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. 2014 Jul;64(7):570-580.
doi: 10.1093/biosci/biu070.

Ionic Current Variability and Functional Stability in the Nervous System

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Free PMC article

Ionic Current Variability and Functional Stability in the Nervous System

Jorge Golowasch. Bioscience. .
Free PMC article

Abstract

Identified neurons in different animals express ionic currents at highly variable levels (population variability). If neuronal identity is associated with stereotypical function, as is the case in genetically identical neurons or in unambiguously identified individual neurons, this variability poses a conundrum: How is activity the same if the components that generate it-ionic current levels-are different? In some cases, ionic current variability across similar neurons generates an output gradient. However, many neurons produce very similar output activity, despite substantial variability in ionic conductances. It appears that, in many such cells, conductance levels of one ionic current vary in proportion to the conductance levels of another current. As a result, in a population of neurons, these conductances appear to be correlated. Here, I review theoretical and experimental work that suggests that neuronal ionic current correlation can reduce the global ionic current variability and can contribute to functional stability.

Keywords: animal physiology; conductances; homeostasis; neurobiology; variability.

Figures

Figure 1.
Figure 1.
Constancy of activity with variable currents. (a) Partial schematic diagram of the pyloric network of the crab Cancer borealis, including the pacemaker (AB), two pyloric dilator (PD), the lateral pyloric (LP), and the pyloric constrictor (PY) neurons. (b) Extracellular recordings from two pyloric motor nerves (lvn and pdn) from two different animals (the different color labels). Notice the different periods of the rhythmic activity. (c) Ionic currents IA (top) and high-threshold potassium ion current, IHTK (bottom) from PD neurons of the two preparations (red and orange) shown in panel (b). Notice the large amplitude differences. (d) Phase values (i.e., the proportion of the period, beginning with the first spike of the PD burst), for the end of PD burst (PDoff) and the beginning and end of LP burst (LPon, LPoff) as indicated in panel (b), as a function of the period. The coefficient of variation (CoV) for each phase is indicated at the right. Note the low CoVs for each phase value; n = 9. (e) The maximal current levels (measured at the peak; e.g., the arrow in panel [c]) for intrinsic currents in PD: IA, IHTK, and Ih (top panel) and synaptic currents between PD and LP (bottom panel) as a function of the pyloric rhythm period in the same preparation as in panel (d). Note that the CoV values (right) are approximately one order of magnitude higher than those for the phase values shown in panel (d). The colored boxes in panels (d) and (e) highlight the phase and ionic current values, respectively, of the animals whose activity is shown in panel (b) and whose raw currents are shown in panel (c). Abbreviations: ms, milliseconds; nA, nanoamperes.

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