Brain-derived neurotrophic factor triggers a rapid glutamate release through increase of intracellular Ca(2+) and Na(+) in cultured cerebellar neurons

Jiawei-Xiaoyao pill elicits a rapid antidepressant effect, dependent on activating CaMKII/mTOR/BDNF signaling pathway in the hippocampus

ETHNOPHARMACOLOGICAL RELEVANCE

Jiawei-Xiaoyao pill (JWX), a traditional Chinese medicine, was recorded in ancient Chinese medicine pharmacopoeia using for treatment of various diseases, including mood disorders. Current mainstream antidepressants have a disadvantage in delayed onset of action. The rapid antidepressant potential of JWX and the underlying mechanisms remain unclear.

AIM OF THE STUDY

We aimed to assess the rapid antidepressant potential of JWX, within the prescription dose range, and the distinct underlying neuroplasticity signaling mechanism.

MATERIALS AND METHODS

The rapid antidepressant response of JWX were determined using various behavioral paradigms, and in a corticosterone (CORT)-induced depression model in mice. The molecular neuroplasticity signaling and the expression of BDNF in the hippocampus was evaluated using immunoblotting and immunostaining. The contribution of specific signaling was investigated using pharmacological interventions.

RESULTS

A single dose of JWX induced rapid and persistent antidepressant effects in both the normal and chronic CORT-exposed mice. The phosphorylation of CaMKII, mTOR, ERK and the expressions of BDNF, synapsin1 and PSD95 increased at 30 min post JWX. JWX restored the expression of BDNF in the hippocampal dentate gyrus reduced by CORT-exposure. The rapid antidepressant effect and upregulation of BDNF expression by JWX was blunted by a mTOR antagonist, rapamycin, or a CaMKII antagonist, KN-93. CaMKII signaling blockade blunted mTOR signaling activated by JWX, but not vice versa.

CONCLUSION

JWX elicits a rapid antidepressant effect, via quickly stimulating CaMKII signaling, subsequently activating mTOR-BDNF signaling pathway, and thus enhancing hippocampal neuroplasticity.

PLCγ1 in dopamine neurons critically regulates striatal dopamine release via VMAT2 and synapsin III

Dopamine neurons are essential for voluntary movement, reward learning, and motivation, and their dysfunction is closely linked to various psychological and neurodegenerative diseases. Hence, understanding the detailed signaling mechanisms that functionally modulate dopamine neurons is crucial for the development of better therapeutic strategies against dopamine-related disorders. Phospholipase Cγ1 (PLCγ1) is a key enzyme in intracellular signaling that regulates diverse neuronal functions in the brain. It was proposed that PLCγ1 is implicated in the development of dopaminergic neurons, while the physiological function of PLCγ1 remains to be determined. In this study, we investigated the physiological role of PLCγ1, one of the key effector enzymes in intracellular signaling, in regulating dopaminergic function in vivo. We found that cell type-specific deletion of PLCγ1 does not adversely affect the development and cellular morphology of midbrain dopamine neurons but does facilitate dopamine release from dopaminergic axon terminals in the striatum. The enhancement of dopamine release was accompanied by increased colocalization of vesicular monoamine transporter 2 (VMAT2) at dopaminergic axon terminals. Notably, dopamine neuron-specific knockout of PLCγ1 also led to heightened expression and colocalization of synapsin III, which controls the trafficking of synaptic vesicles. Furthermore, the knockdown of VMAT2 and synapsin III in dopamine neurons resulted in a significant attenuation of dopamine release, while this attenuation was less severe in PLCγ1 cKO mice. Our findings suggest that PLCγ1 in dopamine neurons could critically modulate dopamine release at axon terminals by directly or indirectly interacting with synaptic machinery, including VMAT2 and synapsin III.

How Oxidative Stress Induces Depression?

Depression increasingly affects a wide range and a large number of people worldwide, both physically and psychologically, which makes it a social problem requiring prompt attention and management. Accumulating clinical and animal studies have provided us with substantial insights of disease pathogenesis, especially central monoamine deficiency, which considerably promotes antidepressant research and clinical treatment. The first-line antidepressants mainly target the monoamine system, whose drawbacks mainly include slow action and treatment resistant. The novel antidepressant esketamine, targeting on central glutamatergic system, rapidly and robustly alleviates depression (including treatment-resistant depression), whose efficiency is shadowed by potential addictive and psychotomimetic side effects. Thus, exploring novel depression pathogenesis is necessary, for seeking more safe and effective therapeutic methods. Emerging evidence has revealed vital involvement of oxidative stress (OS) in depression, which inspires us to pursue antioxidant pathway for depression prevention and treatment. Fully uncovering the underlying mechanisms of OS-induced depression is the first step towards the avenue, thus we summarize and expound possible downstream pathways of OS, including mitochondrial impairment and related ATP deficiency, neuroinflammation, central glutamate excitotoxicity, brain-derived neurotrophic factor/tyrosine receptor kinase B dysfunction and serotonin deficiency, the microbiota-gut-brain axis disturbance and hypothalamic-pituitary-adrenocortical axis dysregulation. We also elaborate on the intricate interactions between the multiple aspects, and molecular mechanisms mediating the interplay. Through reviewing the related research progress in the field, we hope to depict an integral overview of how OS induces depression, in order to provide fresh ideas and novel targets for the final goal of efficient treatment of the disease.

BDNF Therapeutic Mechanisms in Neuropsychiatric Disorders

Brain-derived neurotrophic factor (BDNF) is the most abundant neurotrophin in the adult brain and functions as both a primary neurotrophic signal and a neuromodulator. It serves essential roles in neuronal development, maintenance, transmission, and plasticity, thereby influencing aging, cognition, and behavior. Accumulating evidence associates reduced central and peripheral BDNF levels with various neuropsychiatric disorders, supporting its potential utilization as a biomarker of central pathologies. Subsequently, extensive research has been conducted to evaluate restoring, or otherwise augmenting, BDNF transmission as a potential therapeutic approach. Promising results were indeed observed for genetic BDNF upregulation or exogenous administration using a multitude of murine models of neurological and psychiatric diseases. However, varying mechanisms have been proposed to underlie the observed therapeutic effects, and many findings indicate the engagement of disease-specific and other non-specific mechanisms. This is because BDNF essentially affects all aspects of neuronal cellular function through tropomyosin receptor kinase B (TrkB) receptor signaling, the disruptions of which vary between brain regions across different pathologies leading to diversified consequences on cognition and behavior. Herein, we review the neurophysiology of BDNF transmission and signaling and classify the converging and diverging molecular mechanisms underlying its therapeutic potentials in neuropsychiatric disorders. These include neuroprotection, synaptic maintenance, immunomodulation, plasticity facilitation, secondary neuromodulation, and preservation of neurovascular unit integrity and cellular viability. Lastly, we discuss several findings suggesting BDNF as a common mediator of the therapeutic actions of centrally acting pharmacological agents used in the treatment of neurological and psychiatric illness.

Co-Treatment With Verapamil and Curcumin Attenuates the Behavioral Alterations Observed in Williams-Beuren Syndrome Mice by Regulation of MAPK Pathway and Microglia Overexpression

Williams-Beuren syndrome (WBS) is a rare neurodevelopmental disorder characterized by a distinctive cognitive phenotype for which there are currently no effective treatments. We investigated the progression of behavioral deficits present in WBS complete deletion (CD) mice, after chronic treatment with curcumin, verapamil, and a combination of both. These compounds have been proven to have beneficial effects over different cognitive aspects of various murine models and, thus, may have neuroprotective effects in WBS. Treatment was administered orally dissolved in drinking water. A set of behavioral tests demonstrated the efficiency of combinatorial treatment. Some histological and molecular analyses were performed to analyze the effects of treatment and its underlying mechanism. CD mice showed an increased density of activated microglia in the motor cortex and CA1 hippocampal region, which was prevented by co-treatment. Behavioral improvement correlated with the molecular recovery of several affected pathways regarding MAPK signaling, in tight relation to the control of synaptic transmission, and inflammation. Therefore, the results show that co-treatment prevented behavioral deficits by recovering altered gene expression in the cortex of CD mice and reducing activated microglia. These findings unravel the mechanisms underlying the beneficial effects of this novel treatment on behavioral deficits observed in CD mice and suggest that the combination of curcumin and verapamil could be a potential candidate to treat the cognitive impairments in WBS patients.

Prevention of excitotoxicity-induced processing of BDNF receptor TrkB-FL leads to stroke neuroprotection

Neuroprotective strategies aimed to pharmacologically treat stroke, a prominent cause of death, disability, and dementia, have remained elusive. A promising approach is restriction of excitotoxic neuronal death in the infarct penumbra through enhancement of survival pathways initiated by brain-derived neurotrophic factor (BDNF). However, boosting of neurotrophic signaling after ischemia is challenged by downregulation of BDNF high-affinity receptor, full-length tropomyosin-related kinase B (TrkB-FL), due to calpain-degradation, and, secondarily, regulated intramembrane proteolysis. Here, we have designed a blood-brain barrier (BBB) permeable peptide containing TrkB-FL sequences (TFL457 ) which prevents receptor disappearance from the neuronal surface, early induced after excitotoxicity. In this way, TFL457 interferes TrkB-FL cleavage by both proteolytic systems and increases neuronal viability via a PLCγ-dependent mechanism. By preserving downstream CREB and MEF2 promoter activities, TFL457 initiates a feedback mechanism favoring increased levels in excitotoxic neurons of critical prosurvival mRNAs and proteins. This neuroprotective peptide could be highly relevant for stroke therapy since, in a mouse ischemia model, it counteracts TrkB-FL downregulation in the infarcted brain, efficiently decreases infarct size, and improves neurological outcome.

EXPRESS: Phospholipase C gamma mediates endogenous brain-derived neurotrophic factor - regulated calcitonin gene-related peptide expression in colitis - induced visceral pain

BACKGROUND

Visceral hypersensitivity is a complex pathophysiological paradigm with unclear mechanisms. Primary afferent neuronal plasticity marked by alterations in neuroactive compounds such as calcitonin gene-related peptide is suggested to underlie the heightened sensory responses. Signal transduction that leads to calcitonin gene-related peptide expression thereby sensory neuroplasticity during colitis remains to be elucidated.

RESULTS

In a rat model with colitis induced by 2,4,6-trinitrobenzene sulfonic acid, we found that endogenously elevated brain-derived neurotrophic factor elicited an up-regulation of calcitonin gene-related peptide in the lumbar L1 dorsal root ganglia. At seven days of colitis, neutralization of brain-derived neurotrophic factor with a specific brain-derived neurotrophic factor antibody reversed calcitonin gene-related peptide up-regulation in the dorsal root ganglia. Colitis-induced calcitonin gene-related peptide transcription was also inhibited by brain-derived neurotrophic factor antibody treatment. Signal transduction studies with dorsal root ganglia explants showed that brain-derived neurotrophic factor-induced calcitonin generelated peptide expression was mediated by the phospholipase C gamma, but not the phosphatidylinositol 3-kinase/Akt or the mitogen-activated protein kinase/extracellular signal-regulated protein kinase pathway. Application of PLC inhibitor U73122 in vivo confirmed that colitis-induced and brain-derived neurotrophic factor-mediated calcitonin gene-related peptide up-regulation in the dorsal root ganglia was regulated by the phospholipase C gamma pathway. In contrast, suppression of the phosphatidylinositol 3-kinase activity in vivo had no effect on colitis-induced calcitonin gene-related peptide expression. During colitis, calcitonin gene-related peptide also co-expressed with phospholipase C gamma but not with p-Akt. Calcitonin gene-related peptide up-regulation during colitis correlated to the activation of cAMP-responsive element binding protein in the same neurons. Consistently, colitis-induced cAMP-responsive element binding protein activation in the dorsal root ganglia was attenuated by brain-derived neurotrophic factor antibody treatment.

CONCLUSION

These results suggest that colitis-induced and brain-derived neurotrophic factor-mediated calcitonin generelated peptide expression in sensory activation is regulated by a unique pathway involving brain-derived neurotrophic factorphospholipase C gamma-cAMP-responsive element binding protein axis.

Citalopram Ameliorates Synaptic Plasticity Deficits in Different Cognition-Associated Brain Regions Induced by Social Isolation in Middle-Aged Rats

Our previous experiments demonstrated that social isolation (SI) caused AD-like tau hyperphosphorylation and spatial memory deficits in middle-aged rats. However, the underlying mechanisms of SI-induced spatial memory deficits remain elusive. Middle-aged rats (10 months) were group or isolation reared for 8 weeks. Following the initial 4-week period of rearing, citalopram (10 mg/kg i.p.) was administered for 28 days. Then, pathophysiological changes were assessed by performing behavioral, biochemical, and pathological analyses. We found that SI could cause cognitive dysfunction and decrease synaptic protein (synaptophysin or PSD93) expression in different brain regions associated with cognition, such as the prefrontal cortex, dorsal hippocampus, ventral hippocampus, amygdala, and caudal putamen, but not in the entorhinal cortex or posterior cingulate. Citalopram could significantly improve learning and memory and partially restore synaptophysin or PSD93 expression in the prefrontal cortex, hippocampus, and amygdala in SI rats. Moreover, SI decreased the number of dendritic spines in the prefrontal cortex, dorsal hippocampus, and ventral hippocampus, which could be reversed by citalopram. Furthermore, SI reduced the levels of BDNF, serine-473-phosphorylated Akt (active form), and serine-9-phosphorylated GSK-3β (inactive form) with no significant changes in the levels of total GSK-3β and Akt in the dorsal hippocampus, but not in the posterior cingulate. Our results suggest that decreased synaptic plasticity in cognition-associated regions might contribute to SI-induced cognitive deficits, and citalopram could ameliorate these deficits by promoting synaptic plasticity mainly in the prefrontal cortex, dorsal hippocampus, and ventral hippocampus. The BDNF/Akt/GSK-3β pathway plays an important role in regulating synaptic plasticity in SI rats.

Colitis-induced bladder afferent neuronal activation is regulated by BDNF through PLCγ pathway

Patients with inflammatory bowel disease (IBD) or irritable bowel syndrome (IBS) often experience increased sensory responsiveness in the urinary bladder reflecting neurogenic bladder overactivity. Here we demonstrate that colitis-induced up-regulation of the phospholipase C gamma (PLCγ) pathway downstream of brain-derived neurotrophic factor (BDNF) in bladder afferent neurons in the dorsal root ganglia (DRG) plays essential roles in activating these neurons thereby leading to bladder hyperactivity. Upon induction of colitis with 2,4,6-trinitrobenzenesulfonic acid (TNBS) in rats, we found that the phosphorylation (activation) level of cAMP responsive element-binding (p-CREB) protein, a molecular switch of neuronal plasticity, was increased in specifically labeled bladder afferent neurons in the thoracolumbar and lumbosacral DRGs. In rats having reduced levels of BDNF (BDNF^+/-), colitis failed to elevate CREB protein activity in bladder afferent neurons. Physiological examination also demonstrated that colitis-induced urinary frequency was not shown in BDNF^+/- rats, implicating an essential role of BDNF in mediating colon-to-bladder sensory cross-sensitization. We further implemented in vivo and in vitro studies and demonstrated that BDNF-mediated colon-to-bladder sensory cross-activation involved the TrkB-PLCγ-calcium/calmodulin-dependent protein kinase II (CaMKII) cascade. In contrast, the PI3K/Akt pathway was not activated in bladder afferent neurons during colitis and was not involved in BDNF action in the DRG. Our results suggest that colon-to-bladder sensory cross-sensitization is regulated by specific signal transduction initiated by the up-regulation of BDNF in the DRG.

Brain-derived neurotrophic factor accelerates gut motility in slow-transit constipation

BACKGROUND & AIMS

Brain-derived neurotrophic factor (BDNF) may play a critical role in gut motility. We aimed to investigate BDNF's physiologic effects on gut motility in slow-transit constipation (STC) and to explore the underlying molecular mechanisms.

METHODS

BDNF expression and alterations of colonic nerve fibre density in STC patients were first investigated. BDNF's effects on gastrointestinal motility of both BDNF(+/-) mice and loperamide-induced constipation mice were then examined in vivo and in vitro. Smooth muscle α-actin (α-SMA) expression, and nerve fibre, neuromuscular junction (NMJ) and smooth muscle cell (SMC) alterations were investigated. Finally, the effects of BDNF-induced TrkB-phospholipase C/inositol trisphosphate (TrkB-PLC/IP3) pathway activation on gut motility were investigated.

RESULTS

In STC patients, BDNF expression and nerve fibre density were decreased, and mucosal nerve fibre ultrastructural degenerations were demonstrated. Gut motility was decreased in vivo and in vitro in BDNF(+/-) and constipation mice, with BDNF dose-dependently increasing gut motility. In BDNF(+/-) mice, α-SMA expression and nerve fibre density were decreased, and nerve fibre, NMJ and SMC ultrastructural degenerations were observed. Finally, TrkB-PLC/IP3 pathway antagonists dramatically attenuated BDNF's excitatory effect on gut motility, and exogenous BDNF induced an obvious increase in IP3 expression.

CONCLUSIONS

BDNF plays an important regulatory role in gut motility in STC. It was mediated by altering the intestinal innervation structure, as well as smooth muscle secondary degeneration through a mechanism involving TrkB-PLC/IP3 pathway activation.

BDNF-endocannabinoid interactions at neocortical inhibitory synapses require phospholipase C signaling

Endogenous cannabinoids (endocannabinoids) and neurotrophins, particularly brain-derived neurotrophic factor (BDNF), are potent synaptic modulators that are expressed throughout the forebrain and play critical roles in many behavioral processes. Although the effects of BDNF at excitatory synapses have been well characterized, the mechanisms of action of BDNF at inhibitory synapses are not well understood. Previously we have found that BDNF suppresses presynaptic GABA release in layer 2/3 of the neocortex via postsynaptic tropomyosin-related kinase receptor B (trkB) receptor-induced release of endocannabinoids. To examine the intracellular signaling pathways that underlie this effect, we used pharmacological approaches and whole cell patch-clamp techniques in layer 2/3 pyramidal neurons of somatosensory cortex in brain slices from juvenile Swiss CD1 mice. Our results indicated that phospholipase Cγ (PLCγ) is involved in the CB1 receptor-mediated synaptic effect of BDNF, because the BDNF effect was blocked in the presence of the broad-spectrum PLC inhibitors U-73122 and edelfosine, whereas the inactive analog U-73343 did not alter the suppressive effect of BDNF at inhibitory synapses. Endocannabinoid release can also be triggered by metabotropic glutamate receptor (mGluR)-mediated activation of PLCβ, and BDNF has been shown to enhance spontaneous glutamate release. An mGluR antagonist, E4CPG, however, did not block the BDNF effect. In addition, the effect of BDNF was independent of other signaling pathways downstream of trkB receptor activation, namely, mitogen-activated protein kinase and phosphoinositide 3-kinase pathways, as well as protein kinase C signaling.

Phospholipase C-γ1 involved in brain disorders

Phosphoinositide-specific phospholipase C-γ1 (PLC-γ1) is an important signaling regulator involved in various cellular processes. In brain, PLC-γ1 is highly expressed and participates in neuronal cell functions mediated by neurotrophins. Consistent with essential roles of PLC-γ1, it is involved in development of brain and synaptic transmission. Significantly, abnormal expression and activation of PLC-γ1 appears in various brain disorders such as epilepsy, depression, Huntington's disease and Alzheimer's disease. Thus, PLC-γ1 has been implicated in brain functions as well as related brain disorders. In this review, we discuss the roles of PLC-γ1 in neuronal functions and its pathological relevance to diverse brain diseases.

Dysregulation of BDNF-TrkB signaling in developing hippocampal neurons by Pb(2+): implications for an environmental basis of neurodevelopmental disorders

Dysregulation of synaptic development and function has been implicated in the pathophysiology of neurodegenerative disorders and mental disease. A neurotrophin that has an important function in neuronal and synaptic development is brain-derived neurotrophic factor (BDNF). In this communication, we examined the effects of lead (Pb(2+)) exposure on BDNF-tropomyosin-related kinase B (TrkB) signaling during the period of synaptogenesis in cultured neurons derived from embryonic rat hippocampi. We show that Pb(2+) exposure decreases BDNF gene and protein expression, and it may also alter the transport of BDNF vesicles to sites of release by altering Huntingtin phosphorylation and protein levels. Combined, these effects of Pb(2+) resulted in decreased concentrations of extracellular mature BDNF. The effect of Pb(2+) on BDNF gene expression was associated with a specific decrease in calcium-sensitive exon IV transcript levels and reduced phosphorylation and protein expression of the transcriptional repressor methyl-CpG-binding protein (MeCP2). TrkB protein levels and autophosphorylation at tyrosine 816 were significantly decreased by Pb(2+) exposure with a concomitant increase in p75 neurotrophin receptor (p75(NTR)) levels and altered TrkB-p75(NTR) colocalization. Finally, phosphorylation of Synapsin I, a presynaptic target of BDNF-TrkB signaling, was significantly decreased by Pb(2+) exposure with no effect on total Synapsin I protein levels. This effect of Pb(2+) exposure on Synapsin I phosphorylation may help explain the impairment in vesicular release documented by us previously (Neal, A. P., Stansfield, K. H., Worley, P. F., Thompson, R. E., and Guilarte, T. R. (2010). Lead exposure during synaptogenesis alters vesicular proteins and impairs vesicular release: Potential role of N-Methyl-D-aspartate receptor (NMDAR) dependent BDNF signaling. Toxicol. Sci. 116, 249-263) because it controls vesicle movement from the reserve pool to the readily releasable pool. In summary, the present study demonstrates that Pb(2+) exposure during the period of synaptogenesis of hippocampal neurons in culture disrupts multiple synaptic processes regulated by BDNF-TrkB signaling with long-term consequences for synaptic function and neuronal development.

Dopamine D1-D2 receptor heteromer signaling pathway in the brain: emerging physiological relevance

Dopamine is an important catecholamine neurotransmitter modulating many physiological functions, and is linked to psychopathology of many diseases such as schizophrenia and drug addiction. Dopamine D1 and D2 receptors are the most abundant dopaminergic receptors in the striatum, and although a clear segregation between the pathways expressing these two receptors has been reported in certain subregions, the presence of D1-D2 receptor heteromers within a unique subset of neurons, forming a novel signaling transducing functional entity has been shown. Recently, significant progress has been made in elucidating the signaling pathways activated by the D1-D2 receptor heteromer and their potential physiological relevance.

Correlation between cortical plasticity, motor learning and BDNF genotype in healthy subjects

There is good evidence that synaptic plasticity in human motor cortex is involved in behavioural motor learning; in addition, it is now possible to probe mechanisms of synaptic plasticity using a variety of transcranial brain-stimulation protocols. Interactions between these protocols suggest that they both utilise common mechanisms. The aim of the present experiments was to test how well responsiveness to brain-stimulation protocols and behavioural motor learning correlate with each other in a sample of 21 healthy volunteers. We also examined whether any of these measures were influenced by the presence of a Val66Met polymorphism in the BDNF gene since this is another factor that has been suggested to be able to predict response to tests of synaptic plasticity. In 3 different experimental sessions, volunteers underwent 5-Hz rTMS, intermittent theta-burst stimulation (iTBS) and a motor learning task. Blood samples were collected from each subject for BDNF genotyping. As expected, both 5-Hz rTMS and iTBS significantly facilitated MEPs. Similarly, as expected, kinematic variables of finger movement significantly improved during the motor learning task. Although there was a significant correlation between the effect of iTBS and 5-Hz rTMS, there was no relationship in each subject between the amount of TMS-induced plasticity and the increase in kinematic variables during motor learning. Val66Val and Val66Met carriers did not differ in their response to any of the protocols. The present results emphasise that although some TMS measures of cortical plasticity may correlate with each other, they may not always relate directly to measures of behavioural learning. Similarly, presence of the Val66Met BDNF polymorphism also does not reliably predict responsiveness in small groups of individuals. Individual success in behavioural learning is unlikely to be closely related to any single measure of synaptic plasticity.

Brain-derived neurotrophic factor controls cannabinoid CB1 receptor function in the striatum

The role of brain-derived neurotrophic factor (BDNF) in emotional processes suggests an interaction with the endocannabinoid system. Here, we addressed the functional interplay between BDNF and cannabinoid CB(1) receptors (CB(1)Rs) in the striatum, a brain area in which both BDNF and CB(1)s play a role in the emotional consequences of stress and of rewarding experiences. BDNF potently inhibited CB(1)R function in the striatum, through a mechanism mediated by altered cholesterol metabolism and membrane lipid raft function. The effect of BDNF was restricted to CB(1)Rs controlling GABA-mediated IPSCs (CB(1)R(GABA)), whereas CB(1)Rs modulating glutamate transmission and GABA(B) receptors were not affected. The action of BDNF on CB(1)R(GABA) function was tyrosine kinase dependent and was complete even after receptor sensitization with cocaine or environmental manipulations activating the dopamine (DA)-dependent reward system. In mice lacking one copy of the BDNF gene (BDNF(+/-)), CB(1)R(GABA) responses were potentiated and were preserved from the action of haloperidol, a DA D(2) receptor (D(2)R) antagonist able to fully abolish CB(1)R(GABA) function in rewarded animals. Haloperidol also enhanced BDNF levels in the striatum, suggesting that this neurotrophin may act as a downstream effector of D(2)Rs in the modulation of cannabinoid signaling. Accordingly, 5 d cocaine exposure both reduced striatal BDNF levels and increased CB(1)R(GABA) activity, through a mechanism dependent on D(2)Rs. The present study identifies a novel mechanism of CB(1)R regulation mediated by BDNF and cholesterol metabolism and provides some evidence that DA D(2)R-dependent modulation of striatal CB(1)R activity is mediated by this neurotrophin.

Genetic increase in brain-derived neurotrophic factor levels enhances learning and memory

Brain-derived neurotrophic factor (BDNF), a neurotrophin, is known to promote neuronal differentiation stimulating neurite outgrowth in the developing CNS, and is also known to modulate synaptic plasticity, thereby contributing to learning and memory in the mature brain. Here, we investigated the role of increased levels of intracerebral BDNF in learning and memory function. Using genetically engineered transgenic BDNF overexpressing mice (RTG-BDNF), young adult, homozygous (+/+), heterozygous (+/-), or wild-type (-/-) littermates, we analyzed escape latency to a hidden-platform and swimming velocity in the Morris Water Maze test (MWM) with modifications for the mice. The MWM comprised 4 trials per day over 5 consecutive days (sessions) without prior or subsequent training. In a separate set of animals, BDNF protein levels in the cortex, thalamostriatum and the hippocampus were measured quantitatively using ELISA. In the BDNF (+/-) mice, the BDNF levels in the cortex, the thalamostriatum and the hippocampus were significantly high, compared to the wild-type littermates; 238%, 158%, and 171%, respectively (P<0.01, one-way ANOVA and a post-hoc test in each region). The BDNF levels in the BDNF (+/+) mice were not elevated. The BDNF (+/-), but not the (+/+) mice, demonstrated significantly shorter escape latency, shorter total path length in the MWM, and more frequent arrivals at the location where the platform had been placed previously in the probe trial, compared with the wild-type littermates (P<0.05, at each time pint). Because the maximum swimming velocity was not affected in the BDNF-transgenic mice, increased BDNF levels in the brain were found to enhance spatial learning and memory function. Although it has been postulated that excessive BDNF is deteriorating for neuronal survival or neurite outgrowth, further investigations are needed to clarify the mechanism of paradoxical lack of increase in BDNF levels in the (+/+) mouse brain.

Presynaptic functional trkB receptors mediate the release of excitatory neurotransmitters from primary afferent terminals in lamina II (substantia gelatinosa) of postnatal rat spinal cord

A subset of primary sensory neurons produces BDNF, which is implicated in control of nociceptive neurotransmission. We previously localized full-length trkB receptors on their terminals within lamina II. To functionally study these receptors, we here employed patch-clamp recordings, calcium imaging and immunocytochemistry on slices from 8-12 days post-natal rats. In this preparation, BDNF (100-500 ng/mL) enhances the release of sensory neurotransmitters (glutamate, substance P, CGRP) in lamina II by acting on trkB receptors expressed by primary afferent fibers of the peptidergic nociceptive type (PN-PAFs). Effect was blocked by trk antagonist K252a or anti-trkB antibody clone 47. A pre-synaptic mechanism was demonstrated after (i) patch-clamp recordings where the neurotrophin induced a significant increase in frequency, but not amplitude, of AMPA-mediated mEPSCs, (ii) real time calcium imaging, where sustained application of BDNF evoked an intense response in up to 57% lamina II neurons with a significant frequency rise. Antagonists of ionotropic glutamate receptors and NK(1) receptors completely inhibited the calcium response to BDNF. Reduction of CGRP (a specific marker of PN-PAFs) and substance P content in dorsal horn following BDNF preincubation, and analysis of the calcium response after depletion with capsaicin, confirmed that the neurotrophin presynaptically enhanced neurotransmitter release from PN-PAFs. This is the first demonstration that trkB receptors expressed by PN-PAF terminals in lamina II are functional during postnatal development. Implications of this finding are discussed considering that BDNF can be released by these same terminals and microglia, a fraction of which (as shown here) contains BDNF also in unactivated state.

BDNF induces calcium elevations associated with IBDNF, a nonselective cationic current mediated by TRPC channels

Brain-derived neurotrophic factor (BDNF) has potent actions on hippocampal neurons, but the mechanisms that initiate its effects are poorly understood. We report here that localized BDNF application to apical dendrites of CA1 pyramidal neurons evoked transient elevations in intracellular Ca(2+) concentration, which are independent of membrane depolarization and activation of N-methyl-d-aspartate receptors (NMDAR). These Ca(2+) signals were always associated with I(BDNF), a slow and sustained nonselective cationic current mediated by transient receptor potential canonical (TRPC3) channels. BDNF-induced Ca(2+) elevations required functional Trk and inositol-tris-phosphate (IP(3)) receptors, full intracellular Ca(2+) stores as well as extracellular Ca(2+), suggesting the involvement of TRPC channels. Indeed, the TRPC channel inhibitor SKF-96365 prevented BDNF-induced Ca(2+) elevations and the associated I(BDNF). Thus TRPC channels emerge as novel mediators of BDNF-induced intracellular Ca(2+) elevations associated with sustained cationic membrane currents in hippocampal pyramidal neurons.

Interleukin-1 beta impairs brain derived neurotrophic factor-induced signal transduction

The expression of IL-1 is elevated in the CNS in diverse neurodegenerative disorders, including Alzheimer's disease. The hypothesis was tested that IL-1 beta renders neurons vulnerable to degeneration by interfering with BDNF-induced neuroprotection. In trophic support-deprived neurons, IL-1 beta compromised the PI3-K/Akt pathway-mediated protection by BDNF and suppressed Akt activation. The effect was specific as in addition to Akt, the activation of MAPK/ERK, but not PLC gamma, was decreased. Activation of CREB, a target of these signaling pathways, was severely depressed by IL-1 beta. As the cytokine did not influence TrkB receptor and PLC gamma activation, IL-1 beta might have interfered with BDNF signaling at the docking step conveying activation to the PI3-K/Akt and Ras/MAPK pathways. Indeed, IL-1 beta suppressed the activation of the respective scaffolding proteins IRS-1 and Shc; this effect might involve ceramide generation. IL-1-induced interference with BDNF neuroprotection and signal transduction was corrected, in part, by ceramide production inhibitors and mimicked by the cell-permeable C2-ceramide. These results suggest that IL-1 beta places neurons at risk by interfering with BDNF signaling involving a ceramide-associated mechanism.

Transient receptor potential channels as novel effectors of brain-derived neurotrophic factor signaling: potential implications for Rett syndrome

In addition to their prominent role as survival signals for neurons in the developing nervous system, neurotrophins have established their significance in the adult brain as well, where their modulation of synaptic transmission and plasticity may participate in associative learning and memory. These crucial activities are primarily the result of neurotrophin regulation of intracellular Ca(2+) homeostasis and, ultimately, changes in gene expression. Outlined in the following review is a synopsis of neurotrophin signaling with a particular focus upon brain-derived neurotrophic factor (BDNF) and its role in hippocampal synaptic plasticity and neuronal Ca(2+) homeostasis. Neurotrophin signaling through tropomyosin-related kinase (Trk) and pan-neurotrophin receptor 75 kD (p75(NTR)) receptors are also discussed, reviewing recent results that indicate signaling through these two receptor modalities leads to opposing cellular outcomes. We also provide an intriguing look into the transient receptor potential channel (TRPC) family of ion channels as distinctive targets of BDNF signaling; these channels are critical for capacitative Ca(2+) entry, which, in due course, mediates changes in neuronal structure including dendritic spine density. Finally, we expand these topics into an exploration of mental retardation (MR), in particular Rett Syndrome (RTT), where dendritic spine abnormalities may underlie cognitive impairments. We propose that understanding the role of neurotrophins in synapse formation, plasticity, and maintenance will make fundamental contributions to the development of therapeutic strategies to improve cognitive function in developmental disorders associated with MR.

Effects of NGF and BDNF on baseline glutamate and dopamine release in the hippocampal formation of the adult rat

It has been shown using in vitro techniques that BDNF and NGF evoke neurotransmitter release in the hippocampus but this phenomenon has not been demonstrated in vivo to date. We therefore performed in vivo microdialysis in urethane-anesthetized Fischer 344 rats. The microdialysis probe was implanted stereotaxically into the CA1 area of the hippocampus. Three hours after the implantation of the probe, glutamate (Glu) and dopamine (DA) levels had reached a stable baseline. Four baseline samples were collected every 15 min at a flow rate of 1 microL/min. The growth factors were delivered (1 microL/10 min) using a microinjector attached to the microdialysis probe. We found that BDNF and NGF, when administered into the hippocampus, evoked dopamine and glutamate release in a dose-dependent fashion. NGF produced a biphasic response in the release of Glu, and a uniphasic response in the release of DA, both of which were calcium dependent. The neurotransmitter release induced by NGF was blocked by tetrodotoxin, indicating neuronal origin of this response. The BDNF induced release of DA and Glu was decreased in low calcium conditions, indicating that it is at least partially calcium dependent. Furthermore, BDNF-induced neurotransmitter release was partially blocked by pre-treatment with K252a, an antagonist for tyrosine kinase receptors, indicating that BDNF is acting through Trk receptors to induce neurotransmitter release. These results demonstrate a close relationship between the growth factors BDNF and NGF and the neurotransmitters DA and Glu in the hippocampus of intact animals.

Ginsenoside Rb1 promotes neurotransmitter release by modulating phosphorylation of synapsins through a cAMP-dependent protein kinase pathway

Ginseng, the root of Panax ginseng C.A. Meyer (Araliaceae), has been extensively used in traditional oriental medicine for the prevention and treatment of aging-related disorders for over 2000 years. Accumulating evidence suggests that ginsenosides such as Rg1 and Rb1, which are the pharmacologically active ingredients of ginseng, modulate neurotransmission. Synapsins are abundant phosphoproteins essential for regulating neurotransmitter release. All synapsins contain a short amino-terminal domain A that is highly conserved and phosphorylated by cAMP-dependent protein kinase (PKA), which plays a key role in regulating neurotransmitter release. In the present study, we demonstrated that both Rg1 and Rb1 increased neurotransmitter release in undifferentiated and differentiated PC12 cells. However, in the presence of the PKA inhibitor H89, Rg1, but not Rb1, still induced neurotransmitter release. Moreover, Rb1, but not Rg1, enhanced the phosphorylation of synapsins via PKA pathway. In summary, Rb1 promotes neurotransmitter release by increasing the phosphorylation of synapsins through the PKA pathway, whereas the similar effects observed with Rg1 are independent of the phosphorylation of synapsins.

Chronic antidepressants potentiate via sigma-1 receptors the brain-derived neurotrophic factor-induced signaling for glutamate release

Up-regulation of BDNF (brain-derived neurotrophic factor) has been suggested to contribute to the action of antidepressants. However, it is unclear whether chronic treatment with antidepressants may influence acute BDNF signaling in central nervous system neurons. Because BDNF has been shown by us to reinforce excitatory glutamatergic transmission in cultured cortical neurons via the phospholipase-gamma (PLC-gamma)/inositol 1,4,5-trisphosphate (IP3)/Ca2+ pathway (Numakawa, T., Yamagishi, S., Adachi, N., Matsumoto, T., Yokomaku, D., Yamada, M., and Hatanaka, H. (2002) J. Biol. Chem. 277, 6520-6529), we examined in this study the possible effects of pretreatment with antidepressants on the BDNF signaling through the PLC-gamma)/IP3/Ca2+ pathway. Furthermore, because the PLC-gamma/IP3/Ca2+ pathway is regulated by sigma-1 receptors (Hayashi, T., and Su, T. P. (2001) Proc. Natl. Acad. Sci. U. S. A. 98, 491-496), we examined whether the BDNF signaling is modulated by sigma-1 receptors (Sig-1R). We found that the BDNF-stimulated PLC-gamma activation and the ensued increase in intracellular Ca2+ ([Ca2+]i) were potentiated by pretreatment with imipramine or fluvoxamine, so was the BDNF-induced glutamate release. Furthermore, enhancement of the interaction between PLC-gamma and TrkB (receptor for BDNF) after imipramine pretreatment was observed. Interestingly, BD1047, a potent Sig-1R antagonist, blocked the imipramine-dependent potentiation on the BDNF-induced PLC-gamma activation and glutamate release. In contrast, overexpression of Sig-1R per se, without antidepressant pretreatment, enhances BDNF-induced PLC-gamma activation and glutamate release. These results suggest that antidepressant pretreatment selectively enhance the BDNF signaling on the PLC-gamma/IP3/Ca2+ pathway via Sig-1R, and that Sig-1R plays an important role in BDNF signaling leading to glutamate release.

Brain-derived neurotrophic factor-induced potentiation of glutamate and GABA release: different dependency on signaling pathways and neuronal activity

The mechanisms underlying BDNF-modulated neurotransmitter release remain elusive. Here, we found that 24-h exposure of postnatal cortical neurons to BDNF potentiated depolarization-evoked glutamate and GABA release in a protein synthesis-dependent manner. BDNF-potentiated glutamate release occurred through the PLC-gamma and MAPK pathways. The expression of synapsin I, synaptotagmin, and synaptophysin, but not of syntaxin or SNAP25, increased through the PLC-gamma and MAPK pathways. In contrast, BDNF-up-regulated GABA release and GAD65/67 expression depended on MAPK. Furthermore, neuronal activity was necessary for the up-regulation of glutamate release and synapsin I, synaptotagmin, and synaptophysin expression, but not of GABA or GAD65/67. PLC-gamma inhibitor attenuated BDNF-stimulated long-lasting MAPK activation. As BDNF rapidly potentiates glutamatergic transmission through PLC-gamma (J. Biol. Chem. 277, (2002) 6520-6529), PLC-gamma-mediated neuronal activity might sustain MAPK activation, resulting in BDNF-potentiated glutamate release. In conclusion, BDNF potentiates the excitatory and inhibitory system separately, which may be important for the regulation of synaptic plasticity.

Mercury compounds disrupt neuronal glutamate transport in cultured mouse cerebellar granule cells

Cerebellar granule cells are targeted selectively by mercury compounds in vivo. Despite the affinity of mercury for thiol groups present in all cells, the molecular determinant(s) of selective cerebellar degeneration remain to be elucidated fully. We studied the effect of mercury compounds on neuronal glutamate transport in primary cultures of mouse cerebellar granule cells. Immunoblots probed with an antibody against the excitatory amino acid transporter (EAAT) neuronal glutamate transporter, EAAT3, revealed the presence of a specific band in control and mercury-treated cultures. Micromolar concentrations of both methylmercury and mercuric chloride increased the release of endogenous glutamate, inhibited glutamate uptake, reduced mitochondrial activity, and decreased ATP levels. All these effects were completely prevented by the nonpermeant reducing agent Tris-(2-carboxyethyl)phosphine (TCEP). Reduction of mitochondrial activity by mercuric chloride, but not by methylmercury, was inhibited significantly by 4,4'-diisothiocyanato-stilbene-2,2'-disulfonic acid (DIDS) and by reduced extracellular Cl- ion concentration. In addition, DIDS and low extracellular Cl- completely inhibited the release of glutamate induced by mercuric chloride, and produced a partial although significant reduction of that induced by methylmercury. We suggest that a direct inhibition of glutamate uptake triggers an imbalance in cell homeostasis, leading to neuronal failure and Cl(-)-regulated cellular glutamate efflux. Our results demonstrate that neuronal glutamate transport is a novel target to be taken into account when assessing mercury-induced neurotoxicity.

Beta-amyloid peptide at sublethal concentrations downregulates brain-derived neurotrophic factor functions in cultured cortical neurons

The accumulation of beta-amyloid (Abeta) is one of the etiological factors in Alzheimer's disease (AD). It has been assumed that the underlying mechanism involves a critical role of Abeta-induced neurodegeneration. However, low levels of Abeta, such as will accumulate during the course of the disease, may interfere with neuronal function via mechanisms other than those involving neurodegeneration. We have been testing, therefore, the hypothesis that Abeta at levels insufficient to cause degeneration (sublethal) may interfere with critical signal transduction processes. In cultured cortical neurons Abeta at sublethal concentrations interferes with the brain-derived neurotrophic factor (BDNF)-induced activation of the Ras-mitogen-activated protein kinase/extracellular signal-regulated protein kinase (ERK) and phosphatidylinositol 3-kinase (PI3-K)/Akt pathways. The effect of sublethal Abeta(1-42) on BDNF signaling results in the suppression of the activation of critical transcription factor cAMP response element-binding protein and Elk-1 and cAMP response element-mediated and serum response element-mediated transcription. The site of interference with the Ras/ERK and PI3-K/Akt signaling is downstream of the TrkB receptor and involves docking proteins insulin receptor substrate-1 and Shc, which convey receptor activation to the downstream effectors. The functional consequences of Abeta interference with signaling are robust, causing increased vulnerability of neurons, abrogating BDNF protection against DNA damage- and trophic deprivation-induced apoptosis. These new findings suggest that Abeta engenders a dysfunctional encoding state in neurons and may initiate and/or contribute to cognitive deficit at an early stage of AD before or along with neuronal degeneration.

Different expression of brain-derived neurotrophic factor in the nucleus accumbens of alcohol-preferring (P) and -nonpreferring (NP) rats

Recent studies suggest that the gene that encodes brain-derived neurotrophic factor (BDNF) might be linked with vulnerability to alcohol abuse. We have now compared BDNF protein levels in several brain regions between alcohol-naive alcohol-preferring (P) and -nonpreferring (NP) rats using the enzyme-linked immunosorbent assay (ELISA) procedure. The results showed that BDNF levels in the nucleus accumbens of the P rats were significantly lower than those of the NP rats, suggesting that this innate difference may contribute to the disparate alcohol drinking behavior of the P and NP rats.

Excitotoxic death induced by released glutamate in depolarized primary cultures of mouse cerebellar granule cells is dependent on GABAAreceptors and niflumic acid-sensitive chloride channels

Excitotoxic neuronal death has been linked to neurological and neurodegenerative diseases. Several studies have sought to clarify the involvement of Cl(-) channels in neuronal excitotoxicity using either N-methyl-D-aspartic acid (NMDA) or alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate/kainic acid agonists. In this work we induced excitotoxic death in primary cultures of cerebellar granule cells by means of endogenously released glutamate. Excitotoxicity was provoked by exposure to high extracellular K(+) concentrations ([K(+)](o)) for 5 min. Under these conditions, a Ca(2+)-dependent release of glutamate was evoked. When extracellular glutamate concentration rose to between 2 and 4 microM, cell viability was significantly reduced by 30-40%. The NMDA receptor antagonists (MK-801 and D-2-amino-5-phosphonopentanoic acid) prevented cell death. Exposure to high [K(+)](o) produced a (36)Cl(-) influx which was significantly reduced by picrotoxinin. In addition, the GABA(A) receptor antagonists (bicuculline, picrotoxinin and SR 95531) protected cells from high [K(+)](o)-triggered excitotoxicity and reduced extracellular glutamate concentration. The Cl(-) channel blockers niflumic acid and 5-nitro-2-(3-phenylpropylamino)benzoic acid also exerted a neuroprotective effect and reduced extracellular glutamate concentration, even though they did not reduce high [K(+)](o)-induced (36)Cl(-) influx. Primary cultures of cerebellar granule cells also contain a population of GABAergic neurons that released GABA in response to high [K(+)](o). Chronic treatment of primary cultures with kainic acid abolished GABA release and rendered granule cells insensitive to high [K(+)](o) exposure, even though NMDA receptors were functional. Altogether, these results demonstrate that, under conditions of membrane depolarization, low micromolar concentrations of extracellular glutamate might induce an excitotoxic process through both NMDA and GABA(A) receptors and niflumic acid-sensitive Cl(-) channels.

From modulator to mediator: rapid effects of BDNF on ion channels

Neurotrophins (NTs) are [?AUTHOR] a family of structurally related, secreted proteins that regulate the survival, differentiation and maintenance of function of different populations of peripheral and central neurons.1,2 Among these, BDNF (brain-derived neurotrophic factor) has drawn considerable interest because both its synthesis and secretion are increased by physiological levels of activity, indicating a unique role of this neurotrophin in coupling neuronal activity to structural and functional properties of neuronal circuits. In addition to its classical neurotrophic effects, which are evident within hours or days and which usually result from changes in cellular gene expression, BDNF exerts acute effects on synaptic transmission and is involved in the induction of long-term potentiation. Many of these rapid effects of BDNF are mediated by its modulation of ion channel properties following TrkB-mediated activation of intracellular second messenger cascades and protein phosphorylation. However, recent reports have shown that BDNF not only acts as a modulator of ion channels, but can also directly and rapidly gate a Na(+) channel, thereby assigning BDNF the properties of a classical excitatory transmitter. Thus, BDNF, in addition its role as a potent neuromodulator, emerges as an excitatory transmitter-like substance which acutely controls resting membrane potential, neuronal excitability, synaptic transmission and participates in the induction of synaptic plasticity.

The effects of brain-derived neurotrophic factor (BDNF) administration on kindling induction, Trk expression and seizure-related morphological changes

Brain-derived neurotrophic factor (BDNF) is a member of the neurotrophin family that mediates synaptic plasticity and excitability in the CNS. Recent evidence has shown that increased BDNF levels can lead to hyperexcitability and epileptiform activities, while suppression of BDNF function in transgenic mice or by antagonist administration retards the development of seizures. However, several groups, including our own, have reported that increasing BDNF levels by continuous intrahippocampal infusion inhibits epileptogenesis. It is possible that the continuous administration of BDNF produces a down-regulation of its high-affinity TrkB receptor, leading to a decrease of neuronal responsiveness to BDNF. If so, then animals should respond differently to bolus injections of BDNF, which presumably do not alter Trk expression, compared with continuous infusion. To test this hypothesis, we compared the effects of intrahippocampal BDNF continuous infusion and bolus injections on kindling induction. We showed that continuous infusion of BDNF inhibited the development of behavioral seizures and decreased the level of phosphorylated Trks or TrkB receptors. In contrast, multiple bolus microinjections of BDNF accelerated kindling development and did not affect the level of phosphorylated Trks or TrkB receptors. Our results indicate that different administration protocols yield opposite effects of BDNF on neuronal excitability, epileptogenesis and Trk expression. Unlike nerve growth factor and neurotrophin-3, which affect mossy fiber sprouting, we found that BDNF administration had no effect on the mossy fiber system in naive or kindled rats. Such results suggest that the effects of BDNF on epileptogenesis are not modulated by its effect on sprouting, but rather by its effects on excitability.

Evidence of novel neuronal functions of dysbindin, a susceptibility gene for schizophrenia

Genetic variation in dysbindin (DTNBP1: dystrobrevin-binding protein 1) has recently been shown to be associated with schizophrenia. The dysbindin gene is located at chromosome 6p22.3, one of the most promising susceptibility loci in schizophrenia linkage studies. We attempted to replicate this association in a Japanese sample of 670 patients with schizophrenia and 588 controls. We found a nominally significant association with schizophrenia for four single nucleotide polymorphisms and stronger evidence for association in a multi-marker haplotype analysis (P = 0.00028). We then explored functions of dysbindin protein in primary cortical neuronal culture. Overexpression of dysbindin induced the expression of two pre-synaptic proteins, SNAP25 and synapsin I, and increased extracellular basal glutamate levels and release of glutamate evoked by high potassium. Conversely, knockdown of endogenous dysbindin protein by small interfering RNA (siRNA) resulted in the reduction of pre-synaptic protein expression and glutamate release, suggesting that dysbindin might influence exocytotic glutamate release via upregulation of the molecules in pre-synaptic machinery. The overexpression of dysbindin increased phosphorylation of Akt protein and protected cortical neurons against neuronal death due to serum deprivation and these effects were blocked by LY294002, a phosphatidylinositol 3-kinase (PI3-kinase) inhibitor. SiRNA-mediated silencing of dysbindin protein diminished Akt phosphorylation and facilitated neuronal death induced by serum deprivation, suggesting that dysbindin promotes neuronal viability through PI3-kinase-Akt signaling. Genetic variants associated with impairments of these functions of dysbindin could play an important role in the pathogenesis of schizophrenia.

Neuronal roles of the integrin-associated protein (IAP/CD47) in developing cortical neurons

Little is known about the role of the integrin-associated protein (IAP, or CD47) in neuronal development and its function in the central nervous system. We investigated neuronal responses in IAP-overexpressing cortical neurons using a virus-gene transfer system. We found that dendritic outgrowth was significantly enhanced in IAP (form 4)-transfected neurons. Furthermore, synaptic proteins including synaptotagmin, syntaxin, synapsin I, and SNAP25 (25-kDa synaptosomal associated protein) were up-regulated. In accordance with this finding, the release of the excitatory transmitter glutamate and the frequencies of Ca2+ oscillations (glutamate-mediated synaptic transmission) were increased. Interestingly, the overexpression of IAP activated mitogen-activated protein kinase (MAPK), and this activation was required for the IAP-dependent biological effects. After down-regulation of the endogenous IAP by small interfering RNA, MAPK activity, synaptic protein levels, and glutamate release decreased. These observations suggest that the IAP plays important roles in dendritic outgrowth and synaptic transmission in developing cortical neurons through the activation of MAPK.

α-Sialylcholesterol enhances the depolarization-induced release of acetylcholine and glutamate in rat hippocampus: in vivo microdialysis study

The effects of alpha-sialylcholesterol (alpha-SC), a synthetic ganglioside analogue, on synaptic neurotransmission were studied using in vivo microdialysis technique. Application of alpha-SC through a microdialysis probe enhanced high potassium-evoked release of acetylcholine and glutamate in the hippocampal CA3 region of Wistar rats. The experiments using synaptosomes and FM1-43, a fluorescent styryl dye used for studies of neurotransmitter release mechanisms, showed that alpha-SC increased depolarization-induced loss of dye but it did not evoke the dye loss at resting condition. These results indicate that alpha-SC promotes a depolarization-induced exocytotic neurotransmitter release in the brain under in vivo conditions. Application of alpha-SC increased the level of glutamate but not that of acetylcholine, suggesting that alpha-SC affects spontaneous glutamate release and/or transport system at the brain region.

Brain-derived neurotrophic factor protects cultured rat hippocampal neurons from aluminum maltolate neurotoxicity

Aluminum is environmentally abundant but not an essential trace element. Although there is increasing evidence suggesting the implication of aluminum in the pathogenesis of Alzheimer's disease, it is still controversial. We found and report here that aluminum maltolate, a stable and hydrophilic aluminum complex, causes death of primary cultured rat hippocampal neurons in a time- and dose-dependent manner. Degenerated neurons were TUNEL-positive. Immunohistochemical detection of synapsin I and microtubule associated protein 2 revealed the synapse loss between neurons intoxicated by aluminum maltolate. To explore the mechanism underlying its neurotoxicity, we administered various pharmacological compounds prior to the application of aluminum maltolate, and found that brain-derived neurotrophic factor (BDNF) markedly attenuated the neurotoxicity. Furthermore, aluminum maltolate inhibited the elevation of intracellular calcium levels caused by BDNF. Our results suggest the involvement of BDNF in the molecular mechanism underlying neurotoxicity induced by aluminum maltolate.

Nerve growth factor-induced glutamate release is via p75 receptor, ceramide, and Ca(2+) from ryanodine receptor in developing cerebellar neurons

Very little is known about the contribution of a low affinity neurotrophin receptor, p75, to neurotransmitter release. Here we show that nerve growth factor (NGF) induced a rapid release of glutamate and an increase of Ca2+ in cerebellar neurons through a p75-dependent pathway. The NGF-induced release occurred even in the presence of the Trk inhibitor K252a. The release caused by NGF but not brain-derived neurotrophic factor was enhanced in neurons overexpressing p75. Further, after transfection of p75-small interfering RNA, which down-regulated the endogenous p75 expression, the NGF-induced release was inhibited, suggesting that the NGF-induced glutamate release was through p75. We found that the NGF-increased Ca2+ was derived from the ryanodine-sensitive Ca2+ receptor and that the NGF-increased Ca2+ was essential for the NGF-induced glutamate release. Furthermore, scyphostatin, a sphingomyelinase inhibitor, blocked the NGF-dependent Ca2+ increase and glutamate release, suggesting that a ceramide produced by sphingomyelinase was required for the NGF-stimulated Ca2+ increase and glutamate release. This action of NGF only occurred in developing neurons whereas the brain-derived neurotrophic factor-mediated Ca2+ increase and glutamate release was observed at the mature neuronal stage. Thus, we demonstrate that NGF-mediated neurotransmitter release via the p75-dependent pathway has an important role in developing neurons.

Calmodulin mediates brain-derived neurotrophic factor cell survival signaling upstream of Akt kinase in embryonic neocortical neurons

As a calcium-sensing protein, calmodulin acts as a transducer of the intracellular calcium signal for a variety of cellular responses. Although calcium is an important regulator of neuronal survival during development of the nervous system and is also implicated in the pathogenesis of neurodegenerative disorders, it is not known if calmodulin mediates these actions of calcium. To determine the role of calmodulin in regulating neuronal survival and death, we overexpressed calmodulin with mutations in all four Ca(2+)-binding sites (CaM(1-4)) or with disabled C-terminal Ca(2+)-binding sites (CaM(3,4)) in cultured neocortical neurons by adenoviral gene transfer. Long-term neuronal survival was decreased in neurons overexpressing CaM(1-4) and CaM(3,4), which could not be rescued by brain-derived neurotrophic factor (BDNF). The basal level of Akt kinase activation was decreased, and the ability of BDNF to activate Akt was completely abolished in neurons overexpressing CaM(1-4) or CaM(3,4). In contrast, BDNF-induced activation of p42/44 MAPKs was unaffected by calmodulin mutations. Treatment of neurons with calmodulin antagonists and a phosphatidylinositol 3-kinase inhibitor blocked the ability of BDNF to prevent neuronal death, whereas inhibitors of calcium/ calmodulin-dependent protein kinase II did not. Our findings demonstrate a pivotal role for calmodulin in survival signaling by BDNF in developing neocortical neurons by activating a transduction pathway involving phosphatidylinositol 3-kinase and Akt. In addition, our findings show that the C-terminal Ca(2+)-binding sites are critical for calmodulin-mediated cell survival signaling.

Trophic support of mouse inner ear by neural stem cell transplantation

In the auditory system, efforts to reduce degeneration of spiral ganglion neurons have the immediate objective of improving clinical benefits of cochlear implants, which are small devices designed to stimulate spiral ganglion neurons electronically. Recent studies have indicated several neurotrophins can enhance survival of spiral ganglion neurons. However, the strategy for application of neurotrophins in inner ear is still a matter of debate. In this study, we examined the potential of cell therapy as a strategy for application of neurotrophins in the inner ear. Neural stem cells obtained from green fluorescent protein-transgenic mice were used as donor cells. Medium containing neural stem cells was injected into mouse inner ear. Histological analysis 4 weeks later revealed that transplant-derived cells survived in inner ear and that most transplant-derived cells in the cochlea had differentiated into glial cells. Moreover, expression of glial cell line-derived neurotrophic factor and brain-derived neurotrophic factor was observed in transplant-derived cells. These findings indicate that transplantation of neural stem cells can be a useful strategy for application of neurotrophins in inner ear.

Distinct usages of phospholipase C gamma and Shc in intracellular signaling stimulated by neurotrophins

Nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF) and neurotrophin-3 (NT-3), members of the neurotrophin family, bind to and activate TrkA, TrkB and TrkC, respectively, members of the Trk receptor tyrosine kinase family, to exert various effects including promotion of differentiation and survival, and regulation of synaptic plasticity in neuronal cells. Many reports have suggested that different neurotrophins show distinct biological functions, although molecular mechanisms by which neurotrophins exert their different functions remain unclear. In the present study, we found distinct usages of phospholipase Cgamma (PLCgamma) and Shc in intracellular signaling stimulated by neurotrophins. BDNF stimulated much stronger interactions of PLCgamma with Trk than NGF and NT-3 in PC12 cells stably expressing TrkB and cultured cerebral cortical neurons, respectively, although BDNF, NGF and NT-3 induced similar levels of tyrosine phosphorylation of Trk. Furthermore, the cultured cortical neurons showed large PLCgamma-dependent increases in intracellular Ca(2+) levels in response to BDNF compared with NT-3. In Shc signaling, NGF, but not BDNF, displayed interactions between Trk and Shc in a phenylarsine oxide (PAO; an inhibitor of tyrosine phosphatase)-dependent manner in TrkB-expressing PC12 cells. These results indicated that neurotrophins stimulate distinct kinds of interactions between Trk and PLCgamma and between Trk and Shc. These differences may lead to the distinct biological functions of neurotrophins.

Brain-derived neurotrophic factor induces long-lasting Ca2+-activated K+ currents in rat visual cortex neurons

Brain-derived neurotrophic factor (BDNF) increases postsynaptic intracellular Ca2+ and modulates synaptic transmission in various types of neurons. Ca2+-activated K+ currents, opened mainly by intracellular Ca2+ elevation, contribute to hyperpolarization following action potentials and modulate synaptic transmission. We asked whether BDNF induces Ca2+-activated K+ currents by postsynaptic elevation of intracellular Ca2+ in acutely dissociated visual cortex neurons of rats. Currents were analysed using the nystatin-perforated patch clamp technique and imaging of intracellular Ca2+ mobilization with fura-2. At a holding potential of -50 mV, BDNF application (20 ng/mL) for 1-2 min induced an outward current (IBDNF-OUT; 80.0 +/- 29.0 pA) lasting for more than 90 min without attenuation in every neuron tested. K252a (200 nm), an inhibitor of Trk receptor tyrosine kinase, and U73122 (3 microm), a specific phospholipase C (PLC)-gamma inhibitor, suppressed IBDNF-OUT completely. IBDNF-OUT was both charybdotoxin- (600 nm) and apamin- (300 nm) sensitive, suggesting that this current was carried by Ca2+-activated K+ channels. BAPTA-AM (150 microm) gradually suppressed IBDNF-OUT. Fura-2 imaging revealed that a brief application of BDNF elicited a long-lasting elevation of intracellular Ca2+. These results show that BDNF induces long-lasting Ca2+-activated K+ currents by sustained intracellular Ca2+ elevation in rat visual cortex neurons. While BDNF, likely acting through the Trk B receptor, was necessary for the induction of long-lasting Ca2+-activated K+ currents via intracellular Ca2+ elevation, BDNF was not necessary for the maintenance of this current.

Basic fibroblast growth factor evokes a rapid glutamate release through activation of the MAPK pathway in cultured cortical neurons

We examined the possibility that basic fibroblast growth factor (bFGF) is involved in synaptic transmissions. We found that bFGF rapidly induced the release of glutamate and an increase in the intracellular Ca2+ concentration through voltage-dependent Ca2+ channels in cultured cerebral cortical neurons. bFGF also evoked a significant influx of Na+. Tetanustoxin inhibited the bFGF-induced glutamate release, revealing that bFGF triggered exocytosis. The mitogen-activated protein kinase (MAPK) pathway was required for these acute effects of bFGF. We also found that pretreatment with bFGF significantly enhanced high K+-elicited glutamate release also in a MAPK activation-dependent manner. Therefore, we propose that bFGF exerts promoting effects on excitatory neuronal transmission via activation of the MAPK pathway.

Brain-derived neurotrophic factor-induced potentiation of Ca(2+) oscillations in developing cortical neurons

Brain-derived neurotrophic factor (BDNF) has been reported to exert an acute potentiation of synaptic activity. Here we examined the action of BDNF on synchronous spontaneous Ca(2+) oscillations in cultured cerebral cortical neurons prepared from postnatal 2-3-day-old rats. The synchronous spontaneous Ca(2+) oscillations began at approximately DIV 5. It was revealed that voltage-dependent Ca(2+) channels and ionotropic glutamate receptors were involved in the synchronous spontaneous oscillatory activity. BDNF potentiated the frequency of these oscillations. The BDNF-potentiated activity reached 207 +/- 20.1% of basal oscillatory activity. NT-3 and NT-4/5 also induced the potentiation. However, nerve growth factor did not. We examined the correlation between BDNF-induced glutamate release and the BDNF-potentiated oscillatory activity. Both up-regulation of phospholipase C-gamma (PLC-gamma) expression and the BDNF-induced glutamate release occurred at approximately DIV 5 when the BDNF-potentiated oscillations appeared. We confirmed that the BDNF-induced glutamate release occurred through a glutamate transporter that was dependent on the PLC-gamma/IP(3)/Ca(2+) pathway. Transporter inhibitors blocked the BDNF-potentiated oscillations, demonstrating that BDNF enhanced the glutamatergic transmissions in the developing cortical network by inducing glutamate release via a glutamate transporter.

Brain-derived neurotrophic factor enhances depolarization-evoked glutamate release in cultured cortical neurons

Brain-derived neurotrophic factor (BDNF) has been reported to play an important role in neuronal plasticity. In this study, we examined the effect of BDNF on an activity-dependent synaptic function in an acute phase. First, we found that short-term treatment (10 min) with BDNF enhanced depolarization-evoked glutamate release in cultured cortical neurons. The enhancement diminished gradually according to the length of BDNF treatment. The BDNF-enhanced release did not require the synthesis of protein and mRNA. Both tetanus toxin and bafilomycin abolished the depolarization-evoked glutamate release with or without BDNF, indicating that BDNF acted via an exocytotic pathway. Next, we investigated the effect of BDNF on intracellular Ca(2+). BDNF potentiated the increase in intracellular Ca(2+) induced by depolarization. The Ca(2+) was derived from intracellular stores, because thapsigargin completely inhibited the potentiation. Furthermore, both thapsigargin and xestospongin C inhibited the effect of BDNF. These results suggested that the release of Ca(2+) from intracellular stores mediated by the IP(3) receptor was involved in the BDNF-enhanced glutamate release. Last, it was revealed that the enhancement of glutamate release by BDNF was dependent on the TrkB-PLC-gamma pathway. These results clearly demonstrate that short-term treatment with BDNF enhances an exocytotic pathway by potentiating the accumulation of intracellular Ca(2+) through intracellular stores.

[Diffuse primary leptomeningeal gliomatosis]

A woman died at the age of 22 years. Lifetime diagnosis had been inflammatory arachnopathy. The course of the disease had taken at least 6 years. Autopsy revealed primary diffuse leptomeningeal astrocytoma of the brain and spinal cord without neoplastic foci in the parenchyma of the central nervous system. Patchy dystrophic calcifications were recorded from the cerebral and cerebellar cortex.