[Prefrontal injection of the alpha 2-adrenergic antagonist yohimbine impairs performance of a delayed GO/NO-GO task in monkeys].

Two rhesus monkeys were trained to perform a delayed GO/NO-GO task, which was initiated by the monkey's pressing a lever. At 0.5 s after the lever-pressing, a white square (1.5 cm x 1.5 cm) was displayed on the right or the left of a computer screen and lasted 0.5 s as a cue. After a delay of 0.0-4.0 s, a red square (1.5 cm x 1.5 cm) appeared between the left-cue and right-cue positions as a signal for response choice. The monkey released the lever within 0.8 s if the cue had been on the right (GO trial), or kept on the lever-pressing for 1.2 s if the cue had been on the left (NO-GO trial). Short-term working memory during the delay was a non-spatially representational one. Local injection of the alpha 2-adrenergic antagonist yohimbine (10 micrograms) into the prefrontal cortex (Walker's areas 46, 9) contralateral to the performing hand decreased the correct rate of performance. The longer the delay period was, the more serious the impairment was. The performing error after injection of yohimbine was expressed mainly as "commissural" response (the monkey made GO response in NO-GO trial or NO-GO response in GO trial). Injection of the alpha 1-adrenergic antagonist prazosin (10 micrograms) or the beta-adrenergic antagonist propranolol (10 micrograms) did not impair the task-performance. Our results suggest that, prefrontal alpha 2-adrenoceptors may play an important role in the short-term working memory with non-spatial representation.