ACETYLCHOLINE-RELEASE FROM THE FRONTAL-CORTEX DURING EXPLORATORY ACTIVITY

The activation of the cortical cholinergic system was investigated in 3- and 25-month-old male Wistar rats, by measuring by transversal micr odialysis the changes in cortical extracellular acetylcholine (ACh) le vels during the performance of simple spontaneous tasks involving expl oratory activity and working memory. Two days after implantation of th e microdialysis probe in the frontal cortex, object recognition was in vestigated by either moving the rats from the home cage to the arena c ontaining the objects or keeping the rats in the arena and introducing the objects. Spontaneous alternation was investigated in a Y runway, Young rats discriminated between familiar and novel objects and altern ated in the Y runway, while aged rats were unable to discriminate. Whe never rats were moved from the home cage to the arena, ACh release inc reased (+70-80%) juring the exploratory activity. Handling per se had no effect on extracellular ACh levels. When young rats were left in th e arena, introduction of the objects caused some exploratory activity and object recognition but no increase in ACh release. ACh release inc reased by about 300% during spontaneous alternation. Tn aging rats bas al extracellular ACh levels and their increase after placement in the arena were less than half that in young rats. Our work demonstrates th at a novel environment activates the cortical cholinergic system, whic h presumably is associated with arousal mechanisms and selective atten tional functions. It also demonstrates that in aging rats the cortical cholinergic hypofunction is associated with a loss of non-spatial wor king memory. (C) 1998 Elsevier Science B.V.