Caffeine Consumption Influences Lidocaine Action via Pain-Related Voltage-Gated Sodium Channels: An In Vivo Animal Study

Figure 1

Experimental design and pain sensation testing. (a) Experimental design: at week 0, animals were allocated into group A, the water drinking group, and group B, the caffeine drinking group (n = 16). At the end of the 9th week, animals were subdivided into 4 subgroups (n = 8): control (Ctrl), receiving an intraplantar lidocaine injection (LIDO), habitual caffeine intake (CAF), and habitual caffeine intake and receiving an intraplantar lidocaine injection (CAF + LIDO). Mechanical testing was conducted on the 1st day of weeks 10, 11, and 12, while thermal testing was conducted on the 2nd day of weeks 10, 11, and 12. Both mechanical testing and thermal testing were performed 4 times per day (0, 30, 60, and 90 minutes) after intraplantar lidocaine or saline injections. (b) Mechanical pressure sensation testing (Randall–Selitto test): the tip of the Analgesy Meter was applied with increasing force on the dorsal surface of the rat’s hind paw until a withdrawal response was obtained. (c) Thermal pain sensation testing (paw withdrawal latency test): an infrared light, a thermal heat stimulus, was placed underneath the injected paw until the withdrawal reflex was recorded.

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