Nerve growth factor regulates synaptophysin expression in developing trigeminal ganglion neurons in vitro

Reduced mastication during growth inhibits cognitive function by affecting trigeminal ganglia and modulating Wnt signaling pathway and ARHGAP33 molecular transmission

Binding of brain-derived neurotrophic factor (BDNF) to its receptor tyrosine kinase B (TrkB) is essential for the development of the hippocampus, which regulates memory and learning. Decreased masticatory stimulation during growth reportedly increases BDNF expression while decreasing TrkB expression in the hippocampus. Increased BDNF expression is associated with Wnt family member 3A (Wnt3a) expression and decreased expression of Rho GTPase Activating Protein 33 (ARHGAP33), which regulates intracellular transport of TrkB. TrkB expression may be decreased at the cell surface and affects the hippocampus via BDNF/TrkB signaling. Mastication affects cerebral blood flow and the neural cascade that occurs through the trigeminal nerve and hippocampus. In the current study, we hypothesized that decreased masticatory stimulation reduces memory/learning in mice due to altered Wnt3a and ARHGAP33 expression, which are related to memory/learning functions in the hippocampus. To test this hypothesis, we fed mice a powdered diet until 14 weeks of age and analyzed the BDNF and TrkB mRNA expression in the right hippocampus using real-time polymerase chain reaction and Wnt3a and ARHGAP33 levels in the left hippocampus using western blotting. Furthermore, we used staining to assess BDNF and TrkB expression in the hippocampus and the number of nerve cells, the average size of each single cell and the area of intercellular spaces of the trigeminal ganglion (TG). We found that decreased masticatory stimulation affected the expression of BDNF, Wnt3a, ARHGAP33, and TrkB proteins in the hippocampus, as well as memory/learning. The experimental group showed significantly decreased numbers of neurons and increased the area of intercellular spaces in the TG. Our findings suggest that reduced masticatory stimulation during growth induces a decline in memory/learning by modulating molecular transmission mechanisms in the hippocampus and TG.

Methods used to achieve different levels of the neuronal differentiation process in SH-SY5Y and Neuro2a cell lines: An integrative review

To study the process of neuronal differentiation, the human neuroblastoma (SH-SY5Y) and the murine neuroblastoma (Neuro2a) cell lines have proven to be effective models. For this approach, different protocols involving known neurotrophic factors and other molecules, such as retinoic acid (RA), have been assessed to better understand the neuronal differentiation process. Thus, the goal of this manuscript was to provide a brief overview of recent studies that have used protocols to promote neurodifferentiation in SH-SY5Y and Neuro2a cell lines and used acquired morphology and neuronal markers to validate whether differentiation was effective. The published results supply some guidance regarding the relationship between RA and neurotrophins for SH-SY5Y, as well a serum concentrations for both cell lines. Furthermore, they demonstrate the potential application of Neuro2a, which is critical for future research on neuronal differentiation.

Neurotrophic effects of GM1 ganglioside, NGF, and FGF2 on canine dorsal root ganglia neurons in vitro

Dogs share many chronic morbidities with humans and thus represent a powerful model for translational research. In comparison to rodents, the canine ganglioside metabolism more closely resembles the human one. Gangliosides are components of the cell plasma membrane playing a role in neuronal development, intercellular communication and cellular differentiation. The present in vitro study aimed to characterize structural and functional changes induced by G_M1 ganglioside (G_M1) in canine dorsal root ganglia (DRG) neurons and interactions of G_M1 with nerve growth factor (NGF) and fibroblast growth factor (FGF2) using immunofluorescence for several cellular proteins including neurofilaments, synaptophysin, and cleaved caspase 3, transmission electron microscopy, and electrophysiology. G_M1 supplementation resulted in increased neurite outgrowth and neuronal survival. This was also observed in DRG neurons challenged with hypoxia mimicking neurodegenerative conditions due to disruptions of energy homeostasis. Immunofluorescence indicated an impact of G_M1 on neurofilament phosphorylation, axonal transport, and synaptogenesis. An increased number of multivesicular bodies in G_M1 treated neurons suggested metabolic changes. Electrophysiological changes induced by G_M1 indicated an increased neuronal excitability. Summarized, G_M1 has neurotrophic and neuroprotective effects on canine DRG neurons and induces functional changes. However, further studies are needed to clarify the therapeutic value of gangliosides in neurodegenerative diseases.

Preparation and effects on neuronal nutrition of plasmenylethonoamine and plasmanylcholine from the mussel Mytilus edulis

Plasmenylethonoamine (pPE) and plasmanylcholine (aPC) are important phospholipid subclasses. Herein we explored optimum conditions for enzymatic purification and preparation of pPE and aPC from the mussel Mytilus edulis and bovine brain. Among them, pPE in Mytilus edulis PE was mainly p18:0-20:5 and p18:0-22:6, and its purity was 92.7%; aPC in PC was primarily a16:0-22:6 and a16:0-20:5, and aPC accounted for 90.2% of PC. We thereafter evaluated neurotrophic effects of Mytilus edulis pPE, aPC, and bovine brain pPE in a NGF-induced PC12 cell model. Morphologically, pPE and aPC could both promote differentiation, manifested in a significant increase in neurite length and number, due to increased expression of synaptophysin and growth protein GAP-43 in a dose-independent and structure-selective manner. Importantly, the effect on neuronal nutrition of pPE was better than aPC, and marine pPE was better than terrestrial pPE, which might be ascribed to vinyl-ether bond and differences in fatty acid composition.Abbreviations: AA: arachidonic acid; DHA: docosahexaenoic acid; EIC: extracted ion chromatogram; EPA: eicosapentanoic acid; GAP: growth-associated protein; HPLC: high-performance liquid chromatography; LC-MS/MS: liquid chromatography-tandem mass spectrometry; LPC: lyso-PC; LPE: lyso-PE; MS: mass spectrometry; NGF: nerve growth factor; PC: phosphatidylcholine; aPC: plasmanylcholine; PE: phosphatidylethanolamine; pPE: plasmenylethonoamine; PG: phosphoglycerols; PLs: phospholipids; PS: phosphoserines; TIC: total ion chromatogram.

Ginger improves cognitive function via NGF-induced ERK/CREB activation in the hippocampus of the mouse

Ginger (the rhizome of Zingiber officinale Roscoe) has been used worldwide for many centuries in cooking and for treatment of several diseases. The main pharmacological properties of ginger include anti-inflammatory, antihyperglycemic, antiarthritic, antiemetic and neuroprotective actions. Recent studies demonstrated that ginger significantly enhances cognitive function in various cognitive disorders as well as in healthy brain. However, the biochemical mechanisms underlying the ginger-mediated enhancement of cognition have not yet been studied in normal or diseased brain. In the present study, we assessed the memory-enhancing effects of dried ginger extract (GE) in a model of scopolamine-induced memory deficits and in normal animals by performing a novel object recognition test. We found that GE administration significantly improved the ability of mice to recognize novel objects, indicating improvements in learning and memory. Furthermore, to elucidate the mechanisms of GE-mediated cognitive enhancement, we focused on nerve growth factor (NGF)-induced signaling pathways. NGF enzyme-linked immunosorbent assay analysis revealed that GE administration led to elevated NGF levels in both the mouse hippocampus and rat glioma C6 cells. GE administration also resulted in phosphorylation of extracellular-signal-regulated kinase (ERK) and cyclic AMP response element-binding protein (CREB), as revealed by Western blotting analysis. Neutralization of NGF with a specific NGF antibody inhibited GE-triggered activation of ERK and CREB in the hippocampus. Also, GE treatment significantly increased pre- and postsynaptic markers, synaptophysin and PSD-95, which are related to synapse formation in the brain. These data suggest that GE has a synaptogenic effect via NGF-induced ERK/CREB activation, resulting in memory enhancement.

Upregulation of brain-derived neurotrophic factor expression in nodose ganglia and the lower brainstem of hypertensive rats

Hypertension leads to structural and functional changes at baroreceptor synapses in the medial nucleus tractus solitarius (NTS), but the underlying molecular mechanisms remain unknown. Our previous studies show that brain-derived neurotrophic factor (BDNF) is abundantly expressed by rat nodose ganglion (NG) neurons, including baroreceptor afferents and their central terminals in the medial NTS. We hypothesized that hypertension leads to upregulation of BDNF expression in NG neurons. To test this hypothesis, we used two mechanistically distinct models of hypertension, the spontaneously hypertensive rat (SHR) and the deoxycorticosterone acetate (DOCA)-salt rat. Young adult SHRs, whose blood pressure was significantly elevated compared with age-matched Wistar-Kyoto (WKY) control rats, exhibited dramatic upregulation of BDNF mRNA and protein in the NG. BDNF transcripts from exon 4, known to be regulated by activity, and exon 9 (protein-coding region) showed the largest increases. Electrical stimulation of dispersed NG neurons with patterns that mimic baroreceptor activity during blood pressure elevations led to increases in BDNF mRNA that were also mediated through promoter 4. The increase in BDNF content of the NG in vivo was associated with a significant increase in the percentage of BDNF-immunoreactive NG neurons. Moreover, upregulation of BDNF in cell bodies of NG neurons was accompanied by a significant increase in BDNF in the NTS region, the primary central target of NG afferents. A dramatic increase in BDNF in the NG was also detected in DOCA-salt hypertensive rats. Together, our study identifies BDNF as a candidate molecular mediator of activity-dependent changes at baroafferent synapses during hypertension.

Tumor necrosis factor-α increases brain-derived neurotrophic factor expression in trigeminal ganglion neurons in an activity-dependent manner

Many chronic trigeminal pain conditions, such as migraine or temporo-mandibular disorders, are associated with inflammation within peripheral endings of trigeminal ganglion (TG) sensory neurons. A critical role in mechanisms of neuroinflammation is attributed to proinflammatory cytokines, such as interleukin-1β and tumor necrosis factor-α (TNFα) that also contribute to mechanisms of persistent neuropathic pain resulting from nerve injury. However, the mechanisms of cytokine-mediated synaptic plasticity and nociceptor sensitization are not completely understood. In the present study, we examined the effects of TNFα on neuronal expression of brain-derived neurotrophic factor (BDNF), whose role in synaptic plasticity and sensitization of nociceptive pathways is well documented. We show that 4- and 24-h treatment with TNFα increases BDNF mRNA and protein, respectively, in neuron-enriched dissociated cultures of rat TG. TNFα increases the phosphorylated form of the cyclic AMP-responsive element binding protein (CREB), a transcription factor involved in regulation of BDNF expression in neurons, and activates transcription of BDNF exon IV (former exon III) and, to a lesser extent, exon VI (former exon IV), but not exon I. TNFα-mediated increase in BDNF expression is accompanied by increase in calcitonin gene-related peptide (CGRP), which is consistent with previously published studies, and indicates that both peptides are similarly regulated in TG neurons by inflammatory mediators. The effect of TNFα on BDNF expression is dependent on sodium influx through TTX-sensitive channels and on p38-mitogen-activated protein kinase. Moreover, electrical stimulation and forskolin, known to increase intracellular cAMP, potentiate the TNFα-mediated upregulation of BDNF expression. This study provides new evidence for a direct action of proinflammatory cytokines on TG primary sensory neurons, and reveals a mechanism through which TNFα stimulates de novo synthesis of BDNF in these neurons. Thus, TNFα should be considered in mechanisms of BDNF-dependent neuronal plasticity.

Integration of neuronally predifferentiated human dental pulp stem cells into rat brain in vivo

Pluripotency and their neural crest origin make dental pulp stem cells (DPSCs) an attractive donor source for neuronal cell replacement. Despite recent encouraging results in this field, little is known about the integration of transplanted DPSC derived neuronal pecursors into the central nervous system. To address this issue, neuronally predifferentiated DPSCs, labeled with a vital cell dye Vybrant DiD were introduced into postnatal rat brain. DPSCs were transplanted into the cerebrospinal fluid of 3-day-old male Wistar rats. Cortical lesion was induced by touching a cold (-60°C) metal stamp to the calvaria over the forelimb motor cortex. Four weeks later cell localization was detected by fluorescent microscopy and neuronal cell markers were studied by immunohistochemistry. To investigate electrophysiological properties of engrafted, fluorescently labeled DPSCs, 300 μm-thick horizontal brain slices were prepared and the presence of voltage-dependent sodium and potassium channels were recorded by patch clamping. Predifferentiated donor DPSCs injected into the cerebrospinal fluid of newborn rats migrated as single cells into a variety of brain regions. Most of the cells were localized in the normal neural progenitor zones of the brain, the subventricular zone (SVZ), subgranular zone (SGZ) and subcallosal zone (SCZ). Immunohistochemical analysis revealed that transplanted DPSCs expressed the early neuronal marker N-tubulin, the neuronal specific intermediate filament protein NF-M, the postmitotic neuronal marker NeuN, and glial GFAP. Moreover, the cells displayed TTX sensitive voltage dependent (VD) sodium currents (I(Na)) and TEA sensitive delayed rectifier potassium currents (K(DR)). Four weeks after injury, fluorescently labeled cells were detected in the lesioned cortex. Neurospecific marker expression was increased in DPSCs found in the area of the cortical lesions compared to that in fluorescent cells of uninjured brain. TTX sensitive VD sodium currents and TEA sensitive K(DR) significantly increased in labeled cells of the cortically injured area. In conclusion, our data demonstrate that engrafted DPSC-derived cells integrate into the host brain and show neuronal properties not only by expressing neuron-specific markers but also by exhibiting voltage dependent sodium and potassium channels. This proof of concept study reveals that predifferentiated hDPSCs may serve as useful sources of neuro- and gliogenesis in vivo, especially when the brain is injured.

Nerve growth factor regulates the firing patterns and synaptic composition of motoneurons

Target-derived neurotrophins exert powerful synaptotrophic actions in the adult brain and are involved in the regulation of different forms of synaptic plasticity. Target disconnection produces a profound synaptic stripping due to the lack of trophic support. Consequently, target reinnervation leads to synaptic remodeling and restoration of cellular functions. Extraocular motoneurons are unique in that they normally express the TrkA neurotrophin receptor in the adult, a feature not seen in other cranial or spinal motoneurons, except after lesions such as axotomy or in neurodegenerative diseases like amyotrophic lateral sclerosis. We investigated the effects of nerve growth factor (NGF) by retrogradely delivering this neurotrophin to abducens motoneurons of adult cats. Axotomy reduced the density of somatic boutons and the overall tonic and phasic firing modulation. Treatment with NGF restored synaptic inputs and firing modulation in axotomized motoneurons. When K252a, a selective inhibitor of tyrosine kinase activity, was applied to specifically test TrkA effects, the NGF-mediated restoration of synapses and firing-related parameters was abolished. Discharge variability and recruitment threshold were, however, increased by NGF compared with control or axotomized motoneurons. Interestingly, these parameters returned to normal following application of REX, an antibody raised against neurotrophin receptor p75 (p75(NTR)). In conclusion, NGF, acting retrogradely through TrkA receptors, supports afferent boutons and regulates the burst and tonic signals correlated with eye movements. On the other hand, p75(NTR) activation regulates recruitment threshold, which impacts on firing regularity. To our knowledge, this is the first report showing powerful synaptotrophic effects of NGF on motoneurons in vivo.

Nitric oxide regulates BDNF release from nodose ganglion neurons in a pattern-dependent and cGMP-independent manner

Activity of arterial baroreceptors is modulated by neurohumoral factors, including nitric oxide (NO), released from endothelial cells. Baroreceptor reflex responses can also be modulated by NO signaling in the brainstem nucleus tractus solitarius (NTS), the primary central target of cardiovascular afferents. Our recent studies indicate that brain-derived neurotrophic factor (BDNF) is abundantly expressed by developing and adult baroreceptor afferents in vivo, and released from cultured nodose ganglion (NG) neurons by patterns of baroreceptor activity. Using electrical field stimulation and ELISA in situ, we show that exogenous NO nearly abolishes BDNF release from newborn rat NG neurons in vitro stimulated with single pulses delivered at 6 Hz, but not 2-pulse bursts delivered at the same 6-Hz frequency, that corresponds to a rat heart rate. Application of L-NAME, a specific inhibitor of endogenous NO synthases, does not have any significant effect on activity-dependent BDNF release, but leads to upregulation of BDNF expression in an activity-dependent manner. The latter effect suggests a novel mechanism of homeostatic regulation of activity-dependent BDNF expression with endogenous NO as a key player. The exogenous NO-mediated effect does not involve the cGMP-protein kinase G (PKG) pathway, but is largely inhibited by N-ethylmaleimide and TEMPOL that are known to prevent S-nitrosylation. Together, our current data identify previously unknown mechanisms regulating BDNF availability, and point to NO as a likely regulator of BDNF at baroafferent synapses in the NTS.