Control of Appetite

Abstract

Appetite is controlled by the arcuate centre in the hypothalamus
Excitatory neurones act to stimulate appetite, and inhibitory neurones act to suppress appetite
There are many peptide hormones involved in appetite control, including neuropeptide-Y, agouti-related peptide, POMC, ghrelin, and PYY
Ghrelin is released in response to an empty stomach to stimulate appetite
Leptin and PYY both act to suppress appetite

Core

Introduction

Appetite is controlled by the arcuate centre in the hypothalamus which prompts feelings of hunger. There is also a satiety centre, which controls the feeling of ‘fullness’, helping to regulate the amount of food intake, and timing of food intake.

The arcuate centre contains primary neurones that sense metabolite and hormone levels. Secondary neurones in other areas of the hypothalamus receive inputs from these arcuate primary neurones, and co-ordinate an appropriate response via the vagus nerve.

The primary neurones in the arcuate nucleus can be sub-divided into excitatory neurones and inhibitory neurones.

Excitatory neurones: stimulate appetite via the release of neuropeptide-Y and agouti-related peptide.
Inhibitory neurones: supress appetite via the release of POMC (pro-opiomelanocortin).

POMC is a polypeptide prohormone, which can be cleaved to produce several peptide hormones (β-endorphin, ACTH, α-MSH).

α-MSH acts on melanocortin-4 receptors to supress the appetite.
β-endorphins create the reward systemin the brain which produces feelings of euphoria and tiredness in response to eating.

Some regions of the brainstem are also involved in appetite control, but this will not be discussed in this article.

Stimulating Appetite

When our stomach is empty, ghrelin (a peptide hormone) is released from the stomach wall, which activates the stimulatory neurones in the arcuate nucleus, which stimulates the appetite. Once eating occurs (in response to the increased appetite), stretch of the stomach wall caused by the food intake inhibits ghrelin release.

Supressing Appetite

PYY (a peptide hormone) is released from the wall of the small intestine in response to digestion, and acts in opposition to ghrelin to suppress appetite.

Leptin (a peptide hormone) is released into the blood by adipocytes (the level of leptin in the blood correlates with the amount of adipose tissue in the body so increased adipose means more leptin). Leptin acts by stimulating inhibitory hormones and inhibiting stimulatory neurones in the arcuate nucleus to suppress appetite. This is an example of a feedback mechanism from the body’s fat stores in order to control food intake

Insulin can supress appetite via the same mechanism as leptin, but leptin is more important in this role. Insulin resistance is associated with obesity, and often leads to type 2 diabetes mellitus.

Amylin is associated with insulin secretion, and is known to supress appetite, whilst also causing a decrease glucagon secretion, and slow gastric emptying.

Neurones in the arcuate nucleus are also able to sense the level of glucose and fatty acids in the blood, which is useful when considering whether the appetite needs to be supressed or stimulated.

Research on the system of appetite control has revealed new hormones and receptor targets, which could lead to the development of therapeutic agents for obesity.

Edited by: Dr. Marcus Judge and Dr. Maddie Swannack

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