Effect of vitamin B12 on functional recovery and histopathologic changes of tibial nerve-crushed rats.

Recent studies have suggested a neuroprotective effect for vitamin B12. The present study investigated the effects of vitamin B12, diclofenac and celecoxib in separate and combined treatments on functional recovery of crushed tibial nerve in rats. In ketamine plus xylazin anesthetized rats, right tibial nerve was crushed using a small hemoatatic forceps. Footprints were recorded 1 day before and on days 7, 14 and 21 after induction of nerve injury. Tibial functional index (TFI) was used to evaluate the recovery of tibial nerve function. Histological changes of tibial nerve were investigated by light microscopy. The recovery of TFI values were significantly accelerated with 10 consecutive days treatments with 0.1 and 0.5 mg/kg of vitamin B12, 5 mg/kg of diclofenac and 1 and 5 mg/kg of celecoxib. The severity of Wallerian degeneration was reduced by above-mentioned doses of vitamin B12, diclofenac and celecoxib. Documented effects were observed when 0.1 mg/kg of vitamin B12 was concurrently used with 1 mg/kg of diclofenac and or 0.2 mg/kg of celecoxib. In the present study, vitamin B12, celecoxib and diclofenac (at a high dose) showed neuroprotective effects. Inhibition of cyclooxygenase (COX) 1 and 2 pathways may be involved in neuroprotective effect of vitamin B12.

Systemic and local peripheral injections of vitamin B12 suppressed orofacial nociception induced by formalin in rats.

Vitamin B12 has many biological functions including antinociceptive property. This study was designed to investigate the effects of local peripheral (into upper lip) and systemic injection of vitamin B12 and diclofenac on the orofacial pain. Orofacial pain was induced by subcutaneous injection 50 µL of a diluted formalin solution (1.5%) in the right upper lip. The time spent face rubbing performed with ipsilateral forepaw was measured in 3 min blocks for a period of 45 min. Formalin produced a biphasic pattern (early phase: 0-3 min and second phase: 15-33 min) of pain response. Systemic (1, 2 and 4 mg/kg) and local peripheral (2.5, 5 and 10 µg/rat) injections of vitamin B12 significantly attenuated the second phase of formalin-induced pain. The same results were obtained from systemic (2 and 4 mg/kg) and local peripheral (100 and 200 µg/rat) injections of diclofenac. Systemic co-administrations of vitamin B12 and diclofenac increased vitamin B12-induced antinociception. Local co-administrations of vitamin B12 and diclofenac enhanced antinociception induced by diclofenac. The obtained results indicated that vitamin B12 and diclofenac produced powerful suppressing effects on orofacial inflammatory pain. Co-treatments with vitamin B12 and diclofenac produced more antinociceptive effects. Inhibition of cyclooxygenase (COX) pathway may be involved in antinociception induced by vitamin B12.

Effects of mepyramine and famotidine on the physostigmine-induced antinociception in the formalin test in rats.

In this study, the effects of mepyramine (H1-receptor antagonist), famotidine (H2-receptor antagonist), physostigmine (a cholinesterase inhibitor) and atropine (muscarinic-receptor antagonist) have investigated on the formalin-induced nociception in rats. The effects of mepyramine and famotidine have also examined on nociceptive changes induced by physostigmine and atropine. Nociception was induced by intraplantar injection of formalin (50 microL, 1%) into the right hind paw and the time spent licking and biting of the injected paw, was taken as a measure of pain. Formalin induced a marked biphasic (first phase: 0-5 min and second phase: 15-45 min) pain response. The used drugs did not change the first phase of formalin-induced pain. Subcutaneous injection of physostigmine significantly (p<0.05) suppressed pain. Subcutaneous injection of atropine alone did not change the intensity of pain, but pretreatment with atropine significantly (p<0.05) prevented physostigmine-induced antinociception. Intraperitoneal injections of mepyramine and famotidine significantly (p<0.05) decreased pain response. Mepyramine did not significantly change, but famotidine significantly (p<0.05) prevented analgesic effect of physostigmine on pain. Atropine did not inhibit the antinociceptive effects of both mepyramine and famotidine on formalin-induced nociception. These results indicate that physostigmine through muscarinic cholinergic receptors suppresses the pain induced by formalin. Both H1 and H2 receptor antagonists produce antinociception. Histamine H2, but no H1 antagonists may be involved in physostigmine-induced antinociception.

Effects of chlorpheniramine and ranitidine on the visceral nociception induced by acetic acid in rats: role of opioid system.

In this study, effects of chlorpheniramine (H1-receptor blocker), ranitidine (H2-receptor blocker), morphine (an opioid agonist) and naloxone (an opioid antagonist) in separate and combined treatments were investigated on the visceral nociception in rats. Visceral nociception was induced by intraperitoneal injection of acetic acid (1 mL, 1%). The latency time to the beginning of the first abdominal wall contraction (first writhe) was measured and the numbers of writhes were counted for 1 h after acetic acid injection. Intraperitoneal injections of chlorpheniramine and ranitidine significantly (p < 0.05) increased the latency time to the beginning of the first writhe and also significantly (p < 0.05) decreased the numbers of writhes. The same results were obtained after subcutaneous injection of morphine. Subcutaneous injection of naloxone did not change the intensity of visceral nociception, but significantly (p < 0.05) prevented the morphine-induced antinociception. Intraperitoneal injection of chlorpheniramine significantly (p < 0.05) enhanced the morphine-induced analgesia, but did not reverse the effect of naloxone on nociceptive responses. Intraperitoneal injection of ranitidine, with no effect on the morphine-induced antinociception, significantly (p < 0.05) reversed the effect of naloxone on pain responses. These results suggest that both chlorpheniramine and ranitidine exert antinociceptive effect in the visceral nociception. In addition, morphine through a naloxone-dependent mechanism produces visceral antinociception. Moreover, the endogenous opioid system may participate in the chlorpheniramine- but not in the ranitidine-induced antinociception.