PENK and viral infectious disease: Our analysis of gene-level expression profiles in the amygdala of pigs exposed to viral infection during gestation exposed the effect of MIA on some members of the neuropeptide system, including the prohormone genes proenkephalin (PENK) and proopiomelanocortin (POMC), and receptor genes corticotropin-releasing hormone receptor 2 (CRHR2), parathyroid hormone 1 receptor (PTH1R), and vasoactive intestinal peptide receptor 2 (VIPR2) [15].