Electrical synapses between layer 1 interneurons in the medial prefrontal cortex

The medial Prefrontal Cortex (mPFC) receives and coordinates signals from many brain regions and is an executive hub for the interplay of sensory, limbic, and motor information. Layer 1 (L1) interneurons are essential for signal integration within the mPFC, and they are known to play a role in the maintenance of brain oscillations. However, little is known about the plasticity of electrical synapses (ES) in the L1 of the mPFC. By paired patch-clamp recordings on acute brain slices, we provide novel and conclusive evidence of functional ES between interneurons in L1 of the mPFC. ES in L1 of mPFC are asymmetric in their bilateral signal conduction, undergo use-dependent and frequency-dependent plasticity, and their coupling strength and low-pass filtering properties appear to be distance-dependent. Plasticity was investigated under five stimulation paradigms, simulating neural activity in the PFC-typical theta range, with unilateral and bilateral communication between coupled neurons. All stimulation patterns caused a decrease in the input resistance (Rin) of coupled cells. Unilateral 6 Hz stimulation caused a long-term 20% decrease in the coupling coefficient (CC) in both transmission directions. However, changes in the CCs after stimulation are probably determined, at least in part, by changes in the Rin, as changes in transjunctional conductance were non-significant, albeit similar in tendency. Furthermore, the plasticity range of electrical synapses seems to be determined by their initial state. These findings of electrical synaptic transmission in L1 are a key step in understanding the mode of operation of the mPFC in a neural network.