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Blockade of NMDA Receptors during Song Model Exposure Impairs Song Development in Juvenile Zebra Finches

Juvenile zebra finches (Poephila guttata) learn their courtship song by memorizing and then reproducing the song of an adult male. Several brain regions involved in song behavior contain N-methyl-D-aspartate (NMDA) receptors, and within one brain nucleus necessary for normal song development, the density of these receptors is twice as high in juveniles that are learning song then in adults that can no longer modify their songs. To determine whether NMDA receptor activation is necessary for normal song development, juvenile zebra finches were systemically injected with the NMDA receptor antagonist MK-801 (0.1 mg/kg) before exposure to an adult male tutor. One control group received the same number of MK-801 injections 24 h out of phase with tutoring, and another received saline before tutoring. In adulthood, birds given MK-801 before tutoring showed little evidence of learning from the tutor, and their songs contained abnormal syllables typical of untutored birds. In contrast, all control birds developed normal songs and copied an average of 72.5% of the tutor's syllables. Acute injections of MK-801 did not alter auditory brainstem evoked potentials in juveniles, indicating that the behavioral effects of MK-801 on song learning were not due to temporary hearing loss. Our results suggest that normal song development in juvenile zebra finches requires NMDA receptor activation during song model presentation.