Transcranial focused ultrasound, pulsed at 40 Hz, activates microglia acutely and reduces Aβ load chronically, as demonstrated in vivo
M S Bobola, Lei Chen, C.K. Ezeokeke, Theresa Olmstead, Christine T. O. Nguyen, A. Sahota, Robert George Williams, Pierre D. Mourad
Abstract
OBJECTIVE: Iaccarino et al. (2016) [1] exposed 1 h of light flickering at 40 Hz to awake 5XFAD Alzheimer's Disease (AD) mouse models, generating action potentials at 40 Hz, activating ∼54% of microglia to colocalize with Aβ plaque, acutely, and clearing ∼ 50% of Aβ plaque after seven days, but only in the visual cortex. HYPOTHESIS: Transcranially delivered, focused ultrasound (tFUS) can replicate the results of Iaccarino et al. (2016) [1] but throughout its area of application. METHODS: ). Acute studies targeted tFUS into one hemisphere of brain centered on its hippocampus for 1 h. Chronic studies targeted comparable brain in each hemisphere for 1 h/day for five days. RESULTS: Acute application of tFUS activated more microglia that colocalized with Aβ plaque relative to sham ultrasound (36.0 ± 4.6% versus 14.2 ± 2.6% [mean ± standard error], z = 2.45, p < 0.014) and relative to the contralateral hemisphere of treated brain (36.0 ± 4.6% versus 14.3 ± 4.0%, z = 2.61, p < 0.009). Chronic application over five days reduced their Aβ plaque burden by nearly half relative to paired sham animals (47.4 ± 5.8%, z = - 2.79, p < 0.005). CONCLUSION: Our results compare to those of Iaccarino et al. (2016) [1] but throughout the area of ultrasound-exposed brain. Our results also compare to those achieved by medications that target Aβ, but over a substantially shorter period of time. The proximity of our ultrasound protocol to those shown safe for non-human primates and humans may motivate its rapid translation to human studies.