Glutamate and imprinting memory: the role of glutamate receptors in the encoding of imprinting memory.

Glutamate-sensitive receptors have been implicated in many forms of neural plasticity and learning, including imprinting of chicks. Previous studies have indicated that glutamate binding levels in the left intermediate medial hyperstriatum ventrale (IMHV) region of the chick forebrain increase as a correlate of the acquisition of an imprinting memory; however, it has not been determined whether this is due to an increase in the number of glutamate receptors or to increased receptor affinity. The area specificity of these changes, within the left and right hemisphere, was also unexplored. We have performed Scatchard displacement binding analyses to examine changes in both the number and affinity of glutamate receptors in the left and right hyperstriatum ventrale (HV) and also the left and right archistriatal/lobus parolfactorius (AS/LPO) areas from imprinted and non-imprinted chicks. The results of this study demonstrate lateralised increases in both the number and affinity of glutamate receptors in the left HV area at 7-8 h after imprinting. Significant increases in the affinity, but not the number, of glutamate receptors were found in the left AS/LPO. This suggests that the left AS/LPO, which has previously been shown to be involved in the acquisition of a passive avoidance memory, may also be involved in the formation of an imprinting memory.