When a person or animal is stimulated at a certain intensity, sensory signals are transmitted to the nerve center and then fed back to the motor center to cause a body response or protective reflex (limb retraction). In the cold hot plate test, the experimental animals are exposed to a cold or hot plate to make the animal feel acute painful stimulus. The animal's behavior in response to pain such as paw licking, jumping, etc. and the reaction time to pain can be used as reliable parameters to evaluate the analgesic effect of the compounds.
Fig. 1 Hot plate and cold plate test. (Deuis, 2017)
Many clinically approved drugs have been shown to delay the reaction time of rodent paws when exposed to thermal stimuli, including opioids and GABA enhancers. For example, when testing the efficacy of a certain analgesic drug, it is often compared between the control group and the administered group, the response time of the animals to heat-induced painful stimuli, if the animals in the administered group also have a significantly longer response time to the stimulus, indicating that the drug has an anti-injury perception effect or analgesic response.