Abstract
Many songbirds sing in non-reproductive contexts while in flocks. Singing in such gregarious contexts is critical for maintaining and learning songs; however, song is not directed towards other individuals and has no obvious, immediate social consequences. Studies using conditioned place preference (CPP) tests of reward indicate that song production in gregarious contexts correlates positively with a bird’s intrinsic reward state and with opioid markers in the medial preoptic nucleus (mPOA). However, the causal involvement of opioids in gregarious song is unknown. Here we report that the selective mu opioid receptor (MOR) agonist fentanyl dose-dependently facilitates gregarious song and reduces stress/anxiety-related behavior in male and female European starlings. Furthermore, infusion of siRNA targeting MORs specifically in mPOA both suppresses gregarious song and disrupts the positive association between affective state and singing behavior, as revealed using CPP tests of song-associated reward. Results strongly implicate opioids in gregarious song and suggest that endogenous opioids in the mPOA may facilitate song by influencing an individual’s intrinsic reward state.
Highlights
Many songbirds sing in non-reproductive contexts while in flocks
Results suggest a role for mu opioid receptor (MOR) in mPOA in gregarious song and the positive affective state associated with singing behavior
We report that peripheral injections of the selective MOR agonist fentanyl cause dose-dependent increases in gregarious singing behavior in male and female starlings, while at the same time decreasing beak wiping, which is considered a sign of stress or anxiety[39,40]
Summary
Many songbirds sing in non-reproductive contexts while in flocks. Singing in such gregarious contexts is critical for maintaining and learning songs; song is not directed towards other individuals and has no obvious, immediate social consequences. Studies using conditioned place preference (CPP) tests of reward indicate that song production in gregarious contexts correlates positively with a bird’s intrinsic reward state and with opioid markers in the medial preoptic nucleus (mPOA). Infusion of siRNA targeting MORs in mPOA both suppresses gregarious song and disrupts the positive association between affective state and singing behavior, as revealed using CPP tests of songassociated reward. Positive correlations were found between gregarious song, a bird’s affective state (measured using CPP), and mRNA measurements in mPOA for MOR as well as the precursor for a MOR ligand, pre-proenkephalin[23] These correlational data strongly suggest that gregarious singing behavior, reward state, and opioid markers are related; the causal nature of these relationships has not been tested
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