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Vm Oscillations (vm + oscillation)
Selected AbstractsTetanic stimulation of Schaffer collaterals induces rhythmic bursts via NMDA receptor activation in rat CA1 pyramidal neuronsHIPPOCAMPUS, Issue 4 2002Christian Bonansco Abstract Exploring the principles that regulate rhythmic membrane potential (Vm) oscillations and bursts in hippocampal CA1 pyramidal neurons is essential to understanding the , rhythm (,). Recordings were performed in vitro in hippocampal slices from young rats, and a group of the recorded CA1 pyramidal cells were dye-filled with carboxifluorescein and immunolabeled for the R1 subunit of the NMDA receptor. Tetanic stimulation of Schaffer collaterals (SCs) and iontophoresis of glutamate evoked rhythmic Vm oscillations and bursts (,10 mV, ,7 Hz, 2,5 spikes per burst) in cells (31%) placed close to the midline ("medial cells"). Rhythmic bursts remained under picrotoxin (10 ,M) and Vm oscillations persisted with tetrodotoxin (1.5 ,M), but bursts were blocked by AP5 (25 ,M) and Mg2+ -free solutions. Depolarization and AMPA never induced rhythmic bursts. The rest of the neurons (69%), recorded closer to the CA3 region ("lateral cells"), discharged rhythmically single repetitive spikes under SC stimulation and glutamate in control conditions, but fired rhythmic bursts under similar stimulation, both when NMDA was applied and when non-NMDA receptors were blocked with CNQX (20 ,M). Medial cells exhibited a larger NMDA current component and a higher NMDAR1 density at the apical dendritic shafts than lateral cells, suggesting that these differences underlie the dissimilar responses of both cell groups. We conclude that the ",-like" rhythmic oscillations and bursts induced by glutamate and SC stimulation relied on the activation of NMDA receptors at the apical dendrites of medial cells. These results suggest a role of CA3 pyramidal neurons in the generation of CA1 , via the activation of NMDA receptors of CA1 pyramidal neurons. Hippocampus 2002;12:434,446. © 2002 Wiley-Liss, Inc. [source] Integration of K+ and Cl, currents regulate steady-state and dynamic membrane potentials in cultured rat microgliaTHE JOURNAL OF PHYSIOLOGY, Issue 3 2005Evan W. Newell The role of ion channels and membrane potential (Vm) in non-excitable cells has recently come under increased scrutiny. Microglia, the brain's resident immune cells, express voltage-gated Kv1.3 channels, a Kir2.1-like inward rectifier, a swelling-activated Cl, current and several other channels. We previously showed that Kv1.3 and Cl, currents are needed for microglial cell proliferation and that Kv1.3 is important for the respiratory burst. Although their mechanisms of action are unknown, one general role for these channels is to maintain a negative Vm. An impediment to measuring Vm in non-excitable cells is that many have a very high electrical resistance, which makes them extremely susceptible to leak-induced depolarization. Using non-invasive Vm -sensitive dyes, we show for the first time that the membrane resistance of microglial cells is several gigaohms; much higher than the seal resistance during patch-clamp recordings. Surprisingly, we observed that small current injections can evoke large Vm oscillations in some microglial cells, and that injection of sinusoidal currents of varying frequency exposes a strong intrinsic electrical resonance in the 5- to 20-Hz frequency range in all microglial cells tested. Using a dynamic current clamp that we developed to actively compensate for the damage done by the patch-clamp electrode, we found that the Vm oscillations and resonance were more prevalent and larger. Both types of electrical behaviour required Kv1.3 channels, as they were eliminated by the Kv1.3 blocker, agitoxin-2. To further determine how the ion currents integrate in these cells, voltage-clamp recordings from microglial cells displaying these behaviours were used to analyse the biophysical properties of the Kv1.3, Kir and Cl, currents. A mathematical model that incorporated only these three currents reproduced the observed Vm oscillations and electrical resonance. Thus, the electrical behaviour of this ,non-excitable' cell type is much more complex than previously suspected, and might reflect a more common oversight in high resistance cells. [source] | ||||||||||