Genetic mapping identifies Homer1 as a developmental modifier of attention.

Attention is required for most higher-order cognitive functions. Prior studies have revealed functional roles for the prefrontal cortex and its extended circuits to enabling attention, but the underlying molecular processes and their impacts on cellular and circuit function remain poorly understood. To develop insights, we here took an unbiased forward genetics approach to identify single genes of large effect on attention. We studied 200 genetically diverse mice on measures of pre-attentive processing and through genetic mapping identified a small locus on chromosome 13 (95%CI: 92.22-94.09 Mb) driving substantial variation (19%) in this trait. Further characterization of the locus revealed a causative gene, Homer1, encoding a synaptic protein, where down-regulation of its short isoforms in prefrontal cortex (PFC) during early postnatal development led to improvements in multiple measures of attention in the adult. Subsequent mechanistic studies revealed that prefrontal Homer1 down-regulation is associated with GABAergic receptor up-regulation in those same cells. This enhanced inhibitory influence, together with dynamic neuromodulatory coupling, led to strikingly low PFC activity at baseline periods of the task but targeted elevations at cue onset, predicting short-latency correct choices. Notably high-Homer1, low-attentional performers, exhibited uniformly elevated PFC activity throughout the task. We thus identify a single gene of large effect on attention - Homer1 - and find that it improves prefrontal inhibitory tone and signal-to-noise (SNR) to enhance attentional performance. A therapeutic strategy focused on reducing prefrontal activity and increasing SNR, rather than uniformly elevating PFC activity, may complement the use of stimulants to improve attention.

Anteromedial thalamus gates the selection and stabilization of long-term memories.

Memories initially formed in hippocampus gradually stabilize to cortex over weeks-to-months for long-term storage. The mechanistic details of this brain re-organization remain poorly understood. We recorded bulk neural activity in circuits that link hippocampus and cortex as mice performed a memory-guided virtual-reality task over weeks. We identified a prominent and sustained neural correlate of memory in anterior thalamus, whose inhibition substantially disrupted memory consolidation. More strikingly, gain amplification enhanced consolidation of otherwise unconsolidated memories. To gain mechanistic insights, we developed a technology for simultaneous cellular-resolution imaging of hippocampus, thalamus, and cortex throughout consolidation. We found that whereas hippocampus equally encodes multiple memories, the anteromedial thalamus preferentially encodes salient memories, and gradually increases correlations with cortex to facilitate tuning and synchronization of cortical ensembles. We thus identify a thalamo-cortical circuit that gates memory consolidation and propose a mechanism suitable for the selection and stabilization of hippocampal memories into longer-term cortical storage.

Anteromedial Thalamus Gates the Selection & Stabilization of Long-Term Memories.

Memories initially formed in hippocampus gradually stabilize to cortex, over weeks-to-months, for long-term storage. The mechanistic details of this brain re-organization process remain poorly understood. In this study, we developed a virtual-reality based behavioral task and observed neural activity patterns associated with memory reorganization and stabilization over weeks-long timescales. Initial photometry recordings in circuits that link hippocampus and cortex revealed a unique and prominent neural correlate of memory in anterior thalamus that emerged in training and persisted for several weeks. Inhibition of the anteromedial thalamus-to-anterior cingulate cortex projections during training resulted in substantial memory consolidation deficits, and gain amplification more strikingly, was sufficient to enhance consolidation of otherwise unconsolidated memories. To provide mechanistic insights, we developed a new behavioral task where mice form two memories, of which only the more salient memory is consolidated, and also a technology for simultaneous and longitudinal cellular resolution imaging of hippocampus, thalamus, and cortex throughout the consolidation window. We found that whereas hippocampus equally encodes multiple memories, the anteromedial thalamus forms preferential tuning to salient memories, and establishes inter-regional correlations with cortex, that are critical for synchronizing and stabilizing cortical representations at remote time. Indeed, inhibition of this thalamo-cortical circuit while imaging in cortex reveals loss of contextual tuning and ensemble synchrony in anterior cingulate, together with behavioral deficits in remote memory retrieval. We thus identify a thalamo-cortical circuit that gates memory consolidation and propose a mechanism suitable for the selection and stabilization of hippocampal memories into longer term cortical storage.

Human Islet Amyloid Polypeptide (hIAPP) Protofibril-Specific Antibodies for Detection and Treatment of Type 2 Diabetes.

Type 2 diabetes mellitus (T2D) is a major public health concern and is characterized by sustained hyperglycemia due to insulin resistance and destruction of insulin-producing ß cells. One pathological hallmark of T2D is the toxic accumulation of human islet amyloid polypeptide (hIAPP) aggregates. Monomeric hIAPP is a hormone normally co-secreted with insulin. However, increased levels of hIAPP in prediabetic and diabetic patients can lead to the formation of hIAPP protofibrils, which are toxic to ß cells. Current therapies fail to address hIAPP aggregation and current screening modalities do not detect it. Using a stabilizing capping protein, monoclonal antibodies (mAbs) can be developed against a previously nonisolatable form of hIAPP protofibrils, which are protofibril specific and do not engage monomeric hIAPP. Shown here are two candidate mAbs that can detect hIAPP protofibrils in serum and hIAPP deposits in pancreatic islets in a mouse model of rapidly progressing T2D. Treatment of diabetic mice with the mAbs delays disease progression and dramatically increases overall survival. These results demonstrate the potential for using novel hIAPP protofibril-specific mAbs as a diagnostic screening tool for early detection of T2D, as well as therapeutically to preserve ß cell function and target one of the underlying pathological mechanisms of T2D.

On the Role of Adenosine A2A Receptor Gene Transcriptional Regulation in Parkinson's Disease.

Adenosine A2A receptors (A2ARs) have attracted considerable attention as an important molecular target for the design of Parkinson's disease (PD) therapeutic compounds. Here, we studied the transcriptional regulation of the A2AR gene in human peripheral blood mononuclear cells (PBMCs) obtained from PD patients and in the striatum of the well-validated, 6-hydroxydopamine (6-OHDA)-induced PD mouse model. We report an increase in A2AR mRNA expression and protein levels in both human cells and mice striata, and in the latter we could also observe a consistent reduction in DNA methylation at gene promoter and an increase in histone H3 acetylation at lysine 9. Of particular relevance in clinical samples, we also observed higher levels in the receptor gene expression in younger subjects, as well as in those with less years from disease onset, and less severe disease according to clinical scores. In conclusion, the present findings provide further evidence of the relevant role of A2AR in PD and, based on the clinical data, highlight its potential role as disease biomarker for PD especially at the initial stages of disease development. Furthermore, our preclinical results also suggest selective epigenetic mechanisms targeting gene promoter as tool for the development of new treatments.

Atypical but not typical antipsychotic drugs ameliorate phencyclidine-induced emotional memory impairments in mice.

Schizophrenia is associated with cognitive impairments related to hypofunction in glutamatergic N-methyl-D-aspartate receptor (NMDAR) transmission. Phencyclidine (PCP), a non-competitive NMDAR antagonist, models schizophrenia-like behavioral symptoms including cognitive deficits in rodents. This study examined the effects of PCP on emotional memory function examined in the passive avoidance (PA) task in mice and the ability of typical and atypical antipsychotic drugs (APDs) to rectify the PCP-mediated impairment. Pre-training administration of PCP (0.5, 1, 2 or 3 mg/kg) dose-dependently interfered with memory consolidation in the PA task. In contrast, PCP was ineffective when administered after training, and immediately before the retention test indicating that NMDAR blockade interferes with memory encoding mechanisms. The typical APD haloperidol and the dopamine D2/3 receptor antagonist raclopride failed to block the PCP-induced PA impairment suggesting a negligible role of D2 receptors in the PCP impairment. In contrast, the memory impairment was blocked by the atypical APDs clozapine and olanzapine in a dose-dependent manner while risperidone was effective only at the highest dose tested (1 mg/kg). The PCP-induced impairment involves 5-HT1A receptor mechanisms since the antagonist NAD-299 blocked the memory impairment caused by PCP and the ability of clozapine to attenuate the impairment by PCP. These results indicate that atypical but not typical APDs can ameliorate NMDAR-mediated memory impairments and support the view that atypical APDs such as clozapine can modulate glutamatergic memory dysfunctions through 5-HT1A receptor mechanisms. These findings suggest that atypical APDs may improve cognitive impairments related to glutamatergic dysfunction relevant for emotional memories in schizophrenia.

Conformation-specific antibodies against multiple amyloid protofibril species from a single amyloid immunogen.

We engineered and employed a chaperone-like amyloid-binding protein Nucleobindin 1 (NUCB1) to stabilize human islet amyloid polypeptide (hIAPP) protofibrils for use as immunogen in mice. We obtained multiple monoclonal antibody (mAb) clones that were reactive against hIAPP protofibrils. A secondary screen was carried out to identify clones that cross-reacted with amyloid beta-peptide (Aß42) protofibrils, but not with Aß40 monomers. These mAbs were further characterized in several in vitro assays, in immunohistological studies of a mouse model of Alzheimer's disease (AD) and in AD patient brain tissue. We show that mAbs obtained by immunizing mice with the NUCB1-hIAPP complex cross-react with Aß42, specifically targeting protofibrils and inhibiting their further aggregation. In line with conformation-specific binding, the mAbs appear to react with an intracellular antigen in diseased tissue, but not with amyloid plaques. We hypothesize that the mAbs we describe here recognize a secondary or quaternary structural epitope that is common to multiple amyloid protofibrils. In summary, we report a method to create mAbs that are conformation-sensitive and sequence-independent and can target more than one type of protofibril species.

Inhibition of mTORC1 Signaling Reverts Cognitive and Affective Deficits in a Mouse Model of Parkinson's Disease.

Non-motor symptoms, including cognitive deficits and affective disorders, are frequently diagnosed in Parkinson's disease (PD) patients and are only partially alleviated by dopamine replacement therapy. Here, we used a 6-hydroxydopamine (6-OHDA) mouse model of PD to examine the effects exerted on non-motor symptoms by inhibition of the mammalian target of rapamycin complex 1 (mTORC1), which is involved in the control of protein synthesis, cell growth, and metabolism. We show that rapamycin, which acts as an allosteric inhibitor of mTORC1, counteracts the impairment of novel object recognition. A similar effect is produced by PF-4708671, an inhibitor of the downstream target of mTORC1, ribosomal protein S6 kinase (S6K). Rapamycin is also able to reduce depression-like behavior in PD mice, as indicated by decreased immobility in the forced swim test. Moreover, rapamycin exerts anxiolytic effects, thereby reducing thigmotaxis in the open field and increasing exploration of the open arm in the elevated plus maze. In contrast to rapamycin, administration of PF-4708671 to PD mice does not counteract depression- and anxiety-like behaviors. Altogether, these results identify mTORC1 as a target for the development of drugs that, in combination with standard antiparkinsonian agents, may widen the efficacy of current therapies for the cognitive and affective symptoms of PD.

Energetics Underlying Twist Polymorphisms in Amyloid Fibrils.

Amyloid fibrils are highly ordered protein aggregates associated with more than 40 human diseases. The exact conditions under which the fibrils are grown determine many types of reported fibril polymorphism, including different twist patterns. Twist-based polymorphs display unique mechanical properties in vitro, and the relevance of twist polymorphism in amyloid diseases has been suggested. We present transmission electron microscopy images of Aß42-derived (amyloid ß) fibrils, which are associated with Alzheimer's disease, demonstrating the presence of twist variability even within a single long fibril. To better understand the molecular underpinnings of twist polymorphism, we present a structural and thermodynamics analysis of molecular dynamics simulations of the twisting of ß-sheet protofilaments of a well-characterized cross-ß model: the GNNQQNY peptide from the yeast prion Sup35. The results show that a protofilament model of GNNQQNY is able to adopt twist angles from -11° on the left-hand side to +8° on the right-hand side in response to various external conditions, keeping an unchanged peptide structure. The potential of mean force (PMF) of this cross-ß structure upon twisting revealed that only ∼2kBT per peptide are needed to stabilize a straight conformation with respect to the left-handed free-energy minimum. The PMF also shows that the canonical structural core of ß-sheets, i.e., the hydrogen-bonded backbone ß-strands, favors the straight conformation. However, the concerted effects of the side chains contribute to twisting, which provides a rationale to correlate polypeptide sequence, environmental growth conditions and number of protofilaments in a fibril with twist polymorphisms.

Dopamine Depletion Impairs Bilateral Sensory Processing in the Striatum in a Pathway-Dependent Manner.

Parkinson's disease (PD) is a movement disorder caused by the loss of dopaminergic innervation, particularly to the striatum. PD patients often exhibit sensory impairments, yet the underlying network mechanisms are unknown. Here we examined how dopamine (DA) depletion affects sensory processing in the mouse striatum. We used the optopatcher for online identification of direct and indirect pathway projection neurons (MSNs) during in vivo whole-cell recordings. In control mice, MSNs encoded the laterality of sensory inputs with larger and earlier responses to contralateral than ipsilateral whisker deflection. This laterality coding was lost in DA-depleted mice due to adaptive changes in the intrinsic and synaptic properties, mainly, of direct pathway MSNs. L-DOPA treatment restored laterality coding by increasing the separation between ipsilateral and contralateral responses. Our results show that DA depletion impairs bilateral tactile acuity in a pathway-dependent manner, thus providing unexpected insights into the network mechanisms underlying sensory deficits in PD. VIDEO ABSTRACT.

Nucleobindin 1 binds to multiple types of pre-fibrillar amyloid and inhibits fibrillization.

During amyloid fibril formation, amyloidogenic polypeptides misfold and self assemble into soluble pre-fibrillar aggregates, i.e., protofibrils, which elongate and mature into insoluble fibrillar aggregates. An emerging class of chaperones, chaperone-like amyloid binding proteins (CLABPs), has been shown to interfere with aggregation of particular misfolded amyloid peptides or proteins. We have discovered that the calcium-binding protein nuclebindin-1 (NUCB1) is a novel CLABP. We show that NUCB1 inhibits aggregation of islet-amyloid polypeptide associated with type 2 diabetes mellitus, a-synuclein associated with Parkinson's disease, transthyretin V30M mutant associated with familial amyloid polyneuropathy, and Aß42 associated with Alzheimer's disease by stabilizing their respective protofibril intermediates. Kinetic studies employing the modeling software AmyloFit show that NUCB1 affects both primary nucleation and secondary nucleation. We hypothesize that NUCB1 binds to the common cross-ß-sheet structure of protofibril aggregates to "cap" and stabilize soluble macromolecular complexes. Transmission electron microscopy and atomic force microscopy were employed to characterize the size, shape and volume distribution of multiple sources of NUCB1-capped protofibrils. Interestingly, NUCB1 prevents Aß42 protofibril toxicity in a cellular assay. NUCB1-stabilized amyloid protofibrils could be used as immunogens to prepare conformation-specific antibodies and as novel tools to develop screens for anti-protofibril diagnostics and therapeutics.

Update on Alzheimer's Disease Therapy and Prevention Strategies.

Alzheimer's disease (AD) is the primary cause of age-related dementia. Effective strategies to prevent and treat AD remain elusive despite major efforts to understand its basic biology and clinical pathophysiology. Significant investments in therapeutic drug discovery programs over the past two decades have yielded some important insights but no blockbuster drugs to alter the course of disease. Because significant memory loss and cognitive decline are associated with neuron death and loss of gray matter, especially in the frontal cortex and hippocampus, some focus in drug development has shifted to early prevention of cellular pathology. Although clinical trial design is challenging, due in part to a lack of robust biomarkers with predictive value, some optimism has come from the identification and study of inherited forms of early-onset AD and genetic risk factors that provide insights about molecular pathophysiology and potential drug targets. In addition, better understanding of the Aß amyloid pathway and the tau pathway-leading to amyloid plaques and neurofibrillary tangles, respectively, which are histopathological hallmarks of AD-continues to drive significant drug research and development programs. The main focus of this review is to summarize the most recent basic biology, biochemistry, and pharmacology that serve as a foundation for more than 50 active advanced-phase clinical trials for AD prevention and therapy.

Differential regulation of the phosphorylation of Trimethyl-lysine27 histone H3 at serine 28 in distinct populations of striatal projection neurons.

Phosphorylation of histone H3 (H3) on serine 28 (S28) at genomic regions marked by trimethylation of lysine 27 (H3K27me3) often correlates with increased expression of genes normally repressed by Polycomb group proteins (PcG). We show that amphetamine, an addictive psychostimulant, and haloperidol, a typical antipsychotic drug, increase the phosphorylation of H3 at S28 and that this effect occurs in the context of H3K27me3. The increases in H3K27me3S28p occur in distinct populations of projection neurons located in the striatum, the major component of the basal ganglia. Genetic inactivation of the protein phosphatase-1 inhibitor, dopamine- and cAMP-regulated phosphoprotein of 32 kDa (DARPP-32), reduces the phosphorylation of H3K27me3S28 produced by amphetamine and haloperidol. In contrast, knockout of the mitogen- and stress activated kinase 1 (MSK1), which is implicated in the phosphorylation of histone H3, decreases the effect of amphetamine, but not that of haloperidol. Chromatin immunoprecipitation analysis shows that amphetamine and haloperidol increase the phosphorylation of H3K27me3S28 at the promoter regions of Atf3, Npas4 and Lipg, three genes repressed by PcG. These results identify H3K27me3S28p as a potential mediator of the effects exerted by amphetamine and haloperidol, and suggest that these drugs may act by re-activating PcG repressed target genes.

Involvement of the Striatal Medium Spiny Neurons of the Direct Pathway in the Motor Stimulant Effects of Phencyclidine.

BACKGROUND: The psychotomimetic phencyclidine (PCP) produces behavioral symptoms similar to those observed in schizophrenia, accompanied by increased motor activity. The dopamine and adenosine 3',5'-cyclic monophosphate-regulated phosphoprotein of 32kDa (DARPP-32) is enriched in the medium spiny neurons (MSNs) of the striatum and has been implicated in the actions of PCP. We examined the effects of deletion of DARPP-32 in distinct populations of striatal MSNs, on the ability of PCP to induce motor activation and memory deficit. METHODS: The effects of PCP were examined in mice with conditional knockout of DARPP-32 in the MSNs of the direct, or indirect pathway. DARPP-32 phosphorylation was determined by Western blotting. The motor stimulant effects of PCP were determined by measuring locomotion following acute and chronic administration. Memory deficit was evaluated using the passive avoidance test. RESULTS: Loss of DARPP-32 in direct MSNs prevents PCP-induced phosphorylation and abolishes the motor stimulation effects of PCP. In contrast, lack of DARPP-32 in indirect MSNs does not affect the ability of PCP to promote DARPP-32 phosphorylation and to increase motor activity. The impairment in passive avoidance induced by PCP is independent of the expression of DARPP-32 in direct or indirect MSNs. CONCLUSIONS: The increase in DARPP-32 phosphorylation induced by PCP occurs selectively in the MSNs of the direct pathway, which are also specifically involved in the motor stimulant effects of this drug. The memory deficit induced by PCP is not linked to the expression of DARPP-32 in striatal MSNs.

A mouse model of non-motor symptoms in Parkinson's disease: focus on pharmacological interventions targeting affective dysfunctions.

Non-motor symptoms, including psychiatric disorders, are increasingly recognized as a major challenge in the treatment of Parkinson's disease (PD). These ailments, which often appear in the early stage of the disease, affect a large number of patients and are only partly resolved by conventional antiparkinsonian medications, such as L-DOPA. Here, we investigated non-motor symptoms of PD in a mouse model based on bilateral injection of the toxin 6-hydroxydopamine (6-OHDA) in the dorsal striatum. This model presented only subtle gait modifications, which did not affect horizontal motor activity in the open-field test. Bilateral 6-OHDA lesion also impaired olfactory discrimination, in line with the anosmia typically observed in early stage parkinsonism. The effect of 6-OHDA was then examined for mood-related dysfunctions. Lesioned mice showed increased immobility in the forced swim test and tail suspension test, two behavioral paradigms of depression. Moreover, the lesion exerted anxiogenic effects, as shown by reduced time spent in the open arms, in the elevated plus maze test, and by increased thigmotaxis in the open-field test. L-DOPA did not modify depressive- and anxiety-like behaviors, which were instead counteracted by the dopamine D2/D3 receptor agonist, pramipexole. Reboxetine, a noradrenaline reuptake inhibitor, was also able to revert the depressive and anxiogenic effects produced by the lesion with 6-OHDA. Interestingly, pre-treatment with desipramine prior to injection of 6-OHDA, which is commonly used to preserve noradrenaline neurons, did not modify the effect of the lesion on depressive- and anxiety-like behaviors. Thus, in the present model, mood-related conditions are independent of the reduction of noradrenaline caused by 6-OHDA. Based on these findings we propose that the anti-depressive and anxiolytic action of reboxetine is mediated by promoting dopamine transmission through blockade of dopamine uptake from residual noradrenergic terminals.

Adenosine A1 receptor stimulation reduces D1 receptor-mediated GABAergic transmission from striato-nigral terminals and attenuates l-DOPA-induced dyskinesia in dopamine-denervated mice.

γ-Aminobutyric acid A receptor (GABAAR)-mediated postsynaptic currents were recorded in brain slices from substantia nigra pars reticulate neurons. The selective adenosine A1 receptor (A1R) antagonist, 8-cyclopentyl-1,3-dipropylxanthine (DPCPX), increased the frequency, but not the amplitude of spontaneous inhibitory post-synaptic currents (IPSCs) in the presence of the dopamine D1 receptor agonist SKF 38393 (SKF) and phosphodiesterase 10A inhibitors (papaverine or AE90074). Under these conditions, DPCPX also increased the amplitude of evoked IPSCs (eIPSCs). The effect of DPCPX was also examined in a mouse model of Parkinson's disease (PD), generated by unilateral denervation of the dopaminergic input to the striatum. In this model, SKF alone was sufficient to increase sIPSCs frequency and eIPSCs amplitude, and these effects were not potentiated by DPCPX. To confirm a depressive effect of A1Rs on the synaptic release of GABA we used the selective A1R agonist 5'-chloro-5'-deoxy-N(6)-(±)-(endo-norborn-2-yl)adenosine (5'Cl5'd-(±)-ENBA) which has limited peripheral actions. We found that 5'Cl5'd-(±)-ENBA decreased sIPSCs frequency, without affecting their amplitude, and decreased eIPSCs amplitude. Importantly, in the PD mouse model, 5'Cl5'd-(±)-ENBA prevented the increase in sIPSC frequency and eIPSC amplitude produced by SKF. Since exaggerated DA transmission along the striato-nigral pathway is involved in the motor complications (e.g. dyskinesia) caused by prolonged and intermittent administration of l-DOPA, we examined the effect of A1R activation in mice with unilateral DA denervation. We found that 5'Cl5'd-(±)-ENBA, administered in combination with l-DOPA, reduced the development of abnormal involuntary movements. These results indicate the potential benefit of A1R agonists for the treatment of l-DOPA-induced dyskinesia and hyperkinetic disorders providing a mechanistic framework for the study of the interaction between DA and adenosine in the striatonigral system.

Cognitive impairment and dentate gyrus synaptic dysfunction in experimental parkinsonism.

BACKGROUND: Parkinson's disease (PD) is characterized by the progressive degeneration of the nigrostriatal dopaminergic pathway and the emergence of rigidity, tremor, and bradykinesia. Accumulating evidence indicates that PD is also accompanied by nonmotor symptoms including cognitive deficits, often manifested as impaired visuospatial memory. METHODS: We studied cognitive performance and synaptic plasticity in a mouse model of PD, characterized by partial lesion of the dopaminergic and noradrenergic inputs to striatum and hippocampus. Sham- and 6-hydroxydopamine-lesioned mice were subjected to the novel object recognition test, and long-term potentiation was examined in the dentate gyrus and CA1 regions of the hippocampus. RESULTS: Bilateral 6-hydroxydopamine lesion reduced long-term but not short-term novel object recognition and decreased long-term potentiation specifically in the dentate gyrus. These abnormalities did not depend on the loss of noradrenaline but were abolished by the antiparkinsonian drug, L-DOPA, or by SKF81297, a dopamine D1-type receptor agonist. In contrast, activation of dopamine D2-type receptors did not modify the effects produced by the lesion. Blockade of the extracellular signal-regulated kinases prevented the ability of SKF81297 to rescue novel object recognition and long-term potentiation. CONCLUSIONS: These findings show that partial dopamine depletion leads to impairment of long-term recognition memory accompanied by abnormal synaptic plasticity in the dentate gyrus. They also demonstrate that activation of dopamine D1 receptors corrects these deficits, through a mechanism that requires intact extracellular signal-regulated kinases signaling.

Phosphodiesterase 10A controls D1-mediated facilitation of GABA release from striato-nigral projections under normal and dopamine-depleted conditions.

In the present study, we found that PDE10A inhibitor papaverine, alone or in combination with the D1 receptor agonist SKF38393, did not change spontaneous IPSCs (sIPSCs) frequency or amplitude in the substantia nigra pars reticulata (SNpr). An increase in frequency, but not in amplitude, of sIPSCs was only observed when SKF38393 and PDE10A inhibitors were associated to perfusion with higher extracellular K(+). On the other hand, the amplitude of evoked IPSCs (eIPSCs) of the striato-nigral projection to SNpr, was increased in response to co-administration of SKF38393 and papaverine in normal extracellular potassium. Of note, both an increase in sIPSCs frequency and eIPSC amplitude could be obtained either by a robust stimulation of adenylyl cyclase (AC) with forskolin (10 µM) or by a lower dose of forskolin (1 µM) associated to PDE inhibition. We next investigated the effects produced by dopamine (DA) depletion in the striatum. Under this condition, SKF38393 alone increased either sIPSCs frequency and eIPSC amplitude. In addition, in the striatum of DA-depleted mice we found reduced PDE10A levels and higher cAMP-dependent phosphorylation in response to D1 receptor stimulation. In accordance with these biochemical data, perfusion with papaverine had no effect on the SKF38393-induced changes of IPSCs in slices of DA-depleted mice. These findings reveal a dynamic interplay between PDE10A activity, level of neuronal network depolarization and degree of dopaminergic tone in the ability of D1 receptors to facilitate the GABAergic transmission to SNpr neurons from the direct nigro-striatal pathway. This article is part of the Special Issue entitled 'The Synaptic Basis of Neurodegenerative Disorders'.

Understanding cognitive deficits in Parkinson's disease: lessons from preclinical animal models.

Parkinson's disease (PD) has been, until recently, mainly defined by the presence of characteristic motor symptoms, such as rigidity, tremor, bradykinesia/akinesia, and postural instability. Accordingly, pharmacological and surgical treatments have so far addressed these motor disturbances, leaving nonmotor, cognitive deficits an unmet clinical condition. At the preclinical level, the large majority of studies aiming at defining mechanisms and testing novel therapies have similarly focused on the motor aspects of PD. Unfortunately, deterioration of the executive functions, such as attention, recognition, working memory, and problem solving, often appear in an early, premotor phase of the disease and progressively increase in intensity, negatively affecting the quality of life of ∼50%-60% of PD patients. At present, the cellular mechanisms underlying cognitive impairments in PD patients are largely unknown and an adequate treatment is still missing. The preclinical research has recently developed new animal models that may open new perspectives for a more integrated approach to the treatment of both motor and cognitive symptoms of the disease. This review will provide an overview on the cognitive symptoms occurring in early PD patients and then focus on the rodent and nonhuman primate models so far available for the study of discriminative and spatial memory attention and learning abilities related to this pathological condition.

Haloperidol promotes mTORC1-dependent phosphorylation of ribosomal protein S6 via dopamine- and cAMP-regulated phosphoprotein of 32 kDa and inhibition of protein phosphatase-1.

The ribosomal protein S6 (rpS6) is a component of the small 40S ribosomal subunit, involved in multiple physiological functions. Here, we examined the effects produced by haloperidol, a typical antipsychotic drug, on the phosphorylation of rpS6 at Ser240/244 in the striatum, a brain region involved in neurodegenerative and neuropsychiatric disorders. We found that administration of haloperidol increased Ser240/244 phosphorylation in a subpopulation of GABA-ergic medium spiny neurons (MSNs), which preferentially express dopamine D2 receptors (D2Rs). This effect was abolished by rapamycin, an inhibitor of the mammalian target of rapamycin complex 1 (mTORC1), or by PF470867, a selective inhibitor of the p70 ribosomal S6 kinase 1 (S6K1). We also found that the effect of haloperidol on Ser240/244 phosphorylation was prevented by functional inactivation of dopamine- and cAMP-regulated phosphoprotein of 32 kDa (DARPP-32), an endogenous inhibitor of protein phosphatase-1 (PP-1). In line with this observation, incubation of striatal slices with okadaic acid and calyculin A, two inhibitors of PP-1, increased Ser240/244 phosphorylation. These results show that haloperidol promotes mTORC1- and S6K1-dependent phosphorylation of rpS6 at Ser240/244, in a subpopulation of striatal MSNs expressing D2Rs. They also indicate that this effect is exerted by suppressing dephosphorylation at Ser240/244, through PKA-dependent activation of DARPP-32 and inhibition of PP-1.