Abstract
Neurons process information through spatiotemporal integration of synaptic input. Synaptic transmission between any given pair of neurons is typically a dynamic process with presynaptic action potentials(APs) evoking depressing or facilitating postsynaptic potentials when presynaptic APs occur within hundreds of milliseconds of each other. In order to understand neocortical function, it is therefore important to investigate such short-term synaptic plasticity at synapses between different types of neocortical neurons. Here, we examine short-term synaptic dynamics between excitatory neurons in different layers of the mouse C2 barrel column through in vitro whole-cell recordings. We find layer-dependent short-term plasticity, with depression being dominant at many synaptic connections. Interestingly, however, presynaptic layer 2 neurons predominantly give rise to facilitating excitatory synaptic output at short interspike intervals of 10 and 30 ms. Previous studies have found prominent burst firing of excitatory neurons in supragranular layers of awake mice. The facilitation we observed in the synaptic output of layer 2 may, therefore, be functionally relevant, possibly serving to enhance the postsynaptic impact of burst firing.
Highlights
The mammalian neocortex contributes to sensory perception, sensorimotor processing, cognition, learning, and memory
Simultaneous whole-cell recordings were obtained in vitro from nearby excitatory neurons located within the same neocortical layer of the C2 barrel column, and suprathreshold current pulses were injected into each recorded neuron in turn to test for synaptic connectivity (Lefort et al 2009)
Short-term synaptic plasticity was quantified by calculating the paired-pulse ratios (PPR)
Summary
The mammalian neocortex contributes to sensory perception, sensorimotor processing, cognition, learning, and memory. In order to understand mechanistically how the neocortex functions, we need to examine the constituent individual neurons and their interactions within the complex neuronal networks of the mammalian brain. Each neocortical neuron receives synaptic inputs from many presynaptic neurons, which are integrated across the somatodendritic arborization. A wiring diagram of synaptic connectivity is of enormous importance for understanding neocortical function, but will not suffice due to nonlinear spatiotemporal integration of the synaptic input and neuromodulatory effects on neuronal network function. The temporal pattern of presynaptic action potentials (APs) dynamically modulates the efficacy of synaptic transmission, a process termed short-term synaptic plasticity. Previous studies have already shown that facilitation and depression are prominent between diverse types of neocortical neurons
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