Aims/hypothesis A new class of treatments termed bioelectronic medicines are now emerging that aim to target individual nerve fibres or specific brain circuits in pathological conditions to repair lost function and reinstate a healthy balance. Carotid sinus nerve (CSN) denervation has been shown to improve glucose homeostasis in insulin-resistant and glucose-intolerant rats; however, these positive effects from surgery appear to diminish over time and are heavily caveated by the severe adverse effects associated with permanent loss of chemosensory function. Herein we characterise the ability of a novel bioelectronic application, classified as kilohertz frequency alternating current (KHFAC) modulation, to suppress neural signals within the CSN of rodents. Methods Rats were fed either a chow or high-fat/high-sucrose (HFHSu) diet (60% lipid-rich diet plus 35% sucrose drinking water) over 14 weeks. Neural interfaces were bilaterally implanted in the CSNs and attached to an external pulse generator. The rats were then randomised to KHFAC or sham modulation groups. KHFAC modulation variables were defined acutely by respiratory and cardiac responses to hypoxia (10% O 2 + 90% N 2 ). Insulin sensitivity was evaluated periodically through an ITT and glucose tolerance by an OGTT. Results KHFAC modulation of the CSN, applied over 9 weeks, restored insulin sensitivity (constant of the insulin tolerance test [K ITT ] HFHSu sham, 2.56 ± 0.41% glucose/min; K ITT HFHSu KHFAC, 5.01 ± 0.52% glucose/min) and glucose tolerance (AUC HFHSu sham, 1278 ± 20.36 mmol/l × min; AUC HFHSu KHFAC, 1054.15 ± 62.64 mmol/l × min) in rat models of type 2 diabetes. Upon cessation of KHFAC, insulin resistance and glucose intolerance returned to normal values within 5 weeks. Conclusions/interpretation KHFAC modulation of the CSN improves metabolic control in rat models of type 2 diabetes. These positive outcomes have significant translational potential as a novel therapeutic modality for the purpose of treating metabolic diseases in humans.

Hypoxia increases the release of neurotransmitters from chemoreceptor cells of the carotid body (CB) and the activity in the carotid sinus nerve (CSN) sensory fibers, elevating ventilatory drive. According to previous reports, perinatal hyperoxia causes CSN hypotrophy and varied diminishment of CB function and the hypoxic ventilatory response. The present study aimed to characterize the presumptive hyperoxic damage. Hyperoxic rats were born and reared for 28 days in 55%-60% O 2 ; subsequent growth (to 3.5-4.5 months) was in a normal atmosphere. The parenchyma of the carotid body (CB) is formed by chemoreceptor and sustentacular cells organized in clusters surrounded by a dense network of capillaries. Sensory nerve terminals of the carotid sinus nerve (CSN) penetrate the clusters to synapse with chemoreceptor cells (Verna, 1997). Functionally, chemoreceptor cells are activated by hypoxia and hypercapnia, and they respond with an increased release of neurotransmitters that activate the sensory nerve endings of the CSN and produce an increase in the action potential frequency in the CSN. Central projections of the CSN produce a ventilatory response, which facilitates homeostasis of blood O 2 and CO 2 levels. Catecholamines (CA) are the most abundant neurotransmitters present in chemoreceptor cells. Many groups have demonstrated that CA metabolism, including rate of synthesis and release, parallel the level of CB stimulation and action potential frequency in the CSN (Gonzalez et al. , 1994 and references therein). In adult mammals the CB is responsible for the entire hyperventilation evoked by hypoxia and for about 30-50% of the hyperventilation triggered by hypercapnia and acidosis (Cherniack & Altose 1997;Gonzalez et al. 2002a). In the intact animal a decrease in arterial P O 2 from 100 to about 75 mmHg produces only minor changes in the basal level of CSN activity or ventilation. At P O 2 below the apparent threshold of 75 mmHg there is an almost exponential increase in either response. CSN activity and ventilation double at about 50-55 mmHg, and increase by a factor of four near 40 mmHg. In the case of CO 2 the activity in the CSN and the ventilation mediated by the CB increase linearly with the P CO 2 , doubling every 15-20 mmHg (Gonzalez et al. 1994). In neonatal animals, the apparent threshold for the hypoxic response is set at a much lower P O 2 , in the range of 20-25 mmHg, i.e. at P O 2 comparable to that found in utero. At lower P O 2 , the hypoxic response increases with a lower slope than in adults. In response to elevated CO 2 there is a comparable hyposensitivity in newborn animals (Hanson & Kumar 1994;Donnelly, 1997). Functional maturation of the CB during postnatal life occurs in the first few weeks after birth, with some differences among species. In the rat, at four weeks of age the responses are fully developed (Eden & Hanson 1987a;Donnelly & Doyle 1994;Rigual et al. 2000;Donnelly, 1997). Maturation of CB function is greatly affected by the ambient P O 2 in the perinatal period. Thus, if animals ...

Key points• Hypoxic pulmonary vasoconstriction (HPV) is a mechanism by which pulmonary arteries maintain blood oxygenation during alveolar hypoxia.• HPV is generally studied using a vasoconstricting co-stimulus that amplifies the HPV but may also distort its properties; we therefore characterised HPV in isolated rat intrapulmonary arteries during 40 min hypoxic challenges in the absence of any such stimulus.• Immediate (phase 1) and sustained (phase 2) components of HPV were unaffected by blocking voltage-gated Ca 2+ channels but were abolished by depletion of sarcoplasmic reticulum Ca 2+ . Phase 2 was attenuated by blockade of store-operated Ca 2+ entry (SOCE), although it largely persisted in Ca 2+ -free physiological saline solution.• HPV was associated with an increase in the intrapulmonary artery ratio of oxidised to reduced glutathione and was inhibited by antioxidants.• HPV resulted primarily from intracellular Ca 2+ release, with SOCE making a contribution, particularly to phase 2. Sustained HPV involves oxidation of the pulmonary artery redox state.Abstract Hypoxic pulmonary vasoconstriction (HPV) maintains blood oxygenation during acute hypoxia but contributes to pulmonary hypertension during chronic hypoxia. The mechanisms of HPV remain controversial, in part because HPV is usually studied in the presence of agonist-induced preconstriction ('pretone'). This potentiates HPV but may obscure and distort its underlying mechanisms. We therefore carried out an extensive assessment of proposed mechanisms contributing to HPV in isolated intrapulmonary arteries (IPAs) in the absence of pretone by using a conventional small vessel myograph. Hypoxia elicited a biphasic constriction consisting of a small transient (phase 1) superimposed upon a sustained (phase 2) component. Neither phase was affected by the L-type Ca 2+ channel antagonists diltiazem (10 and 30 μM) or nifedipine (3 μM). Application of the store-operated Ca 2+ entry (SOCE) blockers BTP2 (10 μM) or SKF96365 (50 μM) attenuated phase 2 but not phase 1, whereas a lengthy (30 min) incubation in Ca 2+ -free physiological saline solution similarly reduced phase 2 but abolished phase 1. No further effect of inhibition of HPV was observed if the sarco/endoplasmic reticulum Ca 2+ -ATPase inhibitor cyclopiazonic acid (30 μM) was also applied during the 30 min incubation in Ca 2+ -free physiological saline solution. Pretreatment with 10 μM ryanodine and 15 mM caffeine abolished both phases, whereas treatment with 100 μM ryanodine attenuated both phases. The two-pore channel blocker NED-19 (1 μM) and the nicotinic acid adenine dinucleotide phosphate (NAADP) antagonist BZ194 (200 μM) had no effect on either phase of HPV. The lysosomal Ca 2+ -depleting agent concanamycin (1 μM) enhanced HPV if applied during hypoxia, but had no effect on HPV during a subsequent hypoxic challenge. The cyclic ADP ribose antagonist 8-bromo-cyclic ADP ribose (30 μM) had no effect on either phase of HPV. Neither the Ca 2+ -sensing receptor (CaSR) blocker NPS2390 (0.1 and 10 μM) nor FK...