Spontaneous morphine withdrawal and protracted withdrawal effects on tail flick (TF) latency and acoustic startle (AS) amplitude. A, from left to right, panels represent the observed number of grooming, wet dog shakes, and ptosis bouts observed in the 15-min recording sessions, with morphine-withdrawn rats showing more of each withdrawal sign. N = 25–32 per group. B, Latency to withdraw tail from warm water bath (TF assay) measured on withdrawal day 5. Male, but not female, rats previously exposed to chronic morphine show a decrease in TF latency N = 19–21 per group. C, Amplitude of acoustic startle response measured on withdrawal day 7. Regardless of treatment, female rats showed lower startle amplitudes because of their lower body weights. N = 25–30 rats per group. *p < 0.05, **p < 0.01 compared to vehicle treated of the same sex or groups indicated with brackets; ^p < 0.05, ^^p < 0.01 main effect of sex; ##p < 0.01 main effect of treatment