B vitamins relieve neuropathic pain behaviors induced by infraorbital nerve constriction in rats

AbstractAimsThere is mounting evidence that use of B vitamins can help control neuropathic pain. This study investigated if treatment with B1, B6 and B12 vitamins, alone or in combination with carbamazepine, can ameliorate distinct nociceptive behaviors in a model of trigeminal neuropathic pain.Main methodsMale Wistar rats were submitted to infraorbital nerve constriction or sham surgery and received a 5-day treatment with one of the B vitamins, a single carbamazepine injection or the association of both treatments and were tested for facial thermal and mechanical hyperalgesia at different time intervals.Key findingsRepeated treatment with B1 (thiamine), B6 (pyridoxine) and B12 (cyanocobalamin) vitamins (at 180, 180 and 18mg/kg/day, respectively, for 5days) prevented the development of heat hyperalgesia after infraorbital nerve injury, but only B12 and B6 treatments attenuated cold and mechanical hyperalgesia, respectively. A single injection of carbamazepine (30mg/kg) significantly reduced thermal, but not mechanical, hyperalgesia after nerve injury. Combinations of lower doses of each B vitamin (B1 and B6 at 18mg/kg/day and B12 at 1.8mg/kg/day for 5days) with carbamazepine (10mg/kg) markedly reduced heat hyperalgesia after infraorbital nerve injury. Treatment with B12 (1.8mg/kg/day) combined with carbamazepine (10mg/kg) also synergized to attenuate cold hyperalgesia at some time points, but combination of B6 (18mg/kg/day) with carbamazepine (30mg/kg) failed to modify mechanical hyperalgesia.SignificanceWe suggest that B vitamins might constitute a relevant adjuvant to control some aspects of the pain afflicting patients suffering from trigeminal neuropathic pain