THE EFFECTS OF MK-801 ON SPATIAL WORKING-MEMORY AND WITHIN-SESSION SPATIAL-LEARNING

The present study investigated the effects of the NMDA channel blocker MK-801 (0.05, 0.10, and 0.15 mg/kg) on a task thar allows for the ass essment of both spatial working memory and within-session spatial lear ning. During the first trial of each-day, subjects were shown the spat ial location of a food reward on a six-arm radial-arm maze. During nin e subsequent free-choice trials, subjects were reinforced for returnin g to that same spatial location. The location of the food reward varie d across days. Thus, choosing correctly on any given trial required su bjects to remember where food had been received during the previous tr ials of that day. The effects of MK-801 on working memory were assesse d by analyzing the overall number of errors committed during the nine free-choice trials of each day. The effects of MK-801 on within-sessio n learning were assessed by comparing the number of errors committed d uring the first three trials of each day to the number of errors commi tted during the last three trials of each day. Only the highest dose o f MK-801 tested (0.15 mg/kg) impaired spatial working memory. No dose of MK-801 impaired the ability of subjects to acquire spatial informat ion within a given session. The failure of MK-801 to impair within-ses sion spatial learning stands in contrast to the well-known effects of MK-801 on spatial learning measured across days. Thus, when coupled wi th previous research, the findings of the present study further sugges t that the NMDA receptor plays a role in the long-term, but not short- term, storage of spatial information. (C) 1998 Elsevier Science Inc.