Early Life Stress Induces Different Behaviors in Adolescence and Adulthood May Related With Abnormal Medial Prefrontal Cortex Excitation/Inhibition Balance

Early life stress is thought to be a risk factor for emotional disorders, particularly depression and anxiety. Although the excitation/inhibition (E/I) imbalance has been implicated in neuropsychiatric disorders, whether early life stress affects the E/I balance in the medial prefrontal cortex at various developmental stages is unclear. In this study, rats exposed to maternal separation (MS) that exhibited a well-established early life stress paradigm were used to evaluate the E/I balance in adolescence (postnatal day P43–60) and adulthood (P82–100) by behavior tests, whole-cell recordings, and microdialysis coupled with high performance liquid chromatography-mass spectrometry (HPLC-MS) analysis. First, the behavioral tests revealed that MS induced both anxiety- and depressive-like behaviors in adolescent rats but only depressive-like behavior in adult rats. Second, MS increased the action potential frequency and E/I balance of synaptic transmission onto L5 pyramidal neurons in the prelimbic (PrL) brain region of adolescent rats while decreasing the action potential frequency and E/I balance in adult rats. Finally, MS increases extracellular glutamate levels and decreased the paired-pulse ratio of evoked excitatory postsynaptic currents (EPSCs) of pyramidal neurons in the PrL of adolescent rats. In contrast, MS decreased extracellular glutamate levels and increased the paired-pulse ratio of evoked EPSCs of pyramidal neurons in the PrL of adult rats. The present results reveal a key role of E/I balance in different MS-induced disorders may related to the altered probability of presynaptic glutamate release at different developmental stages.

(M)Unc13s in Active Zone Diversity: A Drosophila Perspective

The so-called active zones at pre-synaptic terminals are the ultimate filtering devices, which couple between action potential frequency and shape, and the information transferred to the post-synaptic neurons, finally tuning behaviors. Within active zones, the release of the synaptic vesicle operates from specialized “release sites.” The (M)Unc13 class of proteins is meant to define release sites topologically and biochemically, and diversity between Unc13-type release factor isoforms is suspected to steer diversity at active zones. The two major Unc13-type isoforms, namely, Unc13A and Unc13B, have recently been described from the molecular to the behavioral level, exploiting Drosophila being uniquely suited to causally link between these levels. The exact nanoscale distribution of voltage-gated Ca2+ channels relative to release sites (“coupling”) at pre-synaptic active zones fundamentally steers the release of the synaptic vesicle. Unc13A and B were found to be either tightly or loosely coupled across Drosophila synapses. In this review, we reported recent findings on diverse aspects of Drosophila Unc13A and B, importantly, their nano-topological distribution at active zones and their roles in release site generation, active zone assembly, and pre-synaptic homeostatic plasticity. We compared their stoichiometric composition at different synapse types, reviewing the correlation between nanoscale distribution of these two isoforms and release physiology and, finally, discuss how isoform-specific release components might drive the functional heterogeneity of synapses and encode discrete behavior.

Functional Hyperactivity in Long QT Syndrome Type 1 Pluripotent Stem Cell-Derived Sympathetic Neurons

Sympathetic activation is an established trigger of life-threatening cardiac events in long QT syndrome type 1 (LQT1). KCNQ1 loss-of-function variants, which underlie LQT1, have been associated with both cardiac arrhythmia and neuronal hyperactivity pathologies. However, the LQT1 sympathetic neuronal phenotype is unknown. Here we aimed to study human induced pluripotent stem cell (hiPSC)-derived sympathetic neurons (SNs) to evaluate neuronal functional phenotype in LQT1. We generated hiPSC-SNs from two LQT1 patients with a history of sympathetically triggered arrhythmia and KCNQ1 loss-of-function genotypes (c.781_782delinsTC and p.S349W/p.R518X). Characterisation of hiPSC-SNs was performed using immunohistochemistry, enzyme-linked immunosorbent assay and whole-cell patch clamp electrophysiology, and functional LQT1 hiPSC-SN phenotypes compared to healthy control (WT) hiPSC-SNs. hiPSC-SNs stained positive for tyrosine hydroxylase, peripherin, KCNQ1, and secreted noradrenaline. hiPSC-SNs at 60±2.2 days in vitro had healthy resting membrane potentials (-60±1.3 mV), and fired rapid action potentials with mature kinetics in response to stimulation. Significant hyperactivity in LQT1 hiPSC-SNs was evident via increased noradrenaline release, increased spontaneous action potential frequency, increased total inward current density, and reduced afterhyperpolarisation, compared to age-matched WT hiPSC-SNs. A significantly higher action potential frequency upon current injection and larger synaptic current amplitudes in compound heterozygous p.S349W/p.R518X hiPSC-SNs compared to heterozygous c.781_782delinsTC hiPSC-SNs was also observed, suggesting a potential genotype-phenotype correlation. Together our data reveal increased neurotransmission and excitability in heterozygous and compound heterozygous patient-derived LQT1 sympathetic neurons, suggesting that the cellular arrhythmogenic potential in LQT1 is not restricted to cardiomyocytes.

Gq DREADD activation of CaMKIIa MnPO neurons stimulates nitric oxide activity

Rats were injected in the median preoptic nucleus (MnPO) with either an adeno-associated virus (AAV) and excitatory (Gq) designer receptor exclusively activated by designer drugs (DREADD) construct or a control AAV. In the Gq DREADD-injected rats only, clozapine- N-oxide (CNO) increased Fos staining in the MnPO and its targets and increased neuron action potential frequency. In electrophysiology experiments with slices with DREADD cells, unlabeled cells were activated and this was likely due to nitric oxide release by the DREADD cells.

Synaptic deficits in iPSC-derived cortical interneurons in schizophrenia are mediated by NLGN2 and rescued by N-acetylcysteine

Human postmortem studies suggest a major role for abnormalities in GABAergic interneurons in the prefrontal cortex in schizophrenia. Cortical interneurons differentiated from induced pluripotent stem cells (iPSCs) of schizophrenia subjects showed significantly lower levels of glutamate decarboxylase 67 (GAD67), replicating findings from multiple postmortem studies, as well as reduced levels of synaptic proteins gehpyrin and NLGN2. Co-cultures of the interneurons with excitatory cortical pyramidal neurons from schizophrenia iPSCs showed reduced synaptic puncta density and lower action potential frequency. NLGN2 overexpression in schizophrenia neurons rescued synaptic puncta deficits while NLGN2 knockdown in healthy neurons resulted in reduced synaptic puncta density. Schizophrenia interneurons also had significantly smaller nuclear area, suggesting an innate oxidative stressed state. The antioxidant N-acetylcysteine increased the nuclear area in schizophrenia interneurons, increased NLGN2 expression and rescued synaptic deficits. These results implicate specific deficiencies in the synaptic machinery in cortical interneurons as critical regulators of synaptic connections in schizophrenia and point to a nexus between oxidative stress and NLGN2 expression in mediating synaptic deficits in schizophrenia.