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Figures
- Figure 1.
Ionic currents underlying spontaneous firing. A, Spontaneous firing in an isolated Purkinje cell (top trace). Bottom traces show underlying TTX-sensitive voltage-gated Na current activated during spiking by applying the top trace as a voltage-clamp command (Vcmd). Modified from Raman and Bean (1999). B, Close-up of Na current activated at subthreshold potentials, with resurgent Na current apparent on the falling phase of the action potential (dashed box in A). Modified from Raman and Bean (1999). C, Schematic illustration of Na channel gating during a single action potential. Gray lines indicate the approximate times and voltages during the spike that favor each conformation. Channels begin in the closed state, with the inactivation gate (I) and the blocking particle (B) unbound. As the spike proceeds, channels open, block, unblock (producing resurgent current), and close. Note that the binding of the inactivation gate can be prevented by binding of the blocking particle. Modified from Grieco et al. (2002).
- Figure 2.
Plasticity of spontaneous firing. A, Persistent increase in spontaneous firing rate in cerebellar Purkinje cells triggered by application of the nitric oxide donor NOR-4. Top shows traces of spontaneous firing in a cell-attached recording from a Purkinje cell in a cerebellar slice 10 min before and 35 min after NOR-4 application. Calibration: 75 pA, 100 msec. Bottom shows time course of changes in average firing rate caused by NOR-4 for six Purkinje neurons. Modified from Smith and Otis (2003). B, Schematic illustration showing circadian regulation of spontaneous firing in SCN neurons. Left, At night, spontaneous firing rate is low (dashed line, -59 mV), and TTX fails to uncover membrane potential oscillations (-59 mV membrane potential). Right, During the day, spontaneous firing rate is high (dashed line, -54 mV), and TTX reveals a depolarized membrane potential (dashed line, -41 mV), exhibiting oscillations. These changes are attributable to modulation of L-type Ca current and tonic K current. Calibration: spiking traces, 500 msec, 40 mV; TTX traces, 500 msec, 20 mV. For details, see Pennartz et al. (2002).
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- Biophysical mechanisms underlying spontaneous activity
- Plasticity of spontaneous firing in cerebellar Purkinje neurons
- Bistability of Purkinje cell output
- Long-term modulation of spiking by inhibition in the vestibular nuclei
- The rise and fall of spontaneous firing in the mammalian biological clock
- Linking single-cell spontaneous firing to population activity
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