Fig. 5.

Chronic treatment with morphine changed the morphology of dendritic spines even in the presence of TTX. (A) Changes in dendrites before and after treatment with morphine in a neuron that has been chronically treated with TTX for 1 week. TTX was continuously present during the treatment of morphine. Triangles indicate spines that gradually shrank to become tiny philopodia. Arrows indicate where protrusions disappeared. (B) A control neuron that has been treated with TTX alone for 1 week is shown. Arrows indicate no changes in spines. (C and D) Density of protrusions and spines before (b) and after the application of morphine (1–3 days). (E) Chronic treatment with morphine significantly decreased the size of dendritic protrusions (+Mor). Morphine's effect was blocked by naloxone (N+M) but not by TTX (T+M).