Is rapid effect of thyroxine on GABAergic IPSCs purely postsynaptic?

BACKGROUND Thyroid hormones (THs) are well known for their genomic effects but recently several studies revealed their actions as rapid modulators of membrane receptors. In particular, fast thyroxine effect on GABA(A) receptors have been reported. We addressed question whether presynaptic mechanisms can be also involved in modulation of GABAergic transmission by thyroxine. METHODS Using patch-clamp technique we examined fast effects of thyroxine (2 μM) on evoked GABAergic postsynaptic currents. RESULTS We found that in addition to the inhibitory effect on IPSC amplitude, thyroxine changed IPSC coefficient of variation (CV). CONCLUSION This result suggests involvement of a presynaptic mechanism in thyroxine effect on GABAergic transmission.