Pain is an unpleasant sensation occurring in varied degrees of severity, and involving both physical and emotional components.

Specific physiological and behavioral tests have been developed to evaluate pain in animal models so to elucidate the specific neurophysiological mechanisms involved in pain development and expression, as well as to develop efficient treatments (drug screening).

Different tests can be applied depending on the nature of the pain under study:

• Physiological/nociceptive pain and inflammation, usually occurring following an injury (thermal/mechanical/chemical stimulation, hyperalgesia, surgery, arthritis)

• Neuropathic pain, occurring following a pathological transformation of the nervous system (neuropathy, allodynia, spontaneous pain, phantom pain…)

The experimental tests used for the evaluation of pain can be differentiated by the nature of the stimulus or of the experimental procedure: thermal tests (hot, cold), mechanical tests (nociceptive or non-nociceptive stimulus), chemical tests (inflammation, paw volume), weight bearing tests.

A more integrated component of pain can also indirectly be evaluated through the assessment of other behaviors:

•Change in home cage activities (circadian rhythms, activity wheel, food/drink consumption)

• Difficulties in having a normal gait control (the way the animal walks in a corridor)

• Difficulties in learning cognitive tasks relative to control animals

• Change in social behavior