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. © Georg Thieme Verlag KG Stuttgart · New York.