Molecular mechanisms of inhibition of vascular formation and pathfinding by KOR signaling activation. KOR signaling induced by dynorphin activates cAMP/PKA pathway. This pathway reciprocally regulates expression of VEGF receptors, Flk1 and Neuropilin1, and plexinD1 in vascular progenitors. Expression balance of these receptors controls vascular formation and pathfinding during vascular development.