Role of the prefrontal cortex in the integration of cognitive information

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NE levels were significantly higher in WM (spatial delayed alternation) and non-WM (sensory guided control) than that in REST when the awake monkey was sitting quietly without task performance. On the other hand, there were no stage dependent changes in the levels of ACh and 5HT. We observed a significant increase in dopamine but no change in glutamate during the WM task and a significant increase in glutamate but no change in dopamine during the sensory guided task. Simultaneous sampling of dopamine and glutamate showed a significant interaction between them (F=8.34, df=52). In contrast to the chronic observations, there were the significant increases in dopamine releases by glutamate perfusions and that in glutamate releases by dopamine perfusions under the NMDA receptor inhibition. (n=5).We further investigated a DA-glutamate interaction in the PFC in the unanesthetized condition. D1 and D2 agonists simultaneously applied at 1mM each decreased glutamate levels in the PFC significantly (85.01+4.33%, p=0.019, n=8), as similarly seen with an application of 1 mM dopamine (78.87+12.17%, p=0.049, n=8). After a solo application of quinelorane, glutamate levels were decreased in a dose-dependent manner (0.1mM : 86.98+9.91%, 0.5mM : 71.49+6.74%, 1.0mM : 64.56+9.20%, n=8). Furthermore, this decrease of glutamate by quinelorane was not antagonized by 0.5mM muscimol. On the other hand, when SKF38393 was applied, only a slight increase in glutamate was detected (116.95+7.16%, p=0.06, n=8).The results suggest that D2 receptors on the presynaptic terminals or the glia-cells adjacent to the PFC principal neurons are involved in the disfacilitatory mechanism in the WM task.