Hippocampal acetylcholine release correlates with spatial learning performance in freely moving rats

To assess the activity of septohippocampal cholinergic neurons during the l earning of a radial-arm maze task we measured changes in extracellular acet ylcholine levels in the hippocampus by means of the vertical microdialysis technique. During the 12 days spent learning the spatial task the extracell ular concentration of acetylcholine in the hippocampus was monitored while rats performed the test. One week before radial-arm maze training a guide c annula was implanted unilaterally in the hippocampus. On each day of testin g a removable microdialysis probe was inserted through the guide cannula an d the dialysate was collected during the test performance. The concentratio n of acetylcholine in the dialysate was detected by means of a high-perform ance liquid chromatograph coupled to an electrochemical detector. We found that hippocampal acetylcholine release progressively increased from 139% to 245% during the 12 days of radial-maze learning and the magnitude of chang e in acetylcholine output was positively correlated with spatial memory per formance, thus suggesting that changes in the functioning of these neurons are involved in learning. NeuroReport 11:2265-2269 (C) 2000 Lippincott Will iams & Wilkins.