Regulation of action potential waveforms by axonal GABAA receptors in cortical pyramidal neurons.

GABAA receptors distributed in somatodendritic compartments play critical roles in regulating neuronal activities, including spike timing and firing pattern; however, the properties and functions of GABAA receptors at the axon are still poorly understood. By recording from the cut end (bleb) of the main axon trunk of layer -5 pyramidal neurons in prefrontal cortical slices, we found that currents evoked by GABA iontophoresis could be blocked by picrotoxin, indicating the expression of GABAA receptors in axons. Stationary noise analysis revealed that single-channel properties of axonal GABAA receptors were similar to those of somatic receptors. Perforated patch recording with gramicidin revealed that the reversal potential of the GABA response was more negative than the resting membrane potential at the axon trunk, suggesting that GABA may hyperpolarize the axonal membrane potential. Further experiments demonstrated that the activation of axonal GABAA receptors regulated the amplitude and duration of action potentials (APs) and decreased the AP-induced Ca2+ transients at the axon. Together, our results indicate that the waveform of axonal APs and the downstream Ca2+ signals are modulated by axonal GABAA receptors

Endoplasmic reticulum stress is activated in post-ischemic kidneys to promote chronic kidney diseaseResearch in context

Background: Acute kidney injury (AKI) may lead to the development of chronic kidney disease (CKD), i.e. AKI-CKD transition, but the underlying mechanism remains largely unclear. Endoplasmic reticulum (ER) stress is characterized by the accumulation of unfolded or misfolded proteins in ER resulting in a cellular stress response. The role of ER stress in AKI-CKD transition remains unknown. Methods: In this study, we examined ER stress in the mouse model of AKI-CKD transition after unilateral renal ischemia-reperfusion injury (uIR). To determine the role of ER stress in AKI-CKD transition, we tested the effects of two chemical chaperones: Tauroursodeoxycholic acid (TUDCA) and 4-phenylbutyric acid (4-PBA). Findings: uIR led to the induction of ER stress in kidneys, as indicated by increased expression of UPR molecules CHOP (C/EBP homologous protein) and BiP(binding immunoglobulin protein; also called GRP78–78 kDa glucose­regulated protein). Given at 3 days after uIR, both TUDCA and 4-PBA blocked ER stress in post-ischemic kidneys. Notably, both chemicals promoted renal recovery and suppressed tubulointerstitial injury as manifested by the reduction of tubular atrophy, renal fibrosis and myofibroblast activation. Inhibition of ER stress further attenuated renal tubular epithelial cell apoptosis, inflammation and autophagy in post-ischemic kidneys. Interpretation: These findings suggest that ER stress contributes critically to the development of chronic kidney pathologies and CKD following AKI, and inhibition of ER stress may represent a potential therapeutic strategy to impede AKI-CKD transition. Keywords: ER stress, AKI-CKD transition, Renal ischemia-reperfusion, Fibrosis, Apoptosis, Autophag

Hypoxia and Hypoxia-Inducible Factors in Kidney Injury and Repair

Acute kidney injury (AKI) is a major kidney disease characterized by an abrupt loss of renal function. Accumulating evidence indicates that incomplete or maladaptive repair after AKI can result in kidney fibrosis and the development and progression of chronic kidney disease (CKD). Hypoxia, a condition of insufficient supply of oxygen to cells and tissues, occurs in both acute and chronic kidney diseases under a variety of clinical and experimental conditions. Hypoxia-inducible factors (HIFs) are the “master” transcription factors responsible for gene expression in hypoxia. Recent researches demonstrate that HIFs play an important role in kidney injury and repair by regulating HIF target genes, including microRNAs. However, there are controversies regarding the pathological roles of HIFs in kidney injury and repair. In this review, we describe the regulation, expression, and functions of HIFs, and their target genes and related functions. We also discuss the involvement of HIFs in AKI and kidney repair, presenting HIFs as effective therapeutic targets

Activation of axonal GABA_A receptors shapes the AP waveform.

<p>A, Example traces showing the change in AP waveform after GABA iontophoresis to the axon bleb. <i>V</i>_m change was –3.9 mV in this bleb. The amplitude and the half-width of APs decreased to 95.6% and 86.8% of the control, respectively. B, Group data showing that activation of axonal GABA_A receptors shaped AP waveforms by regulating the amplitude and the half-width. Note that the recordings were performed under current-clamp and that the <i>V</i>_m could be manipulated by DC current injection. Black, GABA responses were hyperpolarizing; gray, depolarizing. The blebs were recorded with low-Cl⁻ ICS (7 mM [Cl⁻]_i). C, Increasing [Cl⁻]_i depolarized the <i>V</i>_m but still showed a shunting effect on AP waveforms. Amplitude and half-width were significantly reduced. Modified ICS (20 mM [Cl⁻]_i) was used for these recordings. ***, P<0.001, paired t-test. D, Bath application of PTX could block the GABA-induced <i>V</i>_m depolarization and its shunting effect on AP waveform. Modified ICS was used. E, Example traces showing that GABA application caused a shunting effect on APs evoked by electric shocks (asterisks), although GABA itself could evoke an AP (arrow). High-Cl⁻ ICS (75 mM [Cl⁻]_i) was used here.</p

Lamellation Fractures in the Paleogene Continental Shale Oil Reservoirs in the Qianjiang Depression, Jianghan Basin, China

Based on the data of cores, thin sections, well logs, and test experiments, the characteristics and main controlling factors of lamellation fractures in continental shales of the third and fourth members of the Paleogene Qianjiang Formation in the Qianjiang Depression, Jianghan Basin, are studied. Lamellation fractures mainly develop along laminas in shales. They have various morphological characteristics such as straightness, bending, discontinuity, bifurcation, pinching out, and merging. Lamellation fractures with high density show poor horizontal continuity and connectivity characteristics. The average linear density of the lamellation fractures is mainly between 20 m-1 and 110 m-1, and the aperture is usually less than 160 μm. The density of lamellation fractures is related to their apertures. The smaller the apertures of lamellation fractures are, the higher the density is. The development degree of lamellation fractures is mainly controlled by mineral composition, type, thickness, density of lamination, contents of organic matter and pyrite, lithofacies, structural position, etc. Lamellation fractures develop well, especially under the conditions of medium dolomite content, large lamination density, small lamination thickness, and high total organic carbon (TOC) and pyrite contents. The influences of lithofacies on the lamellation fractures are complex. The lamellation fractures are most developed in carbonaceous layered limestone dolomite and carbonaceous layered dolomite mudstone, followed by stromatolite dolomite filled with carbonaceous pyroxene. The fractures in the massive argillaceous dolomites and carbonaceous massive mudstones are poorly developed. No fractures can be found in the carbonaceous dolomitic, argillaceous glauberites or salt rocks with high glauberite content. Structure is also an important factor controlling lamination fractures. Tectonic uplifts are beneficial to the expansion and extension of lamellation fractures, which increases fracture density. Therefore, when other influence factors are similar, lamellation fractures develop better in the high part of the structure than in the low part

GABA receptors are located at axon bleb and trunk.

<p>A, Left, schematic diagram of bleb recording and GABA iontophoresis in a pyramidal neuron. Positive (but not negative) pulses could induce current responses. V_hold = –50 mV; iontophoresis pulses: 200 nA, 5 ms; retention current: –10 nA. Right, whole-cell recording from an axon bleb (top, fluorescence image; bottom, DIC image). Scale bar: 20 µm. The sharp electrode was used for GABA iontophoresis. Alexa Fluor 488 was added to the patch pipette solution so that the recording pipette was visible. B, Plot of the normalized GABA response as a function of the distance between the bleb and the tip of the iontophoresis electrode. Different symbols indicate different cells. The measurement of distance <i>L</i> is shown in the schematic diagram in panel A (indicated by arrows). C, GABA-induced responses could be observed when GABA was applied to the bleb (site <i>a</i>) or the main axon trunk (site <i>c</i>). The distance between sites <i>a</i> and <i>c</i> was approximately 50 µm, whereas that between <i>a</i> and <i>b</i> was approximately 25 µm. V_hold = –80 mV; iontophoresis pulses: 200 nA, 5 ms.</p

Propagation of GABA-induced hyperpolarization at the axon regulates AP generation.

<p>A, DAB staining of recorded neurons. Simultaneous recording from the soma and axon bleb were performed in a pyramidal neuron (left), and GABA was applied to the axon trunk (right). The axon length was 239 µm in this case. The distance between the iontophoresis site and the soma was 117 µm. Scale bar: 100 µm (left); 50 µm (right). B, The sign of the effect of GABA (hyperpolarization or depolarization) depended on the <i>V</i>_m. Top, traces were taken from the bleb. Bottom, traces were the corresponding responses at the soma. The <i>V_m</i> was clamped through somatic DC current injection. Asterisk indicates application of GABA to the main trunk. C, Left, application of GABA to the axon increased the amplitude but decreased the half-width of propagating APs. GABA iontophoresis hyperpolarized the <i>V</i>_m by 2.3±0.4 mV (n = 7). Right, similar results were obtained when <i>V</i>_m was hyperpolarized by 2.8±0.3 mV (n = 5) through DC current injection. *, P<0.05; **, P<0.01, paired t-test. D, Example traces showing activation of axonal GABA_A receptors reduced firing probability and frequency. The distances between the iontophoresis site and the soma were 100 µm (distal axon) and 18 µm (AIS). E, Left, repetitive firing recorded at an axon bleb induced by 400 pA DC current injection at the soma before (black) and after (red) GABA application to the axon trunk. The arrow indicates GABA iontophoresis. Middle, instantaneous firing frequency of APs decreased after GABA application (same data as shown in the left). Right, group data showing a decrease in the mean frequency of APs after GABA iontophoresis at the axon trunk. **, P<0.01, paired t-test. Low-Cl⁻ ICS was used in these experiments.</p

The presence of GABA_A (but likely not GABA_B) receptors in the axon.

<p>A, Reversal potential of GABA responses (I_GABA) in the axon bleb. Left, representative currents induced by GABA application at different holding potentials (from –100 to –40 mV). At –60 mV (near reversal potential), GABA application induced no obvious change in baseline current (gray). Right, I-V curve of the GABA-induced responses shown on the left. B, I_GABA could be blocked by GABA_A receptor blocker PTX. Left, example traces before (black), during (gray) and after (Wash, dashed line) the bath application of PTX (25 µM). V_hold = –50 mV, GABA was applied via iontophoresis. Middle, time course of the effect of PTX. Right, group data showing the change of I_GABA during (n = 6) and after (n = 3) PTX application. The dashed line indicates 100% of control. C, Left, currents evoked by puffing baclofen (200 µM), a GABA_B receptor agonist, to the soma (16 psi, 15 ms). Right, no response was observed when baclofen was applied to the axon trunk (16 psi, 20 ms). D, Group data showing that GABA-induced currents at the axon blebs could not be blocked by the GABA_B receptor antagonist CGP 35348 (100 µM); however, PTX could diminish these responses. Different symbols indicate different cells.</p

Reversal potential of GABA responses (E_GABA) is more negative than the local RMP.

<p>A, Gramicidin perforated patch recording from an axon bleb. Arrow indicates the recorded bleb. Top, DIC image of the recording; middle, fluorescence image (unlabeled bleb); bottom, fluorescence image (labeled bleb, indicating rupture of patch membrane). Scale bar: 50 µm. B, Example traces showing GABA responses at different holding potentials (from –90 to –50 mV) before (black) and after the break-in (membrane rupture, gray). C, Comparison of E_GABA and RMP. Note that E_GABA at both the soma and the distal axon bleb were more hyperpolarized than their local RMP. *, P<0.05, paired t-test.</p