Fumihito Saitow

The extracellular matrix (ECM) of the brain undergoes dynamic remodeling during development and is crucial for neuronal plasticity. While chondroitin sulfates (CS) regulate oligodendrocyte differentiation and myelination, their relationship with oligodendrocyte precursors (OPCs) and synaptic plasticity remains unclear. This study investigated a novel CS‐rich ECM structure, its origin, and its role in synaptic plasticity. Using immunohistochemistry, disaccharide analysis, and dendritic spine characterization in mice, we examined postnatal development and analyzed single‐cell RNA (scRNA) sequencing data from the National Center for Biotechnology Information database. We identified patch‐like structures labeled with the chondroitin sulfate 56 (CS56) antibody (CS clusters) distinct from Wisteria floribunda agglutinin‐positive perineuronal nets. Oligodendrocyte lineage cells expressing G protein‐coupled receptor 17 (GPR17) localized at CS cluster centers, emerging postnatally and peaking at day 14, preceded CS cluster formation. ScRNA sequencing of Gpr17 + cells revealed the expression of carbohydrate sulfotransferase 3 ( Chst3 ) and uronyl 2‐sulfotransferase ( Ust ), genes coding enzymes synthesizing type C and D CS disaccharides, the primary components of the CS56 antibody epitope. Disaccharide analysis revealed elevated levels of type D chondroitin sulfate at day 35. Notably, dendritic spines within the CS clusters were longer and larger than those outside these regions, suggesting enhanced synaptic connectivity. Our findings reveal a CS‐rich structure in the brain ECM that is causally linked to GPR17+ oligodendrocyte lineage cells and closely related to neuronal circuit development. The morphological differences in dendritic spines within CS clusters and persistence of GPR17+ oligodendrocyte lineage cells beyond the postnatal period suggest additional functions that warrant further investigation.

Modulation of synaptic transmission in the deep cerebellar nuclei, a major output region of the cerebellum, is essential for regulating motor and non-motor functions by controlling information flow from the cerebellar cortex. In this study, we aimed to investigate the effects of dopamine (DA) and noradrenaline (NA) on glutamatergic synaptic transmission using cerebellar slices from both male and female Wistar rats. Stimulation-evoked excitatory postsynaptic currents (eEPSCs) were recorded from deep cerebellar nuclei neurons using whole-cell patch-clamp technique. Bath application of DA or NA decreased the eEPSC amplitude. Pharmacological analysis revealed presynaptic D2-like receptors (D2R) and α₂-adrenergic receptors (α₂-AdR) as mediators of the inhibitory effects induced by DA and NA, respectively. While DA decreased eEPSC amplitude in all tested synapses, the selective D2R agonist, quinpirole showed no effect in approximately 30% of synapses. By contrast, NA and α₂-AdR-selective agonists (clonidine and dexmedetomidine) inhibited synaptic transmission in all tested synapses. Notably, both DA and NA maintained their inhibitory effects even when their respective receptor antagonists (sulpiride and RS79948), were present. This observation suggests cross-receptor interactions: DA acted through α₂-AdRs, while NA operated via D2Rs. These findings reveal novel cross-talk of catecholamines within cerebellar networks, providing new insights into mechanisms underlying synaptic modulation.

Maternally inherited duplication of chromosome 15q11-q13 (Dup15q) is a pathogenic copy number variation (CNV) associated with autism spectrum disorder (ASD). Recently, paternally derived duplication has also been shown to contribute to the development of ASD. The molecular mechanism underlying paternal Dup15q remains unclear. Here, we conduct genetic and overexpression-based screening and identify Necdin (Ndn) as a driver gene for paternal Dup15q resulting in the development of ASD-like phenotypes in mice. An excess amount of Ndn results in enhanced spine formation and density as well as hyperexcitability of cortical pyramidal neurons. We generate 15q dupΔNdn mice with a normalized copy number of Ndn by excising its one copy from Dup15q mice using a CRISPR-Cas9 system. 15q dupΔNdn mice do not show ASD-like phenotypes and show dendritic spine dynamics and cortical excitatory-inhibitory balance similar to wild type animals. Our study provides an insight into the role of Ndn in paternal 15q duplication and a mouse model of paternal Dup15q syndrome.

Serotonin (5-HT) is a well-known modulator of behavioral, physiological, and emotional functions of the forebrain region. We recently discovered alterations of serotonergic synaptic modulations in both, the prefrontal cortex (PFC) and the somatosensory cortex, in the 15q dup mouse model of autism spectrum disorder (ASD). To further understand the roles of the 5-HT system implicated in developmental disorders such as ASD, comparison with model animals exhibiting different phenotypes may be useful. In this study, we investigated the relationship between sociability and the magnitude of 5-HT_1A receptor (5-HT_1AR) activation-induced outward currents from layer 5 pyramidal neurons in the PFC, because a mouse model of Williams-Beuren syndrome (WBS; another developmental disorder exhibiting low innate anxiety and high sociability) reportedly showed larger 5-HT-induced currents. To investigate whether the 5-HT_1AR activation-induced outward currents are involved in the endophenotype determination of social behavior, we examined 15q dup mice with a phenotype opposite to WBS. We found 5-HT elicited significantly larger outward currents in 15q dup mice than in WT controls, regardless of sociability. In contrast, baclofen-induced GABA_B receptor-mediated outward currents were not significantly different between genotypes, although GABA_B receptor was coupled to G_i/o as well as 5-HT_1A. Further, we found the larger 5-HT_1AR-mediated currents in 15q dup mice did not affect the magnitude of inhibitory action of NMDA receptor functions. Taken together, our results provide a potential physiological hallmark for developmental disorders that may involve the imbalance of the neuronal circuity in the PFC.

Although mitochondrial and serotonergic dysfunctions have been implicated in the etiology of bipolar disorder (BD), the relationship between these unrelated pathways has not been elucidated. A family of BD and chronic progressive external ophthalmoplegia (CPEO) caused by a mutation of the mitochondrial adenine nucleotide translocator 1 (ANT1, SLC25A4) implicated that ANT1 mutations confer a risk of BD. Here, we sequenced ANT1 in 324 probands of NIMH bipolar disorder pedigrees and identified two BD patients carrying heterozygous loss-of-function mutations. Behavioral analysis of brain specific Ant1 heterozygous conditional knockout (cKO) mice using lntelliCage showed a selective diminution in delay discounting. Delay discounting is the choice of smaller but immediate reward than larger but delayed reward and an index of impulsivity. Diminution of delay discounting suggests an increase in serotonergic activity. This finding was replicated by a 5-choice serial reaction time test. An anatomical screen showed accumulation of COX (cytochrome c oxidase) negative cells in dorsal raphe. Dorsal raphe neurons in the heterozygous cKO showed hyperexcitability, along with enhanced serotonin turnover in the nucleus accumbens and upregulation of Maob in dorsal raphe. These findings altogether suggest that mitochondrial dysfunction as the genetic risk of BD may cause vulnerability to BD by altering serotonergic neurotransmission.

Outputs from the cerebellar nuclei (CN) are important for generating and controlling movement. The activity of CN neurons is controlled not only by excitatory inputs from mossy and climbing fibers and by γ-aminobutyric acid (GABA)-based inhibitory transmission from Purkinje cells in the cerebellar cortex but is also modulated by inputs from other brain regions, including serotonergic fibers that originate in the dorsal raphe nuclei. We examined the modulatory effects of serotonin (5-HT) on GABAergic synapses during development, using rat cerebellar slices. As previously reported, 5-HT presynaptically decreased the amplitudes of stimulation-evoked inhibitory postsynaptic currents (IPSCs) in CN neurons, with this effect being stronger in slices from younger animals (postnatal days [P] 11–13) than in slices from older animals (P19–21). GABA release probabilities accordingly exhibited significant decreases from P11–13 to P19–21. Although there was a strong correlation between the GABA release probability and the magnitude of 5-HT-induced inhibition, manipulating the release probability by changing extracellular Ca²⁺ concentrations failed to control the extent of 5-HT-induced inhibition. We also found that the IPSCs exhibited slower kinetics at P11–13 than at P19–21. Pharmacological and molecular biological tests revealed that IPSC kinetics were largely determined by the prevalence of α₁ subunits within GABA_A receptors. In summary, pre- and postsynaptic developmental changes in serotonergic modulation and GABAergic synaptic transmission occur during the second to third postnatal weeks and may significantly contribute to the formation of normal adult cerebellar function.

Previous studies have shown that phenotypic modulation of smooth muscle cells (SMCs) plays a pivotal role in human diseases. However, the molecular mechanisms underlying the reversible differentiation of SMCs remain elusive particularly because cultured SMCs that reproducibly exhibit bidirectional phenotypic modulation have not been established. Here we established an immortalized human bladder SMC line designated as hBS11. Under differentiation-inducing conditions, hBS11 cells underwent smooth muscle differentiation accompanied by the robust expression of smooth muscle differentiation markers and isoform-dependent reorganization of actin bundles. The cholinergic receptor agonist carbachol increased intracellular calcium in differentiated hBS11 cells in an acetylcholine muscarinic receptor-dependent manner. Differentiated hBS11 cells displayed contractile properties depending on the elevation in the levels of intracellular calcium. Depolarization of membrane potential triggered inward sodium current in differentiated hBS11 cells. However, differentiated hBS11 cells lost the differentiated phenotype and resumed mitosis when re-fed with growth medium. Our study provides direct evidence pertaining to the human bladder SMCs being able to retain the capacity of reversible differentiation and that the reorganization of actin bundles is involved in the reinstatement of contractility. Moreover, we have established a human SMC line retaining high proliferating potential without compromising differentiation potential.