Heinricher MM, Neubert MJ, Martenson ME, Gonçalves L. Prostaglandin E2 in the medial preoptic area produces hyperalgesia and activates pain-modulating circuitry in the rostral ventromedial medulla. Neuroscience. 2004;128(2):389–98. doi: 10.1016/j.neuroscience.2004.06.050. PMID: 15350650.