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Title A simple model script for the NMDA receptor-mediated depolarizing after-potentials in the basal dendrites of CA1 pyramidal neurons.
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Item Description Abstract / Acknowledgment --- In a published article "NMDA receptor-mediated depolarizing after-potentials in the basal dendrites of CA1 pyramidal neurons" Neuroscience Research 48 (2004) 325-333, we have shown that the basal dendrites of rat hippocampal CA1 pyramidal neurons show a depolarizing after-potential (DAP) on top of a fast decaying potential in response to synapitic inputs to the basal dendrites under blocade of GABA receptors. A DAP was never observed when the input was applied to the apical dendrites. To find an account for the reason why DAP generation was specific to basal dendrites, we compared the properties of AMPA and NMDA receptors in apical and basal dendrites, and the ratio of NMDA/AMPA currentas. But, the differences were not large enough to account for specificity. We hypothesized that a difference in the passive cable properties of dendrites due to differences in morphology is responsible for the specificity. Because basal dendrites are shorter (Pyapali et al, 1998) and thinner (Megias et al., 2001) than apical dendrites, AMPA receptor-mediated synaptic currents generated in basal dendrites should generate greater depolarization than those in apical dendrites, thereby activating NMDA receptors to trigger DAP. To test this idea, we used NEURON, a compartmental neuron simulator (Hines, 1993), to examine whether morphological differences could affect DAP generation.
We made simple models by attaching a single dendrite to a cell body (Fig. 6A, B in the paper). In one model representing a basal dendrite (model 1), the dendrite was short (250 micron) and thin (0.5 micron), while, in the other, representing an apical dendrite, the dendrite was long (500 micron) and thick (1.2 micron). Synaptic conductances were introduced at a location 135 micron away from the cell body. The descriptions of the AMPA receptor and NMDA receptor were adopted from Destexhe et al. (1998), and adjusted so that the voltage-dependency and the kinetics matched the data obtained in our study. The ratio of the maximum conductance of NMDA- and AMPA-receptors was also adjusted to match the NMDA/AMPA ratio obtained in our study. In the basal dendrite model, a DAP was generated when the input intensity was increased (Fig. 6B, Fig. 7B1 in the paper), whereas, in the apical dendrite model, a DAP was not generated unless the input intensity was extremely strong (Fig.6A, Fig. 7A). We added delayed-rectifier K+ channels to curtail the NMDA receptor-mediated depolarization, but this channel was not essential for DAP generation. Basically the same results were obtained (Fig. 8 in the paper) using a realistic morphology constructed based on a real CA1 pyramidal neuron (Pyapali et al, 1998).

Affiliation / E-mail --- Lab. Cellular Neurobiology, Sch. Life Sci., Tokyo Univ.Pharm. Life Sci.,Dpt. Physiol., Keio Univ. Sch. Med., Correspondence:(miyakawa@ls.toyaku.ac.jp)
Last Modified Date Oct 29, 2009 11:23:28
Created Date Oct 29, 2009 11:23:28
Contributor DBPF Administrator 1 (admin)
Item Type Model
Change Log(History)
Model type Neuron
Enoki Ryosuke
Kikuchi Teppei
Koizumi Amane
Sakaki Go
Kudo Yoshihisa
Miyakawa Hiroyoshi.
Model file NMDAdapSimple1.nrnzip 9805 bytes   (Login User only)
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