Figure 2

Changes of neuronal response magnitude following morphine (A), NAL + MOR (B) or NS (C) treatment. Raster and perievent histograms show the noxious induced responses in the four recorded areas. Figures in the top two rows in each panel illustrate typical excitatory responses before and after drug administration in each brain regions. Figures in the bottom row show the results of comparison of the pain-evoked neural activities before (black lines) and after (gray lines) morphine, NAL + MOR or NS administration. The trapezoid markers along the x-axis indicate the statistically significant difference between two sessions (Student's t-test, P < 0.01). Time = 0 on the axis corresponds to the time of noxious stimulation start. Note that a single dose of 5 mg/kg morphine significantly reduced the noxious heat induced activation in all the recorded areas (A), which can be reversed by naloxone pretreatment (B). No change was observed after NS injection (C). NAL: naloxone; MOR: morphine; NS: normal saline.