Dongfeng Li

Castration modulates singing patterns and electrophysiological properties of RA projection neurons in adult male zebra finches

Castration can change levels of plasma testosterone. Androgens such as testosterone play an important role in stabilizing birdsong. The robust nucleus of the arcopallium (RA) is an important premotor nucleus critical for singing. In this study, we investigated the effect of castration on singing patterns and electrophysiological properties of projection neurons (PNs) in the RA of adult male zebra finches. Adult male zebra finches were castrated and the changes in bird song assessed. We also recorded the electrophysiological changes from RA PNs using patch clamp recording. We found that the plasma levels of testosterone were significantly decreased, song syllable’s entropy was increased and the similarity of motif was decreased after castration. Spontaneous and evoked firing rates, membrane time constants, and membrane capacitance of RA PNs in the castration group were lower than those of the control and the sham groups. Afterhyperpolarization AHP time to peak of spontaneous action potential (AP) was prolonged after castration.These findings suggest that castration decreases song stereotypy and excitability of RA PNs in male zebra finches.

Electrophysiological properties of neurons in the robust nucleus of the arcopallium of adult male zebra finches.

Nucleus robust arcopallium (RA) of the songbird is a distinct forebrain region that is essential for song production. To explore the electrophysiological properties, whole cell recordings were made from adult zebra finch RA neurons in slice preparations. Based on the electrophysiological properties, neurons in RA were classified into two distinct classes. Type I neurons were spontaneously active. They had larger input resistance, longer time constant, larger time-peak of an afterhyperpolarization (AHP), and broader action potentials than those of the other class. A slow, time-dependent inward rectification was induced by hyperpolarizing current pulses in this type of neuron, and was blocked by external CsCl (2mM). Type II neurons had a more negative resting membrane potential than that of type I neurons. They were characterized by a steeper slope of the recovery from the peak of the AHP and frequency-current relationships, a higher firing threshold, and irregular spiking in response to depolarizing current injection.

Activation of D1-like dopamine receptors increases the NMDA-induced gain modulation through a PKA-dependent pathway in the premotor nucleus of adult zebra finches

Interaction between dopamine (DA) and N-methyl-d-aspartate (NMDA) in the brain plays an important role in learning and memory. In the songbirds, the premotor robust nucleus of the arcopallium (RA) receives excitatory glutamatergic inputs from the high vocal center (HVC) and lateral magnocellular nucleus of the anterior nidopallium (LMAN), as well as dopaminergic inputs mostly from the periaqueductal gray (PAG) and ventral tegmental area (VTA). In zebra finch, DA potentiates the excitability of projection neurons in the RA through activation of D1-like dopamine receptors (D1 receptors). The relationship between D1 receptors and NMDA in the RA projection neurons is essentially unknown. Our previous work showed that NMDA can induce gain modulation in the RA projection neurons. Here, using the whole-cell current-clamp recording from brain slices of male zebra finches, we observed whether D1 receptors regulate the NMDA-induced gain modulation in the RA projection neurons. Our results showed that activation of D1 receptors further increased the slope (gain) of the firing frequency-injected current (f-I) relationship induced by NMDA in the RA projection neurons. Blocking D1 receptors had no effect on the NMDA-induced gain modulation in the RA projection neurons. The enhanced effects of D1 receptors agonists were blocked by protein kinase A (PKA) inhibitors. Our results suggest that activation of D1 receptors can increase the NMDA-induced gain modulation through a PKA-dependent pathway.

Dopamine modulates the excitability of projection neurons in the robust nucleus of the arcopallium in adult zebra finches.

Background The nervous system in songbirds is an accessible system for studying vocal learning and memory in vertebrates. In the song system, the anterior forebrain pathway (AFP) is essential for song learning and the vocal motor pathway (VMP) is necessary for song production. The premotor robust nucleus of the arcopallium (RA) located in the VMP receives input from the AFP. The RA receives dopaminergic innervations from the periaqueductal gray and ventral tegmental area–substantia nigra pars compacta, but the physiological functions of this projection remain unclear. In this study, we investigated the effects of dopamine (DA) on the excitability of projection neurons (PNs) in the RA. Methodology We recorded the electrophysiological changes from neurons in brain slices of male adult zebra finches using a whole-cell recording technique. Conclusions/Significance We found that DA significantly increased the excitability of RA PNs. Furthermore, a D1-like receptor agonist increased the excitability of RA PNs, and a D1-like receptor antagonist suppressed the excitability induced by DA. However, a D2-like receptor agonist had no effect on the excitability of RA PNs. Moreover, the D2-like receptor agonist did not change the excitability induced by the D1 receptor agonist. These findings suggest that DA can significantly increase the excitability of RA PNs and that D1 receptors play the main role in regulating the excitability of RA PNs in response to DA, thereby providing direct evidence toward understanding the mechanism of DA signal mediation by its receptors to modulate the excitability of RA PNs.

Sexual dimorphism of the electrophysiological properties of the projection neurons in the robust nucleus of the arcopallium in adult zebra finches

To observe the sexual differences in electrophysiological properties of neurons in the robust nucleus of the arcopallium (RA) in adult zebra finches, and to provide the direct electrophysiological evidence for the sexual dimorphism of birdsong. Whole-cell recording was used to record the spontaneous action potential firing rates from RA projection neurons in acute brain slices. The projection neurons of RA in male birds fired spontaneously at 10 Hz or above, while in female birds, the frequency was significantly lower, and even no firings could be detected. There is a sexual difference in electrophysiological properties of projection neurons in RA, which may result from the difference in the levels of steroid hormones in birds. 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。 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。 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10 Hz。 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。 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。ObjectiveTo observe the sexual differences in electrophysiological properties of neurons in the robust nucleus of the arcopallium (RA) in adult zebra finches, and to provide the direct electrophysiological evidence for the sexual dimorphism of birdsong.MethodsWhole-cell recording was used to record the spontaneous action potential firing rates from RA projection neurons in acute brain slices.ResultsThe projection neurons of RA in male birds fired spontaneously at 10 Hz or above, while in female birds, the frequency was significantly lower, and even no firings could be detected.ConclusionThere is a sexual difference in electrophysiological properties of projection neurons in RA, which may result from the difference in the levels of steroid hormones in birds.摘要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10 Hz。 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。

SK channels modulate the excitability and firing precision of projection neurons in the robust nucleus of the arcopallium in adult male zebra finches

ObjectiveMotor 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.MethodsThe firing properties of RA projection neurons were analyzed using patch clamp wholecell and cell-attached recording techniques.ResultsSK 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.ConclusionSK channels contribute to the maintenance of firing regularity in RA projection neurons which requires synaptic activity, and consequently ensures the precision of song encoding.

The Gain Modulation by N-methyl-D-aspartate in the Projection Neurons of Robust Nucleus of the Arcopallium in Adult Zebra Finches

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 songbirds brain, influences the song directly. This variability in adult birdsong is associated with the activity of NMDA receptors in LMAN-RA synapses, but the detailed mechanism is unclear. The control of gain refers to modulation of a neurons 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.

Muscarinic Receptors Are Responsible for the Cholinergic Modulation of Projection Neurons in the Song Production Brain Nucleus RA of Zebra Finches

Songbirds are a useful model for the study of learned vocal behavior in vertebrates. The robust nucleus of the arcopallium (RA) is a premotor nucleus in the vocal motor pathway. It receives excitatory synaptic inputs from the anterior forebrain pathway. RA also receives cholinergic inputs from the ventral paleostriatum of the basal forebrain. Our previous study showed that carbachol, a non-selective cholinergic receptor agonist, modulates the electrophysiology of RA projection neurons (PNs), indicating that cholinergic modulation of RA may play an important role in song production. However, the receptor mechanisms underlying these effects are poorly understood. In the present study, we investigated the electrophysiological properties of two acetylcholine receptors on the RA PNs of adult male zebra finches using in vitro whole-cell current clamp. Our results demonstrate that activation of muscarinic acetylcholine receptors (mAChRs) simulate the effects of carbachol. Both carbachol and the mAChR agonist muscarine produced a decrease in the excitability of RA PNs and a hyperpolarization of the membrane potential. The mAChR antagonist atropine blocked the effects of carbachol. Activation of nicotinic acetylcholine receptors (nAChRs) with nAChR agonist nicotine or DMPP had no effect on the excitability of RA PNs, and the nAChR antagonist mecamylamine failed to inhibit the effects of carbachol. These results suggest that mAChRs, but not nAChRs, primarily modulate the effects of carbachol on the activity of RA PNs. Collectively, these findings contribute to our understanding of the mechanism of cholinergic modulation in the vocal nuclei of songbirds.

Carbachol-Induced Reduction in the Activity of Adult Male Zebra Finch RA Projection Neurons

Cholinergic mechanism is involved in motor behavior. In songbirds, the robust nucleus of the arcopallium (RA) is a song premotor nucleus in the pallium and receives cholinergic inputs from the basal forebrain. The activity of projection neurons in RA determines song motor behavior. Although many evidences suggest that cholinergic system is implicated in song production, the cholinergic modulation of RA is not clear until now. In the present study, the electrophysiological effects of carbachol, a nonselective cholinergic receptor agonist, were investigated on the RA projection neurons of adult male zebra finches through whole-cell patch-clamp techniques in vitro. Our results show that carbachol produced a significant decrease in the spontaneous and evoked action potential (AP) firing frequency of RA projection neurons, accompanying a hyperpolarization of the membrane potential, an increase in the evoked AP latency, afterhyperpolarization (AHP) peak amplitude, and AHP time to peak, and a decrease in the membrane input resistance, membrane time constant, and membrane capacitance. These results indicate that carbachol reduces the activity of RA projection neurons by hyperpolarizing the resting membrane potential and increasing the AHP and the membrane conductance, suggesting that the cholinergic modulation of RA may play an important role in song production.

Sex differences of excitatory synaptic transmission in RA projection neurons of adult zebra finches

Zebra finches are ideal animals to investigate sex difference in songbirds. Only males can sing. The brain nuclei controlling song learning and production in males are considerably larger than in females. The robust nucleus of the arcopallium (RA) is a premotor nucleus, playing a key role in controlling singing. RA receives denser synapse inputs in males than in females. Sex differences of excitatory synaptic transmission in the RA projection neurons (PNs) have not been reported. In the present study, using whole-cell voltage-clamp recording, spontaneous EPSCs (sEPSCs) and miniature EPSCs (mEPSCs) of RA PNs in the intact males and females were recorded. The average frequency and amplitude of sEPSCs/mEPSCs in the intact males were higher than females. The half-width and decay time of sEPSCs/mEPSCs in the intact males were longer than females. In order to verify whether these sex differences related to sex steroids, males were castrated. The average frequency of sEPSCs/mEPSCs in castrated males was lower than intact males and was similar to in females; the amplitude was not changed after castrating. These results demonstrate the sexually dimorphic of the excitatory synaptic transmission in the RA PNs, the RA PNs in males receive more excitatory synaptic transmission and these sex differences were partly affected by sex hormones. These findings contribute to further illuminate the neural mechanisms under the sexually dimorphism in song production of adult zebra finches.