Sncg, Mybpc1, and Parm1 Classify subpopulations of VIP-expressing interneurons in layers 2/3 of the somatosensory cortex.

Neocortical vasoactive intestinal polypeptide-expressing (VIP+) interneurons display highly diverse morpho-electrophysiological and molecular properties. To begin to understand the function of VIP+ interneurons in cortical circuits, they must be clearly and comprehensively classified into distinct subpopulations based on specific molecular markers. Here, we utilized patch-clamp RT-PCR (Patch-PCR) to simultaneously obtain the morpho-electric properties and mRNA profiles of 155 VIP+ interneurons in layers 2 and 3 (L2/3) of the mouse somatosensory cortex. Using an unsupervised clustering method, we identified 3 electrophysiological types (E-types) and 2 morphological types (M-types) of VIP+ interneurons. Joint clustering based on the combined electrophysiological and morphological features resulted in 3 morpho-electric types (ME-types). More importantly, we found these 3 ME-types expressed distinct marker genes: ~94% of Sncg+ cells were ME-type 1, 100% of Mybpc1+ cells were ME-type 2, and ~78% of Parm1+ were ME-type 3. By clarifying the properties of subpopulations of cortical L2/3 VIP+ interneurons, this study establishes a basis for future investigations aiming to elucidate their physiological roles.

Neonatal CX26 removal impairs neocortical development and leads to elevated anxiety.

Electrical coupling between excitatory neurons in the neocortex is developmentally regulated. It is initially prominent but eliminated at later developmental stages when chemical synapses emerge. However, it remains largely unclear whether early electrical coupling networks broadly contribute to neocortical circuit formation and animal behavior. Here, we report that neonatal electrical coupling between neocortical excitatory neurons is critical for proper neuronal development, synapse formation, and animal behavior. Conditional deletion of Connexin 26 (CX26) in the superficial layer excitatory neurons of the mouse neocortex around birth significantly reduces spontaneous firing activity and the frequency and size of spontaneous network oscillations at postnatal day 5-6. Moreover, CX26-conditional knockout (CX26-cKO) neurons tend to have simpler dendritic trees and lower spine density compared with wild-type neurons. Importantly, early, but not late, postnatal deletion of CX26, decreases the frequency of miniature excitatory postsynaptic currents (mEPSCs) in both young and adult mice, whereas miniature inhibitory postsynaptic currents (mIPSCs) were unaffected. Furthermore, CX26-cKO mice exhibit increased anxiety-related behavior. These results suggest that electrical coupling between excitatory neurons at early postnatal stages is a critical step for neocortical development and function.

Effect of post-weaning isolation on anxiety- and depressive-like behaviors of C57BL/6J mice.

Effects of post-weaning isolation on depressive- and anxiety-like behaviors in rodents have been well studied in the past. However, few studies included both sexes in a single experiment to study the sex difference in this animal model. The present study investigated the effect of post-weaning isolation on anxiety- and depressive-like behaviors in both male and female C57BL/6 J mice. Mice were individually or grouped housed from postnatal day 21 for 5 weeks until behavioral tests began. The results showed that social isolation resulted in increased anxiety in the open field. Isolated-reared female, but not male mice showed an increased transition between two compartments in the light-dark box and a decreased immobile time in the forced swim test. We conclude that post-weaning isolation has a sex-specific effect on emotional behaviors.

Gap junctions regulate the development of neural circuits in the neocortex.

Gap junctions between cells are ubiquitously expressed in the developing brain. They are involved in major steps of neocortical development, including neurogenesis, cell migration, synaptogenesis, and neural circuit formation, and have been implicated in cortical column formation. Dysfunctional gap junctions can contribute to or even cause a variety of brain diseases. Although the role of gap junctions in neocortical development is better known, a comprehensive understanding of their functions is far from complete. Here we explore several critical open questions surrounding gap junctions and their involvement in neural circuit development. Addressing them will greatly impact our understanding of the fundamental mechanisms of neocortical structure and function as well as the etiology of brain disease.

mvPPT: A Highly Efficient and Sensitive Pathogenicity Prediction Tool for Missense Variants.

Next-generation sequencing technologies both boost the discovery of variants in the human genome and exacerbate the challenges of pathogenic variant identification. In this study, we developed Pathogenicity Prediction Tool for missense variants (mvPPT), a highly sensitive and accurate missense variant classifier based on gradient boosting. mvPPT adopts high-confidence training sets with a wide spectrum of variant profiles, and extracts three categories of features, including scores from existing prediction tools, frequencies (allele frequencies, amino acid frequencies, and genotype frequencies), and genomic context. Compared with established predictors, mvPPT achieves superior performance in all test sets, regardless of data source. In addition, our study also provides guidance for training set and feature selection strategies, as well as reveals highly relevant features, which may further provide biological insights into variant pathogenicity. mvPPT is freely available at http://www.mvppt.club/.

Correlation Analysis of Molecularly-Defined Cortical Interneuron Populations with Morpho-Electric Properties in Layer V of Mouse Neocortex.

Cortical interneurons can be categorized into distinct populations based on multiple modalities, including molecular signatures and morpho-electrical (M/E) properties. Recently, many transcriptomic signatures based on single-cell RNA-seq have been identified in cortical interneurons. However, whether different interneuron populations defined by transcriptomic signature expressions correspond to distinct M/E subtypes is still unknown. Here, we applied the Patch-PCR approach to simultaneously obtain the M/E properties and messenger RNA (mRNA) expression of >600 interneurons in layer V of the mouse somatosensory cortex (S1). Subsequently, we identified 11 M/E subtypes, 9 neurochemical cell populations (NCs), and 20 transcriptomic cell populations (TCs) in this cortical lamina. Further analysis revealed that cells in many NCs and TCs comprised several M/E types and were difficult to clearly distinguish morpho-electrically. A similar analysis of layer V interneurons of mouse primary visual cortex (V1) and motor cortex (M1) gave results largely comparable to S1. Comparison between S1, V1, and M1 suggested that, compared to V1, S1 interneurons were morpho-electrically more similar to M1. Our study reveals the presence of substantial M/E variations in cortical interneuron populations defined by molecular expression.

Connexin43 in neonatal excitatory neurons is important for short-term motor learning.

In the neocortex, gap junctions are expressed at very early developmental stages, and they are involved in many processes such as neurogenesis, neuronal migration and synapse formation. Connexin43 (Cx43), a gap junction protein, has been found to be abundantly expressed in radial glial cells, excitatory neurons and astrocytes. Although accumulating evidence suggests that Cx43-mediated gap-junctional coupling between astrocytes plays an important role in the central nervous system, the function of Cx43 in early excitatory neurons remains elusive. To investigate the impact of Cx43 deficiency in excitatory neurons at early postnatal stages, we conditionally knocked out Cx43 in excitatory neurons under the Emx1 promoter by tamoxifen induction. We found that deletion of Cx43 around birth did not impair the laminar distribution of excitatory neurons in the neocortex. Moreover, mice with Cx43 deletion during the early postnatal stages had normal anxiety-like behaviors, depression-related behaviors, learning and memory-associated behaviors at adolescent stages. However, Cx43 conditional knockout mice exhibited impaired motor-learning behavior. These results suggested that Cx43 expression in excitatory neurons at early postnatal stages contributes to short-term motor learning capacity.

Early-generated interneurons regulate neuronal circuit formation during early postnatal development.

A small subset of interneurons that are generated earliest as pioneer neurons are the first cohort of neurons that enter the neocortex. However, it remains largely unclear whether these early-generated interneurons (EGIns) predominantly regulate neocortical circuit formation. Using inducible genetic fate mapping to selectively label EGIns and pseudo-random interneurons (pRIns), we found that EGIns exhibited more mature electrophysiological and morphological properties and higher synaptic connectivity than pRIns in the somatosensory cortex at early postnatal stages. In addition, when stimulating one cell, the proportion of EGIns that influence spontaneous network synchronization is significantly higher than that of pRIns. Importantly, toxin-mediated ablation of EGIns after birth significantly reduce spontaneous network synchronization and decrease inhibitory synaptic formation during the first postnatal week. These results suggest that EGIns can shape developing networks and may contribute to the refinement of neuronal connectivity before the establishment of the adult neuronal circuit.

Eye opening differentially modulates inhibitory synaptic transmission in the developing visual cortex.

Eye opening, a natural and timed event during animal development, influences cortical circuit assembly and maturation; yet, little is known about its precise effect on inhibitory synaptic connections. Here, we show that coinciding with eye opening, the strength of unitary inhibitory postsynaptic currents (uIPSCs) from somatostatin-expressing interneurons (Sst-INs) to nearby excitatory neurons, but not interneurons, sharply decreases in layer 2/3 of the mouse visual cortex. In contrast, the strength of uIPSCs from fast-spiking interneurons (FS-INs) to excitatory neurons significantly increases during eye opening. More importantly, these developmental changes can be prevented by dark rearing or binocular lid suture, and reproduced by the artificial opening of sutured lids. Mechanistically, this differential maturation of synaptic transmission is accompanied by a significant change in the postsynaptic quantal size. Together, our study reveals a differential regulation in GABAergic circuits in the cortex driven by eye opening may be crucial for cortical maturation and function.

Fear Erasure Facilitated by Immature Inhibitory Neuron Transplantation.

Transplantation of embryonic γ-aminobutyric acid (GABA)ergic neurons has been shown to modify disease phenotypes in rodent models of neurologic and psychiatric disorders. However, whether transplanted interneurons modulate fear memory remains largely unclear. Here, we report that transplantation of embryonic interneurons into the amygdala does not alter host fear memory formation. Yet approximately 2 weeks after transplantation, but not earlier or later, extinction training produces a marked reduction in spontaneous recovery and renewal of fear response. Further analyses reveal that transplanted interneurons robustly form functional synapses with neurons of the host amygdala and exhibit similar developmental maturation in electrophysiological properties as native amygdala interneurons. Importantly, transplanted immature interneurons reduce the expression of perineuronal nets, promote long-term synaptic plasticity, and modulate both excitatory and inhibitory synaptic transmissions of the host circuits. Our findings demonstrate that transplanted immature interneurons modify amygdala circuitry and suggest a previously unknown strategy for the prevention of extinction-resistant pathological fear.

Diclofenac, a nonsteroidal anti-inflammatory drug, activates the transient outward K+ current in rat cerebellar granule cells.

Diclofenac, a nonsteroidal anti-inflammatory drug (NSAID), has been widely investigated in terms of its pharmacological action, but less is known about its direct effect on ion channels. Here, the effect of diclofenac on voltage-dependent transient outward K+ currents (I(A)) in cultured rat cerebellar granule cells was investigated using the whole-cell voltage-clamp technique. At concentrations of 10(-5)-10(-3) M, diclofenac reversibly increased the I(A) amplitude in a dose-dependent manner and significantly modulated the steady-state inactivation properties of the I(A) channels, but did not alter the steady-state activation properties. Furthermore, diclofenac treatment resulted in a slightly accelerated recovery from I(A) channel inactivation. Intracellular application of diclofenac could mimic the effects induced by extracellular application, although once the intracellular response reached a plateau, extracellular application of diclofenac could induce further increases in the current. These observations indicate that diclofenac might exert its effects on the channel protein at both the inner and outer sides of the cell membrane. Our data provide the first evidence that diclofenac is able to activate transient outward potassium channels in neurons. Although further work will be necessary to define the exact mechanism of diclofenac-induced I(A) channel activation, this study provides evidence that the nonsteroidal anti-inflammatory drug, diclofenac, may play a novel neuronal role that is worthy of future study.

Delayed rectifier outward K+ current mediates the migration of rat cerebellar granule cells stimulated by melatonin.

Melatonin (MT) may work as a neuromodulator through the associated MT receptors in the central nervous system. Previously, our studies have shown that MT increased the I(K) current via a G protein-related pathway. In the present study, patch-clamp whole-cell recording, transwell migration assays and organotypic cerebellar slice cultures were used to examine the effect of MT on granule cell migration. MT increased the I(K) current amplitude and migration of granule cells. Meanwhile, TEA, the I(K) channel blocker, decreased the I(K) current and slowed the migration of granule cells. Furthermore, the effects of MT on the I(K) current and cell migration were not abolished by pre-incubation with P7791, a specific antagonist of MT(3)R, but were eliminated by the application of the MT(2)R antagonists K185 and 4-P-PDOT. I(K) current and cell migration were decreased by the application of dibutyryl cyclic AMP (dbcAMP), which was in contrast to the MT effect on the I(K) current and cell migration. Incubation with dbcAMP essentially blocked the MT-induced increasing effect. Moreover, incubation of isolated cell cultures in the MT-containing medium also decreased the cAMP immunoreactivity in the granule cells. It is concluded, therefore, that I(K) current, downstream of a cAMP transduction pathway, mediates the migration of rat cerebellar granule cells stimulated by MT.

Flufenamic acid bi-directionally modulates the transient outward K(+) current in rat cerebellar granule cells.

In this report, the effect of flufenamic acid on voltage-activated transient outward K(+) current (I(A)) in cultured rat cerebellar granule cells was investigated. At a concentration of 20 microM to 1 mM, flufenamic acid reversibly inhibited I(A) in a dose-dependent manner. However, flufenamic acid at a concentration of 0.1 to 10 microM significantly increased the current amplitude of I(A). In addition to the current amplitude of I(A), a higher concentration of flufenamic acid had a significant effect on the kinetic parameters of the steady-state activation and inactivation process, suggesting that the binding affinity of flufenamic acid to I(A) channels may be state-dependent. Silencing the K(v)4.2, K(v)4.3, and K(v)1.1 genes of I(A) channels using small interfering RNA did not change the inhibitory effect of flufenamic on I(A), indicating that flufenamic acid did not act specifically on any of the subunits of the I(A)-channel protein. Intracellular application of flufenamic acid could significantly increase the I(A) amplitude but did not alter the inhibited effect induced by extracellular application of flufenamic acid, implying that flufenamic acid may exert its effect from both the inside and outside sites of the channel. Furthermore, the activation of current induced by intracellular application of flufenamic acid could mimic other cyclooxygenase inhibitors and arachidonic acid. Our data are the first that demonstrate how flufenamic acid is able to bidirectionally modulate I(A) channels in neurons at different concentrations and by different methods of application and that two different mechanisms may be involved.

The non-steroidal anti-inflammatory drug, diclofenac, inhibits Na(+) current in rat myoblasts.

The inhibitory effect of diclofenac, a non-steroidal anti-inflammatory drug (NSAID), on the voltage-gated inward Na+ current (I(Na)) in cultured rat myoblasts was investigated using the whole-cell voltage-clamp technique. At concentrations of 10 nM-100 microM, diclofenac produced a dose-dependent and reversible inhibition of I(Na) with an IC50 of 8.51 microM, without modulating the fast activation and inactivation process. The inhibitory effect of diclofenac took place at resting channels and increased with more depolarizing holding potential. In addition to inhibiting the Na+ current amplitude, diclofenac significantly modulated the steady-state inactivation properties of the Na+ channels, but did not alter the steady-state activation. The steady-state inactivation curve was significantly shifted towards the hyperpolarizing potential in the presence of diclofenac. Furthermore, diclofenac treatment resulted in a fairly slow recovery from inactivation of the Na+ channel. The inhibitory effect of diclofenac was enhanced by repetitive pulses and was inflected by changing frequency; the blocking effect at higher frequency was significantly greater than at lower frequency. Both intracellular and extracellular application of diclofenac could inhibit I(Na), indicating that diclofenac may exert its channel inhibitory action both inside and outside the channel sites. Our data directly demonstrate that diclofenac can inhibit the inward Na+ channels in rat myoblasts. Some different inhibitory mechanisms from that in neuronal Na+ channels are discussed.

Inhibition of Na+ channel currents in rat myoblasts by 4-aminopyridine.

Our previous study revealed that 4-aminopyridine (4-AP), a specific blocker of A-type current, could also inhibit inward Na+ currents (I(Na)) with a state-independent mechanism in rat cerebellar granule cells. In the present study, we report an inhibitory effect of 4-AP on voltage-gated and tetrodotoxin (TTX)-sensitive I(Na) recorded from cultured rat myoblasts. 4-AP inhibited I(Na) amplitude in a dose-dependent manner between the concentrations of 0.5 and 10 mM without significant alteration in the activation or inactivation kinetics of the channel. By comparison to the 4-AP-induced inhibitory effect on cerebellum neurons, the inhibitory effect on myoblasts was enhanced through repetitive pulse and inflected by changing frequency. Specifically, the lower the frequency of pulse, the higher the inhibition observed, suggesting that block manner is inversely use-dependent. Moreover, experiments adding 4-AP to the intracellular solution indicate that the inhibitory effects are localized inside the cell. Additionally, 4-AP significantly modifies the properties of steady-state activation and inactivation kinetics of the channel. Our data suggest that the K+ channel blocker 4-AP inhibits both neuron and myoblast Na+ channels via different mechanisms. These findings may also provide information regarding 4-AP-induced pharmacological and toxicological effects in clinical use and experimental research.

Ca(2+)-inactivated K+ current is modulated by endothelin-1 in B-16 murine melanoma cells.

It is well established that endothelin-1 (ET-1) plays a role in differentiation and proliferation in a variety of cells such as fibroblasts and human melanoma cells via a receptor-mediated mechanism. However, whether ET-1 modulates ion channel activity in these cell types is still unknown. In this report, we recorded the voltage-dependent outward K+ current in cultured B16 melanoma cells using the patch-clamp technique. Biophysical and pharmacological properties of the K+ current, and the effect of ET-1 on the K+ current were investigated. When cells were loaded with a Ca(2+)-chelating agent (EGTA or BAPTA), the K+ current amplitude gradually increased with time after establishment of the whole cell configuration. Replacement of Ca2+ with Co2+ in the extracellular medium caused no significant modulation of the K+ current amplitude. Addition of BaCl2 or quinidine to the extracellular solution reduced the K+ current amplitude, whereas the K+ current was insensitive to tetraethylammonium. ET-1 (10 nM) reversibly decreased the K+ current amplitude and accelerated the decay of the K+ current. The ET-1-induced inhibitory effect displayed no desensitization following repeated ET-1 application. Pretreatment with pertussis toxin (PTX) or perfusion of cells with the protein kinase C (PKC) inhibitor H-7 abolished the inhibitory effect of ET-1 on the K+ current. We conclude that the outward K+ current recorded in murine B-16 melanoma cells represents a Ca(2+)-inactivated K+ current, and that the inhibitory effect of ET-1 on the K+ current may reveal a novel mechanism to control the differentiation and proliferation of melanoma cells.

ET-1 inhibits B-16 murine melanoma cell migration by decreasing K(+) currents.

Cell migration is mediated by ion channels and transporters, and plays crucial roles in a variety of physiological and pathological processes. Previously, our studies have shown that a Ca(2+)-regulated K(+) current exists in B-16 murine melanoma cells, and that endothelin-1 (ET-1) inhibits the K(+) current via a PKC-dependent pathway. In the present study, patch-clamp whole-cell recording and transwell migration assays were used to examine the effects of ET-1 on B-16 murine melanoma cell migration. ET-1 (100 nM in the injection pipette and 10 nM in the incubation medium) decreased the K(+) current amplitude by 33.0 +/- 2.5% and inhibited migration of B-16 cells by 57.4 +/- 9.4%. Similarly, the Ca(2+)-regulated K(+) channel blockers, BaCl(2) and quinidine, decreased the K(+) current by 20.5 +/- 1.0% and 36.6 +/- 1.2%, respectively, and slowed migration of B-16 melanoma cells by 37.1 +/- 8.6% and 42.7 +/- 8.8%, respectively. The effect of ET-1 on the K(+) current and cell migration was simulated by ET-3. In contrast, the K(+) channel opener, diclofenac, increased the K(+) current by 128.8 +/- 11.7%, 257.4 +/- 35.8% at concentrations of 1 and 5 mM, respectively. Likewise, the migration of B-16 murine melanoma cells dramatically increased by 75.6 +/- 12.7% in the presence of 100 microM diclofenac in incubation medium. Furthermore, the ET-1- and ET-3-induced inhibition of K(+) current and migration was abrogated by diclofenac. In the presence of diclofenac, ET-1 only reduced the K(+) current amplitude by 10.6 +/- 1.1%, and slowed B-16 cell migration by only 10.8 +/- 8.9%. The results suggest that the K(+) channel-dependent migration of B-16 melanoma cells is modulated by ET-1. Cell Motil.