Attenuated bidirectional short-term synaptic plasticity in the dentate gyrus of Schnurri-2 knockout mice, a model of schizophrenia

Oligodendrocyte-derived LGI3 and its receptor ADAM23 organize juxtaparanodal Kv1 channel clustering for short-term synaptic plasticity

Neurodevelopmental disorders, such as intellectual disability (ID), epilepsy, and autism, involve altered synaptic transmission and plasticity. Functional characterization of their associated genes is vital for understanding physio-pathological brain functions. LGI3 is a recently recognized ID-associated gene encoding a secretory protein related to an epilepsy-gene product, LGI1. Here, we find that LGI3 is uniquely secreted from oligodendrocytes in the brain and enriched at juxtaparanodes of myelinated axons, forming nanoscale subclusters. Proteomic analysis using epitope-tagged Lgi3 knockin mice shows that LGI3 uses ADAM23 as a receptor and selectively co-assembles with Kv1 channels. A lack of Lgi3 in mice disrupts juxtaparanodal clustering of ADAM23 and Kv1 channels and suppresses Kv1-channel-mediated short-term synaptic plasticity. Collectively, this study identifies an extracellular organizer of juxtaparanodal Kv1 channel clustering for finely tuned synaptic transmission. Given the defective secretion of the LGI3 missense variant, we propose a molecular pathway, the juxtaparanodal LGI3-ADAM23-Kv1 channel, for understanding neurodevelopmental disorders.

Schnurri-2 promotes the expression of excitatory glutamate receptors and contributes to neuropathic pain

Neuropathic pain is a type of chronic pain with complex mechanisms, and current treatments have shown limited success in treating patients suffering from chronic pain. Accumulating evidence has shown that the pathogenesis of neuropathic pain is mediated by the plasticity of excitatory neurons in the dorsal horn of the spinal cord, which provides insights into the treatment of hyperalgesia. In this study, we found that Schnurri-2 (Shn2) was significantly upregulated in the L4-L6 segments of the spinal cord of C57 mice with spared nerve injury, which was accompanied by an increase in GluN2D subunit and glutamate receptor subunit 1 (GluR1) levels. Knocking down the expression of Shn2 using a lentivirus in the spinal cord decreased the GluN2D subunit and GluR1 levels in spared nerve injury mice and eventually alleviated mechanical allodynia. In summary, Shn2 regulates neuropathic pain, promotes the upregulation of GluN2D in glutamatergic neurons and increases the accumulation of GluR1 in excitatory neurons. Taken together, our study provides a new underlying mechanism for the development of neuropathic pain.

DM1 Transgenic Mice Exhibit Abnormal Neurotransmitter Homeostasis and Synaptic Plasticity in Association with RNA Foci and Mis-Splicing in the Hippocampus

Myotonic dystrophy type 1 (DM1) is a severe neuromuscular disease mediated by a toxic gain of function of mutant RNAs. The neuropsychological manifestations affect multiple domains of cognition and behavior, but their etiology remains elusive. Transgenic DMSXL mice carry the DM1 mutation, show behavioral abnormalities, and express low levels of GLT1, a critical regulator of glutamate concentration in the synaptic cleft. However, the impact of glutamate homeostasis on neurotransmission in DM1 remains unknown. We confirmed reduced glutamate uptake in the DMSXL hippocampus. Patch clamp recordings in hippocampal slices revealed increased amplitude of tonic glutamate currents in DMSXL CA1 pyramidal neurons and DG granule cells, likely mediated by higher levels of ambient glutamate. Unexpectedly, extracellular GABA levels and tonic current were also elevated in DMSXL mice. Finally, we found evidence of synaptic dysfunction in DMSXL mice, suggestive of abnormal short-term plasticity, illustrated by an altered LTP time course in DG and in CA1. Synaptic dysfunction was accompanied by RNA foci accumulation in localized areas of the hippocampus and by the mis-splicing of candidate genes with relevant functions in neurotransmission. Molecular and functional changes triggered by toxic RNA may induce synaptic abnormalities in restricted brain areas that favor neuronal dysfunction.

Moderate maternal separation mitigates the altered synaptic transmission and neuronal activation in amygdala by chronic stress in adult mice

Exposure to moderate level of stress during the perinatal period helps the organisms to cope well with stressful events in their later life, an effect known as stress inoculation. Amygdala is one of the kernel brain regions mediating stress-coping in the brain. However, little is known about whether early life stress may affect amygdala to have its inoculative effect. Here, we observed that moderate maternal separation (MS) from postnatal day 3 to day 21 (D3–21, 1 h per day) significantly alleviated the increased anxiety-like behavior induced by chronic social defeat stress (CSDS) in adulthood, suggesting an obvious inoculative effect of moderate MS. Further studies revealed that MS prevented CSDS-evoked augmentation of glutamatergic transmission onto principal neurons (PNs) in the basolateral amygdala (BLA) by inhibiting presynaptic glutamate release. By contrast, it did not affect GABAergic transmission in BLA PNs, as indicated by unaltered frequency and amplitude of miniature inhibitory postsynaptic currents (mIPSCs). Moreover, the CSDS-induced increase of neuronal excitability was also mitigated by MS in BLA PNs. In conclusion, our results suggest that MS may have its inoculative effect through alleviating the influences of later life stress on the glutamatergic transmission and neuronal activity in amygdala neurons.

Identification of HIVEP2 as a dopaminergic transcription factor related to substance use disorders in rats and humans

Playing an important role in the etiology of substance use disorder (SUD), dopamine (DA) neurons are subject to various regulations but transcriptional regulations are largely understudied. For the first time, we report here that the Human Immunodeficiency Virus Type I Enhancer Binding Protein 2 (HIVEP2) is a dopaminergic transcriptional regulator. HIVEP2 is expressed in both the cytoplasm and nuclei of DA neurons. Therein, HIVEP2 can target the intronic sequence GTGGCTTTCT of SLC6A3 and thereby activate the gene. In naive rats from the bi-directional selectively bred substance-preferring P vs -nonpreferring NP rat model of substance abuse vulnerability, increased gene activity in males was associated with the vulnerability, whereas decreased gene activity in the females was associated with the same vulnerability. In clinical subjects, extensive and significant HIVEP2-SLC6A3 interactions were observed for SUD. Collectively, HIVEP2-mediated transcriptional mechanisms are implicated in dopaminergic pathophysiology of SUD.

Alterations Of Glycerophospholipid And Fatty Acyl Metabolism In Multiple Brain Regions Of Schizophrenia Microbiota Recipient Mice

BACKGROUND

Schizophrenia is a debilitating psychiatric disorder characterized by molecular and anatomical abnormalities of multiple brain regions. Our recent study showed that dysbiosis of the gut microbiota contributes to the onset of schizophrenia-relevant behaviors, but the underlying mechanisms remain largely unknown.

PURPOSE

This study aimed to investigate how gut microbiota shapes metabolic signatures in multiple brain regions of schizophrenia microbiota recipient mice.

METHODS

Gas chromatography-mass spectrometry (GC-MS) and liquid chromatography-mass spectrometry (LC-MS) were used to compare the metabolic signatures in the cortex, cerebellum and striatum of schizophrenia microbiota and healthy microbiota recipient mice. Enrichment analysis was further conducted to uncover the crucial metabolic pathways related to schizophrenia-relevant behaviors.

RESULTS

We found that the metabolic phenotypes of these three regions were substantially different in schizophrenia microbiota recipient mice from those in healthy microbiota recipient mice. In total, we identified 499 differential metabolites that could discriminate the two groups in the three brain regions. These differential metabolites were mainly involved in glycerophospholipid and fatty acyl metabolism. Moreover, we found four of fatty acyl metabolites that were consistently altered in the three brain regions.

CONCLUSION

Taken together, our study suggests that alterations of glycerophospholipid and fatty acyl metabolism are implicated in the onset of schizophrenia-relevant behaviors, which may provide a new understanding of the etiology of schizophrenia.