Tramadol and Tramadol+Caffeine Synergism in the Rat Formalin Test Are Mediated by Central Opioid and Serotonergic Mechanisms

Figure 3

Effect of naloxone (NX) on the antinociceptive effect of caffeine (CAF, p.o.), tramadol (TRAM, s.c.), and tramadol+caffeine (TRAM+CAF). The control group (C) received saline solution by all routes to assess the magnitude of nociception produced by formalin at 2%. The open columns represent the antinociceptive effect of the different treatments with saline solution pretreatment. The dark columns show the effect of NX 15 min before administration of the different treatments. (a) Naloxone was administered i.c.v. (b) Naloxone was administered i.t. Data are presented as mean ± SEM, ; tramadol versus tramadol with naloxone, TRAM+CAF versus TRAM+CAF with naloxone.

(a)

(b)