Chronic constriction sciatic nerve injury in mice delays acquisition, impairs retention, and alters motivation in autoshaping and progressive ratio tasks

Abstract

Persistent pain can produce long‐lasting changes in both physical and psychological functioning in patients. In the present study, we assessed the impact of a prior history of neuropathic pain on subsequent learning and reward processing in mice to further understand the role of past pain states in normal functioning. Under anesthesia, mice (N=19) received two ligatures tied loosely around the right common sciatic nerve and were allowed approximately 20‐30 days to recover. The neuropathic (N=19) and control (N=19) mice learned to respond for a 50:50 (v:v) water:Ensure® solution predicted by an audible tone during two consecutive daily sessions in an autoshaping procedure. After the autoshaping procedure, the mice were trained in a progressive ratio procedure and tested with various concentration of Ensure solution (50, 10, 3, and 0%) over a 4‐8 week period. Neuropathic mice responded with longer latencies and more errors than control mice although the rates of responding were not different between the two groups in the autoshaping procedure. Despite delayed acquisition and impaired retention in the autoshaping procedure, the neuropathic mice responded with higher breakpoint values than control mice for 10% and 3% Ensure solutions, indicating an increase in the reinforcing efficacy of Ensure in the neuropathic mice. Taken together, these data suggest neuropathic pain can modulate learning and reinforcement processes for weeks after surgery.