Glial cell regulation of neuronal activity and blood flow in the retina by release of gliotransmitters

Astrocytes in the brain release transmitters that actively modulate neuronal excitability and synaptic efficacy. Astrocytes also release vasoactive agents that contribute to neurovascular coupling. As reviewed in this article, Müller cells, the principal retinal glial cells, modulate neuronal activity and blood flow in the retina. Stimulated Müller cells release ATP which, following its conversion to adenosine by ectoenzymes, hyperpolarizes retinal ganglion cells by activation of A1 adenosine receptors. This results in the opening of G protein-coupled inwardly rectifying potassium (GIRK) channels and small conductance Ca²⁺-activated K⁺ (SK) channels. Tonic release of ATP also contributes to the generation of tone in the retinal vasculature by activation of P2X receptors on vascular smooth muscle cells. Vascular tone is lost when glial cells are poisoned with the gliotoxin fluorocitrate. The glial release of vasoactive metabolites of arachidonic acid, including prostaglandin E₂ (PGE₂) and epoxyeicosatrienoic acids (EETs), contributes to neurovascular coupling in the retina. Neurovascular coupling is reduced when neuronal stimulation of glial cells is interrupted and when the synthesis of arachidonic acid metabolites is blocked. Neurovascular coupling is compromised in diabetic retinopathy owing to the loss of glial-mediated vasodilation. This loss can be reversed by inhibiting inducible nitric oxide synthase. It is likely that future research will reveal additional important functions of the release of transmitters from glial cells.     

Optical incoherent technique for noninvasive assessment of blood flow in tissues: Theoretical model and experimental study

Laser noninvasive methods for assessment of a tissue blood flow (BF), for example, the Laser Doppler Flowmetry (LDF), are well-known today. However, in such methods, low-frequency fluctuations (LFFs) in the registered optical signal caused by blood volume changes inside a tissue have not been studied in details until now. The aim of this study is to investigate the LFFs formation and to justify the LFFs-based diagnostic technique for cutaneous BF assessment. LFFs are theoretically described and experimentally shown in the input LDF signal inside the frequency range 0 to 10 Hz. They are substantiated as the basis of the new diagnostic method, in which BF is defined as the magnitude of blood volume changes in a tissue per unit time. The hand-made prototype of the promising diagnostic tool with light emitted diodes is used to validate the technique in experiments in vivo on 16 healthy volunteers in comparison with the LDF method. Experimental results show a good similarity of the recorded BF for both coherent and incoherent method. The proposed technique makes it possible the creation of inexpensive diagnostic equipment for assessment of cutaneous BF without using lasers and coherent light, completely and functionally comparable to LDF devices.     

Sympathetic nerve regulation of cochlear blood flow during increases in blood pressure in humans

The purpose of this work was to show that regulation of the blood flow to the cochlea by the sympathetic nervous system occurs in humans at the level of the cochlear microcirculation during increases in blood pressure and that its involvement depends on the pressure level. Eight anaesthetized patients undergoing tympanoplasty for hearing disease took part in a pharmacological protocol of stimulation and inhibition of the autonomic nervous system (ANS) to provide variations in systolic blood pressure (BP_S) and cochlear blood flow (CBF). The CBF was measured by laser-Doppler flowmetry. Changes in autonomic nerve activity were brought about by changes in baroreceptor activity (BR) initiated by the injection of an α adrenergic agent before and after sympathetic and parasympathetic blockade. The CBF variations (δCBF) were plotted against BP_S increases at each stage of the ANS inhibition. The BR diminished significantly after α blockade, after α and β blockade, and after α and β blockade and atropine, by 50% (P < 0.01), 29% (P < 0.05), and 95% (P < 0.001) respectively. The BP_S increased significantly (P < 0.01) by 36 (SD 9)%, 47 (SD 1)%, and 67 (SD 16)% respectively. The CBF response to an increase in BP_S exhibited two opposing variations in the patients: CBF decreased significantly in one group, and increased significantly in the other group. In both groups, δCBF decrease and δCBF increase, respectively, were significant after ANS blockade; even so the decrease and increase, respectively, levelled off at BP_S around 160 mmHg before ANS blockade. For BP_S below 160 mmHg, correlations between δCBF and BP_S were significant before inhibition and after inhibition of ANS. For BP_S above 160 mmHg, BP_S and δCBF were not correlated before inhibition of ANS, and were significantly correlated after inhibition of ANS. For BP_S below 160 mmHg, CBF response to the BP_S increase was the same before and after ANS blockade, i.e. ANS control did not predominate; even so, for BP_S above 160 mmHg, the CBF response to BP_S increase was different before and after ANS blockade: CBF varied significantly after ANS blockade as it varied for BP_S below 160 mmHg, while it remained constant before ANS blockade that elicited ANS control of CBF. In conclusion, sympathetic nerve regulation via its vasomotor tone at the level of cochlear microcirculation occurred markedly when the blood pressure was above 160 mmHg; the autonomic nervous system would appear to control the cochlear blood flow against large variations in blood flow in response to hypertensive phenomena. Accepted: 7 October 1996     

In vitro analysis of blood flow in a microvascular network with realistic geometry

In vitro blood flow was measured in a polydimethysiloxane micro channel to reflect the complex geometry of a microvascular network. Flow rates were determined from the velocities of tracer particles moving along the center line of the flow channel, and the flow rates of two working fluids were then compared: water and blood. In some bifurcating channels, the measured flow rate showed that the effects of bifurcation in the apparent viscosity depend on the hematocrit, such that the flow rate in the daughter channel with the higher (lower) flow rate was lower (higher) for blood than for water. The measured flow rates in other bifurcating channels reflected effects from the surrounding flow channels acting as bypasses, which tended to balance out the effects of bifurcation.     

A fully implantable multi-channel biotelemetry system for measurement of blood flow and temperature: a first evaluation in the green sturgeon

The objective of this study was to evaluate a novel fully implantable radio-based blood flow biotelemetry system which allows simultaneously measurement of blood flow on two channels and temperature on one channel, in fish. These are the first recordings of blood flow from free-swimming fish, showing that the system is capable of recording blood flow in the ventral aorta (cardiac output) and celiacomesenteric artery (gastrointestinal blood flow) in green sturgeon Acipenser medirostris exposed to a series of different stimuli for up to 7 days after implantation. The results showed stable base line recordings and blood flow was used to calculated heart rate (f _H) and stroke volume (V _s). It was possible to reproduce the same type of responses as has previously been reported during exposure to hypoxia, temperature, stress and feeding. The mass of our implant was less than 2% of the body mass which is well within the recommended sizes for surgically implanted telemetry transmitters and it fitted easily within the abdominal cavity of the sturgeon. A fully implantable system minimizes the risk of infection/expulsion and maximizes the likelihood that the studied fish will behave naturally and be treated normally by surrounding fish. The use of biotelemetry in basic comparative physiology and applied animal ecology could help scientists to collect information that has previously been challenging to obtain and to open the possibility for new types of physiological and ecophysiological studies. Handling editor: K. Martens     

Race‐specific differences in the phase coherence between blood flow and oxygenation: A simultaneous NIRS,white light spectroscopy and LDF study

Race‐specific differences in the level of glycated hemoglobin are well known. However, these differences were detected by invasive measurement of mean oxygenation, and their understanding remains far from complete. Given that oxygen is delivered to the cells by hemoglobin through the cardiovascular system, a possible approach is to investigate the phase coherence between blood flow and oxygen transportation. Here we introduce a noninvasive optical method based on simultaneous recordings using NIRS, white light spectroscopy and LDF, combined with wavelet‐based phase coherence analysis. Signals were recorded simultaneously for individuals in two groups of healthy subjects, 16 from Sub‐Saharan Africa (BA group) and 16 Europeans (CA group). It was found that the power of myogenic oscillations in oxygenated and de‐oxygenated hemoglobin is higher in the BA group, but that the phase coherence between blood flow and oxygen saturation, or blood flow and hemoglobin concentrations is higher in the CA group     

人单核细胞系中HIV-1前病毒转录调节新型研究模型的建立

【目的】抗反转录病毒疗法(ART)能够有效控制人免疫缺陷病毒(Human immunodeficiency virus-1,HIV-1)的复制,但是不能将其完全清除。至2012年底,全球仍有3 500万HIV-1感染者,同年约160万人死于艾滋病(Acquired immune deficiency syndrome,AIDS)及其相关疾病。HIV-1感染难以根治的主要原因之一是机体内HIV-1潜伏储存库(Reservoir)的存在。HIV-1潜伏储存库主要由CD4+T细胞和单核巨噬细胞构成,与CD4+T细胞相比,目前研究者对单核巨噬系细胞中HIV-1病毒复制机制尚不明了,且缺乏适宜的研究体系。因此,为探讨单核细胞活化或分化信号对HIV-1复制的影响,我们建立了旨在研究HIV-1前病毒转录调控机制的人单核巨噬细胞系模型。【方法】构建env区域移码突变和nef区域携带EGFP或Nano Luc报告基因的HIV-1 NLn GFP-Kp或NLn Nano Luc-Kp重组病毒,分别感染2种人单核细胞系THP-1或U937细胞。通过有限稀释法制备单克隆细胞系,利用流式细胞术或Nano Luc荧光素酶活性分析检测报告基因的表达。筛选EGFP或Nano Luc阴性表达的细胞克隆,经激活剂佛波酯(Phorbol-12-myristate-13-acetate,PMA)刺激后鉴定潜伏感染的细胞克隆。【结果】研究中鉴定了4个HIV-1潜伏感染的细胞克隆。其中2个是表达EGFP的THP-1克隆,2个是以Nano Luc为报告基因的U937克隆。这些克隆在PMA刺激处理后皆有报告基因的表达,而在恒态条件下未检测到报告基因的表达。【结论】成功建立了4个HIV-1潜伏感染的人单核细胞系克隆,该模型有助于理解单核巨噬系细胞的HIV-1病毒复制机制,可能成为进一步研究HIV-1前病毒转录调控机制的有力工具。     

Real-time technique for conversion of skin temperature into skin blood flow: human skin as a low-pass filter for thermal waves

Monitoring of skin blood flow oscillations related with mechanical activity of vessels is a very useful modality during diagnosis of peripheral hemodynamic disorders. In this study, we developed a new model and technique for real-time conversion of skin temperature into skin blood flow oscillations, and vice versa. The technique is based on the analogy between the thermal properties of the human skin and electrical properties of the special low-pass filter. Analytical and approximated impulse response functions for the low- and high-pass filters are presented. The general algorithm for the reversible conversion of temperature into blood flow is described. The proposed technique was verified using simulated or experimental data of cold stress, deep inspiratory gasp, and post-occlusive reactive hyperaemia tests. The implementation of the described technique will enable to turn a temperature sensor into a blood flow sensor.     

Decline of tactile acuity in aging: a study of body site,blood flow,and lifetime habits of smoking and physical activity

Tactile acuity of 60 older subjects (≥?65 years) and 19 younger subjects (18–28 years) was assessed by two-point gap thresholds at the upper and lower surfaces of the forefinger, at the upper and lower surfaces of the feet, and at the volar surface of the forearm. The older subjects were assigned to one of four groups of 15 subjects each, depending on reported lifetime habits of physical activity and smoking: (1) active smokers, (2) active nonsmokers, (3) inactive smokers, and (4) inactive nonsmokers. Peripheral blood flow was assessed at the forefinger, foot, and forearm by means of laser-Doppler imaging and skin temperature recordings, under resting conditions and during and after a 5-min exposure to mild cooling (28°C). Consistent with previous studies, tactile acuity thresholds in the foot and finger averaged about 80% higher in the older subjects than in the younger subjects, but only about 22% higher in the forearm. Although the upper surface of the fingertip was more sensitive than the lower surface in both younger and older subjects, the age-related decline in tactile acuity was nearly identical on both sides of the finger and foot. The latter finding refutes the hypothesis that the larger effect of aging in the extremities results from greater physical wear and tear on the contact surfaces of the hands and feet. Self-reported lifetime histories of physical activity and smoking were not significantly associated with measures of cutaneous blood flow or tactile thresholds. Possible reasons for this lack of association are discussed, including the inherent limitations of testing only healthy older subjects, and the concept of “successful aging”.     

A method for the direct evaluation of the fatty acid status in a drop of blood from a fingertip in humans: applicability to nutritional and epidemiological studies

Several studies have shown that the fatty acid composition of circulating lipids reflects dietary fat intake, in turn being related to health status. The fatty acid composition of plasma lipids is therefore an important parameter in studies on dietary interventions. The aim of our study was to develop a rapid and inexpensive method for the analysis of circulating fatty acids applicable to large population groups. Drops of blood collected from fingertips have been directly subjected to transmethylation for gas chromatography analysis. This new method, validated for reproducibility, has been compared with the conventional method, based on withdrawal of blood from the antecubital vein followed by lipid extraction, and identical data have been obtained with the two techniques. Observed and predicted differences between blood and plasma fatty acids are related to the contribution of circulating cell membranes in blood. Finally the application of the methods to samples from 100 healthy subjects and the assessed correlation between dietary habits and blood fatty acid profiles demonstrate the validity of the new method and its applicability to nutritional and epidemiological studies.     

Propranolol prevents cerebral blood flow changes and pain-related behaviors in migraine model mice

Propranolol, a β-adrenergic receptor blocker, is one of the most commonly used prophylactic drugs for migraines. Cortical spreading depression (CSD) is the propagation wave of neuronal excitation along with cerebral blood flow (CBF) changes over the cerebral cortex and has been implicated in the pathological process of migraine auras and its pain response. However, the effect of propranolol on CSD-related CBF changes and behavioral responses remains poorly understood. In this study, we measured CSD-related CBF responses using a micro-device with a green light emitting diode (LED) and micro-complementary-metal-oxide-semiconductor (CMOS) image sensor and evaluated pain-related reduced locomotor activity in mice. An injection of KCl into the visual cortex led to CSD-related CBF changes; however, propranolol prevented the increase in CBF as well as delayed the propagation velocity in KCl-induced CSD. Furthermore, an injection of KCl reduced locomotor activity and induced freezing behavior in awake and freely moving mice, which were prevented by propranolol treatment. These results suggest that the modulation of CSD-related CBF responses by the blockade of β-adrenergic receptor contributes to its prophylactic effects on migraines.