Impairment of learning by localized injection of an N-methyl-D-aspartate receptor antagonist into the hyperstriatum ventrale of the domestic chick.

A restricted part of the domestic chick forebrain is critically involved in the learning process of imprinting. This region is the intermediate and medial part of the hyperstriatum ventrale (IMHV). The effect on imprinting of local injection of the N-methyl-D-aspartate (NMDA) receptor blocker D-amino-5-phosphonopentanoic acid (D-AP5) into the left IMHV was studied in chicks in which the right IMHV had been lesioned. The left IMHV is essential for imprinting when chicks have been lesioned in this way. Injection of approximately 0.7 nmol D-AP5 into the left IMHV significantly impaired imprinting. Injection of approximately 0.2 nmol D-AP5 into the left IMHV, or of approximately 0.7 nmol D-AP5 into the left hyperstriatum accessorium, was without significant effect on imprinting. These results suggest that NMDA receptors in the left IMHV may play an important part in this learning process.