Figure 4: Changes in P-CREB staining in the VTA following different morphine treatments ((a) group 1, naïve; (b) group 2, saline; (c) group 3, MorX1; (d) group 5, MorX8; (e) group 6, Esc; (f) group 7, PP24 h; (g) group 8, PM24 h; (h) group 9, PP7d; (i) group 10 PM7d) as determined by immunofluorescence (200X). Quantification of P-CREB (j). See Table 1 for details on the morphine treatment paradigm. per treatment. * versus saline injection, ** versus saline injection, versus 7 d placebo pellet.