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Neurotrophins [e.g., brainderived neurotrophic factor (BDNF), neurotrophin 4 (NT4)], known to affect neuronal structure and function, are expressed in nonneuronal tissues including the airway. However, their function is unclear. We examined the effect of acute vs. prolonged neurotrophin exposure on regulation of airway smooth muscle (ASM) intracellular [Ca.sup.2+] concentration ([[[Ca.sup.2+]].sub.i]): sarcoplasmic reticulum (SR) [Ca.sup.2+] release and [Ca.sup.2+] influx (specifically store-operated [Ca.sup.2+] entry, SOCE). Human ASM cells were incubated for 30 min in medium (control) or 1 or 10 nM BDNF, NT3, or NT4 (acute exposure) or overnight in 1 nM BDNF, NT3, or NT4 (prolonged exposure) and imaged after loading with the [Ca.sup.2+] indicator fura-2 AM. [[[Ca.sup.2+]].sub.i] responses to ACh, histamine, bradykinin, and caffeine and SOCE following SR [Ca.sup.2+] depletion were compared across cell groups. Force measurements were performed in human bronchial strips exposed to neurotrophins. Basal [[[Ca.sup.2+]].sub.i], peak responses to all agonists, SOCE, and force responses to ACh and histamine were all significantly enhanced by both acute and prolonged BDNF exposure (smaller effect of NT4) but decreased by NT3. Inhibition of the BDNF/NT4 receptor trkB by K252a prevented enhancement of [[[Ca.sup.2+]].sub.i] responses. ASM cells showed positive immunostaining for BDNF, NT3, NT4, trkB, and trkC (NT3 receptor). These novel data demonstrate that neurotrophins influence ASM [[[Ca.sup.2+]].sub.i] and force regulation and suggest a potential role for neurotrophins in airway diseases. doi:10.1152/ajplung.00501.2004 brain-derived neurotrophic factor; neurotrophin 4; neurotrophin 3; sarcoplasmic reticulum; capacitative calcium entry

Neurotrophins play an essential role in mammalian development. Most of their functions have been attributed to activation of the kinase-active Trk receptors and the p75 neurotrophin receptor. Truncated Trk receptor isoforms lacking the kinase domain are abundantly expressed during development and in the adult; however, their function and signaling capacity is largely unknown. We show that the neurotrophin-3 (NT3) TrkCT1-truncated receptor binds to the scaffold protein tamalin in a ligand-dependent manner. Moreover, NT3 initiation of this complex leads to activation of the Rac1 GTPase through adenosine diphosphate-ribosylation factor 6 (Arf6). At the cellular level, NT3 binding to TrkCT1-tamalin induces Arf6 translocation to the membrane, which in turn causes membrane ruffling and the formation of cellular protrusions. Thus, our data identify a new signaling pathway elicited by the kinase-deficient TrkCT1 receptor. Moreover, we establish NT3 as an upstream regulator of Arf6.

Role of Brain-derived neurotrophic factor and Neurotrophin 4 over expression on gustatory neuronal morphology is presented.

The role of nerve growth factor in programmed cell death of retinal cells through low-affinity neurotrophin receptor p75 binding is presented.

MicroRNAs (miRNAs) regulate cellular fate by controlling the stability or translation of mRNA transcripts. Although the spatial and temporal patterning of miRNA expression is tightly controlled, little is known about signals that induce their expression nor mechanisms of their transcriptional regulation. Furthermore, few miRNA targets have been validated experimentally. The miRNA, miR132, was identified through a genome-wide screen as a target of the transcription factor, cAMP-response element binding protein (CREB). miR132 is enriched in neurons and, like many neuronal CREB targets, is highly induced by neurotrophins. Expression of miR132 in cortical neurons induced neurite outgrowth. Conversely, inhibition of miR132 function attenuated neuronal outgrowth. We provide evidence that miR132 regulates neuronal morphogenesis by decreasing levels of the GTPase-activating protein, p250GAP. These data reveal that a CREB-regulated miRNA regulates neuronal morphogenesis by responding to extrinsic trophic cues. neurite | neurotrophin | plasticity | microRNA | transcription

Neurotrophins are involved in the modulation of synaptic transmission, including the induction of long-term potentiation (LTP) through the receptor TrkB. Because previous studies have revealed a bidirectional mode of neurotrophin action by virtue of signaling through either the neurotrophin receptor [p.sup.75NTR] or the Trk receptors, we tested the hypothesis that [p75.sup.NTR] is important for long-term depression (LTD) to occur. Although LTP was found to be unaffected in hippocampal slices of two different strains of mice carrying mutations of the [p75.sup.NTR] gene, hippocampal LTD was impaired in both [p75.sup.NTR]-deficient mouse strains. Furthermore, the expression levels of two (RS)-[alpha]-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor subunits, GluR2 and GluR3, but not GluR1 or GluR4, were found to be significantly altered in the hippocampus of [p75.sup.NTR]-deficient mice. These results implicate [p75.sup.NTR] in activity-dependent synaptic plasticity and extend the concept of functional antagonism of the neurotrophin signaling system. neurotrophins | p75 neurotrophin receptor | synaptic plasticity

The developmental events experienced by post-mitotic postganglionic sympathetic neurons are discussed. Proximal and peripheral axon extension, target-controlled neuron survival and death, dendrite formation and growth, synaptogenesis and acquisition of phenotypic heterogeneity are the factors involved in the migration and specification of sympathetic neuron.

It is shown that neurotrophins evoke action potentials in central neurons. Brain derived neurotrophic factor (BDNF) and neurotrophin-4/5 were found to depolarize neurons just as rapidly as the neurotransmitter glutamate. Smaller responses were produced by neurotrophin-3. The neurotrophin-induced depolarization was due to activation of a sodium ion conductance, blocked by K-252a.

A subclass of zinc finger proteins containing a unique protein motif called the positive regulatory (PR) domain has been described. The members include the PRDI-BF1/Blimp-1 protein, the Caenorhabditis elegans egl-43 and EVI1 gene products, and the retinoblastoma interacting protein RIZ. Here we describe a member of this family, SC-1, that exhibits several distinctive features. First, SC-1 interacts with the p75 neurotrophin receptor and is redistributed from the cytoplasm to the nucleus after nerve growth factor (NGF) treatment of transfected COS cells. The translocation of SC-1 to the nucleus was specific for p75, as NGF binding to the TrkA receptor did not lead to nuclear localization of SC-1. Thus, SC-1 provides a downstream transducer for the effects of NGF through the p75 neurotrophin receptor. Under normal growth conditions, SC-1 was found predominantly in the cytoplasm. On serum-starvation, SC-1 also translocated into the nucleus. A direct correlation between nuclear expression of SC.1 with the loss of BrdUrd incorporation was observed. These results imply that SC-1 may be involved in events associated with growth arrest.

The role of neurotrophins in agrin-induced postsynaptic differentiation is studied. A simple system of agrin-induced acethylcholine receptors (AChR) clustering on cultured myotubes is used. The analysis was restricted to events occurring in the postsynaptic cell because no neurons were present in the cultures. The results showed that exogenous brain-derived neurotrophic factor/neurotrophin 4 inhibited agrin-induced AChr clustering through a tyrosine kinase B dependent mechanism.

Tyrosine phosphorylation has been shown to be an important modulator of synaptic transmission in both vertebrates and invertebrates. Such findings hint toward the existence of extracellular ligands capable of activating this widely represented signaling mechanism at or close to the synapse. Examples of such ligands are the peptide growth factors which, on binding, activate receptor tyrosine kinases. To gain insight into the physiological consequences of receptor tyrosine kinase activation in squid giant synapse, a series of growth factors was tested in this preparation. Electrophysiological, pharmacological, and biochemical analysis demonstrated that nerve growth factor (NGF) triggers an acute and specific reduction of the postsynaptic potential amplitude, without affecting the presynaptic spike generation or presynaptic calcium current. The NGF target is localized at a postsynaptic site and involves a new TrkA-like receptor. The squid receptor crossreacts with antibodies generated against mammalian TrkA, is tyrosine phosphorylated in response to NGF stimulation, and is blocked by specific pharmacological inhibitors. The modulation described emphasizes the important role of growth factors on invertebrate synaptic transmission.

A structural examination of the neurotrophin-3 (NT-3) homodimer was conducted using X-ray crystallography to understand the relationship of NT-3 with other growth factors and receptor specificity. The NT-3 protomer from the brain-derived neurotrophic factor-NT-3 (BDNF/NT-3) heterodimer was utilized as a search model for molecular replacement phasing. The results indicated a similar structure among NT-3, nerve growth factor and the BDNF/NT-3 heterodimer. The findings provide an explanation for obligate dimerization of neurotrophins.

Neurotrophins (NTs) have recently been found to regulate synaptic transmission in the hippocampus. Whole-cell and single-channel recordings from cultured hippocampal neurons revealed a mechanism responsible for enhanced synaptic strength. Specifically, brain-derived neurotrophic factor augmented glutamate-evoked, but not acetylcholine-evoked, currents 3-fold and increased N-methyl-D-aspartic acid (NMDA) receptor open probability. Activation of trkB NT receptors was critical, as glutamate currents were not affected by nerve growth factor or NT-3, and increased open probability was prevented by the tyrosine kinase inhibitor K-252a. In addition, the NMDA receptor antagonist MK-801 blocked brain-derived neurotrophic factor enhancement of synaptic transmission, further suggesting that NTs modulate synaptic efficacy via changes in NMDA receptor function.

The impact of the nerve growth factor (NGF) family of neurotrophins and their receptors was examined on the cutaneous innervation in the mystacial pads of mice. Ten sets of unmyelinated and thinly myelinated sensory and autonomic innervation were evaluated that terminated in the epidermis, upper dermis, and upper part of the intervibrissal hair follicles. Mystacial pads were analyzed from newborn to 4-week-old mice that had homozygous functional deletions of the genes for NGF, brain-derived neurotrophic factor (BDNF), neurotrophin-3 (NT-3), neurotrophin-4 (NT-4), tyrosine kinase (trk) A, trkB, trkC, or p75. Mystacial pads were also analyzed in adult transgenic mice that had overproduction of NGF, BDNF, or NT-3 driven by a keratin promoter gene. The innervation was revealed by using immunofluorescence and immunocytochemistry with antibodies for protein gene product (PGP) 9.5, calcitonin gene-related product (CGRP), substance P (SP), galanin (GAL), neuropeptide Y (NPY), tyrosine hydroxylase (TH), and a neurofilament protein. The cumulative results indicated that NGF/trkA signaling plays a major role in the outgrowth and proliferation of sensory axons, whereas NT-3/trkA signaling plays a major role in the formation of sensory endings. TrkC is also essential for the development of three sets of trkA-dependent sensory innervation that coexpress CGRP, SP, and GAL. Another set of sensory innervation that only coexpressed CGRP and SP was solely dependent upon NGF and trkA. Surprisingly, most sets of trkA-dependent sensory innervation are suppressed by trkB perhaps interacting with p75. BDNF and NT-4 appear to mediate this suppressing effect in the upper dermis and NT-4 in the epidermis. In contrast to sensory innervation, sympathetic innervation to the necks of intervibrissal hair follicles depends upon NGF/trkA signaling interacting with p75 for both the axon outgrowth and ending formation. Although NT-3/trkA signaling is essential for the full complement of sympathetic neurons, NT-3 is detrimental to the formation of sympathetic terminations to the necks of hair follicles. TrkB signaling mediated by BDNF but not NT-4 also suppresses these sympathetic terminations. One sparse set of innervation, perhaps parasympathetic, terminating at the necks of hair follicles is dependent solely upon NT-3 and trkC. Taken together, our results indicate that the innervation of the epidermis, upper dermis, and the upper portion of hair follicles is regulated by a competitive balance between promoting and suppressing effects of the various neurotrophins. Key Words: NGF; NT3; NT4; BDNF; trk; p75; trigeminal; unmyelinated; A[Delta]; sensory; autonomic.

Major histocompatibility complex (MHC) molecules are rare in the healthy brain tissue, but are heavily expressed on microglial cells after inflammatory or neurodegenerative processes. We studied the conditions leading to the induction of MHC class II molecules in microglia by using explant cultures of neonatal rat hippocampus, a model of interacting neuronal networks. Interferon-[Gamma] (IFN-[Gamma])dependent MHC class II inducibility in microglia cells was very low, but strongly increased in the hippocampal slices after the blockade of neuronal activity by neurotoxins [tetrodotoxin (TTX), [Omega]-conotoxin] or glutamate antagonists. None of these agents acted directly on isolated microglia cells. We found that neurotrophins modulate microglial MHC class II expression. MHC class II inducibility was enhanced by neutralization of neurotrophins produced locally within the cultured tissues and was inhibited by the addition of nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), or neurotrophin-3 (NT3). NGF and, to a lower extent, NT3 acted directly on isolated microglia via the p75 neurotrophin receptor and inhibited MHC class II inducibility as shown by blockade of the p75 neurotrophin receptor with antibodies. Our data suggest that neurotrophins secreted by electrically active neurons control the antigen-presenting potential of microglia cells, and indicate that this effect is mediated partly via the p75 neurotrophin receptor.

Neurotrophins, secreted in an activity-dependent manner, are thought to be involved in the activity-dependent refinement of synaptic connections. Here we demonstrate that in hippocampal neurons and the rat pheochromocytoma cell line PC12 application of exogenous neurotrophins induces secretion of neurotrophins, an effect that is mediated by the activation of tyrosine kinase neurotrophin receptors (Trks). Like activity-dependent secretion of neurotrophins, neurotrophin-induced neurotrophin secretion requires mobilization of calcium from intracellular stores. Because neurotrophins are likely to be released from both dendrites and axons, neurotrophin-induced neurotrophin release represents a potential positive feedback mechanism, contributing to the reinforcement and stabilization of synaptic connections.

The function of N-glycosylation in apical sorting of transmembrane neurotrophin receptors (p75NTR) localized to a juxtamembrane region of the extracellular domain rich in O-glycosylated residues was investigated. P75 receptors are type I membrane proteins included in the family of cell surface receptors. Results of the study revealed that N-glycans were not responsible in the apical sorting of p75 and that the juxtamembrane domain rich in O-glycans included an apical targeting signal.

The neurotrophins nerve growth factor (NGF) and neurotrophin-3 (NT3) support the survival of subpopulations of primary sensory neurons with defined and distinct physiological characteristics. Only a few genes have been identified as being differentially expressed in these subpopulations, and not much is known about the nature of the molecules involved in the processing of sensory information in NGF-dependent nociceptive neurons or NT3-dependent proprioceptive neurons. We devised a simple dorsal root ganglion (DRG) explant culture system, allowing the selection of neuronal populations preferentially responsive to NGF or NT3. The reliability of this assay was first monitored by the differential expression of the NGF and NT3 receptors trkA and trkC, as well as that of neuropeptides and calcium-binding proteins. We then identified four differentially expressed sodium channels, two enriched in the NGF population and two others in the NT3 population. Finally, using an optimized RNA fingerprinting protocol, we identified 20 additional genes, all differentially expressed in DRG explants cultured with NGF or NT3. This approach thus allows the identification of large number of genes expressed in subpopulations of primary sensory neurons and opens the possibility of studying the molecular mechanisms of nociception and proprioception.

The ongoing dissection of the roles of [p75.sup.NTR] and TrkA, -B and -C in neurotrophin signaling has generated a number of apparent paradoxes. Limiting consideration to the role of [p75.sup.NTR] in cell death, a theory is proposed that is based on the following postulates: (I) that [p75.sup.NTR] displays a pro-apoptotic intrinsic (ligand-independent, Trk-independent) receptor effect (IRE), which is inhibited by ligand binding; (2) that [p75.sup.NTR] and TrkA exhibit mutual repression of signaling; and (3) that [p75.sup.NTR] and TrkA are required for the efficient generation of high-affinity NGF binding sites.

The neurotrophins are signaling factors that are essential for survival and differentiation of distinct neuronal populations during the development and regeneration of the nervous system. The long-term effects of neurotrophins have been studied in detail, but little is known about their acute effects on neuronal activity. Here we use permeabilized whole-cell patch clamp to demonstrate that neurotrophin-3 (NT-3) and nerve growth factor activate calcium-dependent, paxilline-sensitive potassium channels (BK channels) in cortical neurons. Application of NT-3 or nerve growth factor produced a rapid and gradual rise in BK current that was sustained for 30-50 min; brain-derived neurotrophic factor, ciliary neurotrophic factor, and insulin-like growth factor-1 had no significant effect. The response to NT-3 was blocked by inhibitors of protein kinases, phospholipase C, and serine/ threonine protein phosphatase 1 and 2a. Omission of [Ca.sup.2+] from the extracellular medium prevented the NT-3 effect. Our results indicate that NT-3 stimulates BK channel activity in cortical neurons through a signaling pathway that involves Trk tyrosine kinase, phospholipase C, and protein dephosphorylation and is calcium-dependent. Activation of BK channels may be a major mechanism by which neurotrophins acutely regulate neuronal activity.

The ability of neurotrophins to modulate the survival and differentiation of neuronal populations involves the Trk/MAP (mitogen-activated protein kinase) kinase signaling pathway. More recently, neurotrophins have also been shown to regulate synaptic transmission. The synapsins are a family of neuron-specific phosphoproteins that play a role in regulation of neurotransmitter release, in axonal elongation, and in formation and maintenance of synaptic contacts. We report here that synapsin I is a downstream effector for the neurotrophin/Trk/MAP kinase cascade. Using purified components, we show that MAP kinase stoichiometrically phosphorylated synapsin I at three sites (Ser-62, Ser-67, and Ser-549). Phosphorylation of these sites was detected in rat brain homogenates, in cultured cerebrocortical neurons, and in isolated presynaptic terminals. Brain-derived neurotrophic factor and nerve growth factor upregulated phosphorylation of synapsin I at MAP kinase-dependent sites in intact cere-brocortical neurons and PC12 cells, respectively, while KCl-induced depolarization of cultured neurons decreased the phosphorylation state at these sites. MAP kinase-dependent phosphorylation of synapsin I significantly reduced its ability to promote G-actin polymerization and to bundle actin filaments. The results suggest that MAP kinase-dependent phosphorylation of synapsin I may contribute to the modulation of synaptic plasticity by neurotrophins and by other signaling pathways that converge at the level of MAP kinase activation.

A study was conducted on the transport of three neurotrophins nerve growth factor, brain-derived neurotrophic factor, neurotrophin-3, basic fibroblast growth factor and insulin-like growth factor 1 in he retinoectal projection of chick embryos. Results showed that exogenous neurotrophins are conveyed in the anterograde direction. Evidence also suggests that anterogradely-transported neurotrophins may have a significant effect in synaptic plasticity and may influence more than a single synapse beyond the initial release site.

Soon after they segregate from the neural tube, trunk neural crest cells disperse on two spatially and temporally distinct pathways. Only crest cells that migrate early and ventromedially give rise to neurons of the peripheral nervous system. It is also known that neural crest cell-derived populations require appropriate environmental cues early in development in order to generate neurons, and for the subsequent survival of differentiated neurons. We examined whether neurotrophin-3 (NT-3), a survival factor for subsets of peripheral neurons, is also involved in the regulation of neurogenesis by neural crest cells. First, we found that premigratory and migrating neural crest cells on the medial migration pathway of Embryonic Day 2.5 (E 2.5) embryos express mRNAS encoding multiple isoforms of the NT-3 receptor, trkC, as do cells in the neural tube and epithelial dermamyotome. On E4, a subpopulation of neurons in nascent sensory ganglia express trkC message. Second, we demonstrate that trkC mRNA is only expressed in neural crest cell populations that possess neurogenic potential. Third, we show that the presence of NT-3, during the initial development of cultured neural crest cells, is required for neurogenesis by a subpopulation of neurogenic neural crest-derived cells. These results suggest that a subpopulation of neurogenic neural crest cells expresses functional trkC receptors and requires the timely availability of NT-3 for their development before reaching their final embryonic locations. We suggest that developmental heterogeneity exists in the identity and requirements of neural crest cell subsets that harbor neurogenic potential. We also suggest that the 'paradoxical' expression of trkC receptors by the somitic dermamyotome may, in fact, play a role in the exclusive development of crest-derived neurogenic precursors on the medial pathway by limiting the availability of NT-3 on the lateral pathway.

We analyzed the developmental regulation and role of the neurotrophins during metanephric kidney morphogenesis. RNase protection assay revealed the presence of nerve growth factor, neurotrophin 3 (NT-3), and brain-derived neurotrophic factor mRNAs and the regulation of their expression during embryonic development of rat metanephros. NT-3 induced differentiation (neurite outgrowth) and survival (inhibition of apoptosis) of the neuronal precursors in cultured nephrogenic mesenchymes and neuronal differentiation in cultured whole kidneys, whereas NT-4/5, brain-derived neurotrophic factor, and nerve growth factor were without effect. The neurotrophins did not trigger tubular differentiation of isolated nephrogenic cells, which underwent apoptosis when cultured with or without the neurotrophins. NT-3 is thus an inducer of differentiation and a survival factor for renal neuronal cells, but none of the neurotrophins is a morphogen in kidney tubule induction.

Recurrent stress increases the amount of neurotrophin 3 (NT-3) mRNA expressed in the noradrenergic neurons of the locus coeruleus (LC) while antidepressants decreases the amount of NT-3 mRNA. However, only those antidepressants which inhibit the uptake of norepinephrine cause this decrease in NT-3 mRNA while those that inhibit the uptake of serotonin do not have any effect. The amount of NT-3 mRNA in the LC and hippocampus decreases as a effect of electroconvulsive seizures. The level Ntrk3, NT-3 receptor, is unaffected by stress or antidepressants.

A study used a recombinant receptor technique to establish the capacity of the various structural entities within the extracellular domain of neurotrophic receptors (TrkB) to bind the various neutrophins. Brain-derived neurotrophic factor, neurotrophin-3, and neutrophin-4 bound to the LRM3 cassette of TrkB. However, nerve growth factor did not bind. These results indicate in vivo specificities.

A transgenic mouse model was developed to examine the role of nerve growth factor (NGF) during sensory neural development. In the model, NGF expression was increased by placing a NGF minigene under the transcriptional control of the cardiac-specific alpha-myosin heavy chain promoter. Immunohistochemical analysis revealed subpopulation of ectopic cells derived from the neural crest and an increase in myocardial mass. This suggests that increased NGF is produced by hyperinnervation of the heart and expansion of neural crest-cell types.

Pan-neurotrophin 1 (PNT-1), a synthetic trophic factor, helps treat peripheral neuropathies and nerve damage. A combination of the active domains of neurotrophin 3, neurotrophins nerve growth factor and brain-derived neutrophic factor results in PNT-1, which effectively aids the survival of many embryonic dorsal root ganglion neurons. Sensory neurons are affected by PNT-1, which is produced in insect cells infected with baculovirus and in COS cells.

Analysis of explant cultures of adult rat forebrain subependymal zone (SZ) exposed to brain-derived neurotrophic factor (BDNF) suggests that BDNF enhances the survival of neurons generated by this zone. BDNF also enables neuronal recruitment and maturation in adulthood. The high-affinity receptor for BDNF, trkB, is expressed in the surviving cells.

Analysis of the expression of neurotrophins and neurotrophin receptor in medulloblastoma samples reveal that all the tumors display the expression of neurotrophin 3 mRNA and neurotrophin receptor Trkc expression. Trkc expression was variable and patients with high trkC mRNA expression display longer intervals and lack of disease progression than those that display lower levels and a suitable survival. Thus, trkC expression functions as a prognostic indicator of medulloblastoma.

A new member of the nerve growth factor family, neurotrophin-6 (NT-6), is cloned from the teleost fish Xiphophorus. NT-6 is unique from other neurotrophins as it is not present as a soluble protein in the cell proliferation medium. The embryonic valvulla cerebelli records NT-6 expression which remains in a few adult tissues. The NF-6 activity in the nervous system might be regulated by the interaction between NT-6 and heparin binding molecules. Introduction of heparin evokes NT-6 discharge from cell surface and extracellular matrix molecules.

A comparative study of the binding affinities of alpha(2)-macroglobulin with various nerve growth factors and neurotrophins in equilibrium conditions shows that neurotrophin-4 exhibits the highest binding affinity for alpha(2)M. The binding affinity between ciliary neurotrophic factor and alpha(2)M is negligible. Use of the cross-binding agent bis(sulfosyccinimidyl) suberate helps determine the binding in solution and the minimum binding prevents the determination of affinity constant.

Immunocytochemistry and Northern blot analysis of the effect of neurotrophins on the functions of GABA neurotransmitter shows that brain-derived neurotrophic factor (BDNF) increases cellular GABA levels and striatal GABAergic neuron differentiation without affecting neuron viability. BDNF increases the holoenzyme functions of GABA synthetic enzyme glutamic acid decarboxylase (GAD) and GABA uptake activity. Striated neurons have high GAD activity due to the GAD(67)-encoding mRNA upregulation, indicating the catalytic role of BDNF in neuron differentiation.

Neurotrophins (NT) regulate neuronal function during the growth and development of the central nervous system. NTs synthesize transcellular peptides and enzymes, regulate cellular calcium-binding of several proteins and enhance the resistivity of neurons to oxidative stress, axon transections, amino acid damage and elimination of afferent nerve. Three receptor tyrosine kinases, trk A, trk B and trk C, mediate NT functions that are similar to the brain-derived neurotrophic factor (BDNF). NT knockouts determine the number of neurons that enter the maturity stage.

The physiological characteristics of neurotrophin-3-deficient mice produced by gene targeting are investigated. These mice exhibit extreme movement defects in the limbs. Most of them died after birth. The neurons were severely affected due to the absence of neurotrophin.

Human nerve growth factor (hNGF), neurotrophins (NT-3), brain-derived neurotrophic factor (BDNF) and neurotrophins (NT-415) of the neurotrophin family are analyzed using solvent denaturation method. The proteins exhibit structural differences during folding and unfolding. BDNF has the highest structural stability, and hNGF the lowest. The folding and unfolding equilibrium curves of BDNF and NT-3 coincide only at certain pH values. The stability of the proteins decreases with reduction in the pH value.

A study of brain-derived neurotrophic factor (BDNF) null mutation reveals that nervous system cell types such as neurons in multiple sensory ganglia, cerebral cortex, the hippocampus and the striatum require BDNF for normal development. BDNF controls brain differentiation in infants, as indicated by the diminished expression of neuropeptide and calcium binding proteins.

A stably expressed, truncated, p75 receptor in PC12 rat pheochromocytoma cells were used to explore the importance of the two nerve growth factor receptors, low-affinity p75 neurotrophin and the Trk receptor tyrosine kinase. Cells with significantly lowered levels of wild-type p75 and oral Trk levels were obtained. High affinity binding can be operationally unrelated to biological responses, and can be developed only with right proportions of p75 p140 Trk.

The spontaneous and impulse-evoked synaptic activity of developing neuromuscular synapses in culture is rapidly potentiated by the acute exposure to neurotrophin-3 (NT-3)3, 4 or brain derived neurotrophic factor (BDNF)5. The effect, which is presynaptic in origin, is mediated by the Trk family of receptor tryosine kinases. Evidence is provided for the regulation of the function of developing synapses by neurotrophins.

A study was conducted on the effect of brain-derived neurotrophic factor (BDNF), neurotrophin-3 and neurotrophin-5 on the survival of motor neurons obtained from the ventral spinal cord of rat embryos. Results showed that the three neurotrophins, in picomolar concentrations, successfully prevented spinal motor neuron death. mRNA coding for neurotrophins was also detected in spinal cord and limb bud and mRNA for their receptors was also found in motor neurons. These results indicate that BDNF, neurotrophin-5 and neurotrophin-3 are potential physiological motor neuron growth factors.

The gene encoding for the human homologue of neurotrophin-4 (NT-4) was cloned and analyzed using ssequences specific to Xenopus-derived NT-4. Results show that the human NT-4 gene is located at chromosome 19 and contains a truncated pro region not found in previously described neurotrophins. It alsohas a seven-residue insertion at its mature region and has a gene sequence thatis only 65% homologous to Xenopus NT-4. Despite this low homology, human and Xenopus NT-4 contain many neuronal and receptor similarities, and may be considered as functional, as well as structural counterparts.

The first total synthesis of racemic jiadifenin (1), the establishment of a modality for its biological evaluation and the discovery of a potent neurotrophic activity in fully synthetic compound (1R,10S)-2-oxo-3,4-dehydroneomajucin are reported. Measuring the ability of 1 to stimulate NGF-mediated neurite outgrowth under the given protocols validates the neurotrophic activity of the fully synthetic 1.

A study is conducted on developing sympathetic neurons which established that Nerve Growth Factor (NGF), a member of the neurotropin (NT) family, activates TrkA receptors on axon terminals and signals retrograde to cell bodies to regulate survival and differentiation. The difference of NGF and NT-3 is explained as the ability of NGF to support survival and differentiation, but not NT-3, to induce internalization and retrograde transport of activated TrkA.

An introduction of neurotrophins, that are a family of growth factors critical for the development and functioning of the nervous system is given. In addition, studies indicate that the nature of the signaling cascades activated by neurotrophins, and the biological responses that result, are specified not only by the ligand itself, but also by the temporal pattern and spatial location of stimulation.

Gene-targeting of mice to generate gene null mutations to encode receptors for neurotrophins resulted in prominent defects in mice anatomy and behavior. Neurotrophins, which prevent the termination of developing neurons, are essential to cell survival in tissues and are associated with the receptor tyrosine kinases.

A study conducted by Christopher E. Henderson et al revealed that recombinant brain-derived neurotrophic factor (BDNF), neurotrophin-3 (NT-3) and neurotrophin-4/5 can promote the survival of purified rat motor neurons in vitro. In addition, the study found evidence suggesting that each neurotrophin has its own specific receptor and that NT-3 and BDNF mRNAs exist in skeletal muscle during the stage when the neurons grow into the muscle and compete for these factors. These findings bring science closer to the possibility of developing cures for various neurodegenerative motor neuron diseases.