We use photon-counting to measure nonlinear Thomson scattering from low-density electrons in an intense laser focus. The azimuthal and longitudinal polarization components of the second harmonic are measured across much of the full emission sphere. The data show, for the first time experimentally, emission structure in the ‘Northern’ and ‘Southern’ hemispheres, where the ‘North Pole’ aligns with the direction of laser propagation. To obtain these measurements, we installed an additional power amplifier on our Ti:sapphire laser system at BYU. The upgrade delivers ten times more energy to the laser focus than we had previously. This increase comes partly from the additional amplifier and partly from increased grating efficiency in our pulse compressor. We achieve an on-target pulse energy of 200 mJ at 35 fs. The focal spot size has radius w0 = 4 μm. This corresponds to an available peak intensity of over 1019 W/cm2, an order of magnitude above the onset of strong relativistic effects. The interaction region in the laser focus has a length of approximately 100 μm. Photons scattered from this region are collected using a 5-cm-focal-length lens and then focused onto the end of a 100-μm-diameter fiber by a second identical lens. The imaging system requires precise alignment with the laser focus, which must be maintained when rotating the photon-collection system along the longitudinal direction of the emission sphere. We developed an alignment procedure that ensures that the detector rotation axis aligns with region of space that is imaged onto the fiber. This region is then aligned to the laser focal spot.

Recent evidence appears to indicate that neurons, responsible for our perception of the world around us, are not only electrically excitable, but may have mechanical triggers as well. This is well supported through the growing number of observations of focused ultrasound (FUS) perturbations of the neurons located in our central nervous system (CNS). However, while the CNS is largely responsible for turning electrical signals from the periphery into thoughts and understanding, less is known about the effect of which FUS has upon the peripheral signals themselves: our peripheral nervous system (PNS). Given the non-invasive nature of FUS - were it be discovered to influence neuronal signaling, FUS would become a powerful tool for therapy and medicine, especially in conditions involving pain. Thus, we ponder the question, "How can FUS modulate nerve activity and furthermore, what are the interactions on pain signaling?" In this dissertation, a road-map is described for translating insights acquired through pre-clinical study of ultrasound PNS stimulation to clinical investigation on neuropathic pain modulation in humans. More specifically, methods and tools to study excitation of the sciatic nerve bundle and the dorsal root ganglia (DRG) were built and optimized in rodent models. In turn, these methods and findings enabled investigation into pain signaling and translation to human studies. Finally, FUS was shown to mitigate pain sensations in human patients with neuropathic pain. First, using a newly developed in vivo nerve displacement imaging technique, mechanical deformations of the nerve from FUS stimulation were noninvasively mapped in a two-dimensional plane centered at the sciatic nerve. Nerve displacements were positively correlated with downstream compound muscle activation from FUS sciatic nerve stimulation. Furthermore, by focusing ultrasound waves to the DRGs directly in an ex vivo preparation, additional parameters were identified to modulate spike transmission, effectively regulating high frequency signaling. Next, we investigated the feasibility translating FUS nerve stimulation to clinical studies. We first looked at effects on upstream cortical activity and pain signaling from somatosensory stimuli using high-frequency functional ultrasound (fUS) imaging. FUS was shown to both stimulate somatosensation and suppress pain signaling in the cortex. Secondly, nerve displacement imaging was scaled-up for human investigation, essential for in-procedure localization and stimulation of the targeted nerve bundle. Using a combination of imaging and therapeutic excitation, simultaneous nerve targeting, stimulation, and monitoring was established at pressures required for stimulation. Lastly, clinical feasibility was investigated using previously optimized FUS pulse schemes and scaled-up neuromodulation technologies. Specifically, we applied simultaneous FUS to the median nerve and thermal stimulation to the corresponding dermatome in healthy human subjects. Furthermore, patients with robust and repeatable mechanically-assessed neuropathic pain were similarly stimulated with FUS to assess pain suppression. Based on the findings presented herein, noninvasive FUS peripheral stimulation has the potential for radically shifting the traditional pharmaceutical paradigms in chronic and acute pain treatment by altering signals before being processed in the spinal cord and ultimately the brain. The studies outlined herein serve to elucidate mechanisms of FUS in the PNS, as well as provide the starting foundations for further development of FUS as an effective pain treatment.

University evaluations often reflect an individual’s ability to memorize and recall lecture material during exams. Consequently, the ability to effectively encode, store, and later retrieve information is an integral part of learning and academic success. Notably, students who are more physically active tend to have better academic performance. The neurobiology of stress is a strong candidate for the mechanism underlying this exercise-cognition interaction. Given that exercise is a physical stressor, it is hypothesized that exercise-induced adrenocortical activations increase cortisol levels. Critically, cortisol increases memory consolidation for newly learned information. One hundred twenty-eight young adults (36 males; age: M±SD =19.47±1.55 years) viewed a video lecture before exercise (n = 41), after exercise (n = 42), or after rest (n = 45). The exercise was high intensity interval training on a cycle ergometer and memory for the lecture material was assessed using a multiple-choice quiz conducted 14 minutes and 48 hours after the lecture. There was a significant positive correlation between aerobic fitness and grade point average [r(95) = 0.22, p < .05], immediate recall [r(100) = 0.39, p < .001], and delayed recall [r(98) = 0.28, p < .01]. A mixed model ANOVA found a significant main effect of group on comprehension of the lecture material, F(2, 96) = 3.34, p < .05, revealing greater memory benefits at both 14 minutes and 48 hour delays for those who exercised compared to those who did not exercise; however, pairwise comparisons found this effect specific to the exercise post group. There was also a main effect of group on cortisol levels, F(2, 107) = 3.97, p < .05; however, only the exercise prior group exhibited significantly greater levels than the control group. Thus cortisol levels collected during the experimental session did not clearly differentiate the exercise conditions or reflect the observed memory benefits for the exercise post group. This may have resulted from the gradual increase in cortisol following exercise that had time to increase when exercise was completed at the beginning of the exercise session (exercise prior) rather than at the end (exercise post). Overall, this study suggests that both physical fitness and an acute bout of aerobic exercise are associated with academic and memory performance. More research is needed to understand the mechanism. / Thesis / Master of Science (MSc)

In addition to protecting the brain from circulating pathogens and neurotoxins, the blood-brain barrier (BBB) limits both the delivery of drugs to the brain and the migration of neurological disease biomarkers from the brain into the blood. Focused-ultrasound blood-brain barrier opening (FUS-BBBO) addresses both of these transport limitations by transiently and noninvasively opening the BBB. Although originally designed as a drug delivery method, FUS-BBBO has also been shown to be an effective neuroimmunotherapy and method of improving liquid biopsy specificity for neurological disease. Prior to the work presented herein, the mechanism of FUS-BBBO neuroimmunotherapy remained poorly characterized and FUS-BBBO liquid biopsy remained poorly optimized. Initially, we present the temporal response of brain macrophages to FUS-BBBO. Due totheir role as the main phagocyte in the brain and the well-documented association between their dysfunction and neurodegenerative disease progression, we hypothesized that FUS-BBBO affects brain macrophage population composition and phenotype. Utilizing temporal single-cell RNA sequencing, we establish that treatment remodels the immune landscape via a number of processes including microglia proliferation, disease-associated microglia population size increase, and central-nervous-system associated macrophage recruitment. To further elucidate the functional role of the brain macrophage response to FUS-BBBO, we find that their depletion is associated with significantly decelerated BBB restoration. Secondly, we compare FUS-BBBO with two other methods of focused ultrasound neuroimmunotherapy, focused ultrasound neuromodulation (FUS-N) and focused ultrasound with microbubbles without BBBO (FUS+MB). FUS-N utilizes FUS parameters that alter neuronal connectivity via a combination of mechanosensitive receptor interactions and transient hypothermia without the injection of microbubbles (MB). FUS+MB is the combination of MB and FUS below the pressure threshold for BBBO (FUS+MB). FUS+MB has been shown to trigger morphological activation of brain macrophages and has proven efficacious as a method of immunotherapy within the peripheral nervous system. Due to the findings of brain macrophage modulation in response to FUS-BBBO, we compare brain macrophage modulation between all three paradigms both in the presence and absence of Alzheimer’s Disease (AD) pathology. We identify FUS-BBBO as the paradigm which maximizes brain macrophage modulation including an increase in the population of neuroprotective, disease-associated microglia and direct correlation between FUS cavitation dose and brain macrophage phagocytosis. Next, we combine spatial and single-cell transcriptomics with immunohistochemical validation to characterize the effect of FUS-BBBO on brain macrophage distribution in both wild-type and Alzheimer’s disease animals. Given their relevance within neurodegeneration and perturbation response, we emphasize the distribution of three brain macrophage populations - disease- and interferon-associated microglia and central-nervous-system-associated macrophages. We find a genotype-specific redistribution of each population, with an overall trend towards increased interaction with the brain-cerebrospinal fluid barrier after FUS-BBBO, an effect that is found to be more pronounced in the presence of disease pathology. Finally, we investigate the role of extracellular vesicles (EVs) in both the mechanism ofFUS-BBBO neuroimmunotherapy and as a method of improving FUS-BBBO liquid biopsy. EVs are lipid vesicles that are responsible for the transport and exchange of diverse cargo between cells and have been reported to modulate the immune system. Isolation of EVs has emerged as a method of improving biomarker detection. Prior to this study, the effect of FUS-BBBO neuroimmunotherapy on EV concentration and content remained unexplored. We investigate the concentration and content of isolated EVs from the serum of mice and Alzheimer’s Disease patients prior to and after treatment with FUS-BBBO. We illustrate a 100% increase in EV concentration one hour after treatment in both mice and patients. Furthermore, we illustrate an increase in murine EV RNA that is associated with the previously reported neuroimmunotherapeutic responses to FUS-BBBO including synaptic remodeling and neurogenesis. Finally, we illustrate an increase in AD biomarker concentration within the patient EVs three days after treatment that is proportional to the volume of blood-brain barrier opening. Overall, we establish that FUS-BBBO drug-free neuroimmunotherapy triggers complex brain macrophage modulation in a manner incomparable by other FUS neuroimmunotherapy paradigms. Furthermore, we illustrate the effect of FUS-BBBO on EV concentration and content in both preclinical and clinical experiments, indicating the role of EVs in FUS-BBBO neuroimmunotherapy and their utility as a method of improving liquid biopsy specificity. The results presented herein support the potential of FUS-BBBO as both a method of neuroimmunotherapy and a method of amplifying liquid biopsy specificity in Alzheimer’s Disease.

Focused ultrasound (FUS) can modulate activity in the central nervous system of animals, however the mechanism of action is not yet fully understood. FUS is a promising technique for clinical use in treating both physiological and psychological pathology of the nervous system. FUS can noninvasively penetrate the skull deep into the brain and modulate brain targets with millimeter-scale resolution. FUS is less invasive than deep brain stimulation (DBS) and can target deeper structures with greater resolution than transcranial magnetic stimulation (TMS). Functional ultrasound imaging (fUSI) is an emerging modality for monitoring stimulus-evoked brain activity. However, the thick skull of large animals poses a significant obstacle for the noninvasive translation of the technique to nonhuman primates and humans. In this dissertation, FUS is performed in mice and nonhuman primates and an fUSI technique is developed for transcranially imaging FUS-evoked responses in both species. The first aim of this dissertation established a procedure for performing high-resolution FUS in mice in vivo. FUS-evoked motor responses were evaluated using four-limb electromyography (EMG). A detailed quantitative analysis of several EMG characteristics demonstrated that observed motor responses exhibited brain target-specific differences. FUS in the brain was also shown to modulate cardiorespiratory activity. However, simulations conceded that intracranial reverberations may activate brain structures outside acoustic foci, suggesting that direct detection of brain activity is preferable to responses like EMG and cardiorespiratory activity. The second aim of this dissertation developed an fUSI system for monitoring FUS-evoked responses in mice in vivo. fUSI was validated using electrical peripheral nerve stimulation to elicit somatosensory-evoked responses, a well-characterized approach in established techniques like functional magnetic resonance imaging (fMRI). fUSI was later integrated into an ultrasoundbased optogenetic stimulation procedure. Lastly, a dual FUS-fUSI transducer system for performing neuromodulation and functional activity monitoring was developed and successfully demonstrated in mice in vivo. The final aim of this dissertation was to adapt the FUS-fUSI procedure developed in mice for use in nonhuman primates. Two approaches were developed and tested in vivo. The first approach employed a low-frequency ultrasound array for both neuromodulation and activity monitoring. The second approach implemented a dual FUS-fUSI transducer system similar to that used in mice. Preliminary evidence indicated that the adapted dual transducer system can successfully perform fully noninvasive neuromodulation and functional activity monitoring transcranially in nonhuman primates in vivo. The findings presented in this dissertation provide a framework for performing fully noninvasive ultrasound-mediated neuromodulation and functional activity monitoring in non human primates and describes a road map for further translating the technique for clinical use in human subjects. A fully noninvasive FUS-fUSI technique can provide an invaluable tool for clinicians to treat diseases of the nervous system not indicated for invasive procedures, opening the door to a wide range of therapeutic applications.

No description available.

No description available.

No description available.

No description available.

No description available.