Proceedings of The Physiological Society

University of Manchester (2010) Proc Physiol Soc 19, C24

Oral Communications

Distinct timing-dependent LTD induction rules at horizontal and vertical inputs on layer 2/3 cells in mouse barrel cortex

A. Banerjee1, C. Sampaio1, A. Rodriguez-Moreno2, O. Paulsen1,3

1. Dept. of Physiology, Anatomy and Genetics, University of Oxford, Oxford, United Kingdom. 2. Department of Physiology, Anatomy and Cellular Biology, University Pablo de Olavide, Seville, Spain. 3. Department of Physiology, Development and Neuroscience, University of Cambridge, Cambridge, United Kingdom.

Neocortical columns are an important feature of cortical organization. Intra-columnar and cross-columnar synapses perform different computational functions in somatotopically organized barrel cortex. Here, we compared the induction of input-specific timing-dependent LTD (t-LTD) at vertical, intracolumnar layer 4-to-layer 2/3 and horizontal, cross-columnar layer 2/3-to-layer 2/3 excitatory synapses in mouse barrel cortex. Whole-cell recordings were made from layer 2/3 pyramidal neurons and EPSPs were elicited by extracellular stimulation either in layer 4 or in layer 2/3 in slices from barrel cortex. T-LTD was induced using a post-before-pre pairing protocol. Cross-columnar synapses showed a narrower time window of t-LTD induction compared to intracolumnar synapses, and t-LTD induction required different GluN2 subunits at intracolumnar and cross-columnar synapses. Thus, t-LTD at intracolumnar synapses was dependent on GluN2C/D subunit-containing NMDA receptors with slow kinetics, since it was blocked by PPDA (10 microM; mean ± SEM, 110 ± 3 %, n = 5). Whereas t-LTD at cross-columnar synapses was dependent on GluN2B subunit-containing NMDA receptors, since it was blocked by Ro 25-6981 (0.5 microM; 99 ± 6 %, n = 6). Also, a CB1 receptor antagonist AM251 (3 microM) blocked t-LTD at horizontal synapses (104 ± 8 %, n = 5) but not at vertical synapses (68 ± 13 %, n = 9). Thus, we show that distinct t-LTD induction rules exist in intra- and cross-columnar synapses onto layer 2/3 neurons in barrel cortex. Our results also suggest that different excitatory synapses onto the same postsynaptic neurons can have different molecular requirements for induction of t-LTD.

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