Enduring attentional deficits in rats treated with a peripheral nerve injury

The present study investigated the impact of a spared nerve injury (SNI) on the daily performance of rats tested in two instrumental conditioning procedures: the progressive ratio (PR) schedule of food reinforcement to study motivation for an appetitive stimulus, and the 5-choice serial reaction time task (5-CSRTT), a test of attention and reaction time. Separate groups of male, Sprague-Dawley rats of age 8-10 months were trained to asymptotic performance in either task, before undergoing either SNI or sham surgery. After a recovery period of 3-4 days the animals were run 5 days/week for 3 months in either task. Tests of responsivity to evoked tactile (Von Frey) and thermal (acetone) stimuli were also conducted over this period to check integrity of the model. Post SNI surgery, rats showed equivalent responding to sham controls for food available under a PR schedule throughout the test period, implying a similar level of motivation for a food reward. In contrast, a performance deficit emerged in SNI treated rats run in the 5-CSRTT, consistent with an attentional deficit. This deficit emerged during the second month post-surgery and was characterized by slower response speed, reduced accuracy and increased trial omissions. Both SNI groups showed equivalent hypersensitivity to evoked sensory stimuli compared to controls. Since attention based deficits have been reported in individuals with clinical forms of neuropathic pain, the present studies suggest a novel approach to study this phenomena and a means to study the effect of treatments against this cognitive endpoint.