MK-801 DISRUPTS RECONSOLIDATION OF NEW MEMORY AND IMPAIRS OLD MEMORY AT INSTRUMENTAL ALIMENTARY BEHAVIOR IN 8-ARM RADIAL MAZE IN RATS

The spatial original memory at alimentary instrumental behavior in an 8-arm radial maze in rats due to reactivation by a single unreinforced trial and subsequent short-term reverse learning was significantly impaired. A blockade of the NMDA (N-methyl-D-aspartate) receptors by MK-801 ((+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine maleate) partially decreased this impairment in the reactivated group. The impairment of the primary elaborated instrumental behavior ("old" memory) in the reactivated saline group occurred by two reasons: 1) because of the use of a single unreinforced trial in the phase of reactivation which was related with receiving no food in 4 arms of a radial maze (extinction effect), and 2) due to formation of "new" memory during acquisition of reverse learning. As a result of it a conflict between old and new learning was shifted towards a new habit. Together with impairment of the old memory a new memory was also formed. NMDA-receptors antagonism impaired formation of new memory during reverse learning as well: the rats made substantially more errors and spent more time for searching reinforcing arms, than control animals. Thus, the used method of reactivation allowed to distinguish and assess an old memory linked with the original learning and a new memory related with the reverse learning.