Figure 5.

Percentage of Fos-positive neurons that were retrogradely labeled from the RVM (%Fos in FG+ cells) in male (solid bars) and female (open bars) rats injected with either morphine or saline once or twice daily for three days for the rostral ((a); Bregma −6.72, −7.04, −7.74) and caudal ((b); Bregma −8.00, −8.30, −8.80) PAG. A decrease in labeling is evident with an increase in the number of morphine injections for male rats. The # indicates a significant effect of treatment and the ∗ indicates a significant effect of sex. Saline: morphine naïve; 1 dose: saline pretreatment followed by one dose of morphine; 3 doses: one dose of morphine per day; 6 doses: two doses of morphine per day.