Measurement of Neurotransmitters Related to Learning and Memory by Brain Dialysis.

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There are several lines of evidence that catecholaminergic neurotransmitters play important roles on the cognitive processes in the monkey prefrontal cortex. In the present study, using the in vivo perfusion dialysis combined with high-performance liquid chromatography (HPLC) with electrochemical detection, we investigated the role of neurotransmitters on spatial short-term memory functions in the rhesus monkey prefrontal cortex. For this purpose, two monkeys were trained on 8-s delayed response task, which is related to spatial short-term memory, and a control, non-delay position discrimination, task. We measured the amount of dopamine and norepinephrine through dialysis probes implanted in the prefrontal cortex. These two tasks are alternated every 20 minutes periods. By comparing the amount of transmitters released while the monkeys are performing these two tasks, we can estimate the role of each transmitter in the prefrontal cortex on spatial short-term memory functions.There were many places where the amount of dopamine release was higher during delayed response performance than during control task performance. These probes were located around the principal sulcus. Lengthening the delay interval resulted in the elevation of dopamine release, which suggests higher activity in the prefrontal cortex in the long delay condition. Pargyline, a MAO-inhibitor, increased not only dopamine release but also error responses in delayed response performance. This result is difficult to interprete. However, it suggests a new procedure of drug injection by dialysis probes. It was difficult for the dialysis procedure to detect laminar differences in neurotransmitter release.In conclusion, the brain dialysis technique is useful for analyses of relations between cognition and neurotransmitters and between drags and neurotransmitters.