How can you tell that a rat is in pain? - briefly
Altered grooming, reduced locomotion, vocalizations such as high‑frequency squeaks, elevated heart rate, and increased stress‑hormone levels indicate discomfort. Facial grimace scales—showing tightened orbital and whisker muscles—provide a reliable visual marker of pain.
How can you tell that a rat is in pain? - in detail
Observing a rodent for signs of nociception requires systematic assessment of behavior, physiology, and facial expression.
Behavioral indicators include:
- Reduced locomotion, reluctance to explore, or prolonged immobility.
- Altered posture such as hunching, guarding of a limb, or a flattened back.
- Decreased grooming activity and neglect of the nest.
- Changes in social interaction, including avoidance of conspecifics.
- Vocalizations that occur only during handling or when pressure is applied to a body part.
Physiological measures that correlate with discomfort:
- Elevated heart rate and respiratory rate detectable through telemetry.
- Increased plasma corticosterone or cortisol concentrations.
- Pupillary dilation and reduced corneal reflex latency.
- Temperature dysregulation, often manifested as peripheral vasoconstriction.
Facial expression analysis provides a rapid, non‑invasive metric. The Rat Grimace Scale assigns scores to specific action units: orbital tightening, nose/cheek flattening, ear position, whisker change, and muzzle tension. Higher composite scores reliably predict the presence of acute or chronic pain.
Experimental protocols commonly combine these observations with analgesic challenge tests. Administration of an effective analgesic should reverse the documented signs, confirming that the original findings reflected pain rather than unrelated stressors.
Consistent documentation of each parameter, preferably using video recordings and blinded scoring, enhances reproducibility and supports ethical decision‑making regarding humane endpoints.