Mapping the cellular electrophysiology of rat sympathetic preganglionic neurones to their roles in cardiorespiratory reflex integration:A whole cell recording study in situ

Sympathetic preganglionic neurones (SPNs) convey sympathetic activity flowing from the CNS to the periphery to reach the target organs. Although previous in vivo and in vitro cell recording studies have explored their electrophysiological characteristics, it has not been possible to relate these characteristics to their roles in cardiorespiratory reflex integration. We used the working heart–brainstem preparation to make whole cell patch clamp recordings from T3–4 SPNs (n = 98). These SPNs were classified by their distinct responses to activation of the peripheral chemoreflex, diving response and arterial baroreflex, allowing the discrimination of muscle vasoconstrictor-like (MVC(like), 39%) from cutaneous vasoconstrictor-like (CVC(like), 28%) SPNs. The MVC(like) SPNs have higher baseline firing frequencies (2.52 ± 0.33 Hz vs. CVC(like) 1.34 ± 0.17 Hz, P = 0.007). The CVC(like) have longer after-hyperpolarisations (314 ± 36 ms vs. MVC(like) 191 ± 13 ms, P < 0.001) and lower input resistance (346 ± 49  MΩ vs. MVC(like) 496 ± 41 MΩ, P < 0.05). MVC(like) firing was respiratory-modulated with peak discharge in the late inspiratory/early expiratory phase and this activity was generated by both a tonic and respiratory-modulated barrage of synaptic events that were blocked by intrathecal kynurenate. In contrast, the activity of CVC(like) SPNs was underpinned by rhythmical membrane potential oscillations suggestive of gap junctional coupling. Thus, we have related the intrinsic electrophysiological properties of two classes of SPNs in situ to their roles in cardiorespiratory reflex integration and have shown that they deploy different cellular mechanisms that are likely to influence how they integrate and shape the distinctive sympathetic outputs

Modelling the vascular response to sympathetic postganglionic nerve activity

AbstractThis paper explores the influence of burst properties of the sympathetic nervous system on arterial contractility. Specifically, a mathematical model is constructed of the pathway from action potential generation in a sympathetic postganglionic neurone to contraction of an arterial smooth muscle cell. The differential equation model is a synthesis of models of the individual physiological processes, and is shown to be consistent with physiological data.The model is found to be unresponsive to tonic (regular) stimulation at typical frequencies recorded in sympathetic efferents. However, when stimulated at the same average frequency, but with repetitive respiratory-modulated burst patterns, it produces marked contractions. Moreover, the contractile force produced is found to be highly dependent on the number of spikes in each burst. In particular, when the model is driven by preganglionic spike trains recorded from wild-type and spontaneously hypertensive rats (which have increased spiking during each burst) the contractile force was found to be 10-fold greater in the hypertensive case. An explanation is provided in terms of the summative increased release of noradrenaline. Furthermore, the results suggest the marked effect that hypertensive spike trains had on smooth muscle cell tone can provide a significant contribution to the pathology of hypertension

Increased intrinsic excitability of muscle vasoconstrictor preganglionic neurons may contribute to the elevated sympathetic activity in hypertensive rats

Hypertension is associated with pathologically increased sympathetic drive to the vasculature. This has been attributed to increased excitatory drive to sympathetic preganglionic neurons (SPN) from brainstem cardiovascular control centers. However, there is also evidence supporting increased intrinsic excitability of SPN. To test this hypothesis, we made whole cell recordings of muscle vasoconstrictor-like (MVC(like)) SPN in the working-heart brainstem preparation of spontaneously hypertensive (SH) and normotensive Wistar-Kyoto (WKY) rats. The MVC(like) SPN have a higher spontaneous firing frequency in the SH rat (3.85 ± 0.4 vs. 2.44 ± 0.4 Hz in WKY; P = 0.011) with greater respiratory modulation of their activity. The action potentials of SH SPN had smaller, shorter afterhyperpolarizations (AHPs) and showed diminished transient rectification indicating suppression of an A-type potassium conductance (I(A)). We developed mathematical models of the SPN to establish if changes in their intrinsic properties in SH rats could account for their altered firing. Reduction of the maximal conductance density of I(A) by 15–30% changed the excitability and output of the model from the WKY to a SH profile, with increased firing frequency, amplified respiratory modulation, and smaller AHPs. This change in output is predominantly a consequence of altered synaptic integration. Consistent with these in silico predictions, we found that intrathecal 4-aminopyridine (4-AP) increased sympathetic nerve activity, elevated perfusion pressure, and augmented Traube-Hering waves. Our findings indicate that I(A) acts as a powerful filter on incoming synaptic drive to SPN and that its diminution in the SH rat is potentially sufficient to account for the increased sympathetic output underlying hypertension

Reduced somatostatin signalling leads to hypersecretion of glucagon in mice fed a high-fat diet

Objectives:&nbsp;Elevated plasma glucagon is an early symptom of diabetes, occurring in subjects with impaired glucose regulation. Here, we explored alpha-cell function in female mice fed a high-fat diet (HFD)&mdash;a widely used mouse model of prediabetes. Methods:&nbsp;We fed female mice expressing the Ca2+&nbsp;indicator GCaMP3 specifically in alpha-cells an HFD or control (CTL) diet. We then conducted&nbsp;in&nbsp;vivo&nbsp;phenotyping of these mice, as well as experiments on isolated (ex&nbsp;vivo) islets and in the&nbsp;in situ&nbsp;perfused pancreas. Results:&nbsp;In&nbsp;vivo,&nbsp;HFD-fed mice exhibited increased fed plasma glucagon levels and a reduced response to elevations in plasma glucose. Glucagon secretion from isolated islets and in the perfused mouse pancreas was elevated under both hypo- and hyperglycaemic conditions. In mice fed a CTL diet, increasing glucose reduced intracellular Ca2+&nbsp;([Ca2+]i) (oscillation frequency and amplitude). This effect was also observed in HFD mice; however, both the frequency and amplitude of the [Ca2+]i&nbsp;oscillations were higher than those in CTL alpha-cells. Given that alpha-cells are under strong paracrine control from neighbouring somatostatin-secreting delta-cells, we hypothesised that this elevation of alpha-cell output was due to a lack of somatostatin (SST) secretion. Indeed, SST secretion in isolated islets from HFD mice was reduced but exogenous SST also failed to suppress glucagon secretion and [Ca2+]i&nbsp;activity from HFD alpha-cells, in contrast to observations in CTL mice. Conclusions:&nbsp;These findings suggest that reduced delta-cell function, combined with intrinsic changes in alpha-cell sensitivity to somatostatin, accounts for the hyperglucagonaemia in mice fed an HFD.</p

Vitamin-D-Binding Protein Contributes to the Maintenance of α Cell Function and Glucagon Secretion

Vitamin-D-binding protein (DBP) or group-specific component of serum (GC-globulin) carries vitamin D metabolites from the circulation to target tissues. DBP is highly localized to the liver and pancreatic α cells. Although DBP serum levels, gene polymorphisms, and autoantigens have all been associated with diabetes risk, the underlying mechanisms remain unknown. Here, we show that DBP regulates α cell morphology, α cell function, and glucagon secretion. Deletion of DBP leads to smaller and hyperplastic α cells, altered Na+ channel conductance, impaired α cell activation by low glucose, and reduced rates of glucagon secretion both in vivo and in vitro. Mechanistically, this involves reversible changes in islet microfilament abundance and density, as well as changes in glucagon granule distribution. Defects are also seen in β cell and δ cell function. Immunostaining of human pancreata reveals generalized loss of DBP expression as a feature of late-onset and long-standing, but not early-onset, type 1 diabetes. Thus, DBP regulates α cell phenotype, with implications for diabetes pathogenesis.This article is freely available via Open Access. Click on the Publisher URL to access it via the publisher's site.D.J.H. was supported by MRC ( MR/N00275X/1 and MR/S025618/1 ) and Diabetes UK ( 17/0005681 ) project grants. This project has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (Starting Grant 715884 to D.J.H.). L.J.B.B. was supported by a Sir Henry Wellcome Postdoctoral Fellowship ( Wellcome Trust ; 201325/Z/16/Z ) and a Junior Research Fellowship from Trinity College, Oxford . P.E.M. was funded by a foundation grant from the Canadian Institutes of Health Research (grant 148451 ). G.G.L. was supported by a Wellcome Trust Senior Research Fellowship ( 104612/Z/14/Z ). N.G.M. and S.J.R. were supported by Diabetes UK ( 15/0005156 and 16/0005480 ), MRC ( MR/P010695/1 ), and JDRF ( 2-SRA-2018-474-S-B ) project grants. We thank Dr. Deirdre Kavanagh and COMPARE for microscopy assistance. Human pancreas sections were provided by the Alberta Diabetes Institute IsletCore at the University of Alberta in Edmonton, with the assistance of the Human Organ Procurement and Exchange (HOPE) program, Trillium Gift of Life Network (TGLN), and other Canadian organ procurement organizations.published version, accepted version, submitted versio

Wellbeing, alcohol use and sexual activity in young teenagers: Findings from a cross-sectional survey in school children in North West England

BACKGROUND: Adolescent health is a growing concern. High rates of binge drinking and teenage pregnancies, documented in the UK, are two measures defining poor wellbeing. Improving wellbeing through schools is a priority but information on the impact of wellbeing on alcohol use, and on sexual activity among schoolchildren is limited. METHODS: A cross-sectional survey using self-completed questionnaires was conducted among 3,641 schoolchildren aged 11-14 years due to participate in a sex and relationships education pilot programme in 15 high schools in North West England. Bivariate and multivariate analyses were conducted to examine the relationship between wellbeing and alcohol use, and wellbeing and sexual activity. RESULTS: A third of 11 year olds, rising to two-thirds of 14 year olds, had drunk alcohol. Children with positive school wellbeing had lower odds of ever drinking alcohol, drinking often, engaging in any sexual activity, and of having sex. General wellbeing had a smaller effect. The strength of the association between alcohol use and the prevalence of sexual activity in 13-14 year olds, increased incrementally with the higher frequency of alcohol use. Children drinking once a week or more had 12-fold higher odds of any sexual activity, and 10-fold higher odds of having sex. Rare and occasional drinkers had a significantly higher odds compared with non-drinkers. CONCLUSIONS: The relationship between wellbeing and alcohol use, and wellbeing and sexual activity reinforces the importance of initiatives that enhance positive wellbeing in schoolchildren. The association between alcohol use and sexual activity highlights the need for integrated public health programmes. Policies restricting alcohol use may help reduce sexual exposure among young teenagers