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This Article Full Text Full Text (PDF) All Versions of this Article: 577/1/205    most recent jphysiol.2006.113043v1 Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Perreault, M.-C. Articles by Raastad, M. Search for Related Content PubMed PubMed Citation Articles by Perreault, M.-C. Articles by Raastad, M. Related Collections Neuroscience

¹ University of Oslo, Institute of Basic Medical Sciences, Department of Physiology, Sognsvannsveien 9, PO Box 1103 Blindern, N-0317, Oslo, Norway

Thalamocortical cells (TCs) and interneurons (INs) in the lateral geniculate nucleus process visual information from the retina. The TCs have many short dendrites, whereas the INs have fewer and longer dendrites. Because of these morphological differences, it has been suggested that transmission of synaptic signals from dendritic synapses to soma is more efficient in TCs than in INs. However, a higher membrane resistance (R_m) for the INs could, in theory, compensate for the attenuating effect of their long dendrites and allow distal synaptic inputs to significantly depolarize the soma. Compartmental models were made from biocytin filled TCs (n = 15) and INs (n = 3) and adjusted to fit the current- and voltage-clamp recordings from the individual cells. The confidence limits for the passive electrical parameters were explored by simulating the influence of noise, morphometric errors and non-uniform and active conductances. One of the useful findings was that R_m was accurately estimated despite realistic levels of active conductance. Simulations to explore the somatic influence of dendritic synapses showed that a small (0.5 nS) excitatory synapse placed at different dendritic positions gave similar somatic potentials in the individual TCs, within the TC population and also between TCs and INs. A linear increase in the conductance of the synapse gave increases in somatic potentials that were more sublinear in INs than TCs. However, when the total synaptic conductance was increased by simultaneously activating many small, spatially distributed synapses, the INs converted the synaptic signals to soma potentials almost as efficiently as the TCs. Thus, INs can transfer fast synaptic signals to soma as efficiently as TCs except when the focal conductance is large.

(Received 5 May 2006; accepted after revision 30 August 2006; first published online 7 September 2006)
Corresponding author M.-C. Perreault: University of Oslo, Institute of Basic Medical Sciences, Department of Physiology, Sognsvannsveien 9, PO Box 1103 Blindern, N-0317, Oslo, Norway. Email: m.c.perreault{at}basalmed.uio.no