Bidirectional Hebbian Plasticity Induced by Low-Frequency Stimulation in Basal Dendrites of Rat Barrel Cortex Layer 5 Pyramidal Neurons

Abstract

According to Hebb's original hypothesis (Hebb, 1949), synapses are reinforced when presynaptic activity triggers postsynaptic firing, resulting in long-term potentiation (LTP) of synaptic efficacy. Long-term depression (LTD) is a use-dependent decrease in synaptic strength that is thought to be due to synaptic input causing a weak postsynaptic effect. Although the mechanisms that mediate long-term synaptic plasticity have been investigated for at least three decades not all question have as yet been answered. Therefore, we aimed at determining the mechanisms that generate LTP or LTD with the simplest possible protocol. Low-frequency stimulation of basal dendrite inputs in Layer 5 pyramidal neurons of the rat barrel cortex induces LTP. This stimulation triggered an EPSP, an action potential (AP) burst, and a Ca2+ spike. The same stimulation induced LTD following manipulations that reduced the Ca2+ spike and Ca2+ signal or the AP burst. Low-frequency whisker deflections induced similar bidirectional plasticity of action potential evoked responses in anesthetized rats. These results suggest that both in vitro and in vivo similar mechanisms regulate the balance between LTP and LTD. This simple induction form of bidirectional hebbian plasticity could be present in the natural conditions to regulate the detection, flow, and storage of sensorimotor information.

Response Adaptation in Barrel Cortical Neurons Facilitates Stimulus Detection during Rhythmic Whisker Stimulation in Anesthetized Mice

“…A likely mechanism for facilitation when the interval was shorter (125 ms) may be a paired-pulse facilitation mediated by the activation of NMDA receptors (Thomson, 2000; Dan and Poo, 2004; Citri and Malenka, 2008). Many long-term modifications in synaptic efficacy in the cortex have been proposed to be mediated by the activation of NMDA receptors and to be the cellular basis of the learning machinery and the detection of relevant stimuli (Nuñez et al, 2012; Nabavi et al, 2014; Gruart et al, 2015; Díez-García et al, 2017). For example, antagonists of NMDA receptors block cortical plasticity after electrical thalamic stimulation (Heynen and Bear, 2001) or whisker repetitive stimulation (Barros-Zulaica et al, 2014).…”