In vivo voltage-sensitive dye imaging of mouse cortical activity with mesoscopic optical tomography

Optogenetic cortical spreading depression originating from the primary visual cortex induces migraine-like pain and anxiety behaviors in freely moving C57BL/6 J mice

BACKGROUND

Migraine is the second disabling neurological disorder with a high prevalence. Aura occurs in one-third of migraineurs and visual aura accounts for over 90%. Cortical spreading depression (CSD) underlies aura and might trigger migraine headaches. Compared with CSD induction by invasive electrical, chemical, or mechanical stimulation, optogenetics avoids direct influences on meninges in the stimulation process. However, previous optogenetic CSD models mainly use Thy1-ChR2-YFP or CaMKIIα-cre transgenic mice. They are limited when the pathogenesis study requires transgenic mice to express other specific promotor, such as the dopamine or serotonin transporter promotor. In addition, reported behavioral paradigms were based on CSD induction under anesthesia. This study aimed to establish an optogenetic CSD-induced migraine model originating in the primary visual cortex (VISp) in C57BL/6 J mice and presented the behavioral paradigm when CSD induction was under awake condition.

METHODS

We performed viral transduction for the expression of light-sensitive channelrhodopsin-2 in pyramidal neurons of VISp in C57BL/6 J mice. Regional cerebral blood flow (rCBF) was measured by laser speckle flowmetry to confirm CSD induction. The von Frey, light-dark box, elevated plus maze, and open field test were conducted to verify migraine-related behaviors in freely moving mice.

RESULTS

An optogenetic stimulus induced typical spreading triphasic rCBF change with a reduction of over 20%, confirming CSD induction. A single unilateral CSD in freely moving C57BL/6 J mice triggered bilateral periorbital and hind-paw allodynia lasting for 4-24 h. Notably, the ipsilateral periorbital mechanical threshold was significantly lower than the contralateral at 1 h. It also generated photophobia and anxiety behaviors persisting for 24-48 h. Furthermore, cutaneous allodynia and anxiety behaviors were alleviated by sumatriptan.

CONCLUSIONS

This study proposes an optogenetic CSD-induced migraine model originating from VISp in awake and freely moving C57BL/6 J mice and presents the behavioral paradigm in detail. The CSD model in wild-type mice is promising to be wildly used to study the pathogenesis of MwA.

Enhancing anesthetic techniques for improving whisker stimulation response in the barrel cortex

This study adopts and validates an anesthetic protocol designed for rat whisker stimulation experiments, achieving significant enhancements in the neural response of the barrel field cortex. By combining alpha-chloralose, low-dose Isoflurane (0.5%) and Dexdomitor, the protocol not only maintains a stable anesthetic state but also markedly improves the amplitude and latency of local field potential (LFP) signals. Experimental results reveal that LFP amplitudes in the barrel field under this protocol are twice as high as those achieved with Isoflurane and four times as high as those with Ketamine-Xylazine, with significantly shortened latencies and reduced noise interference. For the first time, power spectral analysis reveals a distinct enhancement of oscillatory power in the alpha (8-13 Hz) and beta (13-30 Hz) bands under alpha-chloralose anesthesia, diverging from the traditional dominance of delta (0.5-4 Hz) oscillations observed with other anesthetics. Mechanistically, this phenomenon may be attributed to alpha-chloralose's unique modulation of GABAergic and glutamatergic pathways, promoting cortical desynchronization and enhanced sensory processing. This protocol offers new insights into optimizing sensory-evoked neural signal acquisition and provides a reference for future studies exploring neural modulation in sensory neuroscience.

Design and characterization of a time-domain optical tomography platform for mesoscopic lifetime imaging

We report on the system design and instrumental characteristics of a novel time-domain mesoscopic fluorescence molecular tomography (TD-MFMT) system for multiplexed molecular imaging in turbid media. The system is equipped with a supercontinuum pulsed laser for broad spectral excitation, based on a high-density descanned raster scanning intensity-based acquisition for 2D and 3D imaging and augmented with a high-dynamical range linear time-resolved single-photon avalanche diode (SPAD) array for lifetime quantification. We report on the system's spatio-temporal and spectral characteristics and its sensitivity and specificity in controlled experimental settings. Also, a phantom study is undertaken to test the performance of the system to image deeply-seated fluorescence inclusions in tissue-like media. In addition, ex vivo tumor xenograft imaging is performed to validate the system's applicability to the biological sample. The characterization results manifest the capability to sense small fluorescence concentrations (on the order of nanomolar) while quantifying fluorescence lifetimes and lifetime-based parameters at high resolution. The phantom results demonstrate the system's potential to perform 3D multiplexed imaging thanks to spectral and lifetime contrast in the mesoscopic range (at millimeters depth). The ex vivo imaging exhibits the prospect of TD-MFMT to resolve intra-tumoral heterogeneity in a depth-dependent manner.

Visualizing Oscillations in Brain Slices With Genetically Encoded Voltage Indicators

Genetically encoded voltage indicators (GEVIs) expressed pan-neuronally were able to optically resolve bicuculline induced spontaneous oscillations in brain slices of the mouse motor cortex. Three GEVIs were used that differ in their timing of response to voltage transients as well as in their voltage ranges. The duration, number of cycles, and frequency of the recorded oscillations reflected the characteristics of each GEVI used. Multiple oscillations imaged in the same slice never originated at the same location, indicating the lack of a “hot spot” for induction of the voltage changes. Comparison of pan-neuronal, Ca²⁺/calmodulin-dependent protein kinase II α restricted, and parvalbumin restricted GEVI expression revealed distinct profiles for the excitatory and inhibitory cells in the spontaneous oscillations of the motor cortex. Resolving voltage fluctuations across space, time, and cell types with GEVIs represent a powerful approach to dissecting neuronal circuit activity.