Koichi Tanda

Abnormal Behavior in a Chromosome- Engineered Mouse Model for Human 15q11-13 Duplication Seen in Autism

Summary Substantial evidence suggests that chromosomal abnormalities contribute to the risk of autism. The duplication of human chromosome 15q11-13 is known to be the most frequent cytogenetic abnormality in autism. We have modeled this genetic change in mice by using chromosome engineering to generate a 6.3 Mb duplication of the conserved linkage group on mouse chromosome 7. Mice with a paternal duplication display poor social interaction, behavioral inflexibility, abnormal ultrasonic vocalizations, and correlates of anxiety. An increased MBII52 snoRNA within the duplicated region, affecting the serotonin 2c receptor (5-HT2cR), correlates with altered intracellular Ca2+ responses elicited by a 5-HT2cR agonist in neurons of mice with a paternal duplication. This chromosome-engineered mouse model for autism seems to replicate various aspects of human autistic phenotypes and validates the relevance of the human chromosome abnormality. This model will facilitate forward genetics of developmental brain disorders and serve as an invaluable tool for therapeutic development.

Behavioral Profiles of Three C57BL/6 Substrains

C57BL/6 inbred strains of mice are widely used in knockout and transgenic research. To evaluate the loss-of-function and gain-of-function effects of the gene of interest, animal behaviors are often examined. However, an issue of C57BL/6 substrains that is not always appreciated is that behaviors are known to be strongly influenced by genetic background. To investigate the behavioral characteristics of C57BL/6 substrains, we subjected C57BL/6J, C57BL/6N, and C57BL/6C mice to a behavior test battery. We performed both a regular scale analysis, in which experimental conditions were tightly controlled, and large-scale analysis from large number of behavioral data that we have collected so far through the comprehensive behavioral test battery applied to 700–2,200 mice in total. Significant differences among the substrains were found in the results of various behavioral tests, including the open field, rotarod, elevated plus maze, prepulse inhibition, Porsolt forced swim, and spatial working memory version of the eight-arm radial maze. Our results show a divergence of behavioral performance in C57BL/6 substrains, which suggest that small genetic differences may have a great influence on behavioral phenotypes. Thus, the genetic background of different substrains should be carefully chosen, equated, and considered in the interpretation of mutant behavioral phenotypes.

Abnormal social behavior, hyperactivity, impaired remote spatial memory, and increased D1-mediated dopaminergic signaling in neuronal nitric oxide synthase knockout mice

BackgroundNeuronal nitric oxide synthase (nNOS) is involved in the regulation of a diverse population of intracellular messenger systems in the brain. In humans, abnormal NOS/nitric oxide metabolism is suggested to contribute to the pathogenesis and pathophysiology of some neuropsychiatric disorders, such as schizophrenia and bipolar disorder. Mice with targeted disruption of the nNOS gene exhibit abnormal behaviors. Here, we subjected nNOS knockout (KO) mice to a battery of behavioral tests to further investigate the role of nNOS in neuropsychiatric functions. We also examined the role of nNOS in dopamine/DARPP-32 signaling in striatal slices from nNOS KO mice and the effects of the administration of a dopamine D1 receptor agonist on behavior in nNOS KO mice.ResultsnNOS KO mice showed hyperlocomotor activity in a novel environment, increased social interaction in their home cage, decreased depression-related behavior, and impaired spatial memory retention. In striatal slices from nNOS KO mice, the effects of a dopamine D1 receptor agonist, SKF81297, on the phosphorylation of DARPP-32 and AMPA receptor subunit GluR1 at protein kinase A sites were enhanced. Consistent with the biochemical results, intraperitoneal injection of a low dose of SKF81297 significantly decreased prepulse inhibition in nNOS KO mice, but not in wild-type mice.ConclusionThese findings indicate that nNOS KO upregulates dopamine D1 receptor signaling, and induces abnormal social behavior, hyperactivity and impaired remote spatial memory. nNOS KO mice may serve as a unique animal model of psychiatric disorders.

Comprehensive Behavioral Analysis of Calcium/Calmodulin-Dependent Protein Kinase IV Knockout Mice

Calcium-calmodulin dependent protein kinase IV (CaMKIV) is a protein kinase that activates the transcription factor CREB, the cyclic AMP-response element binding protein. CREB is a key transcription factor in synaptic plasticity and memory consolidation. To elucidate the behavioral effects of CaMKIV deficiency, we subjected CaMKIV knockout (CaMKIV KO) mice to a battery of behavioral tests. CaMKIV KO had no significant effects on locomotor activity, motor coordination, social interaction, pain sensitivity, prepulse inhibition, attention, or depression-like behavior. Consistent with previous reports, CaMKIV KO mice exhibited impaired retention in a fear conditioning test 28 days after training. In contrast, however, CaMKIV KO mice did not show any testing performance deficits in passive avoidance, one of the most commonly used fear memory paradigms, 28 days after training, suggesting that remote fear memory is intact. CaMKIV KO mice exhibited intact spatial reference memory learning in the Barnes circular maze, and normal spatial working memory in an eight-arm radial maze. CaMKIV KO mice also showed mildly decreased anxiety-like behavior, suggesting that CaMKIV is involved in regulating emotional behavior. These findings indicate that CaMKIV might not be essential for fear memory or spatial memory, although it is possible that the activities of other neural mechanisms or signaling pathways compensate for the CaMKIV deficiency.

Mice with Altered Myelin Proteolipid Protein Gene Expression Display Cognitive Deficits Accompanied by Abnormal Neuron–Glia Interactions and Decreased Conduction Velocities

Conduction velocity (CV) of myelinated axons has been shown to be regulated by oligodendrocytes even after myelination has been completed. However, how myelinating oligodendrocytes regulate CV, and what the significance of this regulation is for normal brain function remain unknown. To address these questions, we analyzed a transgenic mouse line harboring extra copies of the myelin proteolipid protein 1 (plp1) gene (plp1 tg/− mice) at 2 months of age. At this stage, the plp1 tg/− mice have an unaffected myelin structure with a normally appearing ion channel distribution, but the CV in all axonal tracts tested in the CNS is greatly reduced. We also found decreased axonal diameters and slightly abnormal paranodal structures, both of which can be a cause for the reduced CV. Interestingly the plp1 tg/− mice showed altered anxiety-like behaviors, reduced prepulse inhibitions, spatial learning deficits and working memory deficit, all of which are schizophrenia-related behaviors. Our results implicate that abnormalities in the neuron-glia interactions at the paranodal junctions can result in reduced CV in the CNS, which then induces behavioral abnormalities related to schizophrenia.

Comprehensive behavioral analysis of pituitary adenylate cyclase-activating polypeptide (PACAP) knockout mice

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a neuropeptide acting as a neurotransmitter, neuromodulator, or neurotrophic factor. PACAP is widely expressed throughout the brain and exerts its functions through the PACAP-specific receptor (PAC1). Recent studies reveal that genetic variants of the PACAP and PAC1 genes are associated with mental disorders, and several behavioral abnormalities of PACAP knockout (KO) mice are reported. However, an insufficient number of backcrosses was made using PACAP KO mice on the C57BL/6J background due to their postnatal mortality. To elucidate the effects of PACAP on neuropsychiatric function, the PACAP gene was knocked out in F1 hybrid mice (C57BL/6J × 129SvEv) for appropriate control of the genetic background. The PACAP KO mice were then subjected to a behavioral test battery. PACAP deficiency had no significant effects on neurological screen. As shown previously, the mice exhibited significantly increased locomotor activity in a novel environment and abnormal anxiety-like behavior, while no obvious differences between genotypes were shown in home cage (HC) activity. In contrast to previous reports, the PACAP KO mice showed normal prepulse inhibition (PPI) and slightly decreased depression-like behavior. Previous study demonstrates that the social interaction (SI) in a resident-intruder test was decreased in PACAP KO mice. On the other hand, we showed that PACAP KO mice exhibited increased SI in Crawleys three-chamber social approach test, although PACAP KO had no significant impact on SI in a HC. PACAP KO mice also exhibited mild performance deficit in working memory in an eight-arm radial maze (RM) and the T-maze (TM), while they did not show any significant abnormalities in the left-right discrimination task in the TM. These results suggest that PACAP has an important role in the regulation of locomotor activity, social behavior, anxiety-like behavior and, potentially, working memory.

Comprehensive Behavioral Phenotyping of Ryanodine Receptor type 3 (RyR3) Knockout Mice: Decreased Social Contact Duration in Two Social Interaction Tests

Dynamic regulation of the intracellular Ca2+ concentration is crucial for various neuronal functions such as synaptic transmission and plasticity, and gene expression. Ryanodine receptors (RyRs) are a family of intracellular calcium release channels that mediate calcium-induced calcium release from the endoplasmic reticulum. Among the three RyR isoforms, RyR3 is preferentially expressed in the brain especially in the hippocampus and striatum. To investigate the behavioral effects of RyR3 deficiency, we subjected RyR3 knockout (RyR3–/–) mice to a battery of behavioral tests. RyR3–/– mice exhibited significantly decreased social contact duration in two different social interaction tests, where two mice can freely move and make contacts with each other. They also exhibited hyperactivity and mildly impaired prepulse inhibition and latent inhibition while they did not show significant abnormalities in motor function and working and reference memory tests. These results indicate that RyR3 has an important role in locomotor activity and social behavior.

Adenomatous polyposis coli heterozygous knockout mice display hypoactivity and age-dependent working memory deficits.

A tumor suppressor gene, Adenomatous polyposis coli (Apc), is expressed in the nervous system from embryonic to adulthood stages, and transmits the Wnt signaling pathway in which schizophrenia susceptibility genes, including T-cell factor 4 (TCF4) and calcineurin (CN), are involved. However, the functions of Apc in the nervous system are largely unknown. In this study, as the first evaluation of Apc function in the nervous system, we have investigated the behavioral significance of the Apc gene, applying a battery of behavioral tests to Apc heterozygous knockout (Apc+/−) mice. Apc+/− mice showed no significant impairment in neurological reflexes or sensory and motor abilities. In various tests, including light/dark transition, open-field, social interaction, eight-arm radial maze, and fear conditioning tests, Apc+/− mice exhibited hypoactivity. In the eight-arm radial maze, Apc+/− mice 6–7 weeks of age displayed almost normal performance, whereas those 11–12 weeks of age showed a severe performance deficit in working memory, suggesting that Apc is involved in working memory performance in an age-dependent manner. The possibility that anemia, which Apc+/− mice develop by 17 weeks of age, impairs working memory performance, however, cannot be excluded. Our results suggest that Apc plays a role in the regulation of locomotor activity and presumably working memory performance.

Enhanced stability of hippocampal place representation caused by reduced magnesium block of NMDA receptors in the dentate gyrus

BackgroundVoltage-dependent block of the NMDA receptor by Mg2+ is thought to be central to the unique involvement of this receptor in higher brain functions. However, the in vivo role of the Mg2+ block in the mammalian brain has not yet been investigated, because brain-wide loss of the Mg2+ block causes perinatal lethality. In this study, we used a brain-region specific knock-in mouse expressing an NMDA receptor that is defective for the Mg2+ block in order to test its role in neural information processing.ResultsWe devised a method to induce a single amino acid substitution (N595Q) in the GluN2A subunit of the NMDA receptor, specifically in the hippocampal dentate gyrus in mice. This mutation reduced the Mg2+ block at the medial perforant path–granule cell synapse and facilitated synaptic potentiation induced by high-frequency stimulation. The mutants had more stable hippocampal place fields in the CA1 than the controls did, and place representation showed lower sensitivity to visual differences. In addition, behavioral tests revealed that the mutants had a spatial working memory deficit.ConclusionsThese results suggest that the Mg2+ block in the dentate gyrus regulates hippocampal spatial information processing by attenuating activity-dependent synaptic potentiation in the dentate gyrus.