The COX–prostaglandin pathway within the ventrolateral PAG preferentially modulates C-fiber-mediated spinal nociception. Histograms of AUC measurements to illustrate the effects of injection of drugs and their vehicles into the VL-PAG on reflex responses to fast and slow rates of skin heating. In each case, AUC was calculated between t = 0 (injection of drug or vehicle) and the endpoint shown in Figures 3 and 5⇓–7. Data are expressed as mean ± SEM. Statistical analysis compared fast and slow ramp responses for each drug using Student's unpaired t test. ns, Not significant. *p < 0.05; **p < 0.01; ***p < 0.001.