title: Balanced ionotropic receptor dynamics support signal estimation via voltage-dependent membrane noise.
abstract: Encoding behaviorally relevant stimuli in a noisy background is critical for animals to survive in their natural environment. We identify core biophysical and synaptic mechanisms that permit the encoding of low-frequency signals in pyramidal neurons of the weakly electric fish Apteronotus leptorhynchus, an animal that can accurately encode even miniscule amplitude modulations of its self-generated electric field. We demonstrate that slow NMDA receptor (NMDA-R)-mediated excitatory postsynaptic potentials (EPSPs) are able to summate over many interspike intervals (ISIs) of the primary electrosensory afferents (EAs), effectively eliminating the baseline EA ISI correlations from the pyramidal cell input. Together with a dynamic balance of NMDA-R and GABA-A-R currents, this permits stimulus-evoked changes in EA spiking to be transmitted efficiently to target electrosensory lobe (ELL) pyramidal cells, for encoding low-frequency signals. Interestingly, AMPA-R activity is depressed and appears to play a negligible role in the generation of action potentials. Instead, we hypothesize that cell-intrinsic voltage-dependent membrane noise supports the encoding of perithreshold sensory input; this noise drives a significant proportion of pyramidal cell spikes. Together, these mechanisms may be sufficient for the ELL to encode signals near the threshold of behavioral detection.
authors.affiliation: Department of Cellular and Molecular Medicine, University of Ottawa, Ottawa, Ontario, Canada;
authors.forename: Curtis M
authors.initials: CM
authors.lastname: Marcoux
authors.affiliation: Department of Cellular and Molecular Medicine, University of Ottawa, Ottawa, Ontario, Canada;
authors.forename: Stephen E
authors.initials: SE
authors.lastname: Clarke
authors.affiliation: Department of Mathematics, University of Utah, Salt Lake City, Utah;
authors.forename: William H
authors.initials: WH
authors.lastname: Nesse
authors.affiliation: Department of Cellular and Molecular Medicine, University of Ottawa, Ottawa, Ontario, Canada; Department of Physics, University of Ottawa, Ottawa, Ontario, Canada; and Brain and Mind Institute and Center for Neural Dynamics, University of Ottawa, Ottawa, Ontario, Canada.
authors.forename: Andre
authors.initials: A
authors.lastname: Longtin
authors.affiliation: Department of Cellular and Molecular Medicine, University of Ottawa, Ottawa, Ontario, Canada; Brain and Mind Institute and Center for Neural Dynamics, University of Ottawa, Ottawa, Ontario, Canada lmaler@uottawa.ca.
authors.forename: Leonard
authors.initials: L
authors.lastname: Maler
mesh_terms: D000344:Afferent Pathways / Q000502:physiology*; D000818:Animals; D004555:Electric Fish; D004558:Electric Stimulation; D005260:Female; D008297:Male; D017966:Pyramidal Cells / Q000502:physiology*; D018091:Receptors, AMPA / Q000502:physiology*; D018079:Receptors, GABA / Q000502:physiology*; D016194:Receptors, N-Methyl-D-Aspartate / Q000502:physiology*; D055366:Synaptic Potentials
chemical_list: D018091:Receptors, AMPA; D018079:Receptors, GABA; D016194:Receptors, N-Methyl-D-Aspartate
keywords: NMDA receptor; correlations; electric fish; signal detection; spike train; stochastic resonance