Encoding and decoding of dendritic excitation during active states in pyramidal neurons

Williams, Stephen R. (2005) Encoding and decoding of dendritic excitation during active states in pyramidal neurons. Journal of Neuroscience, 25 25: 5894-5902. doi:10.1523/JNEUROSCI.0502-05.2005

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Author Williams, Stephen R.
Title Encoding and decoding of dendritic excitation during active states in pyramidal neurons
Journal name Journal of Neuroscience   Check publisher's open access policy
ISSN 0270-6474
Publication date 2005-06-22
Sub-type Article (original research)
DOI 10.1523/JNEUROSCI.0502-05.2005
Open Access Status File (Publisher version)
Volume 25
Issue 25
Start page 5894
End page 5902
Total pages 9
Place of publication Washington, DC, United States
Publisher Society for Neuroscience
Language eng
Abstract The state of metabolic dormancy has fascinated people for hundreds of years, leading to research exploring the identity of natural molecular components that may induce and maintain this state. Many animals lower their metabolism in response to high temperatures and/or arid conditions, a phenomenon called aestivation. The biological significance for this is clear; by strongly suppressing metabolic rate to low levels, animals minimize their exposure to stressful conditions. Understanding blood or hemolymph metabolite changes that occur between active and aestivated animals can provide valuable insights relating to those molecular components that regulate hypometabolism in animals, and how they afford adaptation to their different environmental conditions. In this study, we have investigated the hemolymph metabolite composition from the land snail Theba pisana, a remarkably resilient mollusc that displays an annual aestivation period. Using LC-MS-based metabolomics analysis, we have identified those hemolymph metabolites that show significant changes in relative abundance between active and aestivated states. We show that certain metabolites, including some phospholipids [e.g. LysoPC(14:0)], and amino acids such as l-arginine and l-tyrosine, are present at high levels within aestivated snails. Further investigation of our T. pisana RNA-sequencing data elucidated the entire repertoire of phospholipid-synthesis genes in the snail digestive gland, as a precursor towards future comparative investigation between the genetic components of aestivating and non-aestivating species. In summary, we have identified a large number of metabolites that are elevated in the hemolymph of aestivating snails, supporting their role in protecting against heat or desiccation.
Formatted abstract
Neocortical neurons spontaneously fire action potentials during active network states; how are dendritic synaptic inputs integrated into the ongoing action potential output pattern of neurons? Here, the efficacy of barrages of simulated EPSPs generated at known dendritic sites on the rate and pattern of ongoing action potential firing is determined using multisite whole-cell recording techniques from rat layer 5 neocortical pyramidal neurons in vitro. Under quiescent conditions, the somatic impact of proximal (253 ± 15 µm from soma; n = 28) dendritic barrages of simulated EPSPs was 4.7-fold greater than identical barrages of EPSPs generated from distal (572 ± 13 µm from soma) sites. In contrast, barrages of proximal simulated EPSPs enhanced the rate of ongoing action potential firing, evoked by somatic simulated EPSPs, by only 1.6-fold more than distal simulated EPSPs. This relationship was apparent across a wide frequency range of action potential firing (6-22 Hz) and dendritic excitation (100-500 Hz). The efficacy of distal dendritic EPSPs was formed by the recruitment of active dendritic processes that transformed the ongoing action potential firing pattern, promoting action potential burst firing. Paired recordings (n = 42) revealed that patterns of action potential firing generated by concerted somatic and distal dendritic excitation reliably and powerfully drove postsynaptic excitation as a result of enhanced reliability of transmitter release during bursts of action potential firing. During active states, therefore, distal excitatory synaptic inputs decisively control the excitatory synaptic output of layer 5 neocortical pyramidal neurons and so powerfully influence network activity in the neocortex.
Keyword EPSP
Action potential
Q-Index Code C1
Q-Index Status Provisional Code
Institutional Status Non-UQ

Document type: Journal Article
Sub-type: Article (original research)
Collections: Queensland Brain Institute Publications
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Citation counts: TR Web of Science Citation Count  Cited 26 times in Thomson Reuters Web of Science Article | Citations
Scopus Citation Count Cited 27 times in Scopus Article | Citations
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Created: Fri, 21 Oct 2011, 03:36:25 EST by Stephen Williams on behalf of Queensland Brain Institute