Increased acetylcholine release in the rat medial prefrontal cortex duringperformance of a visual attentional task

Recent studies have suggested a functional link between cortical cholinergi c output and attentional task demands, whereby acetylcholine (ACh) release is regulated according to the outcome of ongoing behaviour. To explore this hypothesis we measured ACh efflux in the rat medial prefrontal cortex (mPF C) during between-session manipulations of the cognitive demands of an atte ntional task. Rats were trained to detect visual stimuli in a five-choice s erial reaction time task (5-CSRTT) which involves sustained and divided att ention. Following habituation to tethering and implantation with a microdia lysis probe in the mPFC, rats were tested in the 5-CSRTT for three consecut ive days, with different lengths of stimulus duration. During performance o f the 5-CSRTT we measured robust, reproducible, task-related increases in A Ch release in the mPFC across all sessions. Variations of the stimulus dura tion from the standard 0.5 s resulted in the predicted behavioural effects (reductions and increases in choice accuracy with 0.25 s and 5 s, respectiv ely), but there was no evidence of either greater changes in ACh release in the more demanding condition or smaller changes in the less demanding cond ition. By contrast, in the session with 5-s stimulus duration there was a p ositive correlation between prefrontal cortical ACh efflux and the total nu mber of trials completed. In summary, the present study shows that ACh effl ux in the rat mPFC is increased during performance of a 5-CSRTT, but has fo und no evidence to support a specific relationship between cholinergic cort ical output and attentional performance.