Abstract
BackgroundThe 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. MethodologyWe recorded the electrophysiological changes from neurons in brain slices of male adult zebra finches using a whole-cell recording technique.Conclusions/SignificanceWe 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.
Highlights
Birdsong is controlled by the song system
Our data indicated that DA caused cell depolarization without any stimulation, suggesting that DA affects the excitability of RA projection neurons (PNs) and modulates their membrane potential
In the presence of TTX, DA caused membrane potential depolarization (Figure 2C, 2D). These results suggested that DA enhanced the excitability of RA PNs via activation of DA receptors, but not through Na+ currents
Summary
Birdsong is controlled by the song system. The song system is a network of discrete areas devoted to song learning and production [1], and consists of two functional pathways: the vocal motor pathway (VMP) required for song production and the anterior forebrain pathway (AFP) necessary for song learning, recognition, and plasticity [2,3,4]. The RA mainly receives dopaminergic (DAergic) inputs from the periaqueductal gray and ventral tegmental area (VTA) DAergic cell groups, and shows expression of D1-like and D2-like family receptors [16,17]. D3 receptors are located in VMP nuclei, suggesting their specialized role for vocal output [17]. These observations indicate that DA in the RA is important for song production, but the detailed mechanism remains unclear. 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
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