Social context-dependent singing-regulated dopamine

Abstract

Like the mammalian striatum, the songbird striatum receives dense dopaminergic input from the midbrain ventral tegmental area-substantia nigra pars compacta complex. The songbird striatum also contains a unique vocal nucleus, Area X, which has been implicated in song learning and social context-dependent song production. Area X shows increased neural firing and activity-dependent gene expression when birds sing, and the level of activation is higher and more variable during undirected singing relative to directed singing to other birds. Here we show in the first report of in vivo microdialysis in awake, behaving songbirds that singing is associated with increased dopamine levels in Area X. Dopamine levels are significantly higher with directed relative to undirected singing. This social context-dependent difference in dopamine levels requires the dopamine transporter, because local in vivo blockade of the transporter caused dopamine levels for undirected singing to increase to levels similar to that for directed singing, eliminating the social context-dependent difference. The increase in dopamine is presumably depolarization and vesicular release dependent, because adding of high K+ increased and removal of Ca2+ increased and decreased extracellular DA levels. Our findings implicate DA and molecules that control DA kinetics in singing behavior and social context-dependent brain function.

Figure 1.

Microdialysis setup and K⁺/Ca²⁺ regulation of DA levels in Area X. A, Vocal pathways showing DA input from VTA–SNc to Area X. White lines, Anterior vocal pathway involved in vocal learning and social context production; black lines, posterior vocal pathway involved in production of learned vocalizations; dashed lines, connections between the two pathways. Abbreviations are according to new nomenclature (Jarvis et al., 2005): DLM, dorsal lateral nucleus of mediodorsal thalamus; DM, dorsal medial nucleus of midbrain; HVC, nucleus HVC; LAreaX, lateral Area X; nXIIts, tracheosyringeal part of XII motor nucleus; RA, robust nucleus of arcopallium. B, Representative sagittal histological photograph of probe track in Area X. Dashed lines, Boundaries of Area X and LMAN. Scale bar, 1 mm. C, Microdialysis probe implanted in a freely moving songbird. The perch and seed were on a clean floor to prevent tubing from being tangled. D, Microdialysis setup showing sound attenuating chamber, video camera, pump, and tubing. E, Effect on DA levels from infusion of high K⁺ through the dialysis probe in Area X (n = 3 birds). F, Effect on DA levels from infusion of Ca²⁺ -free artificial media into Area X (n = 3 birds). *p < 0.05, **p < 0.01 relative to the 0 time point (repeated-measures ANOVA). Error bars indicate SEM.

Figure 2.

Singing behavior and DA levels in Area X. A, Number of songs and microdialysate DA levels in Area X of an example bird. Vertical bars, Singing amounts; lines, DA levels at every 10 min for 290 min; horizontal bars, the three 10 min bins of baseline (black) and singing (white and gray) DA values used to quantify relative DA levels in the graphs in B. B, Extracellular DA levels in Area X during undirected and directed singing with or without nomifensine (n = same 5 birds for each condition). Dashed line, Average nonsinging baseline DA levels normalized to 100%; inside bars, *p < 0.05 (Wilcoxon signed rank test), singing relative to baseline; above bars, *p < 0.05 and **p < 0.01 (repeated-measures ANOVA), between social contexts. Data are averages of three 10 min bins. Error bars indicate SEM. C, Average number of song motifs produced in each 30 min singing session during the periods of DA measurement in B. D, Pattern of singing across the 10 min bins when the birds did not have localized unilateral nomifensine perfusion into Area X. E, Pattern of singing across the 10 min bins when the birds had localized nomifensine perfusion. The statistical test for symbols above bars in C–E are the same as in B.