Brain-derived neurotrophic factor and neurotrophin-3 mRNAs are expressed in ventral midbrain regions containing dopaminergic neurons

Indirect influence on the BDNF/TrkB receptor signaling pathway via GPCRs, an emerging strategy in the treatment of neurodegenerative disorders

Neuronal survival depends on neurotrophins and their receptors. There are two types of neurotrophin receptors: a nonenzymatic, trans-membrane protein of the tumor necrosis factor receptor (TNFR) family-p75 receptor and the tyrosine kinase receptors (TrkR) A, B, and C. Activation of the TrkBR by brain-derived neurotrophic factor (BDNF) or neurotrophin 4/5 (NT-4/5) promotes neuronal survival, differentiation, and synaptic function. It is shown that in the pathogenesis of several neurodegenerative conditions (Alzheimer's disease, Parkinson's disease, Huntington's disease) the BDNF/TrkBR signaling pathway is impaired. Since it is known that GPCRs and TrkR are regulating several cell functions by interacting with each other and generating a cross-communication in this review we have focused on the interaction between different GPCRs and their ligands on BDNF/TrkBR signaling pathway.

Morphogenetic theory of mental and cognitive disorders: the role of neurotrophic and guidance molecules

Mental illness and cognitive disorders represent a serious problem for the modern society. Many studies indicate that mental disorders are polygenic and that impaired brain development may lay the ground for their manifestation. Neural tissue development is a complex and multistage process that involves a large number of distant and contact molecules. In this review, we have considered the key steps of brain morphogenesis, and the major molecule families involved in these process. The review provides many indications of the important contribution of the brain development process and correct functioning of certain genes to human mental health. To our knowledge, this comprehensive review is one of the first in this field. We suppose that this review may be useful to novice researchers and clinicians wishing to navigate the field.

Differential expression of RET and GDNF family receptor, GFR-α1, between striatum and substantia nigra following nigrostriatal lesion: a case for diminished GDNF-signaling

Although glial cell line-derived neurotrophic factor (GDNF) showed efficacy in preclinical and early clinical studies to alleviate parkinsonian signs in Parkinson's disease (PD), later trials did not meet primary endpoints, giving pause to consider further investigation. While GDNF dose and delivery methods may have contributed to diminished efficacy, one crucial aspect of these clinical studies is that GDNF treatment across all studies began ∼8 years after PD diagnosis; a time point representing several years after near 100% depletion of nigrostriatal dopamine markers in striatum and at least 50% in substantia nigra (SN), and is later than the timing of GDNF treatment in preclinical studies. With nigrostriatal terminal loss exceeding 70% at PD diagnosis, we utilized hemi-parkinsonian rats to determine if expression of GDNF family receptor, GFR-α1, and receptor tyrosine kinase, RET, differed between striatum and SN at 1 and 4 weeks following a 6-hydroxydopamine (6-OHDA) lesion. Whereas GDNF expression changed minimally, GFR-α1 expression decreased progressively in striatum and in tyrosine hydroxylase positive (TH+) cells in SN, correlating with reduced TH cell number. However, in nigral astrocytes, GFR-α1 expression increased. RET expression decreased maximally in striatum by 1 week, whereas in the SN, a transient bilateral increase occurred that returned to control levels by 4 weeks. Expression of brain-derived neurotrophic factor (BDNF) or its receptor, TrkB, were unchanged throughout lesion progression. Together, these results reveal that differential GFR-α1 and RET expression between the striatum and SN, and cell-specific differences in GFR-α1 expression in SN, occur during nigrostriatal neuron loss. Targeting loss of GDNF receptors appears critical to enhance GDNF therapeutic efficacy against nigrostriatal neuron loss.

Significance Statement

Although preclinical evidence supports that GDNF provides neuroprotection and improves locomotor function in preclinical studies, clinical data supporting its efficacy to alleviate motor impairment in Parkinson's disease patients remains uncertain. Using the established 6-OHDA hemi-parkinsonian rat model, we determined whether expression of its cognate receptors, GFR-α1 and RET, were differentially affected between striatum and substantia nigra in a timeline study. In striatum, there was early and significant loss of RET, but a gradual, progressive loss of GFR-α1. In contrast, RET transiently increased in lesioned substantia nigra, but GFR-α1 progressively decreased only in nigrostriatal neurons and correlated with TH cell loss. Our results indicate that direct availability of GFR-α1 may be a critical element that determines GDNF efficacy following striatal delivery.

Highlights

GDNF expression was minimally affected by nigrostriatal lesionGDNF family receptor, GFR-α1, progressively decreased in striatum and in TH neurons in SN.GFR-α1 expression decreased along with TH neurons as lesion progressedGFR-α1 increased bilaterally in GFAP+ cells suggesting an inherent response to offset TH neuron lossRET expression was severely reduced in striatum, whereas it increased in SN early after lesion induction.

Molecular and Functional Characterization of BDNF-Overexpressing Human Retinal Pigment Epithelial Cells Established by Sleeping Beauty Transposon-Mediated Gene Transfer

More and more patients suffer from multifactorial neurodegenerative diseases, such as age-related macular degeneration (AMD). However, their pathological mechanisms are still poorly understood, which complicates the development of effective therapies. To improve treatment of multifactorial diseases, cell-based gene therapy can be used to increase the expression of therapeutic factors. To date, there is no approved therapy for dry AMD, including late-stage geographic atrophy. We present a treatment option for dry AMD that transfers the brain-derived neurotrophic factor (BDNF) gene into retinal pigment epithelial (RPE) cells by electroporation using the plasmid-based Sleeping Beauty (SB) transposon system. ARPE-19 cells and primary human RPE cells were co-transfected with two plasmids encoding the SB100X transposase and the transposon carrying a BDNF transcription cassette. We demonstrated efficient expression and secretion of BDNF in both RPE cell types, which were further increased in ARPE-19 cell cultures exposed to hydrogen peroxide. BDNF-transfected cells exhibited lower apoptosis rates and stimulated neurite outgrowth in human SH-SY5Y cells. This study is an important step in the development of a cell-based BDNF gene therapy that could be applied as an advanced therapy medicinal product to treat dry AMD or other degenerative retinal diseases.

Similarities and differences between nigral and enteric dopaminergic neurons unravel distinctive involvement in Parkinson's disease

In addition to the well-known degeneration of midbrain dopaminergic neurons, enteric neurons can also be affected in neurodegenerative disorders such as Parkinson's disease (PD). Dopaminergic neurons have recently been identified in the enteric nervous system (ENS). While ENS dopaminergic neurons have been shown to degenerate in genetic mouse models of PD, analyses of their survival in enteric biopsies of PD patients have provided inconsistent results to date. In this context, this review seeks to highlight the distinctive and shared factors and properties that control the evolution of these two sets of dopaminergic neurons from neuronal precursors to aging neurons. Although their cellular sources and developmental times of origin differ, midbrain and ENS dopaminergic neurons express many transcription factors in common and their respective environments express similar neurotrophic molecules. For example, Foxa2 and Sox6 are expressed by both populations to promote the specification, differentiation, and long-term maintenance of the dopaminergic phenotype. Both populations exhibit sustained patterns of excitability that drive intrinsic vulnerability over time. In disorders such as PD, colon biopsies have revealed aggregation of alpha-synuclein in the submucosal plexus where dopaminergic neurons reside and lack blood barrier protection. Thus, these enteric neurons may be more susceptible to neurotoxic insults and aggregation of α-synuclein that spreads from gut to midbrain. Under sustained stress, inefficient autophagy leads to neurodegeneration, GI motility dysfunction, and PD symptoms. Recent findings suggest that novel neurotrophic factors such as CDNF have the potential to be used as neuroprotective agents to prevent and treat ENS symptoms of PD.

ERRγ ligand HPB2 upregulates BDNF-TrkB and enhances dopaminergic neuronal phenotype

Brain derived neurotrophic factor (BDNF) promotes maturation of dopaminergic (DAergic) neurons in the midbrain and positively regulates their maintenance and outgrowth. Therefore, understanding the mechanisms regulating the BDNF signaling pathway in DAergic neurons may help discover potential therapeutic strategies for neuropsychological disorders associated with dysregulation of DAergic neurotransmission. Because estrogen-related receptor gamma (ERRγ) is highly expressed in both the fetal nervous system and adult brains during DAergic neuronal differentiation, and it is involved in regulating the DAergic neuronal phenotype, we asked in this study whether ERRγ ligand regulates BDNF signaling and subsequent DAergic neuronal phenotype. Based on the X-ray crystal structures of the ligand binding domain of ERRγ, we designed and synthesized the ERRγ agonist, (E)-4-hydroxy-N'-(4-(phenylethynyl)benzylidene)benzohydrazide (HPB2) (K_d value, 8.35 μmol/L). HPB2 increased BDNF mRNA and protein levels, and enhanced the expression of the BDNF receptor tropomyosin receptor kinase B (TrkB) in human neuroblastoma SH-SY5Y, differentiated Lund human mesencephalic (LUHMES) cells, and primary ventral mesencephalic (VM) neurons. HPB2-induced upregulation of BDNF was attenuated by GSK5182, an antagonist of ERRγ, and siRNA-mediated ERRγ silencing. HPB2-induced activation of extracellular-signal-regulated kinase (ERK) and phosphorylation of cAMP-response element binding protein (CREB) was responsible for BDNF upregulation in SH-SY5Y cells. HPB2 enhanced the DAergic neuronal phenotype, namely upregulation of tyrosine hydroxylase (TH) and DA transporter (DAT) with neurite outgrowth, both in SH-SY5Y and primary VM neurons, which was interfered by the inhibition of BDNF-TrkB signaling, ERRγ knockdown, or blockade of ERK activation. HPB2 also upregulated BDNF and TH in the striatum and induced neurite elongation in the substantia nigra of mice brain. In conclusion, ERRγ activation regulated BDNF expression and the subsequent DAergic neuronal phenotype in neuronal cells. Our results might provide new insights into the mechanism underlying the regulation of BDNF expression, leading to novel therapeutic strategies for neuropsychological disorders associated with DAergic dysregulation.

Neuroprotective Effects of Filgrastim in Rotenone-Induced Parkinson's Disease in Rats: Insights into its Anti-Inflammatory, Neurotrophic, and Antiapoptotic Effects

All current treatments of Parkinson's disease (PD) focus on enhancing the dopaminergic effects and providing symptomatic relief; however, they cannot delay the disease progression. Filgrastim, a recombinant methionyl granulocyte colony-stimulating factor, demonstrated neuroprotection in many neurodegenerative and neurological diseases. This study aimed to assess the neuroprotective effects of filgrastim in rotenone-induced rat model of PD and investigate the potential underlying mechanisms of filgrastim actions. The effects of two doses of filgrastim (20 and 40 μg/kg) on spontaneous locomotion, catalepsy, body weight, histology, and striatal dopamine (DA) content, as well as tyrosine hydroxylase (TH) and α-synuclein expression, were evaluated. Then, the effective dose was further tested for its potential anti-inflammatory, neurotrophic, and antiapoptotic effects. Filgrastim (40 μg/kg) prevented rotenone-induced motor deficits, weight reduction, striatal DA depletion, and histological damage. Besides, it significantly inhibited rotenone-induced decrease in TH expression and increase in α-synuclein immunoreactivity in the midbrains and striata of the rats. These effects were associated with reduction of rotenone-induced neuroinflammation, apoptosis, and brain-derived neurotrophic factor depletion. Collectively, these results suggest that filgrastim might be a good candidate for management of PD.

Cell-Mediated Delivery of Brain-Derived Neurotrophic Factor Enhances Dopamine Levels in an Mpp+ Rat Model of Substantia Nigra Degeneration

Brain-derived neurotrophic factor (BDNF) promotes the survival of fetal mesencephalic dopaminergic cells and protects dopaminergic neurons against the toxicity of MPP+ in vitro. Supranigral implantation of fibroblasts genetically engineered to secrete BDNF attenuates the loss of substantia nigra pars compacta (SNc) dopaminergic neurons associated with striatal infusion of MPP+ in the adult rat. Using this MPP+ rat model of nigral degeneration, we evaluated the neurochemical effects of supranigral, cell-mediated delivery of BDNF on substantia nigra (SN) dopamine (DA) content and turnover. Genetically engineered BDNF-secreting fibroblasts (~12 ng BDNF/24 h) were implanted dorsal to the SN 7 days prior to striatal MPP+ administration. The present results demonstrate that BDNF-secreting fibroblasts, as compared to control fibroblasts, enhance SN DA levels ipsilateral as well as contralateral to the graft without altering DA turnover. This augmentation of DA levels suggests that local neurotrophic factor delivery by genetically engineered cells may provide a therapeutic strategy for preventing neuronal death or enhancing neuronal function in neurodegenerative diseases characterized by dopaminergic neuronal dysfunction, such as Parkinson's disease.

The relationship of Chlamydophila pneumoniae with schizophrenia: The role of brain-derived neurotrophic factor (BDNF) and neurotrophin-3 (NT-3) in this relationship

Several pathogens have been suspected of playing a role in the pathogenesis of schizophrenia. Chronic inflammation has been proposed to occur as a result of persistent infection caused by Chlamydophila pneumoniae cells that reside in brain endothelial cells for many years. It was recently hypothesized that brain-derived neurotrophic factor (BDNF) and neurotrophin-3 (NT-3) may play prominent roles in the development of schizophrenia. NT-3 and BDNF levels have been suggested to change in response to various manifestations of infection. Therefore, we aimed to elucidate the roles of BDNF and NT3 in the schizophrenia-C. pneumoniae infection relationship. RT-PCR, immunofluorescence and ELISA methods were used. Fifty patients suffering from schizophrenia and 35 healthy individuals were included as the patient group (PG) and the healthy control group (HCG), respectively. We detected persistent infection in 14 of the 50 individuals in the PG and in 1 of the 35 individuals in the HCG. A significant difference was found between the two groups (p<0.05). Twenty-two individuals in the PG and 13 in the HCG showed seropositivity for past C. pneumoniae infection, and no difference was observed between the groups (p>0.05). C. pneumoniae DNA was not detected in any group. A significant difference in NT-3 levels was observed between the groups, with very low levels in the PG (p<0.001). A significant difference in BDNF levels was also found, with lower levels in the PG (p<0.05). The mean serum NT-3 level was higher in the PG cases with C. pneumoniae seropositivity than in seronegative cases; however, this difference was not statistically significant (p>0.05). In conclusion, we suggest that NT-3 levels during persistent C. pneumoniae infection may play a role in this relationship.

Neuroimmune Regulation of GABAergic Neurons Within the Ventral Tegmental Area During Withdrawal from Chronic Morphine

Opioid dependence is accompanied by neuroplastic changes in reward circuitry leading to a negative affective state contributing to addictive behaviors and risk of relapse. The current study presents a neuroimmune mechanism through which chronic opioids disrupt the ventral tegmental area (VTA) dopaminergic circuitry that contributes to impaired reward behavior. Opioid dependence was induced in rodents by treatment with escalating doses of morphine. Microglial activation was observed in the VTA following spontaneous withdrawal from chronic morphine treatment. Opioid-induced microglial activation resulted in an increase in brain-derived neurotrophic factor (BDNF) expression and a reduction in the expression and function of the K(+)Cl(-) co-transporter KCC2 within VTA GABAergic neurons. Inhibition of microglial activation or interfering with BDNF signaling prevented the loss of Cl(-) extrusion capacity and restored the rewarding effects of cocaine in opioid-dependent animals. Consistent with a microglial-derived BDNF-induced disruption of reward, intra-VTA injection of BDNF or a KCC2 inhibitor resulted in a loss of cocaine-induced place preference in opioid-naïve animals. The loss of the extracellular Cl(-) gradient undermines GABAA-mediated inhibition, and represents a mechanism by which chronic opioid treatments can result in blunted reward circuitry. This study directly implicates microglial-derived BDNF as a negative regulator of reward in opioid-dependent states, identifying new therapeutic targets for opiate addictive behaviors.

Modulation of schizophrenia-related genes in the forebrain of adolescent and adult rats exposed to maternal immune activation

Maternal immune activation (MIA) is an environmental risk factor for schizophrenia, and may contribute to other developmental disorders including autism and epilepsy. Activation of pro-inflammatory cytokine systems by injection of the synthetic double-stranded RNA polyriboinosinic-polyribocytidilic acid (Poly I:C) mediates important neurochemical and behavioral corollaries of MIA, which have relevance to deficits observed in schizophrenia. We examined the consequences of MIA on forebrain expression of neuregulin-1 (NRG-1), brain-derived neurotrophic factor (BDNF) and their receptors, ErbB4 and trkB, respectively, genes associated with schizophrenia. On gestational day 14, pregnant rats were injected with Poly I:C or vehicle. Utilizing in situ hybridization, expression of NRG-1, ErbB4, BDNF, and trkB was examined in male rat offspring at postnatal day (P) 14, P30 and P60. ErbB4 mRNA expression was significantly increased at P30 in the anterior cingulate (AC Ctx), frontal, and parietal cortices, with increases in AC Ctx expression continuing through P60. ErbB4 expression was also elevated in the prefrontal cortex (PFC) at P14. In contrast, NRG-1 mRNA was decreased in the PFC at P60. Expression of BDNF mRNA was significantly upregulated in the PFC at P60 and decreased in the AC Ctx at P14. Expression of trkB was increased in two regions, the piriform cortex at P14 and the striatum at P60. These findings demonstrate developmentally and regionally selective alterations in the expression of schizophrenia-related genes as a consequence of MIA. Further study is needed to determine contributions of these effects to the development of alterations of relevance to neuropsychiatric diseases.

Knockdown of ventral tegmental area mu-opioid receptors in rats prevents effects of social defeat stress: implications for amphetamine cross-sensitization, social avoidance, weight regulation and expression of brain-derived neurotrophic factor

Social defeat stress causes social avoidance and long-lasting cross-sensitization to psychostimulants, both of which are associated with increased brain-derived neurotrophic factor (BDNF) expression in the ventral tegmental area (VTA). Moreover, social stress upregulates VTA mu-opioid receptor (MOR) mRNA. In the VTA, MOR activation inhibits GABA neurons to disinhibit VTA dopamine neurons, thus providing a role for VTA MORs in the regulation of psychostimulant sensitization. The present study determined the effect of lentivirus-mediated MOR knockdown in the VTA on the consequences of intermittent social defeat stress, a salient and profound stressor in humans and rodents. Social stress exposure induced social avoidance and attenuated weight gain in animals with non-manipulated VTA MORs, but both these effects were prevented by VTA MOR knockdown. Rats with non-manipulated VTA MOR expression exhibited cross-sensitization to amphetamine challenge (1.0 mg/kg, i.p.), evidenced by a significant augmentation of locomotion. By contrast, knockdown of VTA MORs prevented stress-induced cross-sensitization without blunting the locomotor-activating effects of amphetamine. At the time point corresponding to amphetamine challenge, immunohistochemical analysis was performed to examine the effect of stress on VTA BDNF expression. Prior stress exposure increased VTA BDNF expression in rats with non-manipulated VTA MOR expression, while VTA MOR knockdown prevented stress-induced expression of VTA BDNF. Taken together, these results suggest that upregulation of VTA MOR is necessary for the behavioral and biochemical changes induced by social defeat stress. Elucidating VTA MOR regulation of stress effects on the mesolimbic system may provide new therapeutic targets for treating stress-induced vulnerability to substance abuse.

Neurotrophins in the ventral tegmental area: Role in social stress, mood disorders and drug abuse

This review discusses the impact of neurotrophins and other trophic factors, including fibroblast growth factor and glial cell line-derived neurotrophic factor, on mood disorders, weight regulation and drug abuse, with an emphasis on stress- and drug-induced changes in the ventral tegmental area (VTA). Neurotrophins, comprising nerve growth factor, brain-derived neurotrophic factor (BDNF), and neurotrophins 3 and 4/5 play important roles in neuronal plasticity and the development of different psychopathologies. In the VTA, most research has focused on the role of BDNF, because other neurotrophins are not found there in significant quantities. BDNF originating in the VTA provides trophic support to dopamine neurons. The diverse intracellular signaling pathways activated by BDNF may underlie precise physiological functions specific to the VTA. In general, VTA BDNF expression increases after psychostimulant exposures, and enhanced BDNF level in the VTA facilitates psychostimulant effects. The impact of VTA BDNF on the behavioral effects of psychostimulants relies primarily on its action within the mesocorticolimbic circuit. In the case of opiates, VTA BDNF expression and effects seem to be dependent on whether an animal is drug-naïve or has a history of drug use, only the latter of which is related to dopamine mechanisms. Social defeat stress that is continuous in mice or intermittent in rats increases VTA BDNF expression, and is associated with depressive and social avoidance behaviors. Intermittent social defeat stress induces persistent VTA BDNF expression that triggers psychostimulant cross-sensitization. Understanding the cellular and molecular substrates of neurotrophin effects may lead to novel therapeutic approaches for the prevention and treatment of substance use and mood disorders.

Primate adult brain cell autotransplantation produces behavioral and biological recovery in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-induced parkinsonian St. Kitts monkeys

The potential for "replacement cells" to restore function in Parkinson's disease has been widely reported over the past 3 decades, rejuvenating the central nervous system rather than just relieving symptoms. Most such experiments have used fetal or embryonic sources that may induce immunological rejection and generate ethical concerns. Autologous sources, in which the cells to be implanted are derived from recipients' own cells after reprogramming to stem cells, direct genetic modifications, or epigenetic modifications in culture, could eliminate many of these problems. In a previous study on autologous brain cell transplantation, we demonstrated that adult monkey brain cells, obtained from cortical biopsies and kept in culture for 7 weeks, exhibited potential as a method of brain repair after low doses of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) caused dopaminergic cell death. The present study exposed monkeys to higher MPTP doses to produce significant parkinsonism and behavioral impairments. Cerebral cortical cells were biopsied from the animals, held in culture for 7 weeks to create an autologous neural cell "ecosystem" and reimplanted bilaterally into the striatum of the same six donor monkeys. These cells expressed neuroectodermal and progenitor markers such as nestin, doublecortin, GFAP, neurofilament, and vimentin. Five to six months after reimplantation, histological analysis with the dye PKH67 and unbiased stereology showed that reimplanted cells survived, migrated bilaterally throughout the striatum, and seemed to exert a neurorestorative effect. More tyrosine hydroxylase-immunoreactive neurons and significant behavioral improvement followed reimplantation of cultured autologous neural cells as a result of unknown trophic factors released by the grafts.

Omega-3 deficiency and neurodegeneration in the substantia nigra: involvement of increased nitric oxide production and reduced BDNF expression

BACKGROUND

Our previous study demonstrated that essential fatty acid (EFA) dietary restriction over two generations induced midbrain dopaminergic cell loss and oxidative stress in the substantia nigra (SN) but not in the striatum of young rats. In the present study we hypothesized that omega-3 deficiency until adulthood would reduce striatum's resilience, increase nitric oxide (NO) levels and the number of BDNF-expressing neurons, both potential mechanisms involved in SN neurodegeneration.

METHODS

Second generation rats were raised from gestation on control or EFA-restricted diets until young or adulthood. Lipoperoxidation, NO content, total superoxide dismutase (t-SOD) and catalase enzymatic activities were assessed in the SN and striatum. The number of tyrosine hydroxylase (TH)- and BDNF-expressing neurons was analyzed in the SN.

RESULTS

Increased NO levels were observed in the striatum of both young and adult EFA-deficient animals but not in the SN, despite a similar omega-3 depletion (~65%) in these regions. Increased lipoperoxidation and decreased catalase activity were found in both regions, while lower tSOD activity was observed only in the striatum. Fewer TH- (~40%) and BDNF-positive cells (~20%) were detected at the SN compared to the control.

CONCLUSION

The present findings demonstrate a differential effect of omega-3 deficiency on NO production in the rat's nigrostriatal system. Prolonging omega-3 depletion until adulthood impaired striatum's anti-oxidant resources and BDNF distribution in the SN, worsening dopaminergic cell degeneration.

GENERAL SIGNIFICANCE

Omega-3 deficiency can reduce the nigrostriatal system's ability to maintain homeostasis under oxidative conditions, which may enhance the risk of Parkinson's disease.

Opiate exposure and withdrawal dynamically regulate mRNA expression in the serotonergic dorsal raphe nucleus

Previous results from our lab suggest that hypofunctioning of the serotonergic (5-HT) dorsal raphe nucleus (DRN) is involved in stress-induced opiate reinstatement. To further investigate the effects of morphine dependence and withdrawal on the 5-HT DRN system, we measured gene expression at the level of mRNA in the DRN during a model of morphine dependence, withdrawal and post withdrawal stress exposure in rats. Morphine pellets were implanted for 72h and then either removed or animals were injected with naloxone to produce spontaneous or precipitated withdrawal, respectively. Animals exposed to these conditions exhibited withdrawal symptoms including weight loss, wet dog shakes and jumping behavior. Gene expression for brain-derived neurotrophic factor (BDNF), tyrosine kinase receptor B (TrkB), corticotrophin releasing-factor (CRF)-R1, CRF-R2, alpha 1 subunit of the GABAA receptor (GABAA-α1), μ-opioid receptor (MOR), 5-HT1A receptor, tryptophan hydroxylase2 (TPH2) and the 5-HT transporter was then measured using quantitative real-time polymerase chain reaction at multiple time-points across the model of morphine exposure, withdrawal and post withdrawal stress. Expression levels of BDNF, TrkB and CRF-R1 mRNA were decreased during both morphine exposure and following 7days of withdrawal. CRF-R2 mRNA expression was elevated after 7days of withdrawal. 5-HT1A receptor mRNA expression was decreased following 3h of morphine exposure, while TPH2 mRNA expression was decreased after 7days of withdrawal with swim stress. There were no changes in the expression of GABAA-α1, MOR or 5-HT transporter mRNA. Collectively these results suggest that alterations in neurotrophin support, CRF-dependent stress signaling, 5-HT synthesis and release may underlie 5-HT DRN hypofunction that can potentially lead to stress-induced opiate relapse.

GDNF, NGF and BDNF as therapeutic options for neurodegeneration

Glial cell-derived neurotrophic factor (GDNF), and the neurotrophin nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF) are important for the survival, maintenance and regeneration of specific neuronal populations in the adult brain. Depletion of these neurotrophic factors has been linked with disease pathology and symptoms, and replacement strategies are considered as potential therapeutics for neurodegenerative diseases such as Parkinson's, Alzheimer's and Huntington's diseases. GDNF administration has recently been shown to be an effective treatment for Parkinson's disease, with clinical trials currently in progress. Trials with NGF for Alzheimer's disease are ongoing, with some degree of success. Preclinical results using BDNF also show much promise, although there are accompanying difficulties. Ultimately, the administration of a therapy involving proteins in the brain has inherent problems. Because of the blood-brain-barrier, the protein must be infused directly, produced by viral constructs, secreted from implanted protein-secreting cells or actively transported across the brain. An alternative to this is the use of a small molecule agonist, a modulator or enhancer targeting the associated receptors. We evaluate these neurotrophic factors as potential short or long-term treatments, weighing up preclinical and clinical results with the possible effects on the underlying neurodegenerative process.

(±)3,4-methylenedioxymethamphetamine ("ecstasy") treatment modulates expression of neurotrophins and their receptors in multiple regions of adult rat brain

(±)3,4-Methylenedioxymethamphetamine (MDMA), a widely used drug of abuse, rapidly reduces serotonin levels in the brain when ingested or administered in sufficient quantities, resulting in deficits in complex route-based learning, spatial learning, and reference memory. Neurotrophins are important for survival and preservation of neurons in the adult brain, including serotonergic neurons. In this study, we examined the effects of MDMA on the expression of brain-derived neurotrophic factor (BDNF) and neurotrophin-3 (NT-3) and their respective high-affinity receptors, tropomyosin receptor kinase (trk)B and trkC, in multiple regions of the rat brain. A serotonergic-depleting dose of MDMA (10 mg/kg × 4 at 2-hour intervals on a single day) was administered to adult Sprague-Dawley rats, and brains were examined 1, 7, or 24 hours after the last dose. Messenger RNA levels of BDNF, NT-3, trkB, and trkC were analyzed by using in situ hybridization with cRNA probes. The prefrontal cortex was particularly vulnerable to MDMA-induced alterations in that BDNF, NT-3, trkB, and trkC mRNAs were all upregulated at multiple time points. MDMA-treated animals had increased BDNF expression in the frontal, parietal, piriform, and entorhinal cortices, increased NT-3 expression in the anterior cingulate cortex, and elevated trkC in the entorhinal cortex. In the nigrostriatal system, BDNF expression was upregulated in the substantia nigra pars compacta, and trkB was elevated in the striatum in MDMA-treated animals. Both neurotrophins and trkB were differentially regulated in several regions of the hippocampal formation. These findings suggest a possible role for neurotrophin signaling in the learning and memory deficits seen following MDMA treatment.

NTS-Polyplex: a potential nanocarrier for neurotrophic therapy of Parkinson's disease

Nanomedicine has focused on targeted neurotrophic gene delivery to the brain as a strategy to stop and reverse neurodegeneration in Parkinson's disease. Because of improved transfection ability, synthetic nanocarriers have become candidates for neurotrophic therapy. Neurotensin (NTS)-polyplex is a "Trojan horse" synthetic nanocarrier system that enters dopaminergic neurons through NTS receptor internalization to deliver a genetic cargo. The success of preclinical studies with different neurotrophic genes supports the possibility of using NTS-polyplex in nanomedicine. In this review, we describe the mechanism of NTS-polyplex transfection. We discuss the concept that an effective neurotrophic therapy requires a simultaneous effect on the axon terminals and soma of the remaining dopaminergic neurons. We also discuss the future of this strategy for the treatment of Parkinson's disease.

FROM THE CLINICAL EDITOR

This review paper focuses on nanomedicine-based treatment of Parkinson's disease, a neurodegenerative condition with existing symptomatic but no curative treatment. Neurotensin-polyplex is a synthetic nanocarrier system that enables delivery of genetic cargo to dopaminergic neurons via NTS receptor internalization.

The TrkB-positive dopaminergic neurons are less sensitive to MPTP insult in the substantia nigra of adult C57/BL mice

Tyrosine kinase receptors TrkB and TrkC mediate neuroprotective effects of the brain-derived neurotrophic factor (BDNF) and neurotrophins in the dopaminergic nigro-striatal system, but it is obscure about their responses or expression changes in the injured substantia nigra under Parkinson's disease. In present study, immunofluorescence, Fluoro-Jade staining and laser scanning confocal microscopy were applied to investigate distribution and changes of TrkB and TrkC in the dopamine neurons of the substantia nigra by comparison of control and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) mouse model. It revealed that TrkB and TrkC-immunoreactivities were substantially localized in cytoplasm and cell membrane of the substantia nigra neurons of control adults. While neurons double-labeled with tyrosine hydroxylase (TH)/TrkB, or TH/TrkC were distributed in a large numbers in the substantia nigra of controls, they apparently went down at 36.2-65.7% of normal level, respectively following MPTP insult. In MPTP model, cell apoptosis or degeneration of nigral neurons were confirmed by caspase-3 and Fluoro-Jade staining. More interestingly, TH/TrkB-positive neurons survived more in cell numbers in comparison with that of TH/TrkC-positive ones in the MPTP model. This study has indicated that TrkB-containing dopamine neurons are less sensitive in the substantia nigra of MPTP mouse model, suggesting that specific organization of Trks may be involved in neuronal vulnerability to MPTP insult, and BDNF-TrkB signaling may play more important role in protecting dopamine neurons and exhibit therapeutic potential for Parkinson's disease.

Facioscapulohumeral muscular dystrophy: do neurotrophins play a role?

Although the molecular defect of facioscapulohumeral muscular dystrophy (FSHD) is well established and involves the contraction of the polymorphic 3.3 kb D4Z4 repeat on the subtelomeric region of chromosome 4q35, the pathologic effects of this deletion remain largely unknown. As a consequence, no specific treatment for FSHD is at present available. Thus, there is the need to explore new areas in an attempt to better characterize pathophysiological alterations in FSHD that might be useful for managing the disease. Neurotrophins (nerve growth factor, brain-derived neurotrophic factor, neurotrophin-3, and neurotrophin-4/5) are a class of proteins involved in the development, maintenance, and function of neurons of the peripheral and central nervous systems. In addition, neurotrophins and their RNAs are expressed in muscle, where they have a role in development and regeneration. In this article we put together the experimental evidence that indicates neurotrophins might be involved in the pathophysiology of FSHD and discuss the possible implications of this assumption.

Effect of CNTF on retinal ganglion cell survival in experimental glaucoma

PURPOSE

To assess the neuroprotective effect of virally mediated overexpression of ciliary-derived neurotrophic factor (CNTF) and brain-derived neurotrophic factor (BDNF) in experimental rat glaucoma.

METHODS

Laser-induced glaucoma was produced in one eye of 224 Wistar rats after injection of adenoassociated viral vectors (type 2) containing either CNTF, BDNF, or both, with saline-injected eyes and noninjected glaucomatous eyes serving as the control. IOP was measured with a hand-held tonometer, and semiautomated optic nerve axon counts were performed by masked observers. IOP exposure over time was adjusted in multivariate regression analysis to calculate the effect of CNTF and BDNF.

RESULTS

By multivariate regression, CNTF had a significant protective effect, with 15% less RGC axon death (P < 0.01). Both combined CNTF-BDNF and BDNF overexpression alone had no statistically significant improvement in RGC axon survival. By Western blot, there was a quantitative increase in CNTF and BDNF expression in retinas exposed to single viral vectors carrying each gene, but no increase with sequential injection of both vectors.

CONCLUSIONS

These data confirm that CNTF can exert a protective effect in experimental glaucoma. The reason for the lack of observed effect in the BDNF overexpression groups is unclear, but it may be a function of the level of neurotrophin expression achieved.

Decreased serum neurotrophin 3 in chronically medicated schizophrenic males

There is evidence that major psychiatric disorders such as schizophrenia (SZ) are associated with deregulation of synaptic plasticity with downstream alterations of neurotrophins. NT3 is an important neurotrophin in the central nervous system, and performs key biological functions, such as promoting the survival, differentiation, and plasticity of neurons. NT3 has a central role in the early neuronal development; enhancing the survival of dopaminergic neurons, suggesting possible involvement in the physiopathology of dopamine related neuropsychiatric disorders such as SZ. Variations in the NT3 gene increase the risk of SZ. Three groups of chronically medicated DSM-IV patients with SZ, on treatment with clozapine (n=12), haloperidol (n=12), risperidone (n=12) and 10 healthy controls had 5 ml blood samples collected by venipuncture. NT3 serum levels were assessed using sandwich-ELISA and were significantly lower in SZ patients (p<0.005) when compared to either controls. These findings suggest that the NT3 signaling system may play a role in the pathophysiology of SZ and might be related to the course of illness or to treatment variables. Longitudinal studies are warranted.

Developmental expression of neurotrophins and their receptors in postnatal rat ventral midbrain

Neurotrophins are a group of structurally related polypeptides that support the survival, differentiation, and maintenance of neuronal populations that express the appropriate high-affinity neurotrophin receptors. Two members of the neurotrophin family, brain-derived neurotrophic factor (BDNF) and neurotrophin-3 (NT-3), have been shown to increase the survival of dopaminergic neurons from the ventral midbrain in vitro. Evidence suggests that ventral midbrain neurons might be able to derive support from these trophic factors in vivo through paracrine or autocrine interactions. Both BDNF and NT-3 mRNAs and their receptor mRNAs, trkB and trkC mRNAs, respectively, have been localized to the ventral mesencephalon. However, the relative expression levels of the neurotrophins and their receptor mRNAs throughout ontogeny and in adulthood have not been elucidated. In the present study, the postnatal developmental expression of BDNF, NT-3, trkB, and trkC mRNAs was analyzed via in situ hybridization to gain insight into the possible roles of these factors in vivo. We found that there was a developmental decline in the expression of BDNF and NT-3 mRNAs in the ventral mesencephalon. In contrast, no alterations in the expression of midbrain trkB or trkC mRNAs could be discerned. The present results suggest a role for BDNF and NT-3 in the earlier postnatal developmental events of responsive populations. The continued, albeit lower, expression of the neurotrophins in the ventral mesencephalon in adulthood also suggests a role for these factors in mature neuronal systems.

The possible role of neurotrophins in the pathogenesis and therapy of schizophrenia

The pathogenesis of schizophrenia may be ascribed to early maldevelopment of brain tissue. Neurotrophins are a group of dimeric proteins that affect the development of the nervous system in all vertebrates' species. Since neurotrophins, as well as other growth factors, play a crucial role in neurodevelopment, they are plausible candidates of taking part in the pathophysiology of schizophrenia. In line with this hypothesis, accumulating preclinical and clinical data indicate that dysfunctions of nerve growth factor (NGF), brain derived neurotrophic factor (BDNF) and neurotrophin-3 (NT-3) may contribute to impaired brain development, neuroplasticity and synaptic "dysconnectivity" leading to the schizophrenic syndrome, or at least some of its presentations. This article reviews the functions of neurotrophins in the complex process of normal brain development, and their possible relevance to the neuropathology and neuropharmacology of schizophrenia. Further research in this area may bring about novel pharmacological therapeutic strategies to this chronic debilitating disorder.

Endogenous brain-derived neurotrophic factor protects dopaminergic nigral neurons against transneuronal degeneration induced by striatal excitotoxic injury

Injury to the central nervous system causes atrophy or death of connecting neurons and can modify the expression of neurotrophic factors. We observed transneuronal upregulation of brain-derived neurotrophic factor (BDNF) expression in the rat ipsilateral substantia nigra pars compacta after a striatal lesion induced by kainate. This effect is developmentally regulated because the enhancement of nigral BDNF expression was only observed when striatal lesion was performed on postnatal day (P) 15 and in adulthood, but not at P7. Interestingly, the lack of regulation of BDNF was coincident with the transynaptic degeneration of nigral neurons after striatal excitotoxic injury. Hence, the number of tyrosine hydroxylase-positive neurons in the substantia nigra pars compacta decreased when the lesion was performed at P7, but not at P15 or at P30. The analysis of the functional significance of this BDNF upregulation was done using trkB-IgG fusion proteins. After striatal injury, blockade of endogenous BDNF by trkB fusion proteins induced an atrophy of the dopaminergic neurons of the pars compacta. The injection of trkB-IgG fusion proteins did not modify the effects of kainate in the substantia nigra pars reticulata. Thus, our results show that BDNF exerts an autocrine/paracrine protective effect selectively on dopaminergic neurons against the loss of trophic support from the target striatum.

Factors promoting survival of mesencephalic dopaminergic neurons

Growth factors promoting survival of mesencephalic dopaminergic neurons are discussed in the context of their requirement during development and adulthood. The expression of growth factors should be detectable in the nigrostriatal system during critical periods of development, i.e., during the period of ontogenetic cell death and synaptogenesis and during neurite extension and neurotransmitter synthesis. Growth factors discussed include members of the family of glial-cell-line-derived neurotrophic factors (GDNF), neurotrophins, transforming growth factors beta, and low molecular compounds mimicking growth factor activities. To date, the available data support the notion that GDNF is a highly promising candidate, although GDNF-null mice lack a dopaminergic phenotype. There remains a possibility that endogenous dopaminotrophic factors remain to be discovered.

Alterations in the expressions of mRNA for GDNF and its receptors in the ventral midbrain of rats exposed to subchronic phencyclidine

Phencyclidine (PCP) produces schizophrenia-like symptoms in normal humans. This suggests that the dysfunction of glutamatergic neurotransmission may play an important role in the pathology of schizophrenia. However, PCP also exerts its effect on the mesolimbic dopamine (DA) system and modulates DA function in the brain, the abnormality of which is proposed to be a main pathology of schizophrenia. Recently, glial cell-line derived neurotrophic factor (GDNF) has been shown to play a protective role for DA neurons against neurotoxic injuries and maintaining DA function in the brain. We hypothesized that subchronic PCP may alter the function of GDNF in the ventral midbrain, where DA cell bodies are localized. Male Wistar rats were injected intraperitoneally with PCP daily for 10 days at 5 or 10 mg/kg, and their brains were removed 24 h after the last injection. The expressions of GDNF and its receptor (GFRalpha-1 and c-ret) mRNAs in the substantia nigra compacta (SNC) and ventral tegmental area (VTA) were determined by non-radioactive in situ hybridization, and those of GDNF and c-ret mRNA were found to be increased after the PCP subchronic administration. No significant changes, however, were observed in the expressions of GFRalpha-1 and basic fibroblast growth factor. These results suggest that subchronic PCP may modulate the function of the GDNF system, which exerts a trophic action on DA neurons in the ventral midbrain.

Integrins regulate neuronal neurotrophin gene expression through effects on voltage-sensitive calcium channels

Integrin adhesion receptors regulate gene expression during growth and differentiation in various cell types. Recent work, implicating integrins in functional synaptic plasticity, suggest they may have similar activities in adult brain. The present study tested if integrins binding the arginine-glycine-aspartate (RGD) matrix sequence regulate neurotrophin and neurotrophin receptor gene expression in cultured hippocampal slices. The soluble RGD-containing peptide glycine-arginine-glycine-aspartate-serine-proline (GRGDSP) increased neurotrophin mRNA levels in transcript- and subfield-specific fashions. Integrin ligand effects were greatest for brain-derived neurotrophic factor transcripts I and II and barely detectable for transcript III. In accordance with increased nerve growth factor mRNA levels, GRGDSP increased c-fos expression as well. In contrast, growth-associated protein-43, amyloid precursor protein and fibroblast growth factor-1 mRNAs were not elevated. Ligand effects on brain-derived neurotrophic factor transcript II and c-fos mRNA did not depend on the integrity of the actin cytoskeleton, neuronal activity, or various signaling pathways but were blocked by L-type voltage-sensitive calcium-channel blockers. These results indicate that in mature hippocampal neurons integrin engagement regulates expression of a subset of growth-related genes at least in part through effects on calcium influx. Accordingly, these synaptic adhesion receptors may play the same role in maintaining an adult, differentiated state in brain as they do in other tissues and changes in integrin activation and/or engagement may contribute to dynamic changes in neurotrophin expression and to neuronal calcium signaling.

Neutralization of neutrophin-3 in the ventral tegmental area or nucleus accumbens differentially modulates cocaine-induced behavioral plasticity in rats

These experiments were designed to assess the influence of neurotrophin-3 (NT-3) and brain-derived neurotrophic factor (BDNF) in the mesoaccumbens dopamine system on the initiation of behavioral sensitization to cocaine. A neutralizing antibody for NT-3, BDNF or their vehicle was administered into the ventral tegmental area (VTA) or nucleus accumbens prior to each of four daily injections of 15 mg/kg cocaine. Behavioral sensitization was operationally defined as a significant increase in the behavioral response to cocaine relative to the first daily injection. Results indicated that the NT-3 antibody had differential effects when administered into the VTA or nucleus accumbens. Intra-VTA microinjection of anti-NT-3 resulted in enhanced sensitization to repeated cocaine injections in that the cocaine-induced behavioral response in the anti-NT-3 group was significantly greater than the vehicle group following the second and third daily injections of cocaine. Administration of anti-NT-3 into the nucleus accumbens increased the behavioral response to cocaine over all 4 days of cocaine administration, with no sensitization of this behavioral response. In contrast, pretreatment with anti-BDNF into the VTA or nucleus accumbens had no influence on the initiation of behavioral sensitization to cocaine. Taken together, these data indicate that neutralization of NT-3 in the VTA enhances cocaine-induced behavioral sensitization, while administration of the NT-3 antibody into the nucleus accumbens increases the hyperactive behavioral response induced by cocaine but impairs the further development of behavioral sensitization.

Models of repair mechanisms for future treatment modalities of Parkinson's disease

Parkinson's disease is one of the most likely neurological disorders to be fully treatable by drugs and new therapeutic modalities. The age-dependent and multifactorial nature of its pathogenesis allows for many strategies of intervention and repair. Most data indicate that the selectively vulnerable dopaminergic neurons in the substantia nigra of patients that have developed Parkinson's disease can be modified by protective and reparative therapies. First, the oxidative stress, protein abnormalities, and cellular inclusions typically seen could be dealt with by anti-oxidants, trophic factors, and proteolytic enhancements. Secondly, if the delay of degeneration is not sufficient, then immature dopamine neurons can be placed in the parkinsonian brain by transplantation. Such neurons can be derived from stem cell sources or even stimulated to repair from endogenous stem cells. Novel molecular and cellular treatments provide new tools to prevent and alleviate Parkinson's disease.

Embryonic ventral mesencephalic grafts to the substantia nigra of MPTP-treated monkeys: feasibility relevant to multiple-target grafting as a therapy for Parkinson's disease

Transplantation of embryonic dopamine (DA) neurons is being studied as an experimental replacement therapy for the DA-deficiency characteristic of Parkinson's disease. Some studies suggest that one of the limitations of this approach is that intrastriatal placement of implants fails to consistently restore completely normal movement. One potential cause of this suboptimal therapeutic outcome is that changes in the neural activity of several structures in the basal ganglia circuitry resulting from striatal DA depletion is not adequately normalized by graft-derived DA replacement in striatum alone. In the present study, we assessed the feasibility of grafting embryonic DA neurons into the substantia nigra (SN) of adult parkinsonian monkeys as an approach to restoration of the DA modulation of striatal-nigral afferents that is lost after degeneration of SN neurons. Sixteen St. Kitts African green monkeys treated with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) received implants of embryonic monkey ventral mesencephalon (VM), or sham implants, aimed at the rostral SN. At 6 months after grafting, staining for tyrosine hydroxylase (TH) indicated that grafted DA neurons survived at this site, albeit often in reduced numbers compared with VM grafts to striatum. Grafted neurons extended neurites into the parenchyma of the SN, but there was no evidence of lengthy extension of graft-derived neurites rostrally along the trajectory of the mesostriatal fiber system. A region-specific, modest increase in DA levels and TH-positive fiber density in the ventral-medial putamen was detected, accompanied by modest but significant decreases in parkinsonian behaviors at 5-6 months after grafting. Our findings support the view that grafting embryonic tissue to the SN is a feasible procedure in nonhuman primates that provides a modest but detectable benefit of its own. These results encourage the further development of multiple-target grafting strategies as a means of restoring modulation of anatomically widespread basal ganglia structures relevant to treatment of Parkinson's disease.

The role of neurotrophic factors in psychostimulant-induced behavioral and neuronal plasticity

Several neurotrophic factors influence the development, maintenance and survival of dopaminergic neurons in the mammalian central nervous system (CNS), including neurotrophin-3 (NT-3), brain derived neurotrophic factor (BDNF), ciliary neurotrophic factor (CNTF), basic fibroblast growth factor (bFGF) and glial derived neurotrophic factor (GDNF). This review focuses on the role of these neurotrophic factors in psychostimulant-induced behavioral sensitization, a form of dopamine-mediated neuronal plasticity that models aspects of paranoid schizophrenia as well as drug craving among psychostimulant addicts. Whereas NT-3, CNTF and bFGF appear to play a positive role in psychostimulant-induced behavioral sensitization, GDNF inhibits this form of behavioral plasticity. The role of BDNF in behavioral sensitization, however, remains elusive. While it has been shown that neurotrophic factors can influence the behavioral, structural and biochemical phenomena related to psychostimulant-induced neuronal plasticity, it is unclear which neurotrophic factors are important physiologically and which have purely pharmacological effects. In either case, examining the role of neurotrophic factors in behavioral sensitization may enhance our understanding of the mechanisms underlying the development of paranoid psychosis and drug craving and lead to the development of novel pharmacological treatments for these disorders.

Arrival of afferents and the differentiation of target neurons: studies of developing cholinergic projections to the dentate gyrus

This study examined the relationship between the development of cholinergic axons originating from the septum and a group of their target cells, the granule cells of the dentate gyrus of the rat. Acetylcholinesterase histochemistry was used to identify septal cholinergic afferents to the dentate gyrus; parallel studies used anterograde movement of a carbocyanine dye to label the septal projections. Septal cholinergic axons are present in the molecular layer of the internal blade of the dentate gyrus shortly after birth, but these axons do not reach the external blade until several days later. Results demonstrate that acetylcholinesterase positive septal axons grow into the external blade of the dentate gyrus only after the recently generated granule cells have coalesced to form a clearly defined layer. Results from studies using in situ hybridization techniques demonstrate that dentate gyrus granule cells express messenger RNAs for brain derived neurotrophic factor and for neurotrophic factor 3 shortly after formation of the granule cell layer. Ingrowth of septal cholinergic axons follows two days after the formation of the external blade of the dentate gyrus and the expression of neurotrophin messenger RNAs by the dentate granule cells. These data support the hypothesis that target cell development is a prerequisite for attracting the ingrowth of septal afferent axons.

Long-lasting induction of brain-derived neurotrophic factor is restricted to resistant cell populations in an animal model of status epilepticus

We have recently characterized an animal model of status epilepticus induced by a single intraseptal injection of kainate. Under these conditions, there is a delayed expanding apoptotic hippocampal and amygdalar cell death. In order to further characterize this animal model, we have performed a detailed time-course analysis of the appearance of cell death, brain-derived neurotrophic factor messenger RNA expression and astroglial and microglial response in different brain areas related to the limbic system. We found a long-lasting delayed apoptotic cell death in the hippocampal formation, amygdala, medial thalamus, dorsal endopiriform nucleus and multiple cortical areas from two to 21 days post-injection. There was a spatiotemporal correlation between the appearance of cell death and induction of brain-derived neurotrophic factor messenger RNA expression in the areas studied, and interestingly this induction was found in non-degenerating cells. We conclude that our animal model of status epilepticus exhibits remarkable features of recurrent seizure activity and provides evidence for a neuroprotective role of brain-derived neurotrophic factor against seizure-induced apoptotic cell death.

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.

Enhanced CREB phosphorylation in immature dentate gyrus granule cells precedes neurotrophin expression and indicates a specific role of CREB in granule cell differentiation

Differentiation and maturation of dentate gyrus granule cells requires coordinated interactions of numerous processes. These must be regulated by protein factors capable of integrating signals mediated through diverse signalling pathways. Such integrators of inter and intracellular physiological stimuli include the cAMP-response element binding protein (CREB), a leucine-zipper class transcription factor that is activated through phosphorylation. Neuronal activity and neurotrophic factors, known to be involved in granule cell differentiation, are major physiologic regulators of CREB function. To examine whether CREB may play a role in governing coordinated gene transcription during granule cell differentiation, we determined the spatial and temporal profiles of phosphorylated (activated) CREB throughout postnatal development in immature rat hippocampus. We demonstrate that CREB activation is confined to discrete, early stages of granule cell differentiation. In addition, CREB phosphorylation occurs prior to expression of the neurotrophins BDNF and NT-3. These data indicate that in a signal transduction cascade connecting CREB and neurotrophins in the process of granule cell maturation, CREB is located upstream of neurotrophins. Importantly, CREB may be a critical component of the machinery regulating the coordinated transcription of genes contributing to the differentiation of granule cells and their integration into the dentate gyrus network.

Influence of time in culture and BDNF pretreatment on survival and function of grafted embryonic rat ventral mesencephalon in the 6-OHDA rat model of Parkinson's disease

Embryonic midbrain can be maintained as free-floating roller tube cultures prior to grafting in experimental Parkinson's disease. We examined the influence of pregrafting culture time and pretreatment with brain-derived neurotrophic factor on graft survival and function. Cultures were prepared from solid pieces of embryonic (E14) rat ventral mesencephalon and maintained 4, 8, or 12 days in vitro with or without brain-derived neurotrophic factor (100 ng/ml) and grafted into the striatum of 6-hydroxydopamine-lesioned rats. Graft survival and function were evaluated by amphetamine-induced rotation behavior, number of tyrosine hydroxylase-immunoreactive neurons, striatal reinnervation, and graft volume. Rats receiving untreated tissue cultured for 4 or 8 days displayed no differences in graft quality, while grafts from 12-day-old cultures contained significantly fewer (P < 0.05) tyrosine hydroxylase-immunoreactive neurons (340 +/- 97, 267 +/- 92, and 62 +/- 19) and displayed a lower survival rate (9.6 +/- 2.7, 7.9 +/- 2.7, and 2.6 +/- 0.8% for 4, 8, and 12 days in vitro, respectively). Only rats grafted with 4- and 8-day-old cultures recovered significantly (P < 0.05) from lesion-induced rotations (69.4 +/- 18.6, 70.3 +/- 13.9, and 23.2 +/- 12.1% for 4, 8, and 12 days in vitro, respectively). Striatal reinnervation decreased with increasing culture time (P < 0.05). Pretreatment of the cultures with brain-derived neurotrophic factor affected only graft-induced fiber reinnervation, which was reduced even after short culture times. We therefore suggest that a storage period of 8 days is well suited to maintain embryonic rat ventral mesencephalon with the free-floating roller tube culture technique prior to transplantation. BDNF pretreatment as a new strategy to improve graft survival and function, however, was not effective.

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.

Reduced BDNF mRNA expression in the Parkinson's disease substantia nigra

Brain-derived neurotrophic factor (BDNF) has potent effects on survival and morphology of dopaminergic neurons and thus its loss could contribute to death of these cells in Parkinson's disease (PD). In situ hybridization revealed that BDNF mRNA is strongly expressed by dopaminergic neurons in control substantia nigra pars compacta (SNpc). In clinically and neuropathologically typical PD, SNpc BDNF mRNA expression is reduced by 70% (P = 0.001). This reduction is due, in part, to loss of dopaminergic neurons which express BDNF. However, surviving dopaminergic neurons in the PD SNpc also expressed less BDNF mRNA (20%, P = 0.02) than their normal counterparts. Moreover, while 15% of control neurons had BDNF mRNA expression >1 SD below the control mean, twice as many (28%) of the surviving PD SNpc dopaminergic neurons had BDNF mRNA expression below this value. This 13% difference in proportions (95% CI 8-17%, P < or = 0.000001) indicates the presence of a subset of neurons in PD with particularly low BDNF mRNA expression. Moreover, both control and PD neurons displayed a direct relationship between the density of BDNF mRNA expression per square micrometer of cell surface and neuronal size (r(2) = 0.93, P </= 0.00001) which was lost only in PD neurons expressing the lowest levels of BDNF mRNA. If BDNF is an autocrine/paracrine factor for SNpc dopaminergic neurons, loss of BDNF-expressing neurons may compromise the well-being of their surviving neighbors. Moreover, neurons expressing particularly low levels of BDNF mRNA may be those at greatest risk of injury in PD and possibly the trigger for the degeneration itself.

Increased cerebrospinal fluid levels of neurotrophin 3 (NT-3) in elderly patients with major depression

Neurotrophin 3 (NT-3) is a member of the neurotrophin gene family which supports the survival of specific neurons. NT-3 was shown to prevent the death of adult central noradrenergic neurons in vivo, a neuronal population which is associated with the pathophysiology of major depression. We quantitated CSF levels of NT-3 in elderly patients with major depression (DE) and compared them to patients with Alzheimer's disease (AD), and mentally healthy control subjects (CTR). CSF levels of NT-3 were markedly and significantly elevated in the DE group, as compared to either the AD or the CTR group (P < 0.01, and P < 0.001, respectively). In terms of diagnostic accuracy, measurement of NT-3 levels in DE resulted in 73.9% sensitivity, and 89.7% specificity. Increased CSF levels of NT-3 may indicate a disturbance of the central noradrenergic system in patients with DE. NT-3 may constitute a biochemical candidate marker for clinical diagnosis and for the evaluation of therapeutic strategies in DE.

Differential expression of neurotrophin and neurotrophin receptor mRNAs in and adjacent to fetal midbrain grafts implanted into the dopamine-denervated striatum

This study examined the expression of neurotrophins and neurotrophin receptors in the lesion/transplanted striatum at four different time points after transplantation. The ventral mesencephalic region was dissected from a single rat fetus at embryonic day 14 (E14) and implanted into the denervated striatum of rats with unilateral 6-hydroxydopamine lesions. Transplanted rats were killed at 1, 2, 3, or 4 weeks after transplantation surgery and the brains subsequently prepared for semiquantitative in situ hybridization analysis of neurotrophin and neurotrophin trk receptors. Hybridization of cRNA probes for trkB or trkC showed a time-dependent reduction within the transplant during the first 4 weeks after transplantation; hybridization of brain-derived neurotrophic factor or tyrosine hydroxylase mRNA probes within the transplant did not change significantly during the same posttransplantation period. Hybridization of the trkB mRNA probe in host striatum adjacent to the transplant was significantly higher than probe hybridization in the corresponding region of the intact striatum during the first 2 weeks after transplantation, but by the 3rd and 4th week, probe hybridization in the denervated/transplanted and intact striatum were the same. Lesioned animals without transplants maintained higher trkB mRNA probe hybridization in the denervated striatum than in the intact striatum at the same postlesion time points suggesting that lesioned/transplanted animals show a normalization of trkB mRNA probe hybridization. Hybridization of the trkC mRNA probe in the lesioned/transplanted striatum was significantly lower than that observed in the intact striatum 4 weeks after transplantation; however, at this same time point we observed a similar reduction of trkC probed hybridization in lesioned animals without transplants. The results of the study show dynamic neurotrophic activity occurring within the transplant and host tissue during the first month of transplant development.

Neurotrophins and development of the rod pathway: an elementary deduction

The rodent retina is a particularly attractive model for the study of neuronal developmental processes since considerable neurogenesis, cellular migration, phenotypic differentiation of retinal cell types and synaptogenesis occurs postnatally. In addition, the retina is readily accessible to surgical intervention, pharmacological manipulation, and local suppression of gene expression-tools that can be utilized to study mechanisms underlying the development of retinal neurons and their interconnections that form distinct functional circuits. Here, I review our studies describing the ontogeny of a specific retinal interneuron, the AII amacrine cell, an integral element in the rod (scotopic) pathway. Specifically, we used a number of approaches to examine the potential role of neurotrophic factors on the morphological and neurochemical differentiation of the AII.

Upregulation of BDNF mRNA and trkB mRNA in the nigrostriatal system and in the lesion site following unilateral transection of the medial forebrain bundle

We have performed unilateral transection of the medial forebrain bundle (MFB) and studied BDNF mRNA and trkB mRNA levels at different postlesion times in the nigrostriatal system by means of in situ hybridization. BDNF mRNA levels were transiently induced in the substantia nigra pars compacta at 1 day postaxotomy. The disposition of BDNF mRNA expressing cells at this postlesion time in substantia nigra mimicked that of the dopaminergic neurons expressing the mRNA for the dopamine transporter. TrkB mRNA levels remained unaltered in the ventral mesencephalon at the different postlesion times examined-1 to 14 days. In contrast, trkB mRNA levels were significantly induced in the striatum at the longer postlesion time examined-14 days-when all neurodegenerative events are completed. It is becoming apparent that nigral BDNF mRNA levels are anterogradely transported to its target tissue in striatum. However, following axotomy, the lesion site represents a second potential target for BDNF action. Consequently, we also analyzed the pattern of mRNA expression for BDNF and trkB at the lesion site where dopaminergic axons are disconnected. There, we found notable inductions of both BDNF mRNA and trkB mRNA levels at 4 days postaxotomy. BDNF mRNA expressing cells were confined at the site of axotomy, which coincided precisely to that showing induction of trkB mRNA. Altogether, our results anticipate promising trophic roles of BNDF in the injured nigrostriatal system.

Parvalbumin immunoreactivity is enhanced by brain-derived neurotrophic factor in organotypic cultures of rat retina

The rodent retina undergoes considerable postnatal neurogenesis and phenotypic differentiation, and it is likely that diffusible neurotrophic factors contribute to this development and to the subsequent formation of functional retinal circuitry. Accordingly, perturbation of specific neurotrophin ligand-receptor interactions has provided valuable information as to the fundamental processes underlying this development. In the present studies we have built upon our previous observation that suppression of expression of trk(B), the high-affinity receptor for brain-derived neurotrophic factor (BDNF), in the postnatal rat retina results in the alteration of a specific interneuron in the rod pathway-the parvalbumin (PV)-immunoreactive AII amacrine cell. Here, we isolated retinas from newborn rats and maintained them in organotypic culture for up to 14 days (approximating the time of eye opening, in vivo) in the presence of individual neurotrophins [BDNF or nerve growth factor (NGF)]. We then examined histological sections of cultures for PV immunoreactivity. In control cultures, only sparse PV-immunostained cells were observed. In cultures supplemented with NGF, numerous lightly immunostained somata were present in the inner nuclear layer (INL) at the border of the inner plexiform layer (IPL). Many of these cells had rudimentary dendritic arborizations in the IPL. Cultures supplemented with BDNF displayed numerous well-immunostained somata at the INL/IPL border that gave rise to elaborate dendritic arborizations that approximated the morphology of mature AII amacrine cells in vivo. These observations indicate that neurotrophins have specific effects upon the neurochemical and, perhaps, morphological differentiation of an important interneuron in a specific functional retinal circuit.

Neurotrophin-3 contributes to the initiation of behavioral sensitization to cocaine by activating the Ras/Mitogen-activated protein kinase signal transduction cascade

These experiments were designed to assess the role of neurotrophins and the Ras/mitogen-activated protein kinase (MAP) signal transduction cascade in behavioral sensitization to cocaine. The first experiments evaluated the effect of three daily intra-ventral tegmental area (VTA) microinjections of neurotrophin-3 (NT-3) or brain-derived neurotrophic factor (BDNF) on the behavioral-activating effects of a subsequent challenge injection of cocaine in rats. Results indicated that, although NT-3 did not influence behavior across the three microinjection days, animals displayed a sensitized behavioral response to the subsequent cocaine challenge injection. In contrast, BDNF microinjections resulted in a progressive increase in behavioral activity but did not influence the subsequent behavioral response to cocaine. A second series of experiments assessed the effect of inhibiting the MAP kinase signal transduction cascade on the initiation of behavioral sensitization to cocaine. The MAP kinase kinase inhibitor PD98059, or its vehicle, was microinjected into the VTA before three daily cocaine injections. Although PD98059 did not influence the acute behavioral response to cocaine, it blocked sensitization. Finally, the effects of acute and repeated cocaine injections on NT-3 and BDNF mRNA levels in the VTA, substantia nigra, and hippocampus were assessed. Results indicated that an acute cocaine injection resulted in a transient increase in NT-3 mRNA levels in the VTA. Collectively, these results suggest that NT-3 contributes to the initiation of behavioral sensitization to cocaine by activating the Ras/MAP kinase signal transduction system. The present data also indicate that BDNF itself produced a progressive augmentation in behavioral activation with repeated administration.

Serotonin hyperinnervation in the adult rat ventral mesencephalon following unilateral transection of the medial forebrain bundle. Correlation with reactive microglial and astroglial populations

We have previously studied changes in the serotoninergic and dopaminergic nigrostriatal systems following transection of the medial forebrain bundle and found a long-term axotomy-induced increase in the levels of serotonin and its main metabolite, 5-hydroxyindolacetic acid in substantia nigra [Venero et al. (1997) J. Neurochem. 68, 2458-2468]. In an attempt to find a rationale for this effect, we have performed an immunohistochemical study. Transection of the medial forebrain bundle of the rat interrupted most of the ascending serotoninergic pathways from the raphe nuclei as revealed by serotonin immunoreactivity. While serotonin immunostaining was almost absent in striatum, it doubled in the ventral mesencephalon at 21 days postlesion. This axotomy-induced increase was accompanied by an increased density of the serotonin nerve terminal network in the ipsilateral substantia nigra and ventral tegmental area. The increase in serotonin immunoreactivity was in line with the measured levels of serotonin and 5-hydroxyindolacetic acid in substantia nigra. In addition, the distribution pattern of glial fibrillary acidic protein-immunoreactive astrocytes and OX42-immunoreactive microglia correlated highly with the location of increased serotonin fibre density in the ventral mesencephalon, especially in ventral tegmental area and in the most medial part of substantia nigra. We suggest that a pruning effect may underly the axotomy-induced increase in serotonin immunoreactivity in the ventral mesencephalon, and further, that activated astroglia and microglia may play a role in directing serotoninergic axonal regeneration following axotomy.