The learning of new skills is characterized by an initial phase of rapid improvement in performance and a phase of more gradual improvements as skills are automatized and performance asymptotes. Using in vivo striatal recordings, we observed region-specific changes in neural activity during the different phases of skill learning, with the associative or dorsomedial striatum being preferentially engaged early in training and the sensorimotor or dorsolateral striatum being engaged later in training. Ex vivo recordings from medium spiny striatal neurons in brain slices of trained mice revealed that the changes observed in vivo corresponded to regionaland training-specific changes in excitatory synaptic transmission in the striatum. Furthermore, the potentiation of glutamatergic transmission observed in dorsolateral striatum after extensive training was preferentially expressed in striatopallidal neurons, rather than striatonigral neurons. These findings demonstrate that region-and pathway-specific plasticity sculpts the circuits involved in the performance of the skill as it becomes automatized.Learning to execute and automatize certain actions is essential for survival. The learning of new skills by trial and error, such as riding a bicycle or playing a piano, is characterized by an initial stage of rapid improvement in performance, followed by a phase of more gradual improvements as the skills are consolidated and performance asymptotes 1-4 . These two different phases of skill learning have distinct behavioral and physiological hallmarks 1,[5][6][7] . For example, the early fast phase is susceptible to interference, whereas the later, more

SUMMARY G protein-coupled receptors form hetero-dimers and higher order hetero-oligomers, yet the significance of receptor heteromerization in cellular and behavioral responses is poorly understood. Atypical antipsychotic drugs, such as clozapine and risperidone all have in common a high affinity for the serotonin 5-HT2A receptor (2AR). However, closely related nonantipsychotic drugs, such as ritanserin and methysergide, while blocking 2AR function, lack comparable neuropsychological effects. Why some but not all drugs that inhibit 2AR-dependent signaling exhibit antipsychotic properties remains unresolved. We found that a heteromeric complex formed between the metabotropic glutamate 2 receptor (mGluR2) and the 2AR critically integrates the action of drugs affecting signaling and behavioral outcomes. Acting through the mGluR2/2AR heterocomplex, both glutamatergic and serotonergic drugs achieve a balance between Gi- and Gq-dependent signaling that predicts their psychoactive behavioral effects. These observations provide a novel mechanistic insight into antipsychotic action that may advance therapeutic strategies for schizophrenia.

Histone deacetylases (HDACs) compact chromatin structure and repress gene transcription. In schizophrenia, clinical studies demonstrate that HDAC inhibitors are efficacious when given in combination with atypical antipsychotics. However, the molecular mechanism that integrates a better response to antipsychotics with changes in chromatin structure remains unknown. Here we show that chronic atypical antipsychotics down-regulate the expression of mGlu2, an effect that is associated with decreased histone acetylation at its promoter in mouse and human frontal cortex. This epigenetic change occurs in concert with a 5-HT2A receptor-dependent up-regulation and increased binding of HDAC2 to the mGlu2 promoter. Viral-mediated over-expression of HDAC2 in frontal cortex decreases mGlu2 transcription and its electrophysiological properties, thereby increasing psychosis-like behavior. Conversely, HDAC inhibitors prevent the repressive histone modifications induced at the mGlu2 promoter by atypical antipsychotics, and augment their therapeutic-like effects. These observations support the view of HDAC2 as a promising new target to improve schizophrenia treatment.

Background:The 5-HT 2A ⅐mGlu2 receptor heterocomplex is involved in psychosis.

Hallucinogenic drugs, including mescaline, psilocybin and lysergic acid diethylamide (LSD), act at serotonin 5-HT2A receptors (5-HT2ARs). Metabotropic glutamate receptor 2/3 (mGluR2/3) ligands show efficacy in modulating the responses induced by activation of 5-HT2ARs. The formation of a 5-HT2AR-mGluR2 complex suggests a functional interaction that affects the hallucinogen-regulated cellular signaling pathways. Here, we tested the cellular and behavioral effects of hallucinogenic 5-HT2AR agonists in mGluR2 knockout (mGluR2-KO) mice. Mice were intraperitoneally injected with the hallucinogens DOI (2 mg/kg) and LSD (0.24 mg/kg), or vehicle. Head-twitch behavioral response, expression of c-fos, which is induced by all 5-HT2AR agonists, and expression of egr-2, which is hallucinogen-specific, were determined in wild type and mGluR2-KO mice. [3H]Ketanserin binding displacement curves by DOI were performed in mouse frontal cortex membrane preparations. Head twitch behavior was abolished in mGluR2-KO mice. The high-affinity binding site of DOI was undetected in mGluR2-KO mice. The hallucinogen DOI induced c-fos in both wild type and mGluR2-KO mice. However, the induction of egr-2 by DOI was eliminated in mGlu2-KO mice. These findings suggest that the 5-HT2AR-mGluR2 complex is necessary for the neuropsychological responses induced by hallucinogens.

Epidemiological studies indicate that maternal influenza viral infection increases

Antipsychotic drugs remain the standard for schizophrenia treatment. Despite their effectiveness in treating hallucinations and delusions, prolonged exposure to antipsychotic medications leads to cognitive deficits in both schizophrenia patients and animal models. The molecular mechanisms underlying these negative effects on cognition remain to be elucidated. Here we demonstrate that chronic antipsychotic drug exposure increases nuclear translocation of NF-κB in both mouse and human frontal cortex, a trafficking event triggered via 5-HT2A-receptor-dependent downregulation of the NF-κB repressor IκBα. This upregulation of NF-κB activity led to its increased binding at the Hdac2 promoter, thereby augmenting Hdac2 transcription. Deletion of HDAC2 in forebrain pyramidal neurons prevented the negative effects of antipsychotic treatment on synaptic remodeling and cognition. Conversely, virally mediated activation of NF-κB signaling decreased cortical synaptic plasticity via HDAC2. Together, these observations may aid in developing therapeutic strategies to improve the outcome of schizophrenia treatment.

It has been suggested that severe adverse life events during pregnancy increase the risk of schizophrenia in the offspring. The serotonin 5-HT2A and the metabotropic glutamate 2 (mGlu2) receptors both have been the target of considerable attention regarding schizophrenia and antipsychotic drug development. We tested the effects of maternal variable stress during pregnancy on expression and behavioral function of these two receptors in mice. Prenatal stress increased 5-HT2A and decreased mGlu2 expression in frontal cortex, a brain region involved in perception, cognition and mood. This pattern of expression of 5-HT2A and mGlu2 receptors was consistent with behavioral alterations, including increased head-twitch response to the hallucinogenic 5-HT2A agonist DOI, and decreased mGlu2-dependent antipsychotic-like effect of the mGlu2/3 agonist LY379268 in adult, but not prepubertal, mice born to stressed mothers during pregnancy. Cross-fostering studies determined that these alterations were not due to effects of prenatal stress on maternal care. Additionally, a similar pattern of biochemical and behavioral changes were observed in mice born to mothers injected with poly-(I:C) during pregnancy as a model of prenatal immune activation. These data strengthen pathophysiological hypotheses that propose an early neurodevelopmental origin for schizophrenia and other psychiatric disorders.