Differential Short-Term Facilitation Of Synaptic Inputs And Spike Transmission At The Retinocollicular SynapseIn Vivo

Abstract

Short-term plasticity (STP) is important for understanding how neuronal circuits can perform different computations. The STP of a neuron pair can be measured directly using paired whole-cell recordings. Besides, the cross-correlation between the presynaptic and postsynaptic neuronal firing is usually used as a proxy for estimating the synaptic properties. However, the relationships between the synaptic inputs and the spiking properties of the postsynaptic neurons during the STP in vivo still remain unclear. Here, we characterized the STP of both synaptic input, measured by the postsynaptic field potential (PFP), and spike transmission at the retinocollicular pathway of mice. We found that the STP of the retinocollicular pathway is mainly facilitating, where the second presynaptic spike induces a larger PFP and higher postsynaptic firing rate than the first presynaptic spike. The facilitation in the postsynaptic firing rate is generally larger than the PFP facilitation. Interestingly, the last postsynaptic spike timing also has a large facilitating effect on the postsynaptic spiking upon receiving a presynaptic input spike. However, the PFP does not depend on the last postsynaptic spike timing, suggesting that there is an input-independent component of spike transmission in STP. Overall, our results indicate that the STP of the retinocollicular pathway is likely a two-stage process, where the spiking plasticity of the postsynaptic neuron could be independent of its inputs.