Calcium imaging of infrared-stimulated activity in rodent brain

Abstract

Summary Infrared neural stimulation (INS) is a promising neurostimulation technique that can activate neural tissue with high spatial precision and without the need for exogenous agents. However, little is understood about how infrared light interacts with neural tissue on a cellular level, particularly within the living brain. In this study, we use calcium sensitive dye imaging on macroscopic and microscopic scales to explore the spatiotemporal effects of INS on cortical calcium dynamics. The INS-evoked calcium signal that was observed exhibited a fast and slow component suggesting activation of multiple cellular mechanisms. The slow component of the evoked signal exhibited wave-like properties suggesting network activation, and was verified to originate from astrocytes through pharmacology and 2-photon imaging. We also provide evidence that the fast calcium signal may have been evoked through modulation of glutamate transients. This study demonstrates that pulsed infrared light can induce intracellular calcium modulations in both astrocytes and neurons, providing new insights into the mechanisms of action of INS in the brain.

Target structures for cochlear infrared neural stimulation

“…The increase in free calcium caused by infrared irradiation was found in the vestibular system 13,15 in cardiomyocytes 14 and the cortex. 16,17 While it has been well documented that the intracellular calcium concentration increases upon irradiation, it is not clear how the increased calcium results in an action potential.…”

“…11,12 Other experiments demonstrated that IR increases the intracellular calcium concentration. [13][14][15][16][17][18] Recently, it has been demonstrated that the increase in intracellular calcium concentration results from a direct interaction of the radiation with intracellular calcium stores. 15 Pulse lengths for INS are typically 100 μs for cochlear stimulation and about 1 ms for peripheral nerve or cortical stimulation.…”

In vitro neuronal depolarization and increased synaptic activity induced by infrared neural stimulation

“…However, there is currently only limited research focusing on interrogation of INS in cells of the central nervous system. One such study relied on calcium imaging to probe the visual cortex's response to INS and demonstrates a fast and slow component of the calcium signal [13], with another study showing that INS increased the spontaneous discharge rate of visual cortex neurons recorded in vivo in the Macaque through extracellular recordings of unit activity [14]. A similar study instead described the use of infrared light to cause neural inhibition [15].…”

Infrared neural stimulation: a new stimulation tool for central nervous system applications

“…16 Using Oregon Green dye as a calcium indicator, they observed wave-like propagation of the calcium signal following INS. The dynamics of the calcium signal consisted of a slow and a fast component.…”

“…The Jansen group used electrophysiological recordings in combination with intrinsic optical calcium dye and flavoprotein fluorescence imaging in rodents to demonstrate the feasibility of INS application in the cortex, explore the optical parameters necessary for successful stimulation, and determine which cell types are affected by INS. 16,17 Intrinsic optical signal imaging is a technique used to detect local changes in blood flow via red light reflectance due to focal metabolic changes. 18 It is a convenient way to detect cortical activation patterns because it requires no contrast agent and can be used to image a relatively wide area (tens of square millimeters) with a resolution of the order of 10 microns.…”