A neuroscientist selectively lesions a small cluster of neurons in the anterior hypothalamus that contain GABA and galanin. The experimental animal shows profound insomnia with inability to initiate sleep. Which nucleus was destroyed?

• A Locus coeruleus
• B Ventrolateral preoptic nucleus ✓
• C Suprachiasmatic nucleus
• D Tuberomammillary nucleus

Explanation

The ventrolateral preoptic nucleus (VLPO) of the anterior hypothalamus contains GABAergic and galaninergic neurons that inhibit all major arousal systems (locus coeruleus, tuberomammillary histamine neurons, raphe nuclei). Its activation produces sleep onset, so its loss causes insomnia. The tuberomammillary nucleus is the opposite pole of the flip-flop switch: it promotes wakefulness via histamine, so destroying it would produce somnolence, not insomnia.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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