Vagal fibers travel inside fascicles and form branches to innervate organs and regulate organ functions. Existing vagus nerve stimulation (VNS) therapies activate vagal fibers non-selectively, often resulting in reduced efficacy and side effects from non-targeted organs. The transverse and longitudinal arrangement of fibers inside the vagal trunk with respect to the functions they mediate and organs they innervate is unknown, however it is crucial for selective VNS. Using micro-computed tomography tracking, we found that, in swine, fascicles are arranged in 2 overlapping axes, with sensory and motor fascicles separated cephalad and merging caudad, and larynx-, heart- and lung-specific fascicles separated caudad and progressively merging cephalad. Using quantified immunohistochemistry, we found that the distribution of single fibers is highly nonuniform: myelinated afferents and efferents occupy separate fascicles, unmyelinated efferents co-localize with myelinated afferents, and small unmyelinated afferents are widely distributed. We developed a multi-contact cuff electrode that accommodates the fascicular organization of the vagal trunk and used it to deliver fascicle-selective cervical VNS in anesthetized and awake swine. Compound action potentials, from distinct fiber types, and physiological responses from different organs, including laryngeal muscle, cough, breathing, heart rate and blood pressure responses are elicited in a radially asymmetric manner, with consistent angular separations that agree with the documented fascicular organization. These results indicate that fibers in the trunk of the vagus nerve are anatomically organized according to functions they mediate and organs they innervate and can be asymmetrically activated by fascicular cervical VNS.
Afferent and efferent fibers in the vagus nerve travel inside fascicles and form branches to innervate organs and regulate organ functions. The spatial organization of fibers and fascicles, with respect to the functions they mediate and the organs they innervate, is unknown. Accordingly, it is unknown whether such organization can be leveraged by bioelectronic devices for function- and organ-specific neurostimulation. To characterize the functional microscopic anatomy of the vagus nerve, we developed a pipeline consisting of micro-computed tomography and 3D reconstruction of fascicles, and immunohistochemistry, annotation and classification of single fibers. In swine, fascicles are organized along two overlapping functional axes: one axis specific to sensory vs. motor somatic and visceral functions, with fascicle clusters increasingly separating in the cephalad direction, and a second axis specific to innervated organs, including larynx, lungs and heart, with increasing separation in the caudad direction. In the cervical vagus, myelinated afferent and efferent fibers occupy separate fascicle clusters, parasympathetic and sympathetic fibers occupy largely non-overlapping fascicles, and small unmyelinated afferents are found in most fascicles. To test whether fibers can be selectively modulated, we used multi-contact cuff electrodes to stimulate separate nerve sections. Spatially selective stimuli evoke compound action potentials from fibers of distinct functional types and elicit differential organ responses, including laryngeal muscle contraction, cough reflex, and changes in breathing, heart rate and blood pressure. Our results indicate that vagus fibers are anatomically organized according to functions they mediate and organs they innervate and can be differentially modulated by spatially selective nerve stimulation.
Huntington’s disease (HD) is one of many deteriorative brain diseases, a class of disease in which neurons progressively die. In its final stages, HD robs patients of the dignity of their humanity; denying control of basic movements necessary for communication, facial expression and personal accomplishment. A means to test for the mutation has been available since 1993, when the Huntington’s Disease Collaborative Research Group exposed the huntingtin gene and characterized the nature of the mutation process. Despite this, children of patients often avoid determining their genotype because such a diagnosis is currently merely bleak without hope of remedy, and because of legitimate fears of employment discrimination or difficulties maintaining health insurance given the legal definition of “pre-existing condition.” In the absence of promising treatments or prospects for cures the devastating loss of muscular control during the final stages of disease progression is ominous. It is therefore not uncommon for HD patients to become aware of their own disease rather late into its progression when motor symptoms begin to emerge. As these movement symptoms arise they may be effectively masked by compensatory behavioral strategies. In time, however, these compensatory tactics fail to keep up with the advancing choreic movements which eventually dominate and negate purposeful motor control.
Abstract Afferent and efferent vagal fibers mediate bidirectional communication between the brain and visceral organs. Small, unmyelinated C-afferents constitute the majority of vagal fibers, play critical roles in numerous interoceptive circuits and autonomic reflexes in health and disease and may contribute to the efficacy and safety of vagus nerve stimulation (VNS). Selective engagement of C-afferents with electrical stimuli has not been feasible, due to the default fiber recruitment order: larger fibers first, smaller fibers last. Here, we determine and optimize an electrical stimulus that selectively engages vagal C-afferents. Intermittent KHz-frequency electrical stimulation (KES) activates motor and, preferentially, sensory vagal neurons in the brainstem. During KES, asynchronous activity of C-afferents increases, while that of larger fibers remains largely unchanged. In parallel, KES effectively blocks excitability of larger fibers while moderately suppressing excitability of C-afferents. By compiling selectivity indices in individual animals, we find that optimal KES parameters for C-afferents are >5KHz frequency and 7-10 times engagement threshold (×T) intensity in rats, 15-25×T in mice. These effects can be explained in computational models by how sodium channel responses to KES are shaped by axonal size and myelin. Our results indicate that selective engagement of vagal C-afferents is attainable by intermittent KES.
ObjectivesLow-intensity, focused ultrasound (FUS) is an emerging noninvasive neuromodulation approach, with improved spatial and temporal resolution and penetration depth compared to other noninvasive electrical stimulation strategies. FUS has been used to modulate circuits in the brain and the peripheral nervous system, however, its potential to modulate spinal circuits is unclear. In this study, we assessed the effect of trans-spinal FUS (tsFUS) on spinal reflexes in healthy rats.Materials and MethodstsFUS targeting different spinal segments was delivered for 1 minute, under anesthesia. Monosynaptic H-reflex of the sciatic nerve, polysynaptic flexor reflex of the sural nerve, and withdrawal reflex tested with a hot plate were measured before, during, and after tsFUS.ResultstsFUS reversibly suppresses the H-reflex in a spinal segment-, acoustic pressure- and pulse-repetition frequency (PRF)-dependent manner. tsFUS with high PRF augments the degree of homosynaptic depression of the H-reflex observed with paired stimuli. It suppresses the windup of components of the flexor reflex associated with slower, C-afferent, but not faster, A- afferent fibers. Finally, it increases the latency of the withdrawal reflex. tsFUS does not elicit neuronal loss in the spinal cord.ConclusionsOur study provides evidence that tsFUS reversibly suppresses spinal reflexes and suggests that tsFUS could be a safe and effective strategy for spinal cord neuromodulation in disorders associated with hyperreflexia, including spasticity after spinal cord injury and painful syndromes.
To restore function after injury to the CNS, axons must be stimulated to extend into denervated territory and, critically, must form functional synapses with appropriate targets. We showed previously that forced overexpression of the transcription factor Sox11 increases axon growth by corticospinal tract (CST) neurons after spinal injury. However, behavioral outcomes were not improved, raising the question of whether the newly sprouted axons are able to form functional synapses. Here we developed an optogenetic strategy, paired with single-unit extracellular recordings, to assess the ability of Sox11-stimulated CST axons to functionally integrate in the circuitry of the cervical spinal cord. Initial time course experiments established the expression and function of virally expressed Channelrhodopsin (ChR2) in CST cell bodies and in axon terminals in cervical spinal cord. Pyramidotomies were performed in adult mice to deprive the left side of the spinal cord of CST input, and the right CST was treated with adeno-associated virus (AAV)–Sox11 or AAV–EBFP control, along with AAV–ChR2. As expected, Sox11 treatment caused robust midline crossing of CST axons into previously denervated left spinal cord. Clear postsynaptic responses resulted from optogenetic activation of CST terminals, demonstrating the ability of Sox11-stimulated axons to form functional synapses. Mapping of the distribution of CST-evoked spinal activity revealed overall similarity between intact and newly innervated spinal tissue. These data demonstrate the formation of functional synapses by Sox11-stimulated CST axons without significant behavioral benefit, suggesting that new synapses may be mistargeted or otherwise impaired in the ability to coordinate functional output. SIGNIFICANCE STATEMENT As continued progress is made in promoting the regeneration of CNS axons, questions of synaptic integration are increasingly prominent. Demonstrating direct synaptic integration by regenerated axons and distinguishing its function from indirect relay circuits and target field plasticity have presented technical challenges. Here we force the overexpression of Sox11 to stimulate the growth of corticospinal tract axons in the cervical spinal cord and then use specific optogenetic activation to assess their ability to directly drive postsynaptic activity in spinal cord neurons. By confirming successful synaptic integration, these data illustrate a novel optogenetic-based strategy to monitor and optimize functional reconnection by newly sprouted axons in the injured CNS.
Ketamine is a parenterally administered non barbiturate anaesthetic agent, in use for more than a decade. It is a safer than Na Pentothal. Administered intramuscularly, in dose of 6 to 15 mgm/Kg body wt. it produces dissociative anaesthesia. But, in smaller sub anaesthetic doses it may act as an abreactant. We report in this study the abreaction effect of Ketamine in dose of .5 to 1.5 mgm/kg body wt. given intramuscularly in 30 selected psychiatric cases requiring narcoanalysis for diagnostic or therapeutic purpose. The results are compared with another ten cases subjected to pentothal interview and five cases subjected to narcoanalysis with intravenous Na Amytal and methidrine. Our findings suggest that Ketamine has property of an efficacious abreactant in doses of 1 to 1.5 mgm/kg body wt. administered intramuscularly and can successfully be used for narcoanalysis in properly selected cases as a good substitute for intravenous pentothal or sodium amytal with methidrine. The relative cardio respiratory safety and ease of administration are its two added advantages.
