Expression and Rapid Experience-Dependent Regulation of Type-A GABAergic Receptors in the Songbird Auditory Forebrain

GABAergic transmission influences sensory processing and experience-dependent plasticity in the adult brain. Little is known about the functional organization of inhibitory circuits in the auditory forebrain of songbirds, a robust model extensively used in the study of central auditory processing of behaviorally relevant communication signals. In particular, no information is currently available on the expression and organization of GABA(A) receptor-expressing neurons. Here, we studied the distribution and regulation of GABA(A) receptors in the songbird auditory forebrain, with a specific focus on alpha 5, a subunit implicated in tonic inhibition and sensory learning. We obtained a zebra finch cDNA that encodes the alpha 5-subunit (GABRA5) and carried out a detailed analysis of its expression via in situ hybridization. GABRA5 was highly expressed in the caudomedial nidopallium (NCM), caudomedial meso-pallium, and field L2. Using double fluorescence in situ hybridization, we demonstrate that a large fraction of GABRA5-expressing neurons is engaged by auditory experience, as revealed by the song-induced expression of the activity-dependent gene zenk. Remarkably, we also found that alpha 5 expression is rapidly regulated by sensory stimulation: 30 min of conspecific song playbacks significantly increase the number of GABRA5-expressing neurons in NCM, but not in other auditory areas. This effect is selective for alpha 5, but not gamma 2 transcripts. Our results suggest that alpha 5-containing GABA(A) receptors likely play a key role in central auditory processing and may contribute to the experience-dependent plasticity underlying auditory learning. (C) 2011 Wiley Periodicals, Inc. Develop Neurobiol 71: 803-817, 2011