INFORMATION ABOUT IMAGE G FOR QUESTIONS 12-15:

12)
GABAB receptors (GABABRs) are G-protein-coupled receptors that can be found on both pre- and postsynaptic neurons. When they are activated by GABA, they can have a range of effects. For the synapse you are studying in the following questions, the effects of GABABRs are indicated in IMAGE G.

You are doing a series of experiments in which you are recording from the pre- and postsynaptic cell at a synapse. The experiments described below for each question are independent of one another (that is, they are performed on the same type of synapse, but in separate experiments).

In order to learn how this type of synapse functions, you are applying various drugs to the synapse. These drugs may be GABABR agonists or antagonists, which would be applied in the fluid bathing the synapse so they can activate or block the channels extracellularly, or they could be drugs that affect the function of G-proteins that are activated when GABA binds to GABABRs, and these would either be applied using an inside-out patch clamp recording technique or injected into the cytoplasm of the cell. Assume the only effects you are seeing are due to activation of the GABABRs and the downstream effects of activating them. That is, there are no channels or GABA receptors other than the ones indicated that affect your results. Unless otherwise stated, assume all ion concentrations are normal and the reversal potentials are: ENa = +60 mV, EK = -80 mV, and ECl = -70 mV.

Key for IMAGE G: If a given G-protein dimer influences the activity of an effector, this is shown by a black line. When that G-protein dimer enhances/increases the activity of the effector, this is symbolized by an arrowhead at the end of the line. In contrast, if there is a perpendicular short, straight line at the end, this indicates that this G-protein dimer reduces/blocks the activity of the effector.

Use this information and IMAGE G to answer the following four questions (12-15).

Question 12:

Control data: stimulate presynaptic neuron and record the postsynaptic response

Experimental data: Apply GABA, then stimulate presynaptic neuron and record the postsynaptic response

Would application of GABA affect neurotransmitter release from the presynaptic neuron at this synapse, compared to when no GABA is present? If yes, how?  For this question, assume activation of adenylyl cyclase does not affect neurotransmitter release, and assume the postsynaptic response you record is an accurate indicator of the amount of neurotransmitter release.


	a.
Yes; neurotransmitter release would be reduced

 	b.
Yes; neurotransmitter release would be increased

 	c.
No; neurotransmitter release would not be affected




13)
Use the information in Question 12 and IMAGE G, as well as the information below, to answer Question 13:

Control data: apply GABA to the synapse and record the K+ current in the postsynaptic neuron when the membrane potential is held at -40 mV; synapse is in normal extracellular solution, with typical ion concentrations. Additionally, action potentials have been blocked with pharmacological agents.

Experimental data: change the extracellular solution to one in which there is no Mg2+. Then, apply GABA to the synapse and record the K+ current when the membrane potential is held at -40 mV. Action potentials are still blocked.

Question 13: How would the zero-Mg2+ extracellular solution affect the K+ current, compared to the control conditions with a normal level Mg2+?

	a.
The K+ current would be larger in the zero-Mg2+ extracellular solution

 	b.
The K+ current would be smaller in the zero-Mg2+ extracellular solution

 	c.
The K+ current would not be affected


14)
Use the information in Question 12 and IMAGE G, as well as the information below, to answer Question 14:

Control data: you apply GABA to the synapse. You depolarize the postsynaptic neuron to -20 mV and record Na+, Ca2+, and K+ currents at this membrane potential.

Experimental data: You administer pertussis toxin to the postsynaptic cell, and record Na+, Ca2+, and K+ currents again, still with GABA present. Note that in this cell, phosphorylation of NMDARs (indicated by the orange circle containing a ‘P’) increases NMDAR conductance.

Question 14: How would the application of pertussis toxin change the postsynaptic currents indicated below, compared to when there was no pertussis toxin present? Remember that GABA is still present (so, GABAB receptors are still being activated). MORE THAN ONE ANSWER MAY BE CORRECT. SELECT ALL THAT APPLY.

	a.
Increased Ca2+ current

 	b.
Decreased Ca2+ current

 	c.
Increased Na+ current

 	d.
Deceased Na+ current


15)
QUESTION 15

Use the information in Question 12 and IMAGE G, as well as the information below, to answer Question 15:

In another experiment on this type of synapse, you have applied a very large amount of ketamine, enough so it exerts its effects on all molecules that ketamine directly affects at this synapse (remember that there are no other neurologically-relevant molecules you need to take into account, other than the ones indicated in IMAGE G).

Control data: Stimulate the presynaptic neuron, which releases GABA, and record K+ currents in the postsynaptic cell in the presence of ketamine, while holding the postsynaptic membrane potential at -60 mV.

Experimental data: Inject a molecule that is a Regulator of G-protein Signaling (RGS) into the postsynaptic neuron. Then stimulate the presynaptic neuron and record K+ currents in the postsynaptic cell (still in the presence of ketamine, and still holding the postsynaptic membrane potential at -60 mV).

Question 15: Which set of graphs (a-f) in IMAGE M (below) indicate how the presence of the RGS affects K+current, in response to presynaptic stimulation (still in the presence of ketamine)?