This group of pain related neurotransmitters is coming into its own. Here is some information to help you read about Orexin in upcoming pain literature.
Any pain specialist worthy of the name knows that Layer I and II of the cord carry chronic pain fibers. Because the hypothalamus is now known to have neurons producing orexins which project to Layer I and II, we here include a review based on Bartsch’s article in Pain, June 2004.
Since orexin neurons also are thought to project to the periaqueductal gray and the raphe nuclei, it is no longer possible to ignore the hypothalamus in pain. Orexin A is inhibitory and reduces pain, whereas Orexin B is excitatory and increases pain.
Orexins are made in the lateral and posterior hypothalamus, which is below the thalamus. Deep brain stimulation has been theorized to help pain by interrupting abnormal thalamic oscillations, ie patterns of current of various frequencies. However, the new information on orexin, makes scientists wonder if deep brain stimulation in the thalamus may actually have some effect on the hypothalamic release of Orexin A or B, which are now thought to modulate the pain experience.