The LH surge triggering ovulation is preceded by a positive feedback effect of rising estradiol on the hypothalamic-pituitary axis. Which neuronal population in the hypothalamus expresses kisspeptin and mediates this estradiol-induced positive feedback, and where is it located?

• A Tuberoinfundibular dopamine neurons that switch to kisspeptin secretion when estradiol rises
• B Arcuate nucleus KNDy neurons (kisspeptin/neurokinin B/dynorphin) mediate negative feedback at low estradiol; anteroventral periventricular (AVPV) nucleus kisspeptin neurons mediate the positive feedback LH surge ✓
• C Supraoptic nucleus neurons that release kisspeptin together with ADH during the follicular phase
• D GnRH neurons themselves produce kisspeptin as a co-transmitter that triggers auto-stimulation

Explanation

Two hypothalamic kisspeptin neuronal populations have opposing responses to estradiol: (1) KNDy neurons in the arcuate nucleus express ER-α and respond to chronic estradiol elevation with reduced kisspeptin secretion (mediating negative feedback and setting pulsatile GnRH/LH). (2) AVPV/periventricular kisspeptin neurons (predominant in females) are paradoxically stimulated by the rising estradiol peak of the mid-cycle, producing a kisspeptin surge → GnRH surge → LH surge → ovulation (positive feedback). This dimorphic kisspeptin population is sexually differentiated by neonatal sex steroids, explaining why males lack an LH surge response.

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

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