained initial results consistent with the notion that neurotrophins are required for the growth of primordial follicles. NGF-deficient mice show a decreased formation of both primary and secondary preantral follicles. Null mutation of the NT-4 gene failed to affect either folliculogenesis or follicular development. However, formation of primary and secondary follicles was compromised in mice carrying a null mutation of both the NT-4 and BDNF genes, suggesting compensation of function by BDNF in NT-4 knockouts. Support for this concept is provided by the similar deficiency in follicular growth observed in animals carrying a null mutation of the gene encoding trkB, the receptors mediating NT-4 and BDNF actions. Initial experiments, using differential display, to isolate genes that may be involved in the process of folliculogenesis and/or early follicular development, resulted in the isolation of a recently identified cell adhesion molecule and a novel transcription factor originally shown to induce cell transformation. It thus appears that formation and development of mammalian follicles requires the concerted action of genes originally thought to be only involved in cell differentiation/survival of neuronal cells, and genes that may control the growth, differentiation, and cell-cell interactions of somatic and germ cells in the ovary.

A 25-year perspective of peripheral nerve surgery: evolving neuroscientific concepts and clinical significance

In spite of an enormous amount of new experimental laboratory data based on evolving neuroscientific concepts during the last 25 years peripheral nerve injuries still belong to the most challenging and difficult surgical reconstructive problems. Our understanding of biological mechanisms regulating posttraumatic nerve regeneration has increased substantially with respect to the role of neurotrophic and neurite-outgrowth promoting substances, but new molecular biological knowledge has so far gained very limited clinical applications. Techniques for clinical approximation of severed nerve ends have reached an optimal technical refinement and new concepts are needed to further increase the results from nerve repair. For bridging gaps in nerve continuity little has changed during the last 25 years. However, evolving principles for immunosuppression may open new perspectives regarding the use of nerve allografts, and various types of tissue engineering combined by bioartificial conduits may also be important. Posttraumatic functional reorganizations occurring in brain cortex are key phenomena explaining much of the inferior functional outcome following nerve repair, and increased knowledge regarding factors involved in brain plasticity may help to further improve the results. Implantation of microchips in the nervous system may provide a new interface between biology and technology and developing gene technology may introduce new possibilities in the manipulation of nerve degeneration and regeneration.

Expression of nerve growth factor, brain-derived neurotrophic factor, and neurotrophin-3 in the somatosensory cortex of the mature rat: coexpression with high-affinity neurotrophin receptors

Neurotrophins, including nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), and neurotrophin-3 (NT-3), are critical for the maintenance and plasticity of central nervous system (CNS) neurons. We tested the hypothesis that cortical neurons participate in redundant autocrine/paracrine systems. Three sets of studies determined the distribution of NGF-, BDNF-, and NT-3-expressing neurons, the frequency of neurons coexpressing NGF and BDNF, and the frequency of neurons expressing a neurotrophin and its associated high-affinity receptor. The distribution of NGF-, BDNF, and NT-3-immunoreactive neurons was identical. Neurotrophin-positive cells were parceled throughout the cortex, although the labeling frequency was not the same in all layers. More than 30% of the neurons in layers II/III, V, and VI were labeled, whereas only 5-10% of the neurons in layer IV was immunopositive for a neurotrophin. Some glia were also neurotrophin positive, particularly BDNF-positive glia. About 70% of the neurons in layers II/III and V coexpressed NGF and BDNF or coexpressed NGF and NT-3. Ligand-receptor colabeling was also common among cortical neurons. For example, nearly 70% of the NGF-, BDNF-, and NT-3-positive neurons in layer V colabeled with their respective high-affinity receptors, i.e., trkA, trkB, and trkC, respectively. Thus, (a) neurons express multiple neurotrophins and (b) cortical neurons (e.g., layer V neurons) contain the components required for autocrine/paracrine and/or anterograde communication (e.g., neurons in layer II/III support layer V neurons). These systems mean that the cortex is capable of regulating itself autonomously.

Ultrastructural identification of storage compartments and localization of activity-dependent secretion of neurotrophin 6 in hippocampal neurons

A modulatory role of neurotrophins (NTs) in activity-dependent neuronal plasticity by pre- and postsynaptic mechanisms is now well established. In this context, it is important to identify the storage compartments and to localize the precise site(s) and mechanism of NT secretion in order to deduce the spatial and temporal availability of NTs. We approached these questions at the ultrastructural level, exploiting the unique property of NT6 to bind tightly to heparan sulfate proteoglycans at the neuronal surface (R. Götz et al., 1994, Nature 372, 266-269), permitting the localization of secretion sites excluding diffusion artifacts. The myc tagging of NT6 permitted glutaraldehyde fixation and hence good preservation of the membrane structure, permitting immunogold labeling of NT6myc at the neuronal surface. NT6myc is preferentially secreted from neurites compared to neuronal cell bodies. In agreement with light-microscopic observations, the ultrastructural localization of NT6myc by postembedding procedures showed a predominant localization in ER-like membrane-confined compartments, partially associated with microtubules.

Quantitative, high-throughput cell-based assays for inhibitors of trkA receptor

Two quantitative, high-throughput cell-based assays for evaluating inhibitors of NGF-stimulated trkA phosphorylation in trkA-transfected NIH3T3 cells have been established. Both assays involve capture of the trkA receptor from cell lysates in microtiter plates coated with an anti-trk antibody. The amount of trkA phosphorylation is then measured using either an anti-phosphotyrosine antibody with a colorimetric readout or a lanthanide (europium)-labeled anti-phosphotyrosine antibody with a fluorometric detection. The two assay formats exhibited at least a fivefold increase in phosphorylated trkA signal in trkA-transfected cells compared to vector control. Inhibition plots generated for trkA kinase inhibitors using the two detection systems yielded comparable IC(50) values. Overall, the two assays represent a marked improvement over the standard gel-based/western blot method in terms of throughput, quantitation, and amenability to automation.

The effect of PKC activation on the survival of rat retinal ganglion cells in culture

Natural cell death is a degenerative phenomenon occurring during the development of the nervous system. Approximately half the neurons initially generated during this period die. The role of trophic molecules produced by target and afferent neurons as well as by glial cells controlling this regressive event has been extensively demonstrated. The aim of this work was to study the role of activated protein kinase C (PKC), an enzyme involved in apoptosis regulation, on the survival of retinal ganglion cells kept "in vitro" for 48 h. For this purpose, we used the phorbol 12-myristate 13-acetate (PMA), a tumor promoter agent that activates PKC. Our results showed that PMA increases the survival of ganglion cells. The effect was dose-dependent and PMA concentrations of 10 or 100 ng/ml produced the maximal effect (a two-fold increase on ganglion cells survival compared with 48 h control). This effect was totally abolished by 1.25 microM chelerythrine chloride (an inhibitor of PKC) and 30 microM genistein (an inhibitor of tyrosine kinase enzymes). Otherwise, PMA was effective only when it was chronically present in the cultures. On the other hand, treatment with 20 microM 5-fluoro-2'-deoxyuridine, an inhibitor of cell proliferation, or 25 microM BAPTA-AM, an intracellular calcium chelator, did not block PMA effect. Our results suggest that the survival of retinal ganglion cells "in vitro" may be mediated by a mechanism that involves PKC activation.

Effect of the nonpeptide neurotrophic compound SR 57746A on the phenotypic survival of purified mouse motoneurons

1. Neurotrophic factors have been used for the treatment of several neurodegenerative diseases. However, their use is limited by their inability to cross the blood-brain barrier, their short half life and their side effects. SR 57746A is a new orally active compound that exhibits in vivo and in vitro neurotrophic effects in several experimental models. 2. We show here that SR 57746A (1 microM) increases the phenotypic survival of embryonic purified mouse motoneurons in vitro to the same extent as brain-derived neurotrophic factor (100 ng ml-1), and increases the outgrowth and number of their neurites. It acts in a dose-dependent manner up to 1 microM which is the optimal concentration. Above this concentration, its neurotrophic effect decreases. 3. Genistein (10 microM), a protein tyrosine kinase inhibitor, also increases the phenotypic survival and differentiation of mouse motoneurons. It does not act in a synergistic or additive manner with SR 57746A. However, at concentrations equal or superior to 25 microM, it decreases the survival of motoneurons. This suggests that the neurotrophic effect of genistein is due to a favourable alteration of equilibrium between phosphorylated and dephosphorylated states of proteins involved in survival and differentiation of motoneurons. 4. Like genistein, SR 57746A should be used at a critical concentration (1 microM) to exert its optimal effects. Since SR 57746A does not act synergistically with genistein, it is likely that its mechanism of action involves a pathway similar to that affected by this tyrosine kinase inhibitor. 5. At the present time, SR 57746A is the only orally active compound and the only synthetic compound shown to be active on motoneurons in vitro. It should thus be considered as a good candidate for the treatment of motoneuron diseases.

Evolution of the vertebrate neurotrophin and Trk receptor gene families

Studies of neurotrophins and Trk receptors in jawless fish have shed light on the course of events underlying the formation of these gene families. They evolved early in vertebrate history during major gene duplication events, before the appearance of cartilaginous fish. The existence of multiple genes has permitted the diversification of neurotrophin and Trk receptor expression, and thereby enabling the acquisition of specific functions in selective neuronal populations.

Crystal structure of nerve growth factor in complex with the ligand-binding domain of the TrkA receptor

Nerve growth factor (NGF) is involved in a variety of processes involving signalling, such as cell differentiation and survival, growth cessation and apoptosis of neurons. These events are mediated by NGF as a result of binding to its two cell-surface receptors, TrkA and p75. TrkA is a receptor with tyrosine kinase activity that forms a high-affinity binding site for NGF. Of the five domains comprising its extracellular portion, the immunoglobulin-like domain proximal to the membrane (TrkA-d5 domain) is necessary and sufficient for NGF binding. Here we present the crystal structure of human NGF in complex with human TrkA-d5 at 2.2 A resolution. The ligand-receptor interface consists of two patches of similar size. One patch involves the central beta-sheet that forms the core of the homodimeric NGF molecule and the loops at the carboxy-terminal pole of TrkA-d5. The second patch comprises the amino-terminal residues of NGF, which adopt a helical conformation upon complex formation, packing against the 'ABED' sheet of TrkA-d5. The structure is consistent with results from mutagenesis experiments for all neurotrophins, and indicates that the first patch may constitute a conserved binding motif for all family members, whereas the second patch is specific for the interaction between NGF and TrkA.

Neurotrophic factors and neuro-muscular disease: II. GDNF, other neurotrophic factors, and future directions

This is the second of two reviews in which we discuss the essential aspects of neurotrophic factor neurobiology, the characteristics of each neurotrophic factor, and their clinical relevance to neuromuscular diseases. The previous paper reviewed the neurotrophin family and neuropoietic cytokines. In the present article, we focus on the GDNF family and other neurotrophic factors and then consider future approaches that may be utilized in neurotrophic factor treatment.

NGF-resistant PC12 cell death induced by arachidonic acid is accompanied by a decrease of active PKC zeta and nuclear factor kappa B

Inflammation and the associated release of inflammatory cytokines such as tumor necrosis factor alpha (TNFalpha) may be a component of neurodegenerative diseases associated with aging or chronic HIV-1 infection. Most of the neurons that are affected under these conditions require a constant supply of trophic factors such as nerve growth factor (NGF) for survival. NGF acts via binding to a specific tyrosine kinase receptor (TrkA). NGF also binds to the common neurotrophin receptor (p75(NTR)), a member of the TNFalpha receptor (TNFR-I) superfamily, whose function may be to modulate apoptosis via the release of ceramide and the activation of the transcription factor nuclear factor kappa B (NFkappaB). The similarity between p75(NTR) and TNFR-I signal transduction pathways suggests that one of the mechanisms by which TNFalpha affects neuronal survival is by impacting upon these pathways that normally promote NGF support of neurons. Here we show that arachidonic acid (AA), a signaling lipid potentially associated with TNFR-I signal cascade, induces apoptosis in PC12 cells through inhibition of both protein kinase C zeta (PKCzeta) and NFkappaB activity. We also show that apoptosis induced by AA cannot be prevented by NGF. These data support the idea that PKCzeta and NFkappaB are both essential signaling elements for mediating NGF-promoted rescue from apoptosis. Our results also suggest that AA, an inflammatory signal lipid induced by TNFalpha via binding to TNFR-I, may reduce neuronal survival by inhibiting elements of the signal cascade induced by NGF.

Crystal structures of the neurotrophin-binding domain of TrkA, TrkB and TrkC

The Trk receptors and their neurotrophin ligands control development and maintenance of the nervous system. The crystal structures of the ligand binding domain of TrkA, TrkB, and TrkC were solved and refined to high resolution. The domains adopt an immunoglobulin-like fold, but crystallized in all three instances as dimers with the N-terminal strand of each molecule replaced by the same strand of a symmetry-related mate. Models of the correctly folded domains could be constructed by changing the position of a single residue, and the resulting model of the binding domain of TrkA is essentially identical with the bound structure as observed in a complex with nerve growth factor. An analysis of the existing mutagenesis data for TrkA and TrkC in light of these structures reveals the structural reasons for the specificity among the Trk receptors, and explains the underpinnings of the multi-functional ligands that have been reported. The overall structure of all three domains belongs to the I-set of immunoglobulin-like domains, but shows several unusual features, such as an exposed disulfide bridge linking two neighboring strands in the same beta-sheet. For all three domains, the residues that deviate from the standard fingerprint pattern common to the I-set family fall in the region of the ligand binding site observed in the complex. Therefore, identification of these deviations in the sequences of other immunoglobulin-like domain-containing receptors may help to identify their ligand binding site even in the absence of structural or mutagenesis data.

Neuroprotective effects of brain-derived neurotrophic factor in seizures during development

Although the immature brain is highly susceptible to seizures, it is more resistant to seizure-induced neuronal loss than the adult brain. The developing brain contains high levels of neurotrophins which are involved in growth, differentiation and survival of neurons. To test the hypothesis that neurotrophins may protect the developing brain from seizure-induced neuronal loss, brain-derived neurotrophic factor up-regulation was blocked by intracerebroventricular infusion of an 18mer antisense oligodeoxynucleotide sequence to brain-derived neurotrophic factor in 19-day-old rats using micro-osmotic pumps. Control rats were infused with sense or missense oligodeoxynucleotide. Status epilepticus was induced by intraperitoneal administration of kainic acid 24 h after the start of oligodeoxynucleotide infusion. Seizure duration was significantly increased in the antisense oligodeoxynucleotide plus kainic acid group compared to groups that received kainic acid alone or kainic acid plus sense or missense oligodeoxynucleotide. There was no difference between groups in the latency to forelimb clonus. A twofold increase in brain-derived neurotrophic factor levels was observed in the hippocampus 20 h following kainic acid-induced seizures. This kainic acid-induced increase was absent in animals receiving infusion of antisense oligodeoxynucleotide to brain-derived neurotrophic factor at time of seizure induction. Hippocampi of rats in this group (antisense oligodeoxynucleotide plus kainic acid) showed a loss of CA1 and CA3 pyramidal cells and hilar interneurons. This neuronal loss was not dependent upon seizure duration since animals injected with diazepam to control seizure activity in the antisense plus kainic acid group also showed similar neuronal loss. Administration of kainic acid or infusion of antisense alone did not produce any cell loss in these regions. Induction of seizures at postnatal day 20, in the presence or absence of antisense oligonucleotide, did not produce an impairment in learning and memory when tested 15 days later in the Morris water maze. The hippocampi of these animals did not show any synaptic reorganization as assessed by growth-associated protein-43 immunostaining and Timm staining. Our findings confirm prior studies demonstrating that seizures in the immature brain are associated with little, if any, cell loss. However, when seizure-induced increase in brain-derived neurotrophic factor is blocked, seizures do result in neuronal loss in the developing brain. Thus, brain-derived neurotrophic factor appears to provide protection against kainic acid seizure-induced neuronal damage in the developing brain.

Cellular aspects of trophic actions in the nervous system

During the past three decades the number of molecules exhibiting trophic actions in the brain has increased drastically. These molecules promote and/or control proliferation, differentiation, migration, and survival (sometimes even the death) of their target cells. In this review a comprehensive overview of small diffusible factors showing trophic actions in the central nervous system (CNS) is given. The factors discussed are neurotrophins, epidermal growth factor, fibroblast growth factor, platelet-derived growth factor, insulin-like growth factors, ciliary neurotrophic factor and related molecules, glial-derived growth factor and related molecules, transforming growth factor-beta and related molecules, neurotransmitters, and hormones. All factors are discussed with respect to their trophic actions, their expression patterns in the brain, and molecular aspects of their receptors and intracellular signaling pathways. It becomes evident that there does not exist "the" trophic factor in the CNS but rather a multitude of them interacting with each other in a complicated network of trophic actions forming and maintaining the adult nervous system.

Neurotrophins and Trk receptors in human pancreatic ductal adenocarcinoma: expression patterns and effects on in vitro invasive behavior

The aggressive and highly metastatic behavior observed in pancreatic ductal adenocarcinoma (PDAC) may be due to autocrine and/or paracrine interactions (tumor/stromal) involving altered expression of peptide growth factors and their corresponding receptors. The neurotrophin (NT) growth factor family and their cognate receptors have been demonstrated to play a role in the invasiveness, chemotactic behavior and tumor cell survival of both neuronal and non-neuronal cancers. We hypothesized that aberrant expression of the NTs and/or the Trk receptors may contribute to the malignant phenotype of PDAC, specifically tumor cell invasiveness, through autocrine and/or paracrine interactions. In this study, we examined the expression of NTs, Trks and p75NGFR by immunohistochemical and in situ hybridization analyses in both normal (n=14) and neoplastic pancreas (n=47) and PDAC-derived cell lines (n=6). Further, we evaluated the effects of various NTs on the in vitro invasive and chemotactic behavior on 6 human PDAC-derived cell lines in a modified Boyden chamber assay. Brain-derived nerve growth factor (BDNF), NT-3, NT-4/5 and Trks A, B and C exhibited diffuse cytoplasmic and membranous immunostaining patterns in both the ducts and the acini of the exocrine pancreas and the islets of the endocrine pancreas of both normal and PDAC specimens. NT expression was primarily within the stromal compartment of the tumor, while Trk expression was weak or absent. We observed a 68%, 64% and 66% increase in the expression of Trks A, B and C, respectively, in the ductal elements of the PDAC samples examined compared with the normal adjacent tissue. Invasiveness of 4 of 6 PDAC cell lines was significantly inhibited (p<0.05) when the cells were incubated with 100 ng/ml NT. However, when select cell lines were incubated with lower concentrations of NT-3 and BDNF (0, 1, 5, 25 and 50 ng/ml), invasiveness was significantly stimulated (p<0.05) through the Matrigel matrix. Collectively, our data suggest the possibility that paracrine and/or autocrine NT-Trk interactions may influence the phenotype (possibly the invasive behavior) of PDAC.

Regulation of Synaptic Function by Neurotrophic Factors in Vertebrates and Invertebrates: Implications for Development and Learning

Recent studies have demonstrated that neurotrophic factors contribute to the molecular events involved in synaptic plasticity, both during vertebrate development and in the mature nervous system. Although it is well established that many of the cellular and molecular mechanisms underlying synaptic plasticity are conserved between invertebrates and vertebrates, there are, as yet, very few neurotrophic factors identified in invertebrate species. Nonetheless, vertebrate neurotrophins can influence invertebrate neuronal growth and plasticity. In addition, homologs of neurotrophic factor receptors have been identified in several invertebrate species. These studies may indicate that the roles of neurotrophins in both developmental and adult plasticity are highly conserved across diverse phyla.

Microsphere embolism-induced elevation of nerve growth factor level and appearance of nerve growth factor immunoreactivity in activated T-lymphocytes in the rat brain

Changes in nerve growth factor (NGF) level and type of cells producing NGF were investigated in the rat brain after sustained cerebral embolism. The NGF level was determined by a two-site enzyme immunoassay specific for NGF. The cerebral cortex, striatum, and hippocampus of the embolized hemisphere maximally contained 2.4-, 2.4-, and 1.7-times higher NGF levels than the corresponding regions of the nonembolized hemisphere. A significant increase was transiently observed for 1 week in the cerebral cortex and striatum, whereas the increase was longer lasting, at least of 4 weeks' duration, in the hippocampus. To examine the localization of NGF-like immunoreactivity (NGF-LI), we used a newly developed anti-NGF peptide antiserum that specifically recognized a 30-kDa molecule(s) in the hippocampal extracts or in NGF cDNA-transfected cells, suggesting that the antibody predominantly reacted with the putative NGF precursor protein(s). NGF-LI, which was localized in neurons of the normal or non-embolized hemisphere, was reduced, and on the embolized side new signals emerged in small non-neuronal cells having a round shape. These included cells with common leukocyte antigen CD45 and T-lymphocyte antigen CD3, which did not appear in the normal or non-embolized hemisphere. NGF-LI and CD3 were colocalized in a substantial number of the cells, suggesting that some activated T-lymphocytes produce NGF for neuronal regeneration after sustained cerebral embolism.

Cellular localization of brain-derived neurotrophic factor-like immunoreactivity in adult monkey brain

Immunohistochemical localization of brain-derived neurotrophic factor (BDNF) in the monkey brain was investigated using a polyclonal anti-BDNF antibody produced in our laboratory. The antibody recognized a single band in monkey brain homogenates, and the estimated molecular weight was approximately 14 kDa, which corresponds well to the molecular weight of BDNF monomer. BDNF-like immunoreactivity was observed in the somata and processes of discrete neuronal subpopulations in the monkey brain. BDNF-positive neurons were widely distributed in various structures of the brain, including the cerebral cortex, hippocampus, basal forebrain, basal ganglia, diencephalon, brainstem and cerebellum. In addition, immunopositive glial cells were found in some brain regions. These data suggest that BDNF may exist widely in the monkey brain, and may be concerned with various types of neurons in the monkey central nervous system.