Rapid enrichment of presynaptic protein in boutons undergoing classical conditioning is mediated by brain-derived neurotrophic factor

Suberoylanilide hydroxamic acid attenuates cognitive impairment in offspring caused by maternal surgery during mid-pregnancy

Some pregnant women have to experience non-obstetric surgery during pregnancy under general anesthesia. Our previous studies showed that maternal exposure to sevoflurane, isoflurane, propofol, and ketamine causes cognitive deficits in offspring. Histone acetylation has been implicated in synaptic plasticity. Propofol is commonly used in non-obstetric procedures on pregnant women. Previous studies in our laboratory showed that maternal propofol exposure in pregnancy impairs learning and memory in offspring by disturbing histone acetylation. The present study aims to investigate whether HDAC inhibitor suberoylanilide hydroxamic acid (SAHA) could attenuate learning and memory deficits in offspring caused by maternal surgery under propofol anesthesia during mid-pregnancy. Maternal rats were exposed to propofol or underwent abdominal surgery under propofol anesthesia during middle pregnancy. The learning and memory abilities of the offspring rats were assessed using the Morris water maze (MWM) test. The protein levels of histone deacetylase 2 (HDAC2), phosphorylated cAMP response-element binding (p-CREB), brain-derived neurotrophic factor (BDNF), and phosphorylated tyrosine kinase B (p-TrkB) in the hippocampus of the offspring rats were evaluated by immunofluorescence staining and western blot. Hippocampal neuroapoptosis was detected by TUNEL staining. Our results showed that maternal propofol exposure during middle pregnancy impaired the water-maze learning and memory of the offspring rats, increased the protein level of HDAC2 and reduced the protein levels of p-CREB, BDNF and p-TrkB in the hippocampus of the offspring, and such effects were exacerbated by surgery. SAHA alleviated the cognitive dysfunction and rescued the changes in the protein levels of p-CREB, BDNF and p-TrkB induced by maternal propofol exposure alone or maternal propofol exposure plus surgery. Therefore, SAHA could be a potential and promising agent for treating the learning and memory deficits in offspring caused by maternal nonobstetric surgery under propofol anesthesia.

Abdominal surgery under ketamine anesthesia during second trimester impairs hippocampal learning and memory of offspring by regulating dendrite spine remodeling in rats

Recent evidence showed that general anesthesia produces long-term neurotoxicity and cognitive dysfunction. However, it remains unclear whether maternal non-obstetric surgery under ketamine anesthesia during second trimester causes cognitive impairment in offspring. The present study assigned pregnant rats into three groups: 1) normal control group receiving no anesthesia and no surgery, 2) ketamine group receiving ketamine anesthesia for 2 h on the 14th day of gestation but no surgery, and 3) surgery group receiving abdominal surgery under ketamine anesthesia on the 14th day of gestation. On postnatal day 1, the offspring rats in Ketamine group and surgery group were assigned to receive intra-peritoneal injection of Senegenin (15 mg/kg), once per day for consecutive 14 days. The offspring's spatial perception, anxiety-like behavior, and learning and memory were evaluated. Then the offspring's hippocampal tissues were collected. The offspring of the surgery group were impaired in the spatial perception in the cliff avoidance test and the spatial learning and memory in the Morris water maze test. Accordingly, the activity of histone deacetylases increased, the protein levels of NEDD9, BDNF, p-TrkB, Syn and PSD-95 decreased, and the density of dendritic spines reduced in the hippocampus of the offspring of the surgery group, and such effects were not seen in the offspring of the ketamine group, neither in the offspring of control group. Senegenin alleviated the learning and memory impairment, and increased the protein levels of NEDD9, BDNF, p-TrkB, Syn and PSD-95 and the density of dendritic spines in the offspring of the surgery group. ketamine anesthesia plus surgery during second trimester impairs hippocampus-dependent learning and memory, and the deficits could be rescued by treatment with Senegenin.

Anxiolytic reversal of classically conditioned / chronic stress-induced gene expression and learning in the Stress Alternatives Model

Social decision-making is critically influenced by neurocircuitries that regulate stress responsiveness. Adaptive choices, therefore, are altered by stress-related neuromodulatory peptide systems, such as corticotropin releasing factor (CRF). Experimental designs that take advantage of ecologically salient fear-inducing stimuli allow for revelation of neural mechanisms that regulate the balance between pro- and anti-stress responsiveness. To accomplish this, we developed a social stress and conditioning protocol, the Stress Alternatives Model (SAM), that utilizes a simple dichotomous choice, and produces distinctive behavioral phenotypes (Escape or Stay). The experiments involve repeated social aggression, a potent unconditioned stimulus (US), from a novel larger conspecific (a 3X larger Rainbow trout). Prior to the social interaction, the smaller test fish is presented with an auditory conditioning stimulus (water off = CS). During the social aggression, an escape route is available, but is only large enough for the smaller test animal. Surprisingly, although the new aggressor provides vigorous attacks each day, only 50% of the test fish choose Escape. Stay fish, treated with the CRF1 antagonist antalarmin, a potent anxiolytic drug, on day 4, promotes Escape behavior for the last 4 days of the SAM protocol. The results suggest that the decision to Escape, required a reduction in stress reactivity. The Stay fish that chose Escape following anxiolytic treatment, learned how to use the escape route prior to stress reduction, as the Escape latency in these fish was significantly faster than first time escapers. In Escape fish, the use of the escape route is learned over several days, reducing the Escape latency over time in the SAM. Fear conditioning (water off + aggression) resulted in elevated hippocampal (DL) Bdnf mRNA levels, with coincident reduction in the AMPA receptor subunit Glua1 expression, a result that is reversed following a one-time treatment (during SAM aggression on day 4) with the anxiolytic CRF1 receptor antagonist antalarmin.

Dysregulation of the SNARE-binding protein Munc18-1 impairs BDNF secretion and synaptic neurotransmission: a novel interventional target to protect the aging brain

Brain-derived neurotrophic factor (BDNF) has a central role in maintaining and strengthening neuronal connections and to stimulate neurogenesis in the adult brain. Decreased levels of BDNF in the aging brain are thought to usher cognitive impairment. BDNF is stored in dense core vesicles and released through exocytosis from the neurites. The exact mechanism for the regulation of BDNF secretion is not well understood. Munc18-1 (STXBP1) was found to be essential for the exocytosis of synaptic vesicles, but its involvement in BDNF secretion is not known. Interestingly, neurons lacking munc18-1 undergo severe degeneration in knock-out mice. Here, we report the effects of BDNF treatment on the presynaptic terminal using munc18-1-deficient neurons. Reduced expression of munc18-1 in heterozygous (+/-) neurons diminishes synaptic transmitter release, as tested here on individual synaptic connections with FM1-43 fluorescence imaging. Transduction of cultured neurons with BDNF markedly increased BDNF secretion in wild-type but was less effective in munc18-1 +/- cells. In turn, BDNF enhanced synaptic functions and restored the severe synaptic dysfunction induced by munc18-1 deficiency. The role of munc18-1 in the synaptic effect of BDNF is highlighted by the finding that BDNF upregulated the expression of munc18-1 in neurons, consistent with enhanced synaptic functions. Accordingly, this is the first evidence showing the functional effect of BDNF in munc18-1 deficient synapses and about the direct role of munc18-1 in the regulation of BDNF secretion. We propose a molecular model of BDNF secretion and discuss its potential as therapeutic target to prevent cognitive decline in the elderly.

Gallic acid activates hippocampal BDNF-Akt-mTOR signaling in chronic mild stress

Gallic acid (3,4,5-trihydroxybenzoic acid) is a naturally occurring polyphenolic compound. Previous study has shown that gallic acid possessed significant antidepressant-like activity in mice, which was partly mediated by increasing serotonin and catecholamine levels. The main aim of the present study is to investigate the possible effects of gallic acid on brain-derived neurotrophic factor (BDNF) signaling activation. Mice were exposed to chronic mild stress (CMS) and orally administrated with gallic acid for four weeks. The behavioral results showed that gallic acid not only reversed the decreased sucrose preference, but also attenuated the increased immobility time. In addition, gallic acid promoted both the BDNF and p-TrkB levels in the hippocampus induced by CMS. Moreover, the results also demonstrated that the inactivated Akt-mTOR signaling pathway, as well as its downstream effectors induced by CMS was activated again by gallic acid. Last, immunofluorescence detection indicated that gallic acid reversed the newborn neurons inhibition in the dentate gyrus by CMS. In conclusion, these results show that the activation of the hippocampal BDNF-Akt-mTOR signaling is involved in the antidepressant-like effects of gallic acid.

OAB-14, a bexarotene derivative, improves Alzheimer's disease-related pathologies and cognitive impairments by increasing β-amyloid clearance in APP/PS1 mice

The pathogenesis of Alzheimer's disease (AD) is complex, though the clinical failures of anti-AD candidates targeting Aβ production (such as β- and γ-secretase inhibitors) make people suspect the Aβ hypothesis, in which the neurotoxicity of Aβ is undoubtedly involved. According to studies, >95% of AD patients with sporadic AD are primarily associated with abnormal Aβ clearance. Therefore, drugs that increase Aβ clearance are becoming new prospects for the treatment of AD. Here, the novel small molecule OAB-14, designed using bexarotene as the lead compound, significantly alleviated cognitive impairments in amyloid precursor protein (APP)/presenilin 1 (PS1) transgenic mice after administration for 15 days or 3 months. OAB-14 rapidly cleared 71% of Aβ by promoting microglia phagocytosis and increasing IDE and NEP expression. This compound also attenuated the downstream pathological events of Aβ accumulation, such as synaptic degeneration, neuronal loss, tau hyperphosphorylation and neuroinflammation in APP/PS1 mice. Moreover, OAB-14 had no significant effect on body weight or liver toxicity after acute and chronic treatment. OAB-14 was well tolerated and its maximum-tolerated dose in mice was >4.0 g/kg. Based on these findings, OAB-14 represents a promising new candidate for AD treatment.

Ginsenoside Rb1 improves leptin sensitivity in the prefrontal cortex in obese mice

AIM

Obesity impairs leptin-induced regulation of brain-derived neurotrophic factor (BDNF) expression and synaptogenesis, which has been considered to be associated with the incidence of neuronal degenerative diseases, cognitive decline, and depression. Ginsenoside Rb1 (Rb1), a major bioactive component of ginseng, is known to have an antiobesity effect and improve cognition. This study examined whether Rb1 can improve central leptin effects on BDNF expression and synaptogenesis in the prefrontal cortex during obesity using an in vivo and an in vitro model.

RESULT

Ginsenoside Rb1 (Rb1) chronic treatment improved central leptin sensitivity, leptin-JAK2-STAT3 signaling, and leptin-induced regulation of BDNF expression in the prefrontal cortex of high-fat diet-induced obese mice. In cultured prefrontal cortical neurons, palmitic acid, the saturated fat, impaired leptin-induced BDNF expression, reduced the immunoreactivity and mRNA expression of synaptic proteins, and impaired leptin-induced neurite outgrowth and synaptogenesis. Importantly, Rb1 significantly prevented these pernicious effects induced by palmitic acid.

CONCLUSION

These results indicate that Rb1 reverses central leptin resistance and improves leptin-BDNF-neurite outgrowth and synaptogenesis in the prefrontal cortical neurons. Thus, Rb1 supplementation may be a beneficial avenue to treat obesity-associated neurodegenerative disorders.

Antidepressant-like effects of standardized gypenosides: involvement of brain-derived neurotrophic factor signaling in hippocampus

RATIONALE

Gypenosides have been reported to produce neuroprotective effects and increase monoamine neurotransmitter levels in the brain.

OBJECTIVE

Considering that depression is involved in monoamine reduction, this study evaluated the antidepressant-like effects of gypenosides in mice exposed to chronic unpredictable mild stress (CUMS).

METHODS

The sucrose preference test and forced swimming test were performed after administration of gypenosides (at 25, 50, or 100 mg/kg) for 4 weeks. Hippocampal brain-derived neurotrophic factor (BDNF) and its downstream targets were analyzed by western blot. Additionally, hippocampal neuronal proliferation was measured by immunohistochemistry.

RESULTS

Four-week treatment with fluoxetine (20 mg/kg) and gypenosides (at either 50 or 100 mg/kg) increased sucrose preference and decreased the immobility time in mice exposed to CUMS. In addition, gypenosides (at either 50 or 100 mg/kg) also increased BDNF expression and neuronal proliferation in the hippocampus of CUMS animals. Further, we showed that treating CUMS mice with K252a, which is an inhibitor of the BDNF receptor TrkB, blocked the effects of gypenosides (100 mg/kg), including behavioral improvements, neuronal proliferation, and up-regulation of p-TrkB, p-ERK, and p-Akt proteins.

CONCLUSIONS

This study demonstrates that gypenosides exhibit antidepressant-like effects in mice, which may be mediated by activation of the BDNF-ERK/Akt signaling pathway in the hippocampus.

Repetitive transcranial magnetic stimulation effectively facilitates spatial cognition and synaptic plasticity associated with increasing the levels of BDNF and synaptic proteins in Wistar rats

Repetitive transcranial magnetic stimulation (rTMS) is a non-invasive technique, by which cognitive deficits can be alleviated. Furthermore, rTMS may facilitate learning and memory. However, its underlying mechanism is still little known. The aim of this study was to investigate if the facilitation of spatial cognition and synaptic plasticity, induced by rTMS, is regulated by enhancing pre- and postsynaptic proteins in normal rats. Morris water maze (MWM) test was performed to examine the spatial cognition. The synaptic plasticity, including long-term potentiation (LTP) and depotentiation (DEP), presynaptic plasticity paired-pulse facilitation (PPF), from the hippocampal Schaffer collaterals to CA1 region was subsequently measured using in vivo electrophysiological techniques. The expressions of brain-derived neurotrophic factor (BDNF), presynaptic protein synaptophysin (SYP) and postsynaptic protein NR2B were measured by Western blot. Our data show that the spatial learning/memory and reversal learning/memory in rTMS rats were remarkably enhanced compared to that in the Sham group. Furthermore, LTP and DEP as well as PPF were effectively facilitated by 5Hz-rTMS. Additionally, the expressions of BDNF, SYP and NR2B were significantly increased via magnetic stimulation. The results suggest that rTMS considerably increases the expressions of BDNF, postsynaptic protein NR2B and presynaptic protein SYP, and thereby significantly enhances the synaptic plasticity and spatial cognition in normal animals.

Propofol exposure during late stages of pregnancy impairs learning and memory in rat offspring via the BDNF-TrkB signalling pathway

The brain‐derived neurotrophic factor (BDNF)‐tyrosine kinase B (TrkB) (BDNF‐TrkB) signalling pathway plays a crucial role in regulating learning and memory. Synaptophysin provides the structural basis for synaptic plasticity and depends on BDNF processing and subsequent TrkB signalling. Our previous studies demonstrated that maternal exposure to propofol during late stages of pregnancy impaired learning and memory in rat offspring. The purpose of this study is to investigate whether the BDNF‐TrkB signalling pathway is involved in propofol‐induced learning and memory impairments. Propofol was intravenously infused into pregnant rats for 4 hrs on gestational day 18 (E18). Thirty days after birth, learning and memory of offspring was assessed by the Morris water maze (MWM) test. After the MWM test, BDNF and TrkB transcript and protein levels were measured in rat offspring hippocampus tissues using real‐time PCR (RT‐PCR) and immunohistochemistry (IHC), respectively. The levels of phosphorylated‐TrkB (phospho‐TrkB) and synaptophysin were measured by western blot. It was discovered that maternal exposure to propofol on day E18 impaired spatial learning and memory of rat offspring, decreased mRNA and protein levels of BDNF and TrkB, and decreased the levels of both phospho‐TrkB and synaptophysin in the hippocampus. Furthermore, the TrkB agonist 7,8‐dihydroxyflavone (7,8‐DHF) reversed all of the observed changes. Treatment with 7,8‐DHF had no significant effects on the offspring that were not exposed to propofol. The results herein indicate that maternal exposure to propofol during the late stages of pregnancy impairs spatial learning and memory of offspring by disturbing the BDNF‐TrkB signalling pathway. The TrkB agonist 7,8‐DHF might be a potential therapy for learning and memory impairments induced by maternal propofol exposure.

Protective effect of the orientin on noise-induced cognitive impairments in mice

There is increasing evidence that chronic noise stress impairs cognition and induces oxidative stress in the brain. Recently, orientin, a phenolic compound abundant in some fruits, millet, and herbs, has been shown to have antioxidant properties. This study investigated the potential effects of orientin against chronic noise-induced cognitive decline and its underlying mechanisms. A moderate-intensity noise exposure model was used to investigate the effects of orientin on behavior and biochemical alterations in mice. After 3 weeks of the noise exposure, the mice were treated with orientin (20mg/kg and 40 mg/kg, oral gavage) for 3 weeks. The chronic noise exposure impaired the learning and memory in mice in the Morris water maze and step-through tests. The noise exposure also decreased exploration and interest in a novel environment in the open field test. The administration of orientin significantly reversed noise-induced alterations in these behavior tests. Moreover, the orientin treatment significantly improved the noise-induced alteration of serum corticosterone and catecholamine levels and oxidative stress in the hippocampus and prefrontal cortex. Furthermore, the orientin treatment ameliorated the noise-induced decrease in brain-derived neurotrophic factor and synapse-associated proteins (synaptophysin and postsynaptic density protein 95) in the hippocampus and prefrontal cortex. Thus, orientin exerts protective effects on noise-induced cognitive decline in mice, specifically by improving central oxidative stress, neurotransmission, and increases synapse-associated proteins. Therefore, supplementation with orientin-enriched food or fruit could be beneficial as a preventive strategy for chronic noise-induced cognitive decline.

Low-frequency transcranial magnetic stimulation is beneficial for enhancing synaptic plasticity in the aging brain

In the aging brain, cognitive function gradually declines and causes a progressive reduction in the structural and functional plasticity of the hippocampus. Transcranial magnetic stimulation is an emerging and novel neurological and psychiatric tool used to investigate the neurobiology of cognitive function. Recent studies have demonstrated that low-frequency transcranial magnetic stimulation (≤1 Hz) ameliorates synaptic plasticity and spatial cognitive deficits in learning-impaired mice. However, the mechanisms by which this treatment improves these deficits during normal aging are still unknown. Therefore, the current study investigated the effects of transcranial magnetic stimulation on the brain-derived neurotrophic factor signal pathway, synaptic protein markers, and spatial memory behavior in the hippocampus of normal aged mice. The study also investigated the downstream regulator, Fyn kinase, and the downstream effectors, synaptophysin and growth-associated protein 43 (both synaptic markers), to determine the possible mechanisms by which transcranial magnetic stimulation regulates cognitive capacity. Transcranial magnetic stimulation with low intensity (110% average resting motor threshold intensity, 1 Hz) increased mRNA and protein levels of brain-derived neurotrophic factor, tropomyosin receptor kinase B, and Fyn in the hippocampus of aged mice. The treatment also upregulated the mRNA and protein expression of synaptophysin and growth-associated protein 43 in the hippocampus of these mice. In conclusion, brain-derived neurotrophic factor signaling may play an important role in sustaining and regulating structural synaptic plasticity induced by transcranial magnetic stimulation in the hippocampus of aging mice, and Fyn may be critical during this regulation. These responses may change the structural plasticity of the aging hippocampus, thereby improving cognitive function.

Sigma 1 receptor activation regulates brain-derived neurotrophic factor through NR2A-CaMKIV-TORC1 pathway to rescue the impairment of learning and memory induced by brain ischaemia/reperfusion

RATIONALE

Sigma-1 receptor (Sig-1R) agonists showed anti-amnesic properties in Alzheimer's disease models and anti-inflammatory properties in cerebrum ischaemia models. The agonist of Sig-1R was reported to up-regulate brain-derived neurotrophic factor (BDNF) levels in the hippocampus of mice. Here, we investigate whether the activation of Sig-1R attenuates the learning and memory impairment induced by ischaemia/reperfusion and how it affects the expression of BDNF.

OBJECTIVES

Bilateral common carotid artery occlusion (BCCAO) was induced for 20 min in C57BL/6 mice.

MATERIALS AND METHODS

Sig-1R agonist, PRE084, sigma 1/2 non-selective agonist, DTG, Sig-1R antagonist and BD1047 were injected once daily throughout the experiment. Behavioural tests were performed from day 8. On day 22 after BCCAO, mice were sacrificed for biochemical analysis.

RESULTS

PRE084 and DTG ameliorated learning and memory impairments in the Y maze, novel object recognition, and water maze tasks and prevented the decline of synaptic proteins and BDNF expression in the hippocampus of BCCAO mice. Furthermore, PRE084 and DTG up-regulated the level of NMDA receptor 2A (NR2A), calcium/calmodulin-dependent protein kinase type IV (CaMKIV) and CREB-specific co-activator transducer of regulated CREB activity 1 (TORC1). Additionally, the effects of PRE084 and DTG were antagonised by the co-administration of BD1047.

CONCLUSIONS

Sig-1R activation showed an attenuation in the ischaemia/reperfusion model and the activation of Sig-1R increased the expression of BDNF, possibly through the NR2A-CaMKIV-TORC1 pathway, and Sig-1R agonists might function as neuroprotectant agents in vascular dementia.

Orientin improves depression-like behavior and BDNF in chronic stressed mice

SCOPE

Oxidative stress is involved in chronic stress-induced depression and the disruption of neurotransmission and neuroplasticity. Recently, orientin, a phenolic compound abundant in some fruits, millet, and herbs, has been shown to have antioxidant properties. This study investigated the potential antidepressant effects of orientin against chronic stress and its underlying mechanisms.

METHODS AND RESULTS

The chronic unpredictable mild stress (CUMS) model was used to investigate the effects of orientin on behavior and biochemical alterations in mice. After 2 weeks of the CUMS protocol, the mice were treated with orientin (20 mg/kg and 40 mg/kg, oral gavage) for 3 weeks. Administration of orientin significantly alleviated the CUMS-induced depression-like behavior, including sucrose preference reduction, locomotor activity decline, and hypomotility. Orientin treatment attenuated the oxidative stress markers and increased the concentrations of serotonin and norepinephrine in the hippocampus and prefrontal cortex of CUMS mice. Orientin treatment also increased the brain-derived neurotrophic factor and synapse-associated proteins (synaptophysin and postsynaptic density protein 95) of CUMS mice.

CONCLUSION

Orientin exerts antidepressant-like effects on CUMS mice, specifically by improving central oxidative stress, neurotransmission, and neuroplasticity. Therefore, supplementation with orientin-enriched food or fruit could be beneficial as a preventive strategy for chronic stress-induced depression.

BDNF-ERK-CREB signalling mediates the role of miR-132 in the regulation of the effects of oleanolic acid in male mice

BACKGROUND

Although previous study has demonstrated that brain-derived neurotrophic factor (BDNF) is involved in the antidepressant-like effect of oleanolic acid, there is little information regarding the details of the molecular mechanism involved in this effect.

METHODS

We used a chronic unpredictable mild stress (CUMS) model to test the antidepressant-like effect of oleanolic acid on depressant-like behaviour, miR-132 expression and synaptic protein expression in the male mouse hippocampus. Furthermore, we explored the possible signalling pathways associated with miR-132 expression that mediate the effect of oleanolic acid on neuronal proliferation.

RESULTS

The results demonstrated that a 3-week treatment with oleanolic acid ameliorated CUMS-induced anhedonic and anxiogenic behaviours. Furthermore, we found that oleanolic acid led to the BDNF-related phosphorylation and activation of extracellular signal-regulated kinases (ERK) and cyclic adenosine monophosphate response element binding protein (CREB), which was associated with the upregulation of miR-132 and hippocampal neuronal proliferation. Moreover, experiments with an miR-132 antagomir revealed that targeting miR-132 led to inhibition of neuronal proliferation and the postsynaptic density protein 95, but did not affect presynaptic protein synapsin I.

LIMITATIONS

Several other stimuli can also induce CREB phosphorylation in the hippocampus. Thus, regulation of miR-132 may not be restricted to neurotrophic signalling.

CONCLUSION

Our results show that oleanolic acid induces the upregulation of miR-132, which serves as an important regulator of neurotrophic actions, mainly through the activation of the hippocampal BDNF-ERK-CREB signalling pathways.

BDNF signaling is necessary for the antidepressant-like effect of naringenin

Previous studies in our laboratory have demonstrated that naringenin produced antidepressant-like action in tail suspension test (TST). However, the underlying mechanisms involved in neurotrophin system by which naringenin works have not been investigated. The present study extends earlier works on the role of brain-derived neurotrophic factor (BDNF) in regulating the antidepressant-like actions of naringenin in chronic unpredictable mild stress (CUMS). We showed that a 21-day regimen with naringenin reversed the decreased sucrose preference in sucrose preference test (SPT) and the prolonged first feeding latency in novelty-suppressed feeding test (NSFT), without affecting home-cage feeding consumption. In addition, we also found that naringenin promoted BDNF expression in the hippocampus but not in the frontal cortex in both non-stressed and CUMS mice. Moreover, the antidepressant-like effect of naringenin in SPT and NSFT induced by naringenin administration were totally abolished by K252a, an inhibitor of BDNF receptor tropomyosin-related kinase receptor B (TrkB). In conclusion, our findings suggest that the antidepressant-like effect of naringenin may be mediated, at least in part, by the activation of BDNF signaling in the hippocampus.

Identification of a functionally distinct truncated BDNF mRNA splice variant and protein in Trachemys scripta elegans

Brain-derived neurotrophic factor (BDNF) has a diverse functional role and complex pattern of gene expression. Alternative splicing of mRNA transcripts leads to further diversity of mRNAs and protein isoforms. Here, we describe the regulation of BDNF mRNA transcripts in an in vitro model of eyeblink classical conditioning and a unique transcript that forms a functionally distinct truncated BDNF protein isoform. Nine different mRNA transcripts from the BDNF gene of the pond turtle Trachemys scripta elegans (tBDNF) are selectively regulated during classical conditioning: exon I mRNA transcripts show no change, exon II transcripts are downregulated, while exon III transcripts are upregulated. One unique transcript that codes from exon II, tBDNF2a, contains a 40 base pair deletion in the protein coding exon that generates a truncated tBDNF protein. The truncated transcript and protein are expressed in the naïve untrained state and are fully repressed during conditioning when full-length mature tBDNF is expressed, thereby having an alternate pattern of expression in conditioning. Truncated BDNF is not restricted to turtles as a truncated mRNA splice variant has been described for the human BDNF gene. Further studies are required to determine the ubiquity of truncated BDNF alternative splice variants across species and the mechanisms of regulation and function of this newly recognized BDNF protein.

CREB phosphorylation regulates striatal transcriptional responses in the self-administration model of methamphetamine addiction in the rat

Neuroplastic changes in the dorsal striatum participate in the transition from casual to habitual drug use and might play a critical role in the development of methamphetamine (METH) addiction. We examined the influence of METH self-administration on gene and protein expression that may form substrates for METH-induced neuronal plasticity in the dorsal striatum. Male Sprague-Dawley rats self-administered METH (0.1mg/kg/injection, i.v.) or received yoked saline infusions during eight 15-h sessions and were euthanized 2h, 24h, or 1month after cessation of METH exposure. Changes in gene and protein expression were assessed using microarray analysis, RT-PCR and Western blots. Chromatin immunoprecipitation (ChIP) followed by PCR was used to examine epigenetic regulation of METH-induced transcription. METH self-administration caused increases in mRNA expression of the transcription factors, c-fos and fosb, the neurotrophic factor, Bdnf, and the synaptic protein, synaptophysin (Syp) in the dorsal striatum. METH also caused changes in ΔFosB, BDNF and TrkB protein levels, with increases after 2 and 24h, but decreases after 1month of drug abstinence. Importantly, ChIP-PCR showed that METH self-administration caused enrichment of phosphorylated CREB (pCREB), but not of histone H3 trimethylated at lysine 4 (H3K4me3), on promoters of c-fos, fosb, Bdnf and Syp at 2h after cessation of drug intake. These findings show that METH-induced changes in gene expression are mediated, in part, by pCREB-dependent epigenetic phenomena. Thus, METH self-administration might trigger epigenetic changes that mediate alterations in expression of genes and proteins serving as substrates for addiction-related synaptic plasticity.

Nobiletin Ameliorates the Deficits in Hippocampal BDNF, TrkB, and Synapsin I Induced by Chronic Unpredictable Mild Stress

Background. Our previous study has demonstrated that nobiletin could reverse the behavioral alterations in stressed mice. However, the relation of its antidepressant-like action with neurotrophic molecular expression remains unknown. This study aimed to explore the antidepressant-like mechanism of nobiletin related to the neurotrophic system in rats exposed to chronic unpredictable mild stress (CUMS). Methods. Depressive-like anhedonia (assessed by sucrose preference) and serum corticosterone secretion were evaluated in the CUMS, followed by brain-derived neurotrophic factor (BDNF), its tropomyosin-related kinase receptor B (TrkB), and the downstream target synapsin I expressions in the hippocampus. Results. Anhedonia, which occurred within week 2, was rapidly ameliorated by nobiletin. While fluoxetine needed additional 2 weeks to improve the anhedonia. In addition, nobiletin administration for 5 weeks significantly ameliorated CUMS-induced increase in serum corticosterone levels. Furthermore, we also found that CUMS-induced deficits of hippocampal BDNF, TrkB, and synapsin I were ameliorated by nobiletin. Conclusions. Taken together, these findings suggest that nobiletin produces rapidly acting antidepressant-like responses in the CUMS and imply that BDNF-TrkB pathway may play an important role in the antidepressant-like effect of nobiletin.

A clinical/translational perspective: can a developmental hormone play a role in the treatment of traumatic brain injury?

Despite decades of laboratory research and clinical trials, a safe and effective treatment for traumatic brain injury (TBI) has yet to be put into successful clinical use. I suggest that much of the problem can be attributed to a reductionist perspective and attendant research strategy directed to finding or designing drugs that target a single receptor mechanism, gene, or brain locus. This approach fails to address the complexity of TBI, which leads to a cascade of systemic toxic events in the brain and throughout the body that may persist over long periods of time. Attention is now turning to pleiotropic drugs: drugs that act on multiple genomic, proteomic and metabolic pathways to enhance morphological and functional outcomes after brain injury. Of the various agents now in clinical trials, the neurosteroid progesterone (PROG) is gaining attention despite the widespread assumption that it is "just a female hormone" with limited, if any, neuroprotective properties. This perspective should change. PROG is also a powerful developmental hormone that plays a critical role in protecting the fetus during gestation. I argue here that development, neuroprotection and cellular repair have a number of properties in common. I discuss evidence that PROG is pleiotropically neuroprotective and may be a useful therapeutic and neuroprotective agent for central nervous system injury and some neurodegenerative diseases.

Two-stage AMPA receptor trafficking in classical conditioning and selective role for glutamate receptor subunit 4 (tGluA4) flop splice variant

Previously, we proposed a two-stage model for an in vitro neural correlate of eyeblink classical conditioning involving the initial synaptic incorporation of glutamate receptor A1 (GluA1)-containing α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid type receptors (AMPARs) followed by delivery of GluA4-containing AMPARs that support acquisition of conditioned responses. To test specific elements of our model for conditioning, selective knockdown of GluA4 AMPAR subunits was used using small-interfering RNAs (siRNAs). Recently, we sequenced and characterized the GluA4 subunit and its splice variants from pond turtles, Trachemys scripta elegans (tGluA4). Analysis of the relative abundance of mRNA expression by real-time RT-PCR showed that the flip/flop variants of tGluA4, tGluA4c, and a novel truncated variant tGluA4trc1 are major isoforms in the turtle brain. Here, transfection of in vitro brain stem preparations with anti-tGluA4 siRNA suppressed conditioning, tGluA4 mRNA and protein expression, and synaptic delivery of tGluA4-containing AMPARs but not tGluA1 subunits. Significantly, transfection of abducens motor neurons by nerve injections of tGluA4 flop rescue plasmid prior to anti-tGluA4 siRNA application restored conditioning and synaptic incorporation of tGluA4-containing AMPARs. In contrast, treatment with rescue plasmids for tGluA4 flip or tGluA4trc1 failed to rescue conditioning. Finally, treatment with a siRNA directed against GluA1 subunits inhibited conditioning and synaptic delivery of tGluA1-containing AMPARs and importantly, those containing tGluA4. These data strongly support our two-stage model of conditioning and our hypothesis that synaptic incorporation of tGluA4-containing AMPARs underlies the acquisition of in vitro classical conditioning. Furthermore, they suggest that tGluA4 flop may have a critical role in conditioning mechanisms compared with the other tGluA4 splice variants.