Neurophysiology Voltage Clamp Quiz

Molecular Neurophysiology: From Molecules to Systems

• The presentation is about molecular neurophysiology, focusing on the transition from molecules to systems.
• The speaker, Jochen Winterer, is from the Lab of Systems Neuroscience and the Institute for Neuroscience at ETH Zurich.
• The presentation includes diagrams and figures illustrating synaptic complexes, pre- and postsynaptic elements, and a canonical design of a central synapse.
• The lecture highlights the interplay between electrical and chemical signaling at the synapse.

Synaptic Complex

• The previous lecture covered electrical signaling, transforming it into a chemical signal at the presynaptic terminal.
• This lecture focuses on the postsynaptic side of the synapse, demonstrating how the chemical signal is translated back into an electrical signal.

Postsynaptic and Transsynaptic Signaling

• This section introduces the concept of postsynaptic and transsynaptic signaling in neurophysiology.
• It emphasizes the importance of the postsynaptic receptors and synaptic cell adhesion molecules.

Canonical Design of a Central Synapse

• The canonical design of a central synapse is discussed, featuring postsynaptic receptors, scaffold (postsynaptic density), and synaptic cell adhesion molecules.
• Components of the presynaptic terminal and postsynaptic cell are highlighted.
• Vesicles, active zones, and other specialized areas are identified.

Postsynaptic Receptors of Neurotransmitters

• Glutamate and GABA are the most prevalent excitatory and inhibitory neurotransmitters in mammalian brains, respectively.
• Postsynaptic receptors for glutamate include ionotropic receptors (AMPAR, NMDAR, Kainate-Rs) and metabotropic receptors (mGluRs).
• Postsynaptic receptors for GABA include ionotropic (GABAA-Rs, GABAB-Rs) and metabotropic receptors.

Glutamatergic and GABAergic Synaptic Transmission

• Glutamatergic transmission leads to depolarization.
• GABAergic transmission leads to hyperpolarization.
• Examples of signals (EPSPs and IPSPs) and their effects are shown graphically.

Synaptic Transmission

• Synapses act as fundamental computational units within neuronal circuits.
• Precise interactions between pre- and postsynaptic neurons shape synaptic properties by using different neurotransmitters and their receptors for the excitation/inhibition.
• Postsynaptic receptor properties dictate the outcomes of activation, by defining which ion fluxes cause depolarization or hyperpolarization.

How to Depolarize/Hyperpolarize a Cell

• Depolarization and hyperpolarization are caused by influx or efflux of ions (cations/anions).
• These processes are not always obvious because of the complexities of the membrane transport mechanisms.

Questions/Learning Objectives

• The presentation outlines questions about the properties of postsynaptic receptors, their anchoring mechanisms, and the role of synaptic adhesion molecules.
• Receptor measurement methods are discussed as learning objectives to characterize their properties.

How to Measure AMPA-R Mediated Excitatory Postsynaptic Potentials/Signals

• Whole-cell patch-clamp allows measuring membrane voltage.
• Current-clamp mode follows the voltage change in the cell membrane.
• Voltage-clamp mode measures current to control the voltage.

Characterizing AMPA-R

• Characterization methods are described, including using quisqualate and recording outward/inward currents.
• How to interpret the results are discussed

I/V Curve

• The relationship between current (I) and voltage (V) is described by the I/V curve.
• Current flow (outward or inward) depends on the voltage where it is measured.

Quick Recap: Ion Concentrations and Membrane Potential

• The presentation reminds students about ion concentrations (intracellular and extracellular) and their gradients, as well as their significance in generating the membrane potential.
• Concentration and electrical gradients are essential in ion transportation/movement

Quick Recap: Ion Concentrations and Membrane Potential

• Equilibrium potential (E_ion) is described with reference to the Nernst equation in combination with membrane potentials.
• Membrane potential differences are compared to equilibrium potentials to determine the direction of the ion flux.

Characterization of the AMPA Receptor

• The method for obtaining unitary currents as a function of holding membrane potential was discussed.

• The presentation explains how to derive and use the equilibrium potential to determine the permeabilities of the ion channels.

Characterization of the AMPA-R

• The effect of changing external Na+ concentration on reversal potential helps identify Na+ permeability.

Summary

• The AMPA receptor permits the passage of Na+ and K+ ions.

Structure and Subunit Composition of AMPA-R

• AMPA receptors are tetramers composed of GluA1, GluA2, GluA3, and GluA4 subunits.
• Different subunit combinations lead to functional distinctions, important in neuronal physiology

AMPA-R Editing

• Editing of GluA2, a process occurring at the M2 transmembrane domain, is described.
• The conversion of glutamine to arginine at codon 586 leads to different Ca2+ permeabilities.

Channel Conductance of GluA2 Containing vs. Lacking AMPA Receptors

• Differences in channel conductance between GluA2-containing and GluA2-lacking AMPA receptors.

GluA2-Editing in Amyotrophic Lateral Sclerosis (ALS)

• Reduced ADAR2 expression in sporadic ALS may affect GluA2 editing leading to Ca2+ permeability and excitotoxicity.
• Ca2+ excitotoxicity is a crucial mechanism contributing to neuronal death in ALS.

Summary

• The summarized information regarding the differences between AMPA receptor subtypes, particularly GluA2-containing and GluA2-lacking receptors.

GABA_A-R Mediated Inhibitory Postsynaptic Potential/Current

• Transmission using GABA and its influence on postsynaptic potentials, and how it can be measured.

Characterizing GABA_A-R Mediated Ion Flux

• The permeable ions across the GABAA receptor are identified, specifically, Cl-.

Intracellular Cl- Concentration Dictates Polarity of Current through GABA_A Receptors

• Intracellular Cl- concentration significantly impacts the polarity of current through GABA_A receptors.
• GABA can be depolarizing.

GABA is Depolarizing During Development

• GABA's role and impact during brain development, where it might be depolarizing rather than inhibitory in immature neurons.

E_GABA During Development

• The change in GABA equilibrium potential (E_GABA) during development is correlated to the change of intracellular chloride concentration (and the timing of expression of ion transporters).

Summary

• The summarized information regarding the different effects, inhibitory and excitatory, that GABA can have based on its influence on intracellular chloride concentration.

The NMDA Receptor

• NMDA receptor-mediated EPSPs are broader than other EPSPs.

Characterization of the NMDA Receptor

• The presentation details how the method to study the NMDA receptor, in particular how to obtain the I/V curve and the involvement of Mg²⁺ ions.

Effect of Physiological [Mg²⁺]_out on the NMDA-R

• NMDA receptors exhibit voltage-dependent Mg²⁺ block.
• The influx of Mg²⁺ alters the shape of the I/V curve.

The NMDA Channel is Highly Permeable to Monovalent Cations and to Ca²⁺

• The NMDA receptor exhibits high permeability to monovalent cations and Ca²⁺.
• The concentration of extracellular Ca²⁺ affects the receptor's current responses.

Summary

• The different qualities unique to NMDA receptors.

Definition of Anatomical and Functional Parts of a Synapse

• Parts of the synapse and their function.

Postsynaptic Scaffold

• The scaffold (postsynaptic density, PSD), including anchoring of postsynaptic neurotransmitter receptors and their interactions using proteins like MAGUKs (especially PSD95) and their PDZ domains.

MAGUKs are Essential for Anchoring AMPA and NMDA Receptor Complexes at the Postsynaptic Density

• Evidence that MAGUKs are crucial for the anchoring of the AMPA and NMDA receptors on the postsynaptic density, and experimental approaches that demonstrate this.

Transsynaptic Signaling

• SAMs are described as synaptic organizers, including their pre- and postsynaptic signaling pathways

SAMs, the "making" and "shaping" of synapses

• The role of synaptic cell adhesion molecules (SAMs) in synapse formation and maturation is described.
• Data shows how changes in these SAMs impact synapse properties.

Cell-Adhesion Molecules and the Postsynaptic Density Protein Shank in Neurodevelopmental Disorders

• Overview of cell adhesion molecules (CAMs) and their involvement in neurodevelopmental disorders.
• The role of SHANK, a postsynaptic density protein, in ASD, schizophrenia, epilepsy, and intellectual disabilities.

Summary

• PSD, its function in holding neurotransmitter receptors.
• SAMs, their function in synaptic signaling and regulation.

Summary

• The overview of findings regarding the postsynaptic density (PSD) and SAMs (synaptic adhesion molecules) emphasizing their function in the brain and implications in disorders.

Test your understanding of voltage clamp techniques and their applications in neurophysiology. This quiz covers key concepts such as membrane potential, ion movement, and the effects of various ions on current reversal. Perfect for students and enthusiasts looking to deepen their knowledge in this area.