Akihiro Mouri

Phencyclidine animal models of schizophrenia: approaches from abnormality of glutamatergic neurotransmission and neurodevelopment.

In humans, phencyclidine (PCP), a non-competitive N-methyl-d-aspartate (NMDA) receptor antagonist, reproduces a schizophrenia-like psychosis including positive symptoms, negative symptoms and cognitive dysfunction. Thus, the glutamatergic neuronal dysfunction hypothesis is one of the main explanatory hypotheses and PCP-treated animals have been utilized as an animal model of schizophrenia. The adult rodents treated with PCP repeatedly exhibit hyperlocomotion as an index of positive symptoms, a social behavioral deficit in a social interaction test and enhanced immobility in a forced swimming test as indices of negative symptoms. They also show a sensorimotor gating deficits and cognitive dysfunctions in several learning and memory tests. Some of these behavioral changes endure after withdrawal from repeated PCP treatment. Furthermore, repeated PCP treatment induces some neurochemical and neuroanatomical changes. On the other hand, the exposure to viral or environmental insult in the second trimester of pregnancy increases the probability of subsequently developing schizophrenia as an adult. NMDA receptor has been implicated in controlling the structure and plasticity of developing brain circuitry. Based on neurodevelopment hypothesis of schizophrenia, schizophrenia model rats treated with PCP at the perinatal stage is developed. Perinatal PCP treatment impairs neuronal development and induces long-lasting schizophrenia-like behaviors in adult period. Many findings suggest that these PCP animal models would be useful for evaluating novel therapeutic candidates and for confirming pathological mechanisms of schizophrenia.

Oral vaccination with a viral vector containing Aβ cDNA attenuates age-related Aβ accumulation and memory deficits without causing inflammation in a mouse Alzheimer model

Immunotherapy with Aβ is expected to bring great improvement for Alzheimer disease (AD). However, clinical trials have been suspended because of meningoencephalitics, which accompanied lympho‐cytic infiltration. We have developed an oral vaccine for AD with a recombinant adeno‐associated viral vector carrying Aβ cDNA (AAV/Aβ). The vaccine reduces the amount of Aβ deposited without lymphocytic infiltration in APP transgenic (Tg2576) mice. In the present study, Tg2576 mice showed progressive cognitive impairments in the novel object recognition test, Y‐maze test, water maze test, and contextual conditioned fear learning test. A single oral administration of AAV/Aβ to Tg2576 mice at the age of 10 months alleviated progressive cognitive impairment with decreased Aβ deposition, insoluble Aβ, soluble Aβ oligomer (Aβ*56), microglial attraction, and synaptic degeneration induced in the brain regions at the age of 13 months. A histological analysis with hematoxylin and eosin and an immunohistochemical analysis with antibodies against CD3, CD4, CD8, and CD19 suggested there was no lymphocytic infiltration or microhemorrhage in the brain of AAV/Aβ‐vaccinated Tg2576 mice at 13 months of age. Taken together, these results suggest that immunotherapy with AAV/Aβ is a safe and effective treatment for AD.–Mouri, A., Noda, Y., Hara, H., Mizoguchi, H., Tabira, T., Nabeshima, T. Oral vaccination with a viral vector containing Aβ cDNA attenuates age‐related Aβ accumulation and memory deficits without causing inflammation in a mouse Alzheimer model. FASEB J. 21, 2135–2148 (2007)

Silibinin prevents amyloid β peptide‐induced memory impairment and oxidative stress in mice

Background and purpose:  Accumulated evidence suggests that oxidative stress is involved in amyloid β (Aβ)‐induced cognitive dysfunction. Silibinin (silybin), a flavonoid derived from the herb milk thistle (Silybum marianum), has been shown to have antioxidative properties; however, it remains unclear whether silibinin improves Aβ‐induced neurotoxicity. In the present study, we examined the effect of silibinin on the memory impairment and accumulation of oxidative stress induced by Aβ25–35 in mice.

Neprilysin-sensitive Synapse-associated Amyloid-β Peptide Oligomers Impair Neuronal Plasticity and Cognitive Function

A subtle but chronic alteration in metabolic balance between amyloid-β peptide (Aβ) anabolic and catabolic activities is thought to cause Aβ accumulation, leading to a decade-long pathological cascade of Alzheimer disease. However, it is still unclear whether a reduction of the catabolic activity of Aβ in the brain causes neuronal dysfunction in vivo. In the present study, to clarify a possible connection between a reduction in neprilysin activity and impairment of synaptic and cognitive functions, we cross-bred amyloid precursor protein (APP) transgenic mice (APP23) with neprilysin-deficient mice and biochemically and immunoelectron-microscopically analyzed Aβ accumulation in the brain. We also examined hippocampal synaptic plasticity using an in vivo recording technique and cognitive function using a battery of learning and memory behavior tests, including Y-maze, novel-object recognition, Morris water maze, and contextual fear conditioning tests at the age of 13–16 weeks. We present direct experimental evidence that reduced activity of neprilysin, the major Aβ-degrading enzyme, in the brain elevates oligomeric forms of Aβ at the synapses and leads to impaired hippocampal synaptic plasticity and cognitive function before the appearance of amyloid plaque load. Thus, reduced neprilysin activity appears to be a causative event that is at least partly responsible for the memory-associated symptoms of Alzheimer disease. This supports the idea that a strategy to reduce Aβ oligomers in the brain by up-regulating neprilysin activity would contribute to alleviation of these symptoms.

Mice with neuron-specific accumulation of mitochondrial DNA mutations show mood disorder-like phenotypes

There is no established genetic model of bipolar disorder or major depression, which hampers research of these mood disorders. Although mood disorders are multifactorial diseases, they are sometimes manifested by one of pleiotropic effects of a single major gene defect. We focused on chronic progressive external ophthalmoplegia (CPEO), patients with which sometimes have comorbid mood disorders. Chronic progressive external ophthalmoplegia is a mitochondrial disease, which is accompanied by accumulation of mitochondrial DNA (mtDNA) deletions caused by mutations in nuclear-encoded genes such as POLG (mtDNA polymerase). We generated transgenic mice, in which mutant POLG was expressed in a neuron-specific manner. The mice showed forebrain-specific defects of mtDNA and had altered monoaminergic functions in the brain. The mutant mice exhibited characteristic behavioral phenotypes, a distorted day–night rhythm and a robust periodic activity pattern associated with estrous cycle. These abnormal behaviors resembling mood disorder were worsened by tricyclic antidepressant treatment and improved by lithium, a mood stabilizer. We also observed antidepressant-induced mania-like behavior and long-lasting irregularity of activity in some mutant animals. Our data suggest that accumulation of mtDNA defects in brain caused mood disorder-like mental symptoms with similar treatment responses to bipolar disorder. These findings are compatible with mitochondrial dysfunction hypothesis of bipolar disorder.

The allosteric potentiation of nicotinic acetylcholine receptors by galantamine ameliorates the cognitive dysfunction in beta amyloid25-35 i.c.v.-injected mice: involvement of dopaminergic systems.

Galantamine, a drug for Alzheimer’s disease, is a novel cholinergic agent with a dual mode of action, which inhibits acetylcholinesterase and allosterically modulates nicotinic acetylcholine receptors (nAChRs), as a result stimulates catecholamine neurotransmission. In the present study, we investigated whether galantamine exerts cognitive improving effects through the allosteric modulation of nAChR in the intracerebroventricular beta amyloid (Aβ)25−35-injected animal model of Alzheimer’s disease. Galantamine (3 mg/kg p.o.) significantly increased the extracellular dopamine release in the hippocampus of saline- and Aβ25−35-injected mice. The effects of nicotine on the extracellular dopamine release were potentiated by galantamine, but antagonized by mecamylamine, a nAChR antagonist. Aβ25−35-injected mice, compared with saline-injected mice, could not discriminate between new and familiar objects in the novel object recognition test and exhibited less freezing response in the fear-conditioning tasks, suggesting Aβ25−35 induced cognitive impairment. Galantamine improved the Aβ25−35-induced cognitive impairment in the novel object recognition and fear-conditioning tasks. These improving effects of galantamine were blocked by the treatment with mecamylamine, SCH-23390, a dopamine-D1 receptor antagonist, and sulpiride, a dopamine-D2 receptor antagonist, but not by scopolamine, a muscarinic acetylcholine receptor antagonist. This study provides the first in vivo evidence that galantamine augments dopaminergic neurotransmission within the hippocampus through the allosteric potentiation of nAChRs. The improving-effects of galantamine on the Aβ25−35-induced cognitive impairment may be mediated through the activation of, at least in part, dopaminergic systems, and the enhancement of dopamine release may be one of multiple mechanisms underlying the therapeutic benefit of galantamine.

Neprilysin-sensitive synapse-associated Aβ oligomers impair neuronal plasticity and cognitive function

A subtle but chronic alteration in metabolic balance between amyloid-β peptide (Aβ) anabolic and catabolic activities is thought to cause Aβ accumulation, leading to a decade-long pathological cascade of Alzheimer disease. However, it is still unclear whether a reduction of the catabolic activity of Aβ in the brain causes neuronal dysfunction in vivo. In the present study, to clarify a possible connection between a reduction in neprilysin activity and impairment of synaptic and cognitive functions, we cross-bred amyloid precursor protein (APP) transgenic mice (APP23) with neprilysin-deficient mice and biochemically and immunoelectron-microscopically analyzed Aβ accumulation in the brain. We also examined hippocampal synaptic plasticity using an in vivo recording technique and cognitive function using a battery of learning and memory behavior tests, including Y-maze, novel-object recognition, Morris water maze, and contextual fear conditioning tests at the age of 13–16 weeks. We present direct experimental evidence that reduced activity of neprilysin, the major Aβ-degrading enzyme, in the brain elevates oligomeric forms of Aβ at the synapses and leads to impaired hippocampal synaptic plasticity and cognitive function before the appearance of amyloid plaque load. Thus, reduced neprilysin activity appears to be a causative event that is at least partly responsible for the memory-associated symptoms of Alzheimer disease. This supports the idea that a strategy to reduce Aβ oligomers in the brain by up-regulating neprilysin activity would contribute to alleviation of these symptoms.

Effects of a Novel Cognitive Enhancer, Spiro[imidazo-[1,2-a]pyridine-3,2-indan]-2(3H)-one (ZSET1446), on Learning Impairments Induced by Amyloid-β1–40 in the Rat

We have previously shown that intracerebroventricular (i.c.v.) infusion of amyloid-β (Aβ)1–40 produces oxidative stress and cholinergic dysfunction, as well as learning and memory deficits, in rats. In the present study, effects of a newly synthesized azaindolizinone derivative, spiro[imidazo[1,2-a]pyridine-3,2-indan]-2(3H)-one (ZSET1446), were assessed in rats with learning deficits induced by Aβ1–40 or scopolamine. The i.c.v. infusion of Aβ1–40 caused impairments in spontaneous alternation behavior in a Y-maze task, spatial reference and short-term memory in a water-maze task, and retention of passive-avoidance learning. Aβ1–40-infused rats also showed reduction in choline acetyltransferase (ChAT) activity in the medial septum and hippocampus, but not in the basal forebrain and cortex, and a decrease in glutathione S-transferase (GST)-like immunoreactivity in the cortex. Nicotine-stimulated acetylcholine (ACh) release in Aβ1–40-infused rats was lower than that in vehicle-infused rats. Oral administration of ZSET1446 at the dose range of 0.01 to 1 mg/kg ameliorated Aβ1–40-induced learning impairment in Y-maze, water-maze, and passive-avoidance tasks. ZSET1446 reversed the decrease of ChAT activity in the medial septum and hippocampus, GST-like immunoreactivity in the cortex, and nicotine-stimulated ACh release of Aβ1–40-treated rats to the levels of vehicle-infused control rats. Furthermore, 0.001 to 0.1 mg/kg ZSET1446 showed ameliorative effects on learning impairments caused by scopolamine in a passive-avoidance task. These results suggest that ZSET1446 may be a potential candidate for development as a therapeutic agent to manage cognitive impairment associated with conditions such as Alzheimers disease.

Identification of Novel Candidate Genes for Treatment Response to Risperidone and Susceptibility for Schizophrenia: Integrated Analysis Among Pharmacogenomics, Mouse Expression, and Genetic Case-Control Association Approaches

BACKGROUND Pharmacogenomic approaches based on genomewide sets of single nucleotide polymorphisms (SNPs) are now feasible and offer the potential to uncover variants that influence drug response. METHODS To detect potential predictor gene variants for risperidone response in schizophrenic subjects, we performed a convergent analysis based on 1) a genomewide (100K SNP) SNP pharmacogenetic study of risperidone response and 2) a global transcriptome study of genes with mRNA levels influenced by risperidone exposure in mouse prefrontal cortex. RESULTS Fourteen genes were highlighted as of potential relevance to risperidone activity in both studies: ATP2B2, HS3ST2, UNC5C, BAG3, PDE7B, PAICS, PTGFRN, NR3C2, ZBTB20, ST6GAL2, PIP5K1B, EPHA6, KCNH5, and AJAP1. The SNPs related to these genes that were associated in the pharmacogenetic study were further assessed for evidence for association with schizophrenia in up to three case-control series comprising 1564 cases and 3862 controls in total (Japanese [JPN] 1st and 2nd samples and UK sample). Of 14 SNPs tested, one (rs9389370) in PDE7B showed significant evidence for association with schizophrenia in a discovery sample (p(allele) = .026 in JPN_1st, two-tailed). This finding replicated in a joint analysis of two independent case-control samples (p(JPN_2nd+UK) = .008, one-tailed, uncorrected) and in all combined data sets (p(all) = .0014, two-tailed, uncorrected and p(all) = .018, two-tailed, Bonferroni correction). CONCLUSIONS We identified novel candidate genes for treatment response to risperidone and provide evidence that one of these additionally may confer susceptibility to schizophrenia. Specifically, PDE7B is an attractive candidate gene, although evidence from integrated methodology, including pharmacogenomics, pharmacotranscriptomic, and case-control association approaches.

Involvement of a dysfunctional dopamine-D1/N-methyl-D-aspartate-NR1 and Ca2+/calmodulin-dependent protein kinase II pathway in the impairment of latent learning in a model of schizophrenia induced by phencyclidine

Continuous ingestion of phencyclidine (PCP) in humans produces long-lasting schizophrenic-like cognitive dysfunction. Although a malfunction of dopaminergic and/or glutamatergic neurotransmission is implicated in the etiology of schizophrenia, involvement of the dopaminergic-glutamatergic neurotransmission in the cognitive dysfunction induced by repeated PCP treatment is minor. We demonstrated that mice treated with PCP (10 mg/kg/day s.c.) for 14 days displayed an impairment of latent learning in a water-finding task and of learning-associated phosphorylation of Ca2+/calmodulin-dependent protein kinase II (CaMKII) and NR1 in the prefrontal cortex even after drug withdrawal. The infusion of a CaMKII inhibitor and NR1 antisense oligonucleotide into the prefrontal cortex produced an impairment of latent learning and decrease of learning-associated phosphorylation of CaMKII, which were observed in the PCP-treated mice. Exogenous NMDA-induced CaMKII activation was not observed in slices of the prefrontal cortex prepared from mice treated repeatedly with PCP. The potentiation of NMDA receptor function by the infusion of glycine into the prefrontal cortex ameliorated these impairments in mice treated repeatedly with PCP. The high potassium-stimulated release of dopamine from the prefrontal cortex was less extensive in the PCP-treated than saline-treated mice. The infusion of a dopamine-D1 receptor agonist into the prefrontal cortex attenuated the impairment of latent learning and decrease of learning-associated NR1 phosphorylation in the PCP-treated mice, suggesting a functional linkage between glutamatergic and dopaminergic signaling. These findings indicate that repeated PCP treatment impairs latent learning through a prefrontal cortical dysfunction of NMDA-CaMKII signaling, which is associated with dopaminergic hypofunction.