Rotterdam Advanced Multiple Plate: a novel method to measure cold hyperalgesia and allodynia in freely behaving rodents.

BACKGROUND

To investigate the pathophysiology of temperature hypersensitivity in neuropathic pain rodent models, it is essential to be able to quantify the phenotype as objective as possible. Current temperature sensitivity measuring paradigms are performed during exposure to external factors, i.e. light, sound and smell, which modulate behavior significantly. In addition the present outcome measure for temperature hypersensitivity in rodents is the examination of the hind paw lift upon exposure to a certain temperature, which reflects more a reflex-flexion than an experience of pain.

NEW METHOD: Therefore the Rotterdam Advanced Multiple Plate (RAMP) was developed to assess cold hyperalgesia and allodynia objectively in freely behaving neuropathic pain rats, which measures the avoidance for certain temperatures and monitoring the location of the rat with an infrared camera while excluding external environmental influences such as light and sound.

RESULTS

Compared to sham rats, the spared nerve injury (SNI) rats demonstrated a higher preference for the comfortable plate (27 °C) when the other three plates were set at 5 °C, 14 °C, 17 °C and 19 °C. We were unable to detect heat hyperalgesia and allodynia with the RAMP.

COMPARISON WITH EXISTING METHOD: The paw withdrawal method displays similar results during cold hypersensitivity measurements as observed with the RAMP. The SNI group did display heat hypersensitivity during the paw withdrawal test.

CONCLUSIONS

The results indicate that the RAMP is able to quantify cold hyperalgesia and allodynia in neuropathic pain rats while resolves some of the problems of conventional temperature sensitivity measuring paradigms in rodents.