Effect of cisplatin on oral ulcer-induced nociception in rats

Objective: The aim of this study is to investigate effects of cisplatin preadministration on oral ulcerative mucositis-induced nociception by using an experimental model of rats. Design: After two rounds of cisplatin administration, oral ulcers developed with topical acetic acid treatment in rats. Spontaneous mouth rubbing behavior was observed as spontaneous nociceptive behavior in a plastic cage. Head-withdrawal behavior was observed as mechanical allodynia by using von Frey test in the oral mucosa of conscious rats. Bacterial invasion and inflammatory cell infiltration into oral ulcerative region and systemic leukocyte phagocytic activity were assessed. Results: Following cisplatin preadministration, oral ulcerative mucositis-induced spontaneous nociceptive behavior was not observed in the model. The preadministration enhanced leukocyte phagocytic activity, leading to reduce bacterial invasion and inflammatory cell infiltration in the oral ulcerative region. In contrast, oral ulcerative mucositis-induced mechanical allodynia was induced. The exaggerated mechanical allodynia in the oral ulcerative region was largely inhibited by topical treatment with the antioxidative drug, ɑ-lipoic acid, or the blocker of N-formyl peptide receptor 1, N-t-butoxycarbonyl-methionyl-leucyl-phenylalanine. Conclusions: These results suggest that cisplatin preadministration suppresses spontaneous nociception in oral ulcerative region, due to antiinflammatory effects by enhancement of leukocyte phagocytic activity, but exaggerates mechanical allodynia due to oxidative stress with N-formyl peptide receptor 1 activation. The suppression of spontaneous nociception is one of the advantages of cisplatin treatment for head and neck cancer patients although the exaggerated allodynia is a serious symptom.