Presynaptic activity regulates Na+ channel distribution at the axon initial segment

Journal name:
Nature
Volume:
465,
Pages:
1075–1078
Date published:
DOI:
doi:10.1038/nature09087
Received
Accepted
Published online

Deprivation of afferent inputs in neural circuits leads to diverse plastic changes in both pre- and postsynaptic elements that restore neural activity1. The axon initial segment (AIS) is the site at which neural signals arise2, 3, and should be the most efficient site to regulate neural activity. However, none of the plasticity currently known involves the AIS. We report here that deprivation of auditory input in an avian brainstem auditory neuron leads to an increase in AIS length, thus augmenting the excitability of the neuron. The length of the AIS, defined by the distribution of voltage-gated Na+ channels and the AIS anchoring protein, increased by 1.7 times in seven days after auditory input deprivation. This was accompanied by an increase in the whole-cell Na+ current, membrane excitability and spontaneous firing. Our work demonstrates homeostatic regulation of the AIS, which may contribute to the maintenance of the auditory pathway after hearing loss. Furthermore, plasticity at the spike initiation site suggests a powerful pathway for refining neuronal computation in the face of strong sensory deprivation.

At a glance

Figures

  1. Auditory deprivation increased the length of the AIS.
    Figure 1: Auditory deprivation increased the length of the AIS.

    a, b, Immunostaining with VGLUT2 (a) and Pan-Nav (b) antibodies seven days after auditory deprivation. NM, nucleus magnocellularis. c, Enlarged views of the boxed regions in b. Arrowheads indicate AISs in this figure and in Fig. 2. d, e, Histograms and cumulative plots of length (d) and width (e) of Nav channel clusters in b (Methods). f, Nav channel clusters (red) are located on the axons of labelled nucleus magnocellularis neurons (green). g, h, Distance (g) and length (h) of Nav channel clusters in f14. Circles indicate values from individual cells. Error bars, s.e.; **P<0.01. i, j, Ankyrin-G (i) and Nav1.6 (j) (green) are co-localized with Pan-Nav (red). n, number of cells.

  2. Elongation of the AIS is activity dependent and develops within several days.
    Figure 2: Elongation of the AIS is activity dependent and develops within several days.

    a, Immunostaining with Pan-Nav antibody at various times (as indicated in days after deprivation) after auditory deprivation. b, Cumulative plots of length of Nav channel clusters from animals in c. c, Time course of relative length of control and deprived sides. Data from 4, 5, 5, 9, 3 animals (left to right). Statistical analysis was made against day-one data. d, e, Effects of different levels of auditory input on the length of the AIS (Methods and Supplementary Fig. 5). Relative length could be increased by elongation on the operated side and/or shortening on the non-operated side. Data from 5, 7, 10, 9, 3, 7 animals (d, left to right). Circles in d indicate values from individual animals. The lengths of Nav channel clusters in d were plotted cumulatively for each group (e). Data from 7, 31, 5, 7, 10, 19 animals (e, top to bottom). Acoustic attenuation shifts the curves rightwards. Coch dep, cochlea deprivation; colum dep, columella deprivation; colum fix, columella fixation; tymp punc, tympanic membrane puncture. Error bars, s.e.; *P<0.05; **P<0.01.

  3. Auditory deprivation increased axonal INa and excitability of neurons.
    Figure 3: Auditory deprivation increased axonal INa and excitability of neurons.

    a, c, INa recorded under whole-cell (a) and cell-attached (c) conditions from the soma. b, d, Auditory deprivation increased whole-cell (b) but not cell-attached (d) INa. e, Action potentials in response to depolarizing current steps. Threshold current is indicated in grey and threshold potential is indicated by arrowheads (Methods). Symbols indicate points where conductance was calculated (Supplementary Fig. 8). f–i, Auditory deprivation increased amplitude (f) and maximum dV/dt (g), and decreased threshold potential (h) and threshold current (i) of spikes. j, Spontaneous firing of nucleus magnocellularis neurons in slices after auditory deprivation; inset, firing frequency. Circles indicate values from individual cells. Error bars, s.e.; *P<0.05; **P<0.01.

  4. Auditory deprivation has little effect on synaptic transmission.
    Figure 4: Auditory deprivation has little effect on synaptic transmission.

    a, VGLUT2 immunolabelling declined within one day after auditory deprivation. b, Evoked excitatory postsynaptic currents (eEPSCs). Four traces of different stimulus intensities are superimposed. Insets, amplitudes as functions of stimulus intensity. c, Ensemble averaged traces of spontaneous excitatory postsynaptic current (sEPSCs). Insets, the relationship between the 10–90% rise time and the amplitude of sEPSCs did not show any differences between the distribution on the control side (541 sEPSCs from 7 cells) and that on the deprived side (523 sEPSCs from 8 cells). d–f, Amplitudes (d), 10–90% rise times (e) and half-amplitude widths (f) of eEPSCs and sEPSCs. g, Frequency of sEPSCs. Error bars, s.e.; *P<0.05.

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Affiliations

  1. Career-Path Promotion Unit for Young Life Scientists,

    • Hiroshi Kuba &
    • Yuki Oichi
  2. Department of Physiology, Kyoto University Graduate School of Medicine, Kyoto 606-8501, Japan

    • Harunori Ohmori

Contributions

H.K. designed and carried out all experiments and wrote the paper. Y.O. carried out preliminary experiments. H.O. helped with acoustic stimulation.

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The authors declare no competing financial interests.

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    This file contains Supplementary Figures 1-8 with legends and References.

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