ZENK expression in vocal nuclei is associated with singing behavior. Area X is an important nucleus for learning and stabilizing birdsong. ZENK expression is higher in Area X compared to that in other vocal nuclei when birds are singing. To reveal the relationship between the ZENK expression in Area X and song crystallization, immunohistochemistry was used to detect ZENK protein expression in Area X after the unilateral vocal nerve (tracheosyringeal nerve) section in adult male zebra finches. Sham operations had no effect on song. In contrast, section of unilateral vocal nerve could induce song decrystallization at the 7th day after the surgery. The spectral and the temporal features of birdsong were distorted more significantly in the right-side vocal nerve section than in the left-side vocal nerve section. In addition, after surgery, ZENK expression was higher in the right-side of Area X than in the left-side. These results indicate that the vocal nerve innervations probably are right-side dominant. ZENK expression in both sides of Area X decreased, as compared to control group after surgery, which suggests that the ZENK expression in Area X is related to birdsong crystallization, and that there is cooperation between the Area X in AFP and syrinx nerve.

成年雄性鸣禽的习得性发声信号——长鸣(long call)和鸣唱(song)是由前脑高级发声中枢启动, 以及由前脑最后一级 输出核团弓状皮质栎核(robust nucleus of the arcopallium, RA)整合输出。RA 投射神经元与位于中脑的基本发声中枢丘间 复合体背内侧核(dorsomedial nucleus of the intercollicular, DM)形成突触连接。该文采用电损毁与声谱分析相结合的方法, 通过依次损毁成年雄性斑胸草雀(Taeniopygia guttata)单侧RA 和DM 核团, 探讨了前脑和中脑对习得性发声的影响。 结果提示, RA 核团与DM 核团共同参与了对雄性斑胸草雀习得性声音的调控, 而且这种控制具有右侧优势。

The song of zebra finch is stable in life after it was learned successfully. Vocal plasticity is thought to be a motor exploration that can support continuous learning and optimization of performance. The activity of RA, an important pre-motor nucleus in songbird’s brain, influences the song directly. This variability in adult birdsong is associated with the activity of NMDA receptors in LMANRA synapses, but the detailed mechanism is unclear. The control of gain refers to modulation of a neuron’s responsiveness to input and is critically important for normal sensory, cognitive, and motor functions. Here, we observed the change of gain in RA projection neurons after exogenous NMDA was applied to activate NMDA receptors using the whole-cell current clamp recording. We found that NMDA substantially increased the slope (gain) of the firing rate-current relationship in RA projection neurons. The AMPA receptor-dependent excitability played a crucial role in the modulation of gain by NMDA. These results suggested that NMDA receptors may regulate the dynamics of RA projection neurons by input-output gain.

Objective Motor control is encoded by neuronal activity. Small conductance Ca2+-activated K+ channels (SK channels) maintain the regularity and precision of firing by contributing to the afterhyperpolarization (AHP) of the action potential in mammals. However, it is not clear how SK channels regulate the output of the vocal motor system in songbirds. The premotor robust nucleus of the arcopallium (RA) in the zebra finch is responsible for the output of song information. The temporal pattern of spike bursts in RA projection neurons is associated with the timing of the acoustic features of birdsong. Methods The firing properties of RA projection neurons were analyzed using patch clamp wholecell and cell-attached recording techniques. Results SK channel blockade by apamin decreased the AHP amplitude and increased the evoked firing rate in RA projection neurons. It also caused reductions in the regularity and precision of firing. RA projection neurons displayed regular spontaneous action potentials, while apamin caused irregular spontaneous firing but had no effect on the firing rate. In the absence of synaptic inputs, RA projection neurons still had spontaneous firing, and apamin had an evident effect on the firing rate, but caused no significant change in the firing regularity, compared with apamin application in the presence of synaptic inputs. Conclusion SK channels contribute to the maintenance of firing regularity in RA projection neurons which requires synaptic activity, and consequently ensures the precision of song encoding.

鸣禽是除了人类以外极少数具有发声信号学习能力的动物，其已成为研究运动序列控制和学习记忆神经过程的理想模型。鸣禽端脑中的高级发声中枢（high vocal center）、弓状皮质栎核（robust nucleus of the arcopallium）和脑干中的运动核团构成了控制发声的运动通路。该文对鸣禽端脑发声运动通路的电生理学特性及其在发声控制和鸣唱学习中的作用进行了全面的分析综述。

目的 通过观察神经元在电生理特性方面的性别差异，为鸣禽鸣唱行为性别二态性提供新证据。方法 采用脑片膜片钳全细胞模式，记录成年斑胸草雀弓状皮质栎核（RA）投射神经元的动作电位自发放。结果 雄鸟RA核团投射神经元均有一定频率的自发放，且多数神经元的自发放频率超过10Hz。而雌鸟RA核团投射神经元的自发放频率相对较低，甚至无自发放。结论 成年斑胸草雀RA 核团神经元的电生理特性存在较大的性别差异。导致这种发放活动差异的主要原因可能是雌雄鸣禽体内及相关脑区激素水平的差异。

BACKGROUND: Electrophysiological properties of the song nucleus have been revealed using conventional techniques, such as intracellular and extracellular recording. Research concerning the neuronal activation properties and regulations of the song system at the cellular and ion channel level may help reveal the neural mechanism of song learning.

对近年来听觉反馈在鸣禽鸣唱学习可塑性方面的研究进行综述．鸣禽的鸣曲学习与人类的语言学习都是一种依赖于听 觉反馈的模仿学习．在鸣曲学习过程中，幼鸟根据听觉反馈的信息对鸣曲进行比较和修正，使其不断完善；在鸣曲维持过程 中，成鸟通过听觉反馈实时监测自己鸣曲的完整性与准确性，使鸣曲保持稳定．鸣曲的输出与听觉反馈信息在鸟脑中得到整 合，并指导下一次鸣唱做出适当的调整．近年来，这种感觉与运动信息在鸣禽发声核团中的整合机制逐渐引起了国内外研究 者的兴趣．其中，新纹状体巨细胞核外侧部(LMAN)神经元对自鸣曲(BOS)高度选择性的听觉应答在鸣曲去稳定化过程中的作 用，以及高级发声中枢(HVC)中镜像神经元的发现，为今后的研究提供了重要的线索．

BACKGROUND: Electrophysiological studies using brain slices have revealed that the developmental regulation of synaptic plasticity in vocal learning pathway is essential for song learning in zebra finches. Publications reporting in vivo electrophysiological investigation are scarce. Many aspects of neural mechanisms underlying song learning and production still remain uncertain. OBJECTIVE: To observe the efficacy of paired pulses and the effect on synaptic transmission induced by low-frequency stimulations, high-frequency stimulations, and theta-burst stimulations. DESIGN, TIME AND SETTING: A comparative observation. The experiment was conducted from October 2006 to October 2007 in the Neurophysiology Laboratory of South-China Normal University. MATERIALS: Twenty-four adult male zebra finches were supplied by the Department of Animal Experiment of College of Life Sciences, South China Normal University. A SEN-7203 stimulator (NIHON KOHDEN), as well as a DSJ-731WF microelectrode amplifier and DSJ-F amplifier (provided by South-China Normal University), were used to stimulate and record, respectively. METHODS: Animals were randomly divided into low-frequency, high-frequency, and theta-burst frequency stimulation groups. After recording evoked potentials, an input-output curve was evaluated. Subsequently, the efficacy of paired pulses with different stimulus intensity (1/3, 1/2, 2/3, or 3/4 of the value that induced the largest synaptic response), as well as interpulse intervals (50, 75, and 100 ms), was measured in each group. The test stimulus intensity was set to a level that evoked 1/2 or 1/3 amplitude of the maximum response. MAIN OUTCOME MEASURES: Changes in amplitude, slope, and area of evoked potentials elicited by different stimulus patterns. RESULTS: (1) Efficacy of paired pulses: there was significant paired-pulse facilitation in the high vocal center and robust nucleus of the arcopallium (HVC-RA) synapse. Efficacy decreased when paired-pulse intervals or stimulus intensities were increased. (2) Low-frequency stimulations at 1 Hz had a negligible effect on efficacy of synaptic transmission, while 5 Hz depressed synaptic transmission for only 5 minutes. (3) High-frequency stimulations at 50 Hz or 100 Hz induced synaptic depression that lasted for up to 30 minutes. (4) Theta-burst stimulation depressed synaptic transmission efficiency significantly for about 10 minutes. However, in contrast to low-frequency or high-frequency stimulations, theta-burst stimulations also induced slight potentiation of synaptic transmission for up to 60 minutes following depression phase, although the slope or area did not change. CONCLUSION: Paired pulses induced a remarkable efficacy of paired pulses in the high vocal center and robust nucleus of the arcopallium pathway. Low-frequency, high-frequency, or theta-burst frequency stimulation did not induce long-lasting changes in synaptic transmission.