Endothelin increases expression of exon III- and exon IV-containing brain-derived neurotrophic factor transcripts in cultured astrocytes and rat brain

The effects of endothelins (ETs) on brain-derived neurotrophic factor (BDNF) production in astrocytes were investigated. ET-1 (100 nM) increased the mRNA level and extracellular release of BDNF in cultured astrocytes. RT-PCR analyses using primer pairs that amplified exon-specific BDNF transcripts revealed that exon III- and exon IV-containing BDNF transcripts existed in cultured astrocytes, whereas exon I- and exon II-containing BDNF transcripts did not. ET-1 and Ala(1,3,11,15)-ET-1, an ET(B) receptor agonist, increased the expressions of the exon III and exon IV transcripts in cultured astrocytes. Intracerebroventricular administration of 500 pmol/day of Ala(1,3,11,15)-ET-1 increased exon III and exon IV BDNF transcripts in the rat striatum. In cultured astrocytes, Ca(2+)-chelation, W-7 (a calmodulin inhibitor), and KN93 (a Ca(2+)/calmodulin kinase inhibitor) inhibited the increases in exon IV BDNF mRNA and CCAAT enhancer-binding protein beta (C/EBPbeta) levels induced by ET-1. The ET-induced increases in exon III BDNF mRNA expression and phosphorylation of cAMP response element binding protein (CREB) were reduced by Ca(2+) chelation, W-7, KN93, PD98059 (a MEK inhibitor), and wortmannin (a phosphatidylinositol 3-kinase inhibitor). These results suggest that ETs stimulate the expressions of exon III and exon IV BDNF transcripts in astrocytes through CREB and C/EBPbeta-mediated mechanisms, respectively.

Neurotrophin-based strategies for neuroprotection

Neurotrophins activate a number of signaling pathways relevant to neuroprotection; however, their poor pharmacological properties and their pleiotropic effects resulting from interaction with the p75(NTR)-Trk-sortilin three-receptor signaling system limit therapeutic application. While local application of neurotrophin proteins addresses some of the pharmacological challenges, selective targeting of neurotrophin receptors might allow for more selective application of neurotrophin receptor signaling modulation. Recent studies have supported the feasibility of developing non-peptidyl small molecules that mimic specific domains of neurotrophins and modulate signaling of specific neurotrophin receptors. The expression of p75(NTR) by populations of neurons most vulnerable in Alzheimer's disease and the linkage of p75(NTR) signaling to aberrant signaling mechanisms occurring in this disorder, point to potential applications for p75(NTR)-based small molecule strategies. Small molecules targeted to p75(NTR) in the settings of neurodegenerative disease and other forms of neural injury might serve to inhibit death signaling, block proNGF-mediated degenerative signaling and minimize deleterious effects promoted by pharmacologically upregulated Trk signaling.

The presence of ascorbate induces expression of brain derived neurotrophic factor in SH-SY5Y neuroblastoma cells after peroxide insult, which is associated with increased survival

Oxidative stress and free radical production have been implicated in Alzheimer's disease, where low levels of the antioxidant vitamin C (ascorbate) have been shown to be associated with the disease. In this study, neuroblastoma SH-SY5Y cells were treated with hydrogen peroxide in the presence of ascorbate in order to elucidate the mechanism(s) of protection against oxidative stress afforded by ascorbate. Protein oxidation, glutathione levels, cell viability and the effects on the proteome and its oxidized counterpart were monitored. SH-SY5Y cells treated with ascorbate prior to co-incubation with peroxide showed increased viability in comparison to cells treated with peroxide alone. This dual treatment also caused an increase in protein carbonyl content and a decrease in glutathione levels within the cells. Proteins, extracted from SH-SY5Y cells that were treated with either ascorbate or peroxide alone or with ascorbate prior to peroxide, were separated by two-dimensional gel electrophoresis and analyzed for oxidation. Co-incubation for 24 hours decreased the number of oxidised proteins (e.g. acyl CoA oxidase 3) and induced brain derived neurotrophic factor (BDNF) expression. Enhanced expression of BDNF may contribute to the protective effects of ascorbate against oxidative stress in neuronal cells.

BDNF in schizophrenia, depression and corresponding animal models

Understanding the etiology and pathogenesis schizophrenia and depression is a major challenge facing psychiatry. One hypothesis is that these disorders are secondary to a malfunction of neurotrophic factors. Inappropriate neurotrophic support during brain development could lead to structural disorganisation in which neuronal networks are established in a nonoptimal manner. Inadequate neurotrophic support in adult individuals could ultimately be an underlying mechanism leading to decreased capacity of brain to adaptive changes and increased vulnerability to neurotoxic damage. Brain-derived neurotrophic factor (BDNF) is a mediator involved in neuronal survival and plasticity of dopaminergic, cholinergic, and serotonergic neurons in the central nervous system (CNS). In this review, we summarize findings regarding altered BDNF in schizophrenia and depression and animal models, as well as the effects of antipsychotic and antidepressive treatments on the expression of BDNF.

[Neurogenesis: a novel strategy for the treatment of depression]

It is now generally accepted that the birth of new neurons occurs in brain areas such as hippocampus throughout the lifespan. The waning and waxing of neurogenesis in hippocampus is proposed as a key factor in the decent into and recovery from depression. If hippocampal neurogenesis was blocked, antidepressant would lose its behavioral effects in behavioral models of depression. Long-term, but not short-term, treatment with different classes of antidepressant could stimulate neurogenesis in the hippocampus remarkably. As the regulation of adult neurogenesis continues to be identified, it will provide novel avenues of studying the mechanism and developing pharmacological agents for depressive disorder.

Fluoxetine-induced change in rat brain expression of brain-derived neurotrophic factor varies depending on length of treatment

Recent studies indicate that brain-derived neurotrophic factor (BDNF) may be implicated in the clinical action of antidepressant drugs. Repeated (2-3 weeks) administration of antidepressant drugs increases BDNF gene expression. The onset of this response as well as concomitant effects on the corresponding BDNF protein is however, unclear. The present study investigated the effects of acute and chronic administration of the selective serotonin reuptake inhibitor, fluoxetine (10mg/kg p.o.), upon regional rat brain levels of BDNF mRNA and protein expression. To improve the clinical significance of the study, fluoxetine was administered orally and mRNA and protein levels were determined ex vivo using the techniques of in situ hybridisation histochemistry and immunocytochemistry respectively. Direct measurement of BDNF protein was also carried out using enzyme-linked immunosorbent assay (ELISA). Four days of once daily oral administration of fluoxetine induced decreases in BDNF mRNA (hippocampus, medial habenular and paraventricular thalamic nuclei). Whilst 7 days of treatment showed a non-significant increase in BDNF mRNA, there were marked and region-specific increases following 14 days of treatment. BDNF protein levels remained unaltered until 21 days of fluoxetine treatment, when the numbers of BDNF immunoreactive cells were increased, reaching significance in the pyramidal cell layer of CA1 and CA3 regions of Ammon's horn (CA1 and CA3) but not in the other sub-regions of the hippocampus. Indicative of the highly regional change within the hippocampus, the ELISA method failed to demonstrate significant up-regulation at 21 days, measuring levels of BDNF protein in the whole hippocampus. In contrast to the detected time dependent and biphasic response of the BDNF gene, activity-regulated, cytoskeletal-associated protein (Arc) mRNA showed a gradual increase during the 14-day course of treatment. The results presented here show that BDNF is expressed differentially depending on length of fluoxetine administration, which could contribute in explaining the slow onset of antidepressant activity observed with selective serotonin reuptake inhibitors.

Environmental enrichment reduces the mnemonic and neural benefits of estrogen

The degree to which memory is enhanced by estrogen replacement in postmenopausal women may depend on environmental factors such as education. The present study utilized an animal model of environmental enrichment to determine whether environmental factors influence the mnemonic and neural response to estrogen. Female mice were raised in standard (SC) or enriched (EC) conditions from weaning until adulthood (7 months). All mice were ovariectomized at 10 weeks, and tested in object recognition and water-escape motivated radial arm maze (WRAM) tasks at 6 months. Each day at the completion of training, mice received injections of 0.1 mg/kg cyclodextrin-encapsulated 17-beta-estradiol (E2), 0.2 mg/kg E2, or cyclodextrin vehicle (VEH). At the completion of behavioral testing, hippocampal levels of the presynaptic protein synaptophysin and of brain-derived neurotrophic factor (BDNF) were measured. Enrichment effects were evident in VEH-treated mice; relative to SC-VEH females, EC-VEH females committed fewer working memory errors in the WRAM and exhibited increased hippocampal synaptophysin levels. Estrogen effects depended on environmental conditions. E2 (0.2 mg/kg) improved object memory only in SC females. The same dose improved working memory in SC females, but somewhat impaired working memory in EC females. Furthermore, both doses reduced hippocampal synaptophysin levels in EC, but not SC, females. In contrast, E2 reduced hippocampal BDNF levels in SC, but not EC, females. This study is the first to compare the effects of estrogen on memory and hippocampal function in enriched and non-enriched female mice. The results suggest that: (1) estrogen benefits object and working memory more in mice raised in non-enriched environments than in those raised in enriched environments, and (2) the changes induced by estrogen and/or enrichment may be associated with alterations in hippocampal synaptic plasticity.

Effects of PRI-2191—A low-calcemic analog of 1,25-dihydroxyvitamin D3 on the seizure-induced changes in brain gene expression and immune system activity in the rat

Apart from the essential role of 1alpha,25-dihydroxyvitamin D3 in calcium and phosphorus metabolism, this compound and its analogs are involved in regulating the functions of the central nervous and immune systems. Active forms of vitamin D3 have been reported to stimulate neurotrophin gene expression and to prevent neuronal damage against a variety of insults. In the present study, we evaluated the effects of PRI-2191-a low-calcemic analog of 1alpha,25-dihydroxyvitamin D3 (50 ng/kg i.p., once daily for 8 days) on seizure-related neuronal degeneration, changes in some brain gene expression and immune system activity. Seizures were induced by pilocarpine (400 mg/kg; i.p.) administration. An in situ hybridization study showed that the pilocarpine-induced seizures led to time-dependent changes in the brain-derived neurotrophic factor (BDNF), heat shock protein 70 (HSP-70) and prepro-thyreoliberin (prepro-TRH) gene expression in several cortical and hippocampal regions. The maximal induction of gene expression was 3 h for BDNF and 24 h for HSP-70 and prepro-TRH; however, only in the case of prepro-TRH that effect was long-lasting. PRI-2191 alone had no effect on gene expression, but it enhanced the seizure-evoked expression of HSP-70, had an opposite effect on BDNF mRNA level and did not affect prepro-TRH mRNA level. Moreover, PRI-2191 had a moderate inhibitory effect on the seizure-related hippocampal damage in the CA1 field only. An immunological study revealed that PRI-2191 reversed the seizure-induced decrease in the proliferative activity of splenocytes and their ability to produce interferon-gamma. Summing up, the present study demonstrated that subchronic administration of PRI-2191 significantly modulated the seizure-related changes in both the brain and the peripheral immune system of rats.

Dietary omega-3 fatty acids normalize BDNF levels, reduce oxidative damage, and counteract learning disability after traumatic brain injury in rats

Omega-3 fatty acids (i.e., docosahexaenoic acid; DHA) regulate signal transduction and gene expression, and protect neurons from death. In this study we examined the capacity of dietary omega3 fatty acids supplementation to help the brain to cope with the effects of traumatic injury. Rats were fed a regular diet or an experimental diet supplemented with omega-3 fatty acids, for 4 weeks before a mild fluid percussion injury (FPI) was performed. FPI increased oxidative stress, and impaired learning ability in the Morris water maze. This type of lesion also reduced levels of brain-derived neurotrophic factor (BDNF), synapsin I, and cAMP responsive element-binding protein (CREB). It is known that BDNF facilitates synaptic transmission and learning ability by modulating synapsin I and CREB. Supplementation of omega-3 fatty acids in the diet counteracted all of the studied effects of FPI, that is, normalized levels of BDNF and associated synapsin I and CREB, reduced oxidative damage, and counteracted learning disability. The reduction of oxidative stress indicates a benevolent effect of this diet on mechanisms that maintain neuronal function and plasticity. These results imply that omega-3 enriched dietary supplements can provide protection against reduced plasticity and impaired learning ability after traumatic brain injury.

Regional selectivity of amyloid mRNA expression and neurotrophins on repetitive inhibition of oxidative phosphorylation

Previously we showed that repetitive inhibition of oxidative phosphorylation impairs synaptic transmission and induces overexpression of amyloid precursor protein mRNA (APP-mRNA) in the hippocampus (Hellweg et al., 2003). Here we show that APP-mRNA remains alike in murine frontal cortex and cerebellum on repetitive treatment with 3-nitropropionate. However, nerve growth factor and brain-derived neurotrophic factor decreased by 28 to 38% in frontal cortex. Taken together, the pattern of change resembles genetic models of Alzheimer's disease with less susceptibility for overexpression of amyloid mRNA in frontal cortex than in hippocampus and reduced neurotrophin levels in frontal cortex. Given the similarity of this pattern to the one observed in human Alzheimer's disease the present model in future may give further insight into the pathophysiology of sporadic Alzheimer's disease.

The effect of chronic antidepressant treatment on serum brain-derived neurotrophic factor levels in depressed patients: a preliminary study

Recent studies suggested a role of brain-derived neurotrophic factor (BDNF) in depression. While BDNF levels are lower in depressed patients, antidepressant treatment increases serum BDNF levels of depressed patients. Our study aims to test the effect of chronic venlafaxine treatment on serum BDNF levels in patients with a major depressive disorder. Ten patients diagnosed as major depressive disorder according to DSM-IV are included in the study. Two of the patients had their first episode and were drug-naive, the other eight patients were drug-free for at least 4 weeks. The severity of depression was assessed with Hamilton Depression Rating Scale (HDRS). The control group consisted of ten age- and sex-matched subjects without any psychiatric disorder. Blood samples were collected at the baseline and after 12 weeks of antidepressant treatment (during remission). At the baseline the mean serum BDNF level was 17.9+/-9.1 ng/ml and the mean HDRS score was 23.2+/-4.6. Serum BDNF levels of the study group were significantly lower than in the control group (31.6+/-8.6 ng/ml). At the end of the study, the mean serum BDNF level was 34.6+/-7.1 ng/ml whereas the mean HDRS score was 8.2+/-3.9. From the baseline to the remission after 12 weeks of treatment, the increase in serum BDNF level and the decrease in HDRS score were statistically significant, respectively. When we compared the serum BDNF level of depressed patients at remission to that of the controls, there was no statistically significant difference. This study shows that venlafaxine treatment of depression improves serum BDNF level which may be considered as a nonspecific peripheral marker of depression.

Atorvastatin induction of VEGF and BDNF promotes brain plasticity after stroke in mice

Molecular mechanisms underlying the role of statins in the induction of brain plasticity and subsequent improvement of neurologic outcome after treatment of stroke have not been adequately investigated. Here, we use both in vivo and in vitro studies to investigate the potential roles of two prominent factors, vascular endothelial growth factor (VEGF) and brain-derived neurotrophic factor (BDNF), in mediating brain plasticity after treatment of stroke with atorvastatin. Treatment of stroke in adult mice with atorvastatin daily for 14 days, starting at 24 hours after MCAO, shows significant improvement in functional recovery compared with control animals. Atorvastatin increases VEGF, VEGFR2 and BDNF expression in the ischemic border. Numbers of migrating neurons, developmental neurons and synaptophysin-positive cells as well as indices of angiogenesis were significantly increased in the atorvastatin treatment group, compared with controls. In addition, atorvastatin significantly increased brain subventricular zone (SVZ) explant cell migration in vitro. Anti-BDNF antibody significantly inhibited atorvastatin-induced SVZ explant cell migration, indicating a prominent role for BDNF in progenitor cell migration. Mouse brain endothelial cell culture expression of BDNF and VEGFR2 was significantly increased in atorvastatin-treated cells compared with control cells. Inhibition of VEGFR2 significantly decreased expression of BDNF in brain endothelial cells. These data indicate that atorvastatin promotes angiogenesis, brain plasticity and enhances functional recovery after stroke. In addition, VEGF, VEGFR2 and BDNF likely contribute to these restorative processes.

Attenuation of brain derived neurotrophic factor (BDNF) by ethanol and cytoprotective effect of exogenous BDNF against ethanol damage in neuronal cells

Ethanol-induced cell damage was investigated using human neuroblastomas SH-SY5Y cells, which can be differentiated by retinoic acid. With 100 mM or more of ethanol, cytotoxicity was significantly higher in undifferentiated cells than in differentiated cells. Thus, a severer effect of ethanol was observed in undifferentiated cells. In differentiated cells it was shown that the secreted amount of brain derived neurotrophic factor (BDNF) and the cyclic AMP responsive element binding protein (CREB) activity were significantly reduced by ethanol. These effects may be involved in ethanol-induced cell damage in differentiated cells. It was reported that neurotrophic factors have protective effects and that the hippocampus exclusively was damaged by ethanol. Since SH-SY5Y cell is a cell line (a neuronal cell model) and similar cytotoxic effect of ethanol was observed in both SH-SY5Y and primary culture neuronal cells, it will be favorable to use primary culture cells to test a protective effect of BDNF. Exogenous BDNF was shown to have a protective effect against ethanol-induced damage in primary culture neurons from rat hippocampi.

Neurotrophic mechanisms in drug addiction

The involvement of neurotrophic factors in neuronal survival and differentiation is well established. The more recent realization that these factors also play pivotal roles in the maintenance and activity-dependent remodeling of neuronal functioning in the adult brain has generated excitement in the neurosciences. Neurotrophic factors have been implicated in the modulation of synaptic transmission and in the mechanisms underlying learning and memory, mood disorders, and drug addiction. Here the evidence for the role of neurotrophins and other neurotrophic factors-and the signaling pathways they activate-in mediating long-term molecular, cellular, and behavioral adaptations associated with drug addiction is reviewed.

Olanzapine counteracts reduction of brain-derived neurotrophic factor and TrkB receptors in rat hippocampus produced by haloperidol

Recently, we have reported studies in rats showing that the atypical antipsychotic olanzapine (OLZ), in contrast to haloperidol (HAL), was not associated with reduction of markers of central cholinergic neurons as well as decrements in cognitive performance after chronic exposure. We compared the effect of 45 day chronic exposure of HAL (2 mg/kg per day) to OLZ (10 mg/kg per day) on brain-derived neurotrophic factor (BDNF)) and its high affinity receptor TrkB in rat hippocampus. Since the use of OLZ is presently preferred over HAL in patients, effects of its post-treatment on HAL-induced changes in the expression of BDNF and its TrkB receptor were also investigated. OLZ was administered after 45 days of HAL exposure. HAL, but not OLZ, significantly reduced the levels of BDNF in hippocampus. These changes in BDNF paralleled the levels of TrkB receptors. Furthermore, post-treatment with OLZ markedly restored the HAL treatment associated reductions in both BDNF and TrkB receptors in hippocampus.

Serum brain-derived neurotrophic factor (BDNF) levels in schizophrenia are indistinguishable from controls

Our previous study showed that serum brain-derived neurotrophic factor (BDNF) was significantly decreased in the antidepressant-naive patients with major depressive disorders. However, it was still unclear whether serum BDNF level was altered in drug-naive patients with schizophrenia. Using ELISA, we measured serum BDNF levels in antipsychotic-naive (n=15) and medicated (n=25) patients with schizophrenia, and in age- and sex-matched normal controls (n=40). There were no significant differences in serum BDNF levels among antipsychotic-naive (n=15) and medicated (n=25) patients and normal controls (n=40). Possible factors such as duration of illness, age of onset, Brief Psychiatric Rating Scale scores, and chlorpromazine equivalent dosages of antipsychotics did not reveal any significant correlations with BDNF levels. Our results do not support the view that serum BDNF levels are associated with schizophrenia.

Spatial learning is delayed and brain-derived neurotrophic factor mRNA expression inhibited by administration of MK-801 in rats

Brain-derived neurotrophic factor (BDNF) is involved in activity-dependent plasticity and interacts with the neurotransmitter glutamate. Glutamate N-methl-D-aspartate (NMDA) receptor activation increases BDNF expression, while BDNF facilitates NMDA activity, with both involved in spatial learning. Administration of the NMDA receptor antagonist MK-801 can impair this leaning. The interaction between NMDA and BDNF in learning is examined in this study. Adult male Sprague-Dawley rats received either i.p. MK-801 or saline and were trained to locate a submerged water maze platform. Sedentary and activity yoked groups were included for biochemical comparisons. Control rats quickly learned the platform location while MK-801-treated rats learned at a significantly slower rate (P < 0.0001). In situ hybridization for hippocampal BDNF mRNA indicated significant increases in the yoked and learning groups. However, MK-801 attenuated the BDNF mRNA increase in the learning and activity-yoked conditions (P < 0.05). Administration of MK-801 to the sedentary group did not alter baseline mRNA levels. These data suggest that BDNF expression is important for NMDA-dependent learning and memory. Interestingly, learning still occurs across trials independent of the NMDA and BDNF interaction. Increases in BDNF and NMDA activity may be significant components in learning and memory, and modulation of these systems may be beneficial for developing strategies to improve cognitive function.

Chronic exposure to ethanol alters neurotrophin content in the basal forebrain-cortex system in the mature rat: Effects on autocrine-paracrine mechanisms

Neurotrophins are broadly expressed in the mammalian forebrain: notably in cerebral cortex and the basal forebrain (e.g., the septal and basal nuclei). These factors promote neuronal survival and plasticity, and have been implicated as key players in learning and memory. Chronic exposure to ethanol causes learning and memory deficits. We tested the hypothesis that ethanol affects neurotrophin expression and predicted that these changes would be consistent with alterations in retrograde or autocrine/paracrine systems. Mature rats were fed a liquid diet containing ethanol daily for 8 or 24 weeks. Weight-matched controls were pair-fed an isocaloric, isonutritive diet. Proteins from five structures (parietal and entorhinal cortices, hippocampus, and the basal and septal nuclei) were studied. ELISAs were used to determine the concentration of nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), and neurotrophin-3 (NT-3). All three neurotrophins were detected in each structure examined. Ethanol treatment significantly (p < 0.05) affected neurotrophin expression in time- and space-dependent manners. NGF content was generally depressed by ethanol exposure, whereas NT-3 content increased. BDNF concentration was differentially affected by ethanol: it increased in the parietal cortex and the basal forebrain and decreased in the hippocampus. With the exception of NGF in the septohippocampal system, the ethanol-induced changes in connected structures were inconsistent with changes that would be predicted from a retrograde model. Thus, the present data (a) support the concept that neurotrophins act through a nonretrograde system (i.e., a local autocrine/paracrine system), and (b) that chronic exposure to ethanol disrupts these regulatory mechanisms.

Progesterone up-regulates neuronal brain-derived neurotrophic factor expression in the injured spinal cord

Progesterone (PROG) provides neuroprotection to the injured central and peripheral nervous system. These effects may be due to regulation of myelin synthesis in glial cells and also to direct actions on neuronal function. Recent studies point to neurotrophins as possible mediators of hormone action. Here, we show that the expression of brain-derived neurotrophic factor (BDNF) at both the mRNA and protein levels was increased by PROG treatment in ventral horn motoneurons from rats with spinal cord injury (SCI). Semiquantitative in situ hybridization revealed that SCI reduced BDNF mRNA levels by 50% in spinal motoneurons (control: 53.5+/-7.5 grains/mm(2) vs. SCI: 27.5+/-1.2, P<0.05), while PROG administration to injured rats (4 mg/kg/day during 3 days, s.c.) elicited a three-fold increase in grain density (SCI+PROG: 77.8+/-8.3 grains/mm(2), P<0.001 vs. SCI). In addition, PROG enhanced BDNF immunoreactivity in motoneurons of the lesioned spinal cord. Analysis of the frequency distribution of immunoreactive densities (chi(2): 812.73, P<0.0001) showed that 70% of SCI+PROG motoneurons scored as dark stained whereas only 6% of neurons in the SCI group belonged to this density score category (P<0.001). PROG also prevented the lesion-induced chromatolytic degeneration of spinal cord motoneurons as determined by Nissl staining. In the normal intact spinal cord, PROG significantly increased BDNF inmunoreactivity in ventral horn neurons, without changes in mRNA levels. Our findings suggest that PROG enhancement of endogenous neuronal BDNF could provide a trophic environment within the lesioned spinal cord and might be part of the PROG activated-pathways to provide neuroprotection.

Differential expression of brain-derived neurotrophic factor transcripts after pilocarpine-induced seizure-like activity is related to mode of Ca2+ entry

Activity-dependent brain-derived neurotrophic factor (BDNF) expression is Ca2+-dependent, yet little is known about the Ca2+ channel contributions that might direct selective expression of the multiple BDNF transcripts. Here, effects of pilocarpine-induced seizure activity on total BDNF expression and on the individual sensitivity of BDNF transcripts to glutamate receptor and Ca2+ channel blockers were evaluated using hippocampal slice cultures and in situ hybridization of transcript-specific cRNA probes directed against mRNAs for the four 5' exons (I-IV) of the BDNF gene. mRNAs for nerve growth factor (NGF) and tyrosine kinase B (trkB) also were studied. Pilocarpine (5 mM) induced a dose- and time-dependent increase in total BDNF (exon V) mRNA expression in the dentate granule cells and CA3-CA1 pyramidal cells with maximal effects at 6 and 24 h, respectively. Increases were blocked by co-treatment with the alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid/kainate 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX: 25 microM) and the N-methyl-d-aspartic acid receptor antagonist 2-amino-5-phosphonovaleric acid (APV; 25 microM), whereas the L-type voltage sensitive Ca2+ channel blocker nifedipine (20 microM) was without detectable effect. Maximal NGF and trkB mRNA expression was induced by pilocarpine at 4 and 12 h, respectively. For the individual BDNF transcripts, APV blocked pilocarpine-induced increases in transcript II, whereas nifedipine blocked increases in transcripts I and III. Transcript IV levels were not altered by treatment. These results indicate that transcript II makes the greatest contribution to pilocarpine effects on total BDNF mRNA content in this model and provides evidence for regional and Ca2+ channel-specific differences in activity-dependent regulation of the different BDNF transcripts in hippocampus.

Short-term, D2 receptor blockade induces synaptic degeneration, reduces levels of tyrosine hydroxylase and brain-derived neurotrophic factor, and enhances D2-mediated firing in the ventral pallidum

Repeated treatments with neuroleptics are associated with biochemical and morphological alterations in forebrain neurons as well as an upregulation of D2-mediated changes in neuronal function. The present study evaluated the histological and physiological effects of three once-daily treatments with two chemically divergent neuroleptics, haloperidol (1 mg/kg i.p./day) and eticlopride (3 mg/kg i.p./day), measured in rats 24 h after the last injection. It was determined that this short-term antagonism of D2-like receptors induced fiber and terminal degeneration and significantly decreased tyrosine hydroxylase (TH) and brain-derived neurotrophic factor (BDNF) immunoreactivity in the ventral pallidum (VP), as determined by optical density measurements. While other forebrain regions demonstrated changes in TH and BDNF, the neurodegeneration profile was unique to the VP. This was accompanied by an enhancement in the efficacy of the D2 agonist quinpirole to increase spiking rate of VP neurons recorded in chloral hydrate-anesthetized rats. These data indicate that short-term treatments with D2 antagonists are sufficient to induce changes in the biochemical and morphological profiles uniquely within the VP. Moreover, the functional ramifications of these changes appear to include profound alterations in the way dopamine regulates neuronal activity in this region.

Nicotine Attenuates Arachidonic Acid-Induced Apoptosis of Spinal Cord Neurons by Preventing Depletion of Neurotrophic Factors

Increased levels of free fatty acids and, in particular, arachidonic acid can lead to induction of apoptosis of spinal cord neurons. Because of the importance of neurotrophic factors in cell survival and death, mRNA and protein levels of brain-derived neurotrophic factor (BDNF) and basic fibroblast growth factor (FGF-2) were studied in cultured spinal cord neurons treated with arachidonic acid. In addition, the present study focused on the effects of nicotine and neuronal nicotinic acetylcholine receptors (nAChRs) on these processes. A 2-h exposure to arachidonic acid markedly diminished expression of BDNF and FGF-2. These effects were fully prevented by pretreatment with 10 microM nicotine. Mecamylamine (a non-specific antagonist of nAChRs) and alpha-bungarotoxin (a specific antagonist of the nAChRalpha7) completely inhibited nicotine-mediated protection against arachidonic acid-induced alterations of BDNF and FGF-2. In addition, nicotine, BDNF and FGF-2 fully protected against arachidonic acid-induced apoptosis of spinal cord neurons. BDNF and FGF-2 were effective in prevention of apoptotic cell death even when applied 2 h after the beginning of arachidonic acid treatment. These results suggest that arachidonic acid can induce apoptosis of spinal cord neurons by depletion of neurotrophic factors and that nicotine can protect against these effects through the nAChRalpha7-mediated pathway.

Early postnatal corticosterone administration regulates neurotrophins and their receptors in septum and hippocampus of the rat

The principal glucocorticoid in rats, corticosterone, interacts with neurons in the limbic system and leads to morphological and behavioral changes. Putative corticosterone-triggered mediators are neurotrophins. In the present study we investigated the effects of early postnatal corticosterone treatment in rats on neurotrophic factors of the nerve growth factor (NGF) family and their receptors. Newborn rats were treated with corticosterone-containing polymers until postnatal day 12. The mRNA and protein levels of the neurotrophins of the NGF family (NGF, BDNF, NT-3 and NT-4/5) and their receptors (trkA, trkB, trkC and p75) were quantified in septum and hippocampus using RT-PCR. In the septal region, we found an unchanged mRNA expression after corticosterone treatment, whereas in the hippocampus there was a general increase in mRNA. Particularly, the gene expression of NGF, NT-3, and the high affinity receptors trkA, trkB and trkC increased significantly. Quantification of the neurotrophin protein levels using an ELISA revealed significant treatment effects for NGF and NT-4/5 in the hippocampus. The present study of corticosterone treatment in young rats demonstrates interactions of steroid hormones with neurotrophic factors and their receptors in the septo-hippocampal system during the first two postnatal weeks.

Effect of early thyroxine treatment on brain-derived neurotrophic factor mRNA expression and protein amount in the rat medial septum/diagonal band of Broca

There is evidence that morphological alterations concerning deficiency or abundance of thyroid hormones (TH) may be mediated by brain-derived neurotrophic factor (BDNF). It has been demonstrated that the mRNA-expression of BDNF is increased after TH-treatment during the first postnatal weeks. After transient treatment of newborn rats with thyroxine mRNA expression, protein concentration and number and size of BDNF-immunopositive neurons were quantified in the medial septum/vertical diagonal Band of Broca (MS/vDB). The number and size of BDNF-immunopositive neurons were estimated in young (P10) and adult (4 months). The amount of mRNA and protein are significantly increased in TH-treated rats at P10 compared to control animals. TH-treated animals showed a significant decrease of BDNF-immunopositive cell numbers in the adulthood. The results demonstrate a correlated increase of BDNF mRNA and protein in the septum at P10 which is an important stage of differentiation processes in the septohippocampal system. These results provide further evidence that BDNF is a possible candidate for the mediation the TH effects in the MS/vDB.

Alterations of serum levels of brain-derived neurotrophic factor (BDNF) in depressed patients with or without antidepressants

BACKGROUND

Because researchers have reported that antidepressants increase the expression of brain-derived neurotrophic factor (BDNF) in the rat hippocampus, we investigated whether serum BDNF levels may be used as a putative biological marker for major depressive disorders (MDD).

METHODS

We measured serum BDNF in the following three groups: antidepressant-naive patients with MDD (n = 16), antidepressant-treated patients with MDD (n = 17), and normal control subjects (n = 50). Patients were evaluated using the Hamilton Rating Scale for Depression (HAM-D). Serum BDNF was assayed with the sandwich ELISA method.

RESULTS

We found that serum BDNF was significantly lower in the antidepressant-naive group (mean, 17.6 ng/mL; SD, 9.6) than in the treated (mean, 30.6 ng/mL; SD, 12.3; p =.001) or in the control group (mean, 27.7 ng/mL; SD, 11.4; p =.002). There was a significant negative correlation (r = -.350, z = -2.003, p =.045) between serum BDNF and HAM-D scores in all patients. In a preliminary examination, reduced BDNF values of three drug-naive patients recovered to basal levels after antidepressant treatment.

CONCLUSIONS

Our study suggests that low BDNF levels may play a pivotal role in the pathophysiology of MDD and that antidepressants may increase BDNF in depressed patients.

Influence of estradiol, stress, and 5-HT2A agonist treatment on brain-derived neurotrophic factor expression in female rats

BACKGROUND

Estradiol affects neuronal plasticity, mood, and cognition. We examined the effects of the estrous cycle, acute and chronic estradiol treatments on BDNF mRNA expression in the hippocampus and cortex of female rats. The roles of 5-HT2A receptors and of stress on the BDNF mRNA regulation were also explored.

METHODS

BDNF mRNA levels were measured using in situ hybridization at proestrus and estrus, and following acute and chronic estradiol treatment of acutely and chronically ovariectomized (OVX) female rats. Some rats were pretreated with 5-HT2A agonist and antagonist, and another group was subjected to two-hour immobilization stress.

RESULTS

BDNF mRNA levels in the dentate gyrus and the medial prefrontal cortex were decreased during estrus, when estradiol levels are highest. Acute estradiol treatment decreased hippocampal BDNF mRNA in acutely OVX rats, but neither acute nor chronic estradiol had effect in chronically OVX rats. Estradiol pretreatment reduced the 5-HT2A receptor-mediated cortical upregulation in BDNF mRNA and did not effect the stress-induced down-regulation of BDNF mRNA in the dentate gyrus.

CONCLUSIONS

The duration of the estradiol treatment and the duration of the ovarian hormone deprivation are important factors in the regulation of BDNF synthesis and possibly in the functional outcome of estrogen treatment.

Effect of antipsychotic drugs on brain-derived neurotrophic factor expression under reduced N-methyl-D-aspartate receptor activity

Brain-derived neurotrophic factor (BDNF) promotes a variety of neuromodulatory processes during development as well as in adulthood. This neurotrophin has been associated with synaptic plasticity, suggesting that its regulation may represent one of the mechanisms through which psychotropic drugs alter brain function. Because reduced glutamatergic function represents a major feature of schizophrenia, we investigated the effects of the concomitant administration of haloperidol or olanzapine with the N-methyl-D-aspartate (NMDA) receptor antagonist MK-801 on BDNF expression. MK-801 reduces the hippocampal expression of the neurotrophin; this effect was exacerbated by haloperidol, but it was normalized by olanzapine. Our data reveal a fine tuning of BDNF biosynthesis and a differential modulation by antipsychotic drugs when NMDA-mediated transmission is reduced, suggesting that haloperidol and olanzapine can produce different effects on brain plasticity through the modulation of BDNF expression.

Aromatase inhibition affects testosterone-induced masculinization of song and the neural song system in female canaries

Songbirds have a specialized steroid-sensitive network of brain nuclei, the song system, for controlling song. Most nuclei of the song system express androgen receptors, and the sensory-motor integration nucleus High Vocal Center (HVC) alone also expresses estrogen receptors. Apart from expressing estrogen receptors in the vocal control system, songbirds are unique among birds because they have high concentrations of the estrogen-synthesizing enzyme aromatase in the neostriatum surrounding HVC. However, the role of estrogen in controlling the development of the song structure has been scarcely investigated. In this work, we show that blocking the production of estrogen during testosterone-induced song motor development in adult female canaries alters the song pattern compared to control females treated with testosterone only. These effects were correlated with inhibition of the expression of estrogen-sensitive genes, such as brain-derived nerve growth factor, in HVC. The expression of the ATP-synthase gene, an indicator of cell activity, in HVC, and the size of HVC, were not affected by the treatment. Our results provide the first example of estrogen-sensitive mechanisms controlling the structural features of adult birdsong.

Cell death in the inner nuclear layer of the retina is modulated by BDNF

Developing amacrine cells in the vertebrate retina undergo naturally-occurring cell death which is accentuated by the early removal of retinal ganglion cells. We show that providing BDNF or decreasing endogenous BDNF via competitive binding with soluble TrkB receptors in a whole-retina culture assay modulates the frequency of dying cells in the amacrine cell layer. Ganglion cells synthesize BDNF, and amacrine cells express TrkB receptors, suggesting a likely signaling mechanism.

Developmental exposure to the antiretroviral drug zidovudine increases brain levels of brain-derived neurotrophic factor in mice

We analyzed brain-derived neurotrophic factor (BDNF) and nerve growth factor (NGF) protein content in the central nervous system (CNS) of developing and adult mice exposed to the antiretroviral agent zidovudine (AZT) during prenatal and early postnatal period. Pregnant CD-1 mice received per os twice daily AZT (160 mg/kg) or vehicle from gestation day 10 until lactation day 7. BDNF and NGF contents were measured by enzyme immunoassays in male and female offspring on day 7, 21 or 60. In AZT-exposed females, BDNF levels were significantly increased in the hippocampus (days 7 and 21), in the cortex (day 60) and in the hypothalamus (day 21), while in males AZT exposure increased BDNF in the cortex on day 21. These findings support the hypothesis that developmental AZT exposure interferes with CNS development.

Brain-derived neurotrophic factor (BDNF) mRNA in rats with neonatal ibotenic acid lesions of the ventral hippocampus

Increasing evidence suggests that schizophrenia is a neurodevelopmental disorder with a progressive course characterized by worsening of symptoms and morphological alterations within the brain. This suggests that a neurodegenerative component may exist in schizophrenia. The role of brain-derived neurotrophic factor (BDNF) in neurodevelopment, cell viability and synaptic plasticity led to the investigation of BDNF as a potential candidate molecule in the pathophysiology of schizophrenia. BDNF mRNA was examined by in situ hybridization in the prefrontal cortex and hippocampus of animals with neonatal ibotenic acid lesions of the ventral hippocampus, a putative neurodevelopmental animal model of schizophrenia. Results demonstrate that animals with neonatal ibotenic acid lesions of the ventral hippocampus have reduced basal levels of BDNF mRNA. It is possible that alterations in this trophic factor render animals more susceptible to neurodegenerative insults.

Alpha-lipoic acid protects the retina against ischemia-reperfusion

The aim of this study was to examine whether the antioxidant alpha-lipoic acid protects retinal neurons from ischemia-reperfusion injury. Rats were injected intraperitoneally with either vehicle or alpha-lipoic acid (100 mg/kg) once daily for 11 days. On the third day, ischemia was delivered to the rat retina by raising the intraocular pressure above systolic blood pressure for 45 min. The electroretinogram was measured prior to ischemia and 5 days after reperfusion. Rats were killed 5 or 8 days after reperfusion and the retinas were processed for immunohistochemistry and for determination of mRNA levels by RT-PCR. Ischemia-reperfusion caused a significant reduction of the a- and b-wave amplitudes of the electroretinogram, a decrease in nitric oxide synthase and Thy-1 immunoreactivities, a decrease of retinal ganglion cell-specific mRNAs and an increase in bFGF and CNTF mRNA levels. All of these changes were clearly counteracted by alpha-lipoic acid. Moreover, in mixed rat retinal cultures, alpha-lipoic acid partially counteracted the loss of GABA-immunoreactive neurons induced by anoxia. The results of the study demonstrate that alpha-lipoic acid provides protection to the retina as a whole, and to ganglion cells in particular, from ischemia-reperfusion injuries. alpha-Lipoic acid also displayed negligible affinity for voltage-dependent sodium and calcium channels.

Differential regulation of hippocampal BDNF mRNA by typical and atypical antipsychotic administration

Apart from their differential propensities to block dopamine D2 and serotonin 5-HT2 receptors, the molecular mechanisms underlying the clinical efficacy of typical and atypical antipsychotics in schizophrenia are largely unknown. Given recent interest in the effects of antipsychotics on neurotrophic and other growth related factors, the effects of antipsychotics on brain-derived neurotrophic factor (BDNF), a neurotrophin crucial to the structural integrity of adult neurons, were investigated in male Wistar rats. Chronic (19 day) but not acute (45 min) antipsychotic administration significantly altered levels of hippocampal BDNF mRNA. In addition, whereas chronic treatment with the strong D2 receptor-blocker haloperidol significantly downregulated hippocampal BDNF mRNA, the selective 5-HT2 receptor-blocker ritanserin significantly upregulated CA1 hippocampal BDNF mRNA in comparison to controls. Since high doses of risperidone and clozapine produce potent inhibition of both 5-HT2 and D2 receptors, while lower doses produce significantly greater 5-HT2 vs. D2 receptor blockade, a dose-response study was employed to determine whether low doses of these atypical antipsychotics would also upregulate hippocampal BDNF mRNA in the absence of significant D2 receptor blockade. Whereas chronic haloperidol and high-dose risperidone significantly downregulated hippocampal BDNF mRNA, intermediate and lower doses of risperidone and clozapine were, unlike ritanserin, without effect when compared to controls. Thus, although the long-term downregulation of hippocampal BDNF mRNA may underlie the different clinical profiles of certain antipsychotics, this effect seems to be associated with antipsychotic doses that not only cause significant D2 receptor inhibition, but are usually associated with side effects rather than therapeutic efficacies.

Brain-derived neurotrophic factor expression is increased in the rat amygdala, piriform cortex and hypothalamus following repeated amphetamine administration

The amygdala plays an important role in the regulation of motivational states, especially those associated with addiction. The amygdala also expresses high levels of brain-derived neurotrophic factor (BDNF), an activity-dependent neurotrophin that can influence the reinforcing and locomotor activating properties of psychostimulants. In the present study, we examined the effects of acute and repeated amphetamine administration on the expression and production of this factor in the forebrain of rats. Animals given a single, acute injection (5 mg/kg, i.p.) of D-amphetamine developed hyperactivity followed by stereotypical behavior but showed no change in the basal expression of BDNF mRNA or its immunocytochemical profile in any region except the piriform cortex. Repeated injections (5 days) of 5 mg/kg amphetamine were accompanied by an enhanced onset of stereotypical behavior and elevated BDNF mRNA in the basolateral amygdala, rostral piriform cortex and paraventricular nucleus of the hypothalamus. Repeated treatment also increased BDNF immunoreactivity in perikarya of these same regions. In addition, increased BDNF immunoreactivity was found in fibers of many projection targets of the basolateral amygdala--the central extended amygdala, olfactory tubercle, medial nucleus accumbens, and in small zones resembling striosomes in the dorsal medial striatum. These results suggest that the upregulation of BDNF expression and protein in the basolateral nucleus of the amygdala and its targets could be an important part of the neuroadaptive response to psychostimulants.

An AMPA receptor potentiator modulates hippocampal expression of BDNF: an in vivo study

AMPA receptor activation has been demonstrated to increase the neuronal expression of brain derived neurotrophic factor (BDNF). In the present study, we investigated the effect of a novel AMPA receptor potentiator (LY404187) and its active isomer (LY451646) on the expression of BDNF protein and mRNA, as well as TrkB mRNA in rat hippocampus. LY404187 administered for 7 days (1 mg/kg) significantly increased the number of BDNF immunopositive cells in the dentate gyrus, but not other hippocampal subfields. Chronic treatment (7 days) with LY451646 (0.5 mg/kg, comparable to 1 mg/kg of LY404187) increased the level of both BDNF and TrkB mRNA expression in the dentate gyrus, CA3 and CA4 of the hippocampus. However, chronic treatment with lower doses of LY451646 (0.125 and 0.25 mg/kg) decreased the level of BDNF and TrkB mRNA in hippocampus, whilst the highest used dose of LY451646 (1 mg/kg) had no effect on BDNF and TrkB mRNA in hippocampus. In contrast, acute treatment with LY451646 produced an increase in BDNF mRNA levels at doses of 0.125 and 0.25 mg/kg in the hippocampus (CA4, CA3 and dentate gyrus, but not in CA1). LY451646 at 0.5 mg/kg had no effect, but at 1.0 mg/kg decreased the level of BDNF mRNA in hippocampus. Acute treatment with LY451646 did not affect the TrkB receptor mRNA levels in hippocampus. Our results demonstrate that biarylpropylsulfonamide AMPA receptor potentiators are capable of modulating the expression of BDNF and TrkB mRNA in a dose- and time-dependent manner. The increase in both BDNF protein and mRNA expression in the dentate gyrus but not in CA1 indicates a specific role of AMPA receptors in the regulation of BDNF expression in this hippocampal subfield. The regulation of BDNF expression by biarylpropylsulfonamids such as LY451646 may have important therapeutical implications for this class of molecule in the treatment of depression and other CNS disorders.

Estrogenic modulation of brain activity: implications for schizophrenia and Parkinson's disease

Evidence suggests the estrogens may play a role in various mental and neurodegenerative diseases. We review the evidence implicating estradiol in schizophrenia and Parkinson's disease. Epidemiologic and clinical studies on the effects of estrogens in schizophrenia are surveyed, and animal studies and in vitro models of the modulatory effects of estrogens on neurotransmitters associated with schizophrenia (i.e., dopamine, serotonin, glutamate) are reviewed. Epidemiologic and clinical data suggesting a role for estrogens in Parkinson's disease and in vivo and in vitro models demonstrating neuroprotective effects of estrogens are then examined. Despite the numerous animal studies on the effects of estrogens in the brain, clinical data are sparse and often contradictory. Compounds with more specific and potent estrogenic activity in the brain are required to further research efforts in this area. Possible candidates are the selective estrogen receptor modulators (SERMs), whose agonist or antagonist properties depend on the target tissue. The effects of various SERMs in the brain are reviewed, and our novel findings on the effects of SERMs on 5-HT2A receptors in the rat cortex and nucleus accumbens are presented. We suggest that drugs with estrogenic activity in the brain may have therapeutic potential, either by modulating brain neurotransmission or through neuroprotective activity.

The influence of inhalative corticosteroids on circulating Nerve Growth Factor, Brain-Derived Neurotrophic Factor and Neurotrophin-3 in allergic asthmatics

BACKGROUND

The neurotrophins Nerve Growth Factor (NGF), Brain-Derived Neurotrophic Factor (BDNF) and Neurotrophin (NT)-3 are produced, stored and released by various immunological cells. The influence of NTs upon the function of these cells is described. Elevated plasma levels were found in inflammatory, autoimmune and allergic diseases with the highest levels in allergic asthma. A connection between bronchial hyper-responsiveness and serum levels has been reported.

OBJECTIVE

Little is known about the influence of treatment with inhaled corticosteroids (ICS) on serum NT levels and their influence on the asthmatic state.

METHODS

Eighty-seven volunteers were studied. Thirty-eight were stable allergic asthmatics with constant ICS doses, 29 were asthmatics not receiving anti-asthmatic treatment and 20 were age- and sex-matched healthy controls. Demographic and lung function data were evaluated. NT serum levels were determined by ELISA.

RESULTS

NGF and BDNF levels were significantly increased in untreated asthmatics compared to the control and the treated group, while NT-3 demonstrated significantly higher levels in treated asthmatics compared to healthy controls. After stabilization of untreated subjects with ICS, the NT levels decreased significantly.

CONCLUSIONS

These results suggest that NTs participate in allergic inflammation and asthma. Effective treatment leads to a decrease of circulating neurotrophic factors.

Involvement of the brain-derived neurotrophic factor/TrkB pathway in neuroprotecive effect of cyclosporin A in forebrain ischemia

Recent studies have shown that cyclosporin A, a specific antagonist of calcineurin, a phosphatase, ameliorates neuronal cell death in the CA1 sector of the hippocampus after forebrain ischemia in animal models. The mechanism of this neuroprotective effect, however, has not yet been established. Brain-derived neurotrophic factor (BDNF), a member of the neurotrophins, is one of the potent survival and developmental factors whose expression is regulated by cyclic AMP-response element-binding protein (CREB). Activation of CREB is dependent on its phosphorylation at Ser(133), and calcineurin has been reported to dephosphorylate CREB via protein phosphatase 1. Based on these observations, we attempted to investigate how cyclosporin A treatment would affect the changes of phosphorylated CREB (pCREB), BDNF and its receptor tyrosine kinase B (TrkB) after forebrain ischemia in rats. Phosphorylation of CREB was kept augmented throughout the time course examined in cyclosporin A-treated animals, while it ceased without cyclosporin A. Reverse transcription-polymerase chain reaction revealed prolonged maintenance of BDNF mRNA expression in the CA1 sector of cyclosporin A-treated animals. The protein expression of BDNF and TrkB appeared to be up-regulated in cyclosporin A-treated animals, whereas it was transiently up-regulated but decreased to the marginal level of expression without cyclosporin A.From these results we suggest that cyclosporin A induces pCREB by an inhibition of calcineurin, resulting in the induction of BDNF. The mechanisms by which cyclosporin A protects the CA1 region from neuronal cell death in forebrain ischemia may involve the interaction of pCREB, BDNF and TrkB.

Transforming growth factor-beta1 enhances expression of brain-derived neurotrophic factor and its receptor, TrkB, in neurons cultured from rat cerebral cortex

The effects of transforming growth factor (TGF)-beta1 on expression of brain-derived neurotrophic factor (BDNF) and its high-affinity receptor, TrkB, in neurons cultured from the cerebral cortex of 18-day-old embryonic rats were examined. BDNF mRNA was significantly increased from 24-48 hr after the TGF-beta1 treatment over 20 ng/ml. Accumulation of BDNF protein in the culture medium was also potentiated by TGF-beta1, although the intracellular content of BDNF was nearly unchanged. The enhancement of BDNF mRNA expression was suppressed by the co-presence of decorin, a small TGF-beta-binding proteoglycan that inhibits the biological activities of TGF-betas. mRNA expression of full-length TrkB, the bioactive high-affinity receptor for BDNF, was also upregulated after treatment with TGF-beta1. These observations suggest that: 1) TGF-beta1 potentiates BDNF/TrkB autocrine or local paracrine system; and 2) the neurotrophic activity of TGF-beta1 is partly responsible for the BDNF induced by TGF-beta1 itself. To test this latter possibility, we examined the neuronal survival activity of TGF-beta1 with or without K252a, a selective inhibitor of Trk family tyrosine kinases. TGF-beta1 significantly enhanced neuronal survival, but the co-presence of K252a completely suppressed the activity, demonstrating the involvement of Trk receptor signaling in TGF-beta1-mediated neuronal survival in cultured rat cortical neurons. These results seem to be in line with recent findings by other investigators that some neurotrophic factors including BDNF require TGF-betas as a cofactor to exert their neurotrophic activities.

Decreased hippocampal BDNF expression after acute systemic injection of quinpirole

We report that acute quinpirole injection reduces BDNF mRNA levels in the rat hippocampus both at 2 and 6 h after the administration. These results suggest that the neurotrophin expression may be inhibited by situations involving dopaminergic overactivity.

Synaptic deprivation and age-related vulnerability to hypoxic-ischemic neuronal injury. A hypothesis

Advanced age is associated with physiological changes, such as cerebral autoregulation dysfunction, atrial fibrillation, reduced cerebral blood flow, elevated blood pressure, and other changes. Stroke-related dementia is associated with brain loss principally due to strokes, and neuropathological examination of the brains of old people shows a direct correlation between the extent of brain loss and dementia. However, the exact mechanism of the age related vulnerability to hypoxic-ischemic neuronal injury remains unknown. The majority of synapses in the brain use excitatory amino acids as their neurotransmitter. Glutamate, a major endogenous excitatory amino acid required for normal physiological excitation, is also involved in the pathophysiology of hypoxic-ischemic neuronal injury. The N-methyl-D-aspartate (NMDA) glutamate receptor subtype plays a major role in mediating hypoxic-ischemic neuronal injury. NMDA receptors also mediate adaptive responses important for synaptic plasticity. This report explores the possible role of synaptic activity as a protective mechanism against neuronal cell death. Specifically, the role of NMDA receptors in neuronal plasticity by upregulating a survival pathway is discussed. Loss of a neuronal population that uses glutamate as its neurotransmitter leads to a loss of activity on the postsynaptic neurons or synaptic deprivation. Deprivation of excitatory amino acids on the postsynaptic neurons results in the failure of activity-dependent induced intrinsic survival pathways induced by NMDA receptors. The loss of neuroprotective intrinsic survival pathways increases the vulnerability of these neurons to more hypoxic-ischemic neuronal damage. Since cerebral infarction is also age related, this hypothesis provides a plausible explanation of how we become more vulnerable to hypoxic-ischemic neuronal injury as a function of age.

BDNF dependence in neuroblastoma

Neuroblastomas are heterogeneous tumors arising from sympathetic precursors in the neural crest. Growth factor stimulation of neuroblastomas promote diverse biological responses (mitogenesis, differentiation, cell death) depending on the particular tumor studied. Here we show that brief treatment with retinoic acid (RA) rendered the human neuroblastoma lines SY5Y, NGP, SMS-KCNR, and SK-N-SH dependent on brain-derived neurotrophic factor (BDNF) for survival. The BDNF- and trkB-expressing line SMS-KCN was dependent on an autocrine BDNF/trkB survival without exposure to RA. We conclude that the BDNF/trkB pathway plays an important role in neuroblastoma survival and speculate on a possible role in tumor pathogenesis.

Expression and estrogen regulation of brain-derived neurotrophic factor gene and protein in the forebrain of female prairie voles

Brain-derived neurotrophic factor (BDNF) has been linked to the development, differentiation, and plasticity of the central nervous system. In the present study, we first used a highly specific affinity-purified antibody and a cRNA probe to generate a detailed mapping of BDNF immunoreactive (BDNF-ir) staining and mRNA labeling throughout the forebrain of female prairie voles. Our data revealed that (1) BDNF-ir cells were present essentially in the brain regions in which BDNF mRNA-labeled cells were found; (2) BDNF-ir fibers were distributed extensively throughout many forebrain regions; and (3) BDNF mRNA was also detected in some thalamic regions in which BDNF-ir fibers, but not immunostained cells, were present. With few exceptions, the distribution pattern of BDNF in the vole brain generally resembled the pattern found in rats. In a second experiment, we examined the effects of estrogen on BDNF expression. Ovariectomized prairie voles that were treated with estradiol benzoate had a higher level of BDNF mRNA labeling in the dentate gyrus and CA3 region of the hippocampus, as well as in the basolateral nucleus of the amygdala, than did ovariectomized voles that were treated with vehicle. In addition, estrogen treatment increased the density of BDNF-ir fibers in the lateral septum, dorsolateral area of the bed nucleus of the stria terminalis, and lateral habenular nucleus. These data suggest that estrogen may regulate BDNF at the level of gene and protein expression, and thus, BDNF may be in a position to mediate the effects of estrogen on the brain of the prairie vole.

Physical activity-antidepressant treatment combination: impact on brain-derived neurotrophic factor and behavior in an animal model

The mechanism of antidepressant action, at the cellular level, is not clearly understood. It has been reported that chronic antidepressant treatment leads to an up-regulation of brain-derived neurotrophic factor (BDNF) mRNA levels in the hippocampus, and that physical activity (voluntary running) enhances this effect. We wished to investigate whether BDNF expression brought about by these interventions may overcome deficits caused by acute stress, and might impact behavior in an animal model. In this report, we have tested the hypothesis that the combination of the antidepressant, tranylcypromine, and physical exercise could lead to decreased neurotrophin deficits and enhanced swimming time in animals that have been forced to swim in an inescapable water tank. Rats were either treated with tranylcypromine, engaged in voluntary running, or both for one week. After these treatments, the animals underwent a two-day forced swimming procedure. BDNF mRNA levels were significantly depressed in untreated animals subjected to forced swimming. Animals that either underwent prior activity or received antidepressant showed BDNF mRNA levels restored to baseline. Animals receiving the combined intervention showed an increase in hippocampal BDNF mRNA well above baseline. Swimming time during a five-minute test was significantly enhanced in animals receiving the combined intervention over untreated animals. Swimming time was not significantly enhanced over that of animals receiving antidepressant alone, however. Enhanced swimming time correlated with increased levels of BDNF mRNA in one hippocampal sub-region (CA4-hilus). These results suggest that the combination of exercise and antidepressant treatment may have significant neurochemical, and possibly behavioral, effects. In addition, these results support the possibility that the enhancement of BDNF expression may be an important element in the clinical response to antidepressant treatment. The induction of BDNF expression by activity/pharmacological treatment combinations could represent an important intervention for further study, to potentially improve depression treatment and management.

Increased synaptic inhibition in dentate gyrus of mice with reduced levels of endogenous brain-derived neurotrophic factor

The aim of this study was to explore the role of endogenous neurotrophins for inhibitory synaptic transmission in the dentate gyrus of adult mice. Heterozygous knockout (+/-) mice or neurotrophin scavenging proteins were used to reduce the levels of endogenous brain-derived neurotrophic factor and neurotrophin-3. Patch-clamp recordings from dentate granule cells in brain slices showed that the frequency, but not the kinetics or amplitude, of miniature inhibitory postsynaptic currents was modulated in brain-derived neurotrophic factor +/- compared to wild-type (+/+) mice. Furthermore, paired-pulse depression of evoked inhibitory synaptic responses was increased in brain-derived neurotrophic factor +/- mice. Similar results were obtained in brain slices from brain-derived neurotrophic factor +/+ mice incubated with tyrosine receptor kinase B-immunoglobulin G, which scavenges endogenous brain-derived neurotrophic factor. The increased inhibitory synaptic activity in brain-derived neurotrophic factor +/- mice was accompanied by decreased excitability of the granule cells. No differences in the frequency, amplitude or kinetics of miniature inhibitory postsynaptic currents were seen between neurotrophin-3 +/- and +/+ mice. From these results we suggest that endogenous brain-derived neurotrophic factor, but not neurotrophin-3, has acute modulatory effects on synaptic inhibition onto dentate granule cells. The site of action seems to be located presynaptically, i.e. brain-derived neurotrophic factor regulates the properties of inhibitory interneurons, leading to increased excitability of dentate granule cells. We propose that through this mechanism, brain-derived neurotrophic factor can change the gating/filtering properties of the dentate gyrus for incoming information from the entorhinal cortex to hippocampus. This will have consequences for the recruitment of hippocampal neural circuitries both under physiological and pathological conditions, such as epileptogenesis.

Changes in the pattern of brain-derived neurotrophic factor immunoreactivity in the rat brain after acute and subchronic haloperidol treatment

Our earlier work has shown that repeated administration of classical neuroleptic drugs gives rise to structural alterations in target regions of the mesolimbic pathway, most notably, nucleus accumbens. Such changes could be responsible for the efficacious or motor side effects associated with these drugs. Growth factors such as brain-derived neurotrophic factor (BDNF) provide trophic support for dopaminergic neurons during development and mediate synaptic and morphological plasticity in numerous regions of the adult CNS. The present study examines whether BDNF is altered in the mesolimbic pathway by classical neuroleptic treatment. Animals were administered haloperidol, 0.5 mg/kg, or vehicle, i.p., for either 3 or 21 days, followed by transcardiac perfusion with fixative. Three days of haloperidol administration dramatically decreased BDNF immunostaining in the neurons and fibers of the prefrontal cortex, hippocampus (dentate gyrus, CA2, and CA3), extended amygdala, and ventral tegmental area. BDNF-immunoreactive fibers virtually disappeared from the neostriatum and nucleus accumbens. Subchronic (21 days) treatment led to a rebound in BDNF immunoreactivity in most cell bodies but not in fibers. These results show that blockade of dopaminergic receptors with haloperidol rapidly downregulates BDNF in reward and emotional centers of the brain. Such rapid inactivation and subsequent reappearance of BDNF immunoreactivity could affect synaptic strength and plasticity and therefore be important preliminary steps in the cascade of neuronal events that lead to the efficacious or detrimental side effects of classical neuroleptic drugs.

Corticosterone inhibits generation of long-term potentiation in rat hippocampal slice: involvement of brain-derived neurotrophic factor

In the present study, the effect of corticosterone (CORT) on the generation of long-term potentiation (LTP) and its underlying mechanism involving neurotrophin gene expression in CA1 synapses of rat hippocampal slice were examined. Our experimental results showed incubation of hippocampal slice with CORT for 3 h had no effect on either the slope or amplitude of excitatory postsynaptic potentials (EPSP) evoked in hippocampal CA1 pyramidal dentrites, indicating no marked change in basal synaptic transmission. However, when tetanic stimulation (100 pulses, 100 Hz) was delivered to the Schaffer collateral pathway, CORT application significantly attenuated the tetanus-induced increases of both EPSP slope and amplitude, demonstrating an inhibitory effect of CORT on LTP generation. In addition, CORT treatment significantly reduced both slope and amplitude ratios of the second evoked EPSP to the first one when paired-pulse facilitation (PPF) was established at different interpulse intervals from 20 to 40 ms, suggesting that a presynaptic mechanism may be involved in CORT-induced hippocampal synaptic plasticity. Reverse-transcription polymerase chain reaction (RT-PCR) analysis showed that CORT-treated hippocampal CA1 cells underwent a significant decrease in the expression of mRNA for nerve growth factor-beta (NGF-beta) and brain-derived neurotrophic factor (BDNF), but not for neurotrophin-3 (NT-3) compared with those in control. Moreover, BDNF co-applied with CORT significantly antagonized CORT-induced deficit in PPF. Taken together, the present results suggest that CORT-induced inhibition of LTP may be, at least to some extent, mediated by a presynaptic mechanism and decrease in the BDNF expression in rat hippocampal CA1 cells induced by CORT may partially account for this presynaptic mechanism.