An important step for cholinergic transmission involves the vesicular storage of acetylcholine (ACh), a process mediated by the vesicular acetylcholine transporter (VAChT). In order to understand the physiological roles of the VAChT, we developed a genetically altered strain of mice with reduced expression of this transporter. Heterozygous and homozygous VAChT knockdown mice have a 45% and 65% decrease in VAChT protein expression, respectively. VAChT deficiency alters synaptic vesicle filling and affects ACh release. Whereas VAChT homozygous mutant mice demonstrate major neuromuscular deficits, VAChT heterozygous mice appear normal in that respect and could be used for analysis of central cholinergic function. Behavioral analyses revealed that aversive learning and memory are not altered in mutant mice; however, performance in cognitive tasks involving object and social recognition is severely impaired. These observations suggest a critical role of VAChT in the regulation of ACh release and physiological functions in the peripheral and central nervous system.

cerebral cortex ͉ glutamatergic signaling ͉ regulatory RNA N MDA receptors (NMDA-R) control many executive brain functions, such as working memory, and their dysfunction is implicated in a host of brain disorders (1-4). Notably, hypofunctional NMDA-R signaling, particularly in the prefrontal cortex (PFC), has been implicated in the cognitive and behavioral disturbances characteristic of schizophrenia (5), autism (6, 7), attention deficit hyperactivity disorder (ADHD) (8, 9), mood disorders (10), and other psychiatric illnesses. The cellular mechanisms by which disrupted NMDA-R transmission drives behavioral pathology are still unclear, although several of the major proteins involved in this pathway, such as calcium/calmodulin-dependent protein kinase II (CaMKII) (11), have been identified. In this study, we examine whether neurobehavioral abnormalities associated with NMDA-R hypofunction can be attributed to a novel class of regulatory RNA molecules, microRNAs (miRNAs).miRNAs have attracted much attention as regulators of neuronal development and synaptic plasticity (12-15). Furthermore, psychiatric disorders such as schizophrenia, autism, and Tourette's syndrome are associated with dysregulated levels of miRNAs (16)(17)(18)(19)(20). miRNAs are small (Ϸ22 nt) noncoding transcripts that can control expression of protein-coding mRNAs at the posttranscriptional level (21). Pleiotropic miRNAs can control gene expression by binding to complementary sequences in the 3Ј untranslated region (3Ј UTR) of target mRNA transcripts to facilitate their degradation and/or inhibit their translation (15,22,23). Understanding this layer of gene regulation therefore promises to enrich our knowledge of brain function and pathology. Dizocilpine is a highly selective phencyclidine-like NMDA-R antagonist that can rapidly produce schizophrenia-like behavioral deficits in humans and rodents (24). We examined whether a psychotomimetic dose of dizocilpine (0.5 mg/kg, i.p.) altered miRNA expression in brain regions of C57BL/6 mice, by using miRNA microarray profiling as an initial screening approach. Our analysis was focused on the PFC because of the considerable evidence linking this brain region with behavioral pathology in psychiatric illnesses (19). We extracted the small RNAs from the PFC of the mice 15 min after administration of a single dose of dizocilpine, i.e., a time-point at which dizocilpine-induced behavioral disturbances such as hyperlocomotion and stereotypy are readily observed (25). Of note, there was a robust reduction of miR-219 out of 182 miRNAs detectable by microarray in PFC tissues (Table S1). miR-219 is a conserved miRNA expressed in both rodent and human brains, but not in other tissues (26,27). These data demonstrate that concentrations of a brain-specific miRNA, which may play a role in regulating NMDA-R function, are altered during states of NMDA-R hypofunction.In support of the microarray data, RT-PCR analyses demonstrated that miR-219 levels were significantly reduced by Ϸ50% (a change from an average cycle th...

The dopamine transporter (DAT) plays a key role in the regulation of dopaminergic signaling wherein it controls both the spatial and temporal actions of dopamine. Here we evaluated the behavioral and neurochemical consequences of increased DAT function by generating DAT transgenic mice (DAT-tg) that overexpress the transporter. These mice were generated by pronuclear injection of a bacterial artificial chromosome containing the mouse DAT locus, yielding an anatomical expression pattern of DAT-tg identical to WT. In DAT-tg mice there is a 3-fold increase in the levels of total and membrane-expressed DAT, but synaptic plasma membrane fractions of DAT-tg mice show only a 30% increase in transporter levels. Functional studies reveal that in the DAT-tg animals there is a 50% increase in the rate of dopamine (DA) uptake resulting in extracellular levels of DA that are decreased by Ϸ40%. Behaviorally, DAT-tg animals display similar locomotor stimulation when treated with DAT blockers such as GBR12909, methylphenidate, and cocaine. However, these mice demonstrate markedly increased locomotor responses to amphetamine compared with WT animals. Furthermore, compared with controls, there is a 3-fold greater increase in the amount of DA released by amphetamine in DAT-tg mice that correlates with the 3-fold increase in protein expression. Finally, DAT-tg animals show reduced operant responding for natural reward while displaying preference for amphetamine at much lower doses (0.2 and 0.5 mg/kg) than WT mice (2 mg/kg). These results suggest that overexpression of DAT leads to a marked increase in sensitivity to psychomotor and rewarding properties of amphetamine.bacterial artificial chromosome transgenic ͉ locomotion ͉ addiction ͉ ADHD D opamine (DA) is a key neurotransmitter regulating motivated behaviors such as food intake, locomotion, and reward, and its dysregulation is associated with a number of psychiatric and neurological disorders including schizophrenia, Parkinson's disease, drug addiction, attention deficit hyperactivity disorder (ADHD), and depression (1-3). A key step in the control of DA neurotransmission is the reuptake of DA into presynaptic neurons by the dopamine transporter (DAT) (4). DAT, as well as the serotonin transporter (SERT) and norepinephrine transporter (NET), belongs to the large family of Na ϩ /Cl Ϫ -dependent transporters that also includes the transporters for glycine and GABA (5, 6). These transporters comprise 12 transmembrane domains and intracellular N-and C-terminal domains. Once at the plasma membrane, DAT cotransports two Na ϩ , one Cl Ϫ , and one DA molecule from the extracellular space into the cytosolic compartment of the neuron.Much insight regarding how DAT affects DA homeostasis has been gained from the study of mice lacking the DAT (DAT knockout; DAT-KO) (4, 7). In these animals, there is a 5-fold increase in the extracellular concentration of DA (8). The crucial role of DAT in determining the duration of action of extracellular DA has also been demonstrated in these animals. Usi...

Trace amines are neurotransmitters whose role in regulating invertebrate physiology has been appreciated for many decades. Recent studies indicate that trace amines may also play a role in mammalian physiology by binding to a novel family of G protein-coupled receptors (GPCRs) that are found throughout the central nervous system. A major obstacle impeding the careful pharmacological characterization of trace amine associated receptors (TAARs) is their extremely poor membrane expression in model cell systems, and a molecular basis for this phenomenon has not been determined. In the present study, we show that the addition of an asparagine-linked glycosylation site to the N terminus of the human trace amine associated receptor 1 (TAAR1) is sufficient to enable its plasma membrane expression, and thus its pharmacological characterization with a novel cAMP EPAC (exchange protein directly activated by cAMP) protein based bioluminescence resonance energy transfer (BRET) biosensor. We applied this novel cAMP BRET biosensor to evaluate the activity of putative TAAR1 ligands. This study represents the first comprehensive investigation of the membrane-expressed human TAAR1 pharmacology. Our strategy to express TAARs and to identify their ligands using a cAMP BRET assay could provide a foundation for characterizing the functional role of trace amines in vivo and suggests a strategy to apply to groups of poorly expressing GPCRs that have remained difficult to investigate in model systems.

Disrupted-in-schizophrenia 1 (DISC1) is a mental illness gene first identified in a Scottish pedigree. So far, DISC1-dependent phenotypes in animal models have been confined to expressing mutant DISC1. Here we investigated how pathology of full-length DISC1 protein could be a major mechanism in sporadic mental illness. We demonstrate that a novel transgenic rat model, modestly overexpressing the full-length DISC1 transgene, showed phenotypes consistent with a significant role of DISC1 misassembly in mental illness. The tgDISC1 rat displayed mainly perinuclear DISC1 aggregates in neurons. Furthermore, the tgDISC1 rat showed a robust signature of behavioral phenotypes that includes amphetamine supersensitivity, hyperexploratory behavior and rotarod deficits, all pointing to changes in dopamine (DA) neurotransmission. To understand the etiology of the behavioral deficits, we undertook a series of molecular studies in the dorsal striatum of tgDISC1 rats. We observed an 80% increase in high-affinity DA D2 receptors, an increased translocation of the dopamine transporter to the plasma membrane and a corresponding increase in DA inflow as observed by cyclic voltammetry. A reciprocal relationship between DISC1 protein assembly and DA homeostasis was corroborated by in vitro studies. Elevated cytosolic dopamine caused an increase in DISC1 multimerization, insolubility and complexing with the dopamine transporter, suggesting a physiological mechanism linking DISC1 assembly and dopamine homeostasis. DISC1 protein pathology and its interaction with dopamine homeostasis is a novel cellular mechanism that is relevant for behavioral control and may have a role in mental illness.

The identification of circulating autoantibodies against neuronal receptors in neuropsychiatric disorders has fostered new conceptual and clinical frameworks. However, detection reliability, putative presence in different diseases and in health have raised questions about potential pathogenic mechanism mediated by autoantibodies. Using a combination of single molecule-based imaging approaches, we here ascertain the presence of circulating autoantibodies against glutamate NMDA receptor (NMDAR-Ab) in about 20% of psychotic patients diagnosed with schizophrenia and very few healthy subjects. NMDAR-Ab from patients and healthy subjects do not compete for binding on native receptor. Strikingly, NMDAR-Ab from patients, but not from healthy subjects, specifically alter the surface dynamics and nanoscale organization of synaptic NMDAR and its anchoring partner the EphrinB2 receptor in heterologous cells, cultured neurons and in mouse brain. Functionally, only patients’ NMDAR-Ab prevent long-term potentiation at glutamatergic synapses, while leaving NMDAR-mediated calcium influx intact. We unveil that NMDAR-Ab from psychotic patients alter NMDAR synaptic transmission, supporting a pathogenically relevant role.

Neural phase signaling has gained attention as a putative coding mechanism through which the brain binds the activity of neurons across distributed brain areas to generate thoughts, percepts, and behaviors. Neural phase signaling has been shown to play a role in various cognitive processes, and it has been suggested that altered phase signaling may play a role in mediating the cognitive deficits observed across neuropsychiatric illness. Here, we investigated neural phase signaling in two mouse models of cognitive dysfunction: mice with genetically induced hyperdopaminergia [dopamine transporter knock-out (DAT-KO) mice] and mice with genetically induced NMDA receptor hypofunction [NMDA receptor subunit-1 knockdown (NR1-KD) mice]. Cognitive function in these mice was assessed using a radial-arm maze task, and local field potentials were recorded from dorsal hippocampus and prefrontal cortex as DAT-KO mice, NR1-KD mice, and their littermate controls engaged in behavioral exploration. Our results demonstrate that both DAT-KO and NR1-KD mice display deficits in spatial cognitive performance. Moreover, we show that persistent hyperdopaminergia alters interstructural phase signaling, whereas NMDA receptor hypofunction alters interstructural and intrastructural phase signaling. These results demonstrate that dopamine and NMDA receptor dependent glutamate signaling play a critical role in coordinating neural phase signaling, and encourage further studies to investigate the role that deficits in phase signaling play in mediating cognitive dysfunction.

The dopamine transporter is a key protein responsible for regulating dopamine homeostasis. Its function is to transport dopamine from the extracellular space into the presynaptic neuron. Studies have suggested that accumulation of dopamine in the cytosol can trigger oxidative stress and neurotoxicity. Previously, ectopic expression of the dopamine transporter was shown to cause damage in non-dopaminergic neurons due to their inability to handle cytosolic dopamine. However, it is unknown whether increasing dopamine transporter activity will be detrimental to dopamine neurons that are inherently capable of storing and degrading dopamine. To address this issue, we characterized transgenic mice that over-express the dopamine transporter selectively in dopamine neurons. We report that dopamine transporter over-expressing (DAT-tg) mice display spontaneous loss of midbrain dopamine neurons that is accompanied by increases in oxidative stress markers, 5-S-cysteinyl-dopamine and 5-S-cysteinyl-DOPAC. In addition, metabolite-to-dopamine ratios are increased and VMAT2 protein expression is decreased in the striatum of these animals. Furthermore, DAT-tg mice also show fine motor deficits on challenging beam traversal that are reversed with L-DOPA treatment. Collectively, our findings demonstrate that even in neurons that routinely handle dopamine, increased uptake of this neurotransmitter through the dopamine transporter results in oxidative damage, neuronal loss and LDOPA reversible motor deficits. In addition, DAT over-expressing animals are highly sensitive to MPTP-induced neurotoxicity. The effects of increased dopamine uptake in these transgenic mice could shed light on the unique vulnerability of dopamine neurons in Parkinson’s disease.