Stimulation of the hepatoportal nerve plexus with focused ultrasound restores glucose homoeostasis in diabetic mice, rats and swine.

Peripheral neurons that sense glucose relay signals of glucose availability to integrative clusters of neurons in the brain. However, the roles of such signalling pathways in the maintenance of glucose homoeostasis and their contribution to disease are unknown. Here we show that the selective activation of the nerve plexus of the hepatic portal system via peripheral focused ultrasound stimulation (pFUS) improves glucose homoeostasis in mice and rats with insulin-resistant diabetes and in swine subject to hyperinsulinemic-euglycaemic clamps. pFUS modulated the activity of sensory projections to the hypothalamus, altered the concentrations of metabolism-regulating neurotransmitters, and enhanced glucose tolerance and utilization in the three species, whereas physical transection or chemical blocking of the liver-brain nerve pathway abolished the effect of pFUS on glucose tolerance. Longitudinal multi-omic profiling of metabolic tissues from the treated animals confirmed pFUS-induced modifications of key metabolic functions in liver, pancreas, muscle, adipose, kidney and intestinal tissues. Non-invasive ultrasound activation of afferent autonomic nerves may represent a non-pharmacologic therapy for the restoration of glucose homoeostasis in type-2 diabetes and other metabolic diseases.

Anodal block permits directional vagus nerve stimulation.

Vagus nerve stimulation (VNS) is a bioelectronic therapy for disorders of the brain and peripheral organs, and a tool to study the physiology of autonomic circuits. Selective activation of afferent or efferent vagal fibers can maximize efficacy and minimize off-target effects of VNS. Anodal block (ABL) has been used to achieve directional fiber activation in nerve stimulation. However, evidence for directional VNS with ABL has been scarce and inconsistent, and it is unknown whether ABL permits directional fiber activation with respect to functional effects of VNS. Through a series of vagotomies, we established physiological markers for afferent and efferent fiber activation by VNS: stimulus-elicited change in breathing rate (ΔBR) and heart rate (ΔHR), respectively. Bipolar VNS trains of both polarities elicited mixed ΔHR and ΔBR responses. Cathode cephalad polarity caused an afferent pattern of responses (relatively stronger ΔBR) whereas cathode caudad caused an efferent pattern (stronger ΔHR). Additionally, left VNS elicited a greater afferent and right VNS a greater efferent response. By analyzing stimulus-evoked compound nerve potentials, we confirmed that such polarity differences in functional responses to VNS can be explained by ABL of A- and B-fiber activation. We conclude that ABL is a mechanism that can be leveraged for directional VNS.

An impedance matching algorithm for common-mode interference removal in vagus nerve recordings.

BACKGROUND: The peripheral nervous system is involved in a multitude of physiological functions. Recording neural signals provides information that can be used by diagnostic bioelectronic medicine devices, closed-loop neuromodulation therapies and other neuroprosthetic applications. The ability to accurately record these signals is challenging, due to the presence of various biological and instrument-related interference sources. NEW METHOD: We developed a common-mode interference rejection algorithm based on an impedance matching approach for bipolar cuff electrodes. Two unipolar channels were recorded from the two electrode contacts of a bipolar cuff. The impedance mismatch was estimated and used to correct one of the two channels. RESULTS: When applied to electrocardiographic (ECG) artifacts collected from three mice using CorTec electrodes, the algorithm reduced the interference to noise ratio (INR) over simple subtraction by 12 dB on average. The algorithm also reduced the INR of stimulation artifacts in recordings from three rats collected using flexible electrodes by an additional 2.4 dB. In the same experiments evoked electromyographic (EMG) interference was suppressed by 1.3 dB. COMPARISON WITH EXISTING METHODS: Simple subtraction is the common approach for reducing common-mode interference in bipolar recordings, however impedance mismatches that exist or emerge compromise its efficiency. CONCLUSIONS: The algorithm significantly reduced the common-mode interference from ECG artifacts, stimulation artifacts, and evoked EMG interference, while retaining neural signals, in two animal models and two recording setups. This approach can be used in a variety of different neurophysiological setups to remove common-mode interference from a variety of sources.

Extraction of Evoked Compound Nerve Action Potentials from Vagus Nerve Recordings.

Cervical vagus nerve stimulation (VNS) is a neuromodulation therapy for the treatment of several chronic disorders. The effects of VNS are mediated by activation of nerve fibers of different types. In order to maximize the desired and minimize the undesired effects of VNS, assessing activation of vagal fiber types by VNS is essential. Evoked compound nerve action potentials (CNAPs) are commonly used as a method to estimate vagal fiber activation in the context of neurostimulation. However, vagal CNAPs are frequently contaminated by signals from non-neural sources, like electrocardiography (ECG), stimulus artifacts and evoked electromyographic (EMG) activity. In this study, we present a systematic methodology for suppressing non-neural signals in CNAP recordings from the rat vagus. The methodology involves intravenous infusion of vecuronium under ventilation, for suppressing EMG, and digital and analog signal processing, for suppressing ECG and stimulus artifacts, respectively. We compiled A-, B- and C-type fiber activation profiles with and without this methodology and found that our method significantly increased the reliability of CNAPs. We found that the A-component is obscured by the stimulus artifact, whereas the B- and C-components are frequently contaminated by evoked EMG. We extracted CNAPs evoked by square pulses of different polarities and amplitudes and documented effects consistent with well-established biophysical attributes of VNS.

A sphingosine-1 phosphate agonist (FTY720) limits trauma/hemorrhagic shock-induced multiple organ dysfunction syndrome.

BACKGROUND: Trauma/hemorrhagic shock (T/HS) is one of the major consequences of battlefield injury as well as civilian trauma. FTY720 (sphingosine-1-phosphate agonist) has the capability to decrease the activity of the innate and adaptive immune systems and, at the same time, maintain endothelial cell barrier function and vascular homeostasis during stress. For this reason, we hypothesize that FTY720, as part of resuscitation therapy, would limit T/HS-induced multiple organ dysfunction syndrome in a rodent T/HS model. METHODS: Rats subjected to trauma/sham shock (T/SS) or T/HS (30 mm Hg × 90 min) were administered FTY720 (1 mg/kg) post-T/HS during volume resuscitation. Lung injury (permeability to Evans blue dye), polymorphonuclear leukocyte (PMN) priming (respiratory burst activity), and red blood cell (RBC) rigidity were measured. In addition, lymph duct-cannulated rats were used to quantify the effect of FTY720 on gut injury (permeability and morphology) and the biologic activity of T/HS versus T/SS lymph on PMN-RBC and RBC deformability. RESULTS: Trauma/hemorrhagic shock-induced increased lung permeability, PMN priming, and RBC rigidity were all abrogated by FTY720. The systemic protective effect of FTY720 was only partially at the gut level, because FTY720 did not prevent T/HS-induced gut injury (morphology or permeability); however, it did abrogate T/HS lymph-induced increased respiratory burst and RBC rigidity. CONCLUSIONS: FTY720 limited T/HS-induced multiple organ dysfunction syndrome (lung injury, red cell injury, and neutrophil priming) as well as T/HS lymph bioactivity, although it did not limit gut injury.

Trauma-hemorrhagic shock induces a CD36-dependent RBC endothelial-adhesive phenotype.

OBJECTIVE: Microvascular dysfunction is a key element in the development of the multiple organ dysfunction syndrome. Although the mechanisms for this response are unclear, RBC adhesion to endothelium may initiate intravascular occlusion leading to ischemic tissue injury. Thus, we tested the hypothesis that trauma-hemorrhage induces RBC-endothelial cell adhesion. DESIGN: Prospective in vivo and in vitro animal study and analysis of patient blood samples. SETTING: University research laboratory and hospital emergency and trauma units. INTERVENTION: We initially assayed RBC adhesion to endothelial cells in vitro using RBCs obtained from rats subjected to trauma-hemorrhagic shock or sham shock as well as from severely injured trauma patients. Subsequently, we measured the role of putative RBCs and endothelial cell receptors in the increased RBC-endothelial cell adhesive response. MAIN RESULTS: In both rats and humans, trauma-hemorrhagic shock increased RBC adhesion to endothelium as well as increasing several putative RBC surface adhesion molecules including CD36. The critical factor leading to RBC-endothelial cell adhesion was increased surface RBC CD36 expression. Adhesion of trauma-hemorrhagic shock RBCs was mediated, at least in part, by the binding of RBC CD36 to its cognate endothelial receptors (αVß3 and VCAM-1). Gut-derived factors carried in the intestinal lymphatics triggered these trauma-hemorrhagic shock-induced RBC changes because 1) preventing trauma-hemorrhagic shock intestinal lymph from reaching the systemic circulation abrogated the RBC effects, 2) in vitro incubation of naïve whole blood with trauma-hemorrhagic shock lymph replicated the in vivo trauma-hemorrhagic shock-induced RBC changes while 3) injection of trauma-hemorrhagic shock lymph into naïve animals recreated the RBC changes observed after actual trauma-hemorrhagic shock. CONCLUSIONS: 1) Trauma-hemorrhagic shock induces rapid RBC adhesion to endothelial cells in patients and animals. 2) Increased RBC CD36 expression characterizes the RBC-adhesive phenotype. 3) The RBC phenotypic and functional changes were induced by gut-derived humoral factors. These novel findings may explain the microvascular dysfunction occurring after trauma-hemorrhagic shock, sepsis, and other stress states.

Early trauma-hemorrhage-induced splenic and thymic apoptosis is gut-mediated and toll-like receptor 4-dependent.

Immune depression after trauma-hemorrhage has been implicated as an important factor in the pathogenesis of sepsis and septic-organ failure. Although recent studies have implicated immune-cell apoptosis as an important factor in the evolution of this posttrauma immune-suppressed state, neither the initial triggers that induce this response nor the cellular pathways through which these triggering pathways act have been fully defined. Thus, the current study tests the hypothesis that acute splenic and thymic immune-cell apoptosis developing after trauma-hemorrhagic shock (T/HS) is due to gut-derived factors carried in intestinal lymph and that this T/HS lymph-induced immune depressed state is mediated through Toll-like receptor 4 (TLR4). The first set of experiments documented that T/HS caused both thymic and splenic immune-cell apoptosis as measured by TUNEL (terminal deoxynucleotidyl transferase dUTP nick end labeling) and caspase-3 immunohistochemistry and that this increase in apoptosis was totally abrogated by mesenteric lymph duct ligation. In subsequent experiments, mesenteric lymph collected from animals subjected to T/HS or trauma-sham shock were injected into TLR4-deficient (TLR4mut) mice or their wild-type (WT) littermates. Trauma-hemorrhagic shock, but not trauma-sham shock, lymph caused splenic apoptosis in the WT mice. However, the TLR4mut mice were resistant to T/HS lymph-induced splenic apoptosis. Furthermore, the WT, but not the TLR4mut mice developed splenic apoptosis after actual T/HS. In conclusion, gut-derived factors appear to initiate a sequence of events that leads to an acute increase in splenic and thymic immune-cell apoptosis, and this process is TLR4-dependent.