Hot Plate Test
Overview
The hot plate test measures supraspinal nociceptive processing by placing a rodent on a heated metal surface (typically 52–55 °C) and recording the latency to a nocifensive response — hind paw lick, hind paw shake, or jumping. Unlike the tail-flick test which primarily involves spinal reflexes, hot plate responses require cortical processing and conscious pain perception, making it a key assay for evaluating analgesics that act at supraspinal sites.
The test is particularly sensitive to opioid analgesics that engage descending pain modulatory circuits (periaqueductal gray → rostral ventromedial medulla → spinal dorsal horn). A cutoff time (typically 30 s) prevents tissue damage. The simplicity and reliability of the assay make it one of the most commonly used acute thermal pain tests, though it is less suitable for repeated testing due to potential sensitization or learned avoidance.
ConductMaze interfaces with the hot plate apparatus to precisely control surface temperature, detect when the animal is placed/removed, and record response latency with video verification. The software supports multiple temperature protocols, calculates percent maximum possible effect (%MPE) for analgesic studies, and generates dose-response curves for ED50 determination.
Trial Flow
Temperature Set
Verify plate at target temperature (±0.1 °C)
Place Animal
Place animal on hot plate, start timer
Observe Response
Watch for hind paw lick, shake, or jump
Record Latency
Stop timer at first nocifensive response
Cutoff Check
Remove animal if cutoff (30 s) reached without response
End
Return animal to home cage; clean plate surface
Parameters
| Parameter | Type | Default | Description |
|---|---|---|---|
| Plate temperature | celsius | 52 | Surface temperature (52–56 °C range) |
| Cutoff time | seconds | 30 | Maximum exposure time to prevent tissue damage |
| Response criteria | enum | hind-paw-lick | Scored behaviors: hind-paw-lick, shake, jump, or any |
| Acclimation | enum | none | Pre-test acclimation to cold plate (none or 5 min at room temp) |
| Number of trials | integer | 1 | Trials per animal (single trial recommended for naive animals) |
Metrics
| Metric | Unit | Description |
|---|---|---|
| Response latency | seconds | Time from placement to first nocifensive response |
| Response type | category | Type of first response (lick, shake, jump) |
| %MPE | % | Percent maximum possible effect: (test − baseline) / (cutoff − baseline) × 100 |
| ED50 | mg/kg | Dose producing 50% maximum possible effect (from dose-response) |
| Thermal hyperalgesia index | ratio | Baseline latency / post-injury latency |
Sample Data
| Subject | Group | Dose (mg/kg) | Baseline (s) | Post-Drug (s) | %MPE |
|---|
Representative data for illustration purposes. Actual values will vary by species, strain, and experimental conditions.
Applications
- 1Opioid analgesic screening — primary assay for mu-opioid agonist potency (ED50 determination)
- 2Supraspinal pain processing — differentiates spinal from supraspinal analgesic mechanisms
- 3Tolerance studies — repeated morphine administration and hot plate latency tracking
- 4Inflammatory hyperalgesia — CFA-induced thermal hyperalgesia time course
- 5Novel analgesic targets — cannabinoids, TRPV1 antagonists, and sigma receptor ligands
Related Protocols
Compatible Products
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