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This Article Full Text Full Text (PDF) All Versions of this Article: 579/2/431    most recent jphysiol.2006.123836v1 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 HighWire Citing Articles via Google Scholar Google Scholar Articles by Bullis, J. B. Articles by Poolos, N. P. Search for Related Content PubMed PubMed Citation Articles by Bullis, J. B. Articles by Poolos, N. P. Related Collections Neuroscience

¹ Neurobiology & Behavior
² Department of Neurology & Regional Epilepsy Center, University of Washington, Seattle, WA 98195-7290, USA

In CA1 and neocortical pyramidal neurons, I_h is present primarily in the dendrites. We asked if all neurons of a pyramidal morphology have a similar density of I_h. We characterized a novel class of hippocampal neurons with pyramidal morphology found in the stratum radiatum, which we termed the ‘pyramidal-like principal’ (PLP) neuron. Morphological similarities to pyramidal neurons were verified by filling the neurons with biocytin. PLPs did not stain for markers associated with interneurons, and projected to both the septum and olfactory bulb. By using cell-attached patch-clamp recordings, we found that these neurons expressed a high density of I_h in the soma that declined to a lower density in the dendrites, a pattern that is reversed compared to pyramidal neurons. The voltage-dependent activation and activation time constants of I_h in the PLPs were similar to pyramidal neurons. Whole-cell patch-clamp recordings from the soma and dendrites of PLP neurons showed no significant differences in input resistance and local temporal summation between the two locations. Blockade of I_h by ZD7288 increased the input resistance and temporal summation of simulated EPSPs, as in pyramidal neurons. When NMDA receptors were blocked, temporal summation at the soma of distal synaptic potentials was similar to that seen with current injections at the soma, suggesting a ‘normalization’ of temporal summation similar to that observed in pyramidal neurons. Thus, we have characterized a principal neuronal subtype in the hippocampus with a similar morphology but reversed I_h somatodendritic gradient to that previously observed in CA1 hippocampal and neocortical pyramidal neurons.

(Received 29 October 2006; accepted after revision 14 December 2006; first published online 21 December 2006)
Corresponding author N. Poolos: Box 359745, Harborview Medical Center, 325 9th Ave., Seattle, WA 98104, USA. Email: npoolos{at}u.washington.edu

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