Bidirectional hebbian plasticity induced by low-frequency stimulationin 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 in put 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 informationWork supported by “Ministerio de Ciencia y Tecnología y Ministerio de Ciencia e Innovación” grants (BFU2005-07486, BFU2008-03488, SAF2009-10339, BFU2011-23522, BFU2012-36107, BFU2013-43668-P and BFU2016-80802-P) and a “Comunidad Autónoma de Madrid” (GR/SAL/0877/2004) grant. Dr .D. Fernández de Sevilla was a post doctoral fellow at the “Instituto Cajal,” funded by GR/SAL/0877/2004 and a “Ministerio de Ciencia and Tecnología” grant (BFU2005-07486).He was subsequently supported by a Ramón y Cajal Contract and is now a Professor at the “Departamento de Anatomía, Histología y Neurociencia, Facultad de Medicina, Universidad Autónoma de Madrid.” Dr. Andrea Diez was a doctoral fellow funded by the BFU2011-23522 grant and is now a post doctoral fellow funded by “Ministerio de Ciencia e Innovación” grant (BFU2013- 43741-P) at the “Departamento de Anatomía, Histología y Neurociencia, Facultad de Medicina, Universidad Autónoma de Madrid.” N. Barros-Zulaica was a doctoral fellow funded by the BFU2012-36107 gran