Two-photon GCaMP6f imaging of infrared neural stimulation evoked calcium signals in mouse cortical neurons in vivo

Abstract

Infrared neural stimulation is a promising tool for stimulating the brain because it can be used to excite with high spatial precision without the need of delivering or inserting any exogenous agent into the tissue. Very few studies have explored its use in the brain, as most investigations have focused on sensory or motor nerve stimulation. Using intravital calcium imaging with the genetically encoded calcium indicator GCaMP6f, here we show that the application of infrared neural stimulation induces intracellular calcium signals in Layer 2/3 neurons in mouse cortex in vivo. The number of neurons exhibiting infrared-induced calcium response as well as the amplitude of those signals are shown to be both increasing with the energy density applied. By studying as well the spatial extent of the stimulation, we show that reproducibility of the stimulation is achieved mainly in the central part of the infrared beam path. Stimulating in vivo at such a degree of precision and without any exogenous chromophores enables multiple applications, from mapping the brain’s connectome to applications in systems neuroscience and the development of new therapeutic tools for investigating the pathological brain.

Bidirectional modulation of evoked synaptic transmission by pulsed infrared light

“…The suppression and the blocking of synaptic transmission occurred at local temperatures that are close to and slightly higher than the mammalian physiological temperature. Since an IR light pulse can increase the local temperature transiently beyond the physiological level without causing tissue damage 63 , 64 , it would be interesting to examine the behavior of mammalian synapses when the local temperature is transiently raised from the mammalian physiological temperature, similar to what will happen during in vivo INM applications 11 , 12 , 32 , 34 . In addition to INM applications, the presented study also highlights the potential of pulsed IR light as a novel and convenient tool for fundamental research where transient and localized control of synaptic activity is needed.…”

Advantages, Pitfalls, and Developments of All Optical Interrogation Strategies of Microcircuits in vivo

“…For example, NIR is shown to block action potential conduction along axons ( Walsh et al, 2016 ), in cultured neurons ( Feyen et al, 2016 ) and that this is coupled to blockade of potassium voltage-gated channels, although a direct modulation of sodium channels has also been shown ( Li et al, 2014 ). Noticeably, the field remains controversial as there are clear experimental indication that NIR can depolarize and induce spike in artificial membranes ( Shapiro et al, 2017 ), can activate ganglion neurons ( Paris et al, 2017 ), can induce calcium transients in neurons ( Kaszas et al, 2021 ), or increases visual cortical responsiveness in primates as assessed by intrinsic signal imaging and extracellular electrophysiology ( Cayce et al, 2014 ). Other reports show instead a decrease in visual responsiveness in rat visual cortex ( Wu et al, 2013 ), as well as decreases of intrinsic signal response in rat somatosensory cortex ( Cayce et al, 2011 ).…”

“Multiphoton holographic photostimulation induces potassium-dependent spike silencing in label-free mouse cortex in vivo”

“…[6]), while other excitatory (e.g. [7]) effects. This knowledge is needed to optimize/interpret all-optical interrogation studies, but also promising NIR-based therapies in psychiatry (e.g.…”