Neurosteroids Exhibit Differential Effects on mIPSCs Recorded From Normal and Seizure Prone Rats

2005 ◽  
Vol 94 (3) ◽  
pp. 2171-2181 ◽  
Author(s):  
Kerstin Schwabe ◽  
Cezar Gavrilovici ◽  
Dan C. McIntyre ◽  
Michael O. Poulter
Keyword(s):  
Time Course ◽  
Brain Slices ◽  
Perirhinal Cortex ◽  
Synaptic Activity ◽  
Inhibitory Input ◽  
Patch Clamp Recording ◽  
Rat Strains ◽  
Subunit Expression ◽  
Tonic Current ◽  
Α1 Subunit

In the perirhinal cortex of seizure prone (SP) rats, GABAA-mediated miniature inhibitory postsynaptic currents (mIPSCs) are smaller in amplitude but have longer deactivation phases than mIPSCs recorded in normal control (NC; outbred) rats. These differences in mIPSCs are correlated to the relatively higher α1 subunit expression in the NC rat strains and the higher α2, α3, and α5 subunit expression in the SP strain. Using patch-clamp recording, we investigated how the neurosteroids tetrahydrodeoxcorticosterone (THDOC) and allopregnanolone at physiological and pharmacological concentrations may differentially affect the mIPSCs in the perirhinal cortex of brain slices isolated from SP and NC rats. We found that 100 nM THDOC prolonged the time course and increased the amplitude of both the mono- and biphasic mIPSCs in the SP rats, but these effects were smaller in the NC rats. By comparison, allopregnanolone (100 nM) had small effects in both the NC and SP rats. At 1.0 μM, THDOC enhanced mIPSCs in both strains, but this effect was not greater in the SP rat than it was at 100 nM. By contrast, allopregnanolone (500 nM) enhanced the time course of the mIPSCs in both strains but it reduced mIPSC amplitudes as well. THDOC (100 nM) was much more effective than 100 nM allopregnanolone in inducing a tonic current in SP and NC rats. These data show that neurosteroids modulate synaptic activity at synapses having different biophysical behaviors. As differing GABAA receptors are targeted by subsets of interneurons, these data suggest these neurosteroids may selectively modulate one inhibitory input over another.

Altered desensitization produces enhancement of EPSPs in neocortical neurons

1994 ◽  
Vol 72 (2) ◽  
pp. 1032-1036 ◽  
Author(s):  
M. R. Pelletier ◽  
J. J. Hablitz
Keyword(s):  
Nmda Receptors ◽  
Time Course ◽  
Glutamate Release ◽  
Epileptiform Activity ◽  
Brain Slices ◽  
Synaptic Activity ◽  
Membrane Properties ◽  
Repetitive Firing ◽  
Resting Membrane Potential ◽  
Bath Application

1. Neocortical brain slices were prepared from rats (35–50 days of age) and maintained in vitro. Intracellular recordings were obtained from neurons in cortical layers II/III. The effect of bath application of cyclothiazide (CYZ), a potent blocker of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) receptor desensitization, on evoked synaptic activity and passive membrane properties was investigated. 2. Bath application of CYZ did not significantly affect resting membrane potential, input resistance, or repetitive firing. CYZ increased both the amplitude and duration of evoked excitatory postsynaptic potentials (EPSPs). Polysynaptic responses were also augumented. These effects persisted after the blockade of N-methyl-D-aspartate (NMDA) receptors with D-2-amino-5-phosphonovaleric acid (D-APV). The magnitude of these effects appeared to vary directly with stimulation intensity and presumably, amount of glutamate release. 3. Epileptiform activity was induced by bath application of bicuculline methiodide. The amplitude and duration of evoked paroxysmal discharges were increased by CYZ. Similar results were seen in presence of D-APV. 4. These results indicate that CYZ has significant effects on synaptic transmission. Desensitization of non-NMDA receptors may be an important mechanism for determining the time course of EPSPs and in curtailing epileptiform responses in the rat neocortex.

scholarly journals Inhibitory-excitatory synaptic balance is shifted toward increased excitation in magnocellular neurosecretory cells of heart failure rats

2011 ◽  
Vol 106 (3) ◽  
pp. 1545-1557 ◽  
Author(s):  
Evgeniy S. Potapenko ◽  
Vinicia C. Biancardi ◽  
Renea M. Florschutz ◽  
Pan D. Ryu ◽  
Javier E. Stern
Keyword(s):  
Heart Failure ◽  
Ampa Receptor ◽  
Time Course ◽  
Neurosecretory Cell ◽  
Brain Slices ◽  
Synaptic Strength ◽  
Neurosecretory Cells ◽  
Synaptic Function ◽  
Synaptic Activity ◽  
Excitatory Drive

Despite the well-established contribution of neurohumoral activation to morbidity and mortality in heart failure (HF) patients, relatively little is known about the underlying central nervous system mechanisms. In this study, we aimed to determine whether changes in GABAergic inhibitory and glutamatergic excitatory synaptic function contribute to altered hypothalamic magnocellular neurosecretory cell (MNC) activity in HF rats. Patch-clamp recordings were obtained from MNCs in brain slices from sham and HF rats. Glutamate excitatory (EPSCs) and GABAergic inhibitory postsynaptic currents (IPSCs) were simultaneously recorded, and changes in their strengths, as well as their interactions, were evaluated. We found a diminished GABAergic synaptic strength in MNCs of HF rats, reflected as faster decaying IPSCs and diminished mean IPSC charge transfer. Opposite changes were observed in glutamate EPSC synaptic strength, resulting in a shift in the GABA-glutamate balance toward a relatively stronger glutamate influence in HF rats. The prolongation of glutamate EPSCs during HF was mediated, at least in part, by an enhanced contribution of AMPA receptor desensitization to the EPSC decay time course. EPSC prolongation, and consequently increased unitary strength, resulted in a stronger AMPA receptor-mediated excitatory drive to firing discharge in MNCs of HF rats. Blockade of GABAA synaptic activity diminished the EPSC waveform variability observed among events in sham rats, an effect that was blunted in HF rats. Together, our results suggest that opposing changes in postsynaptic properties of GABAergic and glutamatergic synaptic function contribute to enhanced magnocellular neurosecretory activity in HF rats.

scholarly journals Cell Type–Specific GABAA Receptor–Mediated Tonic Inhibition in Mouse Neocortex

2008 ◽  
Vol 100 (1) ◽  
pp. 526-532 ◽  
Author(s):  
Irina Vardya ◽  
Kim R. Drasbek ◽  
Zita Dósa ◽  
Kimmo Jensen
Keyword(s):  
Fluorescent Protein ◽  
Brain Slices ◽  
Pyramidal Cells ◽  
Tonic Inhibition ◽  
Synaptic Activity ◽  
Inhibitory Input ◽  
Cell Type ◽  
Specific Expression ◽  
Cell Type Specific ◽  
Green Fluorescent

Activity of extrasynaptic GABAA receptors mediating tonic inhibition is thought to play an important role for the excitability of the mammalian cerebral cortex. However, little is known about the cell type–specific expression of tonic inhibition in particular types of cortical interneurons. Here, we used transgenic mice expressing green fluorescent protein (GFP) in somatostatin-positive (SOM) interneurons and investigated tonic inhibition in SOM interneurons versus pyramidal cells in neocortical layers 2/3. In brain slices, pyramidal cells showed a tonic current of 66 ± 19 pA in response to the δ-subunit selective GABAA agonist THIP (1 μM). On the other hand, tonic inhibition was absent in SOM interneurons (8 ± 1 pA) in response to THIP. As opposed to pyramidal cells, SOM interneurons were also insensitive to the δ-subunit preferring neurosteroid allotetrahydrodeoxycorticosterone (THDOC) (100 nM) and to elevated endogenous GABA levels in the slice. Finally, SOM interneurons received only 45% of the phasic charge transfer during GABAA receptor–mediated synaptic activity compared with pyramidal cells. Altogether, our study indicates that SOM interneurons receive relatively weak inhibitory input and cannot be brought under the influence of tonic inhibition.

scholarly journals Orexin depolarizes rat hypothalamic paraventricular nucleus neurons

2001 ◽  
Vol 281 (4) ◽  
pp. R1114-R1118 ◽  
Author(s):  
Tetsuro Shirasaka ◽  
Satoshi Miyahara ◽  
Takato Kunitake ◽  
Qing-Hua Jin ◽  
Kazuo Kato ◽  
...  
Keyword(s):  
Paraventricular Nucleus ◽  
Brain Slices ◽  
Hypothalamic Paraventricular Nucleus ◽  
Dependent Manner ◽  
Patch Clamp Recording ◽  
Concentration Dependent Manner ◽  
Whole Cell Patch Clamp ◽  
Orexin Receptors ◽  
Bath Application

Orexins, also called hypocretins, are newly discovered hypothalamic peptides that are thought to be involved in various physiological functions. In spite of the fact that orexin receptors, especially orexin receptor 2, are abundant in the hypothalamic paraventricular nucleus (PVN), the effects of orexins on PVN neurons remain unknown. Using a whole cell patch-clamp recording technique, we investigated the effects of orexin-B on PVN neurons of rat brain slices. Bath application of orexin-B (0.01–1.0 μM) depolarized 80.8% of type 1 ( n = 26) and 79.2% of type 2 neurons tested ( n = 24) in the PVN in a concentration-dependent manner. The effects of orexin-B persisted in the presence of TTX (1 μM), indicating that these depolarizing effects were generated postsynaptically. Addition of Cd2+(1 mM) to artificial cerebrospinal fluid containing TTX (1 μM) significantly reduced the depolarizing effect in type 2 neurons. These results suggest that orexin-B has excitatory effects on the PVN neurons mediated via a depolarization of the membrane potential.

scholarly journals GPI-1046 Increases Presenilin-1 Expression and Restores NMDA Channel Activity

2010 ◽  
Vol 37 (4) ◽  
pp. 457-467 ◽  
Author(s):  
Joseph P. Steiner ◽  
Kathryn B. Payne ◽  
Christopher Drummond Main ◽  
Sabrina D'Alfonso ◽  
Kirsten X. Jacobsen ◽  
...  
Keyword(s):  
Nmda Receptor ◽  
Synaptic Transmission ◽  
Brain Slices ◽  
Synaptic Activity ◽  
Presenilin 1 ◽  
Receptor Function ◽  
Channel Function ◽  
Nmda Channel ◽  
Nmda Receptor Function ◽  
6 Hydroxydopamine

Background:Previously we showed that 6-hydroxydopamine lesions of the substantia nigra eliminate corticostriatal LTP and that the neuroimmunolophilin ligand (NIL), GPI-1046, restores LTP.Methods:We used cDNA microarrays to determine what mRNAs may be over- or under-expressed in response to lesioning and/or GPI-1046 treatment. Patch clamp recordings were performed to investigate changes in NMDA channel function before and after treatments.Results:We found that 51 gene products were differentially expressed. Among these we found that GPI-1046 treatment up-regulated presenilin-1 (PS-1) mRNA abundance. This finding was confirmed using QPCR. PS-1 protein was also shown to be over-expressed in the striatum of lesioned/GPI-1046-treated rats. As PS-1 has been implicated in controlling NMDA-receptor function and LTP is reduced by lesioning we assayed NMDA mediated synaptic activity in striatal brain slices. The lesion-induced reduction of dopaminergic innervation was accompanied by the near complete loss of NDMA receptor-mediated synaptic transmission between the cortex and striatum. GPI-1046 treatment of the lesioned rats restored NMDA-mediated synaptic transmission but not the dopaminergic innervation. Restoration of NDMA channel function was apparently specific as the sodium channel current density was also reduced due to lesioning but GPI-1046 did not reverse this effect. We also found that restoration of NMDA receptor function was also not associated with either an increase in NMDA receptor mRNA or protein expression.Conclusion:As it has been previously shown that PS-1 is critical for normal NMDA receptor function, our data suggest that the improvement of excitatory neurotransmission occurs through the GPI-1046-induced up-regulation of PS-1.

An Extrasynaptic GABAA Receptor Mediates Tonic Inhibition in Thalamic VB Neurons

2005 ◽  
Vol 94 (6) ◽  
pp. 4491-4501 ◽  
Author(s):  
Fan Jia ◽  
Leonardo Pignataro ◽  
Claude M. Schofield ◽  
Minerva Yue ◽  
Neil L. Harrison ◽  
...  
Keyword(s):  
Critical Role ◽  
Brain Slices ◽  
Oscillatory Activity ◽  
Thalamic Neurons ◽  
Hek 293 ◽  
Subunit Protein ◽  
Whole Cell Patch Clamp ◽  
293 Cells ◽  
Hypnotic Agent ◽  
Tonic Current

Whole cell patch-clamp recordings were obtained from thalamic ventrobasal (VB) and reticular (RTN) neurons in mouse brain slices. A bicuculline-sensitive tonic current was observed in VB, but not in RTN, neurons; this current was increased by the GABAA receptor agonist 4,5,6,7-tetrahydroisothiazolo-[5,4-c]pyridine-3-ol (THIP; 0.1 μM) and decreased by Zn2+ (50 μM) but was unaffected by zolpidem (0.3 μM) or midazolam (0.2 μM). The pharmacological profile of the tonic current is consistent with its generation by activation of GABAA receptors that do not contain the α1 or γ2 subunits. GABAA receptors expressed in HEK 293 cells that contained α4β2δ subunits showed higher sensitivity to THIP (gaboxadol) and GABA than did receptors made up from α1β2δ, α4β2γ2s, or α1β2γ2s subunits. Western blot analysis revealed that there is little, if any, α3 or α5 subunit protein in VB. In addition, co-immunoprecipitation studies showed that antibodies to the δ subunit could precipitate α4, but not α1 subunit protein. Confocal microscopy of thalamic neurons grown in culture confirmed that α4 and δ subunits are extensively co-localized with one another and are found predominantly, but not exclusively, at extrasynaptic sites. We conclude that thalamic VB neurons express extrasynaptic GABAA receptors that are highly sensitive to GABA and THIP and that these receptors are most likely made up of α4β2δ subunits. In view of the critical role of thalamic neurons in the generation of oscillatory activity associated with sleep, these receptors may represent a principal site of action for the novel hypnotic agent gaboxadol.

scholarly journals Saccade-Related Inhibitory Input to Pontine Omnipause Neurons: An Intracellular Study in Alert Cats

1999 ◽  
Vol 82 (3) ◽  
pp. 1198-1208 ◽  
Author(s):  
Kaoru Yoshida ◽  
Yoshiki Iwamoto ◽  
Sohei Chimoto ◽  
Hiroshi Shimazu
Keyword(s):  
Initial Phase ◽  
Time Course ◽  
Inhibitory Input ◽  
Peak Time ◽  
Time Integral ◽  
Intracellular Study ◽  
Afferent Discharge ◽  
Alert Cats ◽  
Eye Velocity ◽  
Omnipause Neurons

Omnipause neurons (OPNs) are midline pontine neurons that are thought to control a number of oculomotor behaviors, especially saccades. Intracellular recordings were made from OPNs in alert cats to elucidate saccade-associated postsynaptic events in OPNs and thereby determine what patterns of afferent discharge impinge on OPNs to cause their saccadic inhibition. The membrane potential of impaled OPNs exhibited steep hyperpolarization before each saccade that lasted for the whole period of the saccade. The hyperpolarization was reversed to depolarization by intracellular injection of Cl− ions, indicating it consisted of temporal summation of inhibitory postsynaptic potentials (IPSPs). The duration of the saccade-related hyperpolarization was almost equal to the duration of the concurrent saccades. The time course of the hyperpolarization was similar to that of the radial eye velocity except for the initial phase. During the falling phase of eye velocity, the correlation between the instantaneous amplitude of hyperpolarization and the instantaneous eye velocity was highly significant. The amplitude of hyperpolarization at the eye velocity peak was correlated significantly with the peak eye velocity. The time integral of the hyperpolarization was correlated with the radial amplitude of saccades. The initial phase disparity between the hyperpolarization and eye velocity was due to the relative constancy of peak time (∼20 ms) of the initial steep hyperpolarization regardless of the later potential profile that covaried with the eye velocity. The initial steep hyperpolarization led the beginning of saccades by 15.9 ± 3.8 (SD) ms, which is longer than the lead time for medium-lead burst neurons. These results demonstrate that the pause of activity in OPNs is caused by IPSPs initiated by an abrupt, intense input and maintained, for the whole duration of the saccade, by afferents conveying eye velocity signals. We suggest that the initial sudden inhibition originates from central structures such as the superior colliculus and frontal eye fields and that the eye velocity-related inhibition originates from the burst generator in the brain stem.

scholarly journals Dopamine-Mediated Volume Transmission in Midbrain Is Regulated by Distinct Extracellular Geometry and Uptake

2001 ◽  
Vol 85 (4) ◽  
pp. 1761-1771 ◽  
Author(s):  
Stephanie J. Cragg ◽  
Charles Nicholson ◽  
June Kume-Kick ◽  
Lian Tao ◽  
Margaret E. Rice
Keyword(s):  
Point Source ◽  
Time Course ◽  
Volume Fraction ◽  
Extracellular Volume ◽  
Brain Slices ◽  
Extracellular Volume Fraction ◽  
Receptor Activation ◽  
Substantia Nigra Pars Compacta ◽  
Volume Transmission ◽  
Carbon Fiber Microelectrodes

Somatodendritic release of dopamine (DA) in midbrain is, at least in part, nonsynaptic; moreover, midbrain DA receptors are predominantly extrasynaptic. Thus somatodendritic DA mediates volume transmission, with an efficacy regulated by the diffusion and uptake characteristics of the local extracellular microenvironment. Here, we quantitatively evaluated diffusion and uptake in substantia nigra pars compacta (SNc) and reticulata (SNr), ventral tegmental area (VTA), and cerebral cortex in guinea pig brain slices. The geometric parameters that govern diffusion, extracellular volume fraction (α) and tortuosity (λ), together with linear uptake ( k′), were determined for tetramethylammonium (TMA+), and for DA, using point-source diffusion combined with ion-selective and carbon-fiber microelectrodes. TMA+-diffusion measurements revealed a large α of 30% in SNc, SNr, and VTA, which was significantly higher than the 22% in cortex. Values for λ and k′ for TMA+ were similar among regions. Point-source DA-diffusion curves fitted theory well with linear uptake, with significantly higher values of k′ for DA in SNc and VTA (0.08–0.09 s− 1) than in SNr (0.006 s− 1), where DA processes are sparser. Inhibition of DA uptake by GBR-12909 caused a greater decrease in k′ in SNc than in VTA. In addition, DA uptake was slightly decreased by the norepinephrine transport inhibitor, desipramine in both regions, although this was statistically significant only in VTA. We used these data to model the radius of influence of DA in midbrain. Simulated release from a 20-vesicle point source produced DA concentrations sufficient for receptor activation up to 20 μm away with a DA half-life at this distance of several hundred milliseconds. Most importantly, this model showed that diffusion rather than uptake was the most important determinant of DA time course in midbrain, which contrasts strikingly with the striatum where uptake dominates. The issues considered here, while specific for DA in midbrain, illustrate fundamental biophysical properties relevant for all extracellular communication.

scholarly journals Spontaneous Synaptic Activity Is Primarily GABAergic in Vestibular Nucleus Neurons of the Chick Embryo

2003 ◽  
Vol 90 (2) ◽  
pp. 1182-1192 ◽  
Author(s):  
Mei Shao ◽  
June C. Hirsch ◽  
Christian Giaume ◽  
Kenna D. Peusner
Keyword(s):  
Glutamate Receptor ◽  
Vestibular Nucleus ◽  
Glycine Receptor ◽  
Brain Slices ◽  
Reversal Potential ◽  
Cell Voltage ◽  
Synaptic Activity ◽  
Pipette Solution ◽  
Principal Cells ◽  
Postsynaptic Currents

The principal cells of the chick tangential nucleus are vestibular nucleus neurons participating in the vestibular reflexes. In 16-day embryos, the application of glutamate receptor antagonists abolished the postsynaptic responses generated on vestibular-nerve stimulation, but spontaneous synaptic activity was largely unaffected. Here, spontaneous synaptic activity was characterized in principal cells from brain slices at E16 using whole cell voltage-clamp recordings. With KCl electrodes, the frequency of spontaneous inward currents was 3.1 Hz at –60 mV, and the reversal potential was +4 mV. Cs-gluconate pipette solution allowed the discrimination of glycine/GABAA versus glutamate receptor-mediated events according to their different reversal potentials. The ratio for spontaneous excitatory to inhibitory events was about 1:4. Seventy-four percent of the outward events were GABAA, whereas 26% were glycine receptor-mediated events. Both pre- and postsynaptic GABAB receptor effects were shown, with presynaptic GABAB receptors inhibiting 40% of spontaneous excitatory postsynaptic currents (sEPSCs) and 53% of spontaneous inhibitory postsynaptic currents (sIPSCs). With TTX, the frequency decreased ∼50% for EPSCs and 23% for IPSCs. These data indicate that the spontaneous synaptic activity recorded in the principal cells at E16 is primarily inhibitory, action potential-independent, and based on the activation of GABAA receptors that can be modulated by presynaptic GABAB receptors.

Dynamic Recording of Cell Death in the In Vitro Dorsal Vagal Nucleus of Rats in Response to Metabolic Arrest

2003 ◽  
Vol 89 (1) ◽  
pp. 551-561 ◽  
Author(s):  
Michael Müller ◽  
Klaus Ballanyi
Keyword(s):  
Cell Death ◽  
Propidium Iodide ◽  
Neuronal Death ◽  
Time Course ◽  
Time Window ◽  
Membrane Integrity ◽  
Brain Slices ◽  
Limited Information ◽  
Histological Techniques ◽  
Metabolic Arrest

Anoxic/ischemic neuronal death is usually assessed in cell cultures or in vivo within a time window of 24 h to several days using the nucleic acid stain propidium iodide or histological techniques. Accordingly, there is limited information on the time course of such neuronal death. We loaded acute rat brain stem slices with propidium iodide for dynamic fluorometric recording of metabolic arrest-related cell death in the dorsal vagal nucleus. This model was chosen because dorsal vagal neurons show a graded response to metabolic inhibition: anoxia and aglycemia cause a sustained hyperpolarization, whereas ischemia induces a glutamate-mediated, irreversible depolarization. We found that the number of propidium iodide–labeled cells increased from 27% to 43% of total cell count within 1–7 h after preparation of slices. Compared with these untreated control slices, cyanide-induced anoxia (30 min) or aglycemia (1 h) did not cause further cell death, whereas 3-h aglycemia destroyed an additional 13% of cells. Ischemia (1 h) due to cyanide plus iodoacetate immediately labeled an additional 20% of cells, and an additional 48% of cells were destroyed within the following 3 h of postischemia. Continuous recording of propidium iodide fluorescence showed that loss of membrane integrity started within 25 min after onset of the ischemic depolarization and the concomitant intracellular Ca2+ rise. The results show that propidium iodide can be used to monitor cell death in acute brain slices. Our findings suggest that pronounced cell death occurs within a period of 1–4 h after onset of metabolic arrest and is apparently due to necrotic/oncotic mechanisms.

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