Skip to main page content
Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
, 101 (1), 234-45

Low-frequency Oscillations in the Cerebellar Cortex of the Tottering Mouse

Affiliations

Low-frequency Oscillations in the Cerebellar Cortex of the Tottering Mouse

Gang Chen et al. J Neurophysiol.

Abstract

The tottering mouse is an autosomal recessive disorder involving a missense mutation in the gene encoding P/Q-type voltage-gated Ca2+ channels. The tottering mouse has a characteristic phenotype consisting of transient attacks of dystonia triggered by stress, caffeine, or ethanol. The neural events underlying these episodes of dystonia are unknown. Flavoprotein autofluorescence optical imaging revealed transient, low-frequency oscillations in the cerebellar cortex of anesthetized and awake tottering mice but not in wild-type mice. Analysis of the frequencies, spatial extent, and power were used to characterize the oscillations. In anesthetized mice, the dominant frequencies of the oscillations are between 0.039 and 0.078 Hz. The spontaneous oscillations in the tottering mouse organize into high power domains that propagate to neighboring cerebellar cortical regions. In the tottering mouse, the spontaneous firing of 83% (73/88) of cerebellar cortical neurons exhibit oscillations at the same low frequencies. The oscillations are reduced by removing extracellular Ca2+ and blocking L-type Ca2+ channels. The oscillations are likely generated intrinsically in the cerebellar cortex because they are not affected by blocking AMPA receptors or by electrical stimulation of the parallel fiber-Purkinje cell circuit. Furthermore, local application of an L-type Ca2+ agonist in the tottering mouse generates oscillations with similar properties. The beam-like response evoked by parallel fiber stimulation is reduced in the tottering mouse. In the awake tottering mouse, transcranial flavoprotein imaging revealed low-frequency oscillations that are accentuated during caffeine-induced attacks of dystonia. During dystonia, oscillations are also present in the face and hindlimb electromyographic (EMG) activity that become significantly coherent with the oscillations in the cerebellar cortex. These low-frequency oscillations and associated cerebellar cortical dysfunction demonstrate a novel abnormality in the tottering mouse. These oscillations are hypothesized to be involved in the episodic movement disorder in this mouse model of episodic ataxia type 2.

Figures

FIG. 1.
FIG. 1.
Spontaneous, low-frequency oscillations in the cerebellar cortex of the anesthetized tg mouse. A: sequential images of the cerebellar cortex show spontaneous oscillations in an anesthetized tg mouse. Large-amplitude oscillations are present in the paramedian lobule (PML) and lower-amplitude oscillations in Crus I and II. Each pseudocolored image shows the difference in fluorescence level relative to the background fluorescence (ΔF/F). Time from image acquisition onset indicated in the top right corner of each image. B: time course of ΔF/F obtained from 3 regions of interest (ROIs) indicated in the first image of A (colored boxes of 20 × 20 pixels). CF: pixel-based spectral analysis shows the frequency (C), phase shift (D), power (E), and high-power domain maps (F) for the same experiment. Each map is superimposed on a background image of the cerebellar cortex. GI: frequency (G), power (H), and high power domain (I) maps from a wild-type (WT) mouse. Note that the frequency (G) and power maps (H) appear almost identical due to the very low power of the frequency band of interest, but in fact are not the same. J: distribution of frequencies shown as percentage of all pixels in anesthetized tg (n = 18) and WT (n = 9) mice.
FIG. 2.
FIG. 2.
Spreading of oscillations and their effects on cerebellar cortical activity. A: frequency maps show the evolution of the oscillations from lobulus simplex (SL) to Crus I and II. In this figure, the frequency maps consist of the dominant frequency at each pixel within the band of interest for areas of oscillations >400 contiguous pixels. B: cerebellar cortical response to surface stimulation (100-μA, 100-μs pulses at 10 Hz for 10 s) in WT mouse (left image) and tg mouse (center and right images) when high power domains were absent (tg, Baseline) and present (tg, Oscillations). Inset shows ΔF/F within the red square and the corresponding absence or presence of large-amplitude oscillations. C: average evoked optical responses for the indicated stimulation amplitudes (100-μs pulses at 10 Hz for 10 s) in WT and tg mice (n = 5 for both groups) during periods without and with high power oscillations. In this and subsequent figures, an asterisk (*) indicates a significant effect between the 2 conditions (see text for details on exact P value and statistical test). Data shown for the 3 PF stimulation amplitudes tested (100, 200, and 300 μA).
FIG. 3.
FIG. 3.
Oscillating activity in the firing of single cells in the anesthetized tg mice. AC: on the left are examples of the spontaneous firing rate of 2 Purkinje cells (A and B) and an unidentified cerebellar cell (C). On the right are the corresponding power spectra. The vertical bars on the y-axis denote the power. D: number of neurons with and without low-frequency oscillations in their spontaneous firing. Neurons were defined as possessing oscillations if the peak power in the firing was between 0.039 and 0.078 Hz, as shown for the example cells in AC.
FIG. 4.
FIG. 4.
Roles of AMPA receptors, extracellular Ca2+, and L-type Ca2+ channel agents on the cerebellar oscillations in anesthetized tg mice. A and B: high power domain maps (A) and average normalized area and power (B) before and after bath application of DNQX (50 μM) in 4 tg mice. CF: similar maps and plots for normal Ringer's (Control) and Ca2+ free Ringer's (0 Ca2+ and 2 mM EGTA) in 6 tg mice (C and D) and before and after diltiazem (50 μM) in 4 tg mice (E and F). G and H: high power domain maps and area and power averages in normal Ringer's and with the addition of FPL (50 μM) to the bath in 5 tg mice.
FIG. 5.
FIG. 5.
Cerebellar oscillations in awake tg mouse and their relationship with episodes of dystonia. A: example high power domain maps in the awake tg mice during baseline and dystonic periods. B: average normalized area and power of the oscillations (means ± SE, n = 7 tg mice). Both measures increase significantly during dystonia (*). C: frequency histograms from the optical recordings during the baseline and dystonia periods (n = 7 tg mice).
FIG. 6.
FIG. 6.
Oscillations in the electromyographic (EMG) activity and relation to the optical signals in the cerebellar cortex. A: power spectrum frequency distributions from a single mouse for the optical (bars) and hamstring EMG recordings (lines) during dystonia (red) and baseline (blue) periods. Inset shows regular, low-frequency bursts in the hamstring EMG during dystonia. B: average power spectrum in the EMG activity in awake tg mice during baseline (blue) and dystonia (red) periods. The data from the hamstring and whisker pad recordings were combined in this plot. C and D: examples of coherence maps between the optical activity within high power domains and the EMG activity for the hamstring (C) and whisker pad (D). Arrow pointing to the scale bar denotes coherence significance level (P < 0.05). Data are from same experiment shown in A. E: average area with significance coherence and average coherence magnitude during baseline and dystonic periods; both are significantly increased during the dystonia (*).
FIG. 7.
FIG. 7.
Effects of L-type Ca2+ channel agonists and antagonists on the oscillations in the awake tg mouse. A: distribution of frequencies as a percentage of all pixels in the baseline period and with application of FPL (50 μM) and diltiazem (Dilt, 50 μM) in 4 tg mice. B: average normalized area and power for oscillations in the baseline, FPL, and diltiazem periods. FPL resulted in an increase in both area and power compared with the baseline (*). Diltiazem resulted in a significant reduction in the FPL-induced oscillations (*).

Similar articles

See all similar articles

Cited by 33 articles

See all "Cited by" articles

Publication types

MeSH terms

LinkOut - more resources

Feedback