Fig. 4: Assessment of the antinociceptive effect of the lead compounds by tail-flick assay.

Compounds (100 μg/mouse) were administered directly to the brain of 8-week old male ICR-CD1 mice by i.c.v. route, either alone or in combination with the MERF (50 μg/mouse) and the maximum possible effect of the compounds was recorded (n = 6–15 animals/group). Naloxone (5 mg/kg, s.c.), an opioid receptor antagonist was injected to confirm the role of opioid receptor activation in the antinociceptive effect of the compounds. The top panel shows a time-course of the tail-flick response after i.c.v. administration of captopril (A), thiorphan (B), and raloxifene (C). The Y-axis denotes the %MPE and the X-axis shows the time points at which the response was recorded. The bottom panel shows the comparison between the anti-nociceptive effect (%MPE ± SEM) for various treatment groups shown in the top panel at 15 min after compound administration. Data are shown as the mean ± SEM, with error bars displaying SEM. Statistical significance was examined by a one-way ANOVA with Sidak’s post hoc multiple comparison test (*p < 0.05, **p < 0.01, ***p < 0.001, ****p < 0.0001). Source data are provided in Supplementary Data 1.