Question

Which Hormone receptor in the orexigenic neurons of the arcuate nucleus inhibit the release of the neuropeptide Y (NPY)?

• A. Glucagon
• B. Adiponetic
• C. Ghrelin
• D. Insulin

Hint:

Think of the balance: Ghrelin is the "hunger hormone" that stimulates NPY release, while Insulin and Leptin are "satiety hormones" that inhibit NPY release to signal that the body has sufficient energy reserves.

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
Appetite and energy homeostasis are regulated by the arcuate nucleus (ARC) of the hypothalamus.
The ARC contains two primary neuronal populations: orexigenic (appetite-stimulating) neurons containing Neuropeptide Y (NPY) and Agouti-Related Peptide (AgRP), and anorexigenic (appetite-suppressing) neurons containing Pro-opiomelanocortin (POMC) and Cocaine- and Amphetamine-Regulated Transcript (CART).

Step 2: Detailed Explanation:
The NPY/AgRP-producing neurons stimulate food intake and decrease energy expenditure.
These neurons are regulated by peripheral hormonal signals:
1. Ghrelin (C): Secreted by the empty stomach, ghrelin binds to its receptors on NPY/AgRP neurons and stimulates their activity, promoting hunger and food intake.
2. Leptin and Insulin (D): These act as adiposity and satiety signals.
Insulin, secreted by pancreatic $\beta$-cells in response to elevated blood glucose, crosses the blood-brain barrier and binds to insulin receptors on the orexigenic NPY/AgRP neurons.
This receptor activation triggers an intracellular signaling cascade (involving PI3K) that hyperpolarizes and inhibits these neurons, thereby inhibiting the synthesis and release of Neuropeptide Y (NPY) to suppress appetite.
Glucagon (A) and adiponectin (B) do not play this primary inhibitory role on NPY release in the arcuate nucleus.

Step 3: Final Answer:
Therefore, Insulin is the hormone that inhibits the release of neuropeptide Y in the orexigenic neurons, corresponding to option (D).