Plantar Test (Hargreaves)
Overview
The plantar test (Hargreaves method) measures thermal nociceptive sensitivity by directing a focused radiant heat source through a glass floor onto the plantar surface of a hind paw in freely moving, unrestrained animals. This approach eliminates restraint stress artifacts present in tail-flick and hot plate tests, and enables repeated bilateral testing of individual paws — making it the preferred thermal pain assay for unilateral injury models.
Animals are placed in acrylic enclosures on a glass floor and allowed to habituate until calm. The infrared beam is positioned beneath the target paw, and the apparatus automatically detects paw withdrawal and records latency. The test is highly sensitive to inflammatory thermal hyperalgesia (CFA, carrageenan) and neuropathic thermal sensitivity changes, and allows within-animal comparison between injured and contralateral paws.
ConductMaze integrates with the Hargreaves apparatus to control beam intensity, detect paw withdrawal via the photodetector, and record latencies. The software supports automated alternation between left and right paws, configurable inter-trial intervals, outlier detection, and longitudinal time-course analysis for chronic pain studies.
Trial Flow
Habituation
Place animal in enclosure on glass floor; habituate 30 min
Position Beam
Align infrared source beneath target hind paw
Activate Heat
Start radiant heat beam; timer begins automatically
Detect Withdrawal
Photodetector senses paw lift; heat stops, latency recorded
Cutoff Check
Stop heat at cutoff (20 s) to prevent tissue damage
Alternate Paw
Test contralateral paw after inter-trial interval
End
Average 3–5 trials per paw for final threshold
Parameters
| Parameter | Type | Default | Description |
|---|---|---|---|
| Beam intensity | arbitrary | 40 | IR beam intensity (calibrate to 8–12 s baseline latency) |
| Cutoff time | seconds | 20 | Maximum heat exposure to prevent tissue damage |
| Trials per paw | integer | 5 | Number of trials averaged for each paw |
| Inter-trial interval | minutes | 5 | Minimum rest between consecutive trials on same paw |
| Habituation time | minutes | 30 | Time in enclosure before testing begins |
| Glass temperature | celsius | 30 | Maintained glass floor temperature |
Metrics
| Metric | Unit | Description |
|---|---|---|
| Paw withdrawal latency | seconds | Time from beam onset to paw withdrawal (averaged across trials) |
| Laterality index | ratio | Ipsilateral / contralateral latency ratio (< 1 indicates hyperalgesia) |
| Thermal hyperalgesia index | % | (Baseline − post-injury) / baseline × 100 |
| %MPE | % | Percent maximum possible effect for drug studies |
| Within-session variability | CV % | Coefficient of variation across trials for data quality |
Sample Data
| Subject | Group | Timepoint | Ipsi Paw (s) | Contra Paw (s) | Laterality Index |
|---|
Representative data for illustration purposes. Actual values will vary by species, strain, and experimental conditions.
Applications
- 1Inflammatory pain — primary assay for CFA and carrageenan thermal hyperalgesia
- 2Neuropathic pain — thermal sensitivity changes in CCI, SNI, and SNL models
- 3Unilateral injury models — within-animal ipsi/contra comparison eliminates inter-animal variability
- 4Analgesic screening — NSAIDs, opioids, TRPV1 antagonists, and novel thermal pain targets
- 5Longitudinal studies — repeated testing over weeks without sensitization artifacts
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