Regulation Of Capillary Flow Research Articles

In vivo Single Cell Optical Ablation of Brain Pericytes.

Pericytes have myriad functions in cerebrovascular regulation but remain understudied in the living brain. To dissect pericyte functions in vivo, prior studies have used genetic approaches to induce global pericyte loss in the rodent brain. However, this leads to complex outcomes, making it challenging to disentangle the physiological roles of pericytes from the pathophysiological effects of their depletion. Here, we describe a protocol to optically ablate individual pericytes of the mouse cerebral cortex in vivo for fine-scale studies of pericyte function. The strategy relies on two-photon microscopy and cranial window-implanted transgenic mice with mural cell-specific expression of fluorescent proteins. Single pericyte somata are precisely targeted with pulsed infrared laser light to induce selective pericyte death, but without overt blood-brain barrier leakage. Following pericyte ablation, the changes to the local capillary network and remaining pericytes can be examined longitudinally. The approach has been used to study pericyte roles in capillary flow regulation, and the structural remodeling of pericytes involved in restoration of endothelial coverage after pericyte loss.

Brain pericytes: emerging concepts and functional roles in brain homeostasis.

Brain pericytes are an important constituent of neurovascular unit. They encircle endothelial cells and contribute to the maturation and stabilization of the capillaries in the brain. Recent studies have revealed that brain pericytes play pivotal roles in a variety of brain functions, such as regulation of capillary flow, angiogenesis, blood brain barrier, immune responses, and hemostasis. In addition, brain pericytes are pluripotent and can differentiate into different lineages similar to mesenchymal stem cells. The brain pericytes are revisited as a key player to maintain brain function and repair brain damage.

Evolution of the microvascular distensibility during the embryo growth. Example of the chick chorioallantoic membrane (CAM)

Evolution of the microvascular distensibility during embryo growth. Example of the chick chorioallantoic membrane (CAM). The purpose of this work was to determine the evolution of the microvascular distensibility during the embryo growth. The microvascular distensibility was involved in capillary flow regulation, therefore in tissular irrigation and capillaries network growth during the angiogenesis. Its value fluctuated with the arteriolar tone. We worked on the CAM of the chick embryo, because of the vessel wall structure quickly changes during its development. We performed the measurements at three stages of development: at day 6, day 12 and day 16 of incubation. We carried out the measurements on in situ vessels visualized by microscopy, without vasoactive substances in order to preserve the vascular tone. Each vessel was canulated with a micropipette, occluded by a distal compression and inflated with a saline injection under controlled pressures. The distensibility was expressed as the relative increase in diameter. We determined that: 1) The distensibility was significantly higher in the vessels smaller than 58 μm diameter than in the larger vessels at day 6 and day 12 (the 58 μm value was the average diameter of the studied vessels). 2) The distensibility of the arteries, whatever their diameter (small or large) significantly decreased between day 12 and day 16 of incubation. 3) The distensibility of the smallest veins significantly decreases between day 12 and day 16, whereas the distensibility of the largest veins did not change during the same period. 4) The arteriolar distensibility was significantly smaller than the venular distensibility at day 12 and day 16.

MORPHOLOGICAL STUDY ON THE PERICYTES OF GOAT'S PLACENTOMAL CAPILLARIES

Pcricytcs arc connective tissue cells associated abluminally with capillary and postcapillary venulcs, They share a common basal lamina with endothelial cells (Majno, 1965: Schor et al., 1995). Such rnicrovcssels arc involved with the exchangeof material and extracellular space (Nehls and Drenckhahn, 1993). Perleytes were first described in the nictitating membrane of the frog by Rouget (1873). and have been seen surrounding capillaries in a wide variety of tissues(Zimmerman, 1923: Majno, 1965: Lunam and Roger, 1981: Sims, 1986: Hirschi and D'Amore, 1996; Sundberg et al., 1996; Wisse et al., 1996). The most probable function for pcricytcs is the regulation of capillary flow by their contraction (Epling, 1966; Rhodin, 1968: Wieble, 1974: Tilton et al., 1979). A possible functional role of the pericytes is the control of material exchange through the vessel wall (lmayama and Urab, 1984) and its participation in angiogenesis has been proposed (Crocker et at, 1970; Schor et at, 1995). A further role that has been attributed to pericytcs is to stabilize the capillary wall (Cohen et al., 1980; Frank et al., 1990: Jeon et at., 1996). In rat uterus. the increase in pericytes coincides with the time of implantation (Lunam and Roger, 1983). Steven and Samuel (1979) have suggested that there arc few pericytes associated with the maternal capillaries in sheep placenta to perform an important regulatory function on the transport of material from the mother to the fetus. However, Yasear et HI. (1987) found a considerably largenumber of pcricytcs in association with the maternal microvessels in sheep placenta throughout pregnancy. In the gOHt'S placenta. the materno-Ictal interface is characterized by the presence of syncytial tissue covering the maternal side of placentomes. The plcentomes arc ruminant-specific fetomatcrnal contact zones characterized by the presence ofmicrovillar junction between syncytium and fetal trophoblastic layer (Steven, 1975; Wooding and Flint, 1994). Due to the lack of information on the distribution of pericytes in the goat's placenta the present study was initiated to evaluatethe distribution of the pericytes surrounding the materna! capillaries which are located close to the syncytium, i.e. those most closely involved in the materno-fetal exchanges throughout pregnancy.

Nitric oxide from neuronal NOS plays critical role in cerebral capillary flow response to hypoxia.

We investigated, using a direct, intravital microscopic technique, whether nitric oxide (NO) from neuronal nitric oxide synthase (nNOS) plays a role in the cerebral capillary flow response to acute hypoxia. Erythrocyte flow in subsurface capillaries of the frontoparietal cortex of adult Sprague-Dawley rats was visualized using epifluorescence videomicroscopy after fluorescent labeling of red blood cells (RBC) in tracer concentrations. The velocity of labeled RBC in individual capillaries was measured off-line using an image analysis system. Hypoxia was produced by lowering the inspired O2 concentration to 15% for 5 min in control animals and in those pretreated with the selective nNOS inhibitor 7-nitroindazole (7-NI; 20 mg/kg ip). In the control group, hypoxia increased RBC velocity by 34 +/- 8%. In the group treated with 7-NI, this response was reversed to a statistically significant 8 +/- 3% decrease. This paradoxical response to hypoxia after 7-NI was observed in nearly all capillaries. 7-NI itself decreased the baseline RBC velocity by 12 +/- 4%. The cerebral hyperemic response to hypoxia was also assessed with the laser Doppler flow (LDF) technique. In control animals, hypoxia produced a 33 +/- 6% increase in LDF, similar to the increase in RBC velocity. After 7-NI treatment, the response to hypoxia was moderately attenuated but still significant at a 19 +/- 2% increase in LDF. These results support the role of NO from nNOS in the cerebral hyperemic response to hypoxia. They imply that 7-NI interfered with a physiological mechanism that was fundamental to cerebral capillary flow regulation and provide direct evidence that cerebral capillary perfusion may be dissociated from a concurrent change in regional tissue perfusion as reflected by LDF. In conclusion, NO from nNOS contributes to the maintenance of RBC flow in cerebral capillaries and plays a critically important role in the selective regulation of cerebral capillary flow during hypoxia.