Both non-NMDA and NMDA glutamate receptors are necessary for memory consolidation in the day-old chick

Abstract

Day-old chicks (black Australorp-white Leghorn) trained to avoid an aversive stimulus will usually retain memory for this event indefinitely. The passive avoidance task used involves a period of pretraining where chicks peck freely at two differently colored glass beads, a single training trial where one of the beads is coated in a chemical aversant eliciting typical disgust reactions from the chicks, and a test trial where both beads are presented dry, and discrimination memory is demonstrated by avoidance of the previously aversive bead with continued pecking of the nonaversive bead. Intracranial administration of a N-methyl-D-aspartate glutamate receptor antagonist (50 microM 2-amino-5-phosphopentanoate) immediately after or prior to learning, or a non-N-methyl-D-aspartate glutamate receptor antagonist (100 microM 6,7-dinitro-quinoxaline-2,3-dione) between 10 and 25 min after learning, resulted in amnesia for this task at 80 to 90 min post-training. These data indicate that processes dependent on N-methyl-D-aspartate and non-N-methyl-D-aspartate glutamate receptor activation are necessary for memory consolidation of a passive avoidance task in the day-old chick. Since these agents must be administered during the earlier stages of memory formation to cause amnesia, the receptors are probably activated close to the time of learning. The delayed effect of these antagonists, however, suggests that memory is independent of these receptors until quite late in the memory consolidation process.