The Peripheral Nervous System: From Molecular Mechanisms to Non-Invasive Therapeutics

• Main Author: Hoffman, Benjamin U
• Format: Dissertation
• Language: English
• Published: ProQuest Dissertations & Theses 01-01-2019
• Subjects: Neurosciences; Physiology
• ISBN: 1392017440; 9781392017449

The peripheral nervous system (PNS) is composed of a diverse array of neurons that mediate sensation. This includes sensory circuits that encode external stimuli, as well as circuits that provide information flow from our internal organs. My PhD training has focused on addressing two questions: 1) what molecular mechanisms underlie this functional diversity, and 2) can we engineer non-invasive therapeutics to modulate PNS activity? To study the molecular mechanisms of sensory function, I employed the Merkel-cell neurite complex as a model system. Merkel cells are mechanosensory epidermal cells that have long been proposed to activate neuronal afferents through chemical synaptic transmission. RNA sequencing of adult mouse Merkel cells demonstrated that they express presynaptic molecules and biosynthetic machinery for adrenergic transmission. Moreover, live-cell imaging showed that Merkel cells mediate activity- and VMAT-dependent release of fluorescent catecholamine neurotransmitter analogues. Touch-evoked firing in Merkel-cell afferents was inhibited either by silencing of SNARE-mediated vesicle fusion from Merkel cells or by neuronal deletion of β2-adrenergic receptors. Next, to develop non-invasive technologies for peripheral nerve modulation, I employed targeted focused ultrasound (FUS) stimulation and electrophysiology to record activity of individual mechanosensory neurons. Parameter space exploration showed that stimulating neuronal receptive fields with high-intensity, millisecond FUS sonication reliably and repeatedly evoked action potentials in peripheral neurons. FUS elicited action potentials with latencies comparable to electrical stimulation, demonstrating both speed and reliability of the technique. Lastly, I show that peripheral neurons can be both excited by FUS stimulation targeted to either skin receptive fields or peripheral nerve trunks, a key finding that increases the therapeutic range of FUS-based peripheral neuromodulation.