Chronic pain impact on rodents' behavioral repertoire.

Rodent models have been fundamental to understand chronic pain (CP) pathophysiology and to test for potential treatments. Pain assessment in CP models is most frequently based on the evaluation of allodynia or hyperalgesia. However, these correspond only to a part of CP-related problems which include ongoing pain, depression, anxiety, disrupted sleep and attentional deficits. A growing number of preclinical studies have been assessing these manifestations in CP rodent models. We reviewed and systematized this information by behavioral domain. Observational studies in ethologically relevant conditions, paradigms of anxiety- and depressive-like behavior as well as of memory and executive function were selected. A considerable number of studies reported deficits similar to those observed in CP patients. These behavioral alterations are informative regarding ongoing maladaptive plasticity in multiple brain regions and its use as pain proxies has the potential to greatly improve the predictive value of CP models. However, the inclusion of female and/or older rodents is rare which is in clear dissonance with the clinical representation of CP.