Haghighi Practice problems 2
Practice :
At a vertebrate neuromuscular junction the resting membrane potential is -70 mV and ENa, EK and ECl are 50, -100 and -70 mV, respectively. Electrophysiological analysis indicates that the ACh-gated channels at this junction show identical conductance for sodium and pottasium. Figure 1 shows a single channel recording of ACh-gated channels that are normally expressed postsynaptically at a holding potential of -55 mV. And Figure 2 shows a representative MEPSP recorded from the muscle. The muscle input resistance and time constant during the rise of the MEPSP were 5 MΩ and 4 ms, respectively. Finally, our voltage clamp recordings allowed us to get the average amplitude of EPSCs at this NMJ in response to presynaptic stimulation. We found that at a holding potential of -100 mV the average EPSC amplitude was -150 nA. A) Draw (in the space bellow) the I-V relationship for the EPSCs over a range of membrane potentials from -100 to +40 mV. Show your calculations.
B) What is the quantal content at this NMJ?
C) How many single channels are opened in response to the release of one vesicle?
FIGURE 1
close 1 pA
open 1 ms
FIGURE 2
1 mV
2 ms
Practice At an NMJ, the muscle resting membrane potential and the threshold for AP are -80 mV and -35 mV, respectively. We have determined that the average size of MEPSPs is 0.8 mV and the conductance change associated with each MEPSP is 10 nS. Figure 1 shows the response of the muscle membrane potential to a small current injection. The I-V curve for the synaptic currents in response to stimulation of the presynaptic motor nerve is given in Figure 2. EPSCs recorded from the muscle rise very rapidly and last 3 ms before rapidly decaying, resembling a square current pulse. A) What is the quantal content at this NMJ under the above experimental conditions? B) If we stimulate the motor nerve twice, 8 ms apart, will the first and/or second AP in the motor nerve cause the muscle to fire an AP? Assume a synaptic delay of 1 ms and assume that there is little contribution of residual calcium in the terminals of the motor nerve 6 ms after each presynaptic AP. Please show your calculations and state your reasoning clearly.
Figure 1
Figure 2
I
I(nA)
1 nA
V
5 ms 20
Vm(mV)
-80
-40
40
2 mV 5 ms
-20
80
QUESTION (2) The firing of striatal neurons in caudate-putamen is differentially modulated by glutamatergic inputs from the cortex and dopaminergic inputs from the nigrostriatum. (Briefly explain the logic behind your answers). a) Briefly and clearly propose one model for how the glutamatergic and dopaminergic signal transduction pathways could interact to modulate the firing rate of striatal neurons.
b) How would this interaction be affected if the NMDA receptors carried a mutation so that they no longer conducted calcium?
c) How would this interaction be affected if AMPA receptors were blocked?
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Practice:
A shows glutamate-evoked single channel records obtained from a postsynaptic muscle at a Drosophila larval NMJ. The resting membrane potential of this muscle is -65 mV. ENa, EK and ECl are 50, -100 and -70 mV, respectively. We have found that the postsynaptic glutamate channels at this NMJ are all of the same subunit composition with identical single channel conductance and show no voltage dependence.
Figure B shows representative traces for EPSPs and mEPSPs recorded from the same muscle. From the data we have estimated the mean amplitude of mEPSPs to be 0.8 mV. Our records show that each vesicle of glutamate opens 500 channels at this NMJ.
For all questions please show your calculations and/or state your reasoning that supports your answer. QUESTION 1 IS OBLIGATORY. YOU HAVE A CHOICE BETWEEN QUESTIONS 2 AND 3. PLEASE ANSWER EITHER 2 OR 3.
1- Draw the I-V curve corresponding to EPSCs at this junction and show all your calculations. What is the value of gNa/gK for the postsynaptic receptors at this NMJ?
2- If a mutation in the pore of the GluRs at this junction increases the single channel mean open time 2-fold, how will (a) the mean amplitude of mEPSPs (b) the number of Glutamate receptors opened by one quantum, (c) the concentration of calcium in the presynaptic terminal and (d) the average amplitude of EPSCs be affected? 3- In another experiment we have introduced two other mutations at this NMJ. One in the glutamate receptors and one in the presynaptic calcium channels. Both mutations lead to a decrease in the apparent quantal content. Propose two reasonable mechanisms that could explain this decrease.
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A Vm(mV) 90
-40
-85
B
4mV/40ms (EPSP) 3mV/400ms(mEPSP)
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Physiology 311A. Quiz #3. Synaptic Transmission. October 20, 2006
Name:
Student ID:
a) At a glutamatergic synapse, we have found that almost every AP in the presynaptic neuron leads to the firing of an AP in the postsynaptic neuron. Draw the changes in membrane potential in the pre- and postsynaptic cells 50 ms before and after a postsynaptic AP has been fired. . The time and amplitudes can be approximate but they should be reasonable. Assume that both neurons have a Vm of -70 mV. b) Application of FMRFamide to the synapse above influences the probability of firing an AP in the postsynaptic cell. Explain the mechanism of action of FMRFamide in the postsynaptic neuron and the final effect of FMRFamide on the firing ability of this neuron.
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3- What would be the most likely effect of a loss-of-function mutation in the synaptotagmine gene on the size of MEPSP and quantal content at this NMJ? What would be the effect on fast and slow neurotransmitter release process?
4- If a mutation in the pore of the ACh receptors at this junction causes a doubling of the single channel mean open time, how will (a) the mean amplitude of the MEPSPs and (b) the number of AChR channels opened by one quantum be changed?
Some formulas that may be useful for answering the questions: I = g (V – E ) X X –E IX = g m (V ) EEPSP = EPSP (E + E m g EPSP /g )/(1 + g /g ) EPSP K Na Na K g /g = (E – E )/(E – ENa )K K K EPSP EPSP Na mNa = EPSC/MEPSC m = ln (N/n ) 0
PRACTICE .:
The above graph shows the relation between the post-synaptic current (I) and the membrane potential (V) of a motor neuron in a newborn animal when a glycinergic synapse on the motor neuron’s cell body is activated by electrical stimulation of a sensory nerve. We have determined that the entire glycine-evoked current is carried by chloride. Resting membrane potential and resting conductance of the newborn motoneuron are -60 mV and 20 nS, respectively. The conductance associated with the action of one quantum of glycine on the motoneuron is 5 nS. Later in development in the mature motoneuron the single channel conductance of glycine receptors reduces by 20% but their numbers remain unchanged. E , E and E are 50, -100
Nathe K Cl and -70 mV for mature motoneuron. All properties of the presynaptic sensory nerve remain unchanged during development. (Please clearly explain your answers and describe the reasoning for every step. a) (35%) What would be the size and direction of the synaptic current at -50mV recorded from the mature motoneuron in response to electrical stimulation of the sensory nerve?
b. What would be the size of the postsynaptic potential in the newborn motoneuron in response to electrical stimulation of the sensory neuron?
Question 2: The newborn motoneuron in question 1 receives two other presynaptic inputs from a serotonergic neuron and a glutamatergic neuron. We have determined the presence of only three types of neurotransmitter gated receptors at the postsynaptic motoneuron: glycine receptors (as explained in question 1), metabotropic serotonin receptors and NMDA receptors. Also we found nicotinic ACh receptors at the presynaptic terminals of the serotonergic neuron. Assuming physiological conditions, draw the synaptic currents (with a brief explanation) that you would expect to record from the motoneuron in response to a) stimulation of the glutamatergic neuron. b) stimulation of the serotonergic neuron, c) simultaneous stimulation of both presynaptic neurons, and d) simultaneous stimulation of both neurons while applying ACh to the preparation. Use the same time scale for your drawings.
a)
b)
c)
d)
At a vertebrate neuromuscular junction the resting membrane potential is -70 mV and ENa, EK and ECl are 50, -100 and -70 mV, respectively. Electrophysiological analysis indicates that the ACh-gated channels at this junction show identical conductance for sodium and pottasium. Figure 1 shows a single channel recording of ACh-gated channels that are normally expressed postsynaptically at a holding potential of -55 mV. And Figure 2 shows a representative MEPSP recorded from the muscle. The muscle input resistance and time constant during the rise of the MEPSP were 5 MΩ and 4 ms, respectively. Finally, our voltage clamp recordings allowed us to get the average amplitude of EPSCs at this NMJ in response to presynaptic stimulation. We found that at a holding potential of -100 mV the average EPSC amplitude was -150 nA. A) Draw (in the space bellow) the I-V relationship for the EPSCs over a range of membrane potentials from -100 to +40 mV. Show your calculations.
B) What is the quantal content at this NMJ?
C) How many single channels are opened in response to the release of one vesicle?
FIGURE 1
close 1 pA
open 1 ms
FIGURE 2
1 mV
2 ms
Practice At an NMJ, the muscle resting membrane potential and the threshold for AP are -80 mV and -35 mV, respectively. We have determined that the average size of MEPSPs is 0.8 mV and the conductance change associated with each MEPSP is 10 nS. Figure 1 shows the response of the muscle membrane potential to a small current injection. The I-V curve for the synaptic currents in response to stimulation of the presynaptic motor nerve is given in Figure 2. EPSCs recorded from the muscle rise very rapidly and last 3 ms before rapidly decaying, resembling a square current pulse. A) What is the quantal content at this NMJ under the above experimental conditions? B) If we stimulate the motor nerve twice, 8 ms apart, will the first and/or second AP in the motor nerve cause the muscle to fire an AP? Assume a synaptic delay of 1 ms and assume that there is little contribution of residual calcium in the terminals of the motor nerve 6 ms after each presynaptic AP. Please show your calculations and state your reasoning clearly.
Figure 1
Figure 2
I
I(nA)
1 nA
V
5 ms 20
Vm(mV)
-80
-40
40
2 mV 5 ms
-20
80
QUESTION (2) The firing of striatal neurons in caudate-putamen is differentially modulated by glutamatergic inputs from the cortex and dopaminergic inputs from the nigrostriatum. (Briefly explain the logic behind your answers). a) Briefly and clearly propose one model for how the glutamatergic and dopaminergic signal transduction pathways could interact to modulate the firing rate of striatal neurons.
b) How would this interaction be affected if the NMDA receptors carried a mutation so that they no longer conducted calcium?
c) How would this interaction be affected if AMPA receptors were blocked?
Page 1/2
Practice:
A shows glutamate-evoked single channel records obtained from a postsynaptic muscle at a Drosophila larval NMJ. The resting membrane potential of this muscle is -65 mV. ENa, EK and ECl are 50, -100 and -70 mV, respectively. We have found that the postsynaptic glutamate channels at this NMJ are all of the same subunit composition with identical single channel conductance and show no voltage dependence.
Figure B shows representative traces for EPSPs and mEPSPs recorded from the same muscle. From the data we have estimated the mean amplitude of mEPSPs to be 0.8 mV. Our records show that each vesicle of glutamate opens 500 channels at this NMJ.
For all questions please show your calculations and/or state your reasoning that supports your answer. QUESTION 1 IS OBLIGATORY. YOU HAVE A CHOICE BETWEEN QUESTIONS 2 AND 3. PLEASE ANSWER EITHER 2 OR 3.
1- Draw the I-V curve corresponding to EPSCs at this junction and show all your calculations. What is the value of gNa/gK for the postsynaptic receptors at this NMJ?
2- If a mutation in the pore of the GluRs at this junction increases the single channel mean open time 2-fold, how will (a) the mean amplitude of mEPSPs (b) the number of Glutamate receptors opened by one quantum, (c) the concentration of calcium in the presynaptic terminal and (d) the average amplitude of EPSCs be affected? 3- In another experiment we have introduced two other mutations at this NMJ. One in the glutamate receptors and one in the presynaptic calcium channels. Both mutations lead to a decrease in the apparent quantal content. Propose two reasonable mechanisms that could explain this decrease.
Page 2/2
A Vm(mV) 90
-40
-85
B
4mV/40ms (EPSP) 3mV/400ms(mEPSP)
Page 1/3
Physiology 311A. Quiz #3. Synaptic Transmission. October 20, 2006
Name:
Student ID:
a) At a glutamatergic synapse, we have found that almost every AP in the presynaptic neuron leads to the firing of an AP in the postsynaptic neuron. Draw the changes in membrane potential in the pre- and postsynaptic cells 50 ms before and after a postsynaptic AP has been fired. . The time and amplitudes can be approximate but they should be reasonable. Assume that both neurons have a Vm of -70 mV. b) Application of FMRFamide to the synapse above influences the probability of firing an AP in the postsynaptic cell. Explain the mechanism of action of FMRFamide in the postsynaptic neuron and the final effect of FMRFamide on the firing ability of this neuron.
Page 2/3
3- What would be the most likely effect of a loss-of-function mutation in the synaptotagmine gene on the size of MEPSP and quantal content at this NMJ? What would be the effect on fast and slow neurotransmitter release process?
4- If a mutation in the pore of the ACh receptors at this junction causes a doubling of the single channel mean open time, how will (a) the mean amplitude of the MEPSPs and (b) the number of AChR channels opened by one quantum be changed?
Some formulas that may be useful for answering the questions: I = g (V – E ) X X –E IX = g m (V ) EEPSP = EPSP (E + E m g EPSP /g )/(1 + g /g ) EPSP K Na Na K g /g = (E – E )/(E – ENa )K K K EPSP EPSP Na mNa = EPSC/MEPSC m = ln (N/n ) 0
PRACTICE .:
The above graph shows the relation between the post-synaptic current (I) and the membrane potential (V) of a motor neuron in a newborn animal when a glycinergic synapse on the motor neuron’s cell body is activated by electrical stimulation of a sensory nerve. We have determined that the entire glycine-evoked current is carried by chloride. Resting membrane potential and resting conductance of the newborn motoneuron are -60 mV and 20 nS, respectively. The conductance associated with the action of one quantum of glycine on the motoneuron is 5 nS. Later in development in the mature motoneuron the single channel conductance of glycine receptors reduces by 20% but their numbers remain unchanged. E , E and E are 50, -100
Nathe K Cl and -70 mV for mature motoneuron. All properties of the presynaptic sensory nerve remain unchanged during development. (Please clearly explain your answers and describe the reasoning for every step. a) (35%) What would be the size and direction of the synaptic current at -50mV recorded from the mature motoneuron in response to electrical stimulation of the sensory nerve?
b. What would be the size of the postsynaptic potential in the newborn motoneuron in response to electrical stimulation of the sensory neuron?
Question 2: The newborn motoneuron in question 1 receives two other presynaptic inputs from a serotonergic neuron and a glutamatergic neuron. We have determined the presence of only three types of neurotransmitter gated receptors at the postsynaptic motoneuron: glycine receptors (as explained in question 1), metabotropic serotonin receptors and NMDA receptors. Also we found nicotinic ACh receptors at the presynaptic terminals of the serotonergic neuron. Assuming physiological conditions, draw the synaptic currents (with a brief explanation) that you would expect to record from the motoneuron in response to a) stimulation of the glutamatergic neuron. b) stimulation of the serotonergic neuron, c) simultaneous stimulation of both presynaptic neurons, and d) simultaneous stimulation of both neurons while applying ACh to the preparation. Use the same time scale for your drawings.
a)
b)
c)
d)
