Altered projection-specific synaptic remodeling and its modification by oxytocin in an idiopathic autism marmoset model.

Alterations in the experience-dependent and autonomous elaboration of neural circuits are assumed to underlie autism spectrum disorder (ASD), though it is unclear what synaptic traits are responsible. Here, utilizing a valproic acid-induced ASD marmoset model, which shares common molecular features with idiopathic ASD, we investigate changes in the structural dynamics of tuft dendrites of upper-layer pyramidal neurons and adjacent axons in the dorsomedial prefrontal cortex through two-photon microscopy. In model marmosets, dendritic spine turnover is upregulated, and spines are generated in clusters and survived more often than in control marmosets. Presynaptic boutons in local axons, but not in commissural long-range axons, demonstrate hyperdynamic turnover in model marmosets, suggesting alterations in projection-specific plasticity. Intriguingly, nasal oxytocin administration attenuates clustered spine emergence in model marmosets. Enhanced clustered spine generation, possibly unique to certain presynaptic partners, may be associated with ASD and be a potential therapeutic target.

Functional and molecular characterization of a non-human primate model of autism spectrum disorder shows similarity with the human disease.

Autism spectrum disorder (ASD) is a multifactorial disorder with characteristic synaptic and gene expression changes. Early intervention during childhood is thought to benefit prognosis. Here, we examined the changes in cortical synaptogenesis, synaptic function, and gene expression from birth to the juvenile stage in a marmoset model of ASD induced by valproic acid (VPA) treatment. Early postnatally, synaptogenesis was reduced in this model, while juvenile-age VPA-treated marmosets showed increased synaptogenesis, similar to observations in human tissue. During infancy, synaptic plasticity transiently increased and was associated with altered vocalization. Synaptogenesis-related genes were downregulated early postnatally. At three months of age, the differentially expressed genes were associated with circuit remodeling, similar to the expression changes observed in humans. In summary, we provide a functional and molecular characterization of a non-human primate model of ASD, highlighting its similarity to features observed in human ASD.

Abnormal axon guidance signals and reduced interhemispheric connection via anterior commissure in neonates of marmoset ASD model.

In autism spectrum disorder (ASD), disrupted functional and structural connectivity in the social brain has been suggested as the core biological mechanism underlying the social recognition deficits of this neurodevelopmental disorder. In this study, we aimed to identify genetic and neurostructural abnormalities at birth in a non-human primate model of ASD, the common marmoset with maternal exposure to valproic acid (VPA), which has been reported to display social recognition deficit in adulthood. Using a comprehensive gene expression analysis, we found that 20 genes were significantly downregulated in VPA-exposed neonates. Of these, Frizzled3 (FZD3) and PIK3CA were identified in an axon guidance signaling pathway. FZD3 is essential for the normal development of the anterior commissure (AC) and corpus callosum (CC); hence, we performed diffusion tensor magnetic resonance imaging with a 7-Tesla scanner to measure the midsagittal sizes of these structures. We found that the AC size in VPA-exposed neonates was significantly smaller than that in age-matched controls, while the CC size did not differ. These results suggest that downregulation of the genes related to axon guidance and decreased AC size in neonatal primates may be linked to social brain dysfunctions that can happen later in life.

Synthesis and optimization of 4,5,6,7-tetrahydrooxazolo[4,5-c]pyridines as potent and orally-active metabotropic glutamate receptor 5 negative allosteric modulators.

We describe here the design, synthesis and characterization of a series of 4,5,6,7-tetrahydrooxazolo[4,5-c]pyridines as metabotropic glutamate receptor (mGluR) 5 negative allosteric modulators (NAMs). Optimization of the substituents led to the identification of several compounds with good pharmacokinetic profiles, including long half life and high oral bioavailability, in both rats and monkeys. The receptor occupancy test in the rat cortex revealed favorable brain penetration of these compounds. The reprsentative compound 13 produced oral antidepressant-like effect in the rat forced swimming test (MED: 0.3mg/kg, q.d.).

Developmental expression profiles of axon guidance signaling and the immune system in the marmoset cortex: potential molecular mechanisms of pruning of dendritic spines during primate synapse formation in late infancy and prepuberty (I).

The synapse number and the related dendritic spine number in the cerebral cortex of primates shows a rapid increase after birth. Depending on the brain region and species, the number of synapses reaches a peak before adulthood, and pruning takes place after this peak (overshoot-type synaptic formation). Human mental disorders, such as autism and schizophrenia, are hypothesized to be a result of either too weak or excessive pruning after the peak is reached. Thus, it is important to study the molecular mechanisms underlying overshoot-type synaptic formation, particularly the pruning phase. To examine the molecular mechanisms, we used common marmosets (Callithrix jacchus). Microarray analysis of the marmoset cortex was performed in the ventrolateral prefrontal, inferior temporal, and primary visual cortices, where changes in the number of dendritic spines have been observed. The spine number of all the brain regions above showed a peak at 3 months (3 M) after birth and gradually decreased (e.g., at 6 M and in adults). In this study, we focused on genes that showed differential expression between ages of 3 M and 6 M and on the differences whose fold change (FC) was greater than 1.2. The selected genes were subjected to canonical pathway analysis, and in this study, we describe axon guidance signaling, which had high plausibility. The results showed a large number of genes belonging to subsystems within the axon guidance signaling pathway, macrophages/immune system, glutamate system, and others. We divided the data and discussion of these results into 2 papers, and this is the first paper, which deals with the axon guidance signaling and macrophage/immune system. Other systems will be described in the next paper. Many components of subsystems within the axon guidance signaling underwent changes in gene expression from 3 M to 6 M so that the synapse/dendritic spine number would decrease at 6 M. Thus, axon guidance signaling probably contributes to the decrease in synapse/dendritic spine number at 6 M, the phenomenon that fits the overshoot-type synaptic formation in primates. Microglial activity (evaluated by quantifying AIF1 expression) and gene expression of molecules that modulate microglia, decreased at 6 M, just like the synapse/dendritic spine number. Thus, although microglial activity is believed to be related to phagocytosis of synapses/dendritic spines, microglial activity alone cannot explain how pruning was accelerated in the pruning phase. On the other hand, expression of molecules that tag synapses/dendritic spines as a target of phagocytosis by microglia (e.g., complement components) increased at 6 M, suggesting that these tagging proteins may be involved in the acceleration of pruning during the pruning phase.

Developmental genetic profiles of glutamate receptor system, neuromodulator system, protector of normal tissue and mitochondria, and reelin in marmoset cortex: potential molecular mechanisms of pruning phase of spines in primate synaptic formation process during the end of infancy and prepuberty (II).

This is the second report of a series paper, which reports molecular mechanisms underlying the occurrence of pruning spine phase after rapid spinogenesis phase in neonates and young infant in the primate brain. We performed microarray analysis between the peak of spine numbers [postnatal 3 months (M)] and spine pruning (postnatal 6M) in prefrontal, inferior temporal, and primary visual cortices of the common marmoset (Callithrix jacchus). The pruning phase is not clearly defined in rodents but is in primates including the marmoset. The differentially expressed genes between 3M and 6M in all three cortical areas were selected by two-way analysis of variance. The list of selected genes was analyzed by canonical pathway analysis using "Ingenuity Pathway Analysis of complex omics data" (IPA; Ingenuity Systems, Qiagen, Hilden, Germany). In this report, we discuss these lists of genes for the glutamate receptor system, G-protein-coupled neuromodulator system, protector of normal tissue and mitochondria, and reelin. (1) Glutamate is a common neurotransmitter. Its receptors AMPA1, GRIK1, and their scaffold protein DLG4 decreased as spine numbers decreased. Instead, GRIN3 (NMDA receptor) increased, suggesting that strong NMDA excitatory currents may be required for a single neuron to receive sufficient net synaptic activity in order to compensate for the decrease in synapse. (2) Most of the G protein-coupled receptor genes (e.g., ADRA1D, HTR2A, HTR4, and DRD1) in the selected list were upregulated at 6M. The downstream gene ROCK2 in these receptor systems plays a role of decreasing synapses, and ROCK2 decreased at 6M. (3) Synaptic phagosytosis by microglia with complement and other cytokines could cause damage to normal tissue and mitochondria. SOD1, XIAP, CD46, and CD55, which play protective roles in normal tissue and mitochondria, showed higher expression at 6M than at 3M, suggesting that normal brain tissue is more protected at 6M. (4) Reelin has an important role in cortical layer formation. In addition, RELN and three different pathways of reelin were expressed at 6M, suggesting that new synapse formation decreased at that age. Moreover, if new synapses were formed, their positions were free and probably dependent on activity.

Spontaneous Rhabdomyosarcoma in a Common Marmoset ( Callithrix jacchus ).

The common marmoset (Callithrix jacchus) is now widely used in various research fields, including toxicology. However, information about the background pathology of this species is scarce. Here, we report a case of rhabdomyosarcoma that spontaneously occurred in a common marmoset. A 44-month-old male common marmoset was euthanized due to bilateral hind limb paralysis. At necropsy, a 2×2×5-cm intramuscular mass was observed in the lower right back. Histologically, the mass was mainly composed of interlacing bundles of spindle-shaped tumor cells. Immunohistochemically, the tumor cells were positive for myogenin, desmin, vimentin and alpha-smooth muscle actin. Ultrastructurally, the tumor cells contained bundles of myofilaments with Z-band-like structures. Thus, the tumor was diagnosed as a rhabdomyosarcoma. To our knowledge, this is the first report of spontaneous rhabdomyosarcoma that was definitely diagnosed in the common marmoset.