In a rat model of rheumatoid arthritis, intravenous administration of orexin A was shown to reduce pain sensation as well as the serum level of nerve growth factor (NGF), a major mediator of inflammatory and neuropathic pain (Mohamed and El-Hadidy, 2014); effects that are likely attributed to the activation of OX-1 receptors (Yamamoto and Shono, 2007). This evidence concerns the gene NGF and rheumatoid arthritis.