Patterned Optogenetic Modulation of Neurovascular and Metabolic Signals

Abstract

The hemodynamic and metabolic response of the cortex depends spatially and temporally on the activity of multiple cell types. Optogenetics enables specific cell types to be modulated with high temporal precision and is therefore an emerging method for studying neurovascular and neurometabolic coupling. Going beyond temporal investigations, we developed a microprojection system to apply spatial photostimulus patterns in vivo. We monitored vascular and metabolic fluorescence signals after photostimulation in Thy1-channelrhodopsin-2 mice. Cerebral arteries increased in diameter rapidly after photostimulation, while nearby veins showed a slower smaller response. The amplitude of the arterial response was depended on the area of cortex stimulated. The fluorescence signal emitted at 450/100 nm and excited with ultraviolet is indicative of reduced nicotinamide adenine dinucleotide, an endogenous fluorescent enzyme involved in glycolysis and the citric acid cycle. This fluorescence signal decreased quickly and transiently after optogenetic stimulation, suggesting that glucose metabolism is tightly locked to optogenetic stimulation. To verify optogenetic stimulation of the cortex, we used a transparent substrate microelectrode array to map cortical potentials resulting from optogenetic stimulation. Spatial optogenetic stimulation is a new tool for studying neurovascular and neurometabolic coupling.

Optical imaging and modulation of neurovascular responses

“…Rodents expressing channelrhodopsin in excitatory neurons have been used to verify that modulation of cortical excitatory activity modulates cortical hemodynamic responses accordingly. 183–185 These findings are similar to those obtained by sensory stimulation except that these optogenetic studies preferentially target Layer 5 (and Layer 2/3 in some studies) pyramidal excitatory neurons, while sensory stimulation is initiated in Layer 4. 186 Nonetheless, modulation of the optogenetic stimulus, modulates both the evoked neuronal activity and size of the vascular response.…”

Fiber bundle-based integrated platform for wide-field fluorescence imaging and patterned optical stimulation for modulation of vasoconstriction in the deep brain of a living animal

“…However, optogenetic technologies can be extended to new methods of studying neurovascular circuits that allow the observation and control of individual neurons, astrocytes, and vascular cells with excellent spatial and temporal resolution [9,[34][35][36]. If the developed platform is used as a general optical stimulus tool rather than an optogenetic stimulation, it can be adapted for focal photothrombosis using a photosensitive dye such as Rose Bengal solution [37], which could be applicable to studies of local ischemia and ischemic stroke [3,26,38].…”

“…Functional changes in cell-level interactions can alter brain activity, hemodynamics, and metabolism in the brain, causing deviations in normal neurological function. Researchers have used brain imaging systems to identify brain structures and vascular distributions, perform specific functional assessments in specific brain areas, and study brain diseases related to various vascular diseases [1,[4][5][6][7][8][9][10][11][12][13][14][15][16]. Functional magnetic resonance imaging (fMRI) and positron emission tomography (PET) scans are the most commonly used imaging techniques exploiting hemodynamic responses to map brain functions [1,6,7].…”

“…However, these imaging techniques have the disadvantage of difficulty in directly detecting intercellular responses, because they can only confirm the reaction to changes in blood flow caused by the simultaneous reaction of thousands of neurons [8]. Highresolution imaging optical systems such as conventional microscopy systems, including epifluorescence [9], confocal microscopy [10], and two-photon microscopy [11][12][13][14], have also been applied to cerebrovascular studies. These high-resolution imaging systems facilitate studies of the hemodynamics and blood cell-vessel wall interactions in the primary somatosensory cortex [11,15], limb cortex, and parietal cortex [12,14].…”

Wearable Second Harmonic Generation Imaging: The Sarcomeric Bridge to the Clinic

“…In particular, in vivo imaging methods have gained popularity in the nervous system, as the timescales of many physiological changes are relatively short. Additionally, a number of relevant neurological functions can be assessed with label-free imaging, including injury scarring (Schendel et al, 2014), metabolic activity and blood flow (Richner et al, 2015), and indirect measures of neural activity (Llano et al, 2009). The approach described here could also be employed in a number of different clinical disease diagnosis and treatment paradigms, especially where neural tissue is already exposed during another surgical proce-dure, or where implantable devices are inserted for short periods of time for longitudinal monitoring (Felton et al, 2007).…”