1. Akil H, Watson SJ (1980) The role of endogenous opiates in pain control. In: Kosterlitz HW, Terenius LY (eds) Pain and society. Verlag Chemi, Weinheim, p 201?222
2. Akil H, Watson SJ, Berger PA, Barchas JD (1978) Stress-induced analgesia in humans: Endogenous, opioids and naloxone-reversible depression of pain reflexes. In: Costa E, Trabucchi M (eds) Advances in biochemical psychopharmacology. Raven, New York, pp 125?139
3. Amir S, Amit Z (1978) Endogenous opioid ligands may mediate stress-induced changes in the affective properties of pain-related behavior in rats. Life Sci 23:1143?1152
4. Beecher HK (1957) The measurement of pain. Pharmacol Rev 9:59?209
5. Beluzzi JD, Grant N, Garsky V, Sarantakis D, Wise CD, Stein L (1976) Analgesia induced in vivo by central administration of enkephalin in rat. Nature 260:625?626