Proenkephalin expression and enkephalin release are widely observed in non-neuronal tissues.
Denning GM, Ackermann LW, Barna TJ, Armstrong JG, Stoll LL, Weintraub NL, Dickson EW. Proenkephalin expression and enkephalin release are widely observed in non-neuronal tissues. Peptides. 2008 Jan; 29(1):83-92.