SLOW SYNAPTIC INHIBITION IN NUCLEUS HVC OF THE ADULT ZEBRA FINCH

Nervous systems process information over a broad range of time scales and thus need corresponding cellular mechanisms spanning that range. i n the avian song system, long integration times are likely necessary t o process auditory feedback of the bird's own vocalizations. For examp le, in nucleus HVc, a center that contains both auditory and premotor neurons and that is thought to act as a gateway for auditory informati on into the song system, slow inhibitory mechanisms appear to play an important role in the processing of auditory information. These long-l asting processes include inhibitory potentials thought to shape audito ry selectivity and a vocalization-induced inhibition of auditory respo nses lasting several seconds. To investigate the possible cellular mec hanisms of these long-lasting inhibitory processes, we have made intra cellular recordings from HVc neurons in slices of adult zebra finch br ains and have stimulated extracellularly within HVc. A brief, high-fre quency train of stimuli (50 pulses at 100 Hz) could elicit a hyperpola rizing response that lasted 2-20 sec. The slow hyperpolarization (SH) could still be elicited in the presence of glutamate receptor blockers , suggesting that it does not require polysynaptic excitation. Three m ajor components contribute to this activity-induced SH: a long-lasting GABA(B) receptor-mediated IPSP, a slow afterhyperpotarization requiri ng action potentials but not Ca2+ influx, and a long-tasting IPSP, the neurotransmitter and receptor of which remain unidentified. These thr ee slow hyperpolarizing events are well placed to contribute to the ob served inhibition of HVc neurons after singing and could shape auditor y feedback during song learning.