BLOCKADE OF NMDA RECEPTORS IN THE ANTERIOR FOREBRAIN IMPAIRS SENSORY ACQUISITION IN THE ZEBRA FINCH (POEPHILA-GUTTATA)

Juvenile zebra finches (Poephila guttata) learn song in two stages: du ring sensory acquisition, they memorize the song of an adult tutor, an d during sensorimotor learning, they alter their vocalizations to matc h the stored song model. Like many other forms of neural plasticity an d memory formation, vocal learning in zebra finches is impaired by pha rmacological blockade of NMDA receptors, but the relevant NMDA recepto rs have not yet been localized. During song development, one neural re gion that has been implicated specifically in song learning, the IMAN, exhibits an increased density of NMDA receptors as well as decreased binding affinity for the NMDA antagonist MK-801. To test the hypothesi s that sensory acquisition requires activation of NMDA receptors in or near the IMAN we infused the NMDA receptor antagonist amino-5-phospho nopentanoic acid (AP5; 2.5 mu g in 0.1 mu l) directly into the anterio r forebrain. Birds receiving AP5 infusions prior to each of 10 tutorin g sessions copied significantly less of their tutor's song than did sh am-operated birds, saline-infused birds, birds that received AP5 infus ions on nontutoring days, or birds that received AP5 infusions into th e cerebellum. Furthermore, infusions of AP5 in the anterior forebrain did not impair young birds' ability to discriminate zebra finch from c anary song. These findings are consistent with the hypothesis that NMD A receptor activation in the anterior forebrain is necessary for the m emorization of song material during avian vocal learning. This is also the first report that song-related regions of the anterior forebrain contribute to sensory acquisition specifically. (C) 1996 Academic Pres s, Inc.