Pain is a widespread condition that significantly impacts individuals and society, leading to physical, psychological, and socioeconomic issues. A key factor in both normal and persistent pain is the intrinsic pain-modulating system, which influences nociceptive processing through projections from the brainstem to the dorsal horn. The rostral ventromedial medulla (RVM) mediates this system, either facilitating or suppressing nociceptive activity. Despite the importance of this pathway, the route through which noxious signals reach the RVM remains unclear. The parabrachial complex (PB), a major nociceptive relay, has connections to the RVM. This thesis aims to determine whether the PB conveys nociceptive information to the RVM and to investigate how their interaction changes as acute inflammation develops into persistent pain.