Prolongation of Hippocampal Miniature Inhibitory Postsynaptic Currents in Mice Lacking the GABAA Receptor α1 Subunit

2002 ◽  
Vol 88 (6) ◽  
pp. 3208-3217 ◽  
Author(s):  
Peter A. Goldstein ◽  
Frank P. Elsen ◽  
Shui-Wang Ying ◽  
Carolyn Ferguson ◽  
Gregg E. Homanics ◽  
...  
Keyword(s):  
Pyramidal Cells ◽  
Fluctuation Analysis ◽  
Α Subunit ◽  
Knock Out ◽  
Inhibitory Postsynaptic Currents ◽  
Ca1 Pyramidal Cells ◽  
Postsynaptic Currents ◽  
Decay Times ◽  
Kinetics Of ◽  
Α1 Subunit

GABAA receptors (GABAA-Rs) are pentameric structures consisting of two α, two β, and one γ subunit. The α subunit influences agonist efficacy, benzodiazepine pharmacology, and kinetics of activation/deactivation. To investigate the contribution of the α1 subunit to native GABAA-Rs, we analyzed miniature inhibitory postsynaptic currents (mIPSCs) in CA1 hippocampal pyramidal cells and interneurons from wild-type (WT) and α1 subunit knock-out (α1 KO) mice. mIPSCs recorded from interneurons and pyramidal cells obtained from α1 KO mice were detected less frequently, were smaller in amplitude, and decayed more slowly than mIPSCs recorded in neurons from WT mice. The effect of zolpidem was examined in view of its reported selectivity for receptors containing the α1 subunit. In interneurons and pyramidal cells from WT mice, zolpidem significantly increased mIPSC frequency, prolonged mIPSC decay, and increased mIPSC amplitude; those effects were diminished or absent in neurons from α1 KO mice. Nonstationary fluctuation analysis of mIPSCs indicated that the zolpidem-induced increase in mIPSC amplitude was associated with an increase in the number of open receptors rather than a change in the unitary conductance of individual channels. These data indicate that the α1 subunit is present at synapses on WT interneurons and pyramidal cells, although differences in mIPSC decay times and zolpidem sensitivity suggest that the degree to which the α1 subunit is functionally expressed at synapses on CA1 interneurons may be greater than that at synapses on CA1 pyramidal cells.

Development of GABAA Receptor-Mediated Inhibitory Postsynaptic Currents in Hippocampus

2002 ◽  
Vol 88 (6) ◽  
pp. 3097-3107 ◽  
Author(s):  
Matthew I. Banks ◽  
Jason B. Hardie ◽  
Robert A. Pearce
Keyword(s):  
Developmental Regulation ◽  
Brain Slices ◽  
Pyramidal Cells ◽  
Cell Voltage ◽  
Fold Increase ◽  
Developmental Changes ◽  
Inhibitory Postsynaptic Currents ◽  
Postsynaptic Currents ◽  
Age Range ◽  
Kinetics Of

Hippocampal CA1 pyramidal cells receive two kinetic classes of GABAA receptor-mediated inhibition: slow dendritic inhibitory postsynaptic currents (GABAA,slow IPSCs) and fast perisomatic (GABAA,fast) IPSCs. These two classes of IPSCs are likely generated by two distinct groups of interneurons, and we have previously shown that the kinetics of the IPSCs have important functional consequences for generating synchronous firing patterns. Here, we studied developmental changes in the properties of GABAA,fast and GABAA,slowspontaneous, miniature, and evoked IPSCs (sIPSCs, mIPSCs, and eIPSCs, respectively) using whole cell voltage-clamp recordings in brain slices from animals aged P10–P35. We found that the rate of GABAA,slow sIPSCs increased by over 70-fold between P11 and P35 (from 0.0017 to 0.12 s−1). Over this same age range, we observed a >3.5-fold increase in the maximal amplitude of GABAA,slow eIPSCs evoked by stratum lacunosum-moleculare (SL-M) stimuli. However, the rate and amplitude of GABAA,slow mIPSCs remained unchanged between P10 and P30, suggesting that the properties of GABAA,slow synapses remained stable over this age range, and that the increase in sIPSC rate and in eIPSC amplitude was due to increased excitability or excitation of GABAA,slow interneurons. This hypothesis was tested using bath application of norepinephrine (NE), which we found at low concentrations (1 μM) selectively increased the rate of GABAA,slow sIPSCs while leaving GABAA,fast sIPSCs unchanged. This effect was observed in animals as young as P13 and was blocked by coapplication of tetrodotoxin, suggesting that NE was acting to increase the spontaneous firing rate of GABAA,slow interneurons and consistent with our hypothesis that developmental changes in GABAA,slow IPSCs are due to changes in presynaptic excitability. In contrast to the changes we observed in GABAA,slow IPSCs, the properties of GABAA,fast sIPSCs remained largely constant between P11 and P35, whereas the rate, amplitude, and kinetics of GABAA,fast mIPSCs showed significant changes between P10 and P30, suggesting counterbalancing changes in action potential-dependent GABAA,fast sIPSCs. These observations suggest differential developmental regulation of the firing properties of GABAA,fast and GABAA,slow interneurons in CA1 between P10 and P35.

GABAA Receptor β3 Subunit Deletion Decreases α2/3 Subunits and IPSC Duration

2003 ◽  
Vol 89 (1) ◽  
pp. 128-134 ◽  
Author(s):  
Epolia Ramadan ◽  
Zhanyan Fu ◽  
Gabriele Losi ◽  
Gregg E. Homanics ◽  
Joseph H. Neale ◽  
...  
Keyword(s):  
Gabaa Receptor ◽  
Cortical Neurons ◽  
Behavioral Deficits ◽  
Inhibitory Postsynaptic Currents ◽  
Postsynaptic Currents ◽  
Surface Staining ◽  
Α1 Subunit

Deletion of the β3 subunit of the GABAA receptor produces severe behavioral deficits and epilepsy. GABAA receptor-mediated miniature inhibitory postsynaptic currents (mIPSCs) in cortical neurons in cultures from β3 −/− mice were significantly faster than those in β3 +/+ mice and were more prolonged by zolpidem. Surface staining revealed that the number of β2/3, α2, and α3 (but not of α1) subunit-expressing neurons and the intensity of subunit clusters were significantly reduced in β3 −/− mice. Transfection of β3 −/− neurons with β3 cDNA restored β2/3, α2, and α3 subunits immunostaining and slowed mIPSCs decay. We show that the deletion of the β3 subunit causes the loss of a subset of GABAA receptors with α2 and α3 subunits while leaving a receptor population containing predominantly α1 subunit with fast spontaneous IPSC decay and increased zolpidem sensitivity.

scholarly journals The Role of Na,k-Atpase α Subunit Serine 775 and Glutamate 779 in Determining the Extracellular K+And Membrane Potential–Dependent Properties of the Na,k -Pump

2000 ◽  
Vol 116 (1) ◽  
pp. 47-60 ◽  
Author(s):  
R. Daniel Peluffo ◽  
José M. Argüello ◽  
Joshua R. Berlin
Keyword(s):  
Membrane Potential ◽  
Voltage Dependence ◽  
Protein Structures ◽  
Pump Current ◽  
Transmembrane Segment ◽  
Α Subunit ◽  
Voltage Dependent ◽  
Kinetics Of ◽  
Α1 Subunit

The roles of Ser775 and Glu779, two amino acids in the putative fifth transmembrane segment of the Na,K -ATPase α subunit, in determining the voltage and extracellular K + (K +o) dependence of enzyme-mediated ion transport, were examined in this study. HeLa cells expressing the α1 subunit of sheep Na,K -ATPase were voltage clamped via patch electrodes containing solutions with 115 mM Na+ (37°C). Na,K -pump current produced by the ouabain-resistant control enzyme (RD), containing amino acid substitutions Gln111Arg and Asn122Asp, displayed a membrane potential and K +o dependence similar to wild-type Na,K -ATPase during superfusion with 0 and 148 mM Na+-containing salt solutions. Additional substitution of alanine at Ser775 or Glu779 produced 155- and 15-fold increases, respectively, in the K +o concentration that half-maximally activated Na,K -pump current at 0 mV in extracellular Na+-free solutions. However, the voltage dependence of Na,K -pump current was unchanged in RD and alanine-substituted enzymes. Thus, large changes in apparent K +o affinity could be produced by mutations in the fifth transmembrane segment of the Na,K -ATPase with little effect on voltage-dependent properties of K + transport. One interpretation of these results is that protein structures responsible for the kinetics of K +o binding and/or occlusion may be distinct, at least in part, from those that are responsible for the voltage dependence of K +o binding to the Na,K -ATPase.

scholarly journals Homeostatic Plasticity Hypothesis and Mechanisms of Neocortical Epilepsies

2005 ◽  
Vol 5 (4) ◽  
pp. 133-135 ◽  
Author(s):  
Jaideep Kapur ◽  
Stacey Trotter
Keyword(s):  
Synaptic Plasticity ◽  
Neuronal Activity ◽  
Pyramidal Neurons ◽  
Pyramidal Cells ◽  
Homeostatic Plasticity ◽  
Excitatory Synapses ◽  
Excitatory Postsynaptic Currents ◽  
Inhibitory Postsynaptic Currents ◽  
Postsynaptic Currents ◽  
Homeostatic Synaptic Plasticity

Homeostatic Synaptic Plasticity Can Explain Posttraumatic Epileptogenesis in Chronically Isolated Neocortex Houweling AR, Bazhenov M, Timofeev I, Steriade M, Sejnowski TJ Cereb Cortex 2004 [Epub ahead of print] Permanently isolated neocortex develops chronic hyperexcitability and focal epileptogenesis in a period of days to weeks. The mechanisms operating in this model of posttraumatic epileptogenesis are not well understood. We hypothesized that the spontaneous burst discharges recorded in permanently isolated neocortex result from homeostatic plasticity (a mechanism generally assumed to stabilize neuronal activity) induced by low neuronal activity after deafferentation. To test this hypothesis, we constructed computer models of neocortex incorporating a biologically based homeostatic plasticity rule that operates to maintain firing rates. After deafferentation, homeostatic upregulation of excitatory synapses on pyramidal cells, either with or without concurrent downregulation of inhibitory synapses or upregulation of intrinsic excitability, initiated slowly repeating burst discharges that closely resembled the epileptiform burst discharges recorded in permanently isolated neocortex. These burst discharges lasted a few hundred milliseconds, propagated at 1 to 3 cm/s and consisted of large (10–15 mV) intracellular depolarizations topped by a small number of action potentials. Our results support a role for homeostatic synaptic plasticity as a novel mechanism of posttraumatic epileptogenesis. Excitatory and Inhibitory Postsynaptic Currents in a Rat Model of Epileptogenic Microgyria Jacobs KM, Prince DA J Neurophysiol 2005;93:687–696 Developmental cortical malformations are common in patients with intractable epilepsy; however, mechanisms contributing to this epileptogenesis are currently poorly understood. We previously characterized hyperexcitability in a rat model that mimics the histopathology of human four-layered microgyria. Here we examined inhibitory and excitatory postsynaptic currents in this model to identify functional alterations that might contribute to epileptogenesis associated with microgyria. We recorded isolated whole-cell excitatory postsynaptic currents and GABAA receptor–mediated inhibitory currents from layer V pyramidal neurons in the region previously shown to be epileptogenic (paramicrogyral area) and in homotopic control cortex. Epileptiform-like activity could be evoked in 60% of paramicrogyral (PMG) cells by local stimulation. The peak conductance of both spontaneous and evoked inhibitory postsynaptic currents was significantly larger in all PMG cells compared with controls. This difference in amplitude was not present after blockade of ionotropic glutamatergic currents or for miniature (m) inhibitory postsynaptic currents, suggesting that it was due to the excitatory afferent activity driving inhibitory neurons. This conclusion was supported by the finding that glutamatereceptor antagonist application resulted in a significantly greater reduction in spontaneous inhibitory postsynaptic current frequency in one PMG cell group (PMGE) compared with control cells. The frequency of both spontaneous and miniature excitatory postsynaptic currents was significantly greater in all PMG cells, suggesting that pyramidal neurons adjacent to a microgyrus receive more excitatory input than do those in control cortex. These findings suggest that there is an increase in numbers of functional excitatory synapses on both interneurons and pyramidal cells in the PMG cortex, perhaps due to hyperinnervation by cortical afferents originally destined for the microgyrus proper.

scholarly journals LSO:Ce Inorganic Scintillators are Biocompatible with Neuronal and Circuit Function

2019 ◽  
Author(s):  
Aundrea F. Bartley ◽  
Kavitha Abiraman ◽  
Luke T. Stewart ◽  
Mohammed Iqbal Hossain ◽  
David M Gahan ◽  
...  
Keyword(s):  
Neural Circuits ◽  
Pyramidal Cells ◽  
Synaptic Function ◽  
Whole Cell ◽  
X Ray ◽  
Ca1 Pyramidal Cells ◽  
Postsynaptic Currents ◽  
Light Delivery ◽  
Inorganic Scintillators

AbstractOptogenetics is widely used in neuroscience to control neural circuits. However, non-invasive methods for light delivery in brain are needed to avoid physical damage caused by current methods. One potential strategy could employ x-ray activation of radioluminescent particles (RPLs), enabling localized light generation within the brain. RPLs composed of inorganic scintillators can emit light at various wavelengths depending upon composition. Cerium doped lutetium oxyorthosilicate (LSO:Ce), an inorganic scintillator that emits blue light in response to x-ray or UV stimulation, could potentially be used to control neural circuits through activation of channelrhodopsin-2 (ChR2), a light-gated cation channel. Whether inorganic scintillators themselves negatively impact neuronal processes and synaptic function is unknown, and was investigated here using cellular, molecular, and electrophysiological approaches. As proof of principle, we applied UV stimulation to 4 μm LSO:Ce particles during whole-cell recording of CA1 pyramidal cells in acutely prepared hippocampal slices from mice that expressed ChR2 in glutamatergic neurons. We observed an increase in frequency and amplitude of spontaneous excitatory postsynaptic currents (EPSCs), indicating UV activation of ChR2 and excitation of neurons. Importantly, we found that LSO:Ce particles have no effect on survival of primary mouse cortical neurons, even after 24 hours of exposure. In extracellular dendritic field potential recordings, we observed no change in strength of basal glutamatergic transmission up to 3 hours of exposure to LSO:Ce microparticles. However, there was a slight decrease in the frequency of spontaneous EPSCs in whole-cell voltage-clamp recordings from CA1 pyramidal cells, with no change in current amplitudes. No changes in the amplitude or frequency of spontaneous inhibitory postsynaptic currents (IPSCs) were observed. Finally, long term potentiation (LTP), a synaptic modification believed to underlie learning and memory and a robust measure of synaptic integrity, was successfully induced, although the magnitude was slightly reduced. Together, these results show LSO:Ce particles are biocompatible even though there are modest effects on baseline synaptic function and long-term synaptic plasticity. Importantly, we show that light emitted from LSO:Ce particles is able to activate ChR2 and modify synaptic function. Therefore, LSO:Ce inorganic scintillators are potentially viable for use as a new light delivery system for optogenetics.

Modulation of γ-Aminobutyric Acid Type A Receptor–mediated Spontaneous Inhibitory Postsynaptic Currents in Auditory Cortex by Midazolam and Isoflurane

2005 ◽  
Vol 102 (5) ◽  
pp. 962-969 ◽  
Author(s):  
Yakov I. Verbny ◽  
Elliott B. Merriam ◽  
Matthew I. Banks
Keyword(s):  
Auditory Cortex ◽  
Pyramidal Cells ◽  
Type A ◽  
Aminobutyric Acid ◽  
Gaba A ◽  
Cellular Targets ◽  
Inhibitory Postsynaptic Currents ◽  
Postsynaptic Currents ◽  
Acid Type

Background Anesthetic agents that target gamma-aminobutyric acid type A (GABA(A)) receptors modulate cortical auditory evoked responses in vivo, but the cellular targets involved are unidentified. Also, for agents with multiple protein targets, the relative contribution of modulation of GABA(A) receptors to effects on cortical physiology is unclear. The authors compared effects of the GABA(A) receptor-specific drug midazolam with the volatile anesthetic isoflurane on spontaneous inhibitory postsynaptic currents (sIPSCs) in pyramidal cells of auditory cortex. Methods Whole cell recordings were obtained in murine brain slices at 34 degrees C. GABA(A) sIPSCs were isolated by blocking ionotropic glutamate receptors. Effects of midazolam and isoflurane on time course, amplitude, and frequency of sIPSCs were measured. Results The authors detected no effect of midazolam at 0.01 microM on sIPSCs, whereas midazolam at 0.1 and 1 microM prolonged the decay of sIPSCs by approximately 25 and 70%, respectively. Isoflurane at 0.1, 0.25, and 0.5 mm prolonged sIPSCs by approximately 45, 150, and 240%, respectively. No drug-specific effects were observed on rise time or frequency of sIPSCs. Isoflurane at 0.5 mm caused a significant decrease in sIPSC amplitude. Conclusions The dose dependence of isoflurane effects on GABA(A) sIPSCs in pyramidal cells is consistent with effects on auditory evoked response in vivo. By contrast, comparable effects of midazolam on GABA(A) sIPSCs arise at concentrations exceeding those currently thought to be achieved in vivo, suggesting that the cellular targets of midazolam reside elsewhere in the thalamocortical circuit or that the concentration of midazolam reached in the brain is higher than currently believed.

Effects of volatile anesthetics on the kinetics of inhibitory postsynaptic currents in cultured rat hippocampal neurons

1993 ◽  
Vol 70 (4) ◽  
pp. 1339-1349 ◽  
Author(s):  
M. V. Jones ◽  
N. L. Harrison
Keyword(s):  
Charge Transfer ◽  
Gabaa Receptor ◽  
Hippocampal Neurons ◽  
Slow Component ◽  
Volatile Anesthetics ◽  
Fast Component ◽  
Synaptic Inhibition ◽  
Inhibitory Postsynaptic Currents ◽  
Postsynaptic Currents ◽  
Kinetics Of

1. The effects of the volatile anesthetics enflurane, halothane, and isoflurane on gamma-aminobutyric acid (GABA) receptor-mediated inhibitory postsynaptic currents (IPSCs) were studied in cultured rat hippocampal neurons. The experimental concentrations of anesthetics were measured directly using gas chromatography. All three anesthetics increased the overall duration of IPSCs, measured as the time to half-decay (T1/2). Clinically effective concentrations of anesthetics [between 0.5 and 1.5 times MAC (minimum alveolar concentration)] produced between 100 and 400% increases in T1/2. These effects were fully reversible, and did not involve alterations in the reversal potential for the IPSC (EIPSC). 2. The decay of the IPSC was fitted as a sum of two exponential functions, yielding a fast component (tau fast = 20 ms), and a slow component (tau slow = 77 ms), such that the fast component accounted for 79% of the IPSC amplitude and 52% of the total charge transfer. All three anesthetics produced concentration-related increases in the amplitude and charge transfer of the slow component, while simultaneously decreasing the amplitude and charge transfer of the fast component. Thus T1/2 approximated tau fast under control conditions, but approximated tau slow in the presence of the anesthetics. 3. Varying the calcium chelating agents in the recording pipettes had no effect on the quality or magnitude of alterations in IPSC kinetics produced by halothane, suggesting that variations in intracellular calcium levels are not required for the effect of halothane on the time course of the IPSC. 4. The (+)-stereoisomer of isoflurane produced greater increases in the duration of the IPSC than the (-)-isomer when applied at approximately equal concentrations, suggesting that there is a structurally selective site of interaction for isoflurane that modulates the GABAA receptor. 5. These results suggest that the previously shown abilities of volatile anesthetics to potentiate responses to exogenously applied GABA and to prolong the duration of GABA-mediated synaptic inhibition may be due to an alteration in the gating kinetics of the GABAA receptor/channel complex. Prolongation of synaptic inhibition in the CNS is consistent with the physiological effects that accompany anesthesia and may contribute to the mechanism of anesthetic action.

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