Abstract from draft of forthcoming manuscript (available upon request)
Summary and Conclusions
1. The Higher Vocal Center (HVC, previously nucleus hyperstriatum ventrale, pars caudale) of the songbird forebrain is important for the acquisition, perception, and control of learned vocalizations. We investigated synaptic interactions between neurons in HVC. Whole-cell recordings of HVC neurons were obtained in acute brain slices prepared from 37-55 day old male zebra finches.
2. Antidromic activation of one class of HVC neurons, those that project to the song control area robustus archistriatalis (RA), evoked a monosynaptic excitatory postsynaptic potential (EPSP) in all recorded HVC neurons followed by a polysynaptic inhibitory postsynaptic potential (IPSP). The IPSP reversed at a membrane potential of -68 to -72 mV and was reversibly antagonized by applying to the perfusing solution the GABAA-specific antagonist bicuculline methiodide (BMI; 5 uM).
3. In the presence of 5 uM BMI and 5 uM of 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX, a specific antagonist of AMPA/kainate receptors) and with no magnesium in the perfusing solution, stimulation of the HVC-to-RA fiber tract evoked a slow-rising (time to peak > 10 ms) and long-lasting EPSP that was reversibly abolished by 10-20 uM DL-2-amino-5- phosphonovaleric acid (APV), a specific antagonist of N-methyl-D-aspartate (NMDA) receptors.
4. These findings indicate that excitatory synaptic transmission between HVC neurons involve the release of glutamate and the activation of both AMPA/kainate and NMDA-type glutamate receptors. Additionally, widespread inhibitory interactions exist between HVC neurons that are mediated by postsynaptic GABAA receptors. HVC neurons participate directly in organizing the stereotyped pattern of zebra finch song. The possible functional roles of these neurotransmitter receptors in the auditory selectivity of HV neurons, in the motor control of singing, and in song learning are discussed.
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