MCAT Behavioral Sciences Question 235: Answer and Explanation

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Question: 235

5. AMPA receptors are found throughout the central nervous system and are comprised of four different subunits. Not all AMPA receptors have all the subunits. If a knockout mouse was made deficient for the gene for one of the AMPA receptor subunits, what would be the expected outcome?

  • A. An observed deficit only in LTP and the mouse's ability to learn.
  • B. Altered function in any region containing an AMPA receptor.
  • C. No change in LTP function due to the NMDA receptor still being present and functional.
  • D. Altered function and/or compensatory expression of other AMPA receptor subunits in regions with AMPA receptors that lack the affected subunit.

Correct Answer: D

Explanation:

The question states essentially that AMPA receptors can be varied (have variable subunits) and are found throughout the CNS. Certainly if the gene for one of the subunits was deficient, we would expect some deficit to be present. However, because of the widespread location of these receptors, we would not expect the deficit to be limited to only the region of the brain responsible for LTP (choice A is wrong), nor would we expect the deficit to be found in ANY region with receptors, because some regions may have AMPA receptors that do not have the knocked out subunit (choice B is wrong). According to the diagram, function of both AMPA and NMDA receptors are required during LTP, so if one of the receptors was compromised we might expect some alteration in LTP function (choice C is wrong). The most likely outcome is that there would be altered function or potentially compensatory expression of other AMPA receptor subunits in those regions of the CNS that contain an affected AMPA receptor (choice D is correct).

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