A researcher ablates the hypothalamic arcuate nucleus in a rat. Which endocrine axis would show the MOST profound and sustained disruption?

• A HPA axis, due to loss of CRH neurons in the arcuate nucleus
• B HPG axis, due to loss of GnRH pulse generator neurons (KNDy neurons) ✓
• C HPT axis, due to loss of TRH neurons predominantly located there
• D Growth hormone axis, due to loss of GHRH neurons only in arcuate nucleus

Explanation

The arcuate nucleus houses KNDy neurons (kisspeptin/neurokinin B/dynorphin) which are the master pulse generator for GnRH secretion. Ablation of these neurons profoundly disrupts the HPG axis — abolishing pulsatile LH/FSH release and causing hypogonadotropic hypogonadism. CRH neurons are predominantly in the paraventricular nucleus (option A); TRH neurons are in the paraventricular nucleus and other hypothalamic areas (option C); GHRH neurons are in the arcuate but this axis can partly be regulated from other sites as well.

Reference: Guyton & Hall, Textbook of Medical Physiology, 14th ed.

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Written and medically reviewed by the StethoPrep medical team.