Stress and appetite

All unapproved Citizendium articles may contain errors of fact, bias, grammar etc. A version of an article is unapproved unless it is marked as citable with a dedicated green template at the top of the page, as in this version of the 'Biology' article. Citable articles are intended to be of reasonably high quality. The participants in the Citizendium project make no representations about the reliability of Citizendium articles or, generally, their suitability for any purpose. This article is currently being developed as part of an Eduzendium student project in the framework of a course entitled Appetite and Obesity at University of Edinburgh. The course homepage can be found at CZ:(U00984) Appetite and Obesity, University of Edinburgh 2010. For the course duration, the article is closed to outside editing. Of course you can always leave comments on the discussion page. The anticipated date of course completion is 01 February 2011. One month after that date at the latest, this notice shall be removed. Besides, many other Citizendium articles welcome your collaboration!

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Introduction to the neural mechanisms of appetite control and the interconnections to the HPA axis

In the paragraph above we were introduced to the HPA axis and what it entails. This section aims to give a general understanding to how the brain is involved in regulating appetite, and how it is connected to the HPA axis to allow for stress to have an impact on appetite, which will be discussed in greater detail further along.

In light of the current obesity epidemic there has been a great deal research gone into trying to figure out exactly what causes an obese person to over-eat, or store more energy, compared with a normal weight person. And recent years have seen a great deal of light shed on the neural mechanisms of appetite control. A full account of the control of appetite and its areas in the brain are beyond the scope of this article, but this section aims to highlight the key features so that the connection between stress and appetite can be made.

There are several peptides circulating in our bodies which inform the brain of the body’s nutritional status. These include Insulin (acts to suppress appetite), Leptin (acts to suppress appetite) and Ghrelin (acts to induce appetite) which are able to cross the blood-brain barrier and enter the hypothalamus via the Arcuate Nucleus (ARC) where they have their effect (Schwartz et al, 2000). In ARC there are populations of neurons which produce and release substances which have either orexigenic effect (induce feeding) or anorexigeninc effect (suppress feeding). The orexigenic neurons, which signal hunger, or a negative energy state, are Neuropeptide Y (NPY)/Agouti-related Peptide (AgRP). These are inhibited by increased levels of insulin and leptin, which demonstrates that insulin and leptin act as appetite inhibitors. However, increasing levels of insulin and leptin have excitatory effects on another type of neuron, the anorexigenic peptide releasing neuron Pro-opiomelanocortin (POMC) which releases pro-opiomelanocortin, which is cleaved into melanocortins. Key here is alpha-MSH, a potent anorexigenic molecule, which acts on the MC4 receptor. An additional feature of the orexigenic pathway is that AgRP antagonises MC4, thus increasing NPY/AgRP neurons orexigenic power (Schwartz et al., 2000).

TO ADD PART ON HPA AXIS

The control of appetite is immensely complex and this section only offers a brief overview (please see references for more detail). As has been described, there are several mechanisms in which appetite and stress are related to each other, and the significance of this will be discussed further along. The aim behind most research done in this field is to offer a solution to the growing morbidity of our generation as a result of obesity. Stress induced eating has been shown to play a part and it is the main objective of this paper to discuss the impact of stress on eating.

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