Sexual dimorphism of inhibitory synaptic transmission in RA projection neurons of songbirds.

The song control system in the brain of songbirds is important for the production and acquisition of song and exhibits some of the largest neural sex differences observed in vertebrates. The robust nucleus of the arcopallium (RA) is a premotor nucleus, playing a key role in controlling singing. RA projection neurons (PNs) receives denser synapse inputs including excitatory in males than in females. However, the inhibitory synaptic transmission in the RA has not been reported. In the present study, using whole-cell voltage-clamp recording, spontaneous inhibitory postsynaptic currents (sIPSCs) and miniature inhibitory postsynaptic currents (mIPSCs) of the males and females were recorded. The average frequency and amplitude of sIPSCs/mIPSCs in males were higher than females. These results demonstrate the sexually dimorphic of the inhibitory synaptic transmission in the RA PNs and the RA PNs in males receive more inhibitory synaptic transmission. These findings contribute to further illuminate the neural mechanisms under the sexually dimorphism song production of adult zebra finches.