Vasomotion and neurovascular coupling in the visual thalamus in vivo

Spontaneous contraction and relaxation of arteries (and in some instances venules) has been termed vasomotion and has been observed in an extensive variety of tissues and species. However, its functions and underlying mechanisms are still under discussion. We demonstrate that in vivo spectrophotometry, measured simultaneously with extracellular recordings at the same locations in the visual thalamus of the cat, reveals vasomotion, measured as an oscillation (0.14 hz) in the recorded oxyhemoglobin (OxyHb) signal, which appears spontaneously in the microcirculation and can last for periods of hours. During some non-oscillatory periods, maintained sensory stimulation evokes vasomotion lasting ~30s, resembling an adaptive vascular phenomenon. This oscillation in the oxyhaemoblobin signal is sensitive to pharmacological manipulation: it is inducible by chloralose anaesthesia and it can be temporarily blocked by systemic administration of adrenaline or acetylcholine (ACh). During these oscillatory periods, neurovascular coupling (i.e. the relationship between local neural activity and the rate of blood supply to that location) appears significantly altered. This raises important questions with regard to the interpretation of results from studies currently dependent upon a linear relationship between neural activity and blood flow, such as neuroimaging.     

Fish oil and neurovascular control in humans

The antihypertensive influence of fish oil is controversial, and the mechanisms remain unclear. Because the inverse relation between fish oil and hypertension appears to be partially dependent on the degree of hypertension, we tested the hypothesis that fish oil would elicit more dramatic reductions in mean arterial pressure (MAP) and muscle sympathetic nerve activity (MSNA) in prehypertensive (PHT) compared with normotensive (NT) subjects. Resting MAP, MSNA, and heart rate (HR) were examined before and after 8 wk of fish oil (9 g/day; 1.6 g eicosapentaenoic acid and 1.1 g docosahexaenoic acid) or placebo (olive oil; 9 g/day) in 38 NT (19 fish oil; 19 placebo) and 29 PHT (15 fish oil; 14 placebo) volunteers. Fish oil did not alter resting MAP, MSNA, or HR in either NT (80 ± 1 to 80 ± 1 mmHg; 11 ± 2 to 10 ± 1 bursts/min; 71 ± 2 to 71 ± 2 beats/min) or PHT (88 ± 2 to 87 ± 1 mmHg; 11 ± 2 to 10 ± 2 bursts/min; 73 ± 2 to 73 ± 2 beats/min) subjects. When NT and PHT groups were consolidated, analysis of covariance confirmed that pretreatment resting MAP was not associated with changes in MSNA after fish oil. In contrast, pretreatment resting HR was correlated with changes in MSNA (r = 0.47; P = 0.007) and MAP (r = 0.42; P < 0.007) after fish oil but not placebo. In conclusion, fish oil did not alter sympathetic neural control in NT or PHT subjects. However, our findings suggest that fish oil is associated with modest sympathoinhibition in individuals with higher resting heart rates, a finding that is consistent with a recent meta-analysis examining the relations among fish oil, HR, and the risk of cardiovascular disease.     

Specialization in cerebral and extracerebral neurovascular mechanisms

The neuroeffector properties of four blood vessels with diverse characteristics are compared and contrasted. The variables include the density and distribution pattern of sympathetic innervation; size, direction, and nerve frequency-characteristics of the neurogenic response, nature of the sympathetic transmitter, receptor types, and receptor-response coupling; and the level and temperature sensitivity of myogenic tone. In many instances, these features can be related to the functional role of the vessels and their pharmacological characteristics. The underlying basis of this diversification, with one exception, which can be related to developmental origin, is entirely unknown.     

Role of astrocytes in neurovascular coupling

Neural activity is intimately tied to blood flow in the brain. This coupling is specific enough in space and time that modern imaging methods use local hemodynamics as a measure of brain activity. In this review, we discuss recent evidence indicating that neuronal activity is coupled to local blood flow changes through an intermediary, the astrocyte. We highlight unresolved issues regarding the role of astrocytes and propose ways to address them using novel techniques. Our focus is on cellular level analysis in?vivo, but we also relate mechanistic insights gained from ex?vivo experiments to native tissue. We also review some strategies to harness advances in optical and genetic methods to study neurovascular coupling in the intact brain.     

NADPH-Diaphorase reactivity and neurovascular coupling in the basal forebrain and motor cortex

Using NADPH-diaphorase histochemistry, distribution of reactive neurons in the forebrain structures and motor cortex of rats was studied. Some reactive (NO-generating) neurons are associated with microvessels and, thus, can be involved in the regulation of regional blood flow. Neirofiziologiya/Neurophysiology, Vol. 39, Nos. 4/5, pp. 405–407, July–October, 2007.     

Writing In and Reading ICU Diaries: Qualitative Study of Families' Experience in the ICU

Purpose

Keeping an ICU patient diary has been reported to benefit the patient''s recovery. Here, we investigated the families'' experience with reading and writing in patient ICU diaries kept by both the family and the staff.

Methods

We conducted a qualitative study involving 32 semi-structured in-depth interviews of relatives of 26 patients (34% of all family members who visited patients) who met our ICU-diary criterion, i.e., ventilation for longer than 48 hours. Grounded theory was used to conceptualise the interview data via a three-step coding process (open coding, axial coding, and selective coding).

Results

Communicative, emotional, and humanising experiences emerged from our data. First, family members used the diaries to access, understand, and assimilate the medical information written in the diaries by staff members, and then to share this information with other family members. Second, the diaries enabled family members to maintain a connection with the patient by documenting their presence and expressing their love and affection. Additionally, families confided in the diaries to maintain hope. Finally, family members felt the diaries humanized the medical staff and patient.

Conclusions

Our findings indicate positive effects of diaries on family members. The diaries served as a powerful tool to deliver holistic patient- and family-centered care despite the potentially dehumanising ICU environment. The diaries made the family members aware of their valuable role in caring for the patient and enhanced their access to and comprehension of medical information. Diaries may play a major role in improving the well-being of ICU-patient families.     

New players in the neurovascular unit: Insights from experimental and clinical epilepsy

The conventional notion that neurons are exclusively responsible for brain signaling is increasingly challenged by the idea that brain function in fact depends on a complex interplay between neurons, glial cells, vascular endothelium, and immune-related blood cells. Recent data demonstrates that neuronal activity is profoundly affected by an entire cellular and extracellular ‘orchestra’, the so-called neurovascular unit (NVU). Among the ‘musical instruments’ of this orchestra, there may be molecules long-known in biomedicine as important mediators of inflammatory and immune responses in the organism, as well as non-neuronal cells, e.g., leukocytes. We here review recent evidence on the structure and function of the NVU, both in the healthy brain and in pathological conditions, such as the abnormal NVU activation observed in epilepsy. We will argue that a better understanding of NVU function will require the addition of new players to the ‘orchestra’.     

Weight loss improves neurovascular and muscle metaboreflex control in obesity

We studied the effects of a hypocaloric diet (D, n = 24, age: 32.2 +/- 1.4 yr, body mass index: 34.7 +/- 0.5 kg/m2) and a hypocaloric diet associated with exercise training (D + T, n = 25, age: 32.3 +/- 1.3 yr, body mass index: 32.9 +/- 0.4 kg/m2) on muscle metaboreflex control, muscle sympathetic nerve activity (MSNA, microneurography), blood pressure, and forearm blood flow (plethysmography) levels during handgrip exercise at 10% and 30% of maximal voluntary contraction in normotensive obese women. An additional 10 women matched by age and body mass index were studied as a nonadherent group. D or D + T significantly decreased body mass index. D or D + T significantly decreased resting MSNA (bursts/100 heartbeats). The absolute levels of MSNA were significantly lower throughout 10% and 30% exercise after D or D + T, although no change was found in the magnitude of response of MSNA. D + T, but not D, significantly increased resting forearm vascular conductance. D + T significantly increased the magnitude of the response of forearm vascular conductance during 30% exercise. D or D + T significantly increased MSNA levels during posthandgrip circulatory arrest when muscle metaboreflex is isolated. In conclusion, weight loss improves muscle metaboreflex control in obese women. Weight loss reduces MSNA, which seems to be centrally mediated. Weight loss by D + T increases forearm vascular conductance at rest and during exercise in obese individuals.     

Combined heat and mental stress alters neurovascular control in humans

This study examined the effect of combined heat and mental stress on neurovascular control. We hypothesized that muscle sympathetic nerve activity (MSNA) and forearm vascular responses to mental stress would be augmented during heat stress. Thirteen subjects performed 5 min of mental stress during normothermia (Tcore; 37 ± 0°C) and heat stress (38 ± 0°C). Heart rate, mean arterial pressure (MAP), MSNA, forearm vascular conductance (FVC; venous occlusion plethysmography), and forearm skin vascular conductance (SkVCf; via laser-Doppler) were analyzed. Heat stress increased heart rate, MSNA, SkVCf, and FVC at rest but did not change MAP. Mental stress increased MSNA and MAP during both thermal conditions; however, the increase in MAP during heat stress was blunted, whereas the increase in MSNA was accentuated, compared with normothermia (time × condition; P < 0.05 for both). Mental stress decreased SkVCf during heat stress but not during normothermia (time × condition, P < 0.01). Mental stress elicited similar increases in heart rate and FVC during both conditions. In one subject combined heat and mental stress induced presyncope coupled with atypical blood pressure and cutaneous vascular responses. In conclusion, these findings indicate that mental stress elicits a blunted increase of MAP during heat stress, despite greater increases in total MSNA and cutaneous vasoconstriction. The neurovascular responses to combined heat and mental stress may be clinically relevant to individuals frequently exposed to mentally demanding tasks in hyperthermic environmental conditions (i.e., soldiers, firefighters, and athletes).     

重症医学科平台ICU集中管理的实践与探索

重症医学科在我国刚刚起步,2008年被定为独立的临床二级学科,其学科建设需要进行科学的管理。通过在重症医学科平台上进行ICU集中管理,在实际工作中收到了较好的效果。这不仅是学科发展的内在需要,也是与各学科之间良性竞争的内在需要,更是医院管理的内在需要。     

The pattern of neurovascular development in the forelimb of the quail embryo

Peripheral nerve and vascular patterns are congruent in the adult vertebrate, but this has been disputed in vertebrate embryos. The most detailed of these studies have used the avian forelimb as a model system, yet neurovascular anatomical relationships and critical vascular remodeling events remain inadequately characterized in this model. To address this, we have used a combination of intravascular marker injection, multilabel fluorescent stereomicroscopy, and confocal microscopy to analyze the spatiotemporal relationships between peripheral nerves and blood vessels in the forelimb of 818 quail embryos from E2 (HH13) to E15 (HH41). We find that the neurovascular anatomical relationships established during development are highly stereotypic and congruent. Blood vessels typically arise before their corresponding nerves, but there are several critical exceptions to this rule. The vascular pattern is extensively remodeled from the earliest stage examined (E2; HH13), whereas the peripheral nerves, the first of which enter the forelimb at E3.5-E4 (HH21-HH24), have a progressively unfolding pattern that, once formed, remains essentially unchanged. The adult neurovascular pattern is not established until E8 (HH34). Peripheral nerves are always found to track close and parallel to the vasculature. As they track distally, peripheral nerves always lie on the side of the vasculature away from the center of the forelimb. Neurovascular patterns have a hierarchy of congruence that is highest in the dorsoventral plane, followed by the anteroposterior, and lastly the proximodistal planes.     

Ultrastructural study of neurovascular contacts in the median eminence of the rat

Summary In the median eminence of the rat axons of the supraoptic-paraventricular-hypophyseal tract with elementary neurosecretory granules (150–200 m) traverse the internal zone. Terminals containing dense core vesicles 60–120 m in diameter end on the portal capillaries of the median eminence. A unique organisation of the primary portal capillaries is shown. Endothelial cells have many fenestrae. The pericapillary space has numerous extensions all of which represent a special zone around the endothelial tube. The fine structural organisation and function of the neurovascular contacts in the median eminence are discussed.     

A model of neurovascular coupling and the BOLD response PART II

A mathematical model is developed which describes a signalling mechanism of neurovascular coupling with a model of a pyramidal neuron and its corresponding fMRI BOLD response. In the first part of two papers (Part I) we described the integration of the neurovascular coupling unit extended to include a complex neuron model, which includes the important Na/K ATPase pump, with a model that provides a BOLD signal taking its input from the cerebral blood flow and the metabolic rate of oxygen consumption. We showed that this produced a viable signal in terms of initial dip, positive and negative BOLD signals. In this paper (PART II) our model predicts the variations of the BOLD response due to variations in neuronal activity and indicates that the BOLD signal could be used as an initial biomarker for neuronal dysfunction or variations in the perfusion of blood to the cerebral tissue. We have compared the simulated hypoxic BOLD response to experimental BOLD signals observed in the hippocampus during hypoxia showing good agreement. This approach of combined quantitative modelling of neurovascular coupling response and its BOLD response will enable more specific assessment of a brain region.