In Vivo Voltage-Sensitive Dye Imaging of Subcortical Brain Function

Abstract

The whisker system of rodents is an excellent model to study peripherally evoked neural activity in the brain. Discrete neural modules represent each whisker in the somatosensory cortex (“barrels”), thalamus (“barreloids”), and brain stem (“barrelettes”). Stimulation of a single whisker evokes neural activity sequentially in its corresponding barrelette, barreloid, and barrel. Conventional optical imaging of functional activation in the brain is limited to surface structures such as the cerebral cortex. To access subcortical structures and image sensory-evoked neural activity, we designed a needle-based optical system using gradient-index (GRIN) rod lens. We performed voltage-sensitive dye imaging (VSDi) with GRIN rod lens to visualize neural activity evoked in the thalamic barreloids by deflection of whiskers in vivo. We stimulated several whiskers together to determine the sensitivity of our approach in differentiating between different barreloid responses. We also carried out stimulation of different whiskers at different times. Finally, we used muscimol in the barrel cortex to silence the corticothalamic inputs while imaging in the thalamus. Our results show that it is possible to obtain functional maps of the sensory periphery in deep brain structures such as the thalamic barreloids. Our approach can be broadly applicable to functional imaging of other core brain structures.

High-dynamic-range fluorescence laminar optical tomography (HDR-FLOT)

“…Increasing the penetration depth would broaden the application of FLOT for neuroscience research. Since the optical properties of the living mouse brain are too complicated to mimic using a simple phantom, a 150-μm glass capillary filled with voltage-sensitive dye (commonly used for reporting neural activities [6, [32][33][34][35]) was inserted into a mouse brain in vivo to demonstrate the feasibility of HDR-FLOT to increase penetration depth.…”

“…The mouse's head was shaved before being placed into a stereotaxic frame (Stoelting Co.) [6,32]. Then, a cranial window was made over the left parietal cortex (about 4 × 4 mm).…”

“…Then, a cranial window was made over the left parietal cortex (about 4 × 4 mm). The surface of the dura mater was cleaned with hemostatic sponges dipped in artificial cerebrospinal fluid (ACSF) as described previously [6,32]. One 150-µm glass capillary filled with voltagesensitive dye RH-1691 (Optical Imaging Ltd.; 1.0 mg/ml in ACSF) was then slowly inserted into the exposed area.…”

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