The increase in known nociceptive and afferent regulators (substance P, pERK) as well as the catabolic and signaling protease MMP-1 in DRG neurons (Figs. 4, 5) adds to growing evidence that trauma- and osteoarthritis-induced joint sensitivity is regulated by dysregulation of a host of neurotransmitters, cell signaling proteins, and matrix-altering proteins in the DRG3,29,48,49. Here, MMP1 is linked to osteoarthritis.