Local Administration of Thiamine Ameliorates Ongoing Pain in a Rat Model of Second-Degree Burn.

The objective of this study was to develop rat model of second-degree burn pain and test analgesic efficacy of local thiamine administration. Automatic temperature-controlled hot plate was set at 85 ± 0.1°C with a filter paper on the top. Rats were thrust on hot plate landing on plantar surface for 4 to 7 and 10 seconds, respectively. Burnt skin was observed. Hematoxylin and eosin staining and Masson staining were used to monitor burn degree. Gait analysis detected change of locomotion. Allodynia and hyperalgesia in the burnt area were evaluated with von Frey test and Hargreaves Test, and ongoing pain was detected with conditional place preference test. Markers for the activity of microglia (Iba1), astrocytes (GFAP), and neurons (c-fos) were detected with immunofluorescence. Finally, thiamine was injected into blisters to observe its effect on burn pain. Blisters on burnt skin, space between dermal and epidermal layers in hematoxylin and eosin staining and burn injury limiting in dermal layer in Masson stain all indicated that burn injury lasting for 7 seconds matched second-degree burn. Behavioral tests revealed allodynia, ongoing pain, and increased expression of c-fos, GFAP, and Iba1, as well as the absence of hyperalgesia in Burn7s. Burn injury reduced distance of second and fourth digits. MK801 could relieve allodynia in Burn7s. Local administration of 1, 2, and 4 mg of thiamine had no effect on the allodynia, but 2 and 4 mg of thiamine also could induce conditional place preference (CPP) in Burn7s. A rat model of second-degree burn pain was developed and local administration of thiamine provided relief from pain.