Regarding the different responsiveness of RT4-D6P2T cells to PACAP and VIP ability to induce tPA, considering the equal affinity of VPAC type receptors for both PACAP and VIP and the lack of activity of VIP on tPA expression (except at micromolar concentrations → see S1 Fig.) these result suggested a major involvement of the PACAP-preferring PAC1 receptor, in agreement with previous reports indicating that PAC1 receptors are also elevated following peripheral nerve injuries [40]. This evidence concerns the gene VIP and peripheral nerve injury.