Amanda Buch

Long-Term Safety of Repeated Blood-Brain Barrier Opening via Focused Ultrasound with Microbubbles in Non-Human Primates Performing a Cognitive Task

Focused Ultrasound (FUS) coupled with intravenous administration of microbubbles (MB) is a non-invasive technique that has been shown to reliably open (increase the permeability of) the blood-brain barrier (BBB) in multiple in vivo models including non-human primates (NHP). This procedure has shown promise for clinical and basic science applications, yet the safety and potential neurological effects of long term application in NHP requires further investigation under parameters shown to be efficacious in that species (500kHz, 200–400 kPa, 4–5μm MB, 2 minute sonication). In this study, we repeatedly opened the BBB in the caudate and putamen regions of the basal ganglia of 4 NHP using FUS with systemically-administered MB over 4–20 months. We assessed the safety of the FUS with MB procedure using MRI to detect edema or hemorrhaging in the brain. Contrast enhanced T1-weighted MRI sequences showed a 98% success rate for openings in the targeted regions. T2-weighted and SWI sequences indicated a lack edema in the majority of the cases. We investigated potential neurological effects of the FUS with MB procedure through quantitative cognitive testing of’ visual, cognitive, motivational, and motor function using a random dot motion task with reward magnitude bias presented on a touchpanel display. Reaction times during the task significantly increased on the day of the FUS with MB procedure. This increase returned to baseline within 4–5 days after the procedure. Visual motion discrimination thresholds were unaffected. Our results indicate FUS with MB can be a safe method for repeated opening of the BBB at the basal ganglia in NHP for up to 20 months without any long-term negative physiological or neurological effects with the parameters used.

Blood-Brain Barrier Opening in Behaving Non-Human Primates via Focused Ultrasound with Systemically Administered Microbubbles

Over the past fifteen years, focused ultrasound coupled with intravenously administered microbubbles (FUS) has been proven an effective, non-invasive technique to open the blood-brain barrier (BBB) in vivo. Here we show that FUS can safely and effectively open the BBB at the basal ganglia and thalamus in alert non-human primates (NHP) while they perform a behavioral task. The BBB was successfully opened in 89% of cases at the targeted brain regions of alert NHP with an average volume of opening 28% larger than prior anesthetized FUS procedures. Safety (lack of edema or microhemorrhage) of FUS was also improved during alert compared to anesthetized procedures. No physiological effects (change in heart rate, motor evoked potentials) were observed during any of the procedures. Furthermore, the application of FUS did not disrupt reaching behavior, but in fact improved performance by decreasing reaction times by 23 ms, and significantly decreasing touch error by 0.76 mm on average.

Characterizing Focused-Ultrasound Mediated Drug Delivery to the Heterogeneous Primate Brain In Vivo with Acoustic Monitoring

Focused ultrasound with microbubbles has been used to noninvasively and selectively deliver pharmacological agents across the blood-brain barrier (BBB) for treating brain diseases. Acoustic cavitation monitoring could serve as an on-line tool to assess and control the treatment. While it demonstrated a strong correlation in small animals, its translation to primates remains in question due to the anatomically different and highly heterogeneous brain structures with gray and white matteras well as dense vasculature. In addition, the drug delivery efficiency and the BBB opening volume have never been shown to be predictable through cavitation monitoring in primates. This study aimed at determining how cavitation activity is correlated with the amount and concentration of gadolinium delivered through the BBB and its associated delivery efficiency as well as the BBB opening volume in non-human primates. Another important finding entails the effect of heterogeneous brain anatomy and vasculature of a primate brain, i.e., presence of large cerebral vessels, gray and white matter that will also affect the cavitation activity associated with variation of BBB opening in different tissue types, which is not typically observed in small animals. Both these new findings are critical in the primate brain and provide essential information for clinical applications.

Non-invasive, Focused Ultrasound-Facilitated Gene Delivery for Optogenetics

Optogenetics, a widely used technique in neuroscience research, is often limited by its invasive nature of application. Here, we present a noninvasive, ultrasound-based technique to introduce optogenetic channels into the brain by temporarily opening the blood-brain barrier (BBB). We demonstrate the efficiency of the method developed and evaluate the bioactivity of the non-invasively introduced channelrhodopsin channels by performing stimulation in freely behaving mice.

Pharmacokinetic analysis and drug delivery efficiency of the focused ultrasound-induced blood-brain barrier opening in non-human primates

PURPOSE Focused Ultrasound (FUS) in conjunction with systemically administered microbubbles has been shown to open the Blood-Brain Barrier (BBB) locally, non-invasively and reversibly in rodents and non-human primates (NHP), suggesting the immense potential of this technique. The objective of this study entailed the investigation of the physiologic changes in the brain following the FUS-induced BBB opening and their relationship with the underlying anatomy. MATERIALS AND METHODS Pharmacokinetic analysis was implemented in NHPs that received FUS at various acoustic pressures. Relaxivity mapping enabled the robust quantitative detection of the BBB opening as well as grey and white matter segmentation. Drug delivery efficiency was measured for pre-clinical validation of the technique. RESULTS Based on our results, the opening volume and the amount of the gadolinium delivered were found mostly contained in the grey matter, while FUS-induced permeability and drug concentration varied depending upon the underlying brain inhomogeneity, and increased with the acoustic pressure. CONCLUSIONS Overall, apart from the in vivo protocols for BBB analysis developed here, this study also suggests the important role that FUS can have in efficient drug delivery via localized and transient BBB opening.

Toward a Cognitive Neural Prosthesis Using Focused Ultrasound

Non-invasive brain stimulation using focused ultrasound has many potential applications as a research and clinical tool, including its incorporation as either an extracorporeal or implantable neural prosthetic. To this end, we investigated the effect of focused ultrasound (FUS) combined with systemically administered microbubbles on visual-motor decision-making behavior in monkeys. We applied FUS to the putamen in one hemisphere to open the blood-brain barrier (BBB), and then tested behavioral performance 3–4 h later. On days when the monkeys were treated with FUS, their decisions were faster and more accurate than days without sonication. The performance improvement suggested both a shift in the decision criterion and an enhancement of the use of sensory evidence in the decision process. FUS also interacted with the effect of a low dose of haloperidol. The findings indicate that a two-minute application of FUS can have a sustained impact on performance of complex cognitive tasks, and may increase the efficacy of psychoactive medications. The results lend further support to the idea that the dorsal striatum plays an integral role in evidence- and reward-based decision-making, and provide motivation for incorporating FUS into cognitive neural prosthetic devices.

Behavioral effects of targeted drug delivery via non-invasive microbubble enhanced focused ultrasound blood brain barrier opening in non-human primates

The Blood Brain Barrier (BBB) in Non-Human Primates (NHP) can be non-invasively opened through the use of Focused Ultrasound (FUS) in conjunction with microbubbles. This procedure allows for a targeted, transient opening in the BBB of the NHP which can be utilized to facilitate drug delivery. While FUS has been used to deliver various pharmacological compounds to promote neurogenesis or treat cancer, no group has investigated if drug delivery can affect behavioral responses. In this study, we show the effects of targeted ME-FUS drug delivery on the responses of NHP to a decision making task.

Pharmacodynamic analysis and concentration mapping for efficient delivery through the FUS-induced BBB opening in non-human primates in vivo

FUS in conjunction with systemically administered microbubbles has been previously shown to open the Blood-Brain Barrier (BBB) locally, non-invasively and reversibly in non-human primates. However, a trans-BBB pharmacodynamic analysis has not been performed as of yet. The objective of this study was to perform such an analysis, i.e. permeability, relaxivity and gadolinium concentration mapping, of the NHP brain in vivo in order to further investigate the effect of FUS, and its dependence on the acoustic parameters used for safe and efficient drug-delivery as well as the gray vs. white matter occurrence.

Monitoring of focused ultrasound-induced blood-brain barrier opening in non-human primates using transcranial cavitation detection in vivo and the primate skull effect

Focused ultrasound (FUS) with microbubbles (MB) is promising for assisting the delivery of drugs across the blood-brain barrier (BBB). To assess the safety and efficacy, the monitoring using passive cavitation detection (PCD) is critical and yet the reliability of transcranial detection in large animals remained questioned. To study the primate skull effect, the PCD through the in-vitro monkey and human skulls and in the in vivo monkeys during the sonication (FUS frequency: 500 kHz) were investigated, with the use of in-house made lipid-shelled, monodisperse MB (median diameter: 4-5 μm) and a flatband hydrophone served as a passive cavitation detector. In the in vitro experiments, the MB were injected to the channel of the phantom under a degassed skull for sonication (peak negative pressure/PNP: 50-450 kPa, pulse length/PL: 0.2 ms, PRF: 10 Hz, duration: 2 s). A diagnostic B-mode imaging system was also used to monitor the cavitation. In the in vivo study, the PCD was realtime monitored during the sonication for PCD calibration (PNP: 50-700 kPa, PL: 0.2 ms and 10 ms, PRF: 2 Hz, duration: 10 s) and BBB opening (PNP: 200-600 kPa, PL: 10 ms, PRF: 2 Hz, duration: 2 min). The stable cavitation dose using harmonics (SCDh) and ultraharmonics (SCDu) and the inertial cavitation dose (ICD) were quantified. Results showed that the SCDh, SCDu, and ICD were detectable in vitro at 50 kPa and above, and the B-mode imaging showed bubble collapse at 200 kPa and above. The detection thresholds increased with the skulls in place, with the signal reduction of 15.4 dB for the monkey skull and 34.1 dB for the human skull. In the in vivo experiments, the SCDh and ICD was detectable at and above 100 kPa and 250 kPa, respectively, and the SCDu was less reliable due to spontaneous occurrence. The BBB was found to be disrupted in 250-600 kPa without edema, hemorrhage, and physiological changes were found. In conclusion, the SCDh was more detectable and reliable than the SCDu in assessing stable cavitation in vivo, and the inertial cavitation was detected at 250 kPa and may occur at lower pressures.

Focused ultrasound enhances sensorimotor decision-making in monkeys

Noninvasive brain stimulation using focused ultrasound has many potential applications as a research and clinical tool. Here, we investigated the effect of focused ultrasound (FUS) combined with systemically administered microbubbles on visual-motor decision-making behavior in monkeys. We applied FUS to the putamen in one hemisphere to open the blood-brain barrier, and then tested behavioral performance 3-4 hours later. On days when the monkeys were treated with FUS, their decisions were faster and more accurate than days without sonication. The performance improvement suggested both a shift in the decision criterion and an enhancement of the use of sensory evidence in the decision process. FUS also interacted with the effect of a low dose of haloperidol. The results suggest that a two-minute application of FUS can have a sustained impact on performance of complex cognitive tasks, and may increase the efficacy of psychoactive medications. The results lend further support to the idea that the dorsal striatum plays an integral role in evidence- and reward-based decision-making.