Module 4Soléy ValenciaCBNS 130L

Electrophysiology

Abstract

Through, “My First Neuron” I observed the different ways EPSP and IPSP work in accordance with GABA A, GABA B, NMDA, and AMPA receptors by altering the concentration, base current, initial

voltage and conductances of each.

IntroductionKatherine Whalley in 2012 published a paper on memory which involved NMDA receptors. She found that the basal ganglia is essential for neurogenesis to occur through repeated actions.The way dopamine acts to modulate learning is still unclear but she found that mice that had dopamine excised showed a decrement in learning habits. This suggests that NMDA receptors passing dopamine is critically important. Gordon B Feld, et.al recently published an article on sleep consolidation titled, “Sleep-Dependent Declarative Memory Consolidation—Unaffected after Blocking NMDA or AMPA Receptors but Enhanced by NMDA Coagonist d-Cycloserine,” in which they explain that reactivation of glutamate driven neurons are the key components in charge of synaptic changes that give rise to long-term memory. To test their hypothesis they administered ketamine (NMDA blocker) and Caroverine (AMPA blocker) during sleep retention and declarative memory;it was not effective. But, in the third experiment they added coagonist d-cycloserine an NMDA receptor, in which case they observed consolidation of declarative memory during retention sleep.

Methods & MaterialsMy First Neuron

Excitatory Postsynaptic Potential: Set IPSP to zero then changed the base current to 1.78nA and the initial voltage to 20mV and compare the graphs to each other.

NMDA Current Clamp: Set the NMDA voltage clamp to make a graph and compared this graph with another I set to -0.52nA and the initial voltage to -90mV. Then I set the base current to -0.52nA and initial voltage to -90mV and magnesium concentration to 0.01mM and compared it to the graph before. I then made the base current to 0.525nA and the initial voltage to -30mV and compared this graph to another I set the with base current of 0.525nA and the initial voltage -30mV and the magnesium concentration outside to 0.01mM.

NMDA Voltage Clamp: I set the graph with a voltage clamp under default settings and compared it with another graph I set under the same conditions as well as changing the external magnesium concentration to 0.001mM.

AMPA receptor with Voltage Clamp: Changed AMPA conductance to one and set all other conductances to zero, then I compared it to another graph I had set with an AMPA conductance to fifty. And repeated the same steps for the NMDA receptor.

Observed IPSP receptor: Ran the default settings and compared this graph with another I set with base current to -0.38nA and initial voltage to -85mV. Then, under these same settings I also changed the external chloride concentration to 7mM. I then compared the graph to change the base current to 0.5nA and the external potassium concentration to 25mM.

IPSP+EPSP: I set the EPSP conductance to zero and the GABA a conductance to 0.2nS. I compared this graph with another graph I set the EPSP conductance to 0.15nS.

Since its EPSP we see higher AMPA current than NMDA because it activates much faster. AMPA current is non selective its reversal potential is close to zero. Since the initial voltage changed from -55mV to 20mV AMPA action potential reaches close to

0.35mV

IPSP gmax= 0

Excitatory Postsynaptic potential

IPSP gmax= 0Base Current= 1.78nA

Initial Voltage 20

AMPA conductance is zero. NMDA conductance decreases in size when the Initial voltage becomes more negative.

NMDA Current Clamp

NMDA Current ClampDefault Settings

Base Current from 0 to -0.52mVInitial Voltage from -55mV to -90mV

NMDA current is larger in amplitude when we lower the concentration of magnesium outside. There is still a significant positive difference in the curves

even when I made the Base current -0.52mV and the Initial voltage more negative, the curve was still more positive because I had lowered the

concentration of magnesium outside of the cell.

NMDA Current Clamp

[Mg++]out from 1.2mM to 0.1mMInitial Voltage -90mV Base Current -0.52

Base Current from 0 to -0.52mVInitial Voltage from -55mV to -90mV

By making the base current more positive at a value of 0.525nA it increases the curve to a more positive voltage, and even more so after I lower the magnesium

concentration outside the cell.

Base Current from 0 to 0.525nAInitial Voltage from -55mV to -30mV

NMDA Current Clamp

[Mg++]out from 1.2mV to 0.1mVBase Current 0.525nAInitial Voltage -30mV

The wide curve lets me know that NMDA current is non selective because after I held it at -20mV voltage its distribution was very wide. When I decrease the magnesium concentration outside the cell, it became more positive because the is not enough

magnesium to inhibit the opening of the NMDA channel.

NMDA Voltage Clamp

Default Settings [Mg++]out from 1mM to 0.001mM

NMDA is set to zero. As AMPA conductance increases the the curve moves towards from 0.1mV to 5mV. increases positively.

AMPA Voltage Clamp

w_ampa =1w_nmda =0

IPSP gmax =0

w_ampa =50w_nmda =0

IPSP gmax =0

Increasing conductibility of NMDA from 1 to 50 leads to a curve from 0.025mV to 1.4mV. Since NMDA conductance increases and its a non selective channel, it allows

passage of ions forming an inward curve from -0.5mV to -25mV.

AMPA Voltage Clamp

w_ampa =0w_nmda =1

IPSP gmax =0

w_ampa =0w_ndma =50

IPSPS gmax =0

Since both AMPA and NMDA receptors are glutamatergic channels so, I set everything else to zero to observe IPSP.

Inhibitory Postsynaptic Potentials

Default Settings Base Current from 0 to -0.38nAInitial Voltage from -55mV to -85mV

When the concentration of chloride outside the cell is reduced from 120mM to 7mM the curve will move towards more positive value given that, chloride will move down

its concentration gradient to reach chloride concentration. Potassium concentration outside is increased from 3.1mM to 25mM so that potassium

will want to move inside the cell, making the cell more positive.

Inhibitory Postsynaptic Potentials

Base Current from 0 to -0.38nAInitial Voltage from -55mV to -85mV

[Cl-]out from 120mM to 7mM

Base Current =-0.5nA[K+]out from 3.1mM to 25mM

Excitatory EPSP and Inhibitory IPSP changes the reversal potential and the driving force

IPSP + EPSP

Default Settings EPSP gmax =0IPSP gmax =0.15w_gabaA =0.2w_gabaB =0

We see a more positive curve move from -60mV to -50mV because EPSP conductance is also open

IPSP + EPSP

EPSP gmax =0.15IPSP gmax =0.15w_gabaA =0.2w_gabaB =0

Default Settings

Discussion- GABAa is inhibitory neurotransmitter, and is a Chloride channel. Chloride equilibrium potential is between -70mV and -75mV.

- When GABAa current moves very little when its close to its reversal potential near -75mV

- GABAb is inhibitory neurotransmitter, and is a Potassium channel. Because it opens at a slower rate than GABAa, it has the capability to hyperpolarize the cell more than GABAa. Potassium equilibrium potential is -95mV.

- NMDA is non-selective so its reversal potential is at 0. NMDA has a magnesium block. When current is close to 0, the response is higher in amplitude compared to Action Potentials seen at higher depolarization. When there is no magnesium block there is a very high amplitude because when NMDA is close to its reversal potential you get a smaller response at very depolarized potential.

- Bicuculline blocks GABAa and removes inhibition causing Excitability and numerous Action Potentials.

- AMPA is a non-selective ion channel that can pass potassium, sodium, magnesium, and calcium with a reversal potential of 0.

- GABAa and AMPA are fast synaptic conductance but are slower than sodium channels because GABAa and AMPA need time to diffuse and bind.

- Synaptic current depends on Maximum Conductance and Driving Force and how far you are from the reversal potential.

Literature Cited

"Learning and Memory: Becoming a Habit: A Role for NMDA Receptors." Review. Nature Review n.d.: n. pag. Web.

"Sleep-Dependent Declarative Memory Consolidation—Unaffected after Blocking NMDA or AMPA Receptors but Enhanced by NMDA Coagonist D-Cycloserine." Nature.com. Nature Publishing Group, n.d. Web. 25 Aug. 2013.