A patient receiving intravenous cisplatin develops severe vomiting despite the drug having negligible penetration into most CNS regions. The region responsible for this response shares which property?

• A It lies within the blood-brain barrier with tight endothelial junctions
• B Its neurons are protected by the blood-CSF barrier at the choroid plexus
• C It has fenestrated capillaries and lies outside the blood-brain barrier ✓
• D It detects emetics through lumbar CSF sampling

Explanation

The area postrema in the floor of the fourth ventricle is one of the circumventricular organs, all of which have fenestrated, leaky capillaries lying outside the blood-brain barrier. It therefore samples circulating toxins and drugs such as cisplatin and mediates vomiting via connections to the nucleus tractus solitarius. The other options are wrong because these regions are defined precisely by the absence of tight-junction endothelium and are not shielded by the blood-CSF barrier.

Reference: Ganong's Review of Medical Physiology, 26th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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