Measuring pain in laboratory animals (1 of 2)
All analgesic drugs licenced for humans are developed and tested for safety and efficacy in laboratory animals.
This would suggest that we should have good methods for assessing pain in these animals, otherwise, how can the effects of these drugs be measured?
In rodents, numerous models for assessing analgesic efficacy have been developed for this purpose, including the paw pressure, hot-plate and tail flick tests. These tests use a defined, brief painful stimulus and measure the withdrawal response, but the stimulus used, and the responses measured, are only useful in these very tightly controlled conditions. The apparatus below, the Hargreaves apparatus, is used for measuring the response to a thermal stimulus in rodents.
However, measuring the intensity of pain experienced after surgery, and the effects of post-operative analgesia, is more challenging.
We have most information about pain following abdominal surgery in rats. Through careful observation of the animal’s behaviour before and after surgery we have identified a series of behaviours that can be used to quantify pain (Ref #7).
These behaviours are almost never observed in normal animals, or those that have been anaesthetised but have not undergone surgery.
After surgery, the behaviours can be observed, and their frequency can be greatly reduced by giving analgesics.