Assignment #2: 1. Dr. Xu conducted an electrophysiological experiment to determine the properties of a synapse between a presynaptic and postsynaptic snail neuron. She conducted the experiment by depolarizing the presynaptic cell and recorded the voltage PDF

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1. Dr. Xu conducted an electrophysiological experiment to determine the properties of a synapse between a presynaptic and postsynaptic snail neuron. She conducted the experiment by depolarizing the presynaptic cell and recorded the voltage in both the pre- and the postsynaptic cell. Below are the el...

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Department of Biology

NEUR/BIOL-3400-01/02, Sp 2021 Instructor: Dr. Fenglian Xu Assignment #2 Due on Feb 28, 2021 at 11:59pm

Name: _Hamzah Bari_ Date: _2/25/21__

Mark:

Collaborators’ name: Joy Chi

Answer the following questions; if necessary, use drawings to help illustrate your point. Use additional space as needed. (Total 100 points) 1. Dr. Xu conducted an electrophysiological experiment to determine the properties of a synapse between a presynaptic and postsynaptic snail neuron. She conducted the experiment by depolarizing the presynaptic cell and recorded the voltage in both the pre- and the postsynaptic cell. Below are the electrophysiological traces she recorded. Please help her analyze the results and determine what kind of synapse these are. How did you draw your conclusion? Please compare and describe the structures of the synapses based on what you have learned in class. (10 points)

Cell A shows an electrical synapse (IPSP) This is because the postsynaptic and presynaptic graphs are lined up/synchronized with each other. The structure of electrical synapses is made of connexin proteins, which form two halves of a connexon. The connexon is non-selective and allows for ions and small molecules to pass in bi-directions. Cell B is a chemical synapse (EPSP) This is because the presynaptic

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and post synaptic graphs are not synchronized, and instead they show a delayed response. Chemical synapses are composed of presynaptic terminals that contain transmitter vesicles. On the postsynaptic neuron, there are postsynaptic receptors that recognize specific transmitters from the presynaptic neuron. In between the presynaptic and post synaptic neurons is a synaptic cleft, that the transmitters must travel across.

2. Dr. Xu conducted another experiment on snail neurons to characterize if a synapse is inhibitory or excitatory. Below are the raw traces she recorded. In figure A and B, she injected currents to trigger action potentials in the presynaptic neuron and recorded the postsynaptic membrane potential (PSP) change from a postsynaptic cell. In figure B, she also exogenously applied a type of neurotransmitter to mimic the action potential-induced effects on PSP (indicated by the upward arrow). (22 points) 1) Please help her determine what is the specificity of synapses (excitatory or inhibitory) in A or B, and why? (10 points) Both cell A and B are excitatory because the peaks of the graphs go from negative to positive, which indicates an action potential indicating excitatory signals. 2) What transmitter is likely added by Dr. Xu to induce a PSP response and Why? Select the ones that are possible from the following transmitters: Glutamate, GABA, Glycine, Serotonin, Acetylcholine. (6 points) The transmitters are Glutamate and Ach, because they are both excitatory neurotransmitters. 3) What does Ai, Aii and Bi indicate? Select all that may apply from the list for each symbols: Action Potential, Graded Potential, Inhibitory postsynaptic potential (IPSP), excitatory postsynaptic potential (EPSP), resting membrane potential. (6 points)

A

Presynaptic, neuron

Bi

Postsynaptic neuron

Ai

Aii

Ai is a graded potential and an EPSP. Aii is an action potential. Bi is a graded potential and an IPSP. 3. What are the physiological roles of serotonin in the nervous system? If you are asked to develop strategies to enhance the effects of serotonin in our brain, what strategies will you use? Please list at least 3 strategies (10 points)

Serotonin has many different roles in the nervous system. Firstly, it acts as an inhibitory neurotransmitter, which means that it will decrease the likelihood that the neuron will fire. Serotonin also plays a role in affecting mood, appetite, digestion, sleep, memory, and social behavior. The first strategy to increase serotonin in the brain is to eat more foods that have tryptophan. Serotonin is made from tryptophan and eating more foods with tryptophan will cause more to be made in the body. A

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second way of increasing the effects of serotonin, is to take SSRI’s. This medicine cause the reuptake of serotonin to be slower, causing it to last longer in the synaptic cleft and produce its effects. One last strategy to increase serotonin is to exercise/ do more physical activities. 4. The following diagrams represent recordings of the electrical activity of a neuron over a period of time. Each vertical line on the diagram represents an electrical impulse, or action potential, occurring in the neuron. The first diagram represents a neuron at rest. For the other recordings, a solution containing neurotransmitter was applied to the neuron. (18 points)

1) Why is saline applied to the resting neuron? (2 points)

The resting neuron is the control group in this experiment. By applying saline to the resting neuron, it shows how a neuron responds to a salt/saline solution that contains no neurotransmitters. 2) When the neurotransmitter glutamate is applied to the neuron, how does its activity change? (2 points)

Glutamate stimulates the neuron which causes it to generate more electrical impulses. 3) How does the application of the two neurotransmitters, glutamate and GABA, change the activity of the neuron? (4 points) By adding both neurotransmitters it shows that GABA makes the neuron generate less impulses. We can see this because we know that Glutamate excites the neuron to generate more impulses. 4) Predict how the activity of the neuron would change if only GABA was applied to the neuron. (2 points) GABA will inhibit the neuron’s ability to generate electrical impulses.

5) Do all neurotransmitters affect a neuron in the same way? Why? (4 points) No neurotransmitters affect neurons in different ways. This is shown by glutamate and GABA, where glutamate stimulates the neuron and GABA inhibits the neuron. These two have opposite effects.

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6) How would the application of glutamate to a neuron change the amount of neurotransmitter released from that neuron? How would the application of GABA to a neuron change the amount of neurotransmitter released from that neuron? (4 points)

If glutamate is applied to a neuron, it causes the neuron to generate more electrical impulses. This would cause an increase in the amount of neurotransmitter that the neuron releases. If GABA is applied to a neuron, it reduces the number of electrical impulses generated by that neuron. The lower number of impulses would decrease the amount of neurotransmitter that the neuron releases from its axon terminals. 5. Using what you have learned about the effects of the neurotransmitters glutamate and GABA, determine how the different signals that affect Neuron #1 can change the release of the neurotransmitter dopamine from Neuron #2. Use the chart to help you work through the cases. You can use a down arrow to indicate a decrease or an up arrow to indicate an increase. (14 points)

1) The signaling molecule is inhibitory. Neuron #1 releases glutamate as its neurotransmitter. Neuron #2 releases dopamine as its neurotransmitter. 2) The signaling molecule is excitatory. Neuron #1 releases glutamate as its neurotransmitter. Neuron #2 releases dopamine as its neurotransmitter. 3) The signaling molecule is inhibitory. Neuron #1 releases GABA as its neurotransmitter. Neuron #2 releases dopamine as its neurotransmitter. 4) The signaling molecule is excitatory. Neuron #1 releases GABA as its neurotransmitter. Neuron #2 releases dopamine as its neurotransmitter.

Does the signal molecule Case excite or inhibit Neuron #1?

Does the activity of Neuron #1 increase or decrease?

Does the amount of neurotransmitter released from Neuron #1 increase or decrease?

What is the name of the neurotransmitter released from Neuron #1?

Is the neurotransmitter released from Neuron #1 excitatory or inhibitory?

Does the activity of Neuron #2 increase or decrease?

Does the amount of dopamine released from Neuron #2 increase or decrease?

1)

Inhibit

↓

↓

Glutamate

Excitatory

↓

↓

2)

Excite

↑

↑

Glutamate

Excitatory

↑

↑

Inhibit

↓

↓

GABA

Inhibitory

↑

↑

3)

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4)

excite

↑

↑

GABA

Inhibitory

↓

↓

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6. There are two types of newly identified G-protein coupled receptors (GPCRs), GPCR-A and GPCR-B. Each of them bind to the same small ligand, but activates different heterotrimeric G-proteins that act on adenylyl cyclase. Upon binding to the ligand, GPCR-A induces an increase in adenylyl cyclase activtity, while GPCR-B causes a decrease in adenylyl cyclase activity. (26 points) 1) Based on the above statements, what type of G-protein is coupled with each receptor? (4 points)

GPCR-A is associated with the α-subunit, GPCR-B is associated with the β-subunit. 2) Suppose that you have a cell line that expresses both GPCR-A and GPCR-B, the corresponding Gproteins, and adenylyl cyclase. There is a basal level of adenylyl cyclase activity that produces a baseline cAMP concentration. You are asked to conduct experiments in which a series of mutations in these components were performed (as listed below). Will each mutation mutation increase or decrease the intracellular levels of cAMP upon ligand addition (note, bote GPCR-A and GPCR-B bind the same ligand) (12 points)

Mutations

Increase in cAMP

A mutation in GPCR-A that prevents G-protein activation A mutation in GPCR-B that prevents G-protein activation

Decrease in cAMP

X X

A mutation in GPCR-A coupled Gα that prevents release of bound GDP

X

A mutation in GPCR-B coupled Gα that prevents release of bound GDP

X

A mutation in GPCR-A coupled Gα that prevents GTP hydrolysis A mutation in GPCR-B coupled Gα that prevents GTP hydrolysis

X X

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3) Your supervisor asked you to test a drug, which is hypothesized to interfere with signaling in response to your ligand. You did a preliminary experiment in which you looked at intracellular cAMP levels in untreated (control) and drug treated cells. Below is the data you obtained.

How did the drug affect adenylyl cyclase activity? Please propose two models that explain how the toxin might act based on this data. (10 points)

The drug caused an increase in adenylyl cyclase activity, which led to an increased concentration of cAMP. One way a toxin can affect the cell is that it prevents the activation of the g-protein, which in turn causes cAMP to not be produced. Another way that the toxin can affect the cell is that it prevents GDP from being released, which causes the Alpha subunit to not activate and attach to adenylyl cyclase....