Q9 - Microglia and Memory Forgetting

Theoretical 2 Real exam question - full text reproduced under IBO's CC BY-NC-SA 4.0 license

Nervous System Physiology Immune Physiology

Brain microglia (a type of macrophage) perform many roles in the central nervous system. The role of microglia in synaptic reorganisation and circuit rewiring, which modulates memory, was tested in mice.

Mice were trained to freeze when receiving a stimulus (A). The % of mice remembering to freeze 5 days, and 35 days, after training is shown in B.

Figures A and B: Training protocol and freezing results at 5 and 35 days

Additional experimental data

The % of mice remembering to freeze 35 days after training were compared with Pexidartinib (PLX) and without (PLX) treatment at the start of the study (shown in D). Pexidartinib (PLX) selectively removes only microglial cells. A single Pexidartinib treatment permanently removes microglial cells.

Figures C and D: PLX treatment protocol and freezing comparison

Experimental results with PLX treatment

True or False?

Q9.1. Forgetting is an active process involving microglial cells.

Q9.2. The microglial population is usually self-renewing, rather than replaced by bone-marrow cells.

Q9.3. Depletion of the microglia in the brain leads to an enhanced ability to forget the behavioural response.

Q9.4. Given that the result in (D) could be mimicked by the application of an inhibitor of phagocytosis, the potential mechanism explaining the results is physical removal of the synapse by microglial phagocytosis.

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Question reproduced from IBO 2023, Theoretical Paper 2, licensed under CC BY-NC-SA 4.0 - attributed to the International Biology Olympiad. Open the full exam PDF