escalate as the aCSF-treated animals did. These initial findings confirmed that MMPs do have a role in dependence-like phenotypes. However, because the chronic FN-439 treatment spanned both the dependence induction period and post-dependence testing, these initial results did not distinguish between the blockade of plasticity (i.e., morphological changes) during dependence formation or acute withdrawal in dependent animals as contributors to the lack of escalation.
