An interneuronal CRH and CRHBP circuit stabilizes birdsong performance

The performance of skilled behaviors requires a balance between consistency and adaptability. Although the neural mechanisms that regulate this balance have been extensively studied at systems and physiological levels, relatively little is known about how the molecular properties of motor circuits influence motor stability versus flexibility. Here, we characterize the region- and cell-type specific expression patterns of neuropeptide systems across the neural circuit that controls the learning and performance of birdsong, a model for skilled behavior. We identify a number of neuropeptide pathways with differential expression between song regions and surrounding areas that are not involved in song production or learning. One of the strongest enriched genes in song regions is corticotropin releasing hormone binding protein (CRHBP), whose product binds corticotropin releasing hormone (CRH), a neuropeptide implicated in neuronal excitability and plasticity. We find that the expression of CRHBP in the song motor pathway decreases upon deafening-induced song destabilization, increases during song acquisition, and increases the more a bird sings. CRH and CRHBP are expressed in distinct interneuronal populations in song motor regions, providing a local neuromodulatory circuit well-positioned to regulate song performance. Consistent with this role, genetic and pharmacological manipulation of the CRH pathway in the song motor pathway resulted in bidirectional modifications of song variability, with elevated CRHBP acting to maintain low variability and elevated CRH acting to increase variability. These data indicate that an interneuronal neuropeptidergic pathway maintains the stability of song, acting as a local mechanism that regulates the balance between motor consistency versus flexibility.