Formalin Test

Like psychomotor stimulants, a weak amphetamine-like agent, such as phenylpropanolamine, enhances the analgesic effects of morphine (MOR). Thus, it is possible that full psychomotor stimulant potency is not required to increase the analgesic action of opiates. The validity of this assumption is here tested by studying the ability of (-)-norpseudoephedrine (NPE), an enantiomer of phenylpropanolamine and a metabolite of cathinone, to influence both the analgesic effects of MOR and its discriminative stimulus properties. In mice NPE (5.6-10.0-17.0 mg/kg i.p.) did not prolong the latency to lick or to remove paws from a plate warmed at 54 degrees C. However, it significantly potentiated the analgesic effect of 3.2 mg/kg of MOR. These results were replicated in rats by use of the formalin test, which measures the numbers of hind paw flinches produced by injecting 50 microl of formalin into the dorsal surface of the paw. The higher dose of NPE (17 mg/kg) increased the effect of sub-analgesic doses of MOR (0.56 and 1.0 mg/kg). In rats trained to discriminate between 0.5 mg/kg of amphetamine and solvent in a two-lever operant behavior reinforced by water access. NPE induced a dose-dependent increment of drug lever responding from 0% at 1.0 mg/kg to 100% at 32.0 mg/kg. In contrast, NPE did not generalize for the MOR cue up to the dose of 56.0 mg/kg, which produced a substantial reduction of the response rate. However, when given in combination, NPE attenuated the discriminative effects of MOR and potentiated its inhibitory action on the response rate. These results exclude a direct action of NPE on the mu opiate system. In conclusion, NPE preserves amphetamine-like properties and these properties are probably responsible for the interaction of the drug with the analgesic and discriminative effects of MOR. Therefore, this study contradicts the assumption that the analgesic effects of MOR can be enhanced by a sympathomimetic drug that lacks significant psychostimulant actions.

The anti-inflammatory and analgesic effects of the aqueous extract of Crinum glaucum were evaluated in mice and rats using the carrageenan- and dextran-induced paw oedema, acetic acid-induced writhing, cold water tail flick and formalin pain tests. The extract (100–400 mg/kg) and acetylsalicylic acid (100 mg/kg) produced a significant (P<0.05) inhibition of the second phase response in the formalin pain model,

Context: Paeonia mascula is used in traditional medicine in North of Algeria for its anti-inflammatory activity. Aims: To evaluate the analgesic and the anti-inflammatory effects of the ethanolic extract of Paeonia mascula (EPM) in mice. Methods: The analgesic activity of EPM was evaluated on the chemical nociception in the animal models of acetic acid-induced writhing and formalin-induced hind paw licking/biting, whereas xylene-induced ear edema and multiapplication of TPA (12-O-tetradecanoylphorbol-13-acetate) were used to determine anti-inflammatory effects of EPM. Results: EPM (100 and 250 mg/kg) produced a significant dose-dependent inhibition of pain-related behaviors elicited by acetic acid. Also, EPM reduced both early and late phases of the formalin test. However, its inhibitory effect was more significant on tonic inflammatory phase, may be related to the anti-inflammatory abilities of this extract. Also, EPM decreased ear edema in acute and sub-chronic models used in the present study. Conclusions: These findings suggest the ethanolic extract from aerial parts of Paeonia mascula presents significant anti-inflammatory and anti-nociceptive effects on chemical behavioral models of nociception and inflammation in mice.