An electrode is used to stimulate a presynaptic nerve that synapses in the denta

Question

An electrode is used to stimulate a presynaptic nerve that synapses in the dentate gyrus (DG) of the hippocampus. Postsynaptic recordings are measured in the DG neurons. First a weak stimulus (stimulus A) is applied, and then a strong stimulus (stimulus B). If a second weak stimulus (stimulus C) is applied after the strong stimulus, which result would you expect?

a. The postsynaptic response to the second weak stimulus (C) will be higher than the response to the strong stimulus (B).

b. The postsynaptic response to the second weak stimulus (C) will be lower than the response to the first weak stimulus (A).

c. The postsynaptic response to the second weak stimulus (C) will be equal to the response to the first weak stimulus (A).

d. The postsynaptic response to the second weak stimulus (C) will be equal to the response to the strong stimulus (B).

e. The postsynaptic response to the second weak stimulus (C) will be higher than the response to the first weak stimulus (A).

A researcher is trying to study synaptic transmission in a glutamatergic hippocampal neuron. She is tasked with measuring calcium flow in the postsynaptic hippocampal neuron after either low or high intensity stimulation to the presynaptic neuron. During the experiment, she measures calcium influx after both low and high stimulation. Which statement best describes the error she made?

a. She forgot to add magnesium to the extracellular solution

b. She forgot to add calcium to the extracellular solution

c. She forgot to add sodium to the extracellular solution

d. She forgot to add potassium to the extracellular solution

e. She completed all steps correctly.

Explanation / Answer

As far as, the strength of stimulation is concerned, the facts are as below:

A weak stimulus causes a weak signal, providing the condition that it must be more than the threshold to instigate generation of action potential, and accordingly, the strong stimulus causes the strong fire. However, once a strong stimulus is received by the neuron, the further weak stimulus even, can create a strong response.

Therefore, in light of above facts the question can be deal as follows:

Option-1 and 2 are incorrect, as they are against the fact.

Option-3 is also against the fact as weak stimulus after strong one, can have the stronger response.

Option-4 seems to be correct because, after a strong stimulation, even weak stimulation can have the stronger response.

Option-5 seems more accurate as it the third weak response shall be comparatively stronger but it may or may not be equal to stronger stimulus. However, it is for the sure the third response shall be stronger than the first weak response.

Thus, the option [e] is appropriate.

The Na+–Ca2+ exchange, Ca2+ uptake into mitochondria, and plasma membrane Ca2+-ATPase (PMCA) are the established for their important role in presynaptic Ca2+ regulation. Therefore, measuring calcium flow in the postsynaptic neuron depends upon the Na+–Ca2+ exchange and plasma membrane Ca2+-ATPase (PMCA). Therefore, the presence of Na+ is essential to the Na+–Ca2+ exchange. Thus, the concentration of the Na+ can affect the results. Thus option [c] seems correct.

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