The Journal of physiology
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Dynamic cerebral autoregulation (CA) is expressed by the temporal pattern of cerebral blood flow (CBF) recovery following a sudden change in arterial blood pressure (BP). Transfer function analysis of BP as input and CBF velocity as output can express dynamic CA through its amplitude (or gain) and phase frequency responses. The upper frequency limit (FupLim ) at which dynamic CA can operate is of considerable physiological interest and can also provide additional information about worsening CA due to disease processes. In healthy subjects FupLim was strongly dependent on arterial P C O 2 changes induced by four different breathing manoeuvres. The considerable intersubject variability in FupLim suggests that fixed frequency bands should not be adopted for averaging values of gain and phase in studies of dynamic CA. ⋯ Dynamic cerebral autoregulation (CA) can be expressed in the frequency domain by the amplitude and phase frequency responses calculated by transfer function analysis of arterial blood pressure (BP) and cerebral blood flow velocity (CBFV). We studied the effects of arterial P C O 2 ( P aC O 2 ) on the upper frequency limit (FupLim ) of these responses and its intersubject variability. Twenty-four healthy subjects (11 female, age 36.0 ± 13.4 years) were recruited. Recordings of CBFV (transcranial Doppler ultrasound), BP (Finometer) and end-tidal CO2 ( P ETC O 2 , capnography) were performed during 5 min at rest (normocapnia) and during four breathing manoeuvres: 5% and 8% CO2 in air and hyperventilation targeting reductions of 5 and 10 mmHg compared to normocapnia. FupLim was determined by the break point of the autoregulation index (ARI) curve as a function of frequency when the phase response was gradually set to zero. The five breathing conditions led to highly significant differences in P ETC O 2 (p < 0.0001), CBFV (P < 0.0001), ARI (p < 0.0001) and FupLim (p < 0.0001). FupLim ranged from 0.167 ± 0.036 Hz at the lowest values of hypocapnia (28.1 ± 1.9 mmHg) to 0.094 ± 0.040 Hz at the highest level of hypercapnia (41.7 ± 5.4 mmHg), showing a correlation of r = -0.53 (p < 0.001) with P ETC O 2 . These findings reinforce the key role of P aC O 2 in CBF regulation. The considerable intersubject variability of FupLim suggests that fixed frequency bands should not be adopted for averaging values of gain and phase in dynamic CA studies, and that the higher frequency band (0.20-0.40 Hz), in particular, does not contain relevant information about dynamic CA. Further investigations are needed to assess the information value of FupLim as a marker of dynamic CA efficiency in physiological and clinical studies.
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The Journal of physiology · Dec 2019
Xenon modulates synaptic transmission to rat hippocampal CA3 neurons at both pre- and postsynaptic sites.
Xenon (Xe) non-competitively inhibited whole-cell excitatory glutamatergic current (IGlu ) and whole-cell currents gated by ionotropic glutamate receptors (IAMPA , IKA , INMDA ), but had no effect on inhibitory GABAergic whole-cell current (IGABA ). Xe decreased only the frequency of glutamatergic spontaneous and miniature excitatory postsynaptic currents and GABAergic spontaneous inhibitory postsynaptic currents without changing the amplitude or decay times of these synaptic responses. Xe decreased the amplitude of both the action potential-evoked excitatory and the action potential-evoked inhibitory postsynaptic currents (eEPSCs and eIPSCs, respectively) via a presynaptic inhibition in transmitter release. We conclude that the main site of action of Xe is presynaptic in both excitatory and inhibitory synapses, and that the Xe inhibition is much greater for eEPSCs than for eIPSCs. ⋯ To clarify how xenon (Xe) modulates excitatory and inhibitory whole-cell and synaptic responses, we conducted an electrophysiological experiment using the 'synapse bouton preparation' dissociated mechanically from the rat hippocampal CA3 region. This technique can evaluate pure single- or multi-synapse responses and enabled us to accurately quantify how Xe influences pre- and postsynaptic aspects of synaptic transmission. Xe inhibited whole-cell glutamatergic current (IGlu ) and whole-cell currents gated by the three subtypes of glutamate receptor (IAMPA , IKA and INMDA ). Inhibition of these ionotropic currents occurred in a concentration-dependent, non-competitive and voltage-independent manner. Xe markedly depressed the slow steady current component of IAMPA almost without altering the fast phasic IAMPA component non-desensitized by cyclothiazide. It decreased current frequency without affecting the amplitude and current kinetics of glutamatergic spontaneous excitatory postsynaptic currents and miniature excitatory postsynaptic currents. It decreased the amplitude, increasing the failure rate (Rf) and paired-pulse rate (PPR) without altering the current kinetics of glutamatergic action potential-evoked excitatory postsynaptic currents. Thus, Xe has a clear presynaptic effect on excitatory synaptic transmission. Xe did not alter the GABA-induced whole-cell current (IGABA ). It decreased the frequency of GABAergic spontaneous inhibitory postsynaptic currents without changing the amplitude and current kinetics. It decreased the amplitude and increased the PPR and Rf of the GABAergic action potential-evoked inhibitory postsynaptic currents without altering the current kinetics. Thus, Xe acts exclusively at presynaptic sites at the GABAergic synapse. In conclusion, our data indicate that a presynaptic decrease of excitatory transmission is likely to be the major mechanism by which Xe induces anaesthesia, with little contribution of effects on GABAergic synapses.
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The Journal of physiology · Sep 2019
Cardiac remodelling in a swine model of chronic thromboembolic pulmonary hypertension: comparison of right vs. left ventricle.
Right ventricle (RV) function is the most important determinant of survival and quality of life in patients with chronic thromboembolic pulmonary hypertension (CTEPH). The changes in right and left ventricle gene expression that contribute to ventricular remodelling are incompletely investigated. RV remodelling in our CTEPH swine model is associated with increased expression of the genes involved in inflammation (TGFβ), oxidative stress (ROCK2, NOX1 and NOX4), and apoptosis (BCL2 and caspase-3). Alterations in ROCK2 expression correlated inversely with RV contractile reserve during exercise. Since ROCK2 has been shown to be involved in hypertrophy, oxidative stress, fibrosis and endothelial dysfunction, ROCK2 inhibition may present a viable therapeutic target in CTEPH. ⋯ Right ventricle (RV) function is the most important determinant of survival and quality of life in patients with chronic thromboembolic pulmonary hypertension (CTEPH). The present study investigated whether the increased cardiac afterload is associated with (i) cardiac remodelling and hypertrophic signalling; (ii) changes in angiogenic factors and capillary density; and (iii) inflammatory changes associated with oxidative stress and interstitial fibrosis. CTEPH was induced in eight chronically instrumented swine by chronic nitric oxide synthase inhibition and up to five weekly pulmonary embolizations. Nine healthy swine served as a control. After 9 weeks, RV function was assessed by single beat analysis of RV-pulmonary artery (PA) coupling at rest and during exercise, as well as by cardiac magnetic resonance imaging. Subsequently, the heart was excised and RV and left ventricle (LV) tissues were processed for molecular and histological analyses. Swine with CTEPH exhibited significant RV hypertrophy in response to the elevated PA pressure. RV-PA coupling was significantly reduced, correlated inversely with pulmonary vascular resistance and did not increase during exercise in CTEPH swine. Expression of genes associated with hypertrophy (BNP), inflammation (TGFβ), oxidative stress (ROCK2, NOX1 and NOX4), apoptosis (BCL2 and caspase-3) and angiogenesis (VEGFA) were increased in the RV of CTEPH swine and correlated inversely with RV-PA coupling during exercise. In the LV, only significant changes in ROCK2 gene-expression occurred. In conclusion, RV remodelling in our CTEPH swine model is associated with increased expression of genes involved in inflammation and oxidative stress, suggesting that these processes contribute to RV remodelling and dysfunction in CTEPH and hence represent potential therapeutic targets.
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The Journal of physiology · Aug 2019
Hyperandrogenism and insulin resistance-induced fetal loss: evidence for placental mitochondrial abnormalities and elevated reactive oxygen species production in pregnant rats that mimic the clinical features of polycystic ovary syndrome.
Women with polycystic ovary syndrome (PCOS) commonly suffer from miscarriage, but the underlying mechanisms remain unknown. Herein, pregnant rats chronically treated with 5α-dihydrotestosterone (DHT) and insulin exhibited hyperandrogenism and insulin resistance, as well as increased fetal loss, and these features are strikingly similar to those observed in pregnant PCOS patients. Fetal loss in our DHT+insulin-treated pregnant rats was associated with mitochondrial dysfunction, disturbed superoxide dismutase 1 and Keap1/Nrf2 antioxidant responses, over-production of reactive oxygen species (ROS) and impaired formation of the placenta. Chronic treatment of pregnant rats with DHT or insulin alone indicated that DHT triggered many of the molecular pathways leading to placental abnormalities and fetal loss, whereas insulin often exerted distinct effects on placental gene expression compared to co-treatment with DHT and insulin. Treatment of DHT+insulin-treated pregnant rats with the antioxidant N-acetylcysteine improved fetal survival but was deleterious in normal pregnant rats. Our results provide insight into the fetal loss associated with hyperandrogenism and insulin resistance in women and suggest that physiological levels of ROS are required for normal placental formation and fetal survival during pregnancy. ⋯ Women with polycystic ovary syndrome (PCOS) commonly suffer from miscarriage, but the underlying mechanism of PCOS-induced fetal loss during pregnancy remains obscure and specific therapies are lacking. We used pregnant rats treated with 5α-dihydrotestosterone (DHT) and insulin to investigate the impact of hyperandrogenism and insulin resistance on fetal survival and to determine the molecular link between PCOS conditions and placental dysfunction during pregnancy. Our study shows that pregnant rats chronically treated with a combination of DHT and insulin exhibited endocrine aberrations such as hyperandrogenism and insulin resistance that are strikingly similar to those in pregnant PCOS patients. Of pathophysiological significance, DHT+insulin-treated pregnant rats had greater fetal loss and subsequently decreased litter sizes compared to normal pregnant rats. This negative effect was accompanied by impaired trophoblast differentiation, increased glycogen accumulation, and decreased angiogenesis in the placenta. Mechanistically, we report that over-production of reactive oxygen species (ROS) in the placenta, mitochondrial dysfunction, and disturbed superoxide dismutase 1 (SOD1) and Keap1/Nrf2 antioxidant responses constitute important contributors to fetal loss in DHT+insulin-treated pregnant rats. Many of the molecular pathways leading to placental abnormalities and fetal loss in DHT+insulin treatment were also seen in pregnant rats treated with DHT alone, whereas pregnant rats treated with insulin alone often exerted distinct effects on placental gene expression compared to insulin treatment in combination with DHT. We also found that treatment with the antioxidant N-acetylcysteine (NAC) improved fetal survival in DHT+insulin-treated pregnant rats, an effect related to changes in Keap1/Nrf2 and nuclear factor-κB signalling. However, NAC administration resulted in fetal loss in normal pregnant rats, most likely due to PCOS-like endocrine abnormality induced by the treatment. Our results suggest that the deleterious effects of hyperandrogenism and insulin resistance on fetal survival are related to a constellation of mitochondria-ROS-SOD1/Nrf2 changes in the placenta. Our findings also suggest that physiological levels of ROS are required for normal placental formation and fetal survival during pregnancy.
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The Journal of physiology · Aug 2019
Observational StudyCore temperature after birth in babies with neonatal encephalopathy in a sub-Saharan African hospital setting.
Therapeutic hypothermia (HT) to 33.0-34.0°C for 72 h provides optimal therapy for infants with neonatal encephalopathy (NE) in high-resource settings. HT is not universally implemented in low- and middle-income countries as a result of both limited resources and evidence. Facilitated passive cooling, comprising infants being allowed to passively lower their body temperature in the days after birth, is an emerging practice in some West African neonatal units. In this observational study, we demonstrate that infants undergoing facilitated passive cooling in a neonatal unit in Accra, Ghana, achieve temperatures within the HT target range ∼20% of the 72 h. Depth of HT fluctuates and can be excessive, as well as not maintained, especially after 24 h. Sustained and deeper passive cooling was evident for severe NE and for those that died. It is important to prevent excessive cooling, to understand that severe NE babies cool more and to be aware of facilitated passive cooling with respect to the design of clinical trials in low- and mid-resource settings. ⋯ Neonatal encephalopathy (NE) is a significant worldwide problem with the greatest burden in sub-Saharan Africa. Therapeutic hypothermia (HT), comprising the standard of care for infants with moderate-to-severe NE in settings with sophisticated intensive care, is not available to infants in many sub-Saharan African countries, including Ghana. We prospectively assessed the temperature response in relation to outcome in the 80 h after birth in a cohort of babies with NE undergoing 'facilitated passive cooling' at Korle Bu Teaching Hospital, Accra, Ghana. We hypothesized that NE infants demonstrate passive cooling. Thirteen infants (69% male) ≥36 weeks with moderate-to-severe NE were enrolled. Ambient mean ± SD temperature was 28.3 ± 0.7°C. Infant core temperature was 34.2 ± 1.2°C over the first 24 h and 35.0 ± 1.0°C over 80 h. Nadir mean temperature occurred at 15 h. Temperatures were within target range for HT with respect to 18 ± 14% of measurements within the first 72 h. Axillary temperature was 0.5 ± 0.2°C below core. Three infants died before discharge. Core temperature over 80 h for surviving infants was 35.3 ± 0.9°C and 33.96 ± 0.7°C for those that died (P = 0.043). Temperature profile negatively correlated with Thompson NE score on day 4 (r2 = 0.66): infants with a Thompson score of 0-6 had higher temperatures than those with a score of 7-15 (P = 0.021) and a score of 16+/deceased (P = 0.007). More severe NE was associated with lower core temperatures. Passive cooling is a physiological response after hypoxia-ischaemia; however, the potential neuroprotective effect of facilitated passive cooling is unknown. An awareness of facilitated passive cooling in babies with NE is important for the design of clinical trials of neuroprotection in low and mid resource settings.