Involvement of nerve growth factor in visual cortex plasticity

NGF and CNTF expression and regulation mechanism by miRNA in acute paralytic strabismus

BACKGROUND

Nerve growth factor (NGF) and ciliary neurotrophic factor (CNTF) are well-known neurotrophic factors and widely used in the clinical treatment for its promotion effect on peripheral nerve regeneration. And they were also recommended for the acute paralytic strabismus treatment. However, whether the NGF and CNTF have protective effect for the extraocular muscles of acute paralytic strabismus patients is still poorly understood.

PURPOSE

In this study, we want to evaluate the biological function of NGF and CNTF on the extraocular muscle cells and reveale the regulation mechanism behind it.

METHODS

Firstly, the relative expression of ngf and cntf was assessed by quantitative real-time RT-PCR. Then, the influence of NGF and CNTF on the extraocular muscle cell proliferation was determined by CCK-8. The inflammatory response in muscle cells after NGF and CNTF treatment was evaluated by ELISA and ROS detection. In addition to this, the up-stream regulation of the ngf and cntf expression was also studied. The TargetScan was used for the predication of potential miRNAs targeting with ngf and cntf 30-UTR, which is soon confirmed by luciferase activity assay.

RESULTS

all the results in this research indicated that NGF and CNTF could promote the muscle cell proliferation and inhibit the inflammatory levels, then exert protective effect on the muscle cell function.

RESULTS

All the results in this research indicated that NGF and CNTF could promote the muscle cell proliferation and inhibit the inflammatory levels, then exert protective effect on the muscle cell function.

CONCLUSION

It was conceivable that let 7-5p was the up-stream regulator of ngf and cntf, and let 7-5p might serve as a potential molecular target for acute paralytic strabismus treatment.

What has intrinsic signal optical imaging taught us about NGF-induced rapid plasticity in adult cortex and its relationship to the cholinergic system?

Intrinsic signal optical imaging (ISI) is a high-resolution functional brain mapping technique that is being used to further our understanding of the neocortex and its interaction with drugs. Recent studies using combination ISI and in vivo pharmacology have advanced our insight into the actions of both acetylcholine and neurotrophins on inducing rapid and large-scale cortical plasticity. In particular, it appears that acetylcholine (ACh), nicotinic ACh receptors, nerve growth factor (NGF), and NGF receptors (TrkA and p75) are involved in an important feedback loop between the basal forebrain cholinergic system (BFCS) and the neocortex. Specifically, recent data suggest that NGF expressed in the cortex may act on multiple time scales on the BFCS: acutely to increase BFCS release of acetylcholine, intermediately to induce sprouting of BFCS axons, and long-term to change gene expression of BFCS neurons. In this article, advances in understanding the links in vivo between the BFCS, neocortex, nicotinic ACh receptors, and NGF are reviewed.

Nerve growth factor and doublecortin expression correlates with improved outcome in children with severe traumatic brain injury

BACKGROUND

In the adult brain, migrating neuroblasts can replace damaged neurons after severe traumatic brain injury (TBI). Little is known about which factors determine the magnitude and amplification of neurogenesis after TBI, but there are some evidences that the nerve growth factor (NGF) and the doublecortin (DCX) can influence neurogenesis and neuronal repair.

METHODS

This study investigates the NGF and DCX levels in the cerebrospinal fluid of 12 children with severe TBI and 12 matched controls, to determine the correlation between the expression of both these factors and the patients outcome. We collected cerebrospinal fluid samples 2 hours (Time T1) and 48 hours (Time T2) after brain injury. NGF levels were measured using a two-site immunoenzymatic assay, whereas the DCX expression by a Western blot analysis.

RESULTS

At time T1 and T2, children with the best outcomes had higher levels of NGF than children with poor outcomes. Evaluating the change of NGF levels from time T1 to time T2, we found that the NGF up-regulation in the early time after injury was significantly associated with good outcomes of patients. Concomitantly, the expression of DCX increased only in patients with NGF up-regulation from time T1 to time T2. In others patients and in controls the expression of DCX remained unchanged.

CONCLUSION

Based on these results, we hypothesize that NGF and DCX contribute to the mechanisms of neuroprotection and neuronal connection reorganization after TBI, playing a key role in the outcome of these patients.

Postnatal expression profile of OBCAM implies its involvement in visual cortex development and plasticity

This study examined the expression of a neuron-specific cell adhesion molecule, OBCAM (opioid-binding cell adhesion molecule), at both the mRNA and protein levels in the cat primary visual cortex at various postnatal ages, using cDNA array analysis and immunocytochemistry. Results obtained using both methods showed that the expression level of OBCAM was high in young and low in older and adult visual cortex. OBCAM-immunoreactivities were associated predominantly with perikarya and dendrites of pyramidal neurons, and OBCAM-immunopositive neurons were present in all cortical layers. Immunostaining of OBCAM in adult visual cortex showed a reduced number of immunopositive neurons and neurites and relatively lower staining intensities as compared with younger animals. In addition, the number of OBCAM-immunopositive neurons was significantly higher in the visual cortex of 4-month-old animals dark-reared from birth than those in age-matched normally reared animals. These results suggest that OBCAM may play an important role in visual cortex development and plasticity.

Microarray analysis of developmental plasticity in monkey primary visual cortex

We performed microarray gene expression analyses on the visual cortex of Old-World monkeys (Cercopithicus aethiops) in an effort to identify transcripts associated with developmental maturation and activity-driven changes during the visual critical period. Samples derived from normal animals and those subjected to monocular enucleation (ME) were hybridized to human Affymetrix HG-U95Av2 oligonucleotide microarrays (N = 12) and the results were independently validated by real-time quantitative RT-PCR. To identify genes exhibiting significant expression differences among our samples, the microarray hybridization data were processed with two software packages that use different analytical models (Affymetrix MicroArray Suite 5.0, dChip 1.2). We identified 108 transcripts within diverse functional categories that differed in their visual cortical expression at the height of the critical period when compared to adults. The expression levels of four transcripts were also globally modulated following ME during the critical period. These transcripts are particularly sensitive to ME during the critical period but are not significantly modulated in ME adults. Three of the ME-driven genes (NGFI-B, egr3, NARP) are known immediate-early genes (IEG) while the other (DUSP6) is a phosphatase that can regulate IEG expression. The putative biological significance of the ME-driven and developmentally regulated genes is discussed with respect to the critical period for activity-dependent visual cortical neuroplasticity.

Postnatal changes in nerve growth factor and brain derived neurotrophic factor levels in the retina, visual cortex, and geniculate nucleus in rats with retinitis pigmentosa

Royal College of Surgeons (RCS) rats are a well established animal model of inherited retinitis pigmentosa (RP). Using RCS rats we examined the distribution of nerve growth factor (NGF) and brain derived neurotrophic factor (BDNF) in the visual cortex, geniculate nucleus and retina at three different postnatal ages. It was found that the retina of rats with RP expresses low amounts of NGF and BDNF in young and adult life. Altered levels of these factors were found in the visual cortex and in the geniculate nucleus. Our findings indicate that NGF and BDNF are differentially affected in the visual system of developing and adult RCS rats, suggesting that neurotrophins may be implicated in the pathogenesis of inherited RP.

Effect of hypergravity on the mouse basal expression of NGF and BDNF in the retina, visual cortex and geniculate nucleus: correlative aspects with NPY immunoreactivity

We investigated the effect of hypergravitation on Nerve growth factor (NGF) and Brain-derived-neurotrophic factor (BDNF) expression in the visual cortex, geniculate nucleus (GN), and retina of adult male mice. The results showed that altered gravity causes an increase in NGF and BDNF in the visual cortex and GN which resulted to be associated with an up-regulation of cells immunoreactive to neuropeptide Y (NPY) in the visual cortex and GN. We also found a decrease in NGF, BDNF, and NPY in the mouse retina exposed to hypergravity. These findings suggest that alteration in gravitational environment differentially affects local neurotrophic factors and NPY expression. The possible functional significance of these observations is discussed.

Conceptualizing functional neuroplasticity

There are at least four major forms of functional neuroplasticity that can be studied in humans: homologous area adaptation, cross-modal reassignment, map expansion, and compensatory masquerade. Homologous area adaptation is the assumption of a particular cognitive process by a homologous region in the opposite hemisphere. Cross-modal reassignment occurs when structures previously devoted to processing a particular kind of sensory input now accepts input from a new sensory method. Map expansion is the enlargement of a functional brain region on the basis of performance. Compensatory masquerade is a novel allocation of a particular cognitive process to perform a task. By focusing on these four forms of functional neuroplasticity, several fundamental questions about how functional cooperation between brain regions is achieved can be addressed.

Effects of neurotrophins on cortical plasticity: same or different?

Neurotrophins are important regulators of visual cortical plasticity. It is still unclear, however, whether they play similar or different roles and which are their effects on the electrical activity of cortical neurons in vivo. We therefore compared the effects of all neurotrophins, nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), neurotrophin-4 (NT-4), and neurotrophin-3 (NT-3) on visual cortical plasticity and on cell spontaneous and visually evoked activity. Rats were monocularly deprived for 1 week at the peak of the critical period, and neurotrophins were infused intracortically. The main finding is that, with the exception of NT-3, all neurotrophins affect the outcome of monocular deprivation, but there are clear differences in their mechanisms of action. In particular, NT-4 and NGF counteract monocular deprivation effects without causing detectable alterations either in spontaneous or visually evoked neuronal activity. BDNF is less effective on ocular dominance plasticity and, in addition, strongly affects spontaneous and visually evoked activity in cortical neurons.

Molecular analysis of trkC in the cat visual cortex

trkC belongs to the trk family of neurotrophin receptors. Several isoforms of trkC have been cloned to date; a full-length catalytic form containing a tyrosine kinase (TK) domain, three full-length isoforms with amino-acid insertions (14, 25, and 39 amino acids) in the TK domain, and five noncatalytic truncated forms that completely lack the TK domain. These isoforms have been studied in several mammalian species, including the pig, rat, mouse, monkey, and human. In this article we report the cloning and sequencing of five trkC isoforms isolated from 30-d postnatal cat visual cortex. The first isoform corresponded to the previously reported full-length trkC transcript containing the 14 amino-acid insert. To search for the presence of other inserts, reverse transcription polymerase chain reaction (RT-PCR) was performed on 30-d postnatal cat visual cortex mRNA using primers that flank the insertion site in the TK domain. Both the isoform containing the 14 amino-acid insert and the isoform lacking any insertion were present in abundant amounts, whereas the other two insert containing isoforms (TK25 and TK39) were much less abundant. The fifth isoform discovered corresponds to the previously reported truncated transcript. Overall, there is a high degree of identity (89-98%) and homology (97-99%) between the cat trkC nucleotide and amino-acid sequences among all mammals. The extracellular juxtamembrane domain was found to be highly divergent among all mammals that have been studied to date. This divergent region also included a proline deletion in the cat trkC sequence. This is the first report of the cloning, sequencing, and RT-PCR analysis of trkC in cat visual cortex, a system extensively studied using anatomical and physiological approaches.

Instructive roles of neurotrophins in synaptic plasticity

Together, these experiments show that neurotrophins regulate neuronal function in a factor-dependent fashion, both in terms of membrane excitability and dendritic growth, and indicate that neurotrophins can play instructive roles in regulating neuronal phenotype and function. Given that neurons generally receive neurotrophic inputs from many different cellular sources, both regional and distant (e.g., via axonal and dendritic projections), instructive actions of neurotrophic factors may contribute to matching the morphology and electrical function of neurons to the neural circuits of which they are part. Moreover, during ongoing development and function of the nervous system, these same or similar neurotrophic factors may be key instructive signals in regulating synaptic plasticity of neural circuits.

Competition for neurotrophic factors: ocular dominance columns

Activity-dependent competition between afferents in the primary visual cortex of many mammals is a quintessential feature of neuronal development. From both experimental and theoretical perspectives, understanding the mechanisms underlying competition is a significant challenge. Recent experimental work suggests that geniculocortical afferents might compete for retrograde neurotrophic factors. We show that a mathematically well-characterized model of retrograde neurotrophic interactions, in which the afferent uptake of neurotrophic factors is activity-dependent and in which the average level of uptake determines the complexity of the axonal arbors of afferents, permits the anatomical segregation of geniculocortical afferents into ocular dominance columns. The model induces segregation provided that the levels of neurotrophic factors available either by activity-independent release from cortical cells or by exogenous cortical infusion are not too high; otherwise segregation breaks down. We show that the model exhibits changes in ocular dominance column periodicity in response to changes in interocular image correlations and that the model predicts that changes in intraocular image correlations should also affect columnar periodicity.

Environmental enrichment results in higher levels of nerve growth factor mRNA in the rat visual cortex and hippocampus

Evidence for structural modifications in the brain following environmental changes have been provided during the last decades. The most pronounced alterations following environmental manipulations have been found in the visual cortex. These plastic changes are supposed to reflect reorganization of neuronal connections involved in postnatal development and adult adjustments of connections involved in sensori-perceptual processing and learning. Potential candidates to mediate these changes are neurotrophins. Nerve growth factor (NGF) has been associated with cognitive functions and shown to improve the performance of aged rats in spatial learning and memory task. In the central nervous system, NGF is of importance for development and maintenance of cholinergic neurons and atrophy of cholinergic neurons is strongly correlated with learning and memory impairments. Exposure to enriched environmental conditions improves learning and problem-solving ability and results in plastic changes in the brain. This study examined the effect of environmental enrichment on expression of NGF mRNA in the rat visual cortex and hippocampus. Rats housed in groups in a stimulus-rich environment for 30 days had significantly higher levels of NGF mRNA than rats housed individually in single cages without stimulus-enrichment. We have recently presented results showing higher levels of neurotrophin-3 (NT-3) mRNA and improved spatial learning following environmental enrichment, and suggest that an interplay involving the neurotrophins NGF and NT-3 may be mediating experience-induced structural changes.

Nerve growth factor induced modification of presynaptic elements in adult visual cortex in vivo

Nerve growth factor (NGF) has been shown to play important roles in neuronal survival, growth and differentiation. Recently, we have found that intracortical infusion of NGF into adult cat visual cortex can recreate ocular dominance plasticity, suggesting that NGF is also involved in activity-dependent modification of synaptic connectivity in the adult brain. To further explore the mechanisms of NGF-induced plasticity in adult visual cortex, we studied two presynaptic markers: GAP-43 and synaptophysin. Immunocytochemical staining showed that NGF-treatment of adult visual cortex selectively increased the level of the phosphorylated form of GAP-43, while the total level of GAP-43 was not changed. These results demonstrate that NGF-treatment stimulates phosphorylation processes of GAP-43 in vivo. In addition, NGF-treatment of adult visual cortex increased the level of synaptophysin immunoreactivity. Since the phosphorylated form of GAP-43 is known to be enriched in the membrane skeleton of growth cones and of developing synapses, and the phosphorylation of GAP-43 has been linked with events that underlie synaptic plasticity, and since synaptophysin is a major component of presynaptic vesicles, our results suggest that NGF-treatment of adult visual cortex modulates presynaptic terminals, possibly by inducing axonal sprouting and formation of new synapses, and that these changes may play a role in the NGF-induced functional plasticity.