Abstract
Dopamine (DA) is an important neuromodulator of motor control across species. In zebra finches, DA levels vary in song nucleus Area X depending upon social context. DA levels are high and song output is less variable when a male finch sings to a female (female directed, FD) compared to when he is singing by himself (undirected, UD). DA modulates glutamatergic input onto cortico-striatal synapses in Area X via N-methyl-d-aspartate (NMDA) and DA receptor mechanisms, but the relationship to UD vs. FD song output is unclear. Here, we investigate the expression of molecular markers of dopaminergic and glutamatergic synaptic transmission (tyrosine hydroxylase - TH, alpha-synuclein - α-syn) and plasticity (NMDA 2B receptor - GRIN2B) following singing (UD vs. FD) and non-singing states to understand the molecular mechanisms driving differences in song output. We identified relationships between protein levels for these biomarkers in Area X based on singing state and the amount of song, measured as the number of motifs and time spent singing. UD song amount drove increases in TH, α-syn, and NMDA 2B receptor protein levels. By contrast, the amount of FD song did not alter TH and NMDA 2B receptor expression. Levels of α-syn showed differential expression patterns based on UD vs. FD song, consistent with its role in modulating synaptic transmission. We propose a molecular pathway model to explain how social context and amount of song are important drivers of molecular changes required for synaptic transmission and plasticity.