Figure 1

Assessment of mechanical hypersensitivity and antianalgesic effect of 5-HT and α₂-adrenergic receptor antagonists. a Time course of the behavioral experiment. PWT was measured by an automated von Frey device five times on each side. After the baseline measurement, SCS (0.2 ms, 50 Hz, 70–80% of the motor threshold) was initiated and PWT was assessed every hour. Methysergide (5-HT receptor antagonist; 30 μg), idazoxan (α₂-adrenergic receptor antagonist; 30 μg), or saline was administered as a bolus via intrathecal catheters in freely moving rats immediately after verifying the antinociceptive effect of 1-h SCS. b Ipsilateral PWT of SNL rats significantly increased after SCS without influencing contralateral PWT (n = 7). Saline (20 µL) was administered via the intrathecal catheters regardless of SCS. c The increase in ipsilateral PWT was completely reversed by intrathecal methysergide administration without influencing contralateral PWT (n = 6). d The increase in ipsilateral PWT was completely reversed by intrathecal idazoxan administration without influencing contralateral PWT (n = 6). Black square ipsilateral PWT with SCS, black diamond contralateral PWT with SCS, gray circle ipsilateral PWT without SCS, gray triangle contralateral PWT without SCS. Data are mean ± SEM (g); *p < 0.05 and ***p < 0.001 versus before SCS by one-way repeated-measures ANOVA followed by the Dunnett test.