Dopaminergic facilitation of GABAergic transmission in layer III of rat medial entorhinal cortex.

The medial entorhinal cortex (MEC) receives a dense dopaminergic innervation and expresses dopamine receptors. However, little is known about the effect of dopamine on GABAergic transmission in this region of the brain. In this study, we recorded GABAA receptor-mediated spontaneous inhibitory postsynaptic currents (sIPSCs) and miniature inhibitory postsynaptic currents (mIPSCs) by using whole-cell patch-clamp technique. Application of dopamine at 10 μM and 100 μM significantly increased the frequency and amplitude of sIPSCs. This effect of dopamine is primarily mediated by acting at D1-like dopamine receptors, but not D2-like and α1 adrenergic receptors, since dopamine-induced increased in frequency and amplitude of the sIPSCs was completely blocked by D1-like, but not D2-like or α1 adrenergic, receptor antagonist. However, application of dopamine did not affect the frequency and amplitude of the mIPSCs, implying that the effect of dopamine on the GABAergic transmission is action potential-dependent. Together, these findings reveal an indirect mechanism by which activation of D1-like receptors could inhibit the excitability of layer III pyramidal neurons in the MEC.