“…It has been shown that melatonin produces a transient antinociceptive effect in rats and mice (Yu et al, 2000a, b;Tu et al, 2004;Onal et al, 2004), modulates lipopolysaccharideinduced hyperalgesia possibly via its influence on the role of proinflammatory cytokines in sensory neurons , and interacts with opioid antinociception (Golombek et al, 1991;Pang et al, 2001;Li et al, 2005;Shavali et al, 2005). In clinical studies, melatonin has been reported to reduce cluster headache, irritable bowel syndrome, and fibromyalgia (Leone et al, 1996;Citera et al, 2000;Song et al, 2005), although the relationship between depression and chronic pain was not specifically examined in these clinical reports. Evidence also exists that implicates melatonin for the mood regulation (Brzezinski, 1997).…”