Because it generally is admitted that neuropathic pain is resistant to opioid analgesia, we investigated the effect of morphine on hyperalgesia in streptozocin-induced diabetes in rats. The antinociceptive effect of morphine (0.5-4 mg/kg i.v.) on mechanical (paw pressure test), thermal (tail immersion test) and chemical (formalin test) hyperalgesia was reduced. To clarify the mechanisms involve...

Formalin as a chemical noxious stimulus evokes a biphasic pain that its second phase as a chronic inflammatory pain is similar to clinical pain. In this study, we used 40 NMRI male rats (250-300 g), and experiments were carried out considering ethical rules. Experiments were performed in normal and morphine addicted rats, the addiction was induced by Leung method. Behaviors of flinching and lic...

Formalin as a chemical noxious stimulus evokes a biphasic pain that its second phase as a chronic inflammatory pain is similar to clinical pain. In this study, we used 40 NMRI male rats (250-300 g), and experiments were carried out considering ethical rules. Experiments were performed in normal and morphine addicted rats, the addiction was induced by Leung method. Behaviors of flinching and lic...

Introduction: N- nitro-L-arginine methyl ester (L-NAME), one of the L-arginine analogs, has been specified as an inhibitor of nitric oxide synthase ( NOS).Nitric oxide synthase is an enzyme which leads to nitric oxide synthesis. Since nitric oxide has been known as a pain mediator, it can be said that L-NAME can decrease and relieve pain. In this research the effect of L-NAME on morphine antino...

A wealth of pharmacological and behavioral data suggests that spinally projecting serotonergic cells mediate opioid analgesia. A population of medullary neurons, located within raphe magnus (RM) and the neighboring reticular nuclei, contains serotonin and is the source of serotonin in the spinal dorsal horn. To test whether serotonergic neurons mediate opioid analgesia, morphine was administere...

BACKGROUND Combination therapy is often used to increase the clinical utility of analgesic agents. The coadministration of two compounds may achieve analgesia at doses lower than those required for either compound alone, leading to enhanced pain relief and reduction of adverse effects. Herein, the authors describe the effect of coadministration of morphine and amitriptyline on cutaneous orofaci...

BACKGROUND Tetrodotoxin (TTX) is a powerful sodium channel blocker extracted from the puffer fish. The analgesic effects of TTX were investigated in different animal pain models. METHODS Wistar rats were submitted to the formalin test and to partial ligation of the sciatic nerve (Seltzer's model). Swiss Webster mice were used in the writhing test. Rodents were divided into six groups receivin...

Background: Tolerance and dependence to anti-nociceptive effect of morphine restricted its use. Nowadays co-administration of morphine and other drugs suggests diminishing this tolerance. Baclofen is one of the drugs that may be beneficial in the attenuation of tolerance to morphine. Studies have shown that changes in transient receptor potential vanilloid type 1 (TRPV-1) expression during admi...

  In this study, we investigated the effect of nicotinic receptor agonists and antagonists on the analgesic response to morphine in the formalin test. In experiments conducted in mice, nicotine produced an early dose-dependent analgesic effect. At a dose of 0.5 mg/kg, mecamylamine, a nicotinic receptor inhibitor, suppressed the analgesic effect induced by 0.1 mg/kg nicotine in both stages of th...