Modulation of neurotransmitter release induced by brain-derived neurotrophic factor in rat brain striatal slices in vitro

Changes in the serotonergic system and in brain-derived neurotrophic factor distribution in the main olfactory bulb of pcd mice before and after mitral cell loss

The serotonergic centrifugal system innervating the main olfactory bulb (MOB) plays a key role in the modulation of olfactory processing. We have previously demonstrated that this system suffers adaptive changes under conditions of a lack of olfactory input. The present work examines the response of this centrifugal system after mitral cell loss in the Purkinje cell degeneration (pcd) mutant mice. The distribution and density of serotonergic centrifugal axons were studied in the MOB of control and pcd mice, both before and after the loss of mitral cells, using serotonin (5-HT) and 5-HT transporter immunohistochemistry. Studies of the amount of 5-HT and its metabolite, 5-hydroxyindole acetic acid (5-HIAA), were performed by means of high-performance liquid chromatography (HPLC), and the relative amounts of brain-derived neurotrophin factor, BDNF, and its major receptor, tropomyosin-related kinase B (TrkB), were measured by Western blot. Our study revealed that the serotonergic system develops adaptive changes after, but not before, mitral cell loss. The lack of the main bulbar projection cells causes a decrease in the serotonergic input received by the MOB, whereas the number of serotonergic cells in the raphe nuclei remains constant. In addition, one of the molecules directly involved in serotonergic sprouting, the neurotrophin BDNF and its main receptor TrkB, underwent alterations in the MOBs of the pcd animals even before the loss of mitral cells. These data indicate that serotonergic function in the MOB is closely related to olfactory activity and that mitral cell loss induces serotonergic plastic responses.

Maladaptive plasticity of serotonin axon terminals in levodopa-induced dyskinesia

OBJECTIVE

Striatal serotonin projections have been implicated in levodopa-induced dyskinesia by providing an unregulated source of dopamine release. We set out to determine whether these projections are affected by levodopa treatment in a way that would favor the occurrence of dyskinesia.

METHODS

As an index of terminal serotonin innervation density, we measured radioligand binding to the plasma membrane serotonin transporter (SERT) in levodopa-treated dyskinetic and nondyskinetic subjects, using brain tissue from both rat and monkey models of Parkinson disease as well as parkinsonian patients. In addition, striatal tissue from dyskinetic rats was used for morphological and ultrastructural analyses of serotonin axon terminals, and for studies of stimulated [³H]dopamine release.

RESULTS

Across all conditions examined, striatal levels of SERT radioligand binding were significantly elevated in dyskinetic subjects compared to nondyskinetic cases. In the rat striatum, dyskinesiogenic levodopa treatment had induced sprouting of serotonin axon varicosities having a relatively high synaptic incidence. This response was associated with increased depolarization-induced [³H]dopamine release and with a stronger release potentiation by brain-derived neurotrophic factor.

INTERPRETATION

This study provides the first evidence that L-dopa treatment induces sprouting of serotonin axon terminals, with an increased incidence of synaptic contacts, and a larger activity-dependent potentiation of dopamine release in the dopamine-denervated striatum. Treatment-induced plasticity of the serotonin innervation may therefore represent a previously unappreciated cause of altered dopamine dynamics. These results are important for understanding the mechanisms by which L-dopa pharmacotherapy predisposes to dyskinesia, and for defining biomarkers of motor complications in Parkinsons disease.

Differential patterns of serum brain-derived neurotrophic factor levels in alcoholic patients with and without delirium tremens during acute withdrawal

BACKGROUND

Brain-derived neurotrophic factor (BDNF) is associated with alcohol addiction and withdrawal-related neurotoxicity. Delirium tremens (DT) is the most serious complication of alcohol withdrawal syndrome (AWS). In this study, we explored the differences in serum BDNF levels, measured at baseline and 1 week after alcohol withdrawal among alcoholic patients with and without DT.

METHODS

Sixty-five inpatients, fulfilling the DSM-IV criteria of alcohol dependence and admitted for alcohol detoxification, as well as 39 healthy control subjects were enrolled. The alcoholic patients were divided by the appearance of DTs into the DT group (n = 25) and non-DT group (n = 40). We collected blood samples of the patient groups on the first and seventh days of alcohol withdrawal and measured serum BDNF levels by sandwich enzyme-linked immunosorbent assay.

RESULTS

Serum BDNF levels differed significantly among the three groups: (i) control group 14.8 ± 4.7 ng/ml; (ii) non-DT group 12.3 ± 3.3 ng/ml; (iii) DT group 6.2 ± 2.6 ng/ml (p < 0.001). One week after alcohol withdrawal, the BDNF levels increased significantly for both alcoholic groups. While non-DT group had comparable BDNF levels (13.4 ± 3.5 ng/ml) with controls, the DT group still exhibited lower levels (8.9 ± 4.4 ng/ml).

CONCLUSIONS

This study suggests chronic drinking leads to a reduction in BDNF levels, and patients with more deficient BDNF expression are vulnerable to the development of DTs. Additionally, BDNF levels elevated after prompt alcohol detoxification treatment. These findings indicate that BDNF could involve modifying the phenotypes of AWS as well as the pertinent neuroadaptive processes of alcohol dependence.

Prolonged fasting as a method of mood enhancement in chronic pain syndromes: a review of clinical evidence and mechanisms

Periods of deliberate fasting with restriction to intake of solid food are practiced worldwide, mostly based on a traditional, cultural, or religious background. Recent evidence from clinical trials shows that medically supervised modified fasting (200-500 kcal nutritional intake/day) with periods from 7 to 21 days is efficacious in the treatment of rheumatic diseases and chronic pain syndromes. Here, fasting is frequently accompanied by increased alertness and mood enhancement. The beneficial claims of fasting are supported by experimental research, which has found fasting to be associated with increased brain availability of serotonin, endogenous opioids, and endocannabinoids. Fasting-induced neuroendocrine activation and mild cellular stress response with increased production of neurotrophic factors may also contribute to the mood enhancement of fasting. Fasting treatments may be useful as an adjunctive therapeutic approach in chronic pain patients. The mood-enhancing and pain-relieving effect of therapeutic fasting should be further evaluated in randomized clinical trials.

Brain derived neurotrophic factor and neurotrophin-4 employ different intracellular pathways to modulate norepinephrine uptake and release in rat hypothalamus

Classical actions of the neurotrophin family are related to cellular survival and differentiation. Moreover, acute effects of neurotrophins have been reported. Although neurotrophins effects on synaptic transmission at central nervous system level have been largely studied, acute effects of neurotrophins on hypothalamic noradrenergic transmission are still poorly understood. Thus, we have studied the effects of the neurotrophin family members nerve growth factor (NGF), brain derived neurotrophic factor (BDNF) and neurotrophin-4 (NT-4) on norepinephrine (NE) neuronal uptake and its evoked release, as well as the receptor and the intracellular pathways involved in these processes in rat hypothalamus. Present results indicate that BDNF increased NE uptake and decreased its evoked release through a mechanism that involve Trk B receptor and phospholipase C. Moreover, NT-4, also through the Trk B receptor, decreased NE uptake and its evoked release by activating phosphatidylinositol 3-OH-kinase. These effects were observed in whole hypothalamus as well as in the anterior hypothalamic zone. On the other hand, NGF did not modify noradrenergic transmission. In conclusion, we showed for the first time that BDNF and NT-4 activate two different intracellular signalling pathways through a Trk B receptor dependent mechanism. Furthermore, present findings support the hypothesis that BDNF and NT-4 acutely applied, could be considered as modulators of noradrenergic transmission and thus may regulate hypothalamic physiological as well as pathophysiological responses.

Synergistic neurochemical and behavioural effects of acute intrahippocampal injection of brain-derived neurotrophic factor and antidepressants in adult mice

Preclinical data support the view that brain-derived neurotrophic factor (BDNF) and serotonergic systems regulate circuits involved in affective disorders. The present study examined neurochemical and behavioural consequences of an acute intrahippocampal injection of BDNF combined with an antidepressant by using in-vivo intracerebral microdialysis in the ventral hippocampus (vHi) in conscious mice and behavioural paradigms predictive of antidepressant and anxiolytic-like effects [the mouse forced swim test (FST), the open-field (OF) paradigm and the elevated plus maze (EPM)]. Neurochemical data revealed that BDNF (100 ng) potentiated the effects of the systemic administration of a serotonin selective reuptake inhibitor (SSRI; paroxetine 4 mg/kg i.p.) and that of a locally applied citalopram perfusion on dialysate 5-HT levels in the vHi. These neurochemical changes correlated with behavioural data since, in the FST, antidepressant-like activity of paroxetine as measured on swimming behaviour was potentiated by BDNF. These data suggest an interesting synergy between BDNF and SSRI on antidepressant-like activity. Furthermore, in both the OF and EPM paradigms BDNF induced an anxiogenic-like activity, whereas paroxetine prevented this effect. Finally, the neurochemical and behavioural effects of BDNF on the serotonergic system might occur at both pre- and post-synaptic levels since by using in-situ hybridization, we showed that TrkB-R mRNA was expressed in the hippocampus and the dorsal raphe nucleus in adult mice. Taken together the neurochemical and behavioural effects of BDNF suggest that these behavioural changes were mediated by increases in 5-HT neurotransmission in vHi. Thus a BDNF+SSRI combination may offer new alternatives to treat mood disorders.

Possible role of sertraline against 3-nitropropionic acid induced behavioral, oxidative stress and mitochondrial dysfunctions in rat brain

Oxidative stress and disrupted energy metabolism are major events leading to nerve cell death. Oxidative stress and related reactive oxygen species is one of the common cooperative sharing pathways involved in neurodegenerative disorders including Huntington's disease. The present study evaluated the possible role of sertraline on the 3-nitropropionic acid induced behavioral, biochemical, and mitochondrial alterations in discrete areas of rat brain. 3-Nitropropionic acid (10 mg/kg) administration for 14 days significantly induced Huntington's disease like symptoms in rats as indicated by change in locomotor activity, body weight, rotarod activity performance, oxidative damage (elevated levels of lipid peroxidation, nitrite concentration, depletion of antioxidant enzyme levels) and mitochondrial dysfunction (Complexes-I, II, II and IV) in striatum, cortex and hippocampal region of brain. Treatment with sertraline (5 and 10 mg/kg) significantly reversed behavioral, biochemical and mitochondrial enzyme dysfunctions in 3-nitropropionic acid treated group. Further, combination of yohimbine (2 mg/kg) (non selective serotonin with the higher dose of sertraline (10 mg/kg) did not influence the protective action of sertraline. The present study suggests the possible antioxidant role of sertraline against 3-nitropropionic acid induced alterations in animals.

Sertraline slows disease progression and increases neurogenesis in N171-82Q mouse model of Huntington's disease

Huntington's disease (HD) is an inherited progressive neurodegenerative disorder resulting from CAG repeat expansion in the gene that encodes for the protein huntingtin. To identify neuroprotective compound (s) that can slow down disease progression and can be administered long term with few side effects in Huntington's disease, we investigated the effect of sertraline, a selective serotonin reuptake inhibitor (SSRI) which has been shown to upregulate BDNF levels in rodent brains. We report here that in HD mice sertraline increased BDNF levels, preserved chaperone protein HSP70 and Bcl-2 levels in brains, attenuated the progression of brain atrophy and behavioral abnormalities and thereby increased survival. Sertraline also enhanced neurogenesis, which appeared to be responsible for mediating the beneficial effects of sertraline in HD mice. Additionally, the effective levels of sertraline are comparable to the safe levels achievable in humans. The findings suggest that sertraline is a potential candidate for treatment of HD patients.

Interaction between BDNF and serotonin: role in mood disorders

Brain-derived neurotrophic factor (BDNF) and serotonin (5-hydroxytryptamine, 5-HT) are two seemingly distinct signaling systems that play regulatory roles in many neuronal functions including survival, neurogenesis, and synaptic plasticity. A common feature of the two systems is their ability to regulate the development and plasticity of neural circuits involved in mood disorders such as depression and anxiety. BDNF promotes the survival and differentiation of 5-HT neurons. Conversely, administration of antidepressant selective serotonin reuptake inhibitors (SSRIs) enhances BDNF gene expression. There is also evidence for synergism between the two systems in affective behaviors and genetic epitasis between BDNF and the serotonin transporter genes.

Interaction between BDNF Val66Met and dopamine transporter gene variation influences anxiety-related traits

The involvement in neural plasticity and the mediation of effects of repeated stress exposure and long-term antidepressant treatment on hippocampal neurogenesis supports a critical role of brain-derived neurotrophic factor (BDNF) in the pathophysiology of affective and other stress-related disorders. A previously reported valine to methionine substitution at amino-acid position 66 (BDNF Val66Met) seems to account for memory disturbance and hippocampal dysfunction. In the present study, we evaluated the impact of the BDNF Val66Met polymorphism on individual differences in personality traits in a sample of healthy volunteers in relation to other common gene variants thought to be involved in the pathophysiology of affective disorders, such as the serotonin transporter promoter polymorphism (5-HTTLPR) and a variable number of tandem repeat polymorphism of the dopamine transporter gene (DAT VNTR). Personality traits were assessed using the NEO personality inventory (NEO-PI-R) and Tridimensional Personality Questionnaire (TPQ). There was a significant DAT VNTR-dependent association between NEO-PI-R Neuroticism and the BDNF Val66Met polymorphism. Among individuals with at least one copy of the DAT 9-repeat allele, carriers of the BDNF Met allele exhibited significantly lower Neuroticism scores than noncarriers. This interaction was also observed for TPQ Harm Avoidance, a personality dimension related to Neuroticism. Our results support the notion that allelic variation at the BDNF locus--in interaction with other gene variants--influences anxiety- and depression-related personality traits.

The antidepressant sertraline improves the phenotype, promotes neurogenesis and increases BDNF levels in the R6/2 Huntington's disease mouse model

Huntington's disease (HD) is an inherited progressive neurodegenerative disorder characterized by progressive movement, psychiatric and cognitive disturbances. Previous studies have indicated that HD pathogenesis may be mediated in part by loss of brain derived neurotrophic factor (BDNF). Antidepressants selectively blocking serotonin reuptake can increase BDNF levels, and also may increase neurogenesis. Here we report that an SSRI antidepressant, sertraline, prolongs survival, improves motor performance, and ameliorates brain atrophy in the R6/2 HD mouse model. Six-week-old R6/2 mice and nontransgenic control mice were administered either sertraline or vehicle daily. Motor function was assessed in an accelerating rotarod test and evaluated at 10 weeks. R6/2 mice exhibited reduced time on the rod. Sertraline treatment improved the motor performance in R6/2 mice, but did not affect nontransgenic mice. R6/2 mice showed significant striatal atrophy which was reduced by sertraline treatment. These beneficial effects of sertraline are associated with enhanced neurogenesis and increased BDNF levels in brain treated with sertraline. The effective serum and brain levels of sertraline are comparable to the levels achieved in human antidepressant treatment. Our findings provide evidence that sertraline is neuroprotective in this HD model. Successful treatment with sertraline in depressed HD patients has been reported; moreover, sertraline is safe and well-tolerated for long-term administration, including in HD patients. Our findings suggest that a clinical trial of SSRI treatment in order to retard disease progression in human HD may be warranted.

Decreased plasma brain-derived neurotrophic factor levels in patients with alcohol dependence

BACKGROUND

Many reports have suggested possible relationships between brain-derived neurotrophic factor (BDNF) and alcohol dependence. A protective effect of BDNF against ethanol-induced cell damage has been suggested, and this effect may contribute to the development or maintenance of alcohol dependence. This study was carried out in order to verify the significance of BDNF in alcohol dependence.

METHODS

Peripheral BDNF levels were measured in alcohol-dependent patients and control subjects using an enzyme-linked immunosorbent assay. A physician's interview and standardized questionnaire were used to obtain information regarding each patient's history of alcohol consumption.

RESULTS

The mean BDNF level was lower in the alcohol dependence group (389.5 +/- 501.7 pg/ml) than in the normal controls (822.5 +/- 420.7 pg/ml) by analysis of covariance (ANCOVA) (F = 25.79, p < 0.01). The mean BDNF level was lower in the alcohol-dependent patients with a positive family history of alcohol dependence (247.6 +/- 289.2 pg/ml) than in those with a negative family history of alcohol dependence (583.9 +/- 652.8 pg/ml) by ANCOVA (F = 6.51, p = 0.01). The BDNF levels did not correlate significantly with any of the variables analyzed in this study, including Beck depression inventory, state and trait anxiety inventory (STAI-S and T), and various drinking behaviors.

CONCLUSIONS

Changes in the levels of BDNF might play a role in the pathophysiology and inheritance of alcohol dependence.

Reduced brain-derived neurotrophic factor is associated with a loss of serotonergic innervation in the hippocampus of aging mice

Brain-derived neurotrophic factor (BDNF) regulates monoamine neuronal growth, survival and function in development and throughout adulthood. At 18 months of age, mice with constitutive reductions in BDNF expression show decreased serotonin innervation in the hippocampus compared with age-matched wildtype mice. It is not known, however, whether age-accelerated loss of serotonergic innervation in BDNF(+/-) mice occurs in other brain regions, advances beyond 18 months or is associated with alterations in other neurotransmitter systems. In this study, immunocytochemistry was used to assess serotonergic and catecholaminergic innervation in 26-month-old BDNF(+/-) mice. Age-related loss of serotonin axons in the hippocampus was potentiated in BDNF(+/-) mice compared with wildtype mice at this late age, particularly in the CA1 subregion. By contrast, aging BDNF(+/-) mice showed increased serotonin innervation of the basomedial nucleus of the amygdala. In the noradrenergic system, BDNF(+/-) mice showed reduced numbers of cell bodies and fibers in the locus coeruleus compared with age-matched wildtype mice, whereas no changes were observed in dopaminergic innervation with respect to genotype. In vivo zero net flux microdialysis in awake mice showed a significant decrease in extracellular serotonin levels in the hippocampus in BDNF(+/-) mice at 20 months of age. Thus, reduced BDNF is associated with altered serotonergic and noradrenergic innervation in aging mice and, in particular, with accelerated loss of serotonergic innervation to the hippocampus that is manifest as a decrease in basal neurotransmission.

Genetic analyses of the brain-derived neurotrophic factor (BDNF) gene in autism

Autism is a severe neurodevelopmental disorder defined by social and communication deficits and ritualistic-repetitive behaviors that are detectable in early childhood. Brain-derived neurotrophic factor (BDNF) plays a critical role in the pathogenesis of autism. In this study, we examined the SNP- and haplotypic-association of BDNF with autism in a trios-based association study (the Autism Genetic Resource Exchange). We also examined the expression of BDNF mRNA in the peripheral blood lymphocytes of drug-naïve autism patients and control subjects. In the TDT of autism trios, the SNP haplotype combinations showed significant associations in the autism group. BDNF expression in the drug-naïve autistic group was found to be significantly higher than in the control group. We suggest that BDNF has a possible role in the pathogenesis of autism through its neurotrophic effects on the serotonergic system.

Changes in the serotonergic system in the main olfactory bulb of rats unilaterally deprived from birth to adulthood

The serotonergic system plays a key role in the modulation of olfactory processing. The present study examined the plastic response of this centrifugal system after unilateral naris occlusion, analysing both serotonergic afferents and receptors in the main olfactory bulb. After 60 days of sensory deprivation, the serotonergic system exhibited adaptive changes. Olfactory deprivation caused a general increase in the number of fibres immunopositive for serotonin but not of those immunopositive for the serotonin transporter. HPLC data revealed an increase in serotonin levels but not in those of its major metabolite, 5-hydroxyindole acetic acid, resulting in a decrease in the 5-hydroxyindole acetic acid/serotonin ratio. These changes were observed not only in the deprived but also in the contralateral olfactory bulb. Double serotonin-tyrosine hydroxylase immunolabelling revealed that the glomerular regions of the deprived olfactory bulb with a high serotonergic fibre density showed a strong reduction in tyrosine hydroxylase. Finally, the serotonin(2A) receptor distribution density and the number of juxtaglomerular cells immunopositive for serotonin(2A) receptor remained unaltered after olfactory deprivation. Environmental stimulation modulated the serotonergic afferents to the olfactory bulb. Our results indicate the presence of a bilateral accumulation of serotonin in the serotonergic axon network, with no changes in serotonin(2A) receptor density after unilateral olfactory deprivation.

Gender-dependent modulation of brain monoamines and anxiety-like behaviors in mice with genetic serotonin transporter and BDNF deficiencies

1. Brain-derived neurotrophic factor (BDNF) supports serotonergic neuronal development and our recent study found that heterozygous mice lacking one BDNF gene allele interbred with male serotonin transporter (SERT) knockout mice had greater reductions in brain tissue serotonin concentrations, greater increases in anxiety-like behaviors and greater ACTH responses to stress than found in the SERT knockout mice alone. 2. We investigated here whether there might be gender differences in these consequences of combined SERT and BDNF deficiencies by extending the original studies to female mice, and also to an examination of the effects of ovariectomy and tamoxifen in these female mice, and of 21-day 17-beta estradiol implantation to male mice. 3. We found that unlike the male SERTxBDNF-deficient mice, female SERTxBDNF mice appeared protected by their gender in having significantly lesser reductions in serotonin concentrations in hypothalamus and other brain regions than males, relative to controls. Likewise, in the elevated plus maze, female SERTxBDNF-deficient mice demonstrated no increases in the anxiety-like behaviors previously found in males. 4. Furthermore, female SERTxBDNF mice did not manifest the approximately 40% reduction in the expression of TrkB receptors or the approximately 30% reductions in dopamine and its metabolites that male SERTxBDNF did. After estradiol implantation in male SERTxBDNF mice, hypothalamic serotonin was significantly increased compared to vehicle-implanted mice. These findings support the hypothesis that estrogen may enhance BDNF function via its TrkB receptor, leading to alterations in the serotonin circuits, which modulate anxiety-like behaviors. 5. This double-mutant mouse model contributes to the knowledge base that will help in understanding genexgenexgender interactions in studies of SERT and BDNF gene polymorphisms in human genetic diseases such as anxiety disorders and depression.

Semax, an ACTH(4-10) analogue with nootropic properties, activates dopaminergic and serotoninergic brain systems in rodents

Corticotrophin (ACTH) and its analogues, particularly Semax (Met-Glu-His-Phe-Pro-Gly-Pro), demonstrate nootropic activity. Close functional and anatomical links have been established between melanocortinergic and monoaminergic brain systems. The aim of present work was to investigate the effects of Semax on neurochemical parameters of dopaminergic- and serotonergic systems in rodents. The tissue content of 5-hydroxyindoleacetic acid (5-HIAA) in the striatum was significantly increased (+25%) 2 h after Semax administration. The extracellular striatal level of 5-HIAA gradually increased up to 180% within 1-4 h after Semax (0.15 mg/kg, ip) administration. This peptide alone failed to alter the tissue and extracellular concentrations of dopamine and its metabolites. Semax injected 20 min prior D: -amphetamine dramatically enhanced the effects of the latter on the extracellular level of dopamine and on the locomotor activity of animals. Our results reveal the positive modulatory effect of Semax on the striatal serotonergic system and the ability of Semax to enhance both the striatal release of dopamine and locomotor behavior elicited by D-amphetamine.

Brain-derived neurotrophic factor augments peristalsis by augmenting 5-HT and calcitonin gene-related peptide release

BACKGROUND & AIMS

Brain-derived neurotrophic factor (BDNF) acts rapidly to modulate synaptic neurotransmission in the brain. Although present in neurons, glial cells, and mucosal cells of the colon, and in higher concentrations than in brain, the action of BDNF in gut have not been characterized. The aim of this study was to identify the role of BDNF in mediating the peristaltic reflex.

METHODS

BDNF and a specific antiserum were examined for their effects on the peristaltic reflex and release of the sensory mediators serotonin and calcitonin gene-related peptide in rat colon. The peristaltic reflex and release of serotonin and calcitonin gene-related peptide were also examined in genetically modified mice (BDNF(+/-)) with reduced levels of BDNF.

RESULTS

Endogenous brain-derived neurotrophic factor was released into the sensory compartment in a stimulus-dependent manner during the peristaltic reflex induced by mucosal stimulation but not muscle stretch. BDNF stimulated and immunoneutralization of endogenous BDNF reduced ascending contraction and descending relaxation of circular muscle and release of serotonin and calcitonin gene-related peptide during the peristaltic reflex induced by mucosal stimulation but not muscle stretch. The peristaltic reflex and release of serotonin and calcitonin gene-related peptide during the peristaltic reflex induced by mucosal stimulation but not muscle stretch were significantly reduced in BDNF(+/-) mice.

CONCLUSIONS

Endogenous BDNF enhances the peristaltic reflex by augmenting the release of serotonin and calcitonin gene-related peptide that mediate the sensory limb of the reflex induced by mucosal stimulation.

Rodent BDNF genes, novel promoters, novel splice variants, and regulation by cocaine

Results from studies using molecular and genetic methods in humans and rodents suggest that brain-derived neurotrophic factor (BDNF) is involved in the behavioral effects of abused drugs, making understanding of its genomic structure and regulation of substantial interest. Recently, we have reported that the human BDNF gene contains seven upstream exons that can each be spliced independently to the major BDNF coding exon to form diverse bipartite BDNF transcripts. We also identified a novel "BDNFOS" gene that is transcribed to produce alternatively spliced natural antisense transcripts (NATs); its fifth exon overlaps with the protein coding exon VIII of human BDNF. To better understand BDNF's genomic structure and differential regulation, we now describe the rodent BDNF gene and transcripts. This gene includes six bipartite transcripts that are generated by six independently transcribed exons, each of which is spliced to a major coding exon and a tripartite transcript that is composed of two upstream exons and one coding exon. In addition, we found no evidence for antisense, opposite strand BDNFOS gene transcripts in mice or rats. The BDNF rodent splice variants display specific patterns of differential expression in different brain regions and peripheral tissues. Acute cocaine administration increased striatal expression of a specific BDNF4 splice variant by up to 5-fold. Interestingly, however, neither experimenter- nor self-administered chronic cocaine administration enhanced striatal BDNF expression. These data suggest a role of specific BDNF promoter regions and regulatory sequences in stimulant-induced alterations in BDNF expression, and in the alterations that changed BDNF expression is likely to confer in the brain.

Prophylactic activation of neuroprotective stress response pathways by dietary and behavioral manipulations

It is well established that when most types of cells, including neurons, are exposed to a mild stress they increase their ability to resist more severe stress. This "preconditioning" phenomenon involves up-regulation of genes that encode cytoprotective proteins such as heat-shock proteins and growth factors. We found that a similar beneficial cellular stress response can be induced in neurons throughout the brain by a "meal-skipping" dietary restriction (DR) regimen in rats and mice. DR is effective in protecting neurons and improving functional outcome in models of stroke, Alzheimer's, Parkinson's and Huntington's diseases. DR induces an increase in the levels of brain-derived neurotrophic factor (BDNF) and heat-shock proteins in neurons. DR also stimulates neurogenesis in the hippocampus, and BDNF plays a role in this effect of DR. Physical exercise and environmental enrichment are two other manipulations that have been shown to induce BDNF expression in the brain, presumably because it is a mild cellular stress. When taken together with epidemiological and clinical studies in humans, the data from animal studies suggest that it may be possible to reduce the risk for age-related neurodegenerative disorders through dietary and behavioral modifications that act by promoting neuronal plasticity and survival.

RACK1 and brain-derived neurotrophic factor: a homeostatic pathway that regulates alcohol addiction

Alcoholism is a devastating disease that manifests as uncontrolled drinking. Consumption of alcohol is regulated by neurochemical systems within specific neural circuits, but endogenous systems that may counteract and thus suppress the behavioral effects of ethanol intake are unknown. Here we demonstrate that BDNF plays a role in reducing the behavioral effects of ethanol, including consumption, in rodents. We found that decreasing the levels of BDNF leads to increased behavioral responses to ethanol, whereas increases in the levels of BDNF, mediated by the scaffolding protein RACK1, attenuate these behaviors. Interestingly, we found that acute exposure of neurons to ethanol leads to increased levels of BDNF mRNA via RACK1. Importantly, acute systemic administration of ethanol and voluntary ethanol consumption lead to increased levels of BDNF expression in the dorsal striatum. Taken together, these findings suggest that RACK1 and BDNF are part of a regulatory pathway that opposes adaptations that lead to the development of alcohol addiction.

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

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

Exploring the relationship between serotonin and brain-derived neurotrophic factor: analysis of BDNF protein and extraneuronal 5-HT in mice with reduced serotonin transporter or BDNF expression

Serotonin (5-HT) has been proposed to promote neuronal plasticity during the treatment of mood and anxiety disorders and following neurodegenerative insult by altering the expression of critical genes including brain-derived neurotrophic factor (BDNF). In this study, mice with constitutive reductions in the serotonin transporter (SERT) or BDNF were investigated to further assess the functional relationship between serotonin neurotransmission and BDNF expression. Using a modified extraction procedure and a commercial enzyme-linked immunosorbant assay, 50% decreases in BDNF protein in hippocampus, frontal cortex and brain stem were confirmed in 4-month-old mice lacking one copy of the BDNF gene (BDNF(+/-)). By contrast, 4-month-old male and female mice with partial (SERT(+/-)) or complete (SERT(-/-)) reductions in SERT expression showed no differences in BDNF protein levels compared to SERT(+/+) mice, although male SERT knockout mice of all genotypes had higher BDNF levels in hippocampus, frontal cortex, and brain stem than female animals. Microdialysis also was performed in BDNF(+/-) mice. In addition to other phenotypic aspects suggestive of altered serotonin neurotransmission, BDNF(+/-) mice show accelerated age-related degeneration of 5-HT forebrain innervation. Nevertheless, extracellular 5-HT levels determined by zero net flux microdialysis were similar between BDNF(+/+) and BDNF(+/-) mice in striatum and frontal cortex at 8-12 months of age. These data illustrate that a 50% decrease in BDNF does not appear to be sufficient to cause measurable changes in basal extracellular 5-HT concentrations and, furthermore, that constitutive reductions in SERT expression are not associated with altered BDNF protein levels at the ages and in the brain regions examined in this study.

Neuroplasticity: from MRI to depressive symptoms

Morphological and functional changes have been repeatedly reported in the brain organization of depressed patients. The main modifications demonstrated by structural magnetic resonance imaging (MRI) are a reduction in the gray matter volume within the prefrontal cortex, the hippocampus, and the striatum. The reduction in gray matter volume and the morphological atrophy are probably due to an excess of neural loss (apoptosis) and an altered regulation of the neurotrophic processes. Hence, a deficit in neurotrophic factor synthesis (brain-derived neurotrophic factor [BDNF], neurotrophin [NT]-3, NT-4/5, Bcl-2, etc.) may be responsible for increased apoptosis in the hippocampus and prefrontal cortex corresponding to the cognitive impairment described in depression. This hypothesis seems to be confirmed by the decreased expression of neurotrophic factors (e.g., BDNF mRNA) in animal models of depression. In parallel, the neural plasticity (functional aspects of synaptic connectivity and long-term potential activity [LTP]) is decreased. However, the most interesting data concern the possible reversibility of this dysregulation with antidepressant treatment. For example, communication between the hippocampus and the prefrontal cortex could be re-established, enabling in a way the cognitive processes to be "reset." From a clinical point of view, the consequences of such a phenomenon are manifold:

Identification of brain-derived neurotrophic factor in nestin-expressing astroglial cells in the neostriatum of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-treated mice

Up-regulation of nestin expression was significantly induced in the caudate-putamen of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated mice in our previous observation [Brain Res 925 (2002) 9]. We hypothesized that the nestin-expressing cells might play an important role in the pathogenesis of parkinsonian model, and characterization of these nestin-expressing cells was studied by RT-PCR, immunohistochemistry and semi-quantitative analysis for various markers of glial fibrillary acid protein (GFAP), S-100, neuronal nuclear specific protein (NeuN), beta-tubulin, Ki-67 and brain-derived neurotrophic factor (BDNF) expression in MPTP-treated C57/BL mice. Firstly, significant increasing in both nestin protein and mRNA was found in MPTP-treated mice. Up-regulation of nestin expression started at day 1, peaked at day 3, and gradually went down at days 7-21 in the neostriatum after MPTP treatment. Secondly, double immunofluorescence indicated that almost all of nestin-positive cells exhibited GFAP (98%) or S-100 (96%)-immunoreactivity, whereas NeuN or beta-tubulin was hardly detected in these nestin-positive cells. Thirdly, a minor population (7.0%) of nestin-positive cells showed Ki-67 (cell proliferation marker)-immunoreactivity, showing some of them went into cell mitotic state. Finally but more interestingly, a major population (86%) of nestin-expressing cells also exhibited immunoreactivity for BDNF, one neurotrophic factor. These results present time-dependent up-regulation of nestin expression in neostriatum, the proliferative and neurotrophic properties of nestin-expressing astroglial cells in MPTP-treated C57/BL mice. Taken together with previous observations, this study suggests that nestin-expressing activated astroglial cells, possibly partially through synthesizing and releasing neurotrophic factors such as BDNF in the basal ganglia, may play important roles in protection of nigrostriatal dopamine neurons and in the pathogenesis of Parkinson's disease in mammals.

Voltage-gated Na+ channel activation induces both action potentials in utricular hair cells and brain-derived neurotrophic factor release in the rat utricle during a restricted period of development

The mammalian utricular sensory receptors are commonly believed to be non-spiking cells with electrical activity limited to graded membrane potential changes. Here we provide evidence that during the first post-natal week, the sensory hair cells of the rat utricle express a tetrodotoxin (TTX)-sensitive voltage-gated Na+ current that displays most of the biophysical and pharmacological characteristics of neuronal Na+ current. Single-cell RT-PCR reveals that several alpha-subunit isoforms of the Na+ channels are co-expressed within a single hair cell, with a major expression of Nav1.2 and Nav1.6 subunits. In neonatal hair cells, 30 % of the Na+ channels are available for activation at the resting potential. Depolarizing current injections in the range of the transduction currents are able to trigger TTX-sensitive action potentials. We also provide evidence of a TTX-sensitive activity-dependent brain-derived neurotrophic factor (BDNF) release by early post-natal utricle explants. Developmental analysis shows that Na+ currents decrease dramatically from post-natal day 0 (P0) to P8 and become almost undetectable at P21. Concomitantly, depolarizing stimuli fail to induce both action potential and BDNF release at P20. The present findings reveal that vestibular hair cells express neuronal-like TTX-sensitive Na+ channels able to generate Na+-driven action potentials only during the early post-natal period of development. During the same period an activity-dependent BDNF secretion by utricular explants has been demonstrated. This could be an important mechanism involved in vestibular sensory system differentiation and synaptogenesis.

Environmental enrichment: effects on stereotyped behavior and neurotrophin levels

The present study evaluated whether environmental enrichment-related effects on the development of stereotyped behavior in deer mice were associated with alterations in neurotrophin levels. Deer mice were reared in enriched or standard cage conditions for 60 days. The mice were then tested in automated photocell detectors and classified as either stereotypic or nonstereotypic. This testing paradigm yielded four behaviorally distinct groups: enriched stereotypic, enriched nonstereotypic, standard cage stereotypic, and standard cage nonstereotypic. The motor cortex, striatum, and hippocampus were dissected, and the levels of brain-derived neurotrophin factor (BDNF) and nerve growth factor (NGF) in each brain region were analyzed using Promega ELISA kits. There were no differences in either NGF or BDNF in either the motor cortex or the hippocampus. In the striatum, the enriched nonstereotypic mice exhibited significantly more BDNF than the enriched stereotypic, the standard cage nonstereotypic, or the standard cage stereotypic mice. There were no differences in NGF in the striatum. These results provide evidence that the enrichment-related prevention of stereotyped behavior in deer mice is associated with increased BDNF in the striatum.

Release of BDNF and GABA in the dorsal horn of neuropathic rats

Damage to peripheral nerves is associated with changes in excitability and/or phenotype of primary afferent neurons as well as increased neuronal excitability (central sensitization) and reduced inhibitory tone in the dorsal horn. For instance, in dorsal root ganglia (DRG) brain derived neurotrophic factor (BDNF) is down-regulated in small cells whilst de novo expressed in large diameter cells. In the dorsal horn, GABA content is decreased. In this study, in a dorsal horn, 'with dorsal roots attached' preparation obtained from spinal nerve lesioned Wistar rats, stimulation of ipsilateral dorsal roots at either A fibre or A + C fibre strength did not evoke release of BDNF. In separate experiments, activity-induced release of GABA in the isolated dorsal horn of neuropathic rats was significantly reduced compared to release in sham operated rats. GABA release could be significantly restored following topical application of BDNF through the dorsal horn preparation. Finally, neuropathic rats developed thermal and mechanical hypersensitivity and thermal hyperalgesia was reduced by intrathecal injection of BDNF. We concluded that BDNF-induced release of GABA could be a mechanism to explain the antinociceptive action of intrathecal BDNF in neuropathic animals. Furthermore, reduced availability of sensory neuron-derived BDNF might contribute to the reduced GABAergic tone in the dorsal horn of neuropathic rats.

Effects of chronic exercise and imipramine on mRNA for BDNF after olfactory bulbectomy in rat

We examined the effects of chronic activity wheel running and antidepressant treatment on brain-derived neurotrophic factor (BDNF) messenger RNA (mRNA) in multiple brain regions-hippocampal formation (HF), ventral tegmental area/substantia nigra (VTA/SN), nucleus accumbens (NAc), and piriform cortex (PFx)-after bilateral olfactory bulbectomy (OBX). Male, Long-Evans rats (n=72) underwent either sham or OBX surgery and were randomly divided into eight experimental groups in a 2 (sham vs. OBX) x 2 (sedentary vs. activity wheel)x2 (saline vs. imipramine) factorial design. Animals were killed after 21 days of treatment. Drug x exercise interaction effects were observed for HF (P=0.006-0.023) and VTA/SN (P=0.021); exercise increased BDNF mRNA in the saline treated animals but not in the imipramine treated animals. OBX did not affect BDNF mRNA in the HF or VTA/SN (P>0.05). BDNF mRNA levels in the PFx were not altered by exercise, drug, or OBX (P>0.05). These results suggest that the effect of exercise on BDNF mRNA extends beyond the HF to the mesolimbic ventral tegmental area and that the potentiation of BDNF mRNA by exercise and antidepressant pharmacotherapy, reported by other investigators, is time limited.

Enhancing neuronal plasticity and cellular resilience to develop novel, improved therapeutics for difficult-to-treat depression

There is growing evidence from neuroimaging and ostmortem studies that severe mood disorders, which have traditionally been conceptualized as neurochemical disorders, are associated with impairments of structural plasticity and cellular resilience. It is thus noteworthy that recent preclinical studies have shown that critical molecules in neurotrophic signaling cascades (most notably cyclic adenosine monophosphate [cAMP] response element binding protein, brain-derived neurotrophic factor, bcl-2, and mitogen activated protein [MAP] kinases) are long-term targets for antidepressant agents and antidepressant potentiating modalities. This suggests that effective treatments provide both trophic and neurochemical support, which serves to enhance and maintainnormal synaptic connectivity, thereby allowing the chemical signal to reinstate the optimal functioning of critical circuits necessary for normal affective functioning. For many refractory patients, drugs mimicking "traditional" strategies, which directly or indirectly alter monoaminergic levels, may be of limited benefit. Newer "plasticity enhancing" strategies that may have utility in the treatment of refractory depression include N-methyl-D-aspartate antagonists, alpha-amino-3-hydroxy-5-methylisoxazole propionate (AMPA) potentiators, cAMP phosphodiesterase inhibitors, and glucocorticoid receptor antagonists. Small-molecule agents that regulate the activity f growth factors, MAP kinases cascades, and the bcl-2 family of proteins are also promising future avenues. The development of novel, nonaminergic-based therapeutics holds much promise for improved treatment of severe, refractory mood disorders.

Signalling pathways involved in the short-term potentiation of dopamine release by BDNF

Brain-derived neurotrophic factor (BDNF) has been shown to modulate synaptic plasticity in the corpus striatum in vitro by activation of the tyrosine kinase linked receptor, TrkB. However, the signalling pathways that mediate this modulation of plasticity are poorly understood. Three proteins mediating signalling pathways are activated by the binding of BDNF to TrkB: phosphoinositol-3 kinase (PI3K); Ras-MEK and phospholipase C-gamma (PLCgamma). The present study investigates which of these pathways are necessary for BDNF-mediated potentiation of synaptic output of dopamine from slices and synaptosomes of rat corpus striatum. The results indicate that activation of the PI3K and Ras-MEK pathways, but not PLCgamma, are involved. Inhibitors of transcription and translation had no effect on the potentiation of depolarisation-stimulated (15 mM KCl) dopamine release mediated by BDNF.

The control of [125I]BDNF release from striatal rat brain slices

The depolarisation-induced release of brain-derived neurotrophic factor (BDNF) from adult rat striatal slices was studied in vitro. The slices were preloaded with [125I]BDNF and exposed to depolarising stimulation with varying concentrations of veratrine (up to 50 microM) and potassium (up to 50 mM) which caused activity-dependent short-term release of [125I]BDNF. The results indicate that this stimulated release of [125I]BDNF is not regulated by a feedback mechanism mediated via the TrkB receptor. The release of [125I]BDNF was found to be dependent on the concentrations of both extracellular and intracellular calcium, since BDNF release was modulated by the addition of both EGTA and BAPTA-AM, agents chelating either external or internal Ca(2+), respectively. BDNF release also proved to be dependent on activation of IP(3) mediated Ca(2+) release from intracellular stores. [125I]BDNF release was also modulated by 5HT(3) receptor ligands and by receptors coupled to adenylate cyclase. Taken together, these results indicate that [125I]BDNF release is activity dependent, and is modulated by changes in Ca(2+) levels. Moreover the release occurs via a mechanism involving cAMP.