Quantitative test of responses to thermal stimulation in spinally injured rats using a Peltier thermode: A new approach to study cold allodynia

In this work, we described a method of testing of responses of spinally injured rats to thermal stimulation (heating and cooling) to the flank area using a Peltier thermode. With a baseline holding temperature at 32 °C and the temperature change rate of 0.5 °C/s, we measured vocalization thresholds of rats to thermal stimulation in the flank area. While normal rats did not vocalize to temperatures changes ranging from 6 °C to 50 °C, the spinally injured rats exhibited significantly increased response to cooling with average response temperature above 15 °C through the 70 day observation period after spinal cord injury. The response temperature to cooling in spinally injured rats is correlated with the magnitude of responses to cold stimulation scored after ethyl chloride spray and with the response threshold to mechanical stimulation. In contrast, we did not observe an increase in response to warm/heat stimuli. The results showed that ischemic spinal cord injury produced cold, but not heat, allodynia in rats. Furthermore, we showed that it is possible to quantitatively measure response of rats to thermal stimulation on the body using temperature as end points which may aid further studies on mechanisms and treatments of thermal stimulation, particularly cold, evoked pain.

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► We developed a method to assess the response of female Sprague–Dawley rats to thermal stimulation (heating and cooling) to the flanks using a Peltier thermode.
► We were able to demonstrate that spinally injured rats exhibited allodynia to cooling, which was correlated with mechanical allodynia.
► No hypersensitivity to heat stimulation was observed following spinal cord injury.
► This method is useful in further studies on the mechanism and treatment of cold evoked pain.