Peripheral Focused Ultrasound Neuromodulation (pFUS)

Abstract

Background A fundamental limit to the study of the peripheral nervous system and its effect on organ function is the lack of tools to selectively target and stimulate specific neurons. Traditional implant and electrode-based systems remain too large and invasive for use at the organ or sub-organ level (without stimulating or effecting neighboring organs and tissues). Recent progress in optical and genetic tools (such as optogenetics) has provided a new level of molecular specificity and selectivity to the neurons that are stimulated by bioelectronic devices. However, the modified neurons that result from use of these tools (that can be selectively activated based on expression of light, heat, or stimuli sensitive ion channels) often still require stimulation by implantable devices and face difficult scientific, technical, and regulatory hurdles for clinical translation. New method Herein, we present a new tool for selective activation of neuronal pathways using anatomical site-specific, peripheral focused ultrasound neuromodulation (pFUS). Results We utilize three experimental models to expand upon and further characterize pFUS beyond data outlined to our initial report (Cotero et al., 2019a), and further demonstrate its importance as a new investigative and translational tool. First, we utilized an interconnected microporous gel scaffold to culture isolated dorsal root ganglion (DRG) neurons in an interconnected, three-dimensional in vitro culture. (Griffin et al., 2015, Tay et al., 2018) Using this system, we directly applied ultrasound (US) stimuli and confirmed US activation of peripheral neurons at pressures consistent with recent in vivo observations. (Cotero et al., 2019a, Zachs, 2019, Gigliotti et al., 2013) Next, we tested the capability of pFUS to activate previously reported nerve pathways at multiple locations within the neural circuit, including primary sensory ganglia (i.e. inferior ganglion of the vagus nerve), peripheral ganglia (i.e. sacral ganglia), and within target end-organs. In addition, we compared selective activation of multiple anatomically overlapping neural pathways (i.e. activation of the cholinergic anti-inflammatory pathway (Tracey, 2009, Pavlov and Tracey, 2012) vs. metabolic sensory pathways (O'Hare and Zsombok, 2015, Roh et al., 2016, Pocai et al., 2005) after stimulation of each separate target site. Finally, we utilized an established model of metabolic dysfunction (the LPS-induced inflammation/hyperglycemia model) to demonstrate pFUS capability to stimulate and assess alternative therapeutic stimulation sites (i.e. liver, pancreas, and intestines) in a simple and clinically relevant manner. This is demonstrated by ultrasound induced attenuation of LPS-induced hyperglycemia by stimulation at all three anatomical targets, and mapping of the effect to a specific molecular product of excitable cell types within each stimulus site. Comparison with existing methods The ease-of-use and non-invasive nature of pFUS provides a solution to many of the challenges facing traditional toolsets, such as implantable electrodes and genetic/optogenetic nerve stimulation strategies. Conclusions The pFUS tool described herein provides a fundamental technology for the future study and manipulation of the peripheral nervous and neuroendocrine systems.

Abstract via europepmc.

Flags from extraction

• exposures[0].unspecified_domain.isppa_w_cm2 — the in vitro results text states the optimal pressure as '0.83 MPa peak positive pressure or 23 mW/cm2 burst average', which conflicts in units with the methods section's '23 W/cm2 (burst average)' for the same nominal pulse amplitude; likely a W/mW typo, flagged rather than corrected.
• exposures[1].unspecified_domain.pressure_kpa — domain (free field vs in situ) is not stated by the paper for the applied acoustic pressure/intensity; the same value (0.83 MPa, 23 W/cm2 burst average, 1.1 MHz, 2000 Hz PRF, 27% duty cycle) is stated to be used across the in vitro culture and all in vivo target sites, so it is repeated identically across all seven exposures.
• n_subjects — different sub-experiments used different group sizes (N=10 per condition for the ganglion/spleen cytokine study, N=12 per group for the hepatic/pancreatic/GI glucose study, N=6 per condition for the hormone/hypothalamic marker study); the paper never states an overall subject total, and the in vitro DRG culture experiments (N>5 per group, cultures not animals) are not included in this animal count.
• sham_type — the comparator condition throughout is an LPS-only, no-ultrasound control group rather than a device-based sham (inactive transducer, sound-only, etc.); classified as 'none'.
• exposures[2].target.terms — the sacral ganglion is not a specific child term in the target vocabulary; the parent term 'ganglion' is used.
• exposures[3].target.terms — the spleen is not present in the target vocabulary (which covers nervous system structures); classified as 'other' with target.label='spleen'.
• exposures[4].target.terms — the liver / porta hepatis is not present in the target vocabulary; classified as 'other' with target.label='liver (porta hepatis)'.
• exposures[5].target.terms — the pancreas / pancreatic tail is not present in the target vocabulary; classified as 'other' with target.label='pancreas (pancreatic tail)'.