Interference with visual memory in rats following infusion of the functional NMDA receptor antagonist, HA-966, into temporal regions.

Results from lesion studies show that selective damage to the temporal cortex or lateral entorhinal cortex impairs visual memory, whereas damage to the hippocampal region does not affect retention of a visual discrimination task. Major input pathways of the above structures use glutamate as neurotransmitter. The glutamate NMDA receptor appears to play an important role for cognitive functions. The objective of the present study was to examine whether microinjections of the functional NMDA receptor antagonist, 3-amino-1-hydroxy-2-pyrrolidinone ((+)-HA-966), might result in effects mimicking those seen in lesion studies. The results show that infusion of HA-966 into the temporal cortex or lateral entorhinal cortex 1.5-3 h after the learning criterion had been obtained led to an impeded visual memory when tested 13 days later, whereas HA-966 infused into the hippocampal region did not affect memory. A similar retention deficit with HA-966 infusions in the temporal cortex or lateral entorhinal cortex was seen when testing took place 23 days later, whereas a markedly weaker effect was observed when the retention period was reduced to 3 days. It is suggested that the hippocampal region is a temporary storing site for nonspatial memory engrams, and later posttraining memory consolidation involves the temporal and lateral entorhinal cortices. Furthermore, the degree of the effect of HA-966 is related to the length of the retention period.