c-fos modulates brain-derived neurotrophic factor mRNA expression in mouse hippocampal CA3 and dentate gyrus neurons

AMPA Receptors Endocytosis Inhibition Attenuates Cognition Deficit Via c-Fos/BDNF Signaling in Amyloid β Neurotoxicity

Glutamatergic imbalance, particularly downregulation of α-amino-3-hydroxy-5-methyl-4- isoxazole propionic acid receptor (AMPARs) endocytosis, has been addressed as a possible reason for cognitive dysfunctions in Alzheimer's disease (AD). We hypothesized that inhibition of AMPAR endocytosis may ameliorate memory impairment in AD model of rats. To approach this, twenty-four adults male Wistar rats were divided into three groups: saline + saline (control group), Aβ + saline, and Aβ + Tat-GluR23Y (AMPA endocytosis inhibitor). Animals received an intracerebroventricular (i.c.v) injection of Aβ (1-42) to induce neuro-toxicity, followed by chronic administration of GluR23Y, and further behavioral assessments by MWM. Afterward, the hippocampal level of Brain Derived Neurotrophic Factor (BDNF) and c-Fos was measured via Western blotting. The results of our study revealed that chronic administration of GluR23Y improved both working and reference memories evidenced by shorter latency time and longer total time spent in the target zone in MWM. Additionally, this improvement was paralleled by an increase in BDNF, but a decrease in c-Fos. In conclusion, GluR23Y improves spatial memory impairment at least partly via elevating neuroprotective factor of BDNF and reducing apoptotic protein of c-Fos.

Investigating the Synergistic Potential of Low-Dose HDAC3 Inhibition and Radiotherapy in Alzheimer's Disease Models

We have previously shown that histone deacetylase (HDAC) inhibition and cranial radiotherapy (RT) independently improve molecular and behavioral Alzheimer's disease (AD)-like phenotypes. In the present study, we investigate the synergistic potential of using both RT and HDACi as a low-dose combination therapy (LDCT) to maximize disease modification (reduce neuroinflammation and amyloidogenic APP processing, increase neurotrophic gene expression) while minimizing the potential for treatment-associated side effects.LDCT consisted of daily administration of the HDAC3 inhibitor RGFP966 and/or bi-weekly cranial x-irradiation. Amyloid-beta precursor protein (APP) processing and innate immune response to LDCT were assessed in vitro and in vivo using human and murine cell models and 3xTg-AD mice. After 2 months of LDCT in mice, behavioral analyses as well as expression and modification of key AD-related targets (Aβ, tau, Csf1r, Bdnf, etc.) were assessed in the hippocampus (HIP) and prefrontal cortex (PFC).LDCT induced a tolerant, anti-inflammatory innate immune response in microglia and increased non-amyloidogenic APP processing in vitro. Both RT and LDCT improved the rate of learning and spatial memory in the Barnes maze test. LDCT induced a unique anti-AD HIP gene expression profile that included upregulation of neurotrophic genes and downregulation of inflammation-related genes. RT lowered HIP Aβ42/40 ratio and Bace1 protein, while LDCT lowered PFC p-tau181 and HIP Bace1 levels.Our study supports the rationale for combining complementary therapeutic approaches at low doses to target multifactorial AD pathology synergistically. Namely, LDCT with RGFP966 and cranial RT shows disease-modifying potential against a wide range of AD-related hallmarks.

Post-Weaning Treatment with Probiotic Inhibited Stress-Induced Amnesia in Adulthood Rats: The Mediation of GABAergic System and BDNF/c-Fos Signaling Pathways

The current study aimed to examine the effect of post-weaning treatment with probiotics on memory formation under stress during the adult period in male Wistar rats. Considering GABA is a potential mediator between probiotics and the host, the present study also investigated the involvement of the GABAergic system in the probiotic response. The hippocampal and prefrontal cortical (PFC) expression levels of BDNF and c-Fos were also assessed to show whether the treatments affect the memory-related signaling pathway. Three weeks after birth, the post-weaning rats were fed with probiotic water (PW) or tap water (TW) for 2, 3, 4, or 5 weeks. Exposure to acute stress impaired memory formation in a passive avoidance learning task. Feeding the post-weaning animals with probiotic strains (3, 4, or 5 weeks) inhibited stress-induced amnesia of the adult period. Post-training intracerebroventricular (ICV) microinjection of muscimol improved stress-induced amnesia in the animals fed with TW. ICV microinjection of muscimol inhibited probiotic treatment's significant effect on the stress response in the memory task. The expression levels of BDNF and c-Fos in the PFC and the hippocampus were significantly decreased in the stress animal group. The levels of BDNF and c-Fos were increased in the PW/stress animal group. The muscimol response was compounded with the decreased levels of BDNF and c-Fos in the PFC and the hippocampus. Thus, the GABA-A receptor mechanism may mediate the inhibitory effect of this probiotic mixture on stress-induced amnesia, which may be associated with the PFC and hippocampal BDNF/c-Fos signaling changes.

Dioscin-Mediated Autophagy Alleviates MPP+-Induced Neuronal Degeneration: An In Vitro Parkinson's Disease Model

Autophagy is a cellular homeostatic process by which cells degrade and recycle their malfunctioned contents, and impairment in this process could lead to Parkinson’s disease (PD) pathogenesis. Dioscin, a steroidal saponin, has induced autophagy in several cell lines and animal models. The role of dioscin-mediated autophagy in PD remains to be investigated. Therefore, this study aims to investigate the hypothesis that dioscin-regulated autophagy and autophagy-related (ATG) proteins could protect neuronal cells in PD via reducing apoptosis and enhancing neurogenesis. In this study, the 1-methyl-4-phenylpyridinium ion (MPP⁺) was used to induce neurotoxicity and impair autophagic flux in a human neuroblastoma cell line (SH-SY5Y). The result showed that dioscin pre-treatment counters MPP⁺-mediated autophagic flux impairment and alleviates MPP⁺-induced apoptosis by downregulating activated caspase-3 and BCL2 associated X, apoptosis regulator (Bax) expression while increasing B-cell lymphoma 2 (Bcl-2) expression. In addition, dioscin pre-treatment was found to increase neurotrophic factors and tyrosine hydroxylase expression, suggesting that dioscin could ameliorate MPP⁺-induced degeneration in dopaminergic neurons and benefit the PD model. To conclude, we showed dioscin’s neuroprotective activity in neuronal SH-SY5Y cells might be partly related to its autophagy induction and suppression of the mitochondrial apoptosis pathway.

Ultrasound Used for Diagnostic Imaging Facilitates Dendritic Branching of Developing Neurons in the Mouse Cortex

Neuronal differentiation and synaptogenesis are regulated by precise orchestration of intrinsic and extrinsic chemical and mechanical factors throughout all developmental steps critical for the assembly of neurons into functional circuits. While ultrasound is known to alter neuronal migration and activity acutely, its chronic effect on neuronal behavior or morphology is not well characterized. Furthermore, higher-frequency (3–5 MHz) ultrasound (HFU) is extensively used in gynecological practice for imaging, and while it has not been shown harmful for the developing brain, it might be associated with mild alterations that may have functional consequences. To shed light on the neurobiological effects of HFU on the developing brain, we examined cortical pyramidal cell morphology in a transgenic mouse model, following a single and short dose of high-frequency ultrasound. Layer V neurons in the retrosplenial cortex of mouse embryos were labeled with green and red fluorescent proteins by in utero electroporation at the time of their appearance (E14.5). At the time of their presumptive arrival to layer V (E18.5), HFU stimulation was performed with parameters matched to those used in human prenatal examinations. On the third postnatal day (P3), basic morphometric analyses were performed on labeled neurons reconstructed with Neurolucida. Low-intensity HFU-treated cells showed significantly increased dendritic branching compared to control (non-stimulated) neurons and showed elevated c-fos immunoreactivity. Labeled neurons were immunopositive for the mechanosensitive receptor TRPC4 at E18.5, suggesting the role of this receptor and the associated signaling pathways in the effects of HFU stimulation.

Basolateral amygdala stimulation plus water maze training restore dentate gyrus LTP and improve spatial learning and memory

Synaptic plasticity is a key mechanism of neural plasticity involved in learning and memory. A reduced or impaired synaptic plasticity could lead to a deficient learning and memory. On the other hand, besides reducing hipocampal dependent learning and memory, fimbria-fornix lesion affects LTP. However, we have consistently shown that stimulation of the basolateral amygdala (BLA) 15 min after water maze training is able to improve spatial learning and memory in fimbria fornix lesioned rats while also inducing changes in the expression of plasticity-related genes expression in memory associated brain regions like the hippocampus and prefrontal cortex. In this study we test that hypothesis: whether BLA stimulation 15 min after water maze training can improve LTP in the hippocampus of fimbria-fornix lesioned rats. To address this question, we trained fimbria-fornix lesioned rats in water maze for four consecutive days, and the BLA was bilaterally stimulated 15 min after each training session.Our data show that trained fimbria-fornix lesioned rats develop a partially improved LTP in dentated gyrus compared with the non-trained fimbria-fornix lesioned rats. In contrast, dentated gyrus LTP in trained and BLA stimulated fimbria-fornix lesioned rats improved significantly compared to the trained fimbria-fornix lesioned rats, but was not different from that shown by healthy animals. BLA stimulation in non-trained FF lesioned rats did not improve LTP; instead produces a transient synaptic depression. Restoration of the ability to develop LTP by the combination of training and BLA stimulation would be one of the mechanisms involved in ameliorating memory deficits in lesioned animals.

Effects of Ozone on Hippocampus BDNF and Fos Expressions in Rats with Chronic Compression of Dorsal Root Ganglia

The effects of ozone on hippocampal expression levels of brain-derived neurotrophic factor (BDNF) and c-fos protein (Fos) were evaluated in rats with chronic compression of dorsal root ganglia (CCD). Forty-eight adult female Sprague-Dawley rats were randomly divided into the following 4 groups (n = 12): sham operation (sham group), CCD group, CCD with 20 μg/ml of ozone (CCD + AO₃ group), and CCD with 40 μg/ml of ozone (CCD + BO₃ group). Except the sham group, unilateral L5 dorsal root ganglion (DRG) compression was performed on all other groups. On days 1, 2, and 4 after the operation, the CCD + AO₃ and CCD + BO₃ groups were injected with 100 μl of ozone with concentrations of 20 and 40 μg/ml, respectively. Thermal withdrawal latencies (TWLs) and mechanical withdrawal thresholds (MWTs) were measured at various time points before and after the operation. BDNF and Fos expressions were examined in the extracted hippocampi using immunohistochemistry. The TWLs and MWTs of CCD model rats that received ozone were lower with decreased BDNF and increased Fos expression levels, on day 21 after the operation, compared to those of the sham group (P < 0.05). The TWLs and MWTs of the CCD + AO₃ and CCD + BO₃ groups were higher with increased BDNF and decreased Fos expression levels, on day 21 after the operation, compared to those of the CCD group (P < 0.05). The TWLs were longer and the MWTs were higher in the CCD + BO₃ group at each time point with increased BDNF and decreased Fos expression levels, on day 21 after the operation, compared to those of the CCD + AO₃ group (P < 0.05). Our results revealed that ozone can relieve the neuropathic pain caused by the pathological neuralgia resulting from DRG compression in rats. The mechanism of action for ozone is likely associated with changes in BDNF and Fos expression levels in the hippocampus.

How does elevated water temperature affect fish brain? (A neurophysiological and experimental study: Assessment of brain derived neurotrophic factor, cFOS, apoptotic genes, heat shock genes, ER-stress genes and oxidative stress genes)

Water temperature is one of the most important environmental factors affecting the growth and survival of fish. Increased water temperature became a global problem and it is estimated that there will be an increase in water temperature due to global climate change. The physiological mechanism for the effects of high water temperature on the fish brain is not fully known. In the present study, fish were exposed to different temperatures (10 °C/15 °C/20 °C/25°) and brain tissues were sampled 2 h-4h-6h-8h per hour respectively and then we investigated transcriptional changes of BDNF, cFOS, apoptotic genes (caspase 3, Bax, Bcl2), heat shock genes (Hsp70 and Hsp 90) ER-Stress genes (grp78, atf6, and ire1) and oxidative stress genes (CAT, SOD, and GPx) and also immunoflourescence changes of BDNF and cFOSin rainbow trout brain. The results indicated that high temperature stress lead to physiological changes in the fish brain by causing a decrease in mRNA expression levels of CAT, SOD, GPx and Bcl2 and by causing an increase in mRNA expression of BDNF, cFOS, apoptotic genes (caspase 3, Bax), heat shock genes (Hsp70 and Hsp 90) ER-Stress genes (grp78, atf6, and ire1). This study will provide important information to elucidate the physiological mechanisms related to the effects of high water temperature on the fish brain.

Kaempferia parviflora Rhizome Extract Inhibits Glutamate-Induced Toxicity in HT-22 Mouse Hippocampal Neuronal Cells and Extends Longevity in Caenorhabditis elegans

Kaempferia parviflora Wall. ex Baker (KP) or "Kra-chai-dam" has been shown to exhibit several pharmacological effects including anti-inflammation, antimicrobial, and sexual-enhancing activity. The objectives of this study included an investigation of the effect of KP rhizome extract against glutamate-induced toxicity in mouse hippocampal HT-22 neuronal cells, determination of the underlying mechanism of neuroprotection, and an evaluation of the effect of KP extract on the longevity of Caenorhabditis elegans. HT-22 cells were co-treated with glutamate (5 mM) and KP extract (25, 50, and 75 μg/mL) for 14 h. Cell viability, intracellular reactive oxygen species (ROS) assay, fluorescence-activated cell sorting (FACS) analysis, and Western blotting were performed. The longevity effect of KP extract on C. elegans was studied by lifespan measurement. In HT-22 cells, co-treatment of glutamate with KP extract significantly inhibited glutamate-mediated cytotoxicity and decreased intracellular ROS production. Additionally, the glutamate-induced apoptosis and apoptotic-inducing factor (AIF) translocation were blocked by KP extract co-treatment. Western blot analysis also demonstrated that KP extract significantly diminished extracellular signal-regulated kinase (ERK) phosphorylation induced by glutamate, and brain-derived neurotrophic factor (BDNF) was recovered to the control. Moreover, this KP extract treatment prolonged the lifespan of C. elegans. Altogether, this study suggested that KP extract possesses both neuroprotective and longevity-inducing properties, thus serving as a promising candidate for development of innovative health products.

Amygdala stimulation ameliorates memory impairments and promotes c-Fos activity in fimbria-fornix-lesioned rats

Recently we provided data showing that amygdala stimulation can ameliorate spatial memory impairments in rats with lesion in the fimbria-fornix (FF). The mechanisms for this improvement involve early gene expression and synthesis of BDNF, MAP-2, and GAP43 in the hippocampus and prefrontal cortex. Now we have studied which brain structures are activated by the amygdala using c-Fos as a marker of neural activation. First, we studied neuronal activation after tetanic stimulation to the amygdala in intact rats. We then carried out a second study in FF-lesioned rats in which the amygdala was stimulated 15 min after daily spatial memory training in the water maze. Our results showed that amygdala stimulation produces widespread brain activation, that includes cortical, thalamic, and brain stem structures. Activation was particularly intense in the dentate gyrus and the prefrontal cortex. Training in the water maze increased c-Fos positive nuclei in the dentate gyrus of the hippocampus and in medial prefrontal cortex. Amygdala stimulation to trained FF-lesioned rats induced an increase of neural activity in the dentate gyrus and medial prefrontal cortex relative to the FF-lesioned, but not stimulated group, like the c-Fos activity seen in trained control rats. Based on these and previous results we explain the mechanisms of amygdala reinforcement of neural plasticity and the partial recovery of spatial memory deficits.

Chronic Supplementation with a Mix of Salvia officinalis and Salvia lavandulaefolia Improves Morris Water Maze Learning in Normal Adult C57Bl/6J Mice

Background: Two different species of sage, Salvia officinalis and Salvia lavandulaefolia, have demonstrated activities in cognitive function during preclinical and clinical studies related to impaired health situations or single administration. Different memory processes have been described to be significantly and positively impacted. Objective: Our objective is to explore the potential of these Salvia, and their additional activities, in healthy situations, and during prolonged administration, on memory and subsequent mechanisms of action related to putative effects. Design: This mouse study has implicated four investigational arms dedicated to control, Salvia officinalis aqueous extract, Salvia lavandulaefolia-encapsulated essential oil and a mix thereof (Cognivia™) for 2 weeks of administration. Cognitive functions have been assessed throughout Y-maze and Morris water maze models. The impact of supplementation on lipid peroxidation, oxidative stress, neurogenesis, neuronal activity, neurotrophins, neurotrophin receptors, CaM kinase II and glucocorticoid receptors has been assessed via post-interventional tissue collection. Results: All Salvia groups had a significant effect on Y-maze markers on day 1 of administration. Only the mix of two Salvia species demonstrated significant improvements in Morris water maze markers at the end of administration. Considering all biological and histological markers, we did not observe any significant effect of S. officinalis, S. lavandulaefolia and a mix of Salvia supplementation on lipid peroxidation, oxidative stress and neuronal plasticity (neurogenesis, neuronal activity, neurotrophins). Interestingly, CaM kinase II protein expression is significantly increased in animals supplemented with Salvia. Conclusion: The activities of Salvia alone after one intake have been confirmed; however, a particular combination of different types of Salvia have been shown to improve memory and present specific synergistic effects after chronic administration in healthy mice.

Impaired social behaviour and molecular mediators of associated neural circuits during chronic Toxoplasma gondii infection in female mice

Toxoplasma gondii (T. gondii) is a neurotropic parasite that is associated with various neuropsychiatric disorders. Rodents infected with T. gondii display a plethora of behavioural alterations, and Toxoplasma infection in humans has been strongly associated with disorders such as schizophrenia, in which impaired social behaviour is an important feature. Elucidating changes at the cellular level relevant to neuropsychiatric conditions can lead to effective therapies. Here, we compare changes in behaviour during an acute and chronic T. gondii infection in female mice. Further, we notice that during chronic phase of infection, mice display impaired sociability when exposed to a novel conspecific. Also, we show that T. gondii infected mice display impaired short-term social recognition memory. However, object recognition memory remains intact. Using c-Fos as a marker of neuronal activity, we show that infection leads to an impairment in neuronal activation in the medial prefrontal cortex, hippocampus as well as the amygdala when mice are exposed to a social environment and a change in functional connectivity between these regions. We found changes in synaptic proteins that play a role in the process of neuronal activation such as synaptophysin, PSD-95 and changes in downstream substrates of cell activity such as cyclic AMP, phospho-CREB and BDNF. Our results point towards an imbalance in neuronal activity that can lead to a wider range of neuropsychiatric problems upon T. gondii infection.

Reversible Functional Changes Evoked by Anodal Epidural Direct Current Electrical Stimulation of the Rat Auditory Cortex

Rat auditory cortex was subjected to 0.1 mA anodal direct current in seven 10-min sessions on alternate days. Based on the well-known auditory cortex control of olivocochlear regulation through corticofugal projections, auditory brainstem responses (ABRs) were recorded as an indirect test of the effectiveness and reversibility of the multisession protocol of epidural stimulation. Increases of 20-30 dB ABR auditory thresholds shown after epidural stimulation reverted back to control levels 10 min after a single session. However, increases in thresholds revert 4 days after multisession stimulation. Less changes in wave amplitudes and threshold shifts were shown in ABR recorded contralaterally to the electrically stimulated side of the brain. To assess tissue effects of epidural electric stimulation on the brain cortex, well characterized functional anatomical markers of glial cells (GFAP/astrocytes and Iba1/microglial cells) and neurons (c-Fos) were analyzed in alternate serial sections by quantitative immunocytochemistry. Restricted astroglial and microglial reactivity was observed within the cytoarchitectural limits of the auditory cortex. However, interstitial GFAP overstaining was also observed in the ventricular surface and around blood vessels, thus supporting a potential global electrolytic stimulation of the brain. These results correlate with extensive changes in the distribution of c-Fos immunoreactive neurons among layers along sensory cortices after multisession stimulation. Quantitative immunocytochemical analysis supported this idea by showing a significant increase in the number of positive neurons in supragranular layers and a decrease in layer 6 with no quantitative changes detected in layer 5. Our data indicate that epidural stimulation of the auditory cortex induces a reversible decrease in hearing sensitivity due to local, restricted epidural stimulation. A global plastic response of the sensory cortices, also reported here, may be related to electrolytic effects of electric currents.

Modulation of mTOR and CREB pathways following mGluR5 blockade contribute to improved Huntington's pathology in zQ175 mice

Huntington’s disease (HD) is a neurodegenerative disorder caused by a genetic abnormality in the huntingtin gene that leads to a polyglutamine repeat expansion of the huntingtin protein. The cleaved polyglutamine expansion of mutant huntingtin (mHTT) protein can form aggregates strongly correlated with HD progression. We have previously shown that the inhibition of mGluR5 using CTEP, a selective negative allosteric mGluR5 modulator, can delay disease progression and reduce in mHTT aggregates in the zQ175 mouse model of HD. This was paralleled by enhanced catalytic activity of Unc-51-like kinase 1 (ULK1), a kinase modulated by mammalian target of rapamycin (mTOR) and key regulator of autophagy initiation. In the present study, we show that CTEP can correct aberrant phosphoinositide 3-kinase (PI3K)/Akt/mTOR signaling detected in zQ175 mice that may underlie the enhanced ULK1 activity and activation of autophagy. We also show that CTEP can facilitate cAMP response element-binding protein (CREB)-mediated expression of brain-derived neurotrophic factor (BDNF) to foster neuronal survival and reduce apoptosis. Taken together, our findings provide the molecular evidence for how targeting mGluR5 using a well-tolerated selective NAM can mitigate two critical mechanisms of neurodegeneration, autophagy and apoptosis.

Anticonvulsant and Neuroprotective Effects of the Thyroid Hormone Metabolite 3-Iodothyroacetic Acid

BACKGROUND

3-Iodothyroacetic acid (TA1) is among the thyroid hormone (T3) metabolites that can acutely modify behavior in mice. This study aimed to investigate whether TA1 is also able to reduce neuron hyper-excitability and protect from excitotoxic damage.

METHODS

CD1 male mice were treated intraperitoneally with saline solution or TA1 (4, 7, 11, or 33 μg/kg) before receiving 90 mg/kg pentylenetrazole subcutaneously. The following parameters were measured: latency to first seizure onset, number of mice experiencing seizures, hippocampal levels of c-fos, and PI3K/AKT activation levels. Organotypic hippocampal slices were exposed to vehicle or to 5 μM kainic acid (KA) in the absence or presence of 0.01-10 μM TA1. In another set of experiments, slices were exposed to vehicle or 5 μM KA in the absence or presence of 10 μM T3, 3,5,3'-triiodothyroacetic acid (TRIAC), T1AM, thyronamine (T0AM), or thyroacetic acid (TA0). Neuronal cell death was measured fluorimetically. The ability of TA1 and T3, TRIAC, T1AM, T0A, and TA0 to activate the PI3K/AKT cascade was evaluated by Western blot. The effect of TA1 on KA-induced currents in CA3 neurons was evaluated by patch clamp recordings on acute hippocampal slices.

RESULTS

TA1 (7 and 11 μg/kg) significantly reduced the number of mice showing convulsions and increased their latency of onset, restored pentylenetrazole-induced reduction of hippocampal c-fos levels, activated the PI3K/AKT, and reduced GSK-3β activity. In rat organotypic hippocampal slices, TA1 reduced KA-induced cell death by activating the PI3K/AKT cascade and increasing GSK-3β phosphorylation levels. Protection against KA toxicity was also exerted by T3 and other T3 metabolites studied. TA1 did not interact at KA receptors. Both the anticonvulsant and neuroprotective effects of TA1 were abolished by pretreating mice or organotypic hippocampal slices with pyrilamine, an histamine type 1 receptor antagonist (10 mg/kg or 1 μM, respectively).

CONCLUSIONS

TA1 exerts anticonvulsant activity and is neuroprotective in vivo and in vitro. These findings extend the current knowledge on the pharmacological profile of TA1 and indicate possible novel clinical use for this T3 metabolite.

Methamphetamine binge administration during late adolescence induced enduring hippocampal cell damage following prolonged withdrawal in rats

A recent study from our laboratory demonstrated that binge methamphetamine induced hippocampal cell damage (i.e., impaired cell genesis) in rats when administered specifically during late adolescence (postnatal day, PND 54-57) and evaluated 24 h later (PND 58). The results also suggested a possible role for brain-derived neurotrophic factor (BDNF) regulating cell genesis and survival. This subsequent study evaluated whether these effects persisted in time as measured following prolonged withdrawal. Male Sprague-Dawley rats were treated (i.p.) with BrdU (2 × 50 mg/kg, 3 days, PND 48-50) followed by a binge paradigm (3 pulses/day, every 3 h, 4 days, PND 54-57) of methamphetamine (5 mg/kg, n = 14, M) or saline (0.9% NaCl, 1 ml/kg, n = 12, C). Following 34 days of forced withdrawal (PND 91), rats were killed 45 min after a challenge dose of saline (Sal: C-Sal, n = 6; M-Sal, n = 7) or methamphetamine (Meth: C-Meth, n = 6; M-Meth, n = 7). Neurogenesis markers (Ki-67: cell proliferation; NeuroD: early neuronal survival; BrdU: prolonged cell survival, 41-43 days old cells) were evaluated by immunohistochemistry while neuroplasticity markers (BDNF and Fos forms) were evaluated by Western blot. The main results showed that a history of methamphetamine administration (PND 54-57) induced enduring hippocampal cell damage (i.e., observed on PND 91) by decreasing cell survival (BrdU + cells) and mature-BDNF (m-BDNF) protein content, associated with neuronal survival, growth and differentiation. Interestingly, m-BDNF regulation paralleled hippocampal c-Fos protein content, indicating decreased neuronal activity, and thus reinforcing the persisting negative effects induced by methamphetamine in rat hippocampus following prolonged withdrawal.

Low-level laser irradiation modulates brain-derived neurotrophic factor mRNA transcription through calcium-dependent activation of the ERK/CREB pathway

Low-level laser (LLL) irradiation has been reported to promote neuronal differentiation, but the mechanism remains unclear. Brain-derived neurotrophic factor (BDNF) has been confirmed to be one of the most important neurotrophic factors because it is critical for the differentiation and survival of neurons during development. Thus, this study aimed to investigate the effects of LLL irradiation on Bdnf messenger RNA (mRNA) transcription and the molecular pathway involved in LLL-induced Bdnf mRNA transcription in cultured dorsal root ganglion neurons (DRGNs) using Ca²⁺ imaging, pharmacological detections, RNA interference, immunocytochemistry assay, Western blot, and qPCR analysis. We show here that LLL induced increases in the [Ca²⁺] _i level, Bdnf mRNA transcription, cAMP-response element-binding protein (CREB) phosphorylation, and extracellular signal-regulated kinase (ERK) phosphorylation, mediated by Ca²⁺ release via inositol triphosphate receptor (IP3R)-sensitive calcium (Ca²⁺) stores. Blockade of Ca²⁺ increase suppressed Bdnf mRNA transcription, CREB phosphorylation, and ERK phosphorylation. Downregulation of phosphorylated (p)-CREB reduced Bdnf mRNA transcription triggered by LLL. Furthermore, blockade of ERK using PD98059 inhibitor reduced p-CREB and Bdnf mRNA transcription induced by LLL. Taken together, these findings establish the Ca²⁺-ERK-CREB cascade as a potential signaling pathway involved in LLL-induced Bdnf mRNA transcription. To our knowledge, this is the first report of the mechanisms of Ca²⁺-dependent Bdnf mRNA transcription triggered by LLL. These findings may help further explore the complex molecular signaling networks in LLL-triggered nerve regeneration in vivo and may also provide experimental evidence for the development of LLL for clinical applications.

Orthopedic surgery modulates neuropeptides and BDNF expression at the spinal and hippocampal levels

Pain is a critical component hindering recovery and regaining of function after surgery, particularly in the elderly. Understanding the role of pain signaling after surgery may lead to novel interventions for common complications such as delirium and postoperative cognitive dysfunction. Using a model of tibial fracture with intramedullary pinning in male mice, associated with cognitive deficits, we characterized the effects on the primary somatosensory system. Here we show that tibial fracture with pinning triggers cold allodynia and up-regulates nerve injury and inflammatory markers in dorsal root ganglia (DRGs) and spinal cord up to 2 wk after intervention. At 72 h after surgery, there is an increase in activating transcription factor 3 (ATF3), the neuropeptides galanin and neuropeptide Y (NPY), brain-derived neurotrophic factor (BDNF), as well as neuroinflammatory markers including ionized calcium-binding adaptor molecule 1 (Iba1), glial fibrillary acidic protein (GFAP), and the fractalkine receptor CX3CR1 in DRGs. Using an established model of complete transection of the sciatic nerve for comparison, we observed similar but more pronounced changes in these markers. However, protein levels of BDNF remained elevated for a longer period after fracture. In the hippocampus, BDNF protein levels were increased, yet there were no changes in Bdnf mRNA in the parent granule cell bodies. Further, c-Fos was down-regulated in the hippocampus, together with a reduction in neurogenesis in the subgranular zone. Taken together, our results suggest that attenuated BDNF release and signaling in the dentate gyrus may account for cognitive and mental deficits sometimes observed after surgery.

AP-1 Transcription Factors Mediate BDNF-Positive Feedback Loop in Cortical Neurons

Brain-derived neurotrophic factor (BDNF), a member of the neurotrophin family, regulates both survival and differentiation of several neuronal populations in the nervous system during development, as well as synaptic plasticity in the adult brain. BDNF exerts its biological functions through its receptor TrkB. Although the regulation of BDNF transcription by neuronal activity has been widely studied, little is known about TrkB signaling-dependent expression of BDNF. Using rat primary cortical neuron cultures, we show that the BDNF gene is a subject to an extensive autoregulatory loop, where TrkB signaling upregulates the expression of all major BDNF transcripts, mainly through activating MAPK pathways. Investigating the mechanisms behind this autoregulation, we found that AP-1 transcription factors, comprising Jun and Fos family members, participate in the induction of BDNF exon I, III, and VI transcripts. AP-1 transcription factors directly upregulate the expression of exon I transcripts by binding two novel AP-1 cis-elements in promoter I. Moreover, our results show that the effect of AP-1 proteins on the activity of rat BDNF promoters III and VI is indirect, because AP-1 proteins were not detected to bind the respective promoter regions by chromatin immunoprecipitation (ChIP). Collectively, we describe an extensive positive feedback system in BDNF regulation, adding a new layer to the elaborate control of BDNF gene expression.

SIGNIFICANCE STATEMENT

Here, we show for the first time that in rat primary cortical neurons the expression of all major BDNF transcripts (exon I, II, III, IV, VI, and IXa transcripts) is upregulated in response to TrkB signaling, and that AP-1 transcription factors participate in the induction of exon I, III, and VI transcripts. Moreover, we have described two novel functional AP-1 cis-elements in BDNF promoter I, responsible for the activation of the promoter in response to TrkB signaling. Our results indicate the existence of a positive feedback loop for obtaining sufficient BDNF levels necessary for various TrkB signaling-dependent physiological outcomes in neurons.

Glutamate excitotoxicity activates the MAPK/ERK signaling pathway and induces the survival of rat hippocampal neurons in vivo

Current knowledge concerning the molecular mechanisms of the cellular response to excitotoxic insults in neurodegenerative diseases is insufficient. Although glutamate (Glu) has been widely studied as the main excitatory neurotransmitter and principal excitotoxic agent, the neuroprotective response enacted by neurons is not yet completely understood. Some of the molecular participants have been revealed, but the signaling pathways involved in this protective response are just beginning to be identified. Here, we demonstrate in vivo that, in response to the cell damage and death induced by Glu excitotoxicity, neurons orchestrate a survival response through the extracellular signal-regulated kinase (ERK) signaling pathway by increasing ERK expression in the rat hippocampal (CA1) region, allowing increased neuronal survival. In addition, this protective response is specifically reversed by U0126, an ERK inhibitor, which promotes cell death only when it is administered together with Glu. Our findings demonstrate that the ERK signaling pathway has a neuroprotective role in the response to Glu-induced excitotoxicity in hippocampal neurons. Therefore, the ERK signaling pathway may be activated as a cellular response to excitotoxic injury to prevent damage and neural loss, representing a novel therapeutic target in the treatment of neurodegenerative diseases.

Loss of FMR2 further emphasizes the link between deregulation of immediate early response genes FOS and JUN and intellectual disability

Loss of FMR2 causes Fragile X E (FRAXE) site-associated intellectual disability (ID). FMR2 regulates transcription, promotes alternative splicing with preference for G-quartet structure harbouring exons and is localized to the nuclear speckles. In primary skin fibroblasts from FRAXE patients (n = 8), we found a significant reduction in the number, but a significant increase in the size, of nuclear speckles, when compared with the controls (n = 4). Since nuclear speckles are enriched with factors involved in pre-mRNA processing, we explored the consequence of these defects and the loss of FMR2 on the transcriptome. We performed whole genome expression profiling using total RNA extracted from these cell lines and found 27 genes significantly deregulated by at least 2-fold at P < 0.05 in the patients. Among these genes, FOS was significantly upregulated and was further investigated due to its established role in neuronal cell function. We showed that (i) 30% depletion of Fmr2 in mouse primary cortical neurons led to a 2-fold increase in Fos expression, (ii) overexpression of FMR2 significantly decreased FOS promoter activity in luciferase assays, and (iii) as FOS promoter contains a serum response element, we found that not FOS, but JUN, which encodes for a protein that forms a transcriptional activator complex with FOS, was significantly upregulated in the patients' cell lines upon mitogen stimulation. These results suggest that FMR2 is an upstream regulator of FOS and JUN, and further link deregulation of the immediate early response genes to the pathology of ID- and FRAXE-associated ID in particular.

Comparative genomics using teleost fish helps to systematically identify target gene bodies of functionally defined human enhancers

Background

Human genome is enriched with thousands of conserved non-coding elements (CNEs). Recently, a medium throughput strategy was employed to analyze the ability of human CNEs to drive tissue specific expression during mouse embryogenesis. These data led to the establishment of publicly available genome wide catalog of functionally defined human enhancers. Scattering of enhancers over larger regions in vertebrate genomes seriously impede attempts to pinpoint their precise target genes. Such associations are prerequisite to explore the significance of this in vivo characterized catalog of human enhancers in development, disease and evolution.

Results

This study is an attempt to systematically identify the target gene-bodies for functionally defined human CNE-enhancers. For the purpose we adopted the orthology/paralogy mapping approach and compared the CNE induced reporter expression with reported endogenous expression pattern of neighboring genes. This procedure pinpointed specific target gene-bodies for the total of 192 human CNE-enhancers. This enables us to gauge the maximum genomic search space for enhancer hunting: 4 Mb of genomic sequence around the gene of interest (2 Mb on either side). Furthermore, we used human-rodent comparison for a set of 159 orthologous enhancer pairs to infer that the central nervous system (CNS) specific gene expression is closely associated with the cooperative interaction among at least eight distinct transcription factors: SOX5, HFH, SOX17, HNF3β, c-FOS, Tal1beta-E47S, MEF and FREAC.

Conclusions

In conclusion, the systematic wiring of cis-acting sites and their target gene bodies is an important step to unravel the role of in vivo characterized catalog of human enhancers in development, physiology and medicine.

Neonatal whisker clipping alters behavior, neuronal structure and neural activity in adult rats

Early experience plays critical roles during the development of sensory systems. For example, neonatal surgical manipulations of the whiskers in rodents lead to altered neural activity and behaviors later in life. However, while surgical procedures damage the sensory pathway; it is hard to examine the impact of whisker deprivation on adult animals. To address this issue, we performed a neonatal whisker clipping (WC0-3) paradigm, a non-invasive procedure, from the day of birth (P0) to postnatal day (P) 3, and examined behavioral performances in their adult age. With fully regrown whiskers, the WC0-3 rats exhibited shorter crossable distance than controls in a gap-crossing task, suggesting a defect in their whisker-specific tactile function. In their somatosensory cortex, the layer IV spiny stellate neurons had reduced dendritic complexity and spine density. After exploration in a novel environment, the expression of an activity-dependent immediate early gene, c-fos, increased dramatically in the somatosensory cortex. However, in WC0-3 rats, the number of c-Fos positive cells was less than those in control rats, indicating a fault in transducing sensory-related neural activity between cortical layers in WC0-3 rats. Together, our results demonstrate the roles of early tactile experience on the establishment of layer-specific excitatory connection in the barrel cortex. Early sensory insufficiency would leave long-lasting functional deficits in the sensory system.

Network, cellular, and molecular mechanisms underlying long-term memory formation

The neural network stores information through activity-dependent synaptic plasticity that occurs in populations of neurons. Persistent forms of synaptic plasticity may account for long-term memory storage, and the most salient forms are the changes in the structure of synapses. The theory proposes that encoding should use a sparse code and evidence suggests that this can be achieved through offline reactivation or by sparse initial recruitment of the network units. This idea implies that in some cases the neurons that underwent structural synaptic plasticity might be a subpopulation of those originally recruited; However, it is not yet clear whether all the neurons recruited during acquisition are the ones that underwent persistent forms of synaptic plasticity and responsible for memory retrieval. To determine which neural units underlie long-term memory storage, we need to characterize which are the persistent forms of synaptic plasticity occurring in these neural ensembles and the best hints so far are the molecular signals underlying structural modifications of the synapses. Structural synaptic plasticity can be achieved by the activity of various signal transduction pathways, including the NMDA-CaMKII and ACh-MAPK. These pathways converge with the Rho family of GTPases and the consequent ERK 1/2 activation, which regulates multiple cellular functions such as protein translation, protein trafficking, and gene transcription. The most detailed explanation may come from models that allow us to determine the contribution of each piece of this fascinating puzzle that is the neuron and the neural network.

Neurotoxic (+)-methamphetamine treatment in rats increases brain-derived neurotrophic factor and tropomyosin receptor kinase B expression in multiple brain regions

Methamphetamine (MA) is an abused stimulant which can result in cognitive deficits and monoamine depletions. Animal models of neurotoxic MA exposure show reductions in dopamine, serotonin, and their associated transporters. MA abuse can result in long-term attention, working memory, and executive function deficits in humans and deficits in route-based egocentric learning, novel object recognition, and novel odor preference in rodents. MA has also been shown to affect brain-derived neurotrophic factor (BDNF) in humans and rodents. This experiment examined the effects of a MA binge dosing regimen (10 mg/kg x 4 at 2 h intervals, s.c.) in Sprague-Dawley rats on BDNF, tropomyosin receptor kinase B (TrkB), and tyrosine hydroxylase (TH) mRNA expression, and plasma corticosterone. Tissues were collected 1, 7, and 24 h following the last MA dose. Expression of BDNF and TrkB mRNA was analyzed using in situ hybridization with cRNA probes. Frontal, parietal, and entorhinal cortical BDNF mRNA expression were increased by MA exposure at all time-points. Increases in BDNF mRNA were also seen in the hippocampal CA1, prefrontal cortex (PFC), piriform cortex, and locus coeruleus but only at specific times. TrkB mRNA expression was modified in several subregions of the hippocampus as well as in PFC and striatum. TH mRNA was increased at the 1 h time-point in the substantia nigra pars compacta with no differences noted at the other times. Corticosterone levels were increased at all three time-points. The findings suggest that BDNF and its receptor may be upregulated as a compensatory mechanism after MA exposure.

Short- and long-term effects of intermittent social defeat stress on brain-derived neurotrophic factor expression in mesocorticolimbic brain regions

Social defeat stress is an ethologically salient stressor which activates dopaminergic areas and, when experienced repeatedly, has long-term effects on dopaminergic function and related behavior. The mechanism for these long-lasting consequences remains unclear. A potential candidate for mediating these effects is brain-derived neurotrophic factor (BDNF), a neurotrophin involved in synaptic plasticity and displaying alterations in dopaminergic regions in response to various types of stress. In this study, we sought to determine whether repeated social defeat stress altered BDNF mRNA and protein expression in dopaminergic brain regions either immediately after the last stress exposure or 4 weeks later. Male Sprague-Dawley rats were subjected to social defeat stress consisting of brief confrontation with an aggressive male rat every third day for 10 days; control rats were handled according to the same schedule. Animals were euthanized either 2 h or 28 days after the last stress or handling episode. Our results show that 2 h after stress, BDNF protein and mRNA expression increased in the medial prefrontal cortex. At this time-point, BDNF mRNA increased in the amygdala and protein expression increased in the substantia nigra. Twenty-eight days after stress, BDNF protein and mRNA expression were elevated in the medial amygdala and ventral tegmental area. Given the role of BDNF in neural plasticity, BDNF alterations that are long-lasting may be significant for neural adaptations to social stress. The dynamic nature of BDNF expression in dopaminergic brain regions in response to repeated social stress may therefore have implications for lasting neurochemical and behavioral changes related to dopaminergic function.

Methamphetamine preconditioning alters midbrain transcriptional responses to methamphetamine-induced injury in the rat striatum

Methamphetamine (METH) is an illicit drug which is neurotoxic to the mammalian brain. Numerous studies have revealed significant decreases in dopamine and serotonin levels in the brains of animals exposed to moderate-to-large METH doses given within short intervals of time. In contrast, repeated injections of small nontoxic doses of the drug followed by a challenge with toxic METH doses afford significant protection against monoamine depletion. The present study was undertaken to test the possibility that repeated injections of the drug might be accompanied by transcriptional changes involved in rendering the nigrostriatal dopaminergic system refractory to METH toxicity. Our results confirm that METH preconditioning can provide significant protection against METH-induced striatal dopamine depletion. In addition, the presence and absence of METH preconditioning were associated with substantial differences in the identity of the genes whose expression was affected by a toxic METH challenge. Quantitative PCR confirmed METH-induced changes in genes of interest and identified additional genes that were differentially impacted by the toxic METH challenge in the presence of METH preconditioning. These genes include small heat shock 27 kD 27 protein 2 (HspB2), thyrotropin-releasing hormone (TRH), brain derived neurotrophic factor (BDNF), c-fos, and some encoding antioxidant proteins including CuZn superoxide dismutase (CuZnSOD), glutathione peroxidase (GPx)-1, and heme oxygenase-1 (Hmox-1). These observations are consistent, in part, with the transcriptional alterations reported in models of lethal ischemic injuries which are preceded by ischemic or pharmacological preconditioning. Our findings suggest that multiple molecular pathways might work in tandem to protect the nigrostriatal dopaminergic pathway against the deleterious effects of the toxic psychostimulant. Further analysis of the molecular and cellular pathways regulated by these genes should help to provide some insight into the neuroadaptive potentials of the brain when repeatedly exposed to drugs of abuse.

Long-term reduction of hippocampal brain-derived neurotrophic factor activity after fetal-neonatal iron deficiency in adult rats

Fetal-neonatal iron deficiency acutely alters hippocampal biochemistry, neural morphology, and electrophysiology accompanied by a downregulation of brain-derived neurotrophic factor (BDNF). These changes provide a cellular and molecular basis for observed short-term learning and memory impairments. However, the etiology of residual, long-term hippocampal neurotransmission abnormalities and learning impairments after treatment remain unclear. Because BDNF modulates learning and memory, we assessed its expression in 65-d-old formerly iron deficient (FID) male rats that had been iron deficient during the fetal-neonatal period and treated with iron since postnatal day 7. BDNF-III and -IV mRNAs and BDNF protein expression remained down-regulated in FID rats when compared with the always iron-sufficient rats. Expressions of BDNF activity-dependent downstream targets (3-hydroxy-3-methylglutaryl CoA reductase and immediate early genes c-fos, early growth response gene 1 and 2) were reduced in FID rats. In turn, hippocampal expressions of direct targets of early-growth response genes, including hypoxia-inducible factor 1, dual-specificity phosphatase 4, IGF 2, and myelin basic protein were also diminished in FID rats. Collectively, fetal-neonatal iron deficiency lowers hippocampal BDNF expression and function beyond the period of iron deficiency. These findings may underlie the persistence of learning deficits seen after fetal-neonatal iron deficiency.

BDNF induction with mild exercise in the rat hippocampus

Although chronic voluntary physical activity has been shown to enhance hippocampal brain-derived neurotrophic factor (BDNF) expression in animals, the effects of forced exercise on a treadmill have not been fully investigated. We assessed induction of c-fos and BDNF expression with acute exercise at different running intensities. The mRNA for c-fos, a marker for neuronal activation, was up-regulated even under low-intensity running (15 m/min), although its induction appeared to be intensity dependent. On the other hand, increases in BDNF mRNA and protein were seen only at low-intensity running. At moderate-intensity running (25 m/min) which elevated blood lactate and corticosterone levels, induction of BDNF mRNA, but not its protein, was even depressed. Our study shows the first evidence that with an acute low-intensity exercise that is minimally stressful, hippocampal activation and BDNF expression can be achieved lending support to the idea that mild exercise could yield to greater benefits in hippocampal functions compared to the more strenuous forms.

Kainic acid induces early and transient autophagic stress in mouse hippocampus

Kainic acid (KA) treatment is a well-established model of hippocampal neuron death mediated in large part by KA receptor-induced excitotoxicity. KA-induced, delayed neuron death has been shown previously to follow the induction of seizures and exhibit characteristics of both apoptosis and necrosis. Growing evidence supports a role of autophagic stress-induced death of neurons in several in vitro and in vivo models of neuron death and neurodegeneration. However, whether autophagic stress also plays a role in KA-induced excitotoxicity has not been previously investigated. To examine whether KA alters the levels of proteins associated with or known to regulate the formation of autophagic vacuoles, we isolated hippocampal extracts from control mice and in mice following 2-16 h KA injection. KA induced a significant increase in the amount of LC3-II, a specific marker of autophagic vacuoles, at 4-6h following KA, which indicates a transient induction of autophagic stress. Levels of autophagy-associated proteins including ATG5 (conjugated to ATG12), ATG6 and ATG7 did not change significantly after treatment with KA. However, ratios of phospho-mTOR/mTOR were elevated from 6 to 16 h, and ratios of phospho-Akt/Akt were elevated at 16 h following KA treatment, suggesting a potential negative feedback loop to inhibit further stimulation of autophagic stress. Together these data indicate the transient induction of autophagic stress by KA which may serve to regulate excitotoxic death in mouse hippocampus.