Hot Plate Test

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Hyperalgesia is a condition of enhanced sensitivity to painful stimuli. The thermal analgesia hot plate assay is a pharmacological test for evaluating the analgesic potential of test compounds. 

A number of clinically approved pharmacological agents have been demonstrated to delay the onset of heat sensitivity upon paw exposure to heat including opioids and GABA potentiators.  Typically, the hot plate assay is included in a battery of assays in evaluating the analgesic potential of test compounds. 

In the study summarized below, the Hot Plate thermal analgesia test is reported with the formalin chemical nociception assay and the von Frey touch sensitivity test.

Latency to paw withdrawl in mice treated with morphine and control mice during the hot plate test.

Latency to pain behavior. 30 minutes after treatment with either vehicle or morphine, mice were placed on a 52°C hot plate apparatus to measure the latency of first hind paw pain response. This response was elicited by a paw lick, shake or escape jump. Mice treated with morphine had significantly increased latencies to respond to thermal stimulation compared to mice treated with vehicle.

The mouse hot plate analgesia assay is a test of painful stimulation from heat sensitivity. Animals that received vehicle displayed an average pain response of 15 seconds. When administered morphine, the pain response was significantly delayed, providing an analgesic effect. Data are mean ± SEM; **p<0.01 compared to vehicle.

The Hot Plate test is typically run in an acute mode (study completed in one day) by evaluating test articles after a single administration. The variability is relatively low and statistical significance may be achieved with group sizes of about 8 to 10 animals. It can be performed in both mice and rats. Since it is non-invasive it can be easily incorporated several times over the course of a chronic study.