Parks, T. V. | bioRxiv Science

bioRxiv2025

Noninvasive focal gene transfer of chemogenetic proteins in the primate brain

The development of chemogenetic neuromodulators, including Designer Receptors Exclusively Activated by Designer Drugs (DREADDs), have enabled focally specific, long-lasting, and reversible neuromodulation in the primate brain. Although systemically delivered synthetic ligands allow for noninvasive actuation of chemogenetic receptors, direct intraparenchymal injection remains atop the available methods to precisely deliver chemogenetic payloads to a specific target of the brain. The requirement of trephination, however, is accompanied by inherent risks of infection, long recovery times, and often tissue damage with concomitant behavioral complications. When considering therapeutic injections, the requirement of transcranial surgery does not translate well to the clinic, especially when repeated administrations are required. Here, we leverage our recent development of transcranial focused ultrasound (tFUS) for noninvasive and focal delivery of adeno-associated viruses (AAVs) carrying excitatory Gq-DREADDs to frontal cortical targets (areas 6DR and 8aD) in the marmoset brain. Using [18F]-fluorodeoxyglucose (FDG) positron emission tomography, we demonstrate significant increases in glucose metabolism at the site of viral delivery after administering the DREADD-specific agonist deschloroclozapine (DCZ), as compared to vehicle control. Focal neuronal DREADD expression was confirmed by immunohistochemistry at the site of opening. Through comparison of awake resting-state functional connectivity (whole brain connectivity with the sites of delivery) and structural connectivity (directly injected viral neuronal tracing at the sites of delivery) we demonstrate that the increase in glucose metabolism occurs at both mono- and polysynaptically connected brain regions. Taken together, these results demonstrate the ability to focally deliver excitatory chemogenetics without the need for surgery, allowing for activation of long-range frontal cortex circuits of the primate brain.

neuroscience↗

bioRxiv2023

Noninvasive focal transgene delivery with viral neuronal tracers in the marmoset monkey

Although preclinical neuroscientific modeling species permit invasive intracranial delivery of targeted neurotropic agents, direct intracranial injections are not readily translatable to clinical therapeutics. Transcranial focused ultrasound (tFUS) has been identified as a technique to circumvent surgical injections altogether by transiently opening the blood-brain barrier (BBB) with selective focus. We have recently characterized the ability to focally deliver substances across the BBB in the marmoset, a non-human primate model with similar husbandry requirements to rodents but with cortical topologies more similar to humans. Here, we establish a reliable method for selectively delivering adeno-associated viral vectors (AAVs) across the BBB in marmoset frontal cortex with tFUS and demonstrate long-range anterograde neuronal tracing. Using a single-element 1.46 MHz transducer, we focally perturbed the BBB ([~]1 x 2 mm) in area 8aD of frontal cortex in four adult marmoset monkeys using low-intensity focused ultrasound aided by microbubbles. We confirmed BBB opening via a gadolinium-enhanced MRI at 9.4 T prior to AAV delivery. Within an hour of opening the BBB, either AAV2 or AAV9 was delivered systemically via tail-vein injection. Four to six weeks later, animals were sacrificed, and microscopy was performed to confirm the presence of neurons transduced as indicated by EGFP or mCherry fluorescence. In all four marmosets, neurons were observed at the site of BBB perturbation, with AAV2 showing an exiguous distribution of transduced neurons when compared to AAV9. The results are compared to direct intracortical injections of anterograde tracers into area 8aD and similar (albeit sparser) long-range connectivity was observed. With evidence of transduced neurons specific to the region of BBB opening as well as long-distance tracing, we establish a framework for focal noninvasive transgene delivery to the marmoset brain. This technique will be of utility for the burgeoning marmoset model, with applications for noninvasive delivery of therapeutics, genetic delivery of precursors for techniques like two-photon imaging, or neuronal tracing across the lifespan.

neuroscience↗