Functional properties and short-term dynamics of unidirectional and reciprocal synaptic connections between layer 2/3...

The interactions between inhibitory fast-spiking (FS) interneurons and excitatory pyramidal neurons contribute to the fundamental properties of cortical networks. An important role for FS interneurons in mediating rapid inhibition in local sensory and motor cortex microcircuits and processing thalamic inputs to the cortex has been shown in multiple reports; however, studies in the prefrontal cortex, a key neocortical region supporting working memory, are less numerous. In the present work, connections between layer 2/3 pyramidal cells and FS interneurons were studied with paired whole-cell recordings in acute neocortical slices of the medial prefrontal cortex from juvenile rats. The connection rate between FS interneurons and pyramidal neurons was about 40% in each direction with 16% of pairs connected reciprocally. Excitatory and inhibitory connections had a high efficacy and a low neurotransmission failure rate. Sustained presynaptic activity decreased the amplitude of responses and increased the failure rate more in excitatory connections than in inhibitory connections. In the reciprocal connections between the FS and pyramidal neurons, inhibitory and excitatory neurotransmission was more efficient and had a lower failure rate than in the unidirectional connections; the differences increased during the train stimulation. These results suggest the presence of distinct preferential subnetworks between FS interneurons and pyramidal cells in the rat prefrontal cortex that might be specific for this cortical area.