Flavoprotein autofluorescence is an activity dependent intrinsic signal. Flavoproteins are involved in the electron
transport chain and change their fluorescence according to the cellular redox state. We have been using flavoprotein
autofluorescence in the cerebellum to examine properties of cerebellar circuits. Studies have also focused on
understanding the cellular and metabolic origins of this intrinsic optical signal. Parallel fiber stimulation evokes a beamlike
response intersected by bands of decreased fluorescence. The beam response is biphasic, with an early fluorescence
increase (light phase) followed by a slower decrease (dark phase). We show this signal originates from flavoproteins as
determined by its wavelength selectivity and sensitivity to blockers of the electron transport chain. Selectively blocking
glutamate receptors abolished the on-beam light phase with the dark phase remaining intact. This demonstrates that the
light phase is due to postsynaptic neuronal activation and suggests the dark phase is primarily due to glial activation.
The bands of reduced fluorescence intersecting the beam are primarily neuronal in origin, mediated by GABAergic
transmission, and due to the inhibitory action of molecular layer interneurons on Purkinje cells and the interneurons
themselves. This parasagittally organized molecular layer inhibition differentially modulates the spatial pattern of
cerebellar cortical activity. Flavoprotein imaging also reveals the functional architectures underlying the responses to
inferior olive and peripheral whisker pad stimulation. Therefore, flavoprotein autofluorescence imaging is providing new
insights into cerebellar cortical function and neurometabolic coupling.
Flavoprotein autofluorescence optical imaging is developing into a powerful research tool to study neural
activity, particularly in vivo. In this study we used this imaging technique to investigate the neuronal mechanism
underlying the episodic movement disorder that is characteristic of the tottering (tg) mouse, a model of episodic ataxia
type 2. Both EA2 and the tg mouse are caused by mutations in the gene encoding Cav2.1 (P/Q-type) voltage-gated Ca2+ channels. These mutations result in a reduction in P/Q Ca2+ channel function. Both EA2 patients and tg mice have a
characteristic phenotype consisting of transient motor attacks triggered by stress, caffeine or ethanol. The neural events
underlying these episodes of dystonia are unknown. Flavoprotein autofluorescence optical imaging revealed
spontaneous, transient, low frequency oscillations in the cerebellar cortex of the tg mouse. Lasting from 30 - 120
minutes, the oscillations originate in one area then spread to surrounding regions over 30 - 60 minutes. The oscillations
are reduced by removing extracellular Ca2+ and blocking Cav 1.2/1.3 (L-type) Ca2+ channels. The oscillations are not affected by blocking AMPA receptors or by electrical stimulation of the parallel fiber - Purkinje cell circuit, suggesting
the oscillations are generated intrinsically in the cerebellar cortex. Conversely, L-type Ca2+ agonists generate
oscillations with similar properties. In the awake tg mouse, transcranial flavoprotein imaging revealed low frequency
oscillations that are accentuated during caffeine induced attacks of dystonia. The oscillations increase during the attacks
of dystonia and are coupled to oscillations in face and hindlimb EMG activity. These transient oscillations and the
associated cerebellar dysfunction provide a novel mechanism by which an ion channel disorder results in episodic motor
dysfunction.
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