Acoustic nanoparticles mediated precise brain stimulation by noninvasive ultrasound

Abstract

Brain stimulation accelerates the probing of brain neural circuits and the treatment of brain diseases. Historically, deep brain stimulation (DBS) is a welcomed approach for rapid neuronal stimulation and treating neurological disorders, such as Depression, Parkinson's Disease, and Epilepsy. However, DBS is invasive with the risk of surgery and has limited spatial precision. Transcranial direct current stimulation (tDCS) and transcranial magnetic stimulation (TMS) can pass through a skull non-invasively for neuromodulation without surgical invasion; however, they provide a spatial accuracy of centimeter-level because of the long wavelength of electromagnetic waves used. Ultrasound (US) is a mechanical wave that has been utilized for noninvasive brain neurostimulation in deep-seated areas, furthermore, it is compatible with MRI for safely modulating the activities of brain. Many animal species were treated with ultrasound and exhibited effective stimulation, such as sheep, rodents, and rabbits in various brain regions. However, the acoustic stimulation precision extremely relies on the frequencies of ultrasound. The retinal stimulation through high-frequency ultrasound has been identified with high spatial precision. In contrast, stimulating a deep neural tissue, such as the brain, requires lower frequencies to penetrate deep tissue, which results in lower spatial precision. Sonogenetics utilized overexpression of a mechanosensitive ion channel to make specific cells more sensitive to US and obtained targeted neuron stimulation with high spatiotemporal precision. However, such a method involves viral transfection, which makes human applications challenging. Alternatively, nanomaterials have been developed as mediators for localized neuronal stimulation, such as gold nanoparticle-mediated photothermal stimulus, upconversion nanoparticle-enabled near-infrared optogenetics, and magnetic nanoparticle-assisted magnetothermal/magnetomechanical stimulus. Inspired by these aforementioned studies, we then asked whether there are potential nanomaterials that could transform or amplify US effects for localized neuron modulation. A candidate for such a tool is nano-sized bubbles extracted from cyanobacteria, called gas vesicles (GVs). GVs can oscillate under US field, which has been employed as a nanosized ultrasound contrast agent. Therefore, it is reasonable to investigate whether GVs could serve as actuators facilitating US stimulation of adjacent neuron cells. In this thesis work, nano gas vesicles are explored as localized mediators to amplify the acoustic effects and actuate in vitro and in vivo ultrasound neurostimulation with high spatial and temporal precision. Chapter 1 gives a brief introduction to nanomaterials-­mediated ultrasound neurostimulation. In chapter 2, we prepared the gas vesicles, modified the GVs' surface, and characterized their properties. In chapter 3, we designed an ultrasound stimulation system, achieved repeatable and reversible neuronal activation, and identified the possible mechanism of neuronal excitation induced by GVs-mediated ultrasound stimulation (GVs+US). In chapter 4, we verified the precise neural activation in the deep brain region induced by GVs+US, and the PEGylated GVs (PGVs) with improved stability and biocompatibility, and such PGVs-mediated ultrasound stimulus (PGVs+US) activated the mice motor cortex and then altered the movement of the forelimbs. In chapter 5, we confirmed that PGVs+US can control the mice's behaviors by activating targeted deep-seated brain regions precisely. In chapter 6, the therapeutic effects of PGVs+US were validated by alleviating the depression symptoms in depression-like mice models. In chapter 7, we demonstrated the feasibility of cell-types selective stimulation through GV-enabled sonogenetics. In chapter 8, I summarized my current understanding of the thesis work and presented my views of prospects in this field. Taken together, with all the studies in this thesis, we built a precise brain stimulation strategy by nanobubble-enabled low-intensity low-frequency ultrasound (LILFU). Our approach could provide opportunities to understand the mechanism of acoustic neural modulation and the potential for treating neurological disorders by remotely non-invasive ultrasound stimulation.