Essay, Research Paper: Orexin

A bulimic's or anorexic's I-function may also be positively affected by drugs which can change its neuro-chemical environment. In this chemical fashion relief may be found for affected individuals. Numerous hormones, cortisol, orexin A, orexin B, luteinizing hormone, luteinizing-hormone-releasing factor, and follicle-stimulating hormone, have been linked to these eating disorders. These hormones are all present in healthy people, while in those affected with an eating disorder the levels or distributions are abnormal. The brain hormone, cortisol, is found to be at elevated levels in patients with anorexia. This hormone is usually released in response to stress. In these sick individuals it appears to be mis-released by malfunctions in the hypothalamus.(1) Two newly discovered hormones, orexin A and orexin B, are connected with feeding behavior in rats. By modulating feelings of hunger and satiety the scientists can influence how much a rat eats. Following injection of these hormones into the lateral hypothalamus the rats were found to immediately begin eating eight to ten times more food than normal. Following up on this finding they measured elevated hormone levels when the rat was starved. These researchers have not yet been able to see if a decrease of orexin A and B result in decreased appetites, but they are planning on genetically engineering rats which will be missing the gene needed to produce them, thus allowing them to test the deficiency. The hypothesis of this research is that drugs that mimic orexin may help anorexic patients overcome their disorder, while drugs which block orexin action may help bulimics. (10)
Instead of identifying a chemical and then locating the receptor it binds to in order to learn what it does, they first looked for "orphan" receptors, or those with no know function. When a receptor binds to its matched protein, called a ligand, it trips a series of cellular signals that turn genes on and off. After extensive searching, the group zeroed in on two receptors produced in the lateral hypothalamus--a region of the brain thought to control appetite. They bathed the receptors in ground-up brain tissues and eventually isolated two ligands--hormones that they christened orexin A and orexin B, after the Greek word orexis, meaning appetite.
Even so, drugs that mimic orexin might help patients with anorexia or other wasting syndromes by increasing hunger. And those that block orexins might help patients struggling with obesity and binge eating.