Question

Which hypothalamic nucleus is responsible for pulsatile GnRH secretion?

• A. Preoptic nucleus
• B. Supraoptic nucleus
• C. Arcuate nucleus
• D. Paraventricular nucleus

Hint:

KNDy (kisspeptin, neurokinin B, dynorphin) neurons of the arcuate nucleus drive GnRH pulses.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
GnRH is released in pulses from the hypothalamus. The pulse rate matters: a fast pulse favours LH, and a slow pulse favours FSH.
The question asks which hypothalamic nucleus drives this pulsatile release, which is the GnRH pulse generator.

Step 2: Key Fact:
The GnRH pulse generator is made of KNDy neurons in the arcuate nucleus. KNDy stands for kisspeptin, neurokinin B and dynorphin, the three peptides these neurons make.
Neurokinin B excites the network, and dynorphin shuts it off. This gives rhythmic bursts of kisspeptin, which then stimulate GnRH neurons to release GnRH in pulses.
In women, the arcuate nucleus is also the site where oestrogen feedback acts through kisspeptin.

Step 3: Check option (A):
The preoptic area holds the cell bodies of many GnRH neurons, and it drives the pre-ovulatory LH surge through the anteroventral periventricular region.
It does not generate the pulses. So option (A) is wrong.

Step 4: Check option (B):
The supraoptic nucleus makes ADH (vasopressin) and some oxytocin. It has no role in GnRH pulses. So option (B) is wrong.

Step 5: Check option (C):
The arcuate nucleus holds the KNDy neurons that act as the GnRH pulse generator. So option (C) is correct.

Step 6: Check option (D):
The paraventricular nucleus makes oxytocin, ADH, CRH and TRH. It is not the GnRH pulse generator. So option (D) is wrong.

Final Answer:
The arcuate nucleus, through its KNDy neurons, produces pulsatile GnRH secretion. This corresponds to option (C).