Estradiol acutely modifies singing patterns via modulating the synaptic activity of RA in Zebra Finches

Songbirds serve as an appealing animal model for evaluating the hormonal influences on the regulation of fine motor skills, particularly in relation to vocal production. The influence of estrogens on the singing behavior of adult songbirds remains to be explored. The robust nucleus of the arcopallium (RA), a premotor nucleus, assumes a critical role in governing vocalization of songbirds. This study initially examined the rapid effects of 17β-estradiol (E2) on the RA in relation to the singing behavior of adult Zebra Finches (Taeniopygia guttata), followed by an investigation into the impact of E2 on excitatory and inhibitory synaptic transmission within the RA. The expression levels of receptors associated with neuronal excitability and inhibition were also analyzed in the RA nucleus. The results indicated that the action of E2 on the RA rapidly reduces the stability of the song. E2 decreases the frequency and amplitude of sEPSCs/mEPSCs and sIPSCs/mIPSCs in the RA projection neurons (PNs) and it also reduces the amplitude of eEPSCs induced by RA PNs from HVC, LMAN and RA collateral afferent as well as the amplitude of eIPSCs induced by RA PNs from RA collateral afferent. Further analysis showed that E2 changes the synapse transmission through binding to GPER; E2 treatment reduces the expression levels of NR2A, NR2B, AMPAR, and GABAAR in the RA nucleus. The findings suggest that estrogen inhibits song stability by modulating the excitability and the inhibitory synaptic structure and function of the RA nucleus, thereby providing evidence for the neural mechanisms underlying estrogen's regulation of fine motor skills.