Abstract
Cerebellar Purkinje cells in vitro fire recurrent sequences of Sodium and Calcium spikes. Here, we analyze the Purkinje cell using harmonic analysis, and our experiments reveal that its output signal is comprised of three distinct frequency bands, which are combined using Amplitude and Frequency Modulation (AM/FM). We find that the three characteristic frequencies – Sodium, Calcium and Switching – occur in various combinations in all waveforms observed using whole-cell current clamp recordings. We found that the Calcium frequency can display a frequency doubling of its frequency mode, and the Switching frequency can act as a possible generator of pauses that are typically seen in Purkinje output recordings. Using a reversibly photo-switchable kainate receptor agonist, we demonstrate the external modulation of the Calcium and Switching frequencies. These experiments and Fourier analysis suggest that the Purkinje cell can be understood as a harmonic signal oscillator, enabling a higher level of interpretation of Purkinje signaling based on modern signal processing techniques.
Highlights
The Purkinje Cell (PC) in the cerebellum is a perpetually firing cell, with a high degree of basal activity shaping its output to the deep cerebellar nuclei
PURKINJE CELL OUTPUT SHOWS CELL-DEPENDENT VARIATIONS Recordings obtained from current-clamped PCs indicate a variety of cell-dependent firing patterns, consistent with previous reports (Womack and Khodakhah, 2004; McKay et al, 2007)
A typical output displays high frequency (30–300 Hz) Na+ spikes, low frequency Ca2+ spikes (∼1–15 Hz) and sub-Hz patterned oscillations (Llinás and Sugimori, 1980; Chang et al, 1993). These spikes can be grouped into Simple Spikes (SS) consisting entirely of Na+ spikes, or into Calcium Spike bursts (CaS), which consist of a combination of Na+ and Ca2+ spikes
Summary
The Purkinje Cell (PC) in the cerebellum is a perpetually firing cell, with a high degree of basal activity shaping its output to the deep cerebellar nuclei. Prevalent interpretations of PC signal output have focused on either the pauses in the output signal (Jaeger and Bower, 1994; Steuber et al, 2007), or on the bistable nature of the cell, where the PC exists either in a depolarized state of firing, or quiescence (Chang et al, 1993; Womack and Khodakhah, 2002; Loewenstein et al, 2005; McKay et al, 2007). While there is evidence implicating external input control of bistable transitions, the climbing fiber (Loewenstein et al, 2005; McKay et al, 2007; Davie et al, 2008), there is a general disagreement over whether such recurrences are stochastic (Keating and Thach, 1997; Kitazawa and Wolpert, 2005; Hakimian et al, 2008) or periodic (Llinás and Sugimori, 1980; Chang et al, 1993)
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