Caloric restriction increases neurotrophic factor levels and attenuates neurochemical and behavioral deficits in a primate model of Parkinson's disease

We report that a low-calorie diet can lessen the severity of neurochemical deficits and motor dysfunction in a primate model of Parkinson's disease. Adult male rhesus monkeys were maintained for 6 months on a reduced-calorie diet [30% caloric restriction (CR)] or an ad libitum control diet after which they were subjected to treatment with a neurotoxin to produce a hemiparkinson condition. After neurotoxin treatment, CR monkeys exhibited significantly higher levels of locomotor activity compared with control monkeys as well as higher levels of dopamine (DA) and DA metabolites in the striatal region. Increased survival of DA neurons in the substantia nigra and improved manual dexterity were noted but did not reach statistical significance. Levels of glial cell line-derived neurotrophic factor, which is known to promote the survival of DA neurons, were increased significantly in the caudate nucleus of CR monkeys, suggesting a role for glial cell line-derived neurotrophic factor in the anti-Parkinson's disease effect of the low-calorie diet.

Brn-3c (POU4F3) regulates BDNF and NT-3 promoter activity

Brn-3c is a transcription factor necessary for maturation and survival of hair cells in the inner ear. Mutations in Brn-3c are associated with deafness in mice and with hearing loss in humans. Mice lacking Brn-3c also show reduced innervation and loss of sensory neurons presumed to be an indirect effect of hair cell loss potentially through lower BDNF and NT-3 expression. Using transient transfection assays we show that Brn-3c is capable of activating both BDNF and NT-3 promoters in inner ear sensory epithelial cell lines. In vitro analysis shows that Brn-3c binds to specific elements within the promoters of both genes and these elements are sufficient to confer Brn-3c regulation on a heterologous promoter. Additionally, BDNF expression is reduced in the inner ear of a Brn-3c mutant mouse during embryogenesis. Our data suggest that Brn-3c may play a role in regulating neurotrophin gene expression in the inner ear.

Human and murine lymphocyte neurotrophin expression is confined to B cells

Recent reports indicate that autoreactive T cells may produce neurotrophic factors capable of mediating repair and regeneration of damaged neurons. By using semiquantitative RT-PCR, we examined gene expression of nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), neurotrophin-3 (NT-3), and the trkB BDNF receptor in autoreactive T cells from SWXJ mice immunized with the p104-117 encephalitogen of myelin proteolipid protein (PLP 104-117). We observed antigen-inducible expression of NGF and BDNF, but not NT-3 and trkB, in lymph node cells activated with PLP 104-117. To determine which leukocyte subpopulation expressed neurotrophins, CD4(+), CD8(+), B220(+), CD11b(+), and NK1.1(+) cells were purified from activated primary cultures, and their mRNAs were analyzed. Neurotrophin expression was also measured in CD3(+) T cells purified from mouse CNS during acute onset of experimental autoimmune encephalomyelitis as well as in resting and activated human T cells and B cells purified from peripheral blood of normal subjects. In all cases, we found that neurotrophin expression was confined exclusively to B cells (B220(+)) in both mouse and human. CD3(+), CD4(+), and CD8(+) T cells as well as NK1.1(+) cells and CD11b(+) monocytes and macrophages did not express any detectable BDNF, NGF, NT-3, or trkB under any conditions. Our data indicate that B cells rather than T cells are the predominant if not the only source of leukocyte-derived neurotrophins and as such may provide "protective autoimmunity" in repair and regeneration of the injured nervous system.

Continuous supply of the neurotrophins BDNF and NT-3 improve chick motor neuron survival in vivo

Following neurogenesis, motor neurons undergo a phase of large-scale neuronal loss. During this period, the motor neurons are responsive to specific trophic factors for their survival. Several neurotrophic factors, including the neurotrophins BDNF and NT-3, have survival effects although no single factor has been shown to support the survival of all motor neurons. It is unclear whether this is due to factor deprivation during the study or whether there are distinct neuronal subpopulations dependent on different factor requirements. In this study, we have used an expression system to supply a continuous source of BDNF and/or NT-3 to the developing motor neurons in the chick. Continuous supply of BDNF resulted in the survival of 40% of the motor neurons normally lost between embryonic day 6 and embryonic day 10, whereas NT-3 supported 36% of the motor neurons normally lost. In combination, BDNF and NT-3 supported 62% of the motor neurons normally lost indicating that there is some redundancy in neurotrophin requirements. Our results show that a continuous supply of neurotrophins is more effective in promoting motor neuron survival than intermittent administration, particularly for NT-3. However, even with continuous administration of both factors in combination we are unable to support all motor neurons that would normally undergo neuronal degeneration.

Quantitative analyses of mRNA and protein levels of neurotrophin-3 in the rat retina during postnatal development and aging

PURPOSE

In this study, we sought to elucidate changes in the levels of neurotrophin-3 (NT-3) in the rat retina throughout postnatal development and aging.

METHODS

We demonstrated NT-3 localization in the retina by immunohistochemistry. Protein and mRNA levels of NT-3 were quantified by enzyme-linked immunosorbant assay and semiquantitative reverse transcriptase-polymerase chain reaction, respectively. NT-3 protein levels were assayed in the various regions of the central nervous system. Age-associated changes in protein and mRNA levels of NT-3 in the retinas were assessed.

RESULTS

NT-3-immunoreactivity localized in the ganglion cell layer, inner nuclear layer, and outer nuclear layer. NT-3 content in the retina was relatively high in the examined regions of the central nervous system. Retinal NT-3 protein levels decreased after eye opening, whereas mRNA levels were constant. Both mRNA and protein levels of NT-3 in the retinas of aged animals remained constant.

CONCLUSIONS

Our observations suggest that NT-3 regulation in the retina is independent of increasing visual stimuli after eye opening. Stable expression of NT-3 in the adult retina suggests a possible role in the maintenance of the retinal environment throughout later life.

Evidence for the involvement of neurotrophins in muscle transdifferentiation and acetylcholine receptor transformation in the esophagus ofMyf5−/−:MyoD−/−andNT-3−/−embryos

The primary aim of our study was to determine whether the esophageal innervation (i.e., vagal and enteric) and the skeletal muscle-secreted neurotrophins have a role in smooth-to-skeletal muscle transdifferentiation and in the muscarinic-to-nicotinic acetylcholine receptor type transition. To that end, we used genetically engineered embryos and immunohistochemistry. We found that, in the absence of Myf5 and MyoD, the esophageal muscle cells failed to develop the striated phenotype of acetylcholine receptors. In addition, the development of vagal and enteric innervation was delayed in Myf5(-/-):MyoD(-/-) and NT-3(-/-) mutants, but it was reestablished 2 days before the end of gestation. The smooth muscle cells in the esophagus appeared to be a distinct subpopulation of cells and their ability to transdifferentiate was based on their competence to express neurotrophins and their receptors. Finally, our data suggest a role for NT-3 in the esophageal muscle transdifferentiation.

A chemoattractant role for NT-3 in proprioceptive axon guidance

Neurotrophin-3 (NT-3) is required for proprioceptive neuron survival. Deletion of the proapoptotic gene Bax in NT-3 knockout mice rescues these neurons and allows for examination of their axon growth in the absence of NT-3 signaling. TrkC-positive peripheral and central axons from dorsal root ganglia follow proper trajectories and arrive in close proximity to their targets but fail to innervate them. Peripherally, muscle spindles are absent and TrkC-positive axons do not enter their target muscles. Centrally, proprioceptive axons branch in ectopic regions of the spinal cord, even crossing the midline. In vitro assays reveal chemoattractant effects of NT-3 on dorsal root ganglion axons. Our results show that survival factor NT-3 acts as a short-distance axon guidance molecule for muscle sensory afferents as they approach their proper targets.

Ethanol-induced reduction of neurotrophin secretion in neonatal rat cerebellar granule cells is mitigated by vitamin E

Ethanol exposure during nervous system development produces a range of abnormalities, and in humans may lead to the fetal alcohol syndrome. Among the mechanisms hypothesized to play roles in ethanol neurotoxicity are altered expression of supportive neurotrophic factors (NTFs), and cellular disturbances in oxidative processes. In this study, ethanol effects on secretion of two NTFs, brain-derived neurotrophic factor, and neurotrophin-3 were analyzed in neonatal rat cerebellar granule cells, and the potential of the antioxidant vitamin E to modulate ethanol effects was investigated. Ethanol exposure in these preparations reduced NTF secretion, but vitamin E appreciably ameliorated the ethanol effects. Possible mechanisms underlying both the ethanol effects on NTF secretion, and the protection of this antioxidant are considered.

Differences in the surface binding and endocytosis of neurotrophins by p75NTR

Neurotrophins transmit signals retrogradely from synapses to cell bodies by two different types of surface receptors, p75NTR and Trks. Compared to TrkA, the function of p75NTR in nerve growth factor (NGF) endocytosis is less clear, and it is unknown whether p75NTR by itself may internalize other neurotrophins besides NGF. We directly compared TrkA and p75NTR for their ability to internalize NGF, and we also examined the endocytosis of iodinated brain-derived neurotrophic factor (BDNF) and neurotrophin-3 (NT3) by p75NTR. Cells expressing solely TrkA internalized NGF more efficiently than cells expressing p75NTR. Surprisingly, cells expressing only p75NTR internalized far more BDNF or NT3 than NGF. Moreover, p75NTR was more important for surface binding than for intracellular accumulation of each neurotrophin. Finally, we established a mechanistic role for the clathrin pathway in p75NTR endocytosis. Our results suggest that p75NTR may have multiple roles in different subcellular locations, functioning both at the cell surface and also within endocytic compartments.

Going the distance, or not, with neurotrophin signals

NGF and NT-3 both signal through TrkA receptors on the axons of developing sympathetic neurons, but while NGF supports survival and differentiation, NT-3 does not. In this issue of Cell, the difference is explained as the ability of NGF, but not NT-3, to induce internalization and retrograde transport of activated TrkA.

Autocrine regulation of nerve growth factor expression by Trk receptors

Activation of the neurotrophin receptor Trk induces the release of neurotrophins. However, little is known about the ability of released neurotrophins to modulate their own synthesis in an autocrine manner. As a step towards understanding the role of Trk in regulating the synthesis of neurotrophins, we exposed NIH-3T3 cells expressing TrkA or TrkC receptors to their cognate ligands as well as to GM1, a ganglioside that activates TrkA and TrkC by inducing the release of neurotrophin-3. Nerve growth factor and neurotrophin-3 synthesis were then determined by measuring the relative levels of protein and mRNA. TrkA-expressing cells exposed to human recombinant nerve growth factor exhibited higher levels of nerve growth factor mRNA. Human recombinant neurotrophin-3 evoked an increase in nerve growth factor mRNA in both TrkA and TrkC-expressing cells. GM1 elicited a time-dependent increase in nerve growth factor protein and mRNA in NIH-3T3 cells expressing TrkA or TrkC receptor but not in wild-type cells. Surprisingly, GM1 failed to change neurotrophin-3 levels. The ability of GM1 to increase nerve growth factor mRNA levels was blocked by TrkC-IgG but not by TrkB-IgG receptor body. These data suggest that released neurotrophin-3 may activate a positive autocrine loop of nerve growth factor synthesis by Trk activation.

Bone morphogenetic protein-2 and -4 limit the number of enteric neurons but promote development of a TrkC-expressing neurotrophin-3-dependent subset

The hypothesis that BMPs (bone morphogenetic proteins), which act early in gut morphogenesis, also regulate specification and differentiation in the developing enteric nervous system (ENS) was tested. Expression of BMP-2 and BMP-4, BMPR-IA (BMP receptor subunit), BMPR-IB, and BMPR-II, and the BMP antagonists, noggin, gremlin, chordin, and follistatin was found when neurons first appear in the primordial bowel at embryonic day 12 (E12). Agonists, receptors, and antagonists were detected in separated populations of neural crest- and noncrest-derived cells. When applied to immunopurified E12 ENS precursors, BMP-2 and BMP-4 induced nuclear translocation of phosphorylated Smad-1 (Sma and Mad-related protein). The number of neurons developing from these cells was increased by low concentrations and decreased by high concentrations of BMP-2 or BMP-4. BMPs induced the precocious appearance of TrkC-expressing neurons and their dependence on neurotrophin-3 for survival. BMP-4 interacted with glial cell line-derived neurotrophic factor (GDNF) to enhance neuronal development but limited GDNF-driven expansion of the precursor pool. BMPs also promoted development of smooth muscle from mesenchymal cells immunopurified at E12. To determine the physiological significance of these observations, the BMP antagonist noggin was overexpressed in the developing ENS of transgenic mice under the control of the neuron-specific enolase promoter. Neuronal numbers in both enteric plexuses and smooth muscle were increased throughout the postnatal small intestine. These increases were already apparent by E18. In contrast, TrkC-expressing neurons decreased in both plexuses of postnatal noggin-overexpressing animals, again an effect detectable at E18. BMP-2 and/or BMP-4 thus limit the size of the ENS but promote the development of specific subsets of enteric neurons, including those that express TrkC.

PACAP promotes sensory neuron differentiation: blockade by neurotrophic factors

Developing neurons encounter a panoply of extracellular signals as they differentiate. A major goal is to identify these extrinsic cues and define the mechanisms by which neurons simultaneously integrate stimulation by multiple factors yet initiate one specific biological response. Factors that are known to exert potent activities in the developing nervous system include the NGF family of neurotrophic factors, ciliary neurotrophic factor (CNTF), and pituitary adenylate cyclase-activating peptide (PACAP). Here we demonstrate that PACAP promotes the differentiation of nascent dorsal root ganglion (DRG) neurons in that it increases both the number of neural-marker-positive cells and axonogenesis without affecting the proliferation of neural progenitor cells. This response is mediated through the PAC1 receptor and requires MAP kinase activation. Moreover, we find that, in the absence of exogenously added PACAP, blockade of the PAC1 receptor inhibits neuronal differentiation. These data coupled with our finding that both PACAP and the PAC1 receptor are expressed during the peak period of neuronal differentiation in the DRG suggest that PACAP functions in vivo to promote the differentiation of nascent sensory neurons. Interestingly, we also demonstrate that the neurotrophic factors NT-3 and CNTF completely block the PACAP-induced neuronal differentiation. This points to the intricate integration of cellular signals by nascent neurons and, to our knowledge, is the first evidence for neurotrophic factor abrogation of a pathway regulated by G-protein-coupled receptors (GPCRs).

A Neurotrophin Signaling Cascade Coordinates Sympathetic Neuron Development through Differential Control of TrkA Trafficking and Retrograde Signaling

A fundamental question in developmental biology is how a limited number of growth factors and their cognate receptors coordinate the formation of tissues and organs endowed with enormous morphological complexity. We report that the related neurotrophins NGF and NT-3, acting through a common receptor, TrkA, are required for sequential stages of sympathetic axon growth and, thus, innervation of target fields. Yet, while NGF supports TrkA internalization and retrograde signaling from distal axons to cell bodies to promote neuronal survival, NT-3 cannot. Interestingly, final target-derived NGF promotes expression of the p75 neurotrophin receptor, in turn causing a reduction in the sensitivity of axons to intermediate target-derived NT-3. We propose that a hierarchical neurotrophin signaling cascade coordinates sequential stages of sympathetic axon growth, innervation of targets, and survival in a manner dependent on the differential control of TrkA internalization, trafficking, and retrograde axonal signaling.

[Study on early motor neurotrophism of denervated red and white muscles]

OBJECTIVE

To investigate the early change of brain-derived neurotrophic factor (BDNF) in denervated red and white muscles and the regeneration of nerves innervating the muscles and to discuss the effect of the target organs on regeneration of the injured nerves.

METHODS

Forty Wistar rats were divided into 5 groups. The sciatic nerves in 4 groups were sheared to make the models of the denervated muscles and the other one as control group. The amount of BDNF in muscles was measured with immunohistochemistry 1 day, 3 days, 7 days and 14 days after injury. The models of the regeneration of the nerves were made in another 15 rats whose sciatic nerves were disconnected with forceps. The nerve conduction velocity and electromyogram were tested with neuroelectrophysiology 7 days and 14 days after injury.

RESULTS

The expression of BDNF in soleus increased significantly on the 1st day, the 3rd day and the 7th day (P<0.01); the expression in gastrocnemius was lower, but there was no significant difference (P>0.05) on the 1st day, the 3rd day, the 7th day and the 14th day when compared with control group. After 14 days of injury in the nerves innervating GAS and SOL, the nerve conduction velocities and the amplitudes of wave M recovered to (36.60+/-7.40)% and (19.9+/-6.4)% of normal value, and (42.50+/-3.50)% and (13.7+/-4.0)% of normal value respectively; there were no significant differences between the two muscles (P>0.05).

CONCLUSION

There is difference in BDNF amount between the denervated red and white muscles, but the recovery of the two kinds of the motor nerves is similar, and the neurotrophism of denervated muscles was determined by all kinds of neurotrophic factors.

Real-time quantitative RT-PCR for low-abundance transcripts in the inner ear: analysis of neurotrophic factor expression

Real-time quantitative reverse transcription-PCR is a highly sensitive technology that allows high throughput quantification of gene expression. Application of this technique to the inner ear is potentially very important, but is not straightforward because tissue harvesting can be challenging, RNA yield from individual inner ears is low, and cDNA synthesis from scant RNA can be inefficient. To overcome these challenges, we tested many parameters and reagents, and developed an approach to reliably quantitate small changes in low-abundance transcripts. Using this technique we demonstrate the presence and quantify amounts of the neurotrophic factors neurotrophin 3 (NT-3), brain-derived neurotrophic factor (BDNF) and glial cell-line-derived neurotrophic factor (GDNF), in the cochlea and vestibular end organs of postnatal murine inner ear (P26). We show that out of the factors tested, BDNF is the only one differentially expressed between the cochlea and vestibular end organs, being 23.4+/-0.3 times more abundant in the vestibular end organs. Within the cochlea, GDNF gene expression is 4.9+/-0.2 times greater than NT-3 expression. Within the combined vestibular end organs, BDNF expression is 43.0+/-1.5 times greater than NT-3 expression. Our results suggest that neurotrophic factors continue to play a role in the postnatal inner ear, in addition to their previously shown essential role during development.

Neurogenic cells in human amniotic fluid

OBJECTIVE

The purpose of this study was to determine whether human amniotic fluid contains cells that harbor the potential to differentiate into neurogenic cells.

STUDY DESIGN

Amniotic fluid cells (uncultivated or cultivated in standard or in neurogenic differentiation medium) were analyzed for morphologic neurogenic differentiation and for expression of cluster of differentiation 133 (marker for neuronal stem cells), nestin (neuronal progenitor cells), neurofilament (neurons), the p75 common neurotrophin receptor, the brain-derived neurotrophic factor and neurotrophin-3 and cyclic nucleotide phosphodiesterase (oligodendrocytes).

RESULTS

The appearance of neurogenic cells was not detected in uncultivated cells, was sporadic after cultivation in standard medium but strongly increased in neurogenic differentiation medium, and was accompanied by the induction of the expression of the analyzed marker genes.

CONCLUSION

For the first time, this study provides evidence that human amniotic fluid contains cells that express markers for neuronal stem and progenitor cells, which harbor the potential to differentiate into neurogenic cells.

Elevated glial brain-derived neurotrophic factor in Parkinson's diseased nigra

We show the cellular distribution of immunoreactivity (IR) for brain-derived-neurotrophic-factor (BDNF), neurotrophin-3 (NT-3) and tyrosine kinase receptors TRKB and TRKC in idiopathic Parkinson's disease (IPD) and controls at post-mortem. In both groups, nigral neurons, astrocytes, ramified and amoeboid microglia expressed all antigens. Caudate-putamen neurons expressed all antigens except BDNF with similar distribution between groups. In IPD nigra, increased numbers of BDNF-IR and, less frequently, NT-3-IR ramified glia surrounded fragmented neurons, accompanied by BDNF-IR in surrounding neuropil. Amoeboid microglia were abundant only in IPD nigral scars. In IPD, glia might up-regulate neurotrophins in response to signals released from failing nigral neurons.

Blocked MAP kinase activity selectively enhances neurotrophic growth responses

Bone morphogenetic proteins (BMPs) 4 and 6 as well as MEK inhibitors PD98059 and U0126 potentiate neurotrophin 3 (NT3)- and neurturin (NTN)-induced neurite outgrowth and survival of peripheral neurons from the E9 chicken embryo. Preexposure to BMP4 or PD98059 was sufficient to prime the potentiation of subsequently added NT3. Phosphorylation of Erk2, induced by NT3, was reduced by MEK inhibition but unaffected by BMP signaling. Real-time PCR showed that neither BMP stimulation nor MEK inhibition increased Trk receptor expression and that the BMP-induced genes Smad6 and Id1 were not upregulated by PD98059. In contrast, both MEK inhibition and BMP signaling suppressed transcription of the serum-response element (SRE)-driven Egr1 gene. A reporter assay using NGF-stimulated PC12 cells demonstrated that MEK/Erk/Elk-driven transcriptional activity was inhibited by Smad1/5 and by PD98059. Thus, suppression of SRE-controlled transcription represents a likely convergence point for pathways regulating neurotrophic responses.

Neurotrophin-3 and a CREB-mediated signaling pathway regulate Bcl-2 expression in oligodendrocyte progenitor cells

Our previous results suggested that the transcription factor CREB mediates the actions of neuroligands and growth factor signals that coupled to different signaling pathways may play different roles along oligodendrocyte (OLG) development. We showed before that CREB phosphorylation in OLG progenitors is up-regulated by neurotrophin-3 (NT-3); and moreover CREB is required for NT-3 to stimulate the proliferation of these cells. We now show that treatment of OLG progenitors with NT-3 is also accompanied by an increase in the levels of the anti-apoptotic protein Bcl-2. Interestingly, the presence of a putative CREB binding site (CRE) in the Bcl-2 gene raised the possibility that CREB could also be involved in regulating Bcl-2 expression in the OLGs. Supporting this hypothesis, the NT-3 dependent increase in Bcl-2 levels is abolished by inhibition of CREB expression. In addition, transient transfection experiments using various regions of the Bcl-2 promoter and mutation of the CRE site indicate a direct role of CREB in regulating Bcl-2 gene activity in response to NT-3. Furthermore, protein-DNA binding assays show that the CREB protein from freshly isolated OLGs indeed binds to the Bcl-2 promoter CRE. Together with our previous results, these observations suggest that CREB may play an important role in linking proliferation and survival pathways in the OLG progenitors.

Syntheses and activities of new C10 beta-turn peptidomimetics

A program to identify small molecules that mimic or disrupt protein-protein interactions led us to design the peptidomimetics 1-3. Solid-phase syntheses of 1-3 were developed. The purities of the crude materials isolated from the resin tend to be highest for the S- and N-compounds 2 and 3 and better than in the corresponding syntheses of peptidomimetics A. The particular dipeptide units incorporated were chosen to correspond with the turn regions of the neurotrophins (e.g., nerve growth factor [NGF] and the neurotrophin factor-3 [NT-3]). Preliminary studies were performed to access the binding of these analogues to Trk receptors and their ability to induce cell survival (just as NGF and NT-3 do). Several active compounds were identified. However, poor water solubilities of some of the other compounds preclude reliable testing. Consequently, solid-phase modifications to the synthetic procedures were investigated to provide access to the derivatives 12-14 in which the aromatic nitro group is replaced by amine, guanidine, or sulfonamide functionalities. The latter are more acceptable pharmacophores than nitro groups and also tend to increase the water solubilities of the peptidomimetics.

Nerve growth factor, brain-derived neurotrophic factor, and neurotrophin-3 are sorted to dense-core vesicles and released via the regulated pathway in primary rat cortical neurons

Neurotrophins (NTs) play an important role in the modulation of synaptic transmission and in morphological changes in synaptic structures. Although there is agreement that brain-derived neurotrophic factor (BDNF) is sorted to large dense-core vesicles (LDCVs) and released via the regulated secretory pathway, there has been some dispute regarding the mode of secretion of nerve growth factor (NGF) and neurotrophin-3 (NT-3), two structurally related members of the NT family. In this study, we examined the subcellular localization and release characteristics of NGF, BDNF, and NT-3 in adenovirus-infected primary cortical neurons. We found that all members of the NT family colocalized with markers for the endoplasmic reticulum and Golgi within cell bodies and in a punctate manner with a marker for LDCVs within processes. Moreover, their release was triggered by depolarization, indicating that NGF, BDNF, and NT-3 are released via the regulated secretory pathway. When neurons were coinfected with two separate adenoviruses coding for NGF or BDNF, both NTs showed almost complete vesicular colocalization within single cells, suggesting that different NTs might be packaged into shared vesicles. We also examined whether the two splice variants of NGF, the short and long precursors, differ in their release characteristics. We found that neurons infected with viruses coding for either splice variant released NGF in a regulated way. Overall, our study supports the notion that all members of the NT family undergo activity-dependent regulated release from neurons, enabling them to act as "synaptotrophins" on electrically active neurons.

Adrenalectomy further suppresses the NT-3 mRNA response to traumatic brain injury but this effect is not reversed with corticosterone

Fluid percussion injury (FPI) and in situ hybridisation were used to evaluate the expression of NT-3 mRNA in the hippocampus after traumatic brain injury (TBI) in adrenal-intact and adrenalectomised rats (with or without corticosterone replacement). FPI and adrenalectomy independently significantly reduced the expression of NT-3 mRNA in the dentate gyrus (DG) and CA2 region. The effects of adrenalectomy in the CA2 region were partially reversed with corticosterone. In adrenalectomised animals undergoing FPI, a further significant decrease in NT-3 mRNA was observed in the DG, but this was not reversed by corticosterone. Glucocorticoids may, therefore, play a role in the basal regulation of NT-3 in the hippocampus, but the role of glucocorticoids in the modulation of the NT-3 response to TBI is unclear.

Alterations in IGF-I, BDNF and NT-3 levels following experimental brain trauma and the effect of IGF-I administration

The effects of a unilateral, penetrating brain trauma on IGF-I, BDNF and NT-3 were studied immunocytochemically in the rat. BDNF and NT-3 were decreased in the peritraumatic area, but increased in the adjacent region, 4 and 12 h post-injury. One week following the trauma, BDNF remained low in the peritraumatic area, but was restored to normal levels in the adjacent, while no effect of injury on NT-3 levels was detected in either area. Injury resulted in an increase in IGF-I levels in the peritraumatic area, which was most pronounced 1 week following the trauma, indicating that IGF-I could participate in endogenous repair processes. We thus administered IGF-I immediately following the trauma and investigated its effects on injury-induced changes in neurotrophin levels. Administration of IGF-I partially reversed the injury-induced decrease in BDNF and NT-3 in the peritraumatic area observed 4 and 12 h post-injury, while at the same time-points, it completely cancelled the effects of injury in the adjacent region. One week after the trauma, BDNF levels were dramatically increased in both the peritraumatic and adjacent area, reaching levels even higher than those of the sham-operated animals, following IGF-I administration. Our results showing that IGF-I not only counteracts injury-induced changes in neurotrophins, but can also further increase their levels, indicate that this growth factor could mediate repair and/or protective processes, following brain trauma.

The effects of deafferentation and exogenous NGF on neurotrophins and neurotrophin receptor mRNA expression in the adult superior cervical ganglion

Levels of nerve growth factor (NGF) and neurotrophin-3 (NT-3) protein and neurotrophin receptor mRNA in adult sympathetic neurons were investigated following surgical removal of preganglionic input and/or in vivo administration of NGF. Expression of trkC and p75, but not trkA, was significantly decreased following a 3-week deafferentation of the superior cervical ganglion (SCG). Protein levels of NGF and NT-3 in the SCG were unchanged by deafferentation. A 2-week intracerebroventricular infusion of NGF without deafferentation resulted in enhanced mRNA levels of trkA, trkC, and p75 as well as significantly increased NGF and NT-3 protein in the SCG. When NGF infusion followed deafferentation, both trkA and p75 showed significant increases while trkC levels were similar to control values. NGF protein was not increased in the SCG when deafferentation preceded exogenous NGF, yet NT-3 was elevated and levels were similar to cases receiving NGF infusion only. These results support a role for preganglionic input in trkC and p75 expression in adult sympathetic neurons. The increased levels of NT-3 protein and trkC gene expression observed following NGF infusion suggest that NGF influences NT-3 regulation in adult sympathetic neurons. In addition, the present findings provide evidence that, when preganglionic input is removed prior to the NGF infusion, NT-3 effectively competes with NGF for trkA binding. Taken together, we propose that NT-3 may play a role in the robust sprouting of sympathetic cerebrovascular axons previously observed following NGF administration, particularly when deafferentation precedes the NGF infusion period.