Expression Of Brain-derived Neurotrophic Factor Transcripts Research Articles

Transient Forebrain Ischemia Induces Differential Bdnf Transcript Expression and Histone Acetylation Patterns in the Rat Hippocampus.

Forebrain ischemia induces delayed, selective neuronal death in hippocampal CA1. It has been established that BDNF (brain-derived neurotrophic factor) is an important factor in ischemic injury. However, the exact mechanism of BDNF expression in the hippocampus after ischemia is unclear. We found that the decrease of BDNF protein expression in hippocampal CA1 was associated with a decrease of Bdnf transcript IV expression in the same region of the rats after ischemia/reperfusion (I/R). In hippocampal CA3 and DG, the results showed increased expression of BDNF protein and transcripts I, IIc, III, IV, VI, and X1. Furthermore, at the Bdnf promoters, I/R led to decreased H3K27ac, increased H3K9ac, and H3K14ac in CA1; increased H3K9ac, H3K14ac, and H3K27ac in CA3; no significant change of H3K9ac, H3K14ac, and H3K27ac in DG. HDAC inhibitor SAHA increased the expression of Bdnf transcripts IV, VI, and X1 in CA1. These findings suggest a potential of modulation Bdnf transcript expression to resolve ischemic brain injury through histone acetylation patterns at the Bdnf promoters.

Ibogaine Administration Modifies GDNF and BDNF Expression in Brain Regions Involved in Mesocorticolimbic and Nigral Dopaminergic Circuits.

Ibogaine is an atypical psychedelic alkaloid, which has been subject of research due to its reported ability to attenuate drug-seeking behavior. Recent work has suggested that ibogaine effects on alcohol self-administration in rats are related to the release of Glial cell Derived Neurotrophic Factor (GDNF) in the Ventral Tegmental Area (VTA), a mesencephalic region which hosts the soma of dopaminergic neurons. Although previous reports have shown ibogaine’s ability to induce GDNF expression in rat midbrain, there are no studies addressing its effect on the expression of GDNF and other neurotrophic factors (NFs) such as Brain Derived Neurotrophic Factor (BDNF) or Nerve Growth Factor (NGF) in distinct brain regions containing dopaminergic neurons. In this work, we examined the effect of ibogaine acute administration on the expression of these NFs in the VTA, Prefrontal Cortex (PFC), Nucleus Accumbens (NAcc) and the Substantia Nigra (SN). Rats were i.p. treated with ibogaine 20 mg/kg (I20), 40 mg/kg (I40) or vehicle, and NFs expression was analyzed after 3 and 24 h. At 24 h an increase of the expression of the NFs transcripts was observed in a site and dose dependent manner. Only for I40, GDNF was selectively upregulated in the VTA and SN. Both doses elicited a large increase in the expression of BDNF transcripts in the NAcc, SN and PFC, while in the VTA a significant effect was found only for I40. Finally, NGF mRNA was upregulated in all regions after I40, while I20 showed a selective upregulation in PFC and VTA. Regarding protein levels, an increase of GDNF was observed in the VTA only for I40 but no significant increase for BDNF was found in all the studied areas. Interestingly, an increase of proBDNF was detected in the NAcc for both doses. These results show for the first time a selective increase of GDNF specifically in the VTA for I40 but not for I20 after 24 h of administration, which agrees with the effective dose found in previous self-administration studies in rodents. Further research is needed to understand the contribution of these changes to ibogaine’s ability to attenuate drug-seeking behavior.

Chronic social defeat stress differentially regulates the expression of BDNF transcripts and epigenetic modifying enzymes in susceptible and resilient mice

Objectives: Although stress is considered a primary risk factor for neuropsychiatric disorders, a majority of individuals are resilient to the effects of stress exposure and successfully adapt to adverse life events, while others, the so-called susceptible individuals, may have problems to properly adapt to environmental changes. However, the mechanisms underlying these different responses to stress exposure are poorly understood.Methods: Adult male C57BL/6J mice were exposed to chronic social defeat stress protocol and levels of brain derived neurotrophic factor (BDNF) transcripts and epigenetic modifying enzymes were analysed by real-time PCR in the hippocampus (HPC) and prefrontal cortex (PFC) of susceptible and resilient mice.Results: We found a selective reduction of BDNF-6 transcript in the HPC and an increase of BDNF-4 transcript in the PFC of susceptible mice. Moreover, susceptible mice showed a selective reduction of the g9a mRNA levels in the HPC, while HDAC-5 and DNMT3a mRNA levels were specifically reduced in the PFC.Conclusions: Overall, our results, showing a different expression of BDNF transcripts and epigenetic modifying enzymes in susceptible and resilient mice, suggest that stress resilience is not simply a lack of activation of stress-related pathways, but is related to the activation of additional different specific mechanisms.

Effects of early neonatal proinflammatory stress on the expression of BDNF transcripts in the brain regions of prepubertal male rats

Early postnatal proinflammatory stress may evoke behavioral impairments in adulthood; however, the underlying mechanisms are still elusive. The brain-derived neurotrophic factor (BDNF) plays a key role in neuroplastic changes in health, as well as in pathology. The BDNF gene is transcribed to exon-specific mRNAs and the pattern of their expression depends on stimulus. We suggested that disturbances of the exonspecific BDNF mRNA expression in the brain regions after stress induced by proinflammatory stimuli in the early postnatal period could be one of the underlying mechanisms of consequent behavioral impairments. Thus, the aim of the study was to examine the effects of proinflammatory stress in early postnatal ontogeny on the BDNF polypeptide content and the patterns of expression of the BDNF gene in the neocortex and hippocampus of prepubertal male rats. The proinflammatory stress was induced by the subcutaneous administration of bacterial lipopolysaccharide (LPS) to rat pups on postnatal days 3 and 5, while BDNF expression was studied in 36-day-old rats. The BDNF polypeptide content was estimated using an enzyme-linked immunosorbent assay, while a quantitative polymerase chain reaction followed by reverse transcription was used to detect the exon-specific BDNF mRNA expression. The levels of BDNF and its transcripts, containing the common exon IX were similar in the control and LPS-treated rats. In the rats treated with LPS, the level of BDNF mRNA containing exon IV was lower in the neocortex but not in the hippocampus. No changes in the expression of the transcripts containing exons I and VI were observed in any of the brain structures studied. We suggest that specific alterations in BDNF expression may be involved in susceptibility to the development of behavioral impairments of animals subjected to early proinflammatory stress.

Activity-Based Anorexia Alters the Expression of BDNF Transcripts in the Mesocorticolimbic Reward Circuit.

Anorexia nervosa (AN) is a complex eating disorder with severe dysregulation of appetitive behavior. The activity-based anorexia (ABA) paradigm is an animal model in which rodents exposed to both running wheels and scheduled feeding develop aspects of AN including paradoxical hypophagia, dramatic weight loss, and hyperactivity, while animals exposed to only one condition maintain normal body weight. Brain-derived neurotrophic factor (BDNF), an activity-dependent modulator of neuronal plasticity, is reduced in the serum of AN patients, and is a known regulator of feeding and weight maintenance. We assessed the effects of scheduled feeding, running wheel access, or both on the expression of BDNF transcripts within the mesocorticolimbic pathway. We also assessed the expression of neuronal cell adhesion molecule 1 (NCAM1) to explore the specificity of effects on BDNF within the mesocorticolimbic pathway. Scheduled feeding increased the levels of both transcripts in the hippocampus (HPC), increased NCAM1 mRNA expression in the ventral tegmental area (VTA), and decreased BDNF mRNA levels in the medial prefrontal cortex (mPFC). In addition, wheel running increased BDNF mRNA expression in the VTA. No changes in either transcript were observed in the nucleus accumbens (NAc). Furthermore, no changes in either transcript were induced by the combined scheduled feeding and wheel access condition. These data indicate that scheduled feeding or wheel running alter BDNF and NCAM1 expression levels in specific regions of the mesocorticolimbic pathway. These findings contribute to our current knowledge of the molecular alterations induced by ABA and may help elucidate possible mechanisms of AN pathology.

The human BDNF gene: peripheral gene expression and protein levels as biomarkers for psychiatric disorders.

Brain-derived neurotrophic factor (BDNF) regulates the survival and growth of neurons, and influences synaptic efficiency and plasticity. The human BDNF gene consists of 11 exons, and distinct BDNF transcripts are produced through the use of alternative promoters and splicing events. The majority of the BDNF transcripts can be detected not only in the brain but also in the blood cells, although no study has yet investigated the differential expression of BDNF transcripts at the peripheral level. This review provides a description of the human BDNF gene structure as well as a summary of clinical and preclinical evidence supporting the role of BDNF in the pathogenesis of psychiatric disorders. We will discuss several mechanisms as possibly underlying BDNF modulation, including epigenetic mechanisms. We will also discuss the potential use of peripheral BDNF as a biomarker for psychiatric disorders, focusing on the factors that can influence BDNF gene expression and protein levels. Within this context, we have also characterized, for we believe the first time, the expression of BDNF transcripts in the blood, with the aim to provide novel insights into the molecular mechanisms and signaling that may regulate peripheral BDNF gene expression levels.

Effects of early neonatal proinflammatory stress on the expression of BDNF transcripts in the brain regions of prepubertal male rats

Early postnatal proinflammatory stress provokes behavioral impairments in adulthood; however, underlying mechanisms are still elusive. Brain-derived neurotrophic factor (BDNF) plays a crucial role in neuroplastic changes in health as well as at pathology. The BDNF gene is transcribed to exon-specific mRNAs and the pattern of their expression depends on stimulus. We suggest that disturbances of exonspecific BDNF mRNA expression in the brain regions after stress induced by proinflammatory stimuli in early postnatal period could be one of the underlying mechanisms of consequent behavioral impairments. Thus, the aim of the study was to investigate the effects of proinflammatory stress in early postnatal ontogeny on the expression of BDNF and the patterns of expression of the BDNF gene in the neocortex and hippocampus of prepubertal male rats. The proinflammatory stress was induced by subcutaneous administration of bacterial lipopolysaccharide (LPS) to rat pups on postnatal days 3 and 5, while BDNF expression was analyzed in 36-day-old rats. BDNF polypeptide concentration was estimated by means of an enzyme-linked immunosorbent assay, while quantitative polymerase chain reaction followed by reverse transcription was used to detect exon-specific BDNF mRNA expression. The levels of BDNF and transcripts, containing common exon IX were similar in the control and LPS-treated rats. In the rats treated with LPS, the level of BDNF mRNA, containing exon IV, was lower in the neocortex, but not in the hippocampus. No changes in the expression of the transcripts containing exons I and VI were observed in any brain structure studied. We suggest that specific alterations in BDNF expression may be involved in the susceptibility to the development of behavioral impairments of animals subjected to early proinflammatory stress.

Physical exercise and acute restraint stress differentially modulate hippocampal brain-derived neurotrophic factor transcripts and epigenetic mechanisms in mice.

Physical exercise and stressful experiences have been shown to exert opposite effects on behavioral functions and brain plasticity, partly by involving the action of brain-derived neurotrophic factor (BDNF). Although epigenetic modifications are known to play a pivotal role in the regulation of the different BDNF transcripts, it is poorly understood whether epigenetic mechanisms are also implied in the BDNF modulation induced by physical exercise and stress. Here, we show that total BDNF mRNA levels and BDNF transcripts 1, 2, 3, 4, 6, and 7 were reduced immediately after acute restraint stress (RS) in the hippocampus of mice, and returned to control levels 24 h after the stress session. On the contrary, exercise increased BDNF mRNA expression and counteracted the stress-induced decrease of BDNF transcripts. Physical exercise-induced up-regulation of BDNF transcripts was accounted for by increase in histone H3 acetylated levels at specific BDNF promoters, whereas the histone H3 trimethylated lysine 27 and dimethylated lysine 9 levels were unaffected. Acute RS did not change the levels of acetylated and methylated histone H3 at the BDNF promoters. Furthermore, we found that physical exercise and RS were able to differentially modulate the histone deacetylases mRNA levels. Finally, we report that a single treatment with histone deacetylase inhibitors, prior to acute stress exposure, prevented the down-regulation of total BDNF and BDNF transcripts 1, 2, 3, and 6, partially reproducing the effect of physical exercise. Overall, these results suggest that physical exercise and stress are able to differentially modulate the expression of BDNF transcripts by possible different epigenetic mechanisms.

BDNF Influences the Excitability of Subfornical Organ Neurons

Brain‐derived neurotrophic factor (BDNF) is a peptide known to be involved in several mammalian physiological processes. Expression of BDNF transcripts has been identified in the subfornical organ (SFO), a circumventricular organ involved in fluid balance and energy homeostasis. Microarray analysis has demonstrated that levels of transcript expression in the SFO are differentially regulated by fluid and food deprivation, with levels of BDNF expression increasing significantly in response to dehydration, and decreasing in response to starvation (Hindmarch et al 2008). The current study was therefore undertaken in order to determine the effects of BDNF on the excitability of SFO neurons. We used the whole‐cell patch clamp technique to determine the influence of BDNF on the membrane potential of dissociated SFO neurons as well as that of SFO neurons in slice preparation. We found that 86% of dissociated neurons responded when treated with BDNF (2 nM), all of which depolarized (mean 14 mV). Additionally, 75% of neurons tested in the slice preparation responded when treated with BDNF (2 nM). Of these, 67% showed a depolarization (mean 12 mV) and 33% hyperpolarized (mean ‐18 mV). This study suggests the SFO as a potential central nervous system site at which BDNF may act directly to influence homeostatic regulation.Supported by the Canadian Institutes for Health Research

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.

Promoter specific alterations of brain-derived neurotrophic factor mRNA in schizophrenia

The brain-derived neurotrophic factor (BDNF) gene contains multiple 5′ promoters which generate alternate transcripts. Previously, we found that pan-BDNF mRNA and protein are reduced in the dorsolateral prefrontal cortex (DLPFC) from patients with schizophrenia. In this study, we determined which of the four most abundant and best characterized BDNF alternate transcripts, I-IX, II-IX, IV-IX, and VI-IX are altered in schizophrenia. Using a cohort from the NIMH, USA, we found that BDNF II-IX mRNA was significantly reduced in the DLPFC of patients with schizophrenia, and we replicated this finding using a second cohort from Sydney, Australia. Moreover, we show that BDNF protein expression [including prepro (∼32 kDa), pro (∼28 kDa) and mature (∼14 kDa) BDNF] is reduced in the DLPFC of patients with schizophrenia. We next determined the regional specificity of the BDNF mRNA reduction by measuring BDNF transcripts in the parietal cortex and hippocampus and found no significant changes. The effect of antipsychotics on BDNF alternate transcript expression was also examined and we found no relationship between BDNF mRNA expression and antipsychotic use. As schizophrenic patients are often prescribed antidepressants which can up-regulate expression of BDNF, we investigated the relationship between antidepressant treatment and BDNF transcript expression. All four BDNF transcripts were significantly up-regulated in schizophrenic patients treated with antidepressants. Moreover, we found significant reductions in BDNF transcripts II-IX and IV-IX in the parietal cortex and VI-IX in the hippocampus of patients with schizophrenia who did not have a history of treatment with antidepressants. This suggests that down-regulation of at least one out of four major BDNF transcripts occurs in various brain regions of patients with schizophrenia, particularly in the DLPFC which appears to have the most robust BDNF deficit in schizophrenia.

Differential Neuroendocrine Expression of Multiple Brain-Derived Neurotrophic Factor Transcripts

Brain-derived neurotrophic factor (BDNF) is a neurotrophin with important growth-promoting properties. We report here the first characterization of a BDNF gene in an amphibian, Xenopus laevis, and demonstrate that environmental factors can activate this gene in a promoter-specific fashion. The Xenopus BDNF gene contains six promoter-specific 5'-exons and one 3'-protein-encoding exon. We examined the expression of promoter-specific transcripts in Xenopus neuroendocrine melanotrope cells. These cells make a good model to study how environmental factors control gene expression. In animals placed on a black background melanotrope cells more actively produce and release alphaMSH than in animals on a white background. BDNF is cosequestered and coreleased with alphaMSH and stimulates biosynthesis of proopiomelanocortin (POMC), the precursor protein for alphaMSH. Our analysis of the expression of the BDNF transcripts revealed that there is differential use of some BDNF promoters in melanotrope cells, depending on the adaptation state of the frog. During black-background adaptation, stimulation of expression of BDNF transcript IV preceded that of the POMC transcript, suggesting the BDNF gene is an effector gene for POMC expression. The possible mechanisms regulating expression of the various transcripts are discussed on the basis of the potential calcium- and cAMP-responsive elements in the promoter region of exon IV. Finally, we show that the upstream open reading frames of BDNF transcripts I and IV markedly decrease BDNF translation efficiency, giving the first indication for a functional role of untranslated BDNF exons.

Chronic Duloxetine Treatment Induces Specific Changes in the Expression of BDNF Transcripts and in the Subcellular Localization of the Neurotrophin Protein

There is growing evidence that brain-derived neurotrophic factor (BDNF) can be relevant to mood disorders and that modulation of its biosynthesis following prolonged antidepressant treatment may contribute to neuroplastic changes required for clinical response. In the present study, we investigated the effects of the novel antidepressant duloxetine on BDNF in the rat brain. Duloxetine is a serotonin-norepinephrine reuptake inhibitor that differs from other antidepressants by virtue of its balanced potency on both neurotransmitter systems. We found that chronic, but not acute, treatment with duloxetine produces a robust increase of exon V BDNF mRNA levels in frontal cortex when the animals were killed 1 or 24 h after the last administration. The expression of the neurotrophin was also increased in other cortical subregions, but not in the hippocampus. We also found that the increased expression of BDNF in frontal cortex was mainly sustained by enhanced mRNA levels for exons I and III, whereas the expression of exon IV was reduced. Protein analysis in different subcellular fractions showed that chronic treatment with duloxetine, but not with the prototypical SSRI fluoxetine, reduced mature BDNF in the cytosol, but markedly increased its levels in the crude synaptosomal fraction. Our data suggest that chronic treatment with the novel antidepressant duloxetine not only produces a marked upregulation of BDNF mRNA and protein, but may also affect the subcellular redistribution of the neurotrophin. These changes might improve synaptic plasticity and cognitive function that are defective in depressed subjects.

Mouse and rat BDNF gene structure and expression revisited

Brain-derived neurotrophic factor (BDNF) has important functions in the development of the nervous system and in brain plasticity-related processes such as memory, learning, and drug addiction. Despite the fact that the function and regulation of rodent BDNF gene expression have received close attention during the last decade, knowledge of the structural organization of mouse and rat BDNF gene has remained incomplete. We have identified and characterized several mouse and rat BDNF transcripts containing novel 5′ untranslated exons and introduced a new numbering system for mouse and rat BDNF exons. According to our results both mouse and rat BDNF gene consist of eight 5′ untranslated exons and one protein coding 3′ exon. Transcription of the gene results in BDNF transcripts containing one of the eight 5′ exons spliced to the protein coding exon and in a transcript containing only 5′ extended protein coding exon. We also report the distinct tissue-specific expression profiles of each of the mouse and rat 5′ exon-specific transcripts in different brain regions and nonneural tissues. In addition, we show that kainic acid-induced seizures that lead to changes in cellular Ca2+ levels as well as inhibition of DNA methylation and histone deacetylation contribute to the differential regulation of the expression of BDNF transcripts. Finally, we confirm that mouse and rat BDNF gene loci do not encode antisense mRNA transcripts, suggesting that mechanisms of regulation for rodent and human BDNF genes differ substantially. © 2006 Wiley-Liss, Inc.

Rapid induction of BDNF expression in the hippocampus during immobilization stress challenge in adult rats.

Brain-derived neurotrophic factor (BDNF) is strongly expressed in the hippocampus, where it has been associated with memory processes. In the central nervous system, some learning processes, as well as brain insults, including stress, induce modifications in BDNF mRNA expression. Because stress and memory appear to share some neuronal pathways, we studied BDNF mRNA and BDNF peptide variations in response to short times of immobilization stress. Using an RNase protection assay, we demonstrated that short-time stress application induced a significant increase (at 60 min) in BDNF mRNA levels in the whole rat hippocampus. Changes in BDNF mRNA content appear to reflect increased expression of BDNF transcripts containing exons I, II, and III, that were also significantly modified at this time. The time course of stress-induced changes in BDNF transcript levels revealed that mRNA containing exon III was the first increased, significantly elevated by 15 min, attaining maximal levels at 60 min, as BDNF transcripts containing exons I and II. However, at longer times of stress (180 min), BDNF mRNA levels were decreased as well as mRNA containing exon IV. In situ hybridization analysis of discrete hippocampal layers demonstrated that BDNF mRNA expression increased as early as 15 min in most hippocampal regions, with no modification in the number of labeled cells. The same signal pattern, although less pronounced, was determined at 60 min, but at this time a significant increase in BDNF-positive cells was visualized in the CA3 layer. The peptide, measured by immunoassay, was significantly augmented after 180 min of stress exposure whereas at 300 min, levels were similar to those measured in control animals. These data suggest that rapid changes in BDNF expression may be part of a compensatory response to preserve hippocampal homeostasis or a form of neuronal plasticity to cope with new stimuli.

Immobilization Stress Rapidly and Differentially Modulates BDNF and TrkB mRNA Expression in the Pituitary Gland of Adult Male Rats

Brain-derived neurotrophic factor (BDNF) is a neurotrophin involved in neuronal survival and plasticity that binds to high-affinity receptors named TrkB. In the central nervous system, brain insults, including stress, induce modifications in BDNF messenger RNA (mRNA) expression. The present study attempted to determine in the adult rat pituitary, a peripheral structure relevant for the stress response: (1) whether BDNF and TrkB mRNA expression is influenced by different durations (15, 30, 60, 180 and 300 min) of single immobilization stress; (2) the expression of BDNF transcripts containing the different exons and their possible variations after stress exposure. Plasma corticotropin (ACTH) and corticosterone concentrations were strongly and significantly increased as early as 5 min after the stress stimulus. Using RNAse protection assay and in situ hybridization, a rapid increase in BDNF mRNA occurred at 15 min. This was accompanied by an increase in BDNF protein at 60 min, and by a rapid and significant decrease in TrkB mRNA expression observed at 15 and 30 min after stress application. RT-PCR analysis of BNDF transcripts showed strong basal expression of exons III and IV, whereas transcripts containing exons I and II seemed weakly expressed. After stress application, transcripts containing exons III and IV were rapidly and significantly increased at 30 min, whereas transcripts containing exons I and II remained unchanged. These results show that pituitary BDNF transcripts expression is differentially affected by immobilization stress.

BDNF gene transcripts in mesencephalic neurons and its differential regulation by NMDA.

Brain-derived neurotrophic factor (BDNF) enhances survival and protects dopaminergic neurons from neurotoxicity. We have examined in primary cultures of fetal mesencephalic neurons the expression of BDNF transcripts and its regulation by glutamate receptor agonists. RT-PCR experiments showed in these cultures the expression of mRNA encoding for neurotrophin receptors TrkA, TrkB and TrkC as well as a differential expression of alternative BDNF gene transcripts derived from exons 1a, 1b, 1c and 1d. In adult rat mesencephalon we only detected BDNF mRNAs originated from exons 1a and 1c. Quantitative RT-PCR analysis of mesencephalic neurons revealed that NMDA, but not kainate treatment, significantly increased BDNF mRNAs derived from exons 1b and 1d. Our data indicate the existence in mesencephalic neurons of different and alternative promoters within the BDNF gene that may be differentially regulated by glutamate receptor stimulation.

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-day 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.

Differential Effects of Protein Synthesis Inhibition on the Activity-Dependent Expression of BDNF Transcripts: Evidence for Immediate-Early Gene Responses from Specific Promoters

In the adult rat forebrain, brain-derived neurotrophic factor (BDNF) expression is very rapidly induced by neuronal activity, suggesting that this might occur without intervening protein synthesis. The rat BDNF gene has four differentially regulated promoter regions; each gives rise to an mRNA containing a unique 5' exon (I-IV) and a common 3' exon (V) that codes for mature BDNF protein. The present study used exon-specific in situ hybridization and both in vivo and in vitro preparations to determine whether activity induces BDNF as an "immediate-early gene" (IEG) from specific promoter regions and to compare the regulation of BDNF and nerve growth factor (NGF). In cultured hippocampal slices, kainic acid markedly increased pan-BDNF (exon V) and NGF mRNA content; cycloheximide attenuated the effect of kainic acid on both. In vivo stimulation of a paroxysmal afterdischarge increased both pan-BDNF and NGF mRNA levels in the dentate gyrus granule cells; pretreatment with anisomycin modestly attenuated the paroxysmal afterdischarge-induced increase of both transcripts. To determine whether partial drug effects on BDNF expression reflect the differential regulation of transcript species, levels of mRNAs containing exons I-IV were evaluated. A single afterdischarge increased exon I-IV-containing mRNA levels; anisomycin significantly attenuated the increase in exon I- and II-containing mRNAs but had no effect on the increase in exon III- and IV-containing mRNAs. These data show that for mature forebrain neurons, activity induces the expression of BDNF exon III- and IV-containing transcripts as IEG responses.