Silencing of miR490-3p by H. pylori activates DARPP-32 and induces resistance to gefitinib.

Infection with Helicobacter pylori (H. pylori) is the main risk factor for gastric carcinogenesis. In this study, we investigated the expression, molecular functions, and downstream effectors of miR490-3p in gastric cancer. We used in vitro and in vivo models to investigate the role of H. pylori in regulating miR490-3p, DARPP-32-dependent functions, and therapeutic resistance. Human and mouse neoplastic gastric lesions demonstrated a negative correlation between DARPP-32 and miR490-3p expression (R = -0.58, P < 0.01). This was also detected following infection with H. pylori (R = -0.66, P < 0.01). Molecular assays confirmed DARPP-32 as a direct target of miR490-3p. CHRM2, the host gene of miR490-3p, was hypermethylated and downregulated in neoplastic gastric tissues (P < 0.05). H. pylori induced methylation and downregulation of CHRM2 and miR490-3p. Functionally, the reconstitution of miR490-3p sensitized cancer cells to gefitinib by inactivating DRAPP-32-dependent AKT and STAT3 pathways. Patients with low miR490-3p or high DARPP-32 expression had decreased overall survival (P < 0.05). Hypermethylation-mediated silencing of CHRM2 and miR490-3p by H. pylori increased DARPP-32 expression. Downregulation of miR490-3p in gastric cancer plays a role in gefitinib response by inducing DARPP-32-mediated activation of PI3K/AKT, STAT3 signaling pathways.

DARPP-32 in the orchestration of responses to positive natural stimuli.

Dopamine- and cAMP-regulated phosphoprotein (Mr 32 kDa, DARPP-32) is an integrator of multiple neuronal signals and plays a crucial role particularly in mediating the dopaminergic component of the systems involved in the evaluation of stimuli and the ensuing elaboration of complex behavioral responses (e.g., responses to reinforcers and stressors). Dopamine neurons can fire tonically or phasically in distinct timescales and in specific brain regions to code different behaviorally relevant information. Dopamine signaling is mediated mainly through the regulation of adenylyl cyclase activity, stimulated by D1-like or inhibited by D2-like receptors, respectively, that modulates cAMP-dependent protein kinase (PKA) function. The activity of DARPP-32 is finely regulated by its phosphorylation at multiple sites. Phosphorylation at the threonine (Thr) 34 residue by PKA converts DARPP-32 into an inhibitor of protein phosphatase 1, while the phosphorylation at the Thr75 residue turns it into an inhibitor of PKA. Thus, DARPP-32 is critically implicated in regulating striatal output in response to the convergent pathways that influence signaling of the cAMP/PKA pathway. This review summarizes some of the landmark and recent studies of DARPP-32-mediated signaling in the attempt to clarify the role played by DARPP-32 in the response to rewarding natural stimuli. Particularly, the review deals with data derived from rodents studies and discusses the involvement of the cAMP/PKA/DARPP-32 pathway in: 1) appetitive food-sustained motivated behaviors, 2) motivated behaviors sustained by social reward, 3) sexual behavior, and 4) responses to environmental enrichment.

Immunohistochemical Localization of DARPP-32 in the Brain of Two Lungfishes: Further Assessment of Its Relationship with the Dopaminergic System.

The distribution of DARPP-32 (a phosphoprotein related to the dopamine D1 receptor) has been widely used as a means to clarify the brain regions with dopaminoceptive cells, primarily in representative species of tetrapods. The relationship between dopaminergic and dopaminoceptive elements is frequently analyzed using the catecholamine marker tyrosine hydroxylase (TH). In the present study, by means of combined immunohistochemistry, we have analyzed these relationships in lungfishes, the only group of sarcopterygian fishes represented by 6 extant species that are the phylogenetically closest living relatives of tetrapods. We used the Australian lungfish Neoceratodus forsteri and the African lungfish Protopterus dolloi. The DARPP-32 antibody yields a distinct and consistent pattern of neuronal staining in brain areas that, in general, coincide with areas that are densely innervated by TH-immunoreactive fibers. The striatum, thalamus, optic tectum, and torus semicircularis contain intensely DARPP-32-immunoreactive cell bodies and fibers. Cells are also located in the olfactory bulbs, amygdaloid complex, lateral septum, pallidum, preoptic area, suprachiasmatic nucleus, tuberal hypothalamic region, rostral rhombencephalic reticular formation, superior raphe nucleus, octavolateral area, solitary tract nucleus, and spinal cord. Remarkably, DARPP-32-immunoreactive fibers originating in the striatum reach the region of the dopaminergic cells in the mesencephalic tegmentum and represent a well-established striatonigral pathway in lungfishes. Double immunolabeling reveals that DARPP-32 is present in neurons that most likely receive TH input, but it is absent from the catecholaminergic neurons themselves, with the only exception of a few cells in the suprachiasmatic nucleus of Neoceratodus and the solitary tract nucleus of Protopterus. In addition, some species differences exist in the localization of DARPP-32 cells in the pallium, lateral amygdala, thalamus, prethalamus, and octavolateral area. In general, the present study demonstrates that the distribution pattern of DARPP-32, and its relationship with TH, is largely comparable to those reported for tetrapods, highlighting a shared situation among all sarcopterygians.

Characterising the developmental profile of human embryonic stem cell-derived medium spiny neuron progenitors and assessing mature neuron function using a CRISPR-generated human DARPP-32WT/eGFP-AMP reporter line.

In the developing ventral telencephalon, cells of the lateral ganglionic eminence (LGE) give rise to all medium spiny neurons (MSNs). This development occurs in response to a highly orchestrated series of morphogenetic stimuli that pattern the resultant neurons as they develop. Striatal MSNs are characterised by expression of dopamine receptors, dopamine-and cyclic AMP-regulated phosphoprotein (DARPP32) and the neurotransmitter GABA. In this study, we demonstrate that fine tuning Wnt and hedgehog (SHH) signaling early in human embryonic stem cell differentiation can induce a subpallial progenitor molecular profile. Stimulation of TGFß signaling pathway by activin-A further supports patterning of progenitors to striatal precursors which adopt an LGE-specific gene signature. Moreover, we report that these MSNs also express markers associated with mature neuron function (cannabinoid, adenosine and dopamine receptors). To facilitate live-cell identification we generated a human embryonic stem cell line using CRISPR-mediated gene editing at the DARPP32 locus (DARPP32WT/eGFP-AMP-LacZ). The addition of dopamine to MSNs either increased, decreased or had no effect on intracellular calcium, indicating the presence of multiple dopamine receptor subtypes. In summary, we demonstrate greater control over early fate decisions using activin-A, Wnt and SHH to direct differentiation into MSNs. We also generate a DARPP32 reporter line that enables deeper pharmacological profiling and interrogation of complex receptor interactions in human MSNs.

Dyskinesia in Parkinson's disease: mechanisms and current non-pharmacological interventions.

Dopamine replacement therapy in Parkinson's disease is associated with several unwanted effects, of which dyskinesia is the most disabling. The development of new therapeutic interventions to reduce the impact of dyskinesia in Parkinson's disease is therefore a priority need. This review summarizes the key molecular mechanisms that underlie dyskinesia. The role of dopamine receptors and their associated signaling mechanisms including dopamine-cAMP-regulated neuronal phosphoprotein, extracellular signal-regulated kinase, mammalian target of rapamycin, mitogen and stress-activated kinase-1 and Histone H3 are summarized, along with an evaluation of the role of cannabinoid and nicotinic acetylcholine receptors. The role of synaptic plasticity and animal behavioral results on dyskinesia are also evaluated. The most recent therapeutic advances to treat Parkinson's disease are discussed, with emphasis on the possibilities and limitations of non-pharmacological interventions such as physical activity, deep brain stimulation, transcranial magnetic field stimulation and cell replacement therapy. The review suggests new prospects for the management of Parkinson's disease-associated motor symptoms, especially the development of dyskinesia. This review aims at summarizing the key molecular mechanisms underlying dyskinesia and the most recent therapeutic advances to treat Parkinson's disease with emphasis on non-pharmacological interventions such as physical activity, deep brain stimulation (DBS), transcranial magnetic field stimulation (TMS) and cell replacement therapy. These new interventions are discussed from both the experimental and clinical point of view, describing their current strength and limitations.

Genetic polymorphisms regulating dopamine signaling in the frontal cortex interact to affect target detection under high working memory load.

Frontal-dependent task performance is typically modulated by dopamine (DA) according to an inverted-U pattern, whereby intermediate levels of DA signaling optimizes performance. Numerous studies implicate trait differences in DA signaling based on differences in the catechol-O-methyltransferase (COMT) gene in executive function task performance. However, little work has investigated genetic variations in DA signaling downstream from COMT. One candidate is the DA- and cAMP-regulated phosphoprotein of molecular weight 32 kDa (DARPP-32), which mediates signaling through the D1-type DA receptor, the dominant DA receptor in the frontal cortex. Using an n-back task, we used signal detection theory to measure performance in a healthy adult population (n = 97) genotyped for single nucleotide polymorphisms in the COMT (rs4680) and DARPP-32 (rs907094) genes. Correct target detection (hits) and false alarms were used to calculate d' measures for each working memory load (0-, 2-, and 3-back). At the highest load (3-back) only, we observed a significant COMT × DARPP-32 interaction, such that the DARPP-32 T/T genotype enhanced target detection in COMT(ValVal) individuals, but impaired target detection in COMT(Met) carriers. These findings suggest that enhanced dopaminergic signaling via the DARPP-32 T allele aids target detection in individuals with presumed low frontal DA (COMT(ValVal)) but impairs target detection in those with putatively higher frontal DA levels (COMT(Met) carriers). Moreover, these data support an inverted-U model with intermediate levels of DA signaling optimizing performance on tasks requiring maintenance of mental representations in working memory.

A conversation with Paul Greengard. Interview by Eric J Nestler.

Paul Greengard was born in New York City in 1925. After completing high school, he served three years in the US Navy during World War II and then completed his bachelor's degree at Hamilton College where he majored in physics and mathematics. He obtained a PhD in biophysics from Johns Hopkins University in 1953 and pursued postdoctoral training with Wilhelm Feldberg at the National Institute for Medical Research in England. After eight years as head of biochemistry at Geigy, and sabbaticals at Albert Einstein College of Medicine and Vanderbilt University, he joined the Yale University faculty as a full professor of pharmacology in 1968. While he was at Yale, Greengard's laboratory performed groundbreaking research, which demonstrated a role for cyclic nucleotides, protein kinases and protein phosphatases, and their protein substrates in the regulation of synaptic transmission. In 1983, Greengard moved to The Rockefeller University, where he has since served as the Vincent Astor Professor and Head of the Laboratory of Molecular and Cellular Neuroscience. Greengard's paradigm-shifting research has continued at Rockefeller and has informed our understanding and possible treatment of a host of brain disorders, including schizophrenia, Alzheimer's disease, Parkinson's disease, and depression. He is the author of more than 950 research articles and reviews. Greengard has received numerous awards and honors, including the Nobel Prize in Physiology or Medicine in 2000, the Metropolitan Life Foundation Award for Medical Research, The National Academy of Sciences Award in Neuroscience, the Ralph W. Gerard Prize in Neuroscience for the Society for Neuroscience, and the Karolinska Institutet's Bicentennial Gold Medal. He is a member of the US National Academy of Sciences and the Institute of Medicine of the National Academies. The following interview was conducted on May 29, 2012.

Association between PPP1R1B polymorphisms and defense mechanisms in healthy Chinese-Han subjects.

Defense mechanisms resulting from the interaction between biological factors and the environment have been established. In genetic studies, dopamine genes have been recognized to play an important role in the determination of defense mechanisms. DARPP-32 (dopamine- and cAMP-regulated phosphoprotein) plays a central role in the biology of dopamine-receptive neurons; its coding gene (PPP1R1B) has been linked to psychological and psychopathological traits. Here, we aimed to explore the association between PPP1R1B polymorphisms and defense mechanisms measured using the 88-item Defense Style Questionnaire in 400 healthy Chinese-Han subjects. Of the three polymorphisms examined, rs12601930 was associated with projection (P = 0.028) and splitting (P = 0.032), while rs3764352 was associated with splitting (P = 0.042). No significant association was found between rs879606 and defenses. When analyzed separately by gender, no significant association between defense mechanisms and PPP1R1B polymorphisms in males was observed. In females, however, rs12601930 was significantly associated with splitting (P = 0.018), and rs879606, with projection (P = 0.015), help-rejecting complaining (P = 0.030), and immature defense style (P = 0.031), while rs3764352 was not associated with any defense. The distribution of genotypes between the low- and high-scoring subgroups for each defense style showed no significant differences. Our results suggest that PPP1R1B polymorphisms are, at least partially, responsible for immature defenses.

Mesoscopic models of neurotransmission as intermediates between disease simulators and tools for discovering design principles.

Two grand challenges have been declared as premier goals of computational systems biology. The first is the discovery of network motifs and design principles that help us understand and rationalize why biological systems are organized in the manner we encounter them rather than in a different fashion. The second goal is the development of computational models supporting the investigation of complex systems, in particular, as simulation platforms in personalized medicine and predictive health. Interestingly, most published systems models in biology contain between a handful and a few dozen variables. They are usually too complicated for systemic analyses of organizing principles, but they are at the same time too coarse to allow reliable simulations of diseases. While it may thus appear that the modeling efforts of the past have missed the declared targets of systems biology, we argue in this article that midsized mesoscopic models are excellent starting points for pursuing both goals in computational systems biology.

DARPP-32 is required for MAPK/ERK signaling in thyroid cells.

Modulation of MAPK signaling duration by cAMP defines its physiological output by driving cells toward proliferation or differentiation. Understanding how the kinetics of MAPK signaling are integrated with other cellular signals is a key issue in development and cancer. Here we show that dopamine and cAMP-regulated neuronal phosphoprotein, 32 kDa (DARPP-32), a protein required for thyroid cell differentiation, determines whether MAPK/ERK activation is sustained or transient. Serum, a stimulus that activates MAPK signaling and does not independently increase DARPP-32 levels results in transient activation of the MAPK pathway. By contrast, TSH + (IGF-I) activate MAPK signaling but also independently increase DARPP-32 levels. Our results are consistent with a model in which maintenance of DARPP-32 expression by TSH + IGF-I leads to sustained MAPK signaling. Moreover, the sensitivity of MAPK/ERK signaling in thyroid cells is lost when de novo DARPP-32 expression is blocked by small interfering RNA. Because both DARPP-32 levels and function as inhibitor of protein phosphatase 1, a key inhibitor of MAPK kinase activity, are governed by cAMP/protein kinase A, the results may explain why in thyroid cells cAMP signaling downstream from TSH controls the duration of MAPK pathway activity. Thus, fine-tuning of DARPP-32 levels leads to changes in the kinetics or sensitivity of MAPK/ERK signaling. Given the implications of MAPK signaling in thyroid cancer and the loss of DARPP-32 in tumor and transformed thyroid cells, DARPP-32 may represent a key therapeutic target.

Signaling in striatal neurons: the phosphoproteins of reward, addiction, and dyskinesia.

The striatum is a deep region of the forebrain involved in action selection, control of movement, and motivation. It receives a convergent excitatory glutamate input from the cerebral cortex and the thalamus, controlled by dopamine (DA) released in response to unexpected rewards and other salient stimuli. Striatal function and its dysfunction in drug addiction or Parkinson's disease depend on the interplay between these neurotransmitters. Signaling cascades in striatal medium-sized spiny neurons (MSNs) involve multiple kinases, phosphatases, and phosphoproteins, some of which are highly enriched in these neurons. They control the properties of ion channels and the plasticity of MSNs, in part through their effects on gene transcription. This chapter summarizes signaling in MSNs and focuses on the regulation of multiple protein phosphatases through DA and glutamate receptors and the role of ERK. It is hypothesized that these pathways are particularly adapted to the specific computing properties of MSNs and the function of the basal ganglia circuits in which they participate.

Role of CAMKII in reinforcement learning: a computational model of glutamate and dopamine signaling pathways.

Timely release of dopamine (DA) at the striatum seems to be important for reinforcement learning (RL) mediated by the basal ganglia. Houk et al. (in: Houk et al (eds) Models of information processing in the basal ganglia, (1995) proposed a cellular signaling pathway model to characterize the interaction between DA and glutamate pathways that have a role in RL. The model simulation results, using GENESIS KINETIKIT simulator, point out that there is not only prolongation of duration as proposed by Houk et al. (1995), but also an enhancement in the amplitude of autophosphorylation of CaMKII. Further, the autophosphorylated form of CaMKII may form a basis for the "eligibility trace" condition required in RL. This simulation study is the first of its kind to support the comprehensive theoretical proposal of Houk et al. (1995).

Cocaine sensitization models an anhedonia-like condition in rats.

Anhedonia is a core symptom of depression that also characterizes substance abuse-related mood disorders, in particular those secondary to stimulant abuse. This study investigated the long-lasting condition of cocaine sensitization as an inducing condition for anhedonia in rats. Cortical-mesolimbic dopamine plays a central role in assessing the incentive value of a stimulus and an increased dopamine output in these areas after a novel palatable meal seems to correlate with the ability to acquire an instrumental behaviour aimed at earning it again. This dopaminergic response is associated with consistent modifications in the phosphorylation pattern of some cAMP-dependent protein kinase (PKA) substrates and it is mediated by dopamine D1 receptor stimulation. Thus, since behavioural cocaine sensitization is characterized by tonically increased levels of phospho-Thr75 DARPP-32 that is a potent PKA inhibitor, we hypothesized that cocaine-sensitized rats might reveal deficits in palatable food responding. Indeed, non-food-deprived cocaine-sensitized rats showed no interest in palatable food, no dopaminergic response after a palatable meal in terms of increased dopamine output and DARPP-32 phosphorylation changes, and no ability to acquire a palatable food-sustained instrumental behaviour. Repeated administration of an established antidepressant compound, imipramine, corrected these deficits and reinstated the dopaminergic response in the cortico-mesolimbic areas to control values. Thus, the behavioural modifications observed in cocaine-sensitized rats satisfy some requirements for an experimental model of anhedonia since they are induced by repeated cocaine administration (aetiological validity), they mimic an anhedonia-like symptom (construct validity), and are reversed by the administration of imipramine (predictive validity).

Immunohistochemical localization of DARPP-32 in the brain and spinal cord of anuran amphibians and its relation with the catecholaminergic system.

The relationship between dopaminergic neuronal structures and dopaminoceptive structures in the amphibian brain and spinal cord are assessed by means of single and double immunohistochemical techniques with antibodies directed against DARPP-32 (a phosphoprotein related to the dopamine D(1)-receptor) and tyrosine hydroxylase (TH) applied to the brain of the anurans Rana perezi and Xenopus laevis. The DARPP-32 antibody yielded a well-differentiated pattern of staining in the brain of these anurans. In general, areas that are densely innervated by TH-immunoreactive fibers such as the nucleus accumbens, striatum, amygdaloid complex, thalamus, optic tectum, torus semicircularis and spinal cord display a remarkable immunoreactivity for DARPP-32 in cell bodies and neuropil. Distinct cellular DARPP-32 immunoreactivity was also found in the septum, preoptic area, suprachiasmatic nucleus, tuberal hypothalamic region, habenula, retina, midbrain tegmentum, rhombencephalic reticular formation and solitary tract nucleus. Hodological data supported that striatal projection neurons were DARPP-32 immunoreactive. Double immunohistofluorescence staining revealed that catecholaminergic cells generally do not stain for DARPP-32, except for some cells in the ventral mesencephalic tegmentum of Xenopus and cells in the nucleus of the solitary tract of Rana. Several interspecies differences were noted for the DARPP-32 distribution in the brain of the two anurans, namely in the habenula, the thalamus and prethalamus, the cerebellum and octavolateral area and the structures with DARPP-32/TH colocalization. However, in general, the distribution of DARPP-32 in the brain of the anuran amphibians resembles in many aspects the pattern observed in amniotes, especially in reptiles.

Distinct subclasses of medium spiny neurons differentially regulate striatal motor behaviors.

The direct and indirect pathways of the basal ganglia have been proposed to oppositely regulate locomotion and differentially contribute to pathological behaviors. Analysis of the distinct contributions of each pathway to behavior has been a challenge, however, due to the difficulty of selectively investigating the neurons comprising the two pathways using conventional techniques. Here we present two mouse models in which the function of striatonigral or striatopallidal neurons is selectively disrupted due to cell type-specific deletion of the striatal signaling protein dopamine- and cAMP-regulated phosphoprotein Mr 32kDa (DARPP-32). Using these mice, we found that the loss of DARPP-32 in striatonigral neurons decreased basal and cocaine-induced locomotion and abolished dyskinetic behaviors in response to the Parkinson's disease drug L-DOPA. Conversely, the loss of DARPP-32 in striatopallidal neurons produced a robust increase in locomotor activity and a strongly reduced cataleptic response to the antipsychotic drug haloperidol. These findings provide insight into the selective contributions of the direct and indirect pathways to striatal motor behaviors.

Darpp-32 and its truncated variant t-Darpp have antagonistic effects on breast cancer cell growth and herceptin resistance.

BACKGROUND: Herceptin (trastuzumab) is a humanized monoclonal antibody that is approved for the treatment of metastatic breast cancer patients whose tumors overexpress Her2 (erbB2/neu). Up to 70% of Her2-positive breast cancers demonstrate a response to Herceptin-based therapies, but resistance almost inevitably arises within a year of the initial response. To help understand the mechanism of Herceptin resistance, we isolated clonal variants of Her2-positive BT474 human breast cancer cells (BT/Her(R)) that are highly resistant to Herceptin. These cell lines exhibit sustained PI3K/Akt signaling as an essential component of Herceptin-resistant proliferation. Several genes in the protein kinase A (PKA) signaling network have altered expression in BT/Her(R) cells, including PPP1R1B, which encodes a 32 kDa protein known as Darpp-32 and its amino-terminal truncated variant, t-Darpp. The purpose of the current work was to determine the role of Darpp-32 and t-Darpp in Herceptin resistance. METHODOLOGY AND RESULTS: We determined expression of Darpp-32 and t-Darpp in BT/Her(R) cells selected for resistance to Herceptin. Subsequently, cDNAs encoding the two isoforms of Darpp-32 were transfected, separately and together, into Her2-positive SK-Br-3 breast cancer cells. Transfected cells were tested for resistance to Herceptin and Herceptin-mediated dephosphorylation of Akt. DNA binding activity by the cAMP response element binding protein (CREB) was also measured. We found that BT/Her(R) cells overexpressed t-Darpp but not Darpp-32. Moreover, t-Darpp overexpression in SK-Br-3 cells was sufficient for conferring resistance to Herceptin and Herceptin-mediated dephosphorylation of Akt. Darpp-32 co-expression reversed t-Darpp's effects on Herceptin resistance and Akt phosphorylation. t-Darpp overexpression led to increased CREB binding activity, which was also reversible by Darpp-32. CONCLUSIONS: t-Darpp and Darpp-32 appear to have antagonistic effects on Herceptin resistance. We present a unified model by which these effects might be mediated via the PKA regulatory network.

Early long-term exposure with caffeine induces cross-sensitization to methylphenidate with involvement of DARPP-32 in adulthood of rats.

Chronic ingestion of caffeine causes dependence and sleep disturbance in children and adolescents. In rodents, the administration of caffeine may produce behavioral cross-sensitization to some psychostimulants, such as dopaminergic psychoactive drugs. Methylphenidate (MPH; Ritalin) is a psychostimulant used in pediatric- and adult human populations to manage the symptoms associated with attention-deficit hyperactivity disorder (ADHD). Previous studies have suggested that dopamine- and cAMP-regulated phosphoproteins of 32 kDa (DARPP-32) participate in the manifestation of behavioral activity following ingestion of caffeine or MPH. The aim of the present study was to evaluate whether long-term administration of low doses of caffeine in rodents during their adolescence induces cross-sensitization to MPH challenge in their adulthood and investigate the involvement of DARPP-32 in this model. Young rats (P25) consumed water or caffeine (0.3 g/L; mean consumption was 7.5 mg/day/kg) for 28 days. The caffeine consumption was then suspended for 14 days (washout period) when the animals received saline solution or MPH (1, 2, or 10 mg/kg) (P67) intraperitoneally. The locomotor activity of these rats was assessed using the open-field test, following which the immunocontent of DARPP-32 was evaluated in samples of their prefrontal cortex, striatum, or hippocampus. Rats chronically exposed to caffeine in their adolescent period and to inactive doses of MPH (1mg/kg) in adulthood showed augmented locomotor activity. The behavioral effect observed was accompanied by increased levels of DARPP-32 in the striatum and prefrontal cortex compared to control groups (saline or caffeine). However, no alteration caused by these treatments was noted in the hippocampus. In conclusion, chronic caffeine exposure induces likely long-term cross-sensitization to MPH in a DARPP-32-dependent pathway.

Antipsychotic drug actions on gene modulation and signaling mechanisms.

Schizophrenia is a debilitating chronic mental disorder characterized by significant lifetime risk and high social costs. Although its etiology remains unknown, many of its symptoms may be mitigated by treatment with antipsychotic drugs (APDs). These compounds, generally classified as first- or second-generation antipsychotics, have complex receptor profiles that may account for short-term clinical response and normalization of acute manifestation of the disease. However, APDs have additional therapeutic properties that may not be directly related to receptor mechanisms, but rather involve neuroadaptive changes in selected brain regions. Indeed the neurodevelopmental origin of schizophrenia suggests that the disease is characterized by neuroanatomical and pathophysiological impairments that, at molecular level, may reflect compromised neuroplasticity; the process by which the brain adapts to changes in a specific environment. Accordingly, it is possible that the long-term clinical efficacy of APDs might result from their ability in modulating systems crucially involved in neuroplasticity and cellular resilience. We have reviewed and discussed the results of several studies investigating the post-receptor mechanisms in the action of APDs. We specifically focused on intracellular signaling cascades (PKA, DARPP-32, MAPK, Akt/GSK-3, beta arrestin-2), neurotrophic factors and the glutamatergic system as important mediators for antipsychotic drug induced-neuroplasticity. Altogether, these data highlight the possibility that post-receptor mechanisms will eventually be promising targets for the development of novel drugs that, through their impact on neuroplasticity, may contribute to the improved treatment of patients diagnosed with schizophrenia.

Molecular mechanisms of psychostimulant addiction.

Drug addiction represents a pathological form of neuroplasticity along with the emergence of aberrant behaviors involving a cascade of neurochemical changes mainly in the brain's rewarding circuitry. The aberrant behavioral phenotypes can be assessed by an animal model of drug-induced behavioral sensitization, which is characterized by an initiation stage that is formed in the ventral tegmental area and a behavioral expression stage determined mainly in the nucleus accumbens. Numerous studies during past decades demonstrate that the mesocorticolimbic dopamine pathway plays an essential role in the development of behavioral sensitization. Moreover, a series of cellular signaling pathways and gene expression determine the severity of addictive behaviors. In addition to the well-characterized dopamine D1 receptor-mediated cAMP/protein kinase A up-regulation in the nucleus accumbens, recent reports indicate the cellular mediator dopamine- and cAMP-regulated phosphoprotein of 32 kDa (DARPP-32) and transcription regulator DeltaFosB are associated with the accumbal PKA pathway to modulate the development of behavioral sensitization. The finding of cAMP-independent and dopamine D2 receptor-mediated Akt/GSK3 in activation in the nucleus accumbens of behaviorally sensitized animals implies that a signal cascade down-stream of both dopamine D1 and D2 receptors comprises the mainstay of the addiction network. This review outlines the cellular pathways that have been demonstrated to participate in psychostimulant addiction, focused particularly in the nucleus accumbens.

Molecular mechanisms underlying levodopa-induced dyskinesia.

Although levodopa remains the most effective drug for the symptomatic treatment of Parkinson's disease, chronic therapy with this pharmacological compound initiates a complex cascade of cellular and molecular downstream effects resulting in the development of abnormal involuntary movements. The precise mechanisms underlying the development of levodopa induced dyskinesia, however, are far from being completely elucidated. In the present review, we will describe changes in long-term synaptic excitability following dopamine (DA) denervation and long-term levodopa treatment leading to abnormal involuntary movements. In particular, we will address the role of both DA D1 receptors and NMDA glutamate receptors in the induction and maintenance of dyskinesia and abnormal synaptic plasticity. We will also describe the possible interaction between these two receptors in the pathophysiology of dyskinesia taking the advantage of the existing knowledge concerning the mechanisms underlying drug abuse. This latter pathophysiological condition, in fact, seems to share several biochemical transduction pathways with those implicated in levodopa-induced dyskinesia. Finally, we will briefly discuss the possible implication of A2A adenosine receptors in long-term motor complications of levodopa therapy and focus on the interaction between A2A and D2 receptors. Future studies are required to understand how the interaction between these various biochemical steps converge to produce a long-term change in neuronal excitability within the basal ganglia leading to abnormal involuntary movements following levodopa treatment in the DA-denervated state.