BACKGROUND: Preclinical drug discovery for the treatment of chronic pain is at present challenged by the difficulty to study behaviours comparable to the complex human pain experience in animals. Several reports have demonstrated a frequent association of chronic pain in humans with affective disorders, such as anxiety and depression, and impaired cognitive functions, including memory and decision making, and motivation for goal-directed behaviours. In this study, we validated different behavioural outcomes to measure the emotional and cognitive manifestations of neuropathic pain induced in mice by partial sciatic nerve ligation. METHODS: In these mice, we evaluated at different time points the nociceptive responses, the anxiety- and depressive-like behaviours, the anhedonic state, object recognition memory and the operant responding maintained by food and the effects of the repeated administration of pregabalin on these manifestations. RESULTS: Our results demonstrated that the presence of allodynia and hyperalgesia in neuropathic pain mice was associated with increased anxiety- and depressive-like behaviours, reduced memory functions, development of an anhedonic state and impaired motivation to obtain food in the operant task. Chronic pregabalin treatment improved the nociceptive, anxiety-like and anhedonic responses, as well as the memory deficit, but did not modify the depressive-like alterations and the decreased motivation in these mice. CONCLUSIONS: These results indicate that some emotional manifestations of chronic pain do not necessarily resolve when pain is relieved and underline the relevance to evaluate multiple behavioural responses associated with chronic pain, including the affective-motivational and cognitive behaviours, to increase the predictive value of preclinical drug discovery. WHAT DOES THIS STUDY ADD?: In this study, we have validated different behavioural outcomes allowing a reliable measurement of the emotional and cognitive manifestations of neuropathic pain induced in mice by partial sciatic nerve ligation. These results underline the relevance to evaluate these multiple pain-related alterations to improve the predictive value of preclinical drug discovery.

This work was supported by the European Commission, FP7 (#HEALTH-F2-2013-602891), the Spanish Ministerio de Economía y Competitividad-MINECO (#SAF2014-59648-P), the Spanish Instituto de Salud Carlos III, RETICS-RTA (#RD12/0028/0023) and the Generalitat de Catalunya, AGAUR (#2014-SGR-1547). C.L.P. and R.N. are recipients of a predoctoral fellowship from the Spanish Ministerio de Educación, Cultura y Deporte (MECD). I.M.L.M. is a recipient of a predoctoral fellowship from the Mexican Consejo Nacional de Ciencia y Tecnología (CONACyT). FEDER partial funding is also acknowledged