scholarly journals Clustering of Extrasynaptic GABAAReceptors Modulates Tonic Inhibition in Cultured Hippocampal Neurons

2004 ◽  
Vol 279 (44) ◽  
pp. 45833-45843 ◽  
Author(s):  
Enrica Maria Petrini ◽  
Ivan Marchionni ◽  
Paola Zacchi ◽  
Werner Sieghart ◽  
Enrico Cherubini
Keyword(s):  
Hippocampal Neurons ◽  
Neuronal Excitability ◽  
Prolonged Exposure ◽  
Tonic Inhibition ◽  
Aminobutyric Acid ◽  
Action Potential Generation ◽  
Potential Generation ◽  
Acid Type ◽  
Ambient Gaba ◽  
Cultured Hippocampal Neurons

Tonic inhibition plays a crucial role in regulating neuronal excitability because it sets the threshold for action potential generation and integrates excitatory signals. Tonic currents are known to be largely mediated by extrasynaptic γ-aminobutyric acid type A (GABAA) receptors that are persistently activated by submicromo-lar concentrations of ambient GABA. We recently reported that, in cultured hippocampal neurons, the clustering of synaptic GABAAreceptors significantly affects synaptic transmission (Petrini, E. M., Zacchi, P., Barberis, A., Mozrzymas, J. W., and Cherubini, E. (2003)J. Biol. Chem.278, 16271–16279). In this work, we demonstrated that the clustering of extrasynaptic GABAAreceptors modulated tonic inhibition. Depolymerization of the cytoskeleton with nocodazole promoted the disassembly of extrasynaptic clusters of δ and γ2subunit-containing GABAAreceptors. This effect was associated with a reduction in the amplitude of tonic currents and diminished shunting inhibition. Moreover, diffuse GABAAreceptors were less sensitive to the GAT-1 inhibitor NO-711 and to flurazepam. Quantitative analysis of GABA-evoked currents after prolonged exposure to submicromolar concentrations of GABA and model simulations suggest that clustering affects the gating properties of extrasynaptic GABAAreceptors. In particular, a larger occupancy of the singly and doubly bound desensitized states can account for the modulation of tonic inhibition recorded after nocodazole treatment. Moreover, comparison of tonic currents recorded during spontaneous activity and those elicited by exogenously applied low agonist concentrations allows estimation of the concentration of ambient GABA. In conclusion, receptor clustering appears to be an additional regulating factor for tonic inhibition.

Effect of Lamotrigine on the Ca2+-Sensing Cation Current in Cultured Hippocampal Neurons

2001 ◽  
Vol 86 (5) ◽  
pp. 2520-2526 ◽  
Author(s):  
Zhi-Gang Xiong ◽  
Xiang-Ping Chu ◽  
J. F. MacDonald
Keyword(s):  
Action Potentials ◽  
Hippocampal Neurons ◽  
Neuronal Excitability ◽  
Membrane Depolarization ◽  
Slow Inward Current ◽  
Calcium Sensing ◽  
Cation Current ◽  
Imaging Experiment ◽  
Intracellular Ca ◽  
Cultured Hippocampal Neurons

Concentrations of extracellular calcium ([Ca2+]e) in the CNS decrease substantially during seizure activity. We have demonstrated previously that decreases in [Ca2+]e activate a novel calcium-sensing nonselective cation (csNSC) channel in hippocampal neurons. Activation of csNSC channels is responsible for a sustained membrane depolarization and increased neuronal excitability. Our study has suggested that the csNSC channel is likely involved in generating and maintaining seizure activities. In the present study, the effects of anti-epileptic agent lamotrigine (LTG) on csNSC channels were studied in cultured mouse hippocampal neurons using patch-clamp techniques. At a holding potential of −60 mV, a slow inward current through csNSC channels was activated by a step reduction of [Ca2+]e from 1.5 to 0.2 mM. LTG decreased the amplitude of csNSC currents dose dependently with an IC50 of 171 ± 25.8 (SE) μM. The effect of LTG was independent of membrane potential. In the presence of 300 μM LTG, the amplitude of csNSC current was decreased by 31 ± 3% at −60 mV and 29 ± 2.9% at +40 mV ( P > 0.05). LTG depressed csNSC current without affecting the potency of Ca2+ block of the current (IC50 for Ca2+block of csNSC currents in the absence of LTG: 145 ± 18 μM; in the presence of 300 μM LTG: 136 ± 10 μM. n = 5, P > 0.05). In current-clamp recordings, activation of csNSC channel by reducing the [Ca2+]e caused a sustained membrane depolarization and an increase in the frequency of spontaneous firing of action potentials. LTG (300 μM) significantly inhibited csNSC channel-mediated membrane depolarization and the excitation of neurons. Fura-2 ratiometric Ca2+imaging experiment showed that LTG also inhibited the increase in intracellular Ca2+ concentration induced by csNSC channel activation. The effect of LTG on csNSC channels may partially contribute to its broad spectrum of anti-epileptic actions.

Dexmedetomidine Prevents Excessive γ-Aminobutyric Acid Type A Receptor Function after Anesthesia

2018 ◽  
Vol 129 (3) ◽  
pp. 477-489 ◽  
Author(s):  
Dian-Shi Wang ◽  
Kirusanthy Kaneshwaran ◽  
Gang Lei ◽  
Fariya Mostafa ◽  
Junhui Wang ◽  
...  
Keyword(s):  
Problem Solving ◽  
Adrenergic Receptor ◽  
Hippocampal Neurons ◽  
Type A ◽  
Surface Expression ◽  
Aminobutyric Acid ◽  
Cell Surface Expression ◽  
Receptor Function ◽  
Anesthetic Drugs ◽  
Acid Type

Abstract What We Already Know about This Topic What This Article Tells Us That Is New Background Postoperative delirium is associated with poor long-term outcomes and increased mortality. General anesthetic drugs may contribute to delirium because they increase cell-surface expression and function of α5 subunit-containing γ-aminobutyric acid type A receptors, an effect that persists long after the drugs have been eliminated. Dexmedetomidine, an α2 adrenergic receptor agonist, prevents delirium in patients and reduces cognitive deficits in animals. Thus, it was postulated that dexmedetomidine prevents excessive function of α5 γ-aminobutyric acid type A receptors. Methods Injectable (etomidate) and inhaled (sevoflurane) anesthetic drugs were studied using cultured murine hippocampal neurons, cultured murine and human cortical astrocytes, and ex vivo murine hippocampal slices. γ-Aminobutyric acid type A receptor function and cell-signaling pathways were studied using electrophysiologic and biochemical methods. Memory and problem-solving behaviors were also studied. Results The etomidate-induced sustained increase in α5 γ-aminobutyric acid type A receptor cell-surface expression was reduced by dexmedetomidine (mean ± SD, etomidate: 146.4 ± 51.6% vs. etomidate + dexmedetomidine: 118.4 ± 39.1% of control, n = 8 each). Dexmedetomidine also reduced the persistent increase in tonic inhibitory current in hippocampal neurons (etomidate: 1.44 ± 0.33 pA/pF, n = 10; etomidate + dexmedetomidine: 1.01 ± 0.45 pA/pF, n = 9). Similarly, dexmedetomidine prevented a sevoflurane-induced increase in the tonic current. Dexmedetomidine stimulated astrocytes to release brain-derived neurotrophic factor, which acted as a paracrine factor to reduce excessive α5 γ-aminobutyric acid type A receptor function in neurons. Finally, dexmedetomidine attenuated memory and problem-solving deficits after anesthesia. Conclusions Dexmedetomidine prevented excessive α5 γ-aminobutyric acid type A receptor function after anesthesia. This novel α2 adrenergic receptor- and brain-derived neurotrophic factor-dependent pathway may be targeted to prevent delirium.

scholarly journals Dendritic Assembly of Heteromeric γ-Aminobutyric Acid Type B Receptor Subunits in Hippocampal Neurons

2009 ◽  
Vol 284 (19) ◽  
pp. 13077-13085 ◽  
Author(s):  
Omar A. Ramírez ◽  
René L. Vidal ◽  
Judith A. Tello ◽  
Karina J. Vargas ◽  
Stefan Kindler ◽  
...  
Keyword(s):  
Hippocampal Neurons ◽  
Aminobutyric Acid ◽  
Type B ◽  
Acid Type

scholarly journals Cdk-mediated phosphorylation of the Kvβ2 auxiliary subunit regulates Kv1 channel axonal targeting

2011 ◽  
Vol 192 (5) ◽  
pp. 813-824 ◽  
Author(s):  
Hélène Vacher ◽  
Jae-Won Yang ◽  
Oscar Cerda ◽  
Amapola Autillo-Touati ◽  
Bénédicte Dargent ◽  
...  
Keyword(s):  
Hippocampal Neurons ◽  
Neuronal Excitability ◽  
Regulatory Mechanism ◽  
Cyclin Dependent Kinase ◽  
Intracellular Accumulation ◽  
Axonal Membrane ◽  
Auxiliary Subunit ◽  
Cdk Phosphorylation ◽  
Axonal Targeting ◽  
Cultured Hippocampal Neurons

Kv1 channels are concentrated at specific sites in the axonal membrane, where they regulate neuronal excitability. Establishing these distributions requires regulated dissociation of Kv1 channels from the neuronal trafficking machinery and their subsequent insertion into the axonal membrane. We find that the auxiliary Kvβ2 subunit of Kv1 channels purified from brain is phosphorylated on serine residues 9 and 31, and that cyclin-dependent kinase (Cdk)–mediated phosphorylation at these sites negatively regulates the interaction of Kvβ2 with the microtubule plus end–tracking protein EB1. Endogenous Cdks, EB1, and Kvβ2 phosphorylated at serine 31 are colocalized in the axons of cultured hippocampal neurons, with enrichment at the axon initial segment (AIS). Acute inhibition of Cdk activity leads to intracellular accumulation of EB1, Kvβ2, and Kv1 channel subunits within the AIS. These studies reveal a new regulatory mechanism for the targeting of Kv1 complexes to the axonal membrane through the reversible Cdk phosphorylation-dependent binding of Kvβ2 to EB1.

scholarly journals COUP-TFI regulates diameter of the axon initial segment in the mammalian neocortex

2020 ◽  
Author(s):  
Xuanyuan Wu ◽  
Haixiang Li ◽  
Jiechang Huang ◽  
Cheng Xiao ◽  
Shuijin He
Keyword(s):  
Action Potential ◽  
Initial Segment ◽  
Neuronal Excitability ◽  
Developmental Stages ◽  
Pyramidal Cells ◽  
Axon Initial Segment ◽  
Action Potential Generation ◽  
Potential Generation ◽  
Cell Ablation ◽  
Specialized Structure

AbstractThe axon initial segment is a specialized structure that controls neuronal excitability by generating action potentials. Currently, AIS plasticity with regard to changes in length and location in response to neural activity has been extensively investigated, but how AIS diameter is regulated remains elusive. Here we report that COUP-TFI is an essential regulator of AIS diameter in both developing and adult mouse neocortex. Embryonic ablation of COUP-TFI prevented expansion of AIS diameter that occurs during postnatal development in layer II/III pyramidal cells of the mouse motor cortex, thereby leading to an impairment of action potential generation. Inactivation of COUP-TFI in adult neurons also led to reduced AIS diameter and impaired action potential generation. In contrast to different developmental stages, single-cell ablation and global ablation produced opposite effects on spontaneous network in COUP-TFI-deficient neurons. Further, mice exhibited less anxiety-like behaviors after postnatal inactivation of COUP-TFI induced by tamoxifen. Our results demonstrate that COUP-TFI is indispensable for both expansion and maintenance of AIS diameter and that a change in AIS diameter fine-tunes synaptic inputs through a metaplasticity mechanism in the adult neocortex.

scholarly journals Substance P modulates nicotinic responses of intracardiac neurons to acetylcholine in the guinea pig

2001 ◽  
Vol 281 (6) ◽  
pp. R1792-R1800 ◽  
Author(s):  
Lili Zhang ◽  
John D. Tompkins ◽  
John C. Hancock ◽  
Donald B. Hoover
Keyword(s):  
Substance P ◽  
Guinea Pig ◽  
Action Potential ◽  
Action Potentials ◽  
Neuronal Excitability ◽  
Action Potential Generation ◽  
Potential Generation ◽  
Local Pressure ◽  
Slow Depolarization ◽  
Intracardiac Neurons

—Application of substance P (SP) to intracardiac neurons of the guinea pig causes slow depolarization and increases neuronal excitability. The present study was done to determine the influence of SP on fast excitatory responses of intracardiac neurons to ACh. Intracellular recording methods were used to measure responses of intracardiac neurons in whole mount preparations of atrial ganglionated nerve plexus from guinea pig hearts. Local pressure ejection of 100 μM SP (1 s) from a glass micropipette caused slow depolarization of all neurons ( n = 38) and triggered action potential generation in 47% of the cells tested. Bath application of SP (0.5–100 μM) caused a dose-dependent depolarization of intracardiac neurons but rarely evoked action potentials, even at the highest concentration. However, such treatment with SP enhanced nicotinic responses evoked by local pressure ejections of ACh (10 mM, 10- to 100-ms duration) in 77% of intracardiac neurons studied ( n = 52). A significant increase in amplitude of ACh-evoked fast depolarization occurred during treatment with 0.5 μM SP (13.0 ± 1.8 mV for control vs. 17.7 ± 1.9 mV with SP present, n = 7, P = 0.019). At higher concentrations of SP, enhancement of the response to ACh resulted mainly in action potential generation. However, responses to ACh were attenuated by SP in 15% of the intracardiac neurons studied. This attenuation occurred primarily during exposure to 10 and 100 μM SP and was manifest as a reduction in amplitude of nicotinic fast depolarization or inhibition of ACh-evoked action potentials. These findings support the conclusion that SP could function as a neuromodulator and neurotransmitter in intracardiac ganglia of the guinea pig.

Vigabatrin Induces Tonic Inhibition Via GABA Transporter Reversal Without Increasing Vesicular GABA Release

2003 ◽  
Vol 89 (4) ◽  
pp. 2021-2034 ◽  
Author(s):  
Yuanming Wu ◽  
Wengang Wang ◽  
George B. Richerson
Keyword(s):  
Patch Clamp ◽  
Gaba Receptors ◽  
Hippocampal Neurons ◽  
Gaba Release ◽  
Tonic Inhibition ◽  
Gabaergic Inhibition ◽  
Gaba Transporter ◽  
Whole Cell ◽  
Ambient Gaba

Two forms of GABAergic inhibition coexist: fast synaptic neurotransmission and tonic activation of GABA receptors due to ambient GABA. The mechanisms regulating ambient GABA have not been well defined. Here we examined the role of the GABA transporter in the increase in ambient [GABA] induced by the anticonvulsant vigabatrin. Pretreatment of cultured rat hippocampal neurons with vigabatrin (100 μM) for 2–5 days led to a large increase in ambient [GABA] that was measured as the change in holding current induced by bicuculline during patch-clamp recordings. In contrast, there was a decrease in the frequency of spontaneous miniature inhibitory postsynaptic currents mIPSCs with no change in their amplitude distribution, and a decrease in the magnitude of IPSCs evoked by presynaptic stimulation during paired recordings. The increase in ambient [GABA] was not prevented by blockade of vesicular GABA release with tetanus toxin or removal of extracellular calcium. During perforated patch recordings, the increase in ambient [GABA] was prevented by blocking the GABA transporter, indicating that the GABA transporter was continuously operating in reverse and releasing GABA. In contrast, blocking the GABA transporter increased ambient [GABA] during whole cell patch-clamp recordings unless GABA and Na+ were added to the recording electrode solution, indicating that whole cell recordings can lead to erroneous conclusions about the role of the GABA transporter in control of ambient GABA. We conclude that the equilibrium for the GABA transporter is a major determinant of ambient [GABA] and tonic GABAergic inhibition. We propose that fast GABAergic neurotransmission and tonic inhibition can be independently modified and play complementary roles in control of neuronal excitability.

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