Oral Lactobacillus reuteri LR06 or Bifidobacterium BL5b supplement do not produce analgesic effects on neuropathic and inflammatory pain in rats

Background Previous studies have reported that certain bacteria exert visceral antinociceptive activity in visceral pain and may also help to relieve neuropathic and inflammatory pain. Objective: The aim of this study was to explore the analgesic effect of Lactobacillus reuteri LR06 (LR06) or Bifidobacterium BL5b (BL5b) in chronic pain in vivo. Design Rats were randomly assigned into four groups: sham, Chronic Constriction Injury (CCI)/Complete Freund's Adjuvant (CFA) + control, CCI/CFA + LR06, and CCI/CFA + BL5b. Rats from the probiotic groups were treated with 1 x 10(9) cfu (LR06 or BL5b) daily through gavage for 14 days after a pain model was successfully established. Mechanical and thermal hyperalgesia were used to assess the analgesic effect of the probiotics. Iba1 was used to verify the microglial inflammatory reaction in the different groups. Results The results showed that probiotics L. reuteri LR06 or Bifidobacterium BL5b had no significant antinociception effects in chronic pain rats. The chronic pain-induced activation of microglia (Iba1) was not relieved by probiotics in CCI/CFA-induced neuropathic or inflammatory pain rats. Conclusion Our results suggested that L. reuteri LR06 or Bifidobacterium BL5b had no antinociceptive effects on CCI-induced neuropathic pain and CFA-induced inflammatory pain in rats.