Effect of Vocal Nerve Section on Song and ZENK Protein Expression in Area X in Adult Male Zebra Finches

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

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

Dopamine modulates synaptic transmission in the premotor nuclei of songbirds

Songbirds, such as zebra finches, contribute to explore behaviors underlying neural activities. Birdsong is controlled by the song system. The robust nucleus of the arcopallium (RA) is a key nucleus for producing birdsong in the song system. The RA receives dopaminergic （DArgic） inputs from the midbrain, however, the function of these inputs involved excitatory synaptic transmission is still unclear. Excitatory synaptic transmission is critical in the signal integration activities of the brain. We examined the effects of dopamine (DA) on excitatory synaptic transmission of the projection neurons in the RA of adult male zebra finches, using whole-cell recording technique. We found that DA (100 μM) decreases the frequency of spontaneous and miniature excitatory postsynaptic currents (sEPSCs/mEPSCs). In our further study, these effects of DA were reversed by the D1-like dopamine receptor (D1R) antagonist and stimulated by a D1R agonist. However, a D2-like dopamine receptor (D2R) has no influence on the effects of DA. These results demonstrate that DA can inhibit excitatory synaptic transmission mainly via activation of D1R in adult male zebra finches. PeerJ PrePrints | https://doi.org/10.7287/peerj.preprints.1563v1 | CC-BY 4.0 Open Access

Effect of Vocal Nerve Section on Song and ZENK Protein Expression in Area X in Adult Male Zebra Finches

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

Effects of DA (50 μM) on the excitability of RA PNs.

<p>A. Numbers of spikes evoked by suprathreshold current pulses (100 pA; 500 ms). B_1–3. Example traces from the experiment shown in (A). The numbers shown in (B) indicate the timing of each example trace. C. DA significantly increases the normalized spike rate in RA PNs. The dashed line indicates the control level (100%). D. Effects of DA on the membrane potential (*<i>p</i><0.05).</p

Effects of the D1-like receptor antagonist SCH-23390 (20 μM) on the excitability of RA PNs.

<p>A. In the presence of DA (50 μM), SCH-23390 (20 μM) inhibits the increase in evoked firing. B_1–3. Example traces from the experiment shown in (A). The numbers shown in (A) indicate the timing of each example trace. C. The D1-like receptor antagonist SCH-23390 significantly decreases the normalized spike rate induced by DA. The dashed line indicates the control level (100%). D. Effects of DA and SCH-23390 on the membrane potential (*<i>p</i><0.05).</p

Effects of the D2-like receptor agonist quinpirole (10 μM).

<p>A. Application of quinpirole (10 μM) has no effect on the number of evoked firings. B_1–3. Example traces from the experiment shown in (A). The numbers shown in (A) indicate the timing of each example trace. C. Quinpirole does not significantly change the normalized spike rate in PNs in the RA. The dashed line indicates the control level (100%). D. Effects of quinpirole on the membrane potential.</p

Effects of the D1-like and D2-like receptor agonists on the excitability of RA PNs.

<p>A. Effect of quinpirole (10 μM) application after SKF-38393 (10 μM) application. B_1–3. Example traces from the experiment shown in (A). The numbers shown in (A) indicate the timing of each example trace. C. Effects of quinpirole application after SKF-38393 application. The dashed line indicates the control level (100%) (*<i>p</i><0.05). </p

Effects of DA (50 μM) and sulpiride (10 μM) on the excitability of RA PNs.

<p>A. In the presence of DA (50 μM), sulpiride (10 μM) does not influence the evoked firing. B_1–3. Example traces from the experiment shown in (A). The numbers shown in (A) indicate the timing of each example trace. C. The D2-like DA receptor antagonist sulpiride does not significantly change the normalized spike rate induced by DA. The dashed line indicates the control level (100%). D. Effects of DA and sulpiride on the membrane potential (*<i>p</i><0.05).</p