Fig. 3.

(A) Sustained morphine up-regulates SP immunofluorescence in the spinal cord. Tissue from placebo-treated rats is shown in the left column, and that from morphine-treated rats is shown in the right column. No apparent differences in SP immunoreactivity are seen between the spinal sections obtained from placebo-treated and morphine-treated rats 2 days after pellet implant. The staining intensity of SP in tissues from morphine-treated rats on day 6 is enhanced compared to placebo-treated rats on day 6. The enhanced staining is apparent in laminae I and II. Scale bar, 200 μm. (B) Radioimmunoassay shows no differences in SP content between placebo animals in the 2 and 6 days post-pellet implant. Morphine did not alter SP content in rats 2 days post-pellet implant. SP content was elevated 6 days post-morphine pellet implant (*P<0.05). (C) The capsaicin-evoked release of SP from spinal tissues in vitro 2 and 6 days after placebo or morphine pellet implant is represented as the amount of SP above the baseline release for each individual group. Basal levels of SP release did not differ among the treatment groups. Evoked SP release was not different between tissues from placebo- and morphine-treated groups 2 days after pellet implant (P>0.05). However, tissues from the 6-day morphine-treated group showed a significantly greater level of capsaicin-evoked release of SP (*P<0.05). Graphs represent mean±SEM. Each treatment group consisted of 12 rats.