Regulation of BDNF promoters in the rat hippocampus

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.

TrkB Truncated Isoform Receptors as Transducers and Determinants of BDNF Functions

Brain-derived neurotrophic factor (BDNF) belongs to the neurotrophin family of secreted growth factors and binds with high affinity to the TrkB tyrosine kinase receptors. BDNF is a critical player in the development of the central (CNS) and peripheral (PNS) nervous system of vertebrates and its strong pro-survival function on neurons has attracted great interest as a potential therapeutic target for the management of neurodegenerative disorders such as Amyotrophic Lateral Sclerosis (ALS), Huntington, Parkinson's and Alzheimer's disease. The TrkB gene, in addition to the full-length receptor, encodes a number of isoforms, including some lacking the catalytic tyrosine kinase domain. Importantly, one of these truncated isoforms, namely TrkB.T1, is the most widely expressed TrkB receptor in the adult suggesting an important role in the regulation of BDNF signaling. Although some progress has been made, the mechanism of TrkB.T1 function is still largely unknown. Here we critically review the current knowledge on TrkB.T1 distribution and functions that may be helpful to our understanding of how it regulates and participates in BDNF signaling in normal physiological and pathological conditions.

Enhancing cognition through pharmacological and environmental interventions: Examples from preclinical models of neurodevelopmental disorders

In this review we discuss the role of environmental and pharmacological treatments to enhance cognition with special regards to neurodevelopmental related disorders and aging. How the environment influences brain structure and function, and the interactions between rearing conditions and gene expression, are fundamental questions that are still poorly understood. We propose a model that can explain some of the discrepancies in findings for effects of environmental enrichment on outcome measures. Evidence of a direct causal correlation of nootropics and treatments that enhanced cognition also will be presented, and possible molecular mechanisms that include neurotrophin signaling and downstream pathways underlying these processes are discussed. Finally we review recent findings achieved with a wide set of behavioral and cognitive tasks that have translational validity to humans, and should be useful for future work on devising appropriate therapies. As will be discussed, the collective findings suggest that a combinational therapeutic approach of environmental enrichment and nootropics could be particularly successful for improving learning and memory in both developmental disorders and normal aging.

HDAC Inhibitors Induce BDNF Expression and Promote Neurite Outgrowth in Human Neural Progenitor Cells-Derived Neurons

Besides its key role in neural development, brain-derived neurotrophic factor (BDNF) is important for long-term potentiation and neurogenesis, which makes it a critical factor in learning and memory. Due to the important role of BDNF in synaptic function and plasticity, an in-house epigenetic library was screened against human neural progenitor cells (HNPCs) and WS1 human skin fibroblast cells using Cell-to-Ct assay kit to identify the small compounds capable of modulating the BDNF expression. In addition to two well-known hydroxamic acid-based histone deacetylase inhibitors (hb-HDACis), SAHA and TSA, several structurally similar HDAC inhibitors including SB-939, PCI-24781 and JNJ-26481585 with even higher impact on BDNF expression, were discovered in this study. Furthermore, by using well-developed immunohistochemistry assays, the selected compounds were also proved to have neurogenic potential improving the neurite outgrowth in HNPCs-derived neurons. In conclusion, we proved the neurogenic potential of several hb-HDACis, alongside their ability to enhance BDNF expression, which by modulating the neurogenesis and/or compensating for neuronal loss, could be propitious for treatment of neurological disorders.

HIV-1 Tat protein promotes neuronal dysregulation by inhibiting E2F transcription factor 3 (E2F3)

Individuals who are infected with HIV-1 accumulate damage to cells and tissues (e.g. neurons) that are not directly infected by the virus. These include changes known as HIV-associated neurodegenerative disorder (HAND), leading to the loss of neuronal functions, including synaptic long-term potentiation (LTP). Several mechanisms have been proposed for HAND, including direct effects of viral proteins such as the Tat protein. Searching for the mechanisms involved, we found here that HIV-1 Tat inhibits E2F transcription factor 3 (E2F3), CAMP-responsive element-binding protein (CREB), and brain-derived neurotropic factor (BDNF) by up-regulating the microRNA miR-34a. These changes rendered murine neurons dysfunctional by promoting neurite retraction, and we also demonstrate that E2F3 is a specific target of miR-34a. Interestingly, bioinformatics analysis revealed the presence of an E2F3-binding site within the CREB promoter, which we validated with ChIP and transient transfection assays. Of note, luciferase reporter assays revealed that E2F3 up-regulates CREB expression and that Tat interferes with this up-regulation. Further, we show that miR-34a inhibition or E2F3 overexpression neutralizes Tat's effects and restores normal distribution of the synaptic protein synaptophysin, confirming that Tat alters these factors, leading to neurite retraction inhibition. Our results suggest that E2F3 is a key player in neuronal functions and may represent a good target for preventing the development of HAND.

Clinical and Environmental Correlates of Serum BDNF: A Descriptive Study with Plausible Implications for AD Research

BACKGROUND

Brain derived neurotrophic factor (BDNF) may play a central role in the pathogenesis of Alzheimer's disease (AD) through neurotrophic effects on basal cholinergic neurons. Reduced serum levels of BDND are observed among AD patients and may predict AD risk. Nevertheless, knowledge about factors associated with its levels in blood is lacking.

OBJECTIVE

To identify clinical and demographic correlates of serum BDNF levels.

METHODS

BDNF was measured from serum collected between 1992-1996 and 1998-2001 in participants from the Original and Offspring cohorts of the Framingham Study, respectively. A cross-sectional analysis was done to evaluate the relationship between clinical measures and BDNF levels using standard linear regression and stepwise models. Analyses were conducted in the total sample and separately in each cohort, and were adjusted for age and sex.

RESULTS

BDNF was measured in 3,689 participants (mean age 65 years, 56% women; 82% Offspring). Cigarette smoking and high total cholesterol were associated with elevated BDNF levels, and history of atrial fibrillation was associated with decreased levels. Elevated BDNF levels were related to greater physical activity and lower Tumor Necrosis Factor-α levels in Offspring. Stepwise models also revealed associations with statin use, alcohol consumption and Apolipoprotein Eε4 genotype.

CONCLUSION

Serum BDNF correlates with various metabolic, inflammatory and life-style measures which in turn have been linked with risk of AD. Future studies of serum BDNF should adjust for these correlates and are needed to further explore the underlying interplay between BDNF and other factors in the pathophysiology of cognitive impairment and AD.

Mild Maternal Hypothyroxinemia During Pregnancy Induces Persistent DNA Hypermethylation in the Hippocampal Brain-Derived Neurotrophic Factor Gene in Mouse Offspring

BACKGROUND

Thyroid hormones are essential for normal development of the central nervous system (CNS). Experimental rodents have shown that even a subtle thyroid hormone insufficiency in circulating maternal thyroid hormones during pregnancy may adversely affect neurodevelopment in offspring, resulting in irreversible cognitive deficits. This may be due to the persistent reduced expression of the hippocampal brain-derived neurotrophic factor gene Bdnf, which plays a crucial role in CNS development. However, the underlying molecular mechanisms remain unclear.

METHODS

Thiamazole (MMI; 0.025% [w/v]) was administered to dams from two weeks prior to conception until delivery, which succeeded in inducing mild maternal hypothyroxinemia during pregnancy. Serum thyroid hormone and thyrotropin levels of the offspring derived from dams with mild maternal hypothyroxinemia (M offspring) and the control offspring (C offspring) were measured. At 70 days after birth, several behavior tests were performed on the offspring. Gene expression and DNA methylation status were also evaluated in the promoter region of Bdnf exon IV, which is largely responsible for neural activity-dependent Bdnf gene expression, in the hippocampus of the offspring at day 28 and day 70.

RESULTS

No significant differences in serum thyroid hormone or thyrotropin levels were found between M and C offspring at day 28 and day 70. M offspring showed an impaired learning capacity in the behavior tests. Hippocampal steady-state Bdnf exon IV expression was significantly weaker in M offspring than it was in C offspring at day 28. At day 70, hippocampal Bdnf exon IV expression at the basal level was comparable between M and C offspring. However, it was significantly weaker in M offspring than in C offspring after the behavior tests. Persistent DNA hypermethylation was also found in the promoter region of Bdnf exon IV in the hippocampus of M offspring compared to that of C offspring, which may cause the attenuation of Bdnf exon IV expression in M offspring.

CONCLUSIONS

Mild maternal hypothyroxinemia induces persistent DNA hypermethylation in Bdnf exon IV in offspring as epigenetic memory, which may result in long-term cognitive disorders.

Long-term effects of combined neonatal and adolescent stress on brain-derived neurotrophic factor and dopamine receptor expression in the rat forebrain

Altered brain-derived neurotrophic factor (BDNF) signalling and dopaminergic neurotransmission have been shown in the forebrain in schizophrenia. The 'two hit' hypothesis proposes that two major disruptions during development are involved in the pathophysiology of this illness. We therefore used a 'two hit' rat model of combined neonatal and young-adult stress to assess effects on BDNF signalling and dopamine receptor expression. Wistar rats were exposed to neonatal maternal separation (MS) stress and/or adolescent/young-adult corticosterone (CORT) treatment. At adulthood the medial prefrontal cortex (mPFC), caudate putamen (CPu) and nucleus accumbens (NAc) were analysed by qPCR and Western blot. The 'two hit' combination of MS and CORT treatment caused significant increases in BDNF mRNA and protein levels in the mPFC of male, but not female rats. BDNF mRNA expression was unchanged in the CPu but was significantly reduced by CORT in the NAc. DR3 and DR2 mRNA were significantly up-regulated in the mPFC of two-hit rats and a positive correlation was found between BDNF and DR3 expression in male, but not female rats. DR2 and DR3 expression were significantly increased following CORT treatment in the NAc and a significant negative correlation between BDNF and DR3 and DR2 mRNA levels was found. Our data demonstrate male-specific two-hit effects of developmental stress on BDNF and DR3 expression in the mPFC. Furthermore, following chronic adolescent CORT treatment, the relationship between BDNF and dopamine receptor expression was significantly altered in the NAc. These results elucidate the long-term effects of 'two hit' developmental stress on behaviour.

Delayed BDNF alterations in the prefrontal cortex of rats exposed to prenatal stress: preventive effect of lurasidone treatment during adolescence

Psychiatric diseases may often represent the consequence of exposure to adverse events early in life. Accordingly, exposure to stress during gestation in rats has a strong impact on development and can cause long-term abnormalities in adult behavior. Considering that neuronal plasticity has emerged as a major vulnerability element in psychiatric disorders, we investigated the postnatal developmental profile of Brain-Derived Neurotrophic Factor expression (BDNF), an important mediator for long-term functional deterioration associated to mental illness, in male and female rats following exposure to prenatal stress (PNS). Since we found that the majority of alterations became fully manifest at early adulthood, we tried to prevent these abnormalities with an early pharmacological intervention. To address this point, we treated rats during adolescence with the multi-receptor antipsychotic lurasidone, which was proven to be effective in animal models of schizophrenia. Interestingly, we show that lurasidone treatment was able to prevent the reduction of BDNF expression in adult rats that were exposed to PNS. Collectively, our results provide further support to the notion that exposure to early life stress has a negative impact on neuronal plasticity and that pharmacological intervention during critical time windows may prove effective in preventing neuroplastic dysfunction, leading to long-term beneficial effects on brain function.

Sex-specific disruptions in spatial memory and anhedonia in a "two hit" rat model correspond with alterations in hippocampal brain-derived neurotrophic factor expression and signaling

Post-mortem studies have demonstrated reduced expression of brain-derived neurotrophic factor (BDNF) in the hippocampus of schizophrenia and major depression patients. The "two hit" hypothesis proposes that two or more major disruptions at specific time points during development are involved in the pathophysiology of these mental illnesses. However, the role of BDNF in these "two hit" effects is unclear. Our aim was to behaviorally characterize a "two hit" rat model of developmental stress accompanied by an in-depth assessment of BDNF expression and signalling. Wistar rats were exposed to neonatal maternal separation (MS) stress and/or adolescent/young-adult corticosterone (CORT) treatment. In adulthood, models of cognitive and negative symptoms of mental illness were analyzed. The hippocampus was then dissected into dorsal (DHP) and ventral (VHP) regions and analyzed by qPCR for exon-specific BDNF gene expression or by Western blot for BDNF protein expression and downstream signaling. Male "two hit" rats showed marked disruptions in short-term spatial memory (Y-maze) which were absent in females. However, female "two hit" rats showed signs of anhedonia (sucrose preference test), which were absent in males. Novel object recognition and anxiety (elevated plus maze) were unchanged by either of the two "hits". In the DHP, MS caused a male-specific increase in BDNF Exons I, II, IV, VII, and IX mRNA but a decrease in mature BDNF and phosphorylated TrkB (pTrkB) protein expression in adulthood. In the VHP, BDNF transcript expression was unchanged; however, in female rats only, MS significantly decreased mature BDNF and pTrkB protein expression in adulthood. These data demonstrate that MS causes region-specific and sex-specific long-term effects on BDNF expression and signaling and, importantly, mRNA expression does not always infer protein expression. Alterations to BDNF signaling may mediate the sex-specific effects of developmental stress on anhedonic behaviors.

Prenatal stress decreases Bdnf expression and increases methylation of Bdnf exon IV in rats

There is ample evidence that exposure to stress during gestation increases the risk of the offspring to develop mood disorders. Brain-derived neurotrophic factor (Bdnf) plays a critical role during neuronal development and is therefore a prime candidate to modulate neuronal signaling in adult offspring of rat dams that were stressed during gestation. In the current study, we tested the hypothesis that alterations in Bdnf expression in prenatally stressed (PNS) offspring are mediated by changes in DNA methylation in exons IV and VI of the Bdnf gene. We observed decreased Bdnf expression in the amygdala and hippocampus of prenatally stressed rats both at weaning and in adulthood. This decrease in Bdnf expression was accompanied by increased DNA methylation in Bdnf exon IV in the amygdala and hippocampus, suggesting that PNS-induced reduction in Bdnf expression may, at least in part, be mediated by increased DNA methylation of Bdnf exon IV. Expression of DNA methyltransferases (Dnmt) 1 and 3a was increased in PNS rats in the amygdala and hippocampus. Our data suggest that PNS induces decreases in Bdnf expression that may at least in part be mediated by increased DNA methylation of Bdnf exon IV.

Epigenetic regulation of the BDNF gene: implications for psychiatric disorders

Abnormal brain-derived neurotrophic factor (BDNF) signaling seems to have a central role in the course and development of various neurological and psychiatric disorders. In addition, positive effects of psychotropic drugs are known to activate BDNF-mediated signaling. Although the BDNF gene has been associated with several diseases, molecular mechanisms other than functional genetic variations can impact on the regulation of BDNF gene expression and lead to disturbed BDNF signaling and associated pathology. Thus, epigenetic modifications, representing key mechanisms by which environmental factors induce enduring changes in gene expression, are suspected to participate in the onset of various psychiatric disorders. More specifically, various environmental factors, particularly when occurring during development, have been claimed to produce long-lasting epigenetic changes at the BDNF gene, thereby affecting availability and function of the BDNF protein. Such stabile imprints on the BDNF gene might explain, at least in part, the delayed efficacy of treatments as well as the high degree of relapses observed in psychiatric disorders. Moreover, BDNF gene has a complex structure displaying differential exon regulation and usage, suggesting a subcellular- and brain region-specific distribution. As such, developing drugs that modify epigenetic regulation at specific BDNF exons represents a promising strategy for the treatment of psychiatric disorders. Here, we present an overview of the current literature on epigenetic modifications at the BDNF locus in psychiatric disorders and related animal models.

Darkness reduces BDNF expression in the visual cortex and induces repressive chromatin remodeling at the BDNF gene in both hippocampus and visual cortex

Neuronal activity regulates the expression of brain-derived neurotrophic factor (BDNF) in brain. In darkness, reduced neuronal activity in the visual cortex markedly decreases total BDNF transcription level in adult rats. Epigenetic mechanisms are crucially involved in the regulation of gene expression in response to environmental stimuli. In this study, we examined the effect of 1 week of light deprivation (LD) on the activity-dependent changes in BDNF expression from different promoters in the visual cortex and hippocampus. We analyzed the correlation between the chromatin state of Bdnf promoters, exon-specific transcripts levels, and total protein levels in light-deprived rats and in rats reared under normal light-dark cycle. We found that 1 week of LD significantly reduced Bdnf mRNA and protein in the visual cortex but not in the hippocampus. However, epigenetic analysis revealed that LD increased histone-3 methylation and DNA methylation at the Bdnf promoter IV in both the visual cortex and hippocampus. These data highlight the spatial differences in signaling pathways that lead to the BDNF expression in response to diminished ambient light.

2-Deoxy-D-glucose reduces epilepsy progression by NRSF-CtBP-dependent metabolic regulation of chromatin structure

Temporal lobe epilepsy is a common form of drug-resistant epilepsy that sometimes responds to dietary manipulation such as the 'ketogenic diet'. Here we have investigated the effects of the glycolytic inhibitor 2-deoxy-D-glucose (2DG) in the rat kindling model of temporal lobe epilepsy. We show that 2DG potently reduces the progression of kindling and blocks seizure-induced increases in the expression of brain-derived neurotrophic factor and its receptor, TrkB. This reduced expression is mediated by the transcription factor NRSF, which recruits the NADH-binding co-repressor CtBP to generate a repressive chromatin environment around the BDNF promoter. Our results show that 2DG has anticonvulsant and antiepileptic properties, suggesting that anti-glycolytic compounds may represent a new class of drugs for treating epilepsy. The metabolic regulation of neuronal genes by CtBP will open avenues of therapy for neurological disorders and cancer.

BDNF and trkB mRNA expression in the hippocampus and temporal cortex during the human lifespan

Brain-derived neurotrophic factor (BDNF) and its receptor tyrosine kinase B (trkB) influence neuronal survival, differentiation, synaptogenesis, and maintenance. Using in situ hybridization we examined the spatial and temporal expression of mRNAs encoding these proteins during diverse stages of life in the human hippocampus and inferior temporal cortex. We examined six postnatal time points: neonatal (1-3 months), infant (4-12 months), adolescent (14-18 years), young adult (20-24 years), adult (34-43 years), and aged (68-86 years). Within the hippocampus, levels of BDNF mRNA did not change significantly with age. However, levels of both the full-length form of trkB (trkB TK+) mRNA and the truncated form of trkB (trkB TK-) decreased over the life span (p < 0.05). In the temporal cortex, BDNF and trkB TK+ mRNA levels were highest in neonates and decreased with age (r = -0.4 and r = -0.7, respectively, both p < 0.05). In contrast, TrkB TK- mRNA levels remained constant across the life span in the temporal cortex. The peak in both BDNF and trkB TK+ mRNA expression in the neonate temporal cortex differs from that previously described for the frontal cortex where both mRNAs peak in expression during young adulthood. The increase in BDNF and trkB TK+ mRNA in the temporal cortex of the neonate suggests that neurotrophin signaling is important in the early development of the temporal cortex. In addition, since BDNF and both forms of its high affinity receptor are expressed throughout the development, maturation, and aging of the human hippocampus and surrounding neocortex they are likely to play roles not only in early growth but also in maintenance of neurons throughout life.

Antidepressants reverse corticosterone-mediated decrease in brain-derived neurotrophic factor expression: differential regulation of specific exons by antidepressants and corticosterone

Earlier studies have implicated brain-derived neurotrophic factor in stress and in the mechanism of action of antidepressants. It has been shown that antidepressants upregulate, whereas corticosterone downregulates, brain-derived neurotrophic factor expression in rat brain. Whether various classes of antidepressants reverse corticosterone-mediated downregulation of brain-derived neurotrophic factor is unclear. Also not known is how antidepressants or corticosterone regulates brain-derived neurotrophic factor expression. To clarify this, we examined the effects of various classes of antidepressants and corticosterone, alone and in combination, on the mRNA expression of total brain-derived neurotrophic factor and of individual brain-derived neurotrophic factor exons, in rat brain. Normal or corticosterone pellet-implanted (100 mg, 21 days) rats were injected with different classes of antidepressants, fluoxetine, desipramine, or phenelzine, intraperitoneally for 21 days and killed 2 h after the last injection. mRNA expression of total brain-derived neurotrophic factor and of exons I-IV was measured in frontal cortex and hippocampus. Given to normal rats, fluoxetine increased total brain-derived neurotrophic factor mRNA only in hippocampus, whereas desipramine or phenelzine increased brain-derived neurotrophic factor mRNA in both frontal cortex and hippocampus. When specific exons were examined, desipramine increased expression of exons I and III in both brain areas, whereas phenelzine increased exon I in both frontal cortex and hippocampus but exon IV only in hippocampus. On the other hand, fluoxetine increased only exon II in hippocampus. Corticosterone treatment of normal rats decreased expression of total brain-derived neurotrophic factor mRNA in both brain areas, specifically decreasing exons II and IV. Treatment with desipramine or phenelzine of corticosterone pellet-implanted rats reversed the corticosterone-induced decrease in total brain-derived neurotrophic factor expression in both brain areas; however, fluoxetine reversed the decrease only partially in hippocampus. Interestingly, antidepressant treatment of corticosterone pellet-implanted rats increased only those specific exons that are increased during treatment of normal rats with each particular antidepressant. We found that although corticosterone and antidepressants both modulate brain-derived neurotrophic factor expression, and antidepressants reverse the corticosterone-induced brain-derived neurotrophic factor decrease, antidepressants and corticosterone differ in how they regulate the expression of brain-derived neurotrophic factor exon(s).

Corticosterone actions on the hippocampal brain-derived neurotrophic factor expression are mediated by exon IV promoter

Brain-derived neurotrophic factor (BDNF) expression is strongly regulated by adrenocorticosteroids via activated gluco- and mineralocorticoid receptors. Four separate promoters are located upstream of the BDNF noncoding exons I to IV and may thus be involved in adrenocorticosteroid-mediated gene regulation. In adrenalectomised rats, corticosterone (10 mg/kg s.c.) induces a robust down-regulation of both BDNF mRNA and protein levels in the hippocampus peaking at 2-8 h. To study the role of the individual promoters in the corticosterone response, we employed exon-specific riboprobe in situ hybridisation as well as real-time polymerase chain reaction (PCR) in the dentate gyrus. We found a down-regulation, mainly of exon IV and the protein-coding exon V, in nearby all hippocampal subregions, but exon II was only down-regulated in the dentate gyrus. Exon I and exon III transcripts were not affected by corticosterone treatment. The results could be confirmed with real-time PCR in the dentate gyrus. It appears as if the exon IV promoter is the major target for corticosterone-mediated transcriptional regulation of BDNF in the hippocampus.

The role of CaMKII in BDNF-mediated neuroprotection of retinal ganglion cells (RGC-5)

The purpose of the study is to determine if expression or secretion of brain-derived neurotrophic factor (BDNF) in retinal ganglion cells (RGC-5) is mediated by NFkappaB or Ca2+/calmodulin-dependent protein kinase II (CaMKII). RGC-5 cells were exposed to 1 mM glutamate for various periods of time, in the presence or absence of prospective regulatory molecules. BDNF mRNA and protein expression were assessed with the aid of real-time PCR and immunoblots, respectively, and BDNF secretion was determined by ELISA. The NFkappaB inhibitor (TLCK and PTD-p65), or a specific CaMKII inhibitor (m-AIP), was used to study association of NFkappaB or CaMKII with BDNF expression/secretion in RGC-5 cells. Glutamate stimulated a transient increase in BDNF mRNA and protein in RGC-5 cells, and also stimulated an early release of BDNF into the culture media. Neutralizing the BDNF or blocking the TrkB receptor enhanced the glutamate-induced cytotoxicity. NFkappaB nuclear translocation was revealed in response to glutamate treatment. Application of TLCK or PTD-p65 inhibited the glutamate-induced BDNF expression and secretion. Inhibition of CaMKII by m-AIP did not affect expression but significantly enhanced the release of BDNF from glutamate challenged cells. Our data suggest that glutamate treatment may stimulate expression of BDNF in RGC-5 cells through NFkappaB activation. A novel mechanism for neuroprotection is proposed for the CaMKII inhibitor, AIP, which appears to protect RGC-5 cells from cytotoxicity by enhancing the release of BDNF from glutamate challenged cells.

Differential regulation of multiple brain-derived neurotrophic factor transcripts in the postnatal and adult rat hippocampus during development, and in response to kainate administration

Brain-derived neurotrophic factor (BDNF) is expressed at high levels in the hippocampus, where it has been implicated in physiological functions such as the modulation of synaptic strength as well as in the pathophysiology of epileptic seizures. BDNF expression is highly regulated and the BDNF gene can generate multiple transcript isoforms by alternate splicing of four 5' exons (exons I-IV) to one 3' exon (exon V). To gain insight into the regulation of different BDNF transcripts in specific hippocampal subfields during postnatal development, exon-specific riboprobes were used. Our data shows that BDNF exon I and exon II mRNAs are regulated in hippocampal subfields during postnatal development, in contrast to BDNF exon III and exon IV mRNA, which remain relatively stable through this period. Further, exons I and II show distinct temporal patterns of expression in the hippocampus: BDNF I mRNA peaks in adulthood in contrast to BDNF II mRNA which peaks at postnatal day 14 (P14). Finally, we have addressed whether kainate treatment in postnatal pups and adults regulates BDNF through the recruitment of the same, or distinct, BDNF promoters. Our data indicates that kainate-induced seizures induce strikingly different expression of distinct BDNF transcripts, both in magnitude as well as spatial patterns in the hippocampal subfields, of pups as compared to adults. These results suggest that kainate-mediated seizures differentially recruit BDNF promoters in the developing postnatal hippocampus in contrast to the adult hippocampus to achieve a hippocampal subfield specific regulation of exon-specific BDNF mRNAs.

Reduced expression of brain-derived neurotrophic factor in mice deficient for pituitary adenylate cyclase activating polypeptide type-I-receptor

In vitro pituitary adenylate cyclase activating polypeptide (PACAP) induces the expression of brain-derived neurotrophic factor (BDNF) via its specific receptor PAC1. Since BDNF has been implicated in learning paradigms and mice lacking functional PAC1 have deficits in hippocampus-dependent associative learning, we investigated whether PAC1 mutants show alterations in hippocampal expression of BDNF and its receptor TrkB. Semi-quantitative in situ-hybridization using exon-specific BDNF-probes revealed significantly reduced expression of the exon-III and exon-V-specific transcripts within the hippocampal CA3 region in PAC1-deficient mice. A similar trend was observed for the exon-I-specific transcript. The expression of the exon-III-specific transcript was also reduced within the dentate gyrus, while Trk B-expression did not differ between genotypes. Our data demonstrate that even in vivo PAC1-mediated signaling seems to play a pivotal role for the transcriptional regulation of BDNF.

Estrogen affects BDNF expression following chronic constriction nerve injury

To investigate the effect of estrogen on BDNF expression in neuropathic pain. Using chronic constriction injury model, we detected BDNF mRNA and protein level by reverse transcription polymerase chain reaction and enzyme-linked immunosorbent assay, respectively. A hot-plate test was used as a sign of neuropathic pain. The rats with higher estrogen level exhibited more sensitive to thermal stimuli and had a higher level of BDNF mRNA and protein expression. The results suggest that BDNF level can be elevated by estrogen and estrogen may potentiate the sensitivity to thermal stimuli by its effect on BDNF expression. Thus, this study improves our understanding of the role of estrogen in the nociceptive processing.

Reduced brain-derived neurotrophic factor in prefrontal cortex of patients with schizophrenia

Anatomical and molecular abnormalities of excitatory neurons in the dorsolateral prefrontal cortex (DLPFC) are found in schizophrenia. We hypothesized that brain-derived neurotrophic factor (BDNF), a protein capable of increasing pyramidal neuron spine density and augmenting synaptic efficacy of glutamate, may be abnormally expressed in the DLPFC of patients with schizophrenia. Using an RNase protection assay and Western blotting, we detected a significant reduction in BDNF mRNA (mean=23%) and protein (mean=40%) in the DLPFC of patients with schizophrenia compared to normal individuals. At the cellular level, BDNF mRNA was expressed at varying intensities in pyramidal neurons throughout layers II, III, V, and VI of DLPFC. In patients with schizophrenia; neuronal BDNF expression was decreased in layers III, V and VI. Our study demonstrates a reduction in BDNF production and availability in the DLPFC of schizophrenics, and suggests that intrinsic cortical neurons, afferent neurons, and target neurons may receive less trophic support in this disorder.

Expression of brain-derived neurotrophic factor in rat dorsal root ganglia, spinal cord and gracile nuclei in experimental models of neuropathic pain

Chronic constriction injury of the sciatic nerve and lumbar L5 and L6 spinal nerve ligation provide animal models for pain syndromes accompanying peripheral nerve injury and disease. In the present study, we evaluated changes in brain-derived neurotrophic factor (BDNF) immunoreactivity in the rat L4 and L5 dorsal root ganglia (DRG) and areas where afferents from the DRG terminates (the L4/5 spinal cord and gracile nuclei) in these experimental models of neuropathic pain. Chronic constriction injury induced significant increase in the percentage of small, medium and large BDNF-immunoreactive neurons in the ipsilateral L4 and L5 DRG. Following spinal nerve ligation, the percentage of large BDNF-immunoreactive neurons increased significantly, and that of small BDNF-immunoreactive neurons decreased markedly in the ipsilateral L5 DRG, while that of BDNF-immunoreactive L4 DRG neurons of all sizes showed marked increase. Both chronic constriction injury and spinal nerve ligation induced significant increase in the number of BDNF-immunoreactive axonal fibers in the superficial and deeper laminae of the L4/5 dorsal horn and the gracile nuclei on the ipsilateral side. Considering that BDNF may modulate nociceptive sensory inputs and that injection of antiserum to BDNF significantly reduces the sympathetic sprouting in the DRG and allodynic response following sciatic nerve injury, our results also may suggest that endogenous BDNF plays an important role in the induction of neuropathic pain after chronic constriction injury and spinal nerve ligation. In addition, the increase of BDNF in L4 DRG may contribute to evoked pain which is known to be mediated by input from intact afferent from L4 DRG following L5 and L6 spinal nerve ligation.

Brain-derived neurotrophic factor and TrkB tyrosine kinase receptor gene expression in zebrafish embryo and larva

The genes that encode the neurotrophin family of secreted polypeptides and the Trk family of high affinity neurotrophin transmembrane protein tyrosine kinase receptors are induced at the time of neurogenesis in mammals and are known to play critical roles in nervous system development. We show here that in contrast to mammals, the genes encoding the neurotrophin brain-derived neurotrophic factor (BDNF) and the neurotrophin receptor TrkB are expressed throughout embryonic development in the zebrafish. At the embryonic stages preceding transcription of endogenous genes all cells contain BDNF transcripts and immunoreactive BDNF and the trkB transcripts lack the region that encodes a kinase domain. As development proceeds, progressively fewer cells contain BDNF transcripts and by the time of neurogenesis the trkB transcripts encode a kinase-domain. In the 4-day-old larva, a small subset of specialized sensory cells on the surface and cells in deeper structures including the gill arches, fin, and cloaca express the BDNF gene at high levels in a promoter-specific fashion. This progressive restriction of BDNF gene expression must involve an extinction of BDNF gene transcription in some and induction of high levels of transcription in a promoter-specific fashion in other cells.

Differential usage of multiple brain-derived neurotrophic factor promoter in rat dorsal root ganglia following peripheral nerve injuries and inflammation

The brain-derived neurotrophic factor (BDNF) may act as either an autocrine or paracrine survival factor for the dorsal root ganglion (DRG) neurons and may also serve as a neurotransmitter or neuromodulator within the dorsal horn of the spinal cord. The rat BDNF gene consists of four short 5' exons linked to separate promoters and one 3' exon encoding the mature BDNF protein. An exon-specific reverse transcription-polymerase chain reaction analysis was used to study the differential utilization of multiple promoters in the DRG following unilateral sciatic axotomy, dorsal rhizotomy and peripheral inflammation. The exon I transcript showed the highest induction rate with the ipsilateral expression elevated 4.3-5.8 times that of contralateral expression. Both exon II and III mRNAs showed a smaller increase 1 day after the three kinds of stimuli. In addition, exon IV mRNA transcription increased slightly only after rhizotomy, but not after axotomy and peripheral inflammation after 1 day. Furthermore, the elevated exon I mRNA levels 1 day after rhizotomy were sustained for up to 7 days. In contrast, those of the exon I mRNA after axotomy had declined 2.8 times the control level after 7 days. These findings suggest that the promoter linked to exon I may provide a major regulatory point of BDNF mRNA expression by peripheral nerve injuries and inflammation. In addition, both exon I and IV mRNA expression may show different temporal activation patterns according to the types of injury.

Injured primary sensory neurons switch phenotype for brain-derived neurotrophic factor in the rat

Peripheral nerve injury results in plastic changes in the dorsal root ganglia and spinal cord, and is often complicated with neuropathic pain. The mechanisms underlying these changes are not known. We have now investigated the expression of brain-derived neurotrophic factor in the dorsal root ganglia with histochemical and biochemical methods following sciatic nerve lesion in the rat. The percentage of neurons immunoreactive for brain-derived neurotrophic factor in the ipsilateral dorsal root ganglia was significantly increased as early as 24 h after the nerve lesion and the increase lasted for at least two weeks. The level of brain-derived neurotrophic factor messenger RNA was also significantly increased in the ipsibut not contralateral dorsal root ganglia. Both neurons and satellite cells in the lesioned dorsal root ganglia synthesized brain-derived neurotrophic factor messenger RNA after the nerve lesion. There was a dramatic shift in size distribution of positive neurons towards large sizes seven days after sciatic nerve lesion. Morphometric analysis and retrograde tracing studies showed that no injured neurons smaller than 600 microm2 were immunoreactive for brain-derived neurotrophic factor, whereas the majority of large injured neurons were immunoreactive in the ipsilateral dorsal root ganglia seven days postlesion. The brain-derived neurotrophic factor-immunoreactive nerve terminals in the ipsilateral spinal cord were reduced in the central region of lamina II, but increased in more medial regions or deeper into laminae III/IV. These studies indicate that sciatic nerve injury results in a differential regulation of brain-derived neurotrophic factor in different subpopulations of sensory neurons in the dorsal root ganglia. Small neurons switched off their normal synthesis of brain-derived neurotrophic factor, whereas larger ones switched to a brain-derived neurotrophic factor phenotype. The phenotypic switch may have functional implications in neuronal plasticity and generation of neuropathic pain after nerve injury.

Transcript-specific effects of adrenalectomy on seizure-induced BDNF expression in rat hippocampus

Activity-induced brain-derived neurotrophic factor (BDNF) expression is negatively modulated by circulating adrenal steroids. The rat BDNF gene gives rise to four major transcript forms that each contain a unique 5' exon (I-IV) and a common 3' exon (V) that codes for BDNF protein. Exon-specific in situ hybridization was used to determine if adrenalectomy has differential effects on basal and activity-induced BDNF transcript expression in hippocampus. Adrenalectomy alone had only modest effects on BDNF mRNA levels with slight increases in exon III-containing mRNA with 7-10-day survival and in exon II-containing mRNA with 30-days survival. In the dentate gyrus granule cells, adrenalectomy markedly potentiated increases in exon I and II cRNA labeling, but not increases in exon III and IV cRNA labeling, elicited by one hippocampal afterdischarge. Similarly, for the granule cells and CA1 pyramidal cells, hilus lesion (HL)-induced recurrent limbic seizures elicited greater increases in exon I and II cRNA hybridization in adrenalectomized (ADX) as compared to adrenal-intact rats. In this paradigm, adrenalectomy modestly potentiated the increase in exon III-containing mRNA in CA1 but had no effect on exon IV-containing mRNA content. These results demonstrate that the negative effects of adrenal hormones on activity-induced BDNF expression are by far the greatest for transcripts containing exons I and II. Together with evidence for region-specific transcript expression, these results suggest that the effects of stress on adaptive changes in BDNF signalling will be greatest for neurons that predominantly express transcripts I and II.

Neurotrophins and their receptors in the adult hypo- and hyperthyroid rat after kainic acid injection: an in situ hybridization study

Thyroid hormone plays a key role in trophic events during development of the central nervous system. In spite of neurological and psychiatric symptoms associated with adult hypothyroidism, the role of thyroid hormone in mature brain function is less clear. In this paper we investigated the effect of thyroid status on kainic acid-induced up-regulation of mRNAs for members of the nerve growth factor family and related receptors in adult male rats by means of in situ hybridization. We found that in hypothyroid rats there is a dramatic attenuation of the kainic acid-induced up-regulation of mRNA levels for nerve growth factor, brain-derived neurotrophic factor and tyrosine kinase trkB in euthyroid rats. A trend to reduced c-fos mRNA up-regulation, which did not reach significance, was also found, whereas the increase in c-jun mRNA after kainic acid was similar in eu-, hypo- and hyperthyroid rats. These data indicate a severe impairment of the regulation of neurotrophin synthesis after excitotoxin administration in the hippocampus during adult hypothyroidism. Possible roles of thyroid hormone in molecular, biochemical and metabolic mechanisms of this defect are discussed.