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All-optical brain-to-brain behaviour and information transfer

Periodic Reporting for period 4 - BrainBIT (All-optical brain-to-brain behaviour and information transfer)

Reporting period: 2021-06-01 to 2022-05-31

A more detailed information on neuronal encoding of information in the cortex is a crucial point in neuroscience and physiopathology studies. On one hand it is important for a deeper understanding of brain function and on the other hand to dissect the physiological mechanism that are altered in pathologies, diseases and injuries. We setup and characterize new optical imaging and manipulation techniques to address brain functionality over the large scale. We develop new approaches for addressing the brain circuitry and one of the most successful ones is optogenetics.
At UNIFI we have realized an innovative optical system that, exploiting the transparency of the larva of the vertebrate zebrafish and the genomic integration of calcium indicators and optogenetic actuators, enables the recording of five complete acquisitions of the neuronal activity in the whole encephalon every second and, at the same time, allows us to stimulate the activity on arbitrary sets of neurons in the volume. We have used this system to “read” and “write” at the same time the brain activity, giving a particular attention to the activity that could be linked to particular animal behaviours.
We successfully developed an all-optical system allowing the dissection of cortical circuitry at the millimeters scale in awake mice. Combining optical techniques, viral transfection and wide-field microscopy we identified for the first time the cortical pattern underneath the execution of ethologically relevant movements such as grasping-like and locomotion-like movements. Moreover, we described a new cortical area involved in the generation of the grasping movement. We dissected the cortical pattern correlated to the activation of D1 MSNs in the striatum, a class of neurons crucially involved in the motor control in the cortical-basal ganglia-thalamus loop.
By means of behavioral investigations and electrophysiological recordings in the cortex in vivo, at CNR we found that serotoninergic neurons and PV interneurons-mediated Gamma band frequency have a key role after stroke. We first validated a therapeutic protocol based on chemogenetic boosting of the serotoninergic system coupled with robotic rehabilitation that succeeded in improving forelimb motor function after stroke (Conti et al., 2021). We implemented a therapeutic approach based on optogenetic PV-driven 40 Hz stimulation on transgenic animals coupled with robotic rehabilitation. We also translated this treatment in a more clinical approach by using 40 Hz transcranial Alternating Direct Current Stimulation (tACS)together with robotic rehabilitation in stroke mice.
IIT@CBN developed a new family of optoelectronic devices to perform optogenetic experiments based on tapered optical fibers for addressing the brain region of interest. The final device is obtained by fiber metallization and micromachining of the deposited thin gold layer. The distal tapered end is left uncoated and light can be delivered, while the micromachined electrode is built just above the first emission diameter of the fiber, thus minimizing photoelectric artefacts induced by light impinging on the electrode.
In Adam et al. 2018, a multispot two-photon excitation microscope with rolling shutter wide-field detection was developed. This method benefits from the increased penetration depth of two-photon excitation in scattering media and the increased imaging rates of multiplexed excitation while exploiting the rolling shutter of a fast sCMOS camera. Microscope performances were demonstrated in fixed semicleared brain slices by imaging dendritic spines up to 400-μm deep.
In Montagni et al. 2018 we describe the evaluation of different indicators of neuronal activity to identify the most suited for the development of an all-optical system. We tested different red-shifted genetically encoded calcium indicators to identify the best one to reveal the cortical neuronal activity and a combination of indicator and actuator that could be successfully used to read and write from mouse cortex, towards the intra and inter subject transfer of neuronal functionality. We identified jRCaMP1a as the best red-shifted functional indicator that does not show photoswitch, resulting the best choice for the future development of an all-optical system for interrogation of neuronal circuits.
In Sancataldo et al. (Front. Neuroanat. 2019), we described the use of acousto-optic deflectors (AODs) in light-sheet microscopy to mitigate striping artefacts. This work paves the way to a more quantitative functional imaging in zebrafish larvae, which is a key aspect of the project, and which was also previously investigated by our group (Muellenbroich et al., Front. Cell Neurosci. 2018).
Further, the use of AODs has been a technical training for the implementation of multiplexed ultrafast light-sheet microscopy.
In de Vito et al. (Biom. Opt. Express, 2022), we present a microscope that quintuplicated the previous maximal volumetric acquisition speed of a vertebrate brain (zebrafish larva) with cellular resolution. We used this microscope to characterize brain-wide events of fast neuronal activity (caudo-rostral ictal waves) that were previously unreported.
In Pisanello M. et al. (Sci. Rep., 2018), we showed how tapered optical fibers can be a versatile tool for performing light delivery in both shallow and deep brain areas. Moreover, we showed how it is possible to reconfigure and tune light emission patterns in order to be adapted to the brain region of interest, also dynamically switching from restricted or wide illumination of brain volumes.
In Pisano et al. (Nat. Meth., 2019), we described how the modal properties of the tapered optical fibers can also lead to the possibility of collecting light thus performing fiber photometry. In combination with fiber microstructuring and tailoring of the light collection volumes, we demonstrated in vivo fiber photometry of dopaminergic activity in the dorsal vs ventral striatum of behaving mice.
In Spagnolo B. et al. (Nat. Mater., 2022) we implemented microstructured optical windows and microelectrodes on the taper of the fiber by exploiting two-photon lithography in order to pattern different geometries of electrically and optically active elements all along and all around the taper axis. This approach greatly maximizes the possibility of studying deep brain circuitry with customized light-delivery patterns while recording neural activity, with no photoelectric artefacts thanks to the optimized microfabrication protocol.
In Quarta et al., 2022 we investigated the hypothesis that areas beyond the motor regions could participate in reach to grasp planning and execution. We found that a large network of areas is engaged while performing the reach to grasp task and the kinematics correlates mostly with neural activity in sensorimotor areas
In Allegra Mascaro et al., 2019, we investigate how rehabilitation paradigm affects neuronal and vascular plasticity of the mouse cortex after focal stroke. We fund that synaptic stabilization is associated with angiogenesis and recovery of a segregated motor representation.
At CNR we successfully consolidated the results obtained with high impact publications: Spalletti et al. 2017; Sammali et al., 2017; Alia et al., 2017, 2019, 2021; Conti et al., 2021.
Brain activity recording with GCaMP6s in zebrafish