| 1. |
- Karlsson, Anna, et al.
(författare)
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Altered spontaneous synaptic inhibition in an animal model of cerebral heterotopias.
- 2011
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Ingår i: Brain research. - : Elsevier BV. - 1872-6240 .- 0006-8993. ; 1383, s. 54-61
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Tidskriftsartikel (refereegranskat)abstract
- We have investigated spontaneous synaptic transmission in hippocampal nodular heterotopias in rats exposed to methylazoxymethanol (MAM) in utero. Pregnant Wistar rats were injected with MAM at E16. Acute hippocampal slices were prepared from the rat pups P14 to P40. Whole-cell voltage-clamp recordings were made from visually identified neurons using IR-DIC video microscopy. Synaptic events were recorded from either heterotopic neurons in the CA1 region or "slice-matched" normotopic CA1 pyramidal neurons. Both the spontaneous inhibitory (sIPSC) and excitatory synaptic transmission (sEPSC) to the same neurons were recorded. We found a profound reduction in the frequency of sIPSCs in the heterotopic neurons vs. normotopic neurons. No significant differences in the frequency of sEPSCs were found. We also found a profound reduction in the frequency of spontaneous IPSCs in normotopic neurons following application of the GABA reuptake blocker, NO-711, even in the presence of a GABA(B) receptor antagonist (CGP 55845). Preferentially blocking extrasynaptic GABA(A) receptors caused an increased frequency of sIPSCs in the heterotopic neurons. Our data suggest that there is a predominant change in inhibitory synaptic transmission, as measured by changes in sIPSCs, with no change in excitatory synaptic transmission to heterotopic neurons in hippocampus of rats exposed to MAM in utero. We suggest that this change is caused by an increase in the extracellular concentration of GABA but is not mediated via activation of presynaptic GABA(B) receptors. Rather, we propose that the increased extracellular GABA concentration in the heterotopias dampens the activity in inhibitory neurons via activation of extrasynaptic GABA(A) receptors.
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| 2. |
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| 3. |
- Lim, MSF, et al.
(författare)
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Effects of pentobarbital on GABA-activated currents in acutely-isolated rat dentate gyrus granule neurons
- 2003
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Ingår i: Neuroscience Letters. - : Elsevier BV. - 0304-3940 .- 1872-7972. ; 353:2, s. 139-142
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Tidskriftsartikel (refereegranskat)abstract
- Granule neurons from the rat dentate gyrus were acutely isolated and whole-cell currents recorded. Maximal enhancement of 7 muM gamma-aminobutyric acid (GABA; EC30) evoked currents was obtained with 100 muM pentobarbital where the peak-current was 2.1 +/- 0.2 of control. One hundred muM pentobarbital alone evoked no current response whereas I mM pentobarbital elicited a current response that was 0.4 +/- 0.2 of the 100 muM GABA-activated peak current. In 100 muM pentobarbital, the GABA EC50 value shifted from 14 to 3 muM but the peak-saturating-current value was not altered. An off-current was recorded on removal of 100 muM and higher pentobarbital concentrations. Ten mM pentobarbital abolished the peak-current response to 7 and 100 muM GABA. The results show that in the granule neurons the drug potency differs for the different effects of pentobarbital at GABA(A) receptors with the modulatory and inhibitory effects requiring lower concentrations than the direct activation of the receptors. (C) 2003 Elsevier Ireland Ltd. All rights reserved.
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| 4. |
- Lindquist, Catarina, et al.
(författare)
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Extrasynaptic GABA(A) channels activated by THIP are modulated by diazepam in CA1 pyramidal neurons in the rat brain hippocampal slice
- 2003
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Ingår i: Molecular and Cellular Neuroscience. - 1044-7431 .- 1095-9327. ; 24:1, s. 250-257
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Tidskriftsartikel (refereegranskat)abstract
- Single-channel currents were activated by THIP (4,5,6,7-tetrahydroisoxazolo[5,4-c]pyridin-3-ol) in cell-attached patches on CA1 pyramidal neurons in the rat hippocampal slice preparation. THIP activated GABA(A) channels after a delay that was concentration-dependent and decreased by 1 muM diazepam. The currents showed outward rectification. Channels activated at depolarized 40 mV relative to the chloride reversal potential had low conductance (<40 pS) but the conductance increased with time, resulting in high-conductance channels (>40 pS). The average maximal-channel conductances for 2 and 100 muM THIP were 59 and 62 pS (-Vp = 40 mV), respectively, whereas in 2 muM THIP plus 1 muM diazepam, it was 71 pS. The results show that in hippocampal neurons THIP activates channels with characteristics similar to those of channels activated by low concentrations (0.5-5 AM) of GABA. The increase in the inhibitory conductance with membrane depolarization permits gradation of the shunt pathway relative to the level of the excitatory input. (C) 2003 Elsevier Science (USA). All rights reserved.
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| 5. |
- Lindquist, Catarina, et al.
(författare)
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Graded response to GABA by native extrasynaptic GABA(A) receptors
- 2006
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Ingår i: Journal of Neurochemistry. - : Wiley. - 1471-4159 .- 0022-3042. ; 97:5, s. 1349-1356
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Tidskriftsartikel (refereegranskat)abstract
- GABA is the main inhibitory neurotransmitter in the mammalian CNS. GABA in the brain is commonly associated with a fast, point-to-point form of signalling called synaptic transmission (phasic inhibition), but there is growing evidence that GABA participates in another, slower and more diffuse form of signalling often referred to as tonic inhibition. Unresolved questions regarding tonic neuronal inhibition concern activation and functional properties of extrasynaptic GABA(A) receptors (GABARex) present on neurones. Extrasynaptic receptors are exposed to submicromolar GABA concentrations and may modulate the overall excitability of neurones and neuronal networks. Here, we examined GABA-activated single-channel currents in dentate gyrus granule neurones in rat hippocampal slices. We activated three types (I, II, III) of GABARex channels by nanomolar GABA concentrations (EC50 I: 27 +/- 12; II: 4 +/- 3; III: 43 +/- 19 nM). The channels opened after a delay and the single-channel conductance was graded (gamma(max) I: 61 +/- 3; II: 85 +/- 8, III: 40 +/- 3 pS). The channels were differentially modulated by 1 mu M diazepam, 200 nM zolpidem, 1 mu M flumazenil and 50 nM THDOC (3 alpha, 21-dihydroxy-5 alpha-pregnan-20-one), consistent with the following minimal subunit composition of GABARex I alpha(1)beta gamma(2), GABARex II alpha(4)beta gamma(2) and GABARex III alpha beta delta channels.
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| 6. |
- Lindquist, Catarina, et al.
(författare)
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Penicillin blocks human alpha(1)beta(1) and alpha(1)beta(1)gamma(2S) GABA(A) channels that open spontaneously.
- 2004
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Ingår i: European Journal of Pharmacology. - : Elsevier BV. - 1879-0712 .- 0014-2999. ; 496:1-3, s. 23-32
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Tidskriftsartikel (refereegranskat)abstract
- We used the open-channel blocker, penicillin (10 mM), as a tool to investigate if the human α1β1 or α1β1γ2S γ-aminobutyric acid type A (GABAA) receptor channels opened in the absence of GABA. Application of penicillin to cells expressing the receptors resulted in a transient inward whole-cell current, the off-current, upon penicillin removal. The amplitude of the off-current was dependent on the duration of the penicillin application, it reversed in polarity at depolarized potentials and exhibited “run-down” similar to the GABA-activated currents. Bicuculline (100 μM) blocked the off-current response. Pentobarbital (50 μM) enhanced the peak off-current amplitude by 2.8 and 3.4 in α1β1 and α1β1γ2S receptors, respectively. Diazepam (1 μM) only enhanced the off-current peak response in α1β1γ2S receptors (1.6) and induced the development of an inward current when applied alone. The results are consistent with that the α1β1 or α1β1γ2S GABAA receptors can open in the absence of GABA and raise the question of what role spontaneous channel openings have in the function of GABAA receptors.
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| 7. |
- Lindquist, Catarina
(författare)
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Physiology and Pharmacology of GABAA receptors: The Brakes in the Brain
- 2005
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Inhibitory neurotransmission in the brain is mostly mediated by gamma-aminobutyric acid type A (GABAA) receptors. These receptors are involved in both phasic inhibition (point-to-point inhibition, synaptic transmission) and tonic inhibition (diffuse form of inhibition, brain homeostasis). In this thesis the functional and pharmacological properties of GABAA receptors expressed in brain slices or in Sf 9 cells were studied. GABAA receptors expressed extrasynaptically are believed to be involved in tonic inhibition. In hippocampal dentate gyrus granule cells we identified and characterized three types of extrasynaptic receptor types (GABARex) that varied in their affinity for GABA, maximal single-channel conductance and sensitivity to drugs. For the first time we showed how the GABA concentration determines the conductance of GABAA receptors in brain tissue. There is thus a direct link between the extracellular GABA concentration and the level of the tonic inhibition, providing dynamic control. It is only within the last ten years or so that the tonic inhibition was discovered and only recently has it gained widespread interest. One reason is that it has become quite clear that the first site of action and probably often the most important site of action of drugs are the extrasynaptic receptors. We found that a drug now in clinical trials (THIP) at the clinically relevant concentration activates these extrasynaptic receptors. It has been assumed that spontaneous openings of the receptors are only functionally significant in receptor complexes containing the epsilon-subunit or mutations. We show that alpha/beta and alpha/beta/gamma?receptors can open spontaneously and be modified by drugs. The capacity to open spontaneously may be vital for fast responses such as at synapses. This suggests that the functional properties of receptors located at synapses and outside of synapses (extrasynaptic receptors: GABARex) differ. Those at synapses open rapidly (ms) whereas those at extrasynaptic sites open after a delay of ten to hundreds of seconds. This functional difference is very important in terms of brain function as it ensures fast flow of information (synaptic transmission) but in a controlled way that is set by the gain and the time window for synaptic transmission integration via the tonic inhibition. By using the compound SR95531, we constructed a model that accounts for activation and inhibition of both phasic- and tonic-like currents in an expression system. This model can be used to calculate what concentrations of the inhibitor to use to specifically block certain GABARex receptors in brain tissue to study how a particular population of GABARex contributes to the tonic inhibition and how it affects both excitatory and inhibitory synaptic transmission.
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| 8. |
- Lindquist, Catarina, et al.
(författare)
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The mechanism of SR95531 inhibition at GABA receptors examined in human alphabeta and alphabetagamma receptors.
- 2005
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Ingår i: Journal of Neurochemistry. - : Wiley. - 1471-4159 .- 0022-3042. ; 94:2, s. 491-501
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Tidskriftsartikel (refereegranskat)abstract
- We examined the interaction of GABA and the competitive inhibitor SR95531 at human α1β1γ2S and α1β1 GABAA receptors expressed in Sf9 cells. The efficacy and potency of inhibition depended on the relative timing of the GABA and SR95531 applications. In saturating (10 mm) GABA, the half-inhibitory concentrations of SR95531 (IC50) when coapplied with GABA to α1β1γ2S or α1β1 receptors were 49 and 210 µm for the peak and 18 and 130 µm for the plateau current, respectively. Our data are explained by an inhibition mechanism in which SR95531 and GABA bind to two sites on the receptor where the binding of GABA allows channel opening but SR95531 does not. The SR95531 affinity for both receptor types was ~200 nm and the binding rate was found to be 10-fold faster than that for GABA. The dual binding-site model gives insights into the differential effects of GABA and SR95531 on the peak and plateau currents. The model predicts the effect of SR95531 on GABA currents in the synapse (GABA concentration ~ mm) and at extrasynaptic (GABA concentration ≤ µm) sites. The IC50 (50–100 nm) for the synaptic response to SR95531 was insensitive to the GABA affinity of the receptors whereas the IC50 (50–800 nm) for extrasynaptic inhibition correlated with the GABA affinity.
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| 9. |
- Smith, Morten, et al.
(författare)
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Evidence for inhibitory effect of the agonist gaboxadol at human alpha(1)beta(2)gamma S-2 GABA(A) receptors
- 2003
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Ingår i: European Journal of Pharmacology. - : Elsevier BV. - 1879-0712 .- 0014-2999. ; 478:1, s. 21-26
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Tidskriftsartikel (refereegranskat)abstract
- Gaboxadol (THIP; 4,5,6,7-tetrahydroisoxazolo[5,4-c]pyridin-3-ol) is an agonist at GABA(A) receptors. THIP concentrations (0.01-50 mM) were applied rapidly to Sf9 cells expressing the human alpha(1)beta(2)gamma(2S) GABA(A) receptors. The EC50 values for the peak current in THIP alone or THIP plus 1 muM diazepam were 154 and 53 muM, respectively. In supersaturating THIP (10-50 mM) the rate of current decay increased and an off-current developed when THIP was rapidly removed. The mean currents measured over the first 4 s in 10 mM and higher THIP concentrations were 0.6 or less of the 1 mM THIP mean current. Diazepam (1 muM) increased the 4 s mean current when evoked by 10 to 20 mM THIP but not 50 mM THIP. No similar effects on the current time-course were recorded in supersaturating gamma-aminobutyric acid (GABA) concentrations (50 and 80 mM). The results demonstrate an inhibitory as well as agonist effect of THIP at alpha(1)beta(2)gamma(2s) GABA(A) receptors. (C) 2003 Elsevier B.V. All rights reserved.
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| 10. |
- Strandberg, Joakim, 1978, et al.
(författare)
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The endogenous peptide antisecretory factor promotes tonic GABAergic signaling in CA1 stratum radiatum interneurons
- 2014
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Ingår i: Frontiers in Cellular Neuroscience. - : Frontiers Media SA. - 1662-5102. ; 8
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Tidskriftsartikel (refereegranskat)abstract
- Tonic GABAergic inhibition regulates neuronal excitability and has been implicated to be involved in both neurological and psychiatric diseases. We have previously shown that the endogenous peptide antisecretory factor (AF) decreases phasic GABAergic inhibition onto pyramidal CA1 neurons. In the present study, using whole-cell patch-clamp recordings, we investigated the mechanisms behind this disinhibition of CA1 pyramidal neurons by AF We found that application of AF to acute rat hippocampal slices resulted in a reduction of the frequency, but not of the amplitude, of spontaneous inhibitory postsynaptic currents (sIPSCs) in CA1 pyramidal neurons. Miniature inhibitory postsynaptic currents (mIPSCs), recorded in the presence of tetrodotoxin (TTX), were however not affected by AF, neither in CA1 pyramidal cells, nor in stratum radiatum interneurons. Instead, AF caused an increase of the tonic GABA(A) current in stratum radiaturn intemeurons, leaving the tonic GABAergic transmission in CA1 pyramidal cells unaffected. These results show that the endogenous peptide AF enhances tonic, but not phasic, GABAergic signaling in CA1 stratum radiatum interneurons, without affecting tonic GABAergic signaling in CA1 pyramidal neurons. We suggest that this increased tonic GABAergic signaling in GABAergic interneurons could be a mechanism for the AF mediated disinhibition of pyramidal neurons.
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