Chen JX, Li W, Zhao X, Yang JX, Xu HY, Wang ZF, Yue GX. Changes of mRNA expression of enkephalin and prodynorphin in hippocampus of rats with chronic immobilization stress. World J Gastroenterol. 2004 Sep 01;10(17):2547–9. PMID: 15300902; PMCID: PMC4572159.