Evaluation of nigrostriatal dopaminergic function in adult +/+ and +/- BDNF mutant mice

PLCγ1 in dopamine neurons critically regulates striatal dopamine release via VMAT2 and synapsin III

Dopamine neurons are essential for voluntary movement, reward learning, and motivation, and their dysfunction is closely linked to various psychological and neurodegenerative diseases. Hence, understanding the detailed signaling mechanisms that functionally modulate dopamine neurons is crucial for the development of better therapeutic strategies against dopamine-related disorders. Phospholipase Cγ1 (PLCγ1) is a key enzyme in intracellular signaling that regulates diverse neuronal functions in the brain. It was proposed that PLCγ1 is implicated in the development of dopaminergic neurons, while the physiological function of PLCγ1 remains to be determined. In this study, we investigated the physiological role of PLCγ1, one of the key effector enzymes in intracellular signaling, in regulating dopaminergic function in vivo. We found that cell type-specific deletion of PLCγ1 does not adversely affect the development and cellular morphology of midbrain dopamine neurons but does facilitate dopamine release from dopaminergic axon terminals in the striatum. The enhancement of dopamine release was accompanied by increased colocalization of vesicular monoamine transporter 2 (VMAT2) at dopaminergic axon terminals. Notably, dopamine neuron-specific knockout of PLCγ1 also led to heightened expression and colocalization of synapsin III, which controls the trafficking of synaptic vesicles. Furthermore, the knockdown of VMAT2 and synapsin III in dopamine neurons resulted in a significant attenuation of dopamine release, while this attenuation was less severe in PLCγ1 cKO mice. Our findings suggest that PLCγ1 in dopamine neurons could critically modulate dopamine release at axon terminals by directly or indirectly interacting with synaptic machinery, including VMAT2 and synapsin III.

Function of brain-derived neurotrophic factor in the hypothalamus: Implications for depression pathology

Depression is a prevalent mental health disorder and is the number one cause of disability worldwide. Risk factors for depression include genetic predisposition and stressful life events, and depression is twice as prevalent in women compared to men. Both clinical and preclinical research have implicated a critical role for brain-derived neurotrophic factor (BDNF) signaling in depression pathology as well as therapeutics. A preponderance of this research has focused on the role of BDNF and its primary receptor tropomyosin-related kinase B (TrkB) in the cortex and hippocampus. However, much of the symptomatology for depression is consistent with disruptions in functions of the hypothalamus including changes in weight, activity levels, responses to stress, and sociability. Here, we review evidence for the role of BDNF and TrkB signaling in the regions of the hypothalamus and their role in these autonomic and behavioral functions associated with depression. In addition, we identify areas for further research. Understanding the role of BDNF signaling in the hypothalamus will lead to valuable insights for sex- and stress-dependent neurobiological underpinnings of depression pathology.

Role of Mesolimbic Brain-Derived Neurotrophic Factor in Depression

Brain-derived neurotrophic factor (BDNF) is widely accepted as being critical for neural and synaptic plasticity throughout the nervous system. Recent work has shown that BDNF in the mesolimbic dopamine (DA) circuit, originating in ventral tegmental area DA neurons that project to the nucleus accumbens, is crucial in the development of depressive-like behaviors following exposure to chronic social defeat stress in mice. Whereas BDNF modulates DA signaling in encoding responses to acute defeat stress, BDNF signaling alone appears to be responsible for the behavioral effects after chronic social defeat stress. Very different patterns are seen with another widely used chronic stress paradigm in mice, chronic mild stress (also known as chronic variable or unpredictable stress), where DA signaling, but not BDNF signaling, is primarily responsible for the behavioral effects observed. This review discusses the molecular, cellular, and circuit basis of this dramatic discrepancy, which appears to involve the nature of the stress, its severity and duration, and its effects on distinct cell types within the ventral tegmental area-to-nucleus accumbens mesolimbic circuit.

Reduced Efficacy of d-Amphetamine and 3,4-Methylenedioxymethamphetamine in Inducing Hyperactivity in Mice Lacking the Postsynaptic Scaffolding Protein SHANK1

Genetic defects in the three SH3 and multiple ankyrin repeat domains (SHANK) genes (SHANK1, SHANK2, and SHANK3) are associated with multiple major neuropsychiatric disorders, including autism spectrum disorder (ASD), schizophrenia (SCZ), and bipolar disorder (BPD). Psychostimulant-induced hyperactivity is a commonly applied paradigm to assess behavioral phenotypes related to BPD and considered to be the gold standard for modeling mania-like elevated drive in mouse models. Therefore, the goal of our present study was to test whether Shank1 plays a role in the behavioral effects of psychostimulants and whether this is associated with genotype-dependent neurochemical alterations. To this aim, male and female null mutant Shank1^-/- mice were treated with d-amphetamine (AMPH; 2.5 mg/kg) and 3,4-methylenedioxymethamphetamine (MDMA, commonly known as ecstasy; 20 mg/kg), and psychostimulant-induced hyperactivity was compared to heterozygous Shank1^+/- and wildtype Shank1^+/+ littermate controls. Results show that Shank1^-/- mice display reduced psychostimulant-induced hyperactivity, although psychostimulants robustly stimulated locomotor activity in littermate controls. Shank1 deletion effects emerged throughout development, were particularly prominent in adulthood, and seen in response to both psychostimulants, i.e., AMPH and MDMA. Specifically, while AMPH-induced hyperactivity was reduced but still detectable in Shank1^-/- mice, MDMA-induced hyperactivity was robustly blocked and completely absent in Shank1^-/- mice. Reduced efficacy of psychostimulants to stimulate hyperactivity in Shank1^-/- mice might be associated with alterations in the neurochemical architecture in prefrontal cortex, nucleus accumbens, and hypothalamus. Our observation that psychostimulant-induced hyperactivity is reduced rather than enhanced in Shank1^-/- mice clearly speaks against a behavioral phenotype with relevance to BPD. Lack of BPD-like phenotype is consistent with currently available human data linking mutations in SHANK2 and SHANK3 but not SHANK1 to BPD.

Heterodimeric D1-D2 dopamine receptors: a review

This review summarizes modern data on the structure and functions ofheteromersformed by D1 and D2 dopamine receptors focusing on their role in the mechanisms of drug dependence. This article discusses potential functional significance of heterodimeric D1-D2 dopamine receptorsdue to their localization in the brain as well as unique pharmacological propertiesversus constituent monomers. It is shown that heteromerization results in dramatic changes in activated signaling pathways compare to the corresponding monomers. These studies update our current knowledge of ligand-receptor interactions and provide better understanding of dopamine receptors pharmacology. Furthermore elucidation of significance of heterodimeric D1-D2 dopamine receptors as drug targets is important for the development of new effective drug addiction treatment.

Diagnostic Accuracy of Brain-derived Neurotrophic Factor and Nitric Oxide in Patients with Schizophrenia: A pilot study

Background

Brain-derived neurotrophic factor (BDNF) and nitric oxide (NO) play multiple roles in the developing and adult CNS. Since BDNF and NO metabolisms are dysregulated in schizophrenia, we measured these markers simultaneously in the blood of schizophrenics and assessed their diagnostic accuracy.

Methods

Thirty-eight patients with schizophrenia classified according to demographic characteristics, symptomatologyand therapy and 39 age- and gender-matched healthy controls were enrolled. BDNF was determined by the ELISA technique while the concentration of nitrite/nitrate (NO2−/NO3−) was measured by the colorimetric method.

Results

Serum BDNF levels were significantly lower (20.38±3.73 ng/mL, P = 1.339E-05), whilst plasma NO2−/NO3− concentrations were significantly higher (84.3 (72–121) μmol/L, P=4.357E-08) in patients with schizophrenia than in healthy controls (25.65±4.32 ng/mL; 60.9 (50–76) μmol/L, respectively). The lowest value of BDNF (18.14±3.26 ng/mL) and the highest NO2−/NO3− concentration (115.3 (80–138) μmol/L) were found in patients treated with second-generation antipsychotics (SGA). The patients diseased before the age of 24 and the patients suffering for up to one year had significantly lower serum BDNF levels than those diseased after the age of 24 and the patients who were ill longer than one year. Both BDNF and NO2−/NO3− showed good diagnostic accuracy, but BDNF had better ROC curve characteristics, especially in patients with negative symptomatology.

Conclusions

BDNF and nitrite/nitrate showed inverse changes in schizophrenic patients. The most pronounced changes were found in patients treated with second-generation antipsychotics. Although BDNF is not specific of schizophrenia, it may be a clinically useful biomarker for the diagnosis of patients expressing predominantly negative symptoms.

BDNF-Deficient Mice Show Reduced Psychosis-Related Behaviors Following Chronic Methamphetamine

BACKGROUND

One of the most devastating consequences of methamphetamine abuse is increased risk of psychosis. Brain-derived neurotrophic factor has been implicated in both psychosis and neuronal responses to methamphetamine. We therefore examined persistent psychosis-like behavioral effects of methamphetamine in brain-derived neurotrophic factor heterozygous mice.

METHODS

Mice were chronically treated with methamphetamine from 6 to 9 weeks of age, and locomotor hyperactivity to an acute D-amphetamine challenge was tested in photocell cages after a 2-week withdrawal period.

RESULTS

Methamphetamine-treated wild-type mice, but not brain-derived neurotrophic factor heterozygous mice, showed locomotor sensitization to acute 3mg/kg D-amphetamine. Qualitative analysis of exploration revealed tolerance to D-amphetamine effects on entropy in methamphetamine-treated brain-derived neurotrophic factor heterozygous mice, but not wild-type mice.

CONCLUSIONS

Chronic methamphetamine exposure induces contrasting profiles of behavioral changes in wild-type and brain-derived neurotrophic factor heterozygous mice, with attenuation of behaviors relevant to psychosis in methamphetamine-treated brain-derived neurotrophic factor heterozygous mice. This suggests that brain-derived neurotrophic factor signalling changes may contribute to development of psychosis in methamphetamine users.

Effects of acute ethanol exposure on class I HDACs family enzymes in wild-type and BDNF(+/-) mice

BACKGROUND

Alterations of brain-derived neurotrophic factor (BDNF) have been associated with the development of addiction to different drugs of abuse, including ethanol (EtOH). EtOH exposure activates the BDNF-signaling cascade in dorsal striatum, which in turn affects further EtOH intake. Different alcohol exposures have been widely demonstrated to modulate chromatin remodeling, affecting histone acetylation/deacetylation balance. Recently, class I histone deacetylases (HDACs) inhibition has been reported to modulate BDNF mRNA expression and to attenuate morphological and behavioral phenomena related to EtOH exposure. However, the role played by different HDAC isoforms in EtOH-induced plasticity is still unclear.

METHODS

We investigated the effects induced by acute EtOH exposure on the protein levels of class I HDAC 1-3 isoforms of wild-type (WT) and BDNF heterozygous mice (BDNF(+/-)), in nuclear and cytoplasmic extracts of specific brain regions associated with EtOH addiction.

RESULTS

Nuclear HDAC 1-3 levels were markedly reduced after acute EtOH treatment in the caudate putamen (CPu) of WT mice only. Furthermore, CPu basal levels of nuclear HDAC isoforms were significantly lower in BDNF(+/-) mice compared to WT. With the exception of nuclear HDAC 3, no significant changes were observed after acute EtOH treatment in the prefrontal cortex (PFCx) of BDNF(+/-) and WT mice. In this area, the nuclear HDAC basal levels were significantly different between the two experimental groups.

CONCLUSIONS

These results provide details about EtOH effects on class I HDAC isoforms and strongly support a correlation between BDNF and class I HDACs, suggesting a possible influence of BNDF on these enzymes.

Maternal vitamin D deficiency alters fetal brain development in the BALB/c mouse

Prenatal exposure to vitamin D is thought to be critical for optimal fetal neurodevelopment, yet vitamin D deficiency is apparent in a growing proportion of pregnant women. The aim of this study was to determine whether a mouse model of vitamin D-deficiency alters fetal neurodevelopment. Female BALB/c mice were placed on either a vitamin D control (2,195 IU/kg) or deficient (0 IU/kg) diet for 5 weeks prior to and during pregnancy. Fetal brains were collected at embryonic day (E) 14.5 or E17.5 for morphological and gene expression analysis. Vitamin D deficiency during pregnancy reduced fetal crown-rump length and head size. Moreover, lateral ventricle volume was reduced in vitamin D-deficient foetuses. Expression of neurotrophin genes brain-derived neurotrophic factor (Bdnf) and transforming growth factor-β1 (Tgf-β1) was altered, with Bdnf reduced at E14.5 and increased at E17.5 following vitamin D deficiency. Brain expression of forkhead box protein P2 (Foxp2), a gene known to be important in human speech and language, was also altered. Importantly, Foxp2 immunoreactive cells in the developing cortex were reduced in vitamin D-deficient female foetuses. At E17.5, brain tyrosine hydroxylase (TH) gene expression was reduced in females, as was TH protein localization (to identify dopamine neurons) in the substantia nigra of vitamin D-deficient female foetuses. Overall, we show that prenatal vitamin D-deficiency leads to alterations in fetal mouse brain morphology and genes related to neuronal survival, speech and language development, and dopamine synthesis. Vitamin D appears to play an important role in mouse neurodevelopment.

Schizophrenia and Depression Co-Morbidity: What We have Learned from Animal Models

Patients with schizophrenia are at an increased risk for the development of depression. Overlap in the symptoms and genetic risk factors between the two disorders suggests a common etiological mechanism may underlie the presentation of comorbid depression in schizophrenia. Understanding these shared mechanisms will be important in informing the development of new treatments. Rodent models are powerful tools for understanding gene function as it relates to behavior. Examining rodent models relevant to both schizophrenia and depression reveals a number of common mechanisms. Current models which demonstrate endophenotypes of both schizophrenia and depression are reviewed here, including models of CUB and SUSHI multiple domains 1, PDZ and LIM domain 5, glutamate Delta 1 receptor, diabetic db/db mice, neuropeptide Y, disrupted in schizophrenia 1, and its interacting partners, reelin, maternal immune activation, and social isolation. Neurotransmission, brain connectivity, the immune system, the environment, and metabolism emerge as potential common mechanisms linking these models and potentially explaining comorbid depression in schizophrenia.

Potentiated striatal dopamine release leads to hyperdopaminergia in female brain-derived neurotrophic factor heterozygous mice

The goal of this study was to determine whether a reduction in brain-derived neurotrophic factor (BDNF) levels in female mice leads to dopaminergic system dysregulation. Through a series of in vivo brain microdialysis and slice voltammetry experiments, we discerned that female BDNF heterozygous (BDNF(+/-)) mice are hyperdopaminergic, similar to their male BDNF(+/-) counterparts. Zero-net flux microdialysis results showed that female BDNF(+/-) mice had increased striatal extracellular dopamine levels, while stimulated regional release by high potassium concentrations potentiated dopamine release through vesicular-mediated depolarization. Using the complementary technique of fast scan cyclic voltammetry, electrical stimulation evoked greater dopamine release in the female BDNF(+/-) mice, whereas dopamine uptake remained unchanged relative to that of female wildtype mice. Following psychostimulant methamphetamine administration, female BDNF(+/-) mice showed potentiated dopamine release compared to their wildtype counterparts. Taken together, these dopamine release impairments in female mice appear to result in a hyperdopaminergic phenotype without concomitant alterations in dopamine uptake.

Probing the ability of presynaptic tyrosine kinase receptors to regulate striatal dopamine dynamics

Brain-derived neurotrophic factor (BDNF) modulates the synaptic transmission of several monoaminergic neuronal systems. Molecular techniques using synapatosomes in previous studies have suggested that BDNF's receptor, tyrosine kinases (Trk), can quickly regulate dopamine release and transporter dynamics. Our main objective in this study is to determine whether slice fast scan cyclic voltammetry can be used to investigate the role of the TrkB receptor on dopamine release and uptake processes in the caudate-putamen. Fast scan cyclic voltammetry measured dopamine release and uptake rates in the presence of BDNF, or its agonist 7,8-dihydroxyflavone, or a TrkB inhibitor K252a. Superfusion of BDNF led to partial recovery of the electrically stimulated dopamine release response in BDNF(+/-) mice which is blunted compared to wildtype mice, with no effect in wildtype mice. Conversely, infusion of 7,8-dihydroxyflavone increased electrically stimulated dopamine release in wildtype mice with no difference in BDNF(+/-) mice. Overall, BDNF and 7,8-dihydroxyflavone had no effect on dopamine uptake rates. Concentrations greater than 3 μM 7,8-dihydroxyflavone affected dopamine uptake rates in BDNF(+/-) mice only. To demonstrate that BDNF and 7,8-dihydroxyflavone modulate dopamine release by activating the TrkB receptor, both genotypes were pretreated with K252a. K252a was able to block BDNF and 7,8-DHF induced increases during stimulated dopamine release in BDNF(+/-) and wildtype mice, respectively. Fast scan cyclic voltammetry demonstrates that acute TrkB activation potentiates dopamine release in both genotypes.

Rodent models for mania: practical approaches

The scarcity of good animal models for bipolar disorder (BPD) and especially for mania is repeatedly mentioned as one of the rate-limiting factors in the process of gaining a better understanding into its pathophysiology and of developing better treatments. Standard models of BPD have some value but usually represent only one facet of the disease and have partial validity. A number of new approaches for modeling BPD and specifically mania have been suggested in the last few years and can be combined to improve models. These approaches include targeted mutation models representing reverse translation, the identification of advantageous strains for components of the disorder, a search for the most homologous species to address specific human pathology, and the exploration of individual differences of response including the separation between susceptible and resilient animals. Additionally, recent efforts have identified and developed new tests to distinguish between "normal" and "BPD-like" animals including the different utilization of known tests and novel tests such as the female-urine-sniffing test and behavior pattern monitor analysis. Additional tests relating to further domains of BPD are still needed. An ideal model for BPD that will encompass the entire disease and be useful for every demand will probably not become available until we have a full understanding of the pathophysiology of the disorder. However, the current advances in modeling should lead to better comprehension of the disorder and therefore to the gradual development of increasingly improved models.

Custom genotyping for substance addiction susceptibility genes in Jordanians of Arab descent

Background

Both environmental and genetic factors contribute to individual susceptibility to initiation of substance use and vulnerability to addiction. Determining genetic risk factors can make an important contribution to understanding the processes leading to addiction. In order to identify gene(s) and mechanisms associated with substance addiction, a custom platform array search for a genetic association in a case/control of homogenous Jordanian Arab population was undertaken. Patients meeting the DSM-VI criteria for substance dependence (n = 220) and entering eight week treatment program at two Jordanian Drug Rehabilitation Centres were genotyped. In addition, 240 healthy controls were also genotyped. The sequenom MassARRAY system (iPLEX GOLD) was used to genotype 49 single nucleotide polymorphisms (SNPs) within 8 genes (DRD1, DRD2, DRD3, DRD4, DRD5, BDNF, SLC6A3 and COMT).

Results

This study revealed six new associations involving SNPs within DRD2 gene on chromosome 11. These six SNPs within the DRD2 were found to be most strongly associated with substance addiction in the Jordanian Arabic sample. The strongest statistical evidence for these new association signals were from rs1799732 in the C/−C promoter and rs1125394 in A/G intron 1 regions of DRD2, with the overall estimate of effects returning an odds ratio of 3.37 (χ2 (2, N = 460) = 21, p-value = 0.000026) and 1.78 (χ2 (2, N = 460) = 8, p-value = 0.001), respectively. It has been suggested that DRD2, dopamine receptor D2, plays an important role in dopamine secretion and the signal pathways of dopaminergic reward and drug addiction.

Conclusion

This study is the first to show a genetic link to substance addiction in a Jordanian population of Arab descent. These findings may contribute to our understanding of drug addiction mechanisms in Middle Eastern populations and how to manage or dictate therapy for individuals. Comparative analysis with different ethnic groups could assist further improving our understanding of these mechanisms.

Exercise does not protect against MPTP-induced neurotoxicity in BDNF haploinsufficient mice

Exercise has been demonstrated to potently protect substantia nigra pars compacta (SN) dopaminergic neurons from 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced neurotoxicity. One mechanism proposed to account for this neuroprotection is the upregulation of neurotrophic factors. Several neurotrophic factors, including Brain Derived Neurotrophic Factor (BDNF), have been shown to upregulate in response to exercise. In order to determine if exercise-induced neuroprotection is dependent upon BDNF, we compared the neuroprotective effects of voluntary exercise in mice heterozygous for the BDNF gene (BDNF+/-) with strain-matched wild-type (WT) mice. Stereological estimates of SNpc DA neurons from WT mice allowed 90 days exercise via unrestricted running demonstrated complete protection against the MPTP-induced neurotoxicity. However, BDNF+/- mice allowed 90 days of unrestricted exercise were not protected from MPTP-induced SNpc DA neuron loss. Proteomic analysis comparing SN and striatum from 90 day exercised WT and BDNF+/- mice showed differential expression of proteins related to energy regulation, intracellular signaling and trafficking. These results suggest that a full genetic complement of BDNF is critical for the exercise-induced neuroprotection of SNpc DA neurons.

Reduction of BDNF expression in Fmr1 knockout mice worsens cognitive deficits but improves hyperactivity and sensorimotor deficits

Fragile X syndrome (FXS) is a common cause of inherited intellectual disability and a well-characterized form of autism spectrum disorder. As brain-derived neurotrophic factor (BDNF) is implicated in the pathophysiology of FXS we examined the effects of reduced BDNF expression on the behavioral phenotype of an animal model of FXS, Fmr1 knockout (KO) mice, crossed with mice carrying a deletion of one copy of the Bdnf gene (Bdnf(+/-)). Fmr1 KO mice showed age-dependent alterations in hippocampal BDNF expression that declined after the age of 4 months compared to wild-type controls. Mild deficits in water maze learning in Bdnf(+/-) and Fmr1 KO mice were exaggerated and contextual fear learning significantly impaired in double transgenics. Reduced BDNF expression did not alter basal nociceptive responses or central hypersensitivity in Fmr1 KO mice. Paradoxically, the locomotor hyperactivity and deficits in sensorimotor learning and startle responses characteristic of Fmr1 KO mice were ameliorated by reducing BNDF, suggesting changes in simultaneously and in parallel working hippocampus-dependent and striatum-dependent systems. Furthermore, the obesity normally seen in Bdnf(+/-) mice was eliminated by the absence of fragile X mental retardation protein 1 (FMRP). Reduced BDNF decreased the survival of newborn cells in the ventral part of the hippocampus both in the presence and absence of FMRP. Since a short neurite phenotype characteristic of newborn cells lacking FMRP was not found in cells derived from double mutant mice, changes in neuronal maturation likely contributed to the behavioral phenotype. Our results show that the absence of FMRP modifies the diverse effects of BDNF on the FXS phenotype.

Brain-derived neurotrophic factor and neuropsychiatric disorders

Brain derived neurotrophic factor (BDNF) is the most prevalent growth factor in the central nervous system (CNS). It is essential for the development of the CNS and for neuronal plasticity. Because BDNF plays a crucial role in development and plasticity of the brain, it is widely implicated in psychiatric diseases. This review provides a summary of clinical and preclinical evidence for the involvement of this ubiquitous growth factor in major depressive disorder, schizophrenia, addiction, Rett syndrome, as well as other psychiatric and neurodevelopmental diseases. In addition, the review includes a discussion of the role of BDNF in the mechanism of action of pharmacological therapies currently used to treat these diseases, such antidepressants and antipsychotics. The review also covers a critique of experimental therapies such as BDNF mimetics and discusses the value of BDNF as a target for future drug development.

Aberrant striatal dopamine transmitter dynamics in brain-derived neurotrophic factor-deficient mice

Brain-derived neurotrophic factor (BDNF) modulates the synaptic transmission of several monoaminergic neuronal systems, including forebrain dopamine-containing neurons. Recent evidence shows a strong correlation between neuropsychiatric disorders and BDNF hypofunction. The aim of the present study was to characterize the effect of low endogenous levels of BDNF on dopamine system function in the caudate-putamen using heterozygous BDNF (BDNF(+/-) ) mice. Apparent extracellular dopamine levels in the caudate-putamen, determined by quantitative microdialysis, were significantly elevated in BDNF(+/-) mice compared with wildtype controls (12 vs. 5 nM, respectively). BDNF(+/-) mice also had a potentiated increase in dopamine levels following potassium (120 mM)-stimulation (10-fold) relative to wildtype controls (6-fold). Slice fast-scan cyclic voltammetry revealed that BDNF(+/-) mice had reductions in both electrically evoked dopamine release and dopamine uptake rates in the caudate-putamen. Superfusion of BDNF led to partial recovery of the electrically stimulated dopamine release response in BDNF(+/-) mice. Conversely, tissue accumulation of L-3,4-dihydroxyphenylalanine, extracellular levels of dopamine metabolites, and spontaneous locomotor activity were unaltered. Together, this study indicates that endogenous BDNF influences dopamine system homeostasis by regulating the release and uptake dynamics of pre-synaptic dopamine transmission.

The 5-HT(2A) Receptor Antagonist M100907 Produces Antiparkinsonian Effects and Decreases Striatal Glutamate

5-HT plays a regulatory role in voluntary movements of the basal ganglia and has a major impact on disorders of the basal ganglia such as Parkinson's disease (PD). Clinical studies have suggested that 5-HT(2) receptor antagonists may be useful in the treatment of the motor symptoms of PD. We hypothesized that 5-HT(2A) receptor antagonists may restore motor function by regulating glutamatergic activity in the striatum. Mice treated with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) exhibited decreased performance on the beam-walking apparatus. Peripheral administration of the 5-HT(2A) receptor antagonist M100907 improved performance of MPTP-treated mice on the beam-walking apparatus. In vivo microdialysis revealed an increase in striatal extracellular glutamate in MPTP-treated mice and local perfusion of M100907 into the dorsal striatum significantly decreased extracellular glutamate levels in saline and MPTP-treated mice. Our studies suggest that blockade of 5-HT(2A) receptors may represent a novel therapeutic target for the motor symptoms of PD.

Effects of brain-derived neurotrophic factor on dopaminergic function and motor behavior during aging

Brain-derived neurotrophic factor (BDNF) is critical in synaptic plasticity and in the survival and function of midbrain dopamine neurons. In this study, we assessed the effects of a partial genetic deletion of BDNF on motor function and dopamine (DA) neurotransmitter measures by comparing Bdnf(+/-) with wildtype mice (WT) at different ages. Bdnf(+/-) and WT mice had similar body weights until 12 months of age; however, at 21 months, Bdnf(+/-) mice were significantly heavier than WT mice. Horizontal and vertical motor activity was reduced for Bdnf(+/-) compared to WT mice, but was not influenced by age. Performance on an accelerating rotarod declined with age for both genotypes and was exacerbated for Bdnf(+/-) mice. Body weight did not correlate with any of the three behavioral measures studied. Dopamine neurotransmitter markers indicated no genotypic difference in striatal tyrosine hydroxylase, DA transporter (DAT) or vesicular monoamine transporter 2 (VMAT2) immunoreactivity at any age. However, DA transport via DAT (starting at 12 months) and VMAT2 (starting at 3 months) as well as KCl-stimulated DA release were reduced in Bdnf(+/-) mice and declined with age suggesting an increasingly important role for BDNF in the release and uptake of DA with the aging process. These findings suggest that a BDNF expression deficit becomes more critical to dopaminergic dynamics and related behavioral activities with increasing age.

The study of BDNF Val66Met polymorphism in Chinese schizophrenic patients

Accumulating evidence showed that brain-derived neurotrophic factor (BDNF) may be involved in the pathophysiology of schizophrenia. Recent studies have reported that the Val66Met polymorphism of the BDNF gene may be associated with susceptibility for schizophrenia and age of onset of this disease, with mix results. In the present study, the BDNF Val66Met gene polymorphism was examined in 387 inpatients (259 men and 128 women) meeting the DSM-IV criteria for schizophrenia and unrelated 365 healthy controls (255 men and 110 women). The schizophrenia symptomatology was assessed by the Positive and Negative Syndrome Scale (PANSS). Age of onset was defined as the age at which the psychotic symptoms first appeared. Our results showed that genotype frequency distributions and allelic frequencies did not differ between patients and controls. No interaction was found between sex and genotypes. Analysis of covariance (ANCOVA) showed a significance of the BDNF Val66Met genotypes on the age of onset (F=3.76, p<0.02), after adjusting sex, age and duration of illness. Furthermore, ANCOVA showed that the significance of the BDNFVal66Met genotypes on age of onset was increased comparing the Val66Met heterozygotes with the combination of Val66Val and Met66Met homozygotes (F=5.85, p<0.01). Our results suggest that the BDNF Val66Met polymorphism may not contribute directly to the susceptibility to schizophrenia, but to the onset of the disease. Furthermore, our results show the heterozygous effect of the BDNF Val66Met gene on the clinical variability of schizophrenia phenotype.

Modulation of brain-derived neurotrophic factor (BDNF) actions in the nervous system by adenosine A(2A) receptors and the role of lipid rafts

In this paper we review some novel aspects related to the way adenosine A(2A) receptors (A(2A)R) modulate the action of BDNF or its high-affinity receptors, the TrkB receptors, on synaptic transmission and plasticity, as well as upon cholinergic currents and GABA transporters. Evidence has been accumulating that adenosine A(2A)Rs are required for most of the synaptic actions of BDNF. In some cases, where A(2A)Rs are constitutively activated (e.g. by endogenous extracellular adenosine), the need for A(2A)R activation for the maintenance of the synaptic influences of BDNF can be envisaged from the loss of BDNF effects upon blockade of adenosine A(2A)Rs or upon removal of extracellular adenosine with adenosine deaminase. In some other cases, it is necessary to enhance extracellular adenosine levels (e.g. depolarization) or to further activate A(2A)Rs (e.g. with selective agonists) to trigger a BDNF neuromodulatory role at the synapses. Age- and cell-dependent differences may determine the above two possibilities, but in all cases it is quite clear that there is close interplay between adenosine A(2A)Rs and BDNF TrkB receptors at synapses. The role of lipid rafts in this cross-talk will be discussed. This article is part of a Special Issue entitled: "Adenosine Receptors".

5-HT2A receptor antagonists improve motor impairments in the MPTP mouse model of Parkinson's disease

Clinical observations have suggested that ritanserin, a 5-HT(2A/C) receptor antagonist may reduce motor deficits in persons with Parkinson's Disease (PD). To better understand the potential antiparkinsonian actions of ritanserin, we compared the effects of ritanserin with the selective 5-HT(2A) receptor antagonist M100907 and the selective 5-HT(2C) receptor antagonist SB 206553 on motor impairments in mice treated with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). MPTP-treated mice exhibited decreased performance on the beam-walking apparatus. These motor deficits were reversed by acute treatment with L-3,4-dihydroxyphenylalanine (levodopa). Both the mixed 5-HT(2A/C) antagonist ritanserin and the selective 5-HT(2A) antagonist M100907 improved motor performance on the beam-walking apparatus. In contrast, SB 206553 was ineffective in improving the motor deficits in MPTP-treated mice. These data suggest that 5-HT(2A) receptor antagonists may represent a novel approach to ameliorate motor symptoms of Parkinson's disease.

Modeling the positive symptoms of schizophrenia in genetically modified mice: pharmacology and methodology aspects

In recent years, there have been huge advances in the use of genetically modified mice to study pathophysiological mechanisms involved in schizophrenia. This has allowed rapid progress in our understanding of the role of several proposed gene mechanisms in schizophrenia, and yet this research has also revealed how much still remains unresolved. Behavioral studies in genetically modified mice are reviewed with special emphasis on modeling psychotic-like behavior. I will particularly focus on observations on locomotor hyperactivity and disruptions of prepulse inhibition (PPI). Recommendations are included to address pharmacological and methodological aspects in future studies. Mouse models of dopaminergic and glutamatergic dysfunction are then discussed, reflecting the most important and widely studied neurotransmitter systems in schizophrenia. Subsequently, psychosis-like behavior in mice with modifications in the most widely studied schizophrenia susceptibility genes is reviewed. Taken together, the available studies reveal a wealth of available data which have already provided crucial new insight and mechanistic clues which could lead to new treatments or even prevention strategies for schizophrenia.

Brain-derived neurotrophic factor and cocaine addiction

The effects of brain-derived neurotrophic factor (BDNF) on cocaine-seeking are brain region-specific. Infusion of BDNF into subcortical structures, like the nucleus accumbens and ventral tegmental area, enhances cocaine-induced behavioral sensitization and cocaine-seeking. Conversely, repeated administration of BDNF antiserum into the nucleus accumbens during chronic cocaine self-administration attenuates cocaine-induced reinstatement. In contrast, BDNF infusion into the dorsomedial prefrontal cortex immediately following a final session of cocaine self-administration attenuates relapse to cocaine-seeking after abstinence, as well as cue- and cocaine prime-induced reinstatement of cocaine-seeking following extinction. BDNF-induced alterations in the ERK-MAP kinase cascade and in prefronto-accumbens glutamatergic transmission are implicated in BDNF's ability to alter cocaine-seeking. Within 22 hours after infusion into the prefrontal cortex, BDNF increases BDNF protein in prefrontal cortical targets, including nucleus accumbens, and restores cocaine-mediated decreases in phospho-ERK expression in the nucleus accumbens. Furthermore, 3 weeks after BDNF infusion in animals with a cocaine self-administration history, suppressed basal levels of glutamate are normalized and a cocaine prime-induced increase in extracellular glutamate levels in the nucleus accumbens is prevented. Thus, BDNF may have local effects at the site of infusion and distal effects in target areas that are critical to mediating or preventing cocaine-induced dysfunctional neuroadaptations.

Genetic susceptibility to schizophrenia: role of dopaminergic pathway gene polymorphisms

Aim: We investigated 16 polymorphisms from three genes, dopamine receptor D2 (DRD2), catechol-O-methyl transferase (COMT) and brain derived neurotrophic factor (BDNF), which are involved in the dopaminergic pathways, and have been reported to be associated with susceptibility to schizophrenia and response to antipsychotic therapy. Materials & methods: Single-locus association analyses of these polymorphisms were carried out in 254 patients with schizophrenia and 225 controls, all of southern Indian origin. Additionally, multifactor-dimensionality reduction analysis was performed in 422 samples (243 cases and 179 controls) to examine the gene–gene interactions and to identify combinations of multilocus genotypes associated with either high or low risk for the disease. Results: Our results demonstrated initial significant associations of two SNPs for DRD2 (rs11608185, genotype: χ2 = 6.29, p-value = 0.043; rs6275, genotype: χ2 = 8.91, p-value = 0.011), and one SNP in the COMT gene (rs4680, genotype: χ2 = 6.67, p-value = 0.035 and allele: χ2 = 4.75, p-value = 0.029; odds ratio: 1.33, 95% confidence interval: 1.02–1.73), but not after correction for multiple comparisons indicating a weak association of individual markers of DRD2 and COMT with schizophrenia. Multifactor-dimensionality reduction analysis suggested a two locus model (rs6275/DRD2 and rs4680/COMT) as the best model for gene–gene interaction with 90% cross-validation consistency and 42.42% prediction error in predicting disease risk among schizophrenia patients. Conclusion: The present study thus emphasizes the need for multigene interaction studies in complex disorders such as schizophrenia and to understand response to drug treatment, which could lead to a targeted and more effective treatment.

BDNF mediates the neuroprotective effects of positive AMPA receptor modulators against MPP+-induced toxicity in cultured hippocampal and mesencephalic slices

Neurotoxicity is involved in various neurodegenerative diseases including Parkinson's disease (PD), which affects mesencephalic dopaminergic neurons of the substantia nigra (SN). Positive alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor modulators (PARMs, a.k.a. Ampakines, such as CX614) increase brain-derived neurotrophic factor (BDNF) protein levels in vivo and in cultured hippocampal slices. BDNF is a survival factor for various neuronal cell types including mesencephalic dopaminergic neurons. Using cultured mesencephalic and hippocampal slices, we investigated whether preincubation with CX614 could provide neuroprotection against MPP(+) toxicity and whether such neuroprotection was mediated by BDNF. Various treatment protocols were tested to demonstrate CX614-induced neuroprotection against MPP(+). Pretreatment with CX614 significantly reduced MPP(+)-induced toxicity and increased BDNF levels in both hippocampal and mesencephalic cultured slices; CX614 pretreatment for 6 h in hippocampal slices and 24 h in mesencephalic slices was sufficient to produce significant neuroprotection as assessed with lactate dehydrogenase release in slice medium and propidium iodide uptake in slices. Both a BDNF scavenger and an inhibitor of the BDNF receptor TrkB, abrogated CX614-mediated reduction of MPP(+)-induced toxicity. Inhibition of Ca(2+)-activated proteases, calpains, was also protective against MPP(+)-induced toxicity. However, co-application of calpain inhibitor with CX614 abolished CX614-mediated protection, suggesting a dual action of calpains in this model. We conclude that CX614 is neuroprotective against MPP(+)-induced toxicity, an effect mediated by increased BDNF expression and activation of BDNF-dependent signaling pathways. Our results provide support for using PARMs as a new therapy for neurodegenerative disorders, including PD.

Drug-induced activation of dopamine D(1) receptor signaling and inhibition of class I/II histone deacetylase induce chromatin remodeling in reward circuitry and modulate cocaine-related behaviors

Chromatin remodeling, including histone modification, is involved in stimulant-induced gene expression and addiction behavior. To further explore the role of dopamine D(1) receptor signaling, we measured cocaine-related locomotor activity and place preference in mice pretreated for up to 10 days with the D(1) agonist SKF82958 and/or the histone deacetylase inhibitor (HDACi), sodium butyrate. Cotreatment with D(1) agonist and HDACi significantly enhanced cocaine-induced locomotor activity and place preference, in comparison to single-drug regimens. However, butyrate-mediated reward effects were transient and only apparent within 2 days after the last HDACi treatment. These behavioral changes were associated with histone modification changes in striatum and ventral midbrain: (1) a generalized increase in H3 phosphoacetylation in striatal neurons was dependent on activation of D(1) receptors; (2) H3 deacetylation at promoter sequences of tyrosine hydroxylase (Th) and brain-derived neurotrophic factor (Bdnf) in ventral midbrain, together with upregulation of the corresponding gene transcripts after cotreatment with D(1) agonist and HDACi. Collectively, these findings imply that D(1) receptor-regulated histone (phospho)acetylation and gene expression in reward circuitry is differentially regulated in a region-specific manner. Given that the combination of D(1) agonist and HDACi enhances cocaine-related sensitization and reward, the therapeutic benefits of D(1) receptor antagonists and histone acetyl-transferase inhibitors (HATi) warrant further investigation in experimental models of stimulant abuse.

Association study of brain-derived neurotrophic factor (BDNF) and LIN-7 homolog (LIN-7) genes with adult attention-deficit/hyperactivity disorder

Attention-deficit/hyperactivity disorder (ADHD) is a common psychiatric disorder with a large genetic component that has been shown to persist into adulthood in 30-60% of childhood ADHD cases. Adult ADHD confers an increased risk of ADHD in relatives when compared to childhood ADHD, possibly due to a greater genetic liability than the childhood form. Brain-derived neurotrophic factor (BDNF) is a neurotrophin expressed in the brain throughout life and is involved in survival, differentiation, and synaptic plasticity of several neuronal systems including dopaminergic pathways. Mammalian LIN-7 homolog is selectively expressed in specific neuronal populations and is involved in the postsynaptic density of neuronal synapses. LIN-7 is also a positional candidate, as it lies immediately downstream of BDNF. We tested for association between five BDNF polymorphisms, two LIN-7 polymorphisms and adult ADHD. The sample consisted of 80 trios comprised of an adult ADHD proband and their biological parents and an independent sample of 121 adult ADHD cases and a corresponding number of sex, age, and ethnically matched controls (total 201 probands). Allelic and haplotype association was found between both BDNF and adult ADHD, and LIN-7 and adult ADHD. HapMap indicates BDNF and LIN-7 occur in different haplotype blocks, though some linkage disequilibrium exists between the SNPs in these adjacent genes. Further investigations into the pathologic mechanisms of BDNF and LIN-7 in adult ADHD are required.

Amphetamine-induced locomotion and gene expression are altered in BDNF heterozygous mice

Administration of amphetamine overstimulates medium spiny neurons (MSNs) by releasing dopamine and glutamate from afferents in the striatum. However, these afferents also release brain-derived neurotrophic factor (BDNF) that protects striatal MSNs from overstimulation. Intriguingly, all three neurochemicals increase opioid gene expression in MSNs. In contrast, striatal opioid expression is less in naive BDNF heterozygous (BDNF(+/-)) vs. wild-type (WT) mice. This study was designed to determine whether partial genetic depletion of BDNF influences the behavioral and molecular response to an acute amphetamine injection. An acute injection of amphetamine [5 mg/kg, intraperitoneal (i.p.)] or saline was administered to WT and BDNF(+/-) mice. WT and BDNF(+/-) mice exhibited similar locomotor activity during habituation, whereas BDNF(+/-) mice exhibited more prolonged locomotor activation during the third hour after injection of amphetamine. Three hours after amphetamine injection, there was an increase of preprodynorphin mRNA in the caudate putamen and nucleus accumbens (Acb) and dopamine D(3) receptor mRNA levels were increased in the Acb of BDNF(+/-) and WT mice. Striatal/cortical trkB and BDNF, and mesencephalic tyrosine hydroxylase mRNA levels were only increased in WT mice. These results indicate that BDNF modifies the locomotor responses of mice to acute amphetamine and differentially regulates amphetamine-induced gene expression.

Abnormal motor function and dopamine neurotransmission in DYT1 DeltaGAG transgenic mice

A single GAG deletion in Exon 5 of the TOR1A gene is associated with a form of early-onset primary dystonia showing less than 40% penetrance. To provide a framework for cellular and systems study of DYT1 dystonia, we characterized the genetic, behavioral, morphological and neurochemical features of transgenic mice expressing either human wild-type torsinA (hWT) or mutant torsinA (hMT1 and hMT2) and their wild-type (WT) littermates. Relative to human brain, hMT1 mice showed robust neural expression of human torsinA transcript (3.90x). In comparison with WT littermates, hMT1 mice had prolonged traversal times on both square and round raised-beam tasks and more slips on the round raised-beam task. Although there were no effects of genotype on rotarod performance and rope climbing, hMT1 mice exhibited increased hind-base widths in comparison to WT and hWT mice. In contrast to several other mouse models of DYT1 dystonia, we were unable to identify either torsinA- and ubiquitin-positive cytoplasmic inclusion bodies or nuclear bleb formation in hMT1 mice. High-performance liquid chromatography with electrochemical detection was used to determine cerebral cortical, striatal, and cerebellar levels of dopamine (DA), norepinephrine, epinephrine, serotonin, 3,4-dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA) and 5-hydroxyindoleacetic acid. Although there were no differences in striatal DA levels between WT and hMT1 mice, DOPAC and HVA concentrations and DA turnover (DOPAC/DA and HVA/DA) were significantly higher in the mutants. Our findings in DYT1 transgenic mice are compatible with previous neuroimaging and postmortem neurochemical studies of human DYT1 dystonia. Increased striatal dopamine turnover in hMT1 mice suggests that the nigrostriatal pathway may be a site of functional neuropathology in DYT1 dystonia.

Behavioral genetic contributions to the study of addiction-related amphetamine effects

Amphetamines, including methamphetamine, pose a significant cost to society due to significant numbers of amphetamine-abusing individuals who suffer major health-related consequences. In addition, methamphetamine use is associated with heightened rates of violent and property-related crimes. The current paper reviews the existing literature addressing genetic differences in mice that impact behavioral responses thought to be relevant to the abuse of amphetamine and amphetamine-like drugs. Summarized are studies that used inbred strains, selected lines, single-gene knockouts and transgenics, and quantitative trait locus (QTL) mapping populations. Acute sensitivity, neuroadaptive responses, rewarding and conditioned effects are among those reviewed. Some gene mapping work has been accomplished, and although no amphetamine-related complex trait genes have been definitively identified, translational work leading from results in the mouse to studies performed in humans is beginning to emerge. The majority of genetic investigations have utilized single-gene knockout mice and have concentrated on dopamine- and glutamate-related genes. Genes that code for cell support and signaling molecules are also well-represented. There is a large behavioral genetic literature on responsiveness to amphetamines, but a considerably smaller literature focused on genes that influence the development and acceleration of amphetamine use, withdrawal, relapse, and behavioral toxicity. Also missing are genetic investigations into the effects of amphetamines on social behaviors. This information might help to identify at-risk individuals and in the future to develop treatments that take advantage of individualized genetic information.

Brain-derived neurotrophic factor and its intracellular signaling pathways in cocaine addiction

Cocaine addiction is one of the severest health problems faced by western countries, where there is an increasing prevalence of lifelong abuse. The most challenging aspects in the treatment of cocaine addiction are craving and relapse, especially in view of the fact that, at present, there is a lack of effective pharmacological treatment for the disorder. What is required are new pharmacological approaches based on our current understanding of the neurobiological bases of drug addiction. Within the context of the behavioral and neurochemical actions of cocaine, this paper considers the contribution of brain-derived neurotrophic factor (BDNF) and its main intracellular signaling mechanisms, including mitogen-activated protein kinase/extracellular signal-regulated protein kinase (MAPK/ERK) and phosphatidylinositol 3-kinase (PI3K), in psychostimulant addiction. Repeated cocaine administration leads to an increase in BDNF levels and enhanced activity in the intracellular pathways (PI3K and MAPK/ERK) in the reward-related brain areas, which applies especially several days following withdrawal. It has been hypothesized that these neurochemical changes contribute to the enduring synaptic plasticity that underlies sensitized responses to psychostimulants and drug-conditioned memories leading to compulsive drug use and frequent relapse after withdrawal. Nevertheless, increased BDNF levels could also have a role as a protection factor in addiction. The inhibition of the intracellular pathways, ERK and PI3K, leads to a disruption in sensitized responses and conditioned memories associated with cocaine addiction and suggests new, potential therapeutic strategies to explore in the dependence on psychostimulants.

Overexpression of human wildtype torsinA and human DeltaGAG torsinA in a transgenic mouse model causes phenotypic abnormalities

Primary torsion dystonia is an autosomal-dominant inherited movement disorder. Most cases are caused by an in-frame deletion (GAG) of the DYT1 gene encoding torsinA. Reduced penetrance and phenotypic variability suggest that alteration of torsinA amino acid sequence is necessary but not sufficient for development of clinical symptoms and that additional factors must contribute to the factual manifestation of the disease. We generated 4 independent transgenic mouse lines, two overexpressing human mutant torsinA and two overexpressing human wildtype torsinA using a strong murine prion protein promoter. Our data provide for the first time in vivo evidence that not only mutant torsinA is detrimental to neuronal cells but that also wildtype torsinA can lead to neuronal dysfunction when overexpressed at high levels. This hypothesis is supported by (i) neuropathological findings, (ii) neurochemistry, (iii) behavioral abnormalities and (iv) DTI-MRI analysis.

Rapid regulation of dopamine transporters by tyrosine kinases in rat neuronal preparations

Termination of dopamine neurotransmission is primarily controlled by the plasma membrane-localized dopamine transporter. In this study, we investigated how this transporter is regulated by tyrosine kinases in neuronal preparations. In rat dorsal striatal synaptosomes, inhibition of tyrosine kinases by genistein or tyrphostin 23 resulted in a rapid (5-15 min), concentration-dependent decrease in [(3)H]dopamine uptake because of a reduction in maximal [(3)H]dopamine uptake velocity and dopamine transporter cell surface expression. The reduced transporter activity was associated with a decrease in phosphorylated p44/p42 mitogen-activated protein kinases. In primary rat mesencephalic neuronal cultures, the tyrosine kinase inhibitors similarly reduced [(3)H]dopamine uptake. When cultures were serum-deprived, acute activation of tyrosine kinase-coupled TrkB receptors by 100 ng/mL brain-derived neurotrophic factor significantly increased [(3)H]dopamine uptake; the effects were complex with increased maximal velocity but reduced affinity. The facilitatory effect of brain-derived neurotrophic factor on dopamine transporter activity depended on both the mitogen-activated protein kinase and phosphatidylinositol 3-kinase pathways. Taken together, our results suggest that striatal dopamine transporter function and cell surface expression is constitutively up-regulated by tyrosine kinase activation and that brain-derived neurotrophic factor can mediate this type of rapid regulation.

A beam-walking apparatus to assess behavioural impairments in MPTP-treated mice: pharmacological validation with R-(-)-deprenyl

A beam-walking apparatus has been evaluated for its ability to detect motor impairments in mice acutely treated with the dopaminergic neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP, 30 mg/kg, s.c., single or double administration). Mice subjected to MPTP lesioning showed deficits in motor performance on the beam-walking task, for up to 6 days post-MPTP administration, as compared to saline-treated controls. In addition, MPTP-treated mice were detected to have a marked depletion in striatal dopamine levels and a concomitant reduction in substantia nigra (SN) tyrosine hydroxylase (TH) immunoreactivity, at 7 days post-MPTP administration, indicative of dopaminergic neuronal loss. Pre-administration of the potent MAO-B inhibitor R-(-)-deprenyl at 3 or 10 mg/kg, 30 min, s.c, significantly inhibited the MPTP-induced reduction in SN TH-immunoreactivity, striatal dopamine depletions and impairments in mouse motor function. The data described in the present study provides further evidence that functional deficits following an acute MPTP dosing schedule in mice can be quantified and are related to nigro-striatal dopamine function.

Tamoxifen effect on L-DOPA induced response complications in parkinsonian rats and primates

The contribution of striatal protein kinase C (PKC) isoform changes in levodopa (L-DOPA) induced motor response complications in parkinsonian rats was investigated and the ability of tamoxifen, an antiestrogen with a partial PKC antagonist property, to prevent these response alterations in 6-hydroxydopamine (6-OHDA) lesioned rats as well as in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) treated cynomologous monkeys was studied. Following treatment of adult male rats with L-DOPA twice daily for 3 weeks, protein levels of left (lesioned) and right (intact) striatal PKC isoforms were measured. Western blot analysis showed increased protein expression of both the novel PKC epsilon isoform and the atypical PKC lambda isoform ipsilateral to the lesion (174+/-17% for epsilon, 140+/-9% for lambda, of intact striatum in 6-OHDA lesioned plus chronic L-DOPA treated animals) in acute L-DOPA treated rats. No enhancement was observed in PKC immunoreactivity for other isoforms. Tamoxifen (5.0 mg/kg p.o.) significantly attenuated the L-DOPA induced augmentation of protein expression of PKC epsilon and PKC lambda, but had no effect on immunoreactivity for other PKC isoforms. In chronic L-DOPA treated parkinsonian rats, tamoxifen prevented (5.0 mg/kg p.o.) as well as ameliorated (5.0 mg/kg p.o.) the characteristic shortening in duration of motor response to L-DOPA challenge. In MPTP lesioned primates, similar to the ameliorative effect seen in rats, tamoxifen (1 and 3 mg/kg p.o) reduced the appearance of L-DOPA induced dyskinesia by 61% and 55% respectively (p<0.05). These results suggest that changes in specific striatal PKC isoforms contribute to the pathogenesis of L-DOPA induced motor complications and further that drugs able to selectively inhibit these signaling kinases might provide adjunctive benefit in the treatment of Parkinson's disease.

Methylphenidate regulates activity regulated cytoskeletal associated but not brain-derived neurotrophic factor gene expression in the developing rat striatum

Methylphenidate (MPH) is a psychostimulant drug used to treat attention deficit hyperactivity disorder in children. To explore the central effects of chronic MPH, we investigated the expression of an effector immediate early gene, activity regulated cytoskeletal associated (arc), and the neurotrophin, brain-derived neurotrophic factor (bdnf) in the brain of immature and adult rats following repeated MPH. Prepubertal (postnatal day (PD) 25-38) and adult (PD 53-66) male rats were injected once daily for: a) 14 days with saline or MPH (2 or 10 mg/kg; s.c.) or b) 13 days with saline followed by a single dose of MPH (2 or 10 mg/kg; s.c.). To determine possible long-term effects of MPH, prepubertal rats were allowed a drug-free period of 4 weeks following the 14 days of treatment, and then were given a challenge dose of MPH. We demonstrated, for the first time, that an acute injection of MPH increased levels of activity-regulated cytoskeletal protein (ARC) and arc mRNA in the prepubertal rat striatum and cingulate/frontal cortex. This response was significantly attenuated by chronic MPH. The desensitization in arc expression observed in prepubertal rats persisted in the adult striatum following a later MPH challenge. In contrast to these data we observed little effect of MPH on bdnf expression. We also developed an effective, non-stressful technique to treat freely moving immature rats with oral MPH. Consistent with the results described above, we observed that oral MPH (7.5 and 10 mg/kg) also increased arc expression in the prepubertal rat striatum. However, unlike the effects of injected MPH, repeated oral MPH (7.5 mg/kg) did not alter the normal arc response. This result raises the important possibility that oral doses of MPH that reproduce clinically relevant blood levels of MPH may not down-regulate gene expression, at least in the short term (14 days). We confirmed, using mass spectrometry, that the oral doses of MPH used in our experiments yielded blood levels within the clinical range observed in children. The novel oral administration paradigm that we describe thus provides a clinically relevant animal model to further explore the effects of chronic drug exposure on central gene expression in the developing rat brain.

Mice heterozygous for neurotrophin-3 display enhanced vulnerability to excitotoxicity in the striatum through increased expression of N-methyl-D-aspartate receptors

The striatum is one of the brain areas most vulnerable to excitotoxicity, a lesion that can be prevented by neurotrophins. In the present study, intrastriatal injection of the N-methyl-d-aspartate receptor (NMDAR) agonist quinolinate (QUIN) was performed in mice heterozygous for neurotrophin-3 (NT3 +/-) or brain-derived neurotrophic factor (BDNF +/-) to analyze the role of endogenous neurotrophins on the regulation of striatal neurons susceptibility to excitotoxic injury. QUIN injection induced a decrease in dopamine- and cyclic AMP-regulated phosphoprotein of 32 kDa (DARPP-32) protein levels that was higher in NT-3 +/- than in BDNF+/- or wild type animals. This enhanced susceptibility was specific for enkephalin- and tachykinin-positive projection neurons, and also for parvalbumin-positive interneurons. However the excitotoxic damage in large interneurons was not modified in NT-3 +/- mice compared with wild type animals. This effect can be related to the regulation of NMDARs by endogenous NT-3. Thus, our results show that there is an age-dependent regulation of NMDAR subunits NR1 and NR2A, but not NR2B, in NT-3 +/- mice. The deficit of endogenous NT-3 induced a decrease in NR1 and NR2A subunits at postnatal day (P) 0 and P3 mice respectively, whereas an upregulation was observed in 12 week old NT-3 +/- mice. This differential effect was also observed after administration of exogenous NT-3. In primary striatal cultures, NT-3 treatment induced an enhancement in NR2A, but not NR2B, protein levels. However, intrastriatal grafting of NT-3 secreting-cells in adult wild type mice produced a down-regulation of NR2A subunit. In conclusion, NT-3 regulates the expression of NMDAR subunits modifying striatal neuronal properties that confers the differential vulnerability to excitotoxicity in projection neurons and interneurons in the striatum.

Possible Mechanisms of Neurodegeneration in Schizophrenia

Brain morphological alterations in schizophrenic patients have led to the neurodevelopmental hypothesis of schizophrenia. On the other hand, a progressive neurodegenerative process has also been suggested and some follow-up studies have shown progressive morphological changes in schizophrenic patients. Several neurotransmitter systems have been suggested to be involved in this disorder and some of them could lead to neuronal death under certain conditions. This review discusses some of the biochemical pathways that could lead to neurodegeneration in schizophrenia showing that neuronal death may have a role in the etiology or natural course of this disorder.

Cellular plasticity cascades: genes-to-behavior pathways in animal models of bipolar disorder

BACKGROUND

Despite extensive research, the molecular/cellular underpinnings of bipolar disorder (BD) remain to be fully elucidated. Recent data has demonstrated that mood stabilizers exert major effects on signaling that regulate cellular plasticity; however, a direct extrapolation to mechanisms of disease demands proof that manipulation of candidate genes, proteins, or pathways result in relevant behavioral changes.

METHODS

We critique and evaluate the behavioral changes induced by manipulation of cellular plasticity cascades implicated in BD.

RESULTS

Not surprisingly, the behavioral data suggest that several important signaling molecules might play important roles in mediating facets of the complex symptomatology of BD. Notably, the protein kinase C and extracellular signal-regulated kinase cascades might play important roles in the antimanic effects of mood stabilizers, whereas glycogen synthase kinase (GSK)-3 might mediate facets of lithium's antimanic/antidepressant actions. Glucocorticoid receptor (GR) modulation also seems to be capable to inducing affective-like changes observed in mood disorders. And Bcl-2, amino-3-hydroxy-5-methylisoxazole-4-propionic acid receptors, and inositol homeostasis represent important pharmacological targets for mood stabilizers, but additional behavioral research is needed to more fully delineate their behavioral effects.

CONCLUSIONS

Behavioral data support the notion that regulation of cellular plasticity is involved in affective-like behavioral changes observed in BD. These findings are leading to the development of novel therapeutics for this devastating illness.

Molecular genetics of bipolar disorder

Bipolar disorder (BPD) is an often devastating illness characterized by extreme mood dysregulation. Although family, twin and adoption studies consistently indicate a strong genetic component, specific genes that contribute to the illness remain unclear. This study gives an overview of linkage studies of BPD, concluding that the regions with the best evidence for linkage include areas on chromosomes 2p, 4p, 4q, 6q, 8q, 11p, 12q, 13q, 16p, 16q, 18p, 18q, 21q, 22q and Xq. Association studies are summarized, which support a possible role for numerous candidate genes in BPD including COMT, DAT, HTR4, DRD4, DRD2, HTR2A, 5-HTT, the G72/G30 complex, DISC1, P2RX7, MAOA and BDNF. Animal models related to bipolar illness are also reviewed, with special attention paid to those with clear genetic implications. We conclude with suggestions for strategies that may help clarify the genetic bases of this complex illness.

Rotenone produces opposite effects upon mouse striatal dopamine function as a result of environmental temperature

Rotenone is a commonly used pesticide that can function as an environmental neurotoxin. Rotenone is a known mitochondrial complex I inhibitor which can lead to oxidative stress and results in dopaminergic cell death. Another environmental factor known to exacerbate oxidative stress and result in striatal dopaminergic cell death is elevated environmental temperature. In this study we evaluated the effects of a single injection of various doses of rotenone (0.65, 1.3 and 2.6 mg/kg) on striatal dopamine (DA) and 3,4-dihydroxyphenylacetic acid (DOPAC) concentrations in CD-1 mice and compared this with a single injection of two doses of methamphetamine (MA - 10 or 20 mg/kg), a known striatal DA depleting agent, as administered to mice maintained at 21 degrees C (Experiment 1). These results were then compared to striatal DA and DOPAC concentrations of mice treated with rotenone (1.3 or 2.6 mg/kg) or MA (10 or 20 mg/kg) administered to mice maintained at 28 degrees C (Experiment 2). A single injection of rotenone to mice maintained at 21 degrees C resulted in a significant increase in DA and decrease in DOPAC concentrations for all doses tested compared to controls, whereas a single injection of MA at the same temperature resulted in a significant decrease in DA and no change in DOPAC concentrations. At a temperature of 28 degrees C, a single injection of rotenone resulted in a significant decrease in both DA and DOPAC concentrations similar to that seen with the MA-treated mice. Collectively, these results indicate that rotenone interacts with environmental temperature to produce opposite effects upon striatal DA concentrations -- significantly increasing striatal DA when administered at 21 degrees C and significantly decreasing striatal DA when administered at 28 degrees C, while producing similar decreases in striatal DOPAC under both temperatures.

BDNF heterozygous mice demonstrate age-related changes in striatal and nigral gene expression

TrkB receptors mediate the effects of BDNF on striatal medium spiny neurons and mesencephalic dopamine neurons. The effect of partial BDNF gene deletion on locomotor activity and the gene expression of these neurons was evaluated at 3, 12, and 24 months of age in BDNF heterozygous (BDNF(LacZ/neo+)) and wildtype mice. BDNF(LacZ/neo+) mice displayed less spontaneous horizontal activity than wildtypes at 3 and 24 months of age. Whereas striatal preproenkephalin and preprodynorphin mRNA and mesencephalic tyrosine hydroxylase mRNA levels were significantly lower at all ages in BDNF(LacZ/neo+) mice, GAD67 mRNA was only lower at 24 months. In contrast, BDNF(LacZ/neo+) mice expressed more trkB mRNA in the striatum at 3 months and less at 24 months of age than wildtypes. Total striatal cell number in the two genotypes was not different at 12 months of age, whereas Golgi staining revealed that the spine density on distal dendrites of medium spiny neurons was less in BDNF(LacZ/neo+) mice than in wildtypes at 24 months of age. These data indicate that endogenous BDNF is required to maintain the normal phenotype and functioning of striatal projection neurons and mesencephalic dopamine neurons and that exaggerated dysfunction of these neurons and a concomitant decline in locomotor behavior occurs during aging.

Shedding light into the role of BDNF in the pharmacotherapy of Parkinson's disease

Parkinson's disease (PD) is a chronic, neurodegenerative disease with a 1% incidence in the population over 55 years of age. Movement impairments represent undoubtedly the hallmark of the disorder; however, extensive evidence implicates cognitive deficits as concomitant peculiar features. Brain-derived neurotrophic factor (BDNF) colocalizes with dopamine neurons in the substantia nigra, where dopaminergic cell bodies are located, and it has recently garnered attention as a molecule crucial for cognition, a function that is also compromised in PD patients. Thus, due to its colocalization with dopaminergic neurons and its role in cognition, BDNF might possess a dual role in PD, both as a neuroprotective molecule, since its inhibition leads to loss of nigral dopaminergic neurons, and as a neuromodulator, as its enhanced expression ameliorates cognitive processes. In this review, we discuss the mechanism of action of established as well as novel drugs for PD with a particular emphasis to those interfering with BDNF biosynthesis.