KEYWORDS: Neurons, Calcium, Education and training, Two photon imaging, Infrared radiation, Pulse signals, Infrared imaging, Brain, Neurophotonics, In vivo imaging
SignificancePulsed infrared neural stimulation (INS, 1875 nm) is an emerging neurostimulation technology that delivers focal pulsed heat to activate functionally specific mesoscale networks and holds promise for clinical application. However, little is known about its effect on excitatory and inhibitory cell types in cerebral cortex.AimEstimates of summed population neuronal response time courses provide a potential basis for neural and hemodynamic signals described in other studies.ApproachUsing two-photon calcium imaging in mouse somatosensory cortex, we have examined the effect of INS pulse train application on hSyn neurons and mDlx neurons tagged with GCaMP6s.ResultsWe find that, in anesthetized mice, each INS pulse train reliably induces robust response in hSyn neurons exhibiting positive going responses. Surprisingly, mDlx neurons exhibit negative going responses. Quantification using the index of correlation illustrates responses are reproducible, intensity-dependent, and focal. Also, a contralateral activation is observed when INS applied.ConclusionsIn sum, the population of neurons stimulated by INS includes both hSyn and mDlx neurons; within a range of stimulation intensities, this leads to overall excitation in the stimulated population, leading to the previously observed activations at distant post-synaptic sites.
Recent studies have highlighted the importance of understanding the architecture and function of microvasculature, and dysfunctions of these microvessels may underlie neurodegenerative disease. Here, we utilized a highly precision ultrafast laser-induced photothrombosis (PLP) method to occlude single capillaries and then quantitatively studied effects on vasodynamics and surrounding neurons. Analysis of the microvascular architecture and hemodynamics after single-capillary occlusion reveals distinct changes upstream vs downstream branches, which shows rapid regional flow redistribution and local downstream BBB leakage. Focal ischemia via capillary occlusions surrounding labeled target neuron induced dramatic and rapid lamina-specific changes in neuronal dendritic architecture. The adaptive changes in neuronal function networks were correlated to the degree of ischemia core. Further, we find that micro-occlusion at two different depths within the same vascular arbor results in distinct effects on flow profiles in layerin layer 2/3 vs layer 4. The current results raised the possibility that relatively greater impacts on microvascular function contribute to neuronal network function.
Infrared neural stimulation (INS, 1875 nm) is an emerging neuromodulation technology that holds promise for clinical application. However, little is known about its effect on excitatory and inhibitory cell types in the cerebral cortex. Here, using two-photon calcium imaging in the awake mouse somatosensory cortex, we have examined the effect of INS pulse train application on non-GABAergic (hSyn) excitatory neurons and GABAergic (mDlx) inhibitory neurons tagged with GCaMP6s. We find that each INS pulse train reliably induces a robust response in both excitatory and inhibitory neurons characterized by an initial decrease in intracellular calcium signal followed by a positive rebound; cessation of the several pulse trains leads to a large positive rebound, most prominently seen in non-GABAergic neurons. Quantification using indices of correlation, oscillation amplitude, and size of post-stimulation rebound illustrates responses are intensity-dependent and distance-dependent. Estimates of summed population response timecourses provide a potential basis for neural and hemodynamic signals described in other studies.
Significance: Current approaches to stimulating and recording from the brain have combined electrical or optogenetic stimulation with recording approaches, such as two-photon, electrophysiology (EP), and optical intrinsic signal imaging (OISI). However, we lack a label-free, all-optical approach with high spatial and temporal resolution.
Aim: To develop a label-free, all-optical method that simultaneously manipulates and images brain function using pulsed near-infrared light (INS) and functional optical coherence tomography (fOCT), respectively.
Approach: We built a coregistered INS, fOCT, and OISI system. OISI and EP recordings were employed to validate the fOCT signals.
Results: The fOCT signal was reliable and regional, and the area of fOCT signal corresponded with the INS-activated region. The fOCT signal was in synchrony with the INS onset time with a delay of ∼30 ms. The magnitude of fOCT signal exhibited a linear correlation with the INS radiant exposure. The significant correlation between the fOCT signal and INS was further supported by OISI and EP recordings.
Conclusions: The proposed fiber-based, all-optical INS-fOCT method allows simultaneous stimulation and mapping without the risk of interchannel cross-talk and the requirement of contrast injection and viral transfection and offers a deep penetration depth and high resolution.
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