After cardiac arrest, wild-type mice exhibited a decline in activity compared to indoleamine 2,3-dioxygenase–deleted animals during the 7 days after resuscitation (total distance traveled in 7 days: wild-type 506 ± 278 m versus IDO−/− 963 ± 242 m; P = 0.055, n = 4/group; fig. Here, IDO2 is linked to cardiac arrest.