Altered serotonin 1B receptor binding after escitalopram for depression is correlated with treatment effect.

BACKGROUND: Major depressive disorder (MDD) is commonly treated with selective serotonin reuptake inhibitors (SSRIs). SSRIs inhibit the serotonin transporter (5-HTT) but the downstream antidepressant mechanism of action of these drugs is poorly understood. The serotonin 1B (5-HT1B) receptor is functionally linked to 5-HTT and 5-HT1B receptor binding and 5-HT1B receptor mRNA is reduced in the raphe nuclei after SSRI-administration in primates and rodents respectively. The effect of SSRI treatment on 5-HT1B receptor binding in MDD subjects has not been examined previously. This positron emission tomography (PET) study aimed to quantify brain 5-HT1B receptor binding changes in vivo after SSRI treatment for MDD in relation to treatment effect. METHODS: Eight unmedicated patients with moderate to severe MDD underwent PET with the 5-HT1B receptor radioligand [11C]AZ10419369 before and after 3-4 weeks of treatment with the SSRI escitalopram 10mg daily. Depression severity was assessed at time of PET and after 6-7 weeks of treatment with the Montgomery-Åsberg Depression Rating Scale (MADRS). RESULTS: We observed a significant reduction in [11C]AZ10419369 binding in a dorsal brainstem (DBS) region containing the median and dorsal raphe nuclei after escitalopram treatment (p = 0.036). Change in DBS [11C]AZ10419369 binding correlated with MADRS reduction after three (r = 0.78, p = 0.021) and seven (r = 0.94, p < 0.001) weeks' treatment. CONCLUSIONS: Our findings align with the previously reported reduction of 5-HT1B receptor binding in the raphe nuclei after SSRI administration and support future studies testing change in DBS 5-HT1B receptor binding as an SSRI treatment response marker.

Longitudinal DAT changes measured with [18F]FE-PE2I PET in patients with Parkinson's disease; a validation study.

BACKGROUND: Dopamine transporter (DAT) PET provides higher resolution than DAT SPECT and opportunity for integrated imaging with MRI. The radioligand [18F]FE-PE2I is highly selective for the DAT, and PET measurements with this radioligand have good reliability and repeatability in patients with non-advanced Parkinson's disease. OBJECTIVES: To validate [18F]FE-PE2I PET as measurement tool of longitudinal DAT changes in patients with Parkinson's disease. METHODS: Thirty-seven subjects with Parkinson's disease (Hoehn and Yahr stage < 3) were included in a longitudinal PET study with [18F]FE-PE2I. DAT availability (BPND) in the caudate nucleus, putamen, sensorimotor striatum, and substantia nigra, was estimated with parametric imaging using Logan graphical analysis and cerebellum as reference region. For comparison with DAT-SPECT literature, sample size calculations for disease intervention studies were made. RESULTS: Baseline and follow-up PET data (interval: 2.3 ± 0.5 years) were available for 25 patients (9 females, 16 males). Median age was 64.7 years (range 46-76); symptom duration: 3 years (0.25-14); Hoehn and Yahr stage (H&Y): 1 (1-2). Annualized DAT decline and effect size were: -8.5 ± 6.6 % and 1.08 for caudate nucleus; -7.1 ± 6.1 % and 1.02 for putamen; -8.3 ± 8.5 % and 0.99 for sensorimotor striatum; -0.11 ± 9.3 % and 0.11 for substantia nigra. The estimated minimum sample size needed for a treatment trial using [18F]FE-PE2I PET as imaging marker is 2-3 times lower than is reported in literature on [123I]FP-CIT SPECT. CONCLUSIONS: Longitudinal [18F]FE-PE2I PET measurements in non-advanced PD demonstrate a striatal DAT decline consistent with previous SPECT and PET studies. No obvious changes of DAT availability were observed in the substantia nigra, indicating perhaps slower progression or compensatory changes. The effect sizes were numerically larger than reported in the literature for other DAT radioligands, suggesting that [18F]FE-PE2I might detect smaller DAT changes, and can be well used as progression marker in clinical trials.

Broader phenotypic traits and widespread brain hypometabolism in spinocerebellar ataxia 27.

OBJECTIVE: The goal of this study was to characterize a Swedish family with members affected by spinocerebellar ataxia 27 (SCA27), a rare autosomal dominant disease caused by mutations in fibroblast growth factor 14 (FGF14). Despite normal structural neuroimaging, psychiatric manifestations and intellectual disability are part of the SCA27 phenotype raising the need for functional neuroimaging. Here, we used clinical assessments, structural and functional neuroimaging to characterize these new SCA27 patients. Since one patient presents with a psychotic disorder, an exploratory study of markers of schizophrenia associated with GABAergic neurotransmission was performed in fgf14-/- mice, a preclinical model that replicates motor and learning deficits of SCA27. METHODS: A comprehensive characterization that included clinical assessments, cognitive tests, structural neuroimaging studies, brain metabolism with 18 F-fluorodeoxyglucose PET ([18F] FDG PET) and genetic analyses was performed. Brains of fgf14-/- mice were studied with immunohistochemistry. RESULTS: Nine patients had ataxia, and all affected patients harboured an interstitial deletion of chromosome 13q33.1 encompassing the entire FGF14 and integrin subunit beta like 1 (ITGBL1) genes. New features for SCA27 were identified: congenital onset, psychosis, attention deficit hyperactivity disorder and widespread hypometabolism that affected the medial prefrontal cortex (mPFC) in all patients. Hypometabolism in the PFC was far more pronounced in a SCA27 patient with psychosis. Reduced expression of VGAT was found in the mPFC of fgf14-/- mice. CONCLUSIONS: This is the second largest SCA27 family identified to date. We provide new clinical and preclinical evidence for a significant psychiatric component in SCA27, strengthening the hypothesis of FGF14 as an important modulator of psychiatric disease.

GPR37 and GPR37L1 differently interact with dopamine 2 receptors in live cells.

Receptor-receptor interactions are essential to fine tune receptor responses and new techniques enable closer characterization of the interactions between involved proteins directly in the plasma membrane. Fluorescence cross-correlation spectroscopy (FCCS), which analyses concurrent movement of bound molecules with single-molecule detection limit, was here used to, in live N2a cells, study interactions between the Parkinson's disease (PD) associated orphan receptor GPR37, its homologue GPR37L1, and the two splice variants of the dopamine 2 receptor (D2R). An interaction between GPR37 and both splice forms of D2R was detected. 4-phenylbutyrate (4-PBA), a neuroprotective chemical chaperone known to increase GPR37 expression at the cell surface, increased the fraction of interacting molecules. The interaction was also increased by pramipexole, a D2R agonist commonly used in the treatment of PD, indicating a possible clinically relevance. Cross-correlation, indicating interaction between GPR37L1 and the short isoform of D2R, was also detected. However, this interaction was not changed with 4-PBA or pramipexole treatment. Overall, these data provide further evidence that heteromeric GPR37-D2R exist and can be pharmacologically modulated, which is relevant for the treatment of PD. This article is part of the Special Issue entitled 'Receptor heteromers and their allosteric receptor-receptor interactions'.

Ketamine and its metabolite (2R,6R)-hydroxynorketamine induce lasting alterations in glutamatergic synaptic plasticity in the mesolimbic circuit.

Low doses of ketamine trigger rapid and lasting antidepressant effects after one injection in treatment-resistant patients with major depressive disorder. Modulation of AMPA receptors (AMPARs) in the hippocampus and prefrontal cortex is suggested to mediate the antidepressant action of ketamine and of one of its metabolites (2R,6R)-hydroxynorketamine ((2R,6R)-HNK). We have examined whether ketamine and (2R,6R)-HNK affect glutamatergic transmission and plasticity in the mesolimbic system, brain regions known to have key roles in reward-motivated behaviors, mood and hedonic drive. We found that one day after the injection of a low dose of ketamine, long-term potentiation (LTP) in the nucleus accumbens (NAc) was impaired. Loss of LTP was maintained for 7 days and was not associated with an altered basal synaptic transmission mediated by AMPARs and N-methyl-D-aspartate receptors (NMDARs). Inhibition of mammalian target of rapamycin signaling with rapamycin did not prevent the ketamine-induced loss of LTP but inhibited LTP in saline-treated mice. However, ketamine blunted the increase in the phosphorylation of the GluA1 subunit of AMPARs at a calcium/calmodulin-dependent protein kinase II/protein kinase C site induced by an LTP induction protocol. Moreover, ketamine caused a persistent increased phosphorylation of GluA1 at a protein kinase A site. (2R,6R)-HNK also impaired LTP in the NAc. In dopaminergic neurons of the ventral tegmental area from ketamine- or (2R,6R)-HNK-treated mice, AMPAR-mediated responses were depressed, while those mediated by NMDARs were unaltered, which resulted in a reduced AMPA/NMDA ratio, a measure of long-term synaptic depression. These results demonstrate that a single injection of ketamine or (2R,6R)-HNK induces enduring alterations in the function of AMPARs and synaptic plasticity in brain regions involved in reward-related behaviors.

First clinical experience with levodopa/carbidopa microtablets in Parkinson's disease.

BACKGROUND: Levodopa is the most effective symptomatic treatment throughout the course of Parkinson's disease, but as the disease progresses, there may be a need for individualized, fine-tuned treatments. AIM: To evaluate individualized levodopa/carbidopa dosing using microtablets dispensed with a dose dispenser, with respect to efficacy and usability as perceived by patients. METHODS: Patient records and dose dispenser reports from patients previously or currently treated with microtablets and a dose dispenser were reviewed, and a patient questionnaire concerning effect and usability was sent to patients. RESULTS: Eleven patient records, four dose dispenser reports and nine survey responses were obtained. The treatment effect was considered to be improved by six of nine patients. One-third found their bradykinesia to be improved, and the non-troublesome dyskinesia was unchanged according to a majority of patients; however, some experienced the duration and magnitude of troublesome dyskinesia to be worse. The usability was generally rated as good. The four dose dispenser reports obtained showed 97(±5)% total adherence. CONCLUSIONS: The experienced effect of treatment can, for some patients, be improved by the use of microtablets, and the dose dispenser was considered user-friendly. Further studies with a larger study population and prospective design are needed to confirm the results.

Genetic evidence for role of integration of fast and slow neurotransmission in schizophrenia.

The most recent genome-wide association studies (GWAS) of schizophrenia (SCZ) identified hundreds of risk variants potentially implicated in the disease. Further, novel statistical methodology designed for polygenic architecture revealed more potential risk variants. This can provide a link between individual genetic factors and the mechanistic underpinnings of SCZ. Intriguingly, a large number of genes coding for ionotropic and metabotropic receptors for various neurotransmitters-glutamate, γ-aminobutyric acid (GABA), dopamine, serotonin, acetylcholine and opioids-and numerous ion channels were associated with SCZ. Here, we review these findings from the standpoint of classical neurobiological knowledge of neuronal synaptic transmission and regulation of electrical excitability. We show that a substantial proportion of the identified genes are involved in intracellular cascades known to integrate 'slow' (G-protein-coupled receptors) and 'fast' (ionotropic receptors) neurotransmission converging on the protein DARPP-32. Inspection of the Human Brain Transcriptome Project database confirms that that these genes are indeed expressed in the brain, with the expression profile following specific developmental trajectories, underscoring their relevance to brain organization and function. These findings extend the existing pathophysiology hypothesis by suggesting a unifying role of dysregulation in neuronal excitability and synaptic integration in SCZ. This emergent model supports the concept of SCZ as an 'associative' disorder-a breakdown in the communication across different slow and fast neurotransmitter systems through intracellular signaling pathways-and may unify a number of currently competing hypotheses of SCZ pathophysiology.

Emotional memory impairments induced by AAV-mediated overexpression of human α-synuclein in dopaminergic neurons of the ventral tegmental area.

Parkinson's disease (PD) is associated with extensive degeneration of dopaminergic neurons originating in the substantia nigra pars compacta, but neuronal loss is also found in the ventral tegmental area (VTA). The VTA projects to areas involved in cognitive and emotional processes, including hippocampus, amygdala, nucleus accumbens and prefrontal cortex, and has thus been proposed to play a role in emotional memory impairments in PD. Since the formation of α-synuclein inclusions throughout the central nervous system is a pathological hallmark of PD, we studied the progressive effects of α-synuclein overexpression in the VTA on motor functions, emotional behaviour and emotional memory. Adeno-associated viral (AAV) vectors encoding either human α-synuclein or green fluorescent protein (GFP) were injected stereotactically into the VTA, and behaviour was monitored 3 and 8 weeks following AAV injection. At week 8, there was a 22% reduction of TH+ neurons in the VTA. We demonstrate that α-synuclein overexpression in dopaminergic neurons of the VTA induced mild motor deficits that appeared 3 weeks following AAV-α-synuclein injection and were aggravated at week 8. No depressive- or anxiety-like behaviours were found. To address emotional memory, we used the passive avoidance test, a one-trial associative learning paradigm based on contextual conditioning which requires minimal training. Interestingly, emotional memory impairments were found in α-synuclein overexpressing animals at week 8. These findings indicate that α-synuclein overexpression induces progressive memory impairments likely caused by a loss of function of mesolimbic dopaminergic projections.

Depressive-like phenotype induced by AAV-mediated overexpression of human α-synuclein in midbrain dopaminergic neurons.

Parkinson's disease (PD) is a neurodegenerative disorder characterized by a progressive loss of nigral dopaminergic neurons and by the presence of aggregates containing α-synuclein called Lewy bodies. Viral vector-induced overexpression of α-synuclein in dopaminergic neurons represents a model of PD which recapitulates disease progression better than commonly used neurotoxin models. Previous studies using this model have reported motor and cognitive impairments, whereas depression, mood and anxiety phenotypes are less described. To investigate these psychiatric phenotypes, Sprague-Dawley rats received bilateral injections of a recombinant adeno-associated virus (AAV) vector expressing human α-synuclein or GFP into the substantia nigra pars compacta. Behavior was assessed at two timepoints: 3 and 8 weeks post-injection. We report that nigral α-synuclein overexpression led to a pronounced nigral dopaminergic cell loss accompanied by a smaller cell loss in the ventral tegmental area, and to a decreased striatal density of dopaminergic fibers. The AAV-α-synuclein group exhibited modest, but significant motor impairments 8 weeks after vector administration. The AAV-α-synuclein group displayed depressive-like behavior in the forced swim test after 3 weeks, and reduced sucrose preference at week 8. At both timepoints, overexpression of α-synuclein was linked to a hyperactive hypothalamic-pituitary-adrenal (HPA) axis regulation of corticosterone. The depressive-like phenotype was also correlated with decreased nigral brain-derived neurotrophic factor and spinophilin levels, and with decreased striatal levels of the activity-regulated cytoskeleton-associated protein. This study demonstrates that AAV-mediated α-synuclein overexpression in dopamine neurons is not only useful to model motor impairments of PD, but also depression. This study also provides evidence that depression in experimental Parkinsonism is correlated to dysregulation of the HPA axis and to alterations in proteins involved in synaptic plasticity.

NMDA receptor antagonists ketamine and Ro25-6981 inhibit evoked release of glutamate in vivo in the subiculum.

Preclinical and clinical data have identified ketamine, a non-selective NMDAR (N-methyl-D-aspartate receptor) antagonist, as a promising medication for patients who do not respond to treatment with monoamine-based antidepressants. Moreover, unlike the current monoamine-based antidepressants, ketamine has a long-lasting effect already after a single dose. The mechanisms of ketamine action remain to be fully understood. Using a recently developed microelectrode array (MEA), which allows sub-second measurements of fluctuating glutamate concentrations, we studied here the effects of in vivo local application of the ketamine and of the N2B subunit-specific antagonist Ro25-6981 upon evoked glutamate release. Both ligands inhibit glutamate release in subregions of the hippocampus and prefrontal cortex. Likewise, acute systemic ketamine treatment, at an antidepressant dose, caused a reduction in evoked glutamate release in the subiculum. We suggest that the effects of ketamine and Ro25-6981 in the subiculum could involve blockade of presynaptic NMDA receptors containing N2B subunits.

Bidirectional regulation of emotional memory by 5-HT1B receptors involves hippocampal p11.

Cognitive impairments are common in depression and involve dysfunctional serotonin neurotransmission. The 5-HT1B receptor (5-HT(1B)R) regulates serotonin transmission, via presynaptic receptors, but can also affect transmitter release at heterosynaptic sites. This study aimed at investigating the roles of the 5-HT(1B)R, and its adapter protein p11, in emotional memory and object recognition memory processes by the use of p11 knockout (p11KO) mice, a genetic model for aspects of depression-related states. 5-HT(1B)R agonist treatment induced an impairing effect on emotional memory in wild type (WT) mice. In comparison, p11KO mice displayed reduced long-term emotional memory performance. Unexpectedly, 5-HT(1B)R agonist stimulation enhanced memory in p11KO mice, and this atypical switch was reversed after hippocampal adeno-associated virus mediated gene transfer of p11. Notably, 5-HT(1B)R stimulation increased glutamatergic neurotransmission in the hippocampus in p11KO mice, but not in WT mice, as measured by both pre- and postsynaptic criteria. Magnetic resonance spectroscopy demonstrated global hippocampal reductions of inhibitory GABA, which may contribute to the memory enhancement and potentiation of pre- and post-synaptic measures of glutamate transmission by a 5-HT(1B)R agonist in p11KO mice. It is concluded that the level of hippocampal p11 determines the directionality of 5-HT(1B)R action on emotional memory processing and modulates hippocampal functionality. These results emphasize the importance of using relevant disease models when evaluating the role of serotonin neurotransmission in cognitive deficits related to psychiatric disorders.

Clinical trials of dementia with Lewy bodies and Parkinson's disease dementia.

Despite the frequency and importance of dementia associated with Parkinson's disease (PDD) and dementia with Lewy bodies (DLB), there is relatively little evidence on which to base treatment. Evidence from meta-analysis suggests that rivastigmine can improve cognition and functioning in PDD and also reduce risk of falling. There is also evidence supporting its use in DLB. Recent evidence suggests that memantine may also be effective, particularly for PDD, although evidence is more conflicting. Memantine may also improve parkinsonism and dyskinesias. Few clinical trials of cognition in PD without dementia exist, but there is preliminary evidence for atomoxetine, memantine, and piribedil. There is a lack of systematic evidence for the treatment of visual hallucinations and depression in PDD and DLB. In addition, there is a need for studies of whether potentially disease-modifying agents can prevent or delay the progression to dementia in PD.

Emotional memory impairments in a genetic rat model of depression: involvement of 5-HT/MEK/Arc signaling in restoration.

Cognitive dysfunctions are common in major depressive disorder, but have been difficult to recapitulate in animal models. This study shows that Flinders sensitive line (FSL) rats, a genetic rat model of depression, display a pronounced impairment of emotional memory function in the passive avoidance (PA) task, accompanied by reduced transcription of Arc in prefrontal cortex and hippocampus. At the cellular level, FSL rats have selective reductions in levels of NMDA receptor subunits, serotonin 5-HT(1A) receptors and MEK activity. Treatment with chronic escitalopram, but not with an antidepressant regimen of nortriptyline, restored memory performance and increased Arc transcription in FSL rats. Multiple pharmacological manipulations demonstrated that procognitive effects could also be achieved by either disinhibition of 5-HT(1A)R/MEK/Arc or stimulation of 5-HT4R/MEK/Arc signaling cascades. Taken together, studies of FSL rats in the PA task revealed reversible deficits in emotional memory processing, providing a potential model with predictive and construct validity for assessments of procognitive actions of antidepressant drug therapies.

Genetic, pharmacological and lesion analyses reveal a selective role for corticohippocampal GLUN2B in a novel repeated swim stress paradigm.

Glutamate and N-methyl-d-aspartate receptor (NMDAR) dysfunction is strongly implicated in the pathophysiology of mood and anxiety disorders. Treatment with NMDAR antagonists has antidepressant efficacy in treatment-resistant depressives. In preclinical rodent models, NMDAR antagonist administration reduces anxiety- and stress-related behaviors in concert with increases in prefrontal cortical (PFC) dendritic spinogenesis and synaptic proteins. While these effects have been attributed to actions at the NMDAR GluN2B subunit, the precise role of cortical GluN2B in mediating emotional behaviors and stress-responsivity is not fully understood. Here, we employed a novel mutant model in which the GluN2B subunit is postnatally deleted in principal neurons in the cortex and the dorsal CA1 subregion of the hippocampus. GluN2BKO mice were phenotyped on a battery of tests for anxiety-related (light/dark exploration, stress-induced hyperthermia) and antidepressant-sensitive (sucrose preference, novelty-induced hypophagia, single-trial forced swim) behaviors. A novel repeated inescapable forced swim paradigm (riFS) was developed to assess behavioral responses to repeated stress in the GluN2BKO mice. For comparison, non-mutant C57BL/6J mice were tested for single-trial forced swim behavior after systemic Ro 25-6981 treatment and for riFS behavior after lesions of the ventromedial prefrontal cortex. riFS-induced alterations in corticolimbic GluN2B expression were also examined in C57BL/6J mice. We found that GluN2BKO mice reduced "despair-like" behavior in the riFS procedure, as compared to GluN2BFLOX controls. By contrast, GluN2BKO mice showed minimal alterations on anxiety-like or antidepressant-sensitive assays, including the single-trial forced swim test. In C57BL/6J mice, induction of "despair-like" responses in the riFS test was attenuated by vmPFC lesions, and was associated with changes in limbic GluN2B expression. Collectively, these data suggest that cortical GluN2B plays a major role in modulating adaptive responses to stress. Current findings provide further support for GluN2B as a key mechanism underlying stress responsivity, and a novel pharmacotherapeutic target for stress-related neuropsychiatric disorders.

The neurobiological properties of tianeptine (Stablon): from monoamine hypothesis to glutamatergic modulation.

Tianeptine is a clinically used antidepressant that has drawn much attention, because this compound challenges traditional monoaminergic hypotheses of depression. It is now acknowledged that the antidepressant actions of tianeptine, together with its remarkable clinical tolerance, can be attributed to its particular neurobiological properties. The involvement of glutamate in the mechanism of action of the antidepressant tianeptine is consistent with a well-developed preclinical literature demonstrating the key function of glutamate in the mechanism of altered neuroplasticity that underlies the symptoms of depression. This article reviews the latest evidence on tianeptine's mechanism of action with a focus on the glutamatergic system, which could provide a key pathway for its antidepressant action. Converging lines of evidences demonstrate actions of tianeptine on the glutamatergic system, and therefore offer new insights into how tianeptine may be useful in the treatment of depressive disorders.

Neuropeptidomics: expanding proteomics downwards.

Biological function is mainly carried out by a dynamic population of proteins and peptides which may be used as markers for disease diagnosis, prognosis and as a guide for effective treatment. The study of proteins is called proteomics and it is generally performed by two-dimensional gel electrophoresis and mass spectrometric methods. However, gel-based proteomics is methodologically restricted from the low mass region, which includes important endogenous peptides. The study of endogenous peptides, peptidomics, is complicated by protein fragments produced post-mortem during conventional sample handling. Nanoflow liquid chromatography and MS, together with improved methods for sample preparation, have been used to semi-quantitatively monitor endogenous peptides in brain tissue. When rapidly heat-denatured brain tissue was analysed, these methods enabled simultaneous detection of hundreds of peptides and the identification of several endogenous peptides not previously described in the literature. In an application of the MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) model for Parkinson's disease, the expression of the small protein PEP-19 was compared with controls. The levels were found to be significantly decreased in the striatum of MPTP-treated animals.

Depletion of the lipid raft constituents, sphingomyelin and ganglioside, decreases serotonin binding at human 5-HT7(a) receptors in HeLa cells.

AIM: The localization and function of several G protein-coupled receptors, including beta-adrenergic receptors and NK 1 receptors, are regulated via lipid rafts in the plasma membrane. These domains are enriched in cholesterol, gangliosides and sphingolipids, and play an important role in regulating signal transduction in most cell types. Serotonin (5-hydroxytryptamine, 5-HT), acting via 14 different receptors, regulates as diverse effects as mood, metabolism and smooth muscle contraction. 5-HT(7) receptors are involved in the regulation of depression, circadian rhythms, thermoregulation and vasodilatation. Ligand binding and signalling via the 5-HT(7) receptor are regulated by membranous cholesterol. Here we investigated the role of sphingomyelin and gangliosides on binding of 5-HT to 5-HT(7) receptors to further examine the role of lipid raft constituents on 5-HT(7) receptor function. METHODS: HeLa cells stably transfected with the human 5-HT(7) receptor were treated with Fumonisin B(1) or (+/-)-threo-1-Phenyl-2-decanoylamino-3-morpholino-1-propanol (PDMP) to reduce sphingomyelin or ganglioside levels, respectively. The effects of these treatments were investigated by the 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl-tetrazolium bromide (MTT) viability assay, cholesterol analysis and [(3)H]5-HT binding studies on intact cells. RESULTS: Treatments with 20 mum Fumonisin B(1) for 24 h or with 10 mum PDMP for 48 h had no effects of total levels if 5-HT(7) receptors, but caused significant decreases in maximum [(3)H]5-HT binding to 5-HT(7) receptors. The effects were cholesterol-independent as levels of cholesterol remained unaffected by either treatment. CONCLUSION: These data demonstrate a role for sphingomyelin and gangliosides in regulating binding of [(3)H]5-HT to 5-HT(7) receptors. These observations further strengthen that actions of 5-HT via 5-HT(7) receptors are dependent upon lipid raft integrity.

Distinct roles for spinophilin and neurabin in dopamine-mediated plasticity.

Protein phosphatase 1 plays a major role in the governance of excitatory synaptic activity, and is subject to control via the neuromodulatory actions of dopamine. Mechanisms involved in regulating protein phosphatase 1 activity include interactions with the structurally related cytoskeletal elements spinophilin and neurabin, synaptic scaffolding proteins that are highly enriched in dendritic spines. The requirement for these proteins in dopamine-related neuromodulation was tested using knockout mice. Dopamine D1-mediated regulation of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate receptor activity was deficient in both striatal and prefrontal cortical neurons from neurabin knockout mice; in spinophilin knockout mice this deficit was manifest only in striatal neurons. At corticostriatal synapses long-term potentiation was deficient in neurabin knockout mice, but not in spinophilin knockout mice, and was rescued by a D1 receptor agonist. In contrast, long-term depression was deficient in spinophilin knockout mice but not in neurabin knockout mice, and was rescued by D2 receptor activation. Spontaneous excitatory post-synaptic current frequency was increased in neurabin knockout mice, but not in spinophilin knockout mice, and this effect was normalized by D2 receptor agonist application. Both knockout strains displayed increased induction of GluR1 Ser(845) phosphorylation in response to D1 receptor stimulation in slices, and also displayed enhanced locomotor activation in response to cocaine administration. These effects could be dissociated from cocaine reward, which was enhanced only in spinophilin knockout mice, and was accompanied by increased immediate early gene induction. These data establish a requirement for synaptic scaffolding in dopamine-mediated responses, and further indicate that spinophilin and neurabin play distinct roles in dopaminergic signal transduction and psychostimulant response.

Cocaine self-administration in mice is inversely related to phosphorylation at Thr34 (protein kinase A site) and Ser130 (kinase CK1 site) of DARPP-32.

The reinforcing effect of cocaine is associated with increases in dopamine in the striatum. The phosphoprotein DARPP-32 (dopamine- and cAMP-regulated phosphoprotein) has been shown to mediate the intracellular events after activation of dopamine receptors. DARPP-32 is phosphorylated at multiple sites by different protein kinases, but little is known about the functional role of these different sites. Cocaine self-administration and striatal levels of dopamine after acute "binge" cocaine administration were measured in separate lines of mice with alanine mutations introduced into DARPP-32 at either Thr34 (protein kinase A site, Thr34A), Thr75, (cyclin-dependent kinase 5 site, Thr75A), Ser97 (kinase CK2 site, Ser97A), or Ser130 (kinase CK1 site, Ser130A). Acquisition of stable cocaine self-administration required significantly more time in Thr34A-/- mice. Both Thr34A- and Ser130A-DARPP-32 mutant mice self-administered more cocaine than their respective wild-type controls. Also, cocaine-induced increases of dopamine in dorsal striatum were attenuated in the Thr34A- and Ser130A-DARPP-32 phosphomutant mice compared with wild-type mice. Notably, levels of P-Thr34- and P-Ser130-DARPP-32 were reduced after self-administration of cocaine in wild-type mice. Thus, phosphorylation states of Thr34- and Ser130-DARPP-32 play important roles in modulating the reinforcing effects of cocaine.