Behavioral and neurochemical characterization of mice deficient in the phosphodiesterase-1B (PDE1B) enzyme

PDE1B, a potential biomarker associated with tumor microenvironment and clinical prognostic significance in osteosarcoma

PDE1B had been found to be involved in various diseases, including tumors and non-tumors. However, little was known about the definite role of PDE1B in osteosarcoma. Therefore, we mined public data on osteosarcoma to reveal the prognostic values and immunological roles of the PDE1B gene. Three osteosarcoma-related datasets from online websites were utilized for further data analysis. R 4.3.2 software was utilized to conduct difference analysis, prognostic analysis, gene set enrichment analysis (GSEA), nomogram construction, and immunological evaluations, respectively. Experimental verification of the PDE1B gene in osteosarcoma was conducted by qRT-PCR and western blot, based on the manufacturer's instructions. The PDE1B gene was discovered to be lowly expressed in osteosarcoma, and its low expression was associated with poor OS (all P < 0.05). Experimental verifications by qRT-PCR and western blot results remained consistent (all P < 0.05). Univariate and multivariate Cox regression analyses indicated that the PDE1B gene had independent abilities in predicting OS in the TARGET osteosarcoma dataset (both P < 0.05). GSEA revealed that PDE1B was markedly linked to the calcium, cell cycle, chemokine, JAK STAT, and VEGF pathways. Moreover, PDE1B was found to be markedly associated with immunity (all P < 0.05), and the TIDE algorithm further shed light on that patients with high-PDE1B expression would have a better immune response to immunotherapies than those with low-PDE1B expression, suggesting that the PDE1B gene could prevent immune escape from osteosarcoma. The PDE1B gene was found to be a tumor suppressor gene in osteosarcoma, and its high expression was related to a better OS prognosis, suppressing immune escape from osteosarcoma.

A chromosome region linked to neurodevelopmental disorders acts in distinct neuronal circuits in males and females to control locomotor behavior

Biological sex shapes the manifestation and progression of neurodevelopmental disorders (NDDs). These disorders often demonstrate male-specific vulnerabilities; however, the identification of underlying mechanisms remains a significant challenge in the field. Hemideletion of the 16p11.2 region (16p11.2 del/+) is associated with NDDs, and mice modeling 16p11.2 del/+ exhibit sex-specific striatum-related phenotypes relevant to NDDs. Striatal circuits, crucial for locomotor control, consist of two distinct pathways: the direct and indirect pathways originating from D1 dopamine receptor (D1R) and D2 dopamine receptor (D2R) expressing spiny projection neurons (SPNs), respectively. In this study, we define the impact of 16p11.2 del/+ on striatal circuits in male and female mice. Using snRNA-seq, we identify sex- and cell type-specific transcriptomic changes in the D1- and D2-SPNs of 16p11.2 del/+ mice, indicating distinct transcriptomic signatures in D1-SPNs and D2-SPNs in males and females, with a ∼5-fold greater impact in males. Further pathway analysis reveals differential gene expression changes in 16p11.2 del/+ male mice linked to synaptic plasticity in D1- and D2-SPNs and GABA signaling pathway changes in D1-SPNs. Consistent with our snRNA-seq study revealing changes in GABA signaling pathways, we observe distinct changes in miniature inhibitory postsynaptic currents (mIPSCs) in D1- and D2-SPNs from 16p11.2 del/+ male mice. Behaviorally, we utilize conditional genetic approaches to introduce the hemideletion selectively in either D1- or D2-SPNs and find that conditional hemideletion of genes in the 16p11.2 region in D2-SPNs causes hyperactivity in male mice, but hemideletion in D1-SPNs does not. Within the striatum, hemideletion of genes in D2-SPNs in the dorsal lateral striatum leads to hyperactivity in males, demonstrating the importance of this striatal region. Interestingly, conditional 16p11.2 del/+ within the cortex drives hyperactivity in both sexes. Our work reveals that a locus linked to NDDs acts in different striatal circuits, selectively impacting behavior in a sex- and cell type-specific manner, providing new insight into male vulnerability for NDDs.

Highlights

- 16p11.2 hemideletion (16p11.2 del/+) induces sex- and cell type-specific transcriptomic signatures in spiny projection neurons (SPNs). - Transcriptomic changes in GABA signaling in D1-SPNs align with changes in inhibitory synapse function. - 16p11.2 del/+ in D2-SPNs causes hyperactivity in males but not females. - 16p11.2 del/+ in D2-SPNs in the dorsal lateral striatum drives hyperactivity in males. - 16p11.2 del/+ in cortex drives hyperactivity in both sexes.

Graphic abstract

Ethanol inhibits dopamine uptake via organic cation transporter 3: Implications for ethanol and cocaine co-abuse

Concurrent cocaine and alcohol use is among the most frequent drug combination, and among the most dangerous in terms of deleterious outcomes. Cocaine increases extracellular monoamines by blocking dopamine (DA), norepinephrine (NE) and serotonin (5-HT) transporters (DAT, NET and SERT, respectively). Likewise, ethanol also increases extracellular monoamines, however evidence suggests that ethanol does so independently of DAT, NET and SERT. Organic cation transporter 3 (OCT3) is an emergent key player in the regulation of monoamine signaling. Using a battery of in vitro, in vivo electrochemical, and behavioral approaches, as well as wild-type and constitutive OCT3 knockout mice, we show that ethanol's actions to inhibit monoamine uptake are dependent on OCT3. These findings provide a novel mechanistic basis whereby ethanol enhances the neurochemical and behavioral effects of cocaine and encourage further research into OCT3 as a target for therapeutic intervention in the treatment of ethanol and ethanol/cocaine use disorders.

Role of Organic Cation Transporter 3 and Plasma Membrane Monoamine Transporter in the Rewarding Properties and Locomotor Sensitizing Effects of Amphetamine in Male andFemale Mice

A lack of effective treatment and sex-based disparities in psychostimulant addiction and overdose warrant further investigation into mechanisms underlying the abuse-related effects of amphetamine-like stimulants. Uptake-2 transporters such as organic cation transporter 3 (OCT3) and plasma membrane monoamine transporter (PMAT), lesser studied potential targets for the actions of stimulant drugs, are known to play a role in monoaminergic neurotransmission. Our goal was to examine the roles of OCT3 and PMAT in mediating amphetamine (1 mg/kg)-induced conditioned place preference (CPP) and sensitization to its locomotor stimulant effects, in males and females, using pharmacological, decynium-22 (D22; 0.1 mg/kg, a blocker of OCT3 and PMAT) and genetic (constitutive OCT3 and PMAT knockout (−/−) mice) approaches. Our results show that OCT3 is necessary for the development of CPP to amphetamine in males, whereas in females, PMAT is necessary for the ability of D22 to prevent the development of CPP to amphetamine. Both OCT3 and PMAT appear to be important for development of sensitization to the locomotor stimulant effect of amphetamine in females, and PMAT in males. Taken together, these findings support an important, sex-dependent role of OCT3 and PMAT in the rewarding and locomotor stimulant effects of amphetamine.

Role of phosphodiesterase 1 in the pathophysiology of diseases and potential therapeutic opportunities

Cyclic nucleotide phosphodiesterases (PDEs) are superfamily of enzymes that regulate the spatial and temporal relationship of second messenger signaling in the cellular system. Among the 11 different families of PDEs, phosphodiesterase 1 (PDE1) sub-family of enzymes hydrolyze both 3',5'-cyclic adenosine monophosphate (cAMP) and 3',5'-cyclic guanosine monophosphate (cGMP) in a mutually competitive manner. The catalytic activity of PDE1 is stimulated by their binding to Ca²⁺/calmodulin (CaM), resulting in the integration of Ca²⁺ and cyclic nucleotide-mediated signaling in various diseases. The PDE1 family includes three subtypes, PDE1A, PDE1B and PDE1C, which differ for their relative affinities for cAMP and cGMP. These isoforms are differentially expressed throughout the body, including the cardiovascular, central nervous system and other organs. Thus, PDE1 enzymes play a critical role in the pathophysiology of diseases through the fundamental regulation of cAMP and cGMP signaling. This comprehensive review provides the current research on PDE1 and its potential utility as a therapeutic target in diseases including the cardiovascular, pulmonary, metabolic, neurocognitive, renal, cancers and possibly others.

Inhibition of PDE1-B by Vinpocetine Regulates Microglial Exosomes and Polarization Through Enhancing Autophagic Flux for Neuroprotection Against Ischemic Stroke

Exosomes contribute to cell–cell communications. Emerging evidence has shown that microglial exosomes may play crucial role in regulation of neuronal functions under ischemic conditions. However, the underlying mechanisms of microglia-derived exosome biosynthesis are largely unknown. Herein, we reported that the microglial PDE1-B expression was progressively elevated in the peri-infarct region after focal middle cerebral artery occlusion. By an oxygen-glucose-deprivation (OGD) ischemic model in cells, we found that inhibition of PDE1-B by vinpocetine in the microglial cells promoted M2 and inhibited M1 phenotype. In addition, knockdown or inhibition of PDE1-B significantly enhanced the autophagic flux in BV2 cells, and vinpocetine-mediated suppression of M1 phenotype was dependent on autophagy in ischemic conditions. Co-culture of BV2 cells and neurons revealed that vinpocetine-treated BV2 cells alleviated OGD-induced neuronal damage, and treatment of BV2 cells with 3-MA abolished the observed effects of vinpocetine. We further demonstrated that ischemia and vinpocetine treatment significantly altered microglial exosome biogenesis and release, which could be taken up by recipient neurons and regulated neuronal damage. Finally, we showed that the isolated exosome per se from conditioned BV2 cells is sufficient to regulate cortical neuronal survival in vivo. Taken together, these results revealed a novel microglia-neuron interaction mediated by microglia-derived exosomes under ischemic conditions. Our findings further suggest that PDE1-B regulates autophagic flux and exosome biogenesis in microglia which plays a crucial role in neuronal survival under cerebral ischemic conditions.

Phosphodiesterase 1 Bridges Glutamate Inputs with NO- and Dopamine-Induced Cyclic Nucleotide Signals in the Striatum

The calcium-regulated phosphodiesterase 1 (PDE1) family is highly expressed in the brain, but its functional role in neurones is poorly understood. Using the selective PDE1 inhibitor Lu AF64196 and biosensors for cyclic nucleotides including a novel biosensor for cGMP, we analyzed the effect of PDE1 on cAMP and cGMP in individual neurones in brain slices from male newborn mice. Release of caged NMDA triggered a transient increase of intracellular calcium, which was associated with a decrease in cAMP and cGMP in medium spiny neurones in the striatum. Lu AF64196 alone did not increase neuronal cyclic nucleotide levels, but blocked the NMDA-induced reduction in cyclic nucleotides indicating that this was mediated by calcium-activated PDE1. Similar effects were observed in the prefrontal cortex and the hippocampus. Upon corelease of dopamine and NMDA, PDE1 was shown to down-regulate the D1-receptor mediated increase in cAMP. PDE1 inhibition increased long-term potentiation in rat ventral striatum, showing that PDE1 is implicated in the regulation of synaptic plasticity. Overall, our results show that PDE1 reduces cyclic nucleotide signaling in the context of glutamate and dopamine coincidence. This effect could have a therapeutic value for treating brain disorders related to dysfunctions in dopamine neuromodulation.

Advances in the Discovery of PDE10A Inhibitors for CNS-Related Disorders. Part 2: Focus on Schizophrenia

Schizophrenia is a debilitating mental disorder with relatively high prevalence (~1%), during which positive manifestations (such as psychotic states) and negative symptoms (e.g., a withdrawal from social life) occur. Moreover, some researchers consider cognitive impairment as a distinct domain of schizophrenia symptoms. The imbalance in dopamine activity, namely an excessive release of this neurotransmitter in the striatum and insufficient amounts in the prefrontal cortex is believed to be partially responsible for the occurrence of these groups of manifestations. Second-generation antipsychotics are currently the standard treatment of schizophrenia. Nevertheless, the existent treatment is sometimes ineffective and burdened with severe adverse effects, such as extrapyramidal symptoms. Thus, there is an urgent need to search for alternative treatment options of this disease. This review summarizes the results of recent preclinical and clinical studies on phosphodiesterase 10A (PDE10A), which is highly expressed in the mammalian striatum, as a potential drug target for the treatment of schizophrenia. Based on the literature data, not only selective PDE10A inhibitors but also dual PDE2A/10A, and PDE4B/10A inhibitors, as well as multifunctional ligands with a PDE10A inhibitory potency are compounds that may combine antipsychotic, precognitive, and antidepressant functions. Thus, designing such compounds may constitute a new direction of research for new potential medications for schizophrenia. Despite failures of previous clinical trials of selective PDE10A inhibitors for the treatment of schizophrenia, new compounds with this mechanism of action are currently investigated clinically, thus, the search for new inhibitors of PDE10A, both selective and multitarget, is still warranted.

Genetic manipulation of cyclic nucleotide signaling during hippocampal neuroplasticity and memory formation

Decades of research have underscored the importance of cyclic nucleotide signaling in memory formation and synaptic plasticity. In recent years, several new genetic techniques have expanded the neuroscience toolbox, allowing researchers to measure and modulate cyclic nucleotide gradients with high spatiotemporal resolution. Here, we will provide an overview of studies using genetic approaches to interrogate the role cyclic nucleotide signaling plays in hippocampus-dependent memory processes and synaptic plasticity. Particular attention is given to genetic techniques that measure real-time changes in cyclic nucleotide levels as well as newly-developed genetic strategies to transiently manipulate cyclic nucleotide signaling in a subcellular compartment-specific manner with high temporal resolution.

Multiple rare inherited variants in a four generation schizophrenia family offer leads for complex mode of disease inheritance

Schizophrenia is a clinically and genetically heterogeneous neuropsychiatric disorder, with a polygenic basis but identification of the specific determinants is a continuing challenge. In this study, we analyzed a multigenerational family, with all healthy individuals in the first two generations, and four progeny affected with schizophrenia in the subsequent two generations, using whole exome sequencing. We identified five rare protein sequence altering heterozygous variants, in five different genes namely SMARCA5, PDE1B, TNIK, SMARCA2 and FLRT shared among all affected members and predicted to be damaging. Variants in SMARCA5 and PDE1B were inherited from the unaffected father whereas variants in TNIK, SMARCA2 and FLRT1 were inherited from the unaffected mother in all the three affected individuals in the third generation; and notably all these five variants were transmitted by an affected mother to her affected son. Microsatellite based analysis lent a modest linkage support (LOD score of 1.2; θ=0.0 at each variant). Of note, analysis of exome data of an ancestry matched unrelated schizophrenia cohort (n = 350), revealed a total of 16 rare variants (MAF < 0.01) in these five genes. Interestingly, these five genes involved in neurodevelopmental and/or neurotransmitter signaling processes are implicated in the etiology of schizophrenia previously. This study provides good evidence for a likely cumulative contribution of multiple rare variants from disease relevant genes with a threshold effect in disease development and seems to explain the unusual disease transmission pattern generally witnessed in such conditions, but warrants extensive replication efforts in families with similar complex disease inheritance profiles.

Oral Monosodium Glutamate Differentially Affects Open-Field Behaviours, Behavioural Despair and Place Preference in Male and Female Mice

Background:

Monosodium glutamate (MSG) is a flavour enhancer which induces behavioural changes in animals. However the influence of sex on the behavioural response to MSG has not been investigated.

Objective:

The sex-differential effects of MSG on open-field behaviours, anxiety-related behaviour, behavioural despair, place-preference, and plasma/brain glutamate levels in adult mice were assessed.

Methods:

Mice were assigned to three groups (1-3), based on the models used to assess behaviours. Animals in group 1 were for the elevated-plus maze and tail-suspension paradigms, group 2 for the open-field and forced-swim paradigms, while mice in group 3 were for observation in the conditioned place preference paradigm. Mice in all groups were further assigned into five subgroups (10 males and 10 females), and administered vehicle (distilled water at 10 ml/kg) or one of four doses of MSG (20, 40, 80 and 160 mg/kg) daily for 6 weeks, following which they were exposed to the behavioural paradigms. At the end of the behavioural tests, the animals were sacrificed, and blood was taken for estimation of glutamate levels. The brains were also homogenised for estimation of glutamate levels.

Results:

MSG was associated with a reduction in locomotion in males and females (except at 160 mg/kg, male), an anxiolytic response in females, an anxiogenic response in males, and decreased behavioural despair in both sexes (females more responsive). Postconditioning MSG-associated place-preference was significantly higher in females. Plasma/ brain glutamate was not significantly different between sexes.

Conclusion:

Repeated MSG administration alters a range of behaviours in a sex-dependent manner in mice.

A Novel Phosphodiesterase 1 Inhibitor DSR-141562 Exhibits Efficacies in Animal Models for Positive, Negative, and Cognitive Symptoms Associated with Schizophrenia

In our drug discovery program, we identified a novel orally available and brain-penetrant phosphodiesterase (PDE) 1 inhibitor, 3-methyl-7-(tetrahydro-2H-pyran-4-yl)-2-{[trans-4-(trifluoromethyl)cyclohexyl]-methoxy}imidazo[5,1-f][1,2,4]triazin-4(3H)-one (DSR-141562). In the present study, we characterized the preclinical profile of DSR-141562. This compound has preferential selectivity for predominantly brain-expressed PDE1B over other PDE1 family members, and high selectivity for the PDE1 family over other PDE families and 65 other tested biologic targets. Oral administration of DSR-141562 at 10 mg/kg slightly elevated the cGMP concentration, and it potently enhanced the increase of cGMP induced by a dopamine D₁ receptor agonist in mouse brains. The cGMP level in monkey cerebrospinal fluid was also elevated after treatment with DSR-141562 at 30 and 100 mg/kg and could be used as a translational biomarker. Since PDE1B is believed to regulate dopaminergic and glutamatergic signal transduction, we evaluated the effects of this compound using schizophrenia-related behavioral assays. DSR-141562 at 3-30 mg/kg potently inhibited methamphetamine-induced locomotor hyperactivity in rats, while it had only minimal effects on the spontaneous locomotor activity. Furthermore, DSR-141562 at 1-100 mg/kg did not induce any signs of catalepsy in rats. DSR-141562 at 0.3-3 mg/kg reversed social interaction and novel object recognition deficits induced by repeated treatment with an N-methyl-D-aspartate receptor antagonist, phencyclidine, in mice and rats, respectively. In common marmosets, DSR-141562 at 3 and 30 mg/kg improved the performance in object retrieval with detour tasks. These results suggest that DSR-141562 is a therapeutic candidate for positive, negative, and cognitive symptoms in schizophrenia. SIGNIFICANCE STATEMENT: This is the first paper showing that a phosphodiesterase 1 inhibitor is efficacious in animal models for positive and negative symptoms associated with schizophrenia. Furthermore, we demonstrated that this compound improved cognitive function in the common marmoset, a nonhuman primate.

Phosphodiesterase 9A in Brain Regulates cGMP Signaling Independent of Nitric-Oxide

PDE9A is a cGMP-specific phosphodiesterase expressed in neurons throughout the brain that has attracted attention as a therapeutic target to treat cognitive disorders. Indeed, PDE9A inhibitors are under evaluation in clinical trials as a treatment for Alzheimer's disease and schizophrenia. However, little is known about the cGMP signaling cascades regulated by PDE9A. Canonical cGMP signaling in brain follows the activation of neuronal nitric oxide synthase (nNOS) and the generation of nitric oxide, which activates soluble guanylyl cyclase and cGMP synthesis. However, we show that in mice, PDE9A regulates a pool of cGMP that is independent of nNOS, specifically, and nitric oxide signaling in general. This PDE9A-regulated cGMP pool appears to be highly compartmentalized and independent of cGMP pools regulated by several PDEs. These findings provide a new foundation for study of the upstream and downstream signaling elements regulated by PDE9A and its potential as a therapeutic target for brain disease.

iTRAQ-based quantitative proteomics reveals the neuroprotection of rhubarb in experimental intracerebral hemorrhage

ETHNOPHARMACOLOGICAL RELEVANCE

Rhubarb is a traditional Chinese medicine(TCM), that possesses neuroprotective, anti-inflammatory, antibacterial, antioxidative, purgative and anticancer properties, and has been used to treat intracerebral hemorrhage (ICH) and many other diseases.

AIMS OF THE STUDY

This study aimed to investigate the changes of brain protein in ICH rats treated with rhubarb and to explore the multi-target mechanism of rhubarb in the treatment of ICH via bioinformatics analysis of differentially expressed proteins (DEPs).

MATERIALS AND METHODS

Rats were subjected to collagenase-induced ICH and then treated orally with 3 or 12 g/kg rhubarb daily for 2 days following ICH. After sacrifice, total protein of brain tissue was extracted, and isobaric tag for relative and absolute quantification (iTRAQ)-based liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis was employed to quantitatively identify of the DEPs in two treatment groups compared with the vehicle group. The DEPs were analyzed by Gene Ontology (GO), Kyoto Encyclopedia of Genes and Genomes (KEGG) and STRING databases. Bioinformatics Analysis Tool for Molecular mechanism of TCM (BATMAN-TCM) was used to predict the target of rhubarb and western blotting was used for verification.

RESULTS

In total, 1356 proteins were identified with a 1% false discovery rate (FDR). Among them, 55 DEPs were significantly altered in the sham, vehicle, low dose rhubarb group (LDR, 3 g/kg), and high dose rhubarb group (HDR, 12 g/kg). Enrichment analysis of GO annotations indicated that rhubarb mainly regulated expression of some neuron projection proteins involved in the response to drug and nervous system development. The dopaminergic synapse pathway was found to be the most significant DEP in the combined analysis of the KEGG and BATMAN-TCM databases. Based on the results of the STRING analysis, oxidative stress (OS), calcium binding protein regulation, vascularization, and energy metabolism were important in the rhubarb therapeutic process.

CONCLUSION

Rhubarb achieves its effects mainly through the dopaminergic synapse pathway in ICH treatment. The ICH-treating mechanisms of rhubarb may also involve anti-OS, calcium binding protein regulation, angiogenic regulation, and energy metabolism improvement. This study adds new evidence to clinical applications of rhubarb for ICH.

Phosphodiesterase 1b (PDE1B) Regulates Spatial and Contextual Memory in Hippocampus

Augmentation of cyclic nucleotide signaling through inhibition of phosphodiesterase (PDE) activity has long been understood to enhance memory. Efforts in this domain have focused predominantly on PDE4, a cAMP-specific phosphodiesterase implicated in consolidation. But less is known about the function of other PDEs expressed in neuroanatomical regions critical to memory. The PDE1 isoforms are the only PDEs to regulate neuronal cAMP and cGMP levels in a Ca²⁺/Calmodulin (CaM) dependent manner. Here, we show that knock-down of PDE1B in hippocampus of adult mice enhances contextual and spatial memory without effect on non-cognitive behaviors. Pharmacological augmentation of memory in rats was observed with a selective inhibitor of PDE1 dosed before and immediately after training, but not with drug dosed either 1 h after training or before recall. Our data clearly demonstrate a role for the PDE1B isoforms as negative regulators of memory, and they implicate PDE1 in an early phase of consolidation, but not retrieval. Inhibition of PDE1B is a promising therapeutic mechanism for treating memory impairment.

A comparison of the sexually dimorphic dexamethasone transcriptome in mouse cerebral cortical and hypothalamic embryonic neural stem cells

Fetal exposure to synthetic glucocorticoids reprograms distinct neural circuits in the developing brain, often in a sex-specific manner, via mechanisms that remain poorly understood. To reveal whether such reprogramming is associated with select molecular signatures, we characterized the transcriptome of primary, embryonic mouse cerebral cortical and hypothalamic neural progenitor/stem cells derived from individual male and female embryos exposed to the synthetic glucocorticoid, dexamethasone. Gene expression profiling by RNA-Seq identified differential expression of common and unique genes based upon brain region, sex, and/or dexamethasone exposure. These gene expression datasets provide a unique resource that will inform future studies examining the molecular mechanisms responsible for region- and sex-specific reprogramming of the fetal brain brought about by in utero exposure to excess glucocorticoids.

Regulation of Striatal Neuron Activity by Cyclic Nucleotide Signaling and Phosphodiesterase Inhibition: Implications for the Treatment of Parkinson's Disease

Cyclic nucleotide phosphodiesterase (PDE) enzymes catalyze the hydrolysis and inactivation of cyclic nucleotides (cAMP/cGMP) in the brain. Several classes of PDE enzymes with distinct tissue distributions, cyclic nucleotide selectivity, and regulatory factors are highly expressed in brain regions subserving cognitive and motor processes known to be disrupted in neurodegenerative diseases such as Parkinson's disease (PD). Furthermore, small-molecule inhibitors of several different PDE family members alter cyclic nucleotide levels and favorably enhance motor performance and cognition in animal disease models. This chapter will explore the roles and therapeutic potential of non-selective and selective PDE inhibitors on neural processing in fronto-striatal circuits in normal animals and models of DOPA-induced dyskinesias (LIDs) associated with PD. The impact of selective PDE inhibitors and augmentation of cAMP and cGMP signaling on the membrane excitability of striatal medium-sized spiny projection neurons (MSNs) will be discussed. The effects of cyclic nucleotide signaling and PDE inhibitors on synaptic plasticity of striatonigral and striatopallidal MSNs will be also be reviewed. New data on the efficacy of PDE10A inhibitors for reversing behavioral and electrophysiological correlates of L-DOPA-induced dyskinesias in a rat model of PD will also be presented. Together, these data will highlight the potential of novel PDE inhibitors for treatment of movement disorders such as PD which are associated with abnormal corticostriatal transmission.

Phosphodiesterase 1: A Unique Drug Target for Degenerative Diseases and Cognitive Dysfunction

The focus of this chapter is on the cyclic nucleotide phosphodiesterase 1 (PDE1) family. PDE1 is one member of the 11 PDE families (PDE 1-11). It is the only phosphodiesterase family that is calcium/calmodulin activated. As a result, whereas other families of PDEs 2-11 play a dominant role controlling basal levels of cyclic nucleotides, PDE1 is involved when intra-cellular calcium levels are elevated and, thus, has an "on demand" or activity-dependent involvement in the control of cyclic nucleotides in excitatory cells including neurons, cardiomyocytes and smooth muscle. As a Class 1 phosphodiesterase, PDE1 hydrolyzes the 3' bond of 3'-5'-cyclic nucleotides, cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP). Here, we review evidence for this family of enzymes as drug targets for development of therapies aimed to address disorders of the central nervous system (CNS) and of degenerative diseases. The chapter includes sections on the potential for cognitive enhancement in mental disorders, as well as a review of PDE1 enzyme structure, enzymology, tissue distribution, genomics, inhibitors, pharmacology, clinical trials, and therapeutic indications. Information is taken from public databases. A number of excellent reviews of the phosphodiesterase family have been written as well as reviews of the PDE1 family. References cited here are not comprehensive, rather pointing to major reviews and key publications.

Phosphodiesterase-1b deletion confers depression-like behavioral resistance separate from stress-related effects in mice

Phosphodiesterase-1b (Pde1b) is highly expressed in striatum, dentate gyrus, CA3 and substantia nigra. In a new Floxed Pde1b × Cre^CMV global knockout (KO) mouse model, we show an immobility-resistance phenotype that recapitulates that found in constitutive Pde1b KO mice. We use this new mouse model to show that the resistance to acute stress-induced depression-like phenotype is not the product of changes in locomotor activity or reactivity to other stressors (learned helplessness, novelty suppressed feeding or dexamethasone suppression), and is not associated with anhedonia using the sucrose preference test. Using tamoxifen inducible Cre, we show that the immobility-resistant phenotype depends on the age of induction. The effect is present when Pde1b is Reduced from conception, P0 or P32, but not if reduced as adults (P60). We also mapped regional brain expression of PDE1B protein and of the Cre driver. These data add to the suggestion that PDE1B may be a target for drug development with therapeutic potential in depression alone or in combination with existing antidepressants.

Phosphodiesterase-1b (Pde1b) knockout mice are resistant to forced swim and tail suspension induced immobility and show upregulation of Pde10a

RATIONALE

Major depressive disorder is a leading cause of suicide and disability. Despite this, current antidepressants provide insufficient efficacy in more than 60% of patients. Most current antidepressants are presynaptic reuptake inhibitors; postsynaptic signal regulation has not received as much attention as potential treatment targets.

OBJECTIVES

We examined the effects of disruption of the postsynaptic cyclic nucleotide hydrolyzing enzyme, phosphodiesterase (PDE) 1b, on depressive-like behavior and the effects on PDE1B protein in wild-type (WT) mice following stress.

METHODS

Littermate knockout (KO) and WT mice were tested in locomotor activity, tail suspension (TST), and forced swim tests (FST). FST was also used to compare the effects of two antidepressants, fluoxetine and bupropion, in KO versus WT mice. Messenger RNA (mRNA) expression changes were also determined. WT mice underwent acute or chronic stress and markers of stress and PDE1B expression were examined.

RESULTS

Pde1b KO mice exhibited decreased TST and FST immobility. When treated with antidepressants, both WT and KO mice showed decreased FST immobility and the effect was additive in KO mice. Mice lacking Pde1b had increased striatal Pde10a mRNA expression. In WT mice, acute and chronic stress upregulated PDE1B expression while PDE10A expression was downregulated after chronic but not acute stress.

CONCLUSIONS

PDE1B is a potential therapeutic target for depression treatment because of the antidepressant-like phenotype seen in Pde1b KO mice.

Hydrogen sulfide attenuates homocysteine-induced cognitive deficits and neurochemical alterations by improving endogenous hydrogen sulfide levels

Hyperomocysteinemia (HHcy) has been associated with mild cognitive impairment and dementia. Hydrogen sulfide (H₂ S) has been suggested to be an endogenous modulator of neuronal functions. However, the effect and mechanisms involved in beneficial effect of H₂ S has not been investigated in homocysteine (Hcy)-induced cognitive deficits. This study has been designed to evaluate the effect of exogenous H₂ S on behavioral deficits and neurochemical alterations in HHcy animals. Hcy levels were significantly elevated in plasma, cortex, and hippocampus of Hcy administered animals. A progressive decline in memory functions and increased anxiolytic behavior was observed in HHcy animals. This was accompanied by decrease in endogenous H₂ S levels along with decreased activity of cystathionase (CSE) and cystathionine β-synthase (CBS). However, a significant increase in CSE and CBS mRNAs was observed. In addition, the catecholamine and serotonin levels were reduced and the activity of monoamine oxidase A and B were increased in brain regions of HHcy animals. Haematoxylin and eosin staining revealed higher number of pyknotic cells in brain regions of HHcy animals. H₂ S administration was found to lower elevated plasma and brain Hcy levels. The activities of CBS, CSE, and levels of H₂ S were restored in HHcy animals administered H₂ S. Exogenous H₂ S also ameliorated behavioral deficits accompanied by significant increase in catecholamines. Histological analysis revealed normal cell morphology in Hcy-treated animals supplemented with H₂ S. These results clearly demonstrate that the protective effect of H₂ S on Hcy-induced cognitive deficits is mediated through increased catecholamine and H₂ S levels thereby suggesting its beneficial role in preventing HHcy-induced neurodegeneration. © 2016 BioFactors, 43(3):434-450, 2017.

Phosphodiesterase Inhibition and Regulation of Dopaminergic Frontal and Striatal Functioning: Clinical Implications

BACKGROUND

The fronto-striatal circuits are the common neurobiological basis for neuropsychiatric disorders, including schizophrenia, Parkinson's disease, Huntington's disease, attention deficit hyperactivity disorder, obsessive-compulsive disorder, and Tourette's syndrome. Fronto-striatal circuits consist of motor circuits, associative circuits, and limbic circuits. All circuits share 2 common features. First, all fronto-striatal circuits consist of hyper direct, direct, and indirect pathways. Second, all fronto-striatal circuits are modulated by dopamine. Intracellularly, the effect of dopamine is largely mediated through the cyclic adenosine monophosphate/protein kinase A signaling cascade with an additional role for the cyclic guanosine monophosphate/protein kinase G pathway, both of which can be regulated by phosphodiesterases. Phosphodiesterases are thus a potential target for pharmacological intervention in neuropsychiatric disorders related to dopaminergic regulation of fronto-striatal circuits.

METHODS

Clinical studies of the effects of different phosphodiesterase inhibitors on cognition, affect, and motor function in relation to the fronto-striatal circuits are reviewed.

RESULTS

Several selective phosphodiesterase inhibitors have positive effects on cognition, affect, and motor function in relation to the fronto-striatal circuits.

CONCLUSION

Increased understanding of the subcellular localization and unraveling of the signalosome concept of phosphodiesterases including its function and dysfunction in the fronto-striatal circuits will contribute to the design of new specific inhibitors and enhance the potential of phosphodiesterase inhibitors as therapeutics in fronto-striatal circuits.

Preclinical profile of ITI-214, an inhibitor of phosphodiesterase 1, for enhancement of memory performance in rats

RATIONALE

Therapeutic agents for memory enhancement in psychiatric disorders, such as schizophrenia, are urgently needed.

OBJECTIVE

The aim of this study is to characterize the preclinical profile of ITI-214, a potent inhibitor of phosphodiesterase 1 (PDE1).

METHODS

ITI-214 was assayed for inhibition of PDE1 versus other PDE enzyme families using recombinant human PDE enzymes and for off-target binding to 70 substrates (General SEP II diversity panel; Caliper Life Sciences). Effects of ITI-214 (0.1-10 mg/kg, po) on memory performance were assayed in rats using the novel object recognition (NOR) paradigm, with drug given at specified time points prior to or following exposure to objects in an open field. ITI-214 was evaluated for potential drug-drug interaction with risperidone in rats using conditioned avoidance response (CAR) and pharmacokinetic assessments.

RESULTS

ITI-214 inhibited PDE1A (K i = 33 pmol) with >1000-fold selectivity for the nearest other PDE family (PDE4D) and displayed minimal off-target binding interactions in a 70-substrate selectivity profile. By using specific timing of oral ITI-214 administration, it was demonstrated in the NOR that ITI-214 is able to enhance acquisition, consolidation, and retrieval memory processes. All memory effects were in the absence of effects on exploratory behavior. ITI-214 did not disrupt the risperidone pharmacokinetic profile or effects in CAR.

CONCLUSIONS

ITI-214 improved the memory processes of acquisition, consolidation, and retrieval across a broad dose range (0.1-10 mg/kg, po) without disrupting the antipsychotic-like activity of a clinical antipsychotic medication, specifically risperidone. Clinical development of ITI-214 is currently in progress.

Association of novelty-related behaviors and intravenous cocaine self-administration in Diversity Outbred mice

RATIONALE

The preference for and reaction to novelty are strongly associated with addiction to cocaine and other drugs. However, the genetic variants and molecular mechanisms underlying these phenomena remain largely unknown. Although the relationship between novelty- and addiction-related traits has been observed in rats, studies in mice have failed to demonstrate this association. New, genetically diverse, high-precision mouse populations including Diversity Outbred (DO) mice provide an opportunity to assess an expanded range of behavioral variation enabling detection of associations of novelty- and addiction-related traits in mice.

METHODS

To examine the relationship between novelty- and addiction-related traits, male (n = 51) and female (n = 47) DO mice were tested on open field exploration, hole board exploration, and novelty preference followed by intravenous cocaine self-administration (IVSA; ten 2-h sessions of fixed ratio 1 and one 6-h session of progressive ratio).

RESULTS

We observed high variation of cocaine IVSA in DO mice with 43 % reaching and 57 % not reaching conventional acquisition criteria. As a group, mice that did not reach these criteria still demonstrated significant lever discrimination. Mice experiencing catheter occlusion or other technical issues (n = 17) were excluded from the analysis. Novelty-related behaviors were positively associated with cocaine IVSA. Multivariate analysis of associations among novelty- and addiction-related traits revealed a large degree of shared variance (45 %).

CONCLUSIONS

Covariation among cocaine IVSA and novelty-related phenotypes in DO mice indicates that this relationship is amenable to genetic dissection. The high genetic precision and phenotypic diversity in the DO may facilitate discovery of previously undetectable mechanisms underlying predisposition to develop addiction disorders.

Adaptive admixture in the West African bovine hybrid zone: insight from the Borgou population

Understanding the adaptive response to environmental fluctuations represents a central issue in evolutionary biology. Population admixture between divergent ancestries has often been considered as an efficient short-term adaptation strategy. Cattle populations from the West African Bos taurus × Bos indicus hybrid zone represent a valuable resource to characterize the effect of such adaptive admixture at the genome level. We here provide a detailed assessment of the global and local genome ancestries of the Borgou breed, one of the most representative cattle of this hybrid zone. We analysed a large data set consisting of 38,100 SNPs genotyped on 203 Borgou and 591 individuals representative of all the different cattle ancestries. At the global genomic level, we show that Borgou is a stabilized admixed breed whose origin (c. 130 years ago) traces back to the great African rinderpest pandemic, several centuries after the last admixture events, the West African zebus originate from (c. 500 years ago). To identify footprints of adaptive admixture, we combined the identification of signatures of selection and the functional annotation of the underlying genes using systems biology tools. The detection of the SILV coat coloration gene likely under artificial selection may be viewed as a validation of our approach. Overall, our results suggest that the long-term presence of pathogens and the intermediate environmental conditions are the main acting selective pressures. Our analytical framework can be extended to other model or nonmodel species to understand the process that shapes the patterns of genetic variability in hybrid zones.

Advances in targeting cyclic nucleotide phosphodiesterases

Cyclic nucleotide phosphodiesterases (PDEs) catalyse the hydrolysis of cyclic AMP and cyclic GMP, thereby regulating the intracellular concentrations of these cyclic nucleotides, their signalling pathways and, consequently, myriad biological responses in health and disease. Currently, a small number of PDE inhibitors are used clinically for treating the pathophysiological dysregulation of cyclic nucleotide signalling in several disorders, including erectile dysfunction, pulmonary hypertension, acute refractory cardiac failure, intermittent claudication and chronic obstructive pulmonary disease. However, pharmaceutical interest in PDEs has been reignited by the increasing understanding of the roles of individual PDEs in regulating the subcellular compartmentalization of specific cyclic nucleotide signalling pathways, by the structure-based design of novel specific inhibitors and by the development of more sophisticated strategies to target individual PDE variants.

Select 3',5'-cyclic nucleotide phosphodiesterases exhibit altered expression in the aged rodent brain

3',5'-cyclic nucleotide phosphodiesterases (PDEs) are the only known enzymes to compartmentalize cAMP and cGMP, yet little is known about how PDEs are dynamically regulated across the lifespan. We mapped mRNA expression of all 21 PDE isoforms in the adult rat and mouse central nervous system (CNS) using quantitative polymerase chain reaction (qPCR) and in situ hybridization to assess conservation across species. We also compared PDE mRNA and protein in the brains of old (26 months) versus young (5 months) Sprague-Dawley rats, with select experiments replicated in old (9 months) versus young (2 months) BALB/cJ mice. We show that each PDE isoform exhibits a unique expression pattern across the brain that is highly conserved between rats, mice, and humans. PDE1B, PDE1C, PDE2A, PDE4A, PDE4D, PDE5A, PDE7A, PDE8A, PDE8B, PDE10A, and PDE11A showed an age-related increase or decrease in mRNA expression in at least 1 of the 4 brain regions examined (hippocampus, cortex, striatum, and cerebellum). In contrast, mRNA expression of PDE1A, PDE3A, PDE3B, PDE4B, PDE7A, PDE7B, and PDE9A did not change with age. Age-related increases in PDE11A4, PDE8A3, PDE8A4/5, and PDE1C1 protein expression were confirmed in hippocampus of old versus young rodents, as were age-related increases in PDE8A3 protein expression in the striatum. Age-related changes in PDE expression appear to have functional consequences as, relative to young rats, the hippocampi of old rats demonstrated strikingly decreased phosphorylation of GluR1, CaMKIIα, and CaMKIIβ, decreased expression of the transmembrane AMPA regulatory proteins γ2 (a.k.a. stargazin) and γ8, and increased trimethylation of H3K27. Interestingly, expression of PDE11A4, PDE8A4/5, PDE8A3, and PDE1C1 correlate with these functional endpoints in young but not old rats, suggesting that aging is not only associated with a change in PDE expression but also a change in PDE compartmentalization.

Sex differences in novelty- and psychostimulant-induced behaviors of C57BL/6 mice

RATIONALE

Women are more sensitive than men to psychostimulants and progress from initial use to drug addiction more quickly. The mouse has been an under-utilized model to study sex differences in psychostimulant action. Mice could serve as an ideal genetically tractable model for mechanistic studies into sex and hormone effects on psychostimulant behavior.

OBJECTIVES

The objective of this study was to characterize psychostimulant effects in male and female mice with a combination of automated data collection and behavioral observation.

METHODS

Male and female C57BL/6 mice (Charles River) were given a single dose or sequential ascending binge doses of D-amphetamine (AMPH) or cocaine (COC). Behavior was assessed in open field chambers using both automated photobeam interruptions and behavioral observations. Brain psychostimulant concentrations were determined at the time of maximum behavioral stimulation.

RESULTS

Psychostimulants induced behavioral activation in mice including both increased locomotion as detected with an automated system and a sequence of behaviors progressing from stereotyped sniffing at low doses to patterned locomotion and rearing at high doses. Females exhibited more patterned locomotion and a shift towards higher behavior scores after either psychostimulant despite having lower AMPH and equivalent COC brain levels as males.

CONCLUSIONS

Female C57BL/6 mice exhibit enhanced psychostimulant-induced behavior compared to males, similar to reports in rats. The combination of automated behavioral measures and behavioral observation was essential for verifying the existence of these differences. These results indicate the importance of testing both sexes when characterizing genetically manipulated mice to control for potential sex-specific effects.

cGMP Signaling, Phosphodiesterases and Major Depressive Disorder

Deficits in neuroplasticity are hypothesized to underlie the pathophysiology of major depressive disorder (MDD): the effectiveness of antidepressants is thought to be related to the normalization of disrupted synaptic transmission and neurogenesis. The cyclic adenosine monophosphate (cAMP) signaling cascade has received considerable attention for its role in neuroplasticity and MDD. However components of a closely related pathway, the cyclic guanosine monophosphate (cGMP) have been studied with much lower intensity, even though this signaling transduction cascade is also expressed in the brain and the activity of this pathway has been implicated in learning and memory processes. Cyclic GMP acts as a second messenger; it amplifies signals received at postsynaptic receptors and activates downstream effector molecules resulting in gene expression changes and neuronal responses. Phosphodiesterase (PDE) enzymes degrade cGMP into 5’GMP and therefore they are involved in the regulation of intracellular levels of cGMP. Here we review a growing body of evidence suggesting that the cGMP signaling cascade warrants further investigation for its involvement in MDD and antidepressant action.

Mechanisms for the modulation of dopamine d(1) receptor signaling in striatal neurons

In the striatum, dopamine D(1) receptors are preferentially expressed in striatonigral neurons, and increase the neuronal excitability, leading to the increase in GABAergic inhibitory output to substantia nigra pars reticulata. Such roles of D(1) receptors are important for the control of motor functions. In addition, the roles of D(1) receptors are implicated in reward, cognition, and drug addiction. Therefore, elucidation of mechanisms for the regulation of dopamine D(1) receptor signaling is required to identify therapeutic targets for Parkinson's disease and drug addiction. D(1) receptors are coupled to G(s/olf)/adenylyl cyclase/PKA signaling, leading to the phosphorylation of PKA substrates including DARPP-32. Phosphorylated form of DARPP-32 at Thr34 has been shown to inhibit protein phosphatase-1, and thereby controls the phosphorylation states and activity of many downstream physiological effectors. Roles of DARPP-32 and its phosphorylation at Thr34 and other sites in D(1) receptor signaling are extensively studied. In addition, functional roles of the non-canonical D(1) receptor signaling cascades that coupled to G(q)/phospholipase C or Src family kinase become evident. We have recently shown that phosphodiesterases (PDEs), especially PDE10A, play a pivotal role in regulating the tone of D(1) receptor signaling relatively to that of D(2) receptor signaling. We review the current understanding of molecular mechanisms for the modulation of D(1) receptor signaling in the striatum.

Mammalian Cyclic Nucleotide Phosphodiesterases: Molecular Mechanisms and Physiological Functions

The superfamily of cyclic nucleotide (cN) phosphodiesterases (PDEs) is comprised of 11 families of enzymes. PDEs break down cAMP and/or cGMP and are major determinants of cellular cN levels and, consequently, the actions of cN-signaling pathways. PDEs exhibit a range of catalytic efficiencies for breakdown of cAMP and/or cGMP and are regulated by myriad processes including phosphorylation, cN binding to allosteric GAF domains, changes in expression levels, interaction with regulatory or anchoring proteins, and reversible translocation among subcellular compartments. Selective PDE inhibitors are currently in clinical use for treatment of erectile dysfunction, pulmonary hypertension, intermittent claudication, and chronic pulmonary obstructive disease; many new inhibitors are being developed for treatment of these and other maladies. Recently reported x-ray crystallographic structures have defined features that provide for specificity for cAMP or cGMP in PDE catalytic sites or their GAF domains, as well as mechanisms involved in catalysis, oligomerization, autoinhibition, and interactions with inhibitors. In addition, major advances have been made in understanding the physiological impact and the biochemical basis for selective localization and/or recruitment of specific PDE isoenzymes to particular subcellular compartments. The many recent advances in understanding PDE structures, functions, and physiological actions are discussed in this review.

cGMP-dependent protein kinases and cGMP phosphodiesterases in nitric oxide and cGMP action

To date, studies suggest that biological signaling by nitric oxide (NO) is primarily mediated by cGMP, which is synthesized by NO-activated guanylyl cyclases and broken down by cyclic nucleotide phosphodiesterases (PDEs). Effects of cGMP occur through three main groups of cellular targets: cGMP-dependent protein kinases (PKGs), cGMP-gated cation channels, and PDEs. cGMP binding activates PKG, which phosphorylates serines and threonines on many cellular proteins, frequently resulting in changes in activity or function, subcellular localization, or regulatory features. The proteins that are so modified by PKG commonly regulate calcium homeostasis, calcium sensitivity of cellular proteins, platelet activation and adhesion, smooth muscle contraction, cardiac function, gene expression, feedback of the NO-signaling pathway, and other processes. Current therapies that have successfully targeted the NO-signaling pathway include nitrovasodilators (nitroglycerin), PDE5 inhibitors [sildenafil (Viagra and Revatio), vardenafil (Levitra), and tadalafil (Cialis and Adcirca)] for treatment of a number of vascular diseases including angina pectoris, erectile dysfunction, and pulmonary hypertension; the PDE3 inhibitors [cilostazol (Pletal) and milrinone (Primacor)] are used for treatment of intermittent claudication and acute heart failure, respectively. Potential for use of these medications in the treatment of other maladies continues to emerge.

Activity Modes in Thalamocortical Relay Neurons are Modulated by G(q)/G(11) Family G-proteins - Serotonergic and Glutamatergic Signaling

In thalamocortical relay (TC) neurons, G-protein-coupled receptors play an important part in the control of activity modes. A conditional Gα(q) knockout on the background of a constitutive Gα(11) knockout (Gα(q)/Gα(11) (-/-)) was used to determine the contribution of Gq/G11 family G-proteins to metabotropic serotonin (5-HT) and glutamate (Glu) function in the dorsal part of the lateral geniculate nucleus (dLGN). In control mice, current clamp recordings showed that α-m-5-HT induced a depolarization of V(rest) which was sufficient to suppress burst firing. This depolarization was concentration-dependent (100 μM: +6 ± 1 mV, n = 10; 200 μM: +10 ± 1 mV, n = 7) and had a conditioning effect on the activation of other Gα(q)-mediated pathways. The depolarization was significantly reduced in Gα(q)/Gα(11) (-/-) (100 μM: 3 ± 1 mV, n = 11; 200 μM: 5 ± 1 mV, n = 6) and was apparently insufficient to suppress burst firing. Activating Gα(q)-coupled muscarinic receptors affected the magnitude of α-m-5-HT-induced effects in a reciprocal manner. Furthermore, the depolarizing effect of mGluR1 agonists was significantly reduced in Gα(q)/Gα(11) (-/-) mice. Immunohistochemical stainings revealed binding of 5-HT(2C)R- and mGluR1α-, but not of 5-HT(2A)R-specific antibodies in the dLGN of Gα(q)/Gα(11) (-/-) mice. In conclusion, these findings demonstrate that transmitters of ascending brainstem fibers and corticofugal fibers both signal via a central element in the form of Gq/G11-mediated pathways to control activity modes in the TC system.

Phosphodiesterase 11A in brain is enriched in ventral hippocampus and deletion causes psychiatric disease-related phenotypes

Phosphodiesterase 11A (PDE11A) is the most recently identified family of phosphodiesterases (PDEs), the only known enzymes to break down cyclic nucleotides. The tissue expression profile of this dual specificity PDE is controversial, and little is understood of its biological function, particularly in the brain. We seek here to determine if PDE11A is expressed in the brain and to understand its function, using PDE11A(-/-) knockout (KO) mice. We show that PDE11A mRNA and protein are largely restricted to hippocampus CA1, subiculum, and the amygdalohippocampal area, with a two- to threefold enrichment in the ventral vs. dorsal hippocampus, equal distribution between cytosolic and membrane fractions, and increasing levels of protein expression from postnatal day 7 through adulthood. Interestingly, PDE11A KO mice show subtle psychiatric-disease-related deficits, including hyperactivity in an open field, increased sensitivity to the glutamate N-methyl-D-aspartate receptor antagonist MK-801, as well as deficits in social behaviors (social odor recognition memory and social avoidance). In addition, PDE11A KO mice show enlarged lateral ventricles and increased activity in CA1 (as per increased Arc mRNA), phenotypes associated with psychiatric disease. The increased sensitivity to MK-801 exhibited by PDE11A KO mice may be explained by the biochemical dysregulation observed around the glutamate alpha-amino-3-hydroxy-5-methyl-4-isozazolepropionic (AMPA) receptor, including decreased levels of phosphorylated-GluR1 at Ser845 and the prototypical transmembrane AMPA-receptor-associated proteins stargazin (gamma2) and gamma8. Together, our data provide convincing evidence that PDE11A expression is restricted in the brain but plays a significant role in regulating brain function.

Differential function of phosphodiesterase families in the brain: gaining insights through the use of genetically modified animals

Phosphodiesterases (PDEs) are the only known enzymes to degrade cAMP and cGMP, intracellular signaling molecules key to numerous cellular functions. There are 11 PDE families identified to date, and each is expressed in a unique pattern across brain regions. Here, we review genetic mouse models in which PDEs are either directly manipulated (e.g., genetically deleted) or are changed in a compensatory manner due to the manipulation of another target. We believe these genetic mouse models have contributed to our understanding of how the PDE1, PDE4, and PDE10 families contribute uniquely to overall brain function.

The role of phosphodiesterases in schizophrenia : therapeutic implications

Recent studies have suggested that currently available antipsychotic medications, while useful in treating some aspects of schizophrenia, still possess considerable limitations. Improving the treatment of negative symptoms and cognitive dysfunction, and decreasing adverse effects remain significant challenges. Many new drug strategies have been proposed in recent years and increasing evidence suggests that members of the phosphodiesterase (PDE) gene family may play a role in the aetiology or treatment of schizophrenia. PDEs are key enzymes responsible for the degradation of the second messengers cAMP (3',5'-cyclic adenosine monophosphate) and cGMP (3',5'-cyclic guanosine monophosphate). Mammalian PDEs are composed of 21 genes and are categorized into 11 families based on sequence homology, enzymatic properties and sensitivity to pharmacological inhibitors. Representatives from most families have been identified in the brain by the presence of protein or RNA, and numerous studies suggest that PDEs play an important role in the regulation of intracellular signalling downstream of receptor activation in neurons. Insights into the multiple brain processes to which PDEs contribute are emerging from the phenotype of genetically engineered mice that lack activity of specific PDEs (knockout mice), as well as from in vitro and in vivo studies with PDE inhibitors.This article provides a brief overview of recent studies implicating PDE inhibition, focusing on PDE4 and PDE10, as targets for treating the positive, negative or cognitive symptoms associated with schizophrenia.

Attenuation of methamphetamine-induced effects through the antagonism of sigma (sigma) receptors: Evidence from in vivo and in vitro studies

Methamphetamine (METH) and many other abused substances interact with sigma receptors. sigma receptors are found on dopaminergic neurons and can modulate dopaminergic neurotransmission. Antisense knock down of sigma receptors also mitigates METH-induced stimulant effects, suggesting that these proteins are viable medication development targets for treating psychostimulant abuse. In the present study, AC927, a sigma receptor antagonist, was evaluated for its ability to attenuate METH-induced effects in vivo and in vitro. Radioligand binding studies showed that AC927 had preferential affinity for sigma receptors compared to 29 other receptors, transporters and ion channels. Pretreatment of male, Swiss Webster mice with AC927 significantly attenuated METH-induced locomotor stimulation, striatal dopamine depletions, striatal dopamine transporter reductions, and hyperthermia. When the neurotoxicity of METH was further examined in vitro under temperature-controlled conditions, co-incubation with AC927 mitigated METH-induced cytotoxicity. Together, the results demonstrate that AC927 protects against METH-induced effects, and suggests a new strategy for treating psychostimulant abuse.

Behavioral and neurochemical characterization of mice deficient in the phosphodiesterase-4B (PDE4B) enzyme

RATIONALE

Phosphodiesterases (PDEs) belonging to the PDE4 family control intracellular concentrations of cyclic adenosine monophosphate (cAMP) by catalyzing its hydrolysis. Four separate PDE4 genes (PDE4A, PDE4B, PDE4C, and PDE4D) have been identified. PDE4 has been reported to be involved in various central nervous system (CNS) functions including depression, memory, and schizophrenia, although the specific subtype mediating these effects remains unclear.

OBJECTIVE

To investigate the role of PDE4B in the CNS, PDE4B wild-type and knockout mice (C57BL/6N background) were assessed in a variety of well-characterized behavioral tasks, and their brains were assayed for monoamine content.

RESULTS

Knockout mice showed a significant reduction in prepulse inhibition. Spontaneous locomotor activity was decreased (16%) in knockout mice. Furthermore, when challenged with amphetamine, both groups of mice responded similarly to a low dose of d-amphetamine (1.0 mg/kg), but knockout mice showed an enhanced response to a higher dose (1.78 mg/kg). Decreases in baseline levels of monoamines and their metabolites within the striatum of knockout mice were also observed. PDE4B knockout mice showed a modest decrease in immobility time in the forced swim test that approached significance. In several other tests, including the elevated plus maze, hot plate, passive avoidance, and Morris water maze, wild-type and knockout mice performed similarly.

CONCLUSION

The present studies demonstrate decreased striatal DA and 5-HT activity in the PDE4B knockout mice associated with decreased prepulse inhibition, decreased baseline motor activity, and an exaggerated locomotor response to amphetamine. These data further support a role for PDE4B in psychiatric diseases and striatal function.