Systemic morphine treatment induces changes in firing patterns and responses of nociceptive afferent fibers in mouse glabrous skin

Chronic morphine alters the firing pattern and sensitivity of peripheral nociceptors, inducing afterdischarge and spontaneous activity, as well as increased sensitivity to cold. The emergence of a larger proportion of mechanically and cold-sensitive fibers in the morphine-treated compared to saline-treated mice suggests that silent nociceptors have become activated.