Non-invasive disruption of the blood-brain barrier in the marmoset monkey

The common marmoset monkey (Callithrix jacchus) is a species of rising prominence in the neurosciences due to their small size, ease of handling, fast breeding, and their shared functional and structural brain characteristics with Old World primates. With increasing attention on modeling human brain diseases in marmosets, understanding how to deliver therapeutic or neurotropic agents to the marmoset brain non-invasively is of great preclinical importance. In other species, including humans, transcranial focused ultrasound (tFUS) aided by intravenously injected microbubbles has proven to be a transient, reliable, and safe method for disrupting the blood-brain barrier (BBB), allowing for the focal passage of therapeutic agents that do not otherwise readily traverse the tight endothelial junctions of the BBB. The critical gap that we address here is to document parameters to disrupt the BBB reliably and safely in marmosets using tFUS. By integrating our marmoset brain atlases and the use of a marmoset-specific stereotactic targeting system, we conducted a series of systematic transcranial sonication experiments in nine marmosets. We demonstrate the effects of center frequency, acoustic pressure, burst period and duration, establish a minimum microbubble dose, estimate microbubble clearance time, and estimate the duration that the BBB remained open to passage. Successful BBB disruption was reported in vivo with MRI-based contrast agents, as well as Evans blue staining assessed ex vivo. Histology (Hematoxylin and Eosin staining) and immunohistochemistry indicated that the BBB can be safely and reliably opened with the parameters derived from these experiments.