Cerebral cortex blood flow and vascular smooth muscle contractility in a rat model of ischemia: a correlative laser Doppler flowmetric and scanning electron microscopic study

Abstract

The present study was undertaken to ascertain the role of smooth muscles and pericytes in the microcirculation during hyperperfusion and hypoperfusion following ischemia in rats. Paired external carotids, the pterygopalatine branch of the internal carotids and the basilar artery were exposed and divided. Reversible inflatable occluders were placed around the common carotids. After 24 h, the unanesthetized rat underwent 10-min ischemia by inflating the occluders. Continuous cortical cerebral blood flow (c-CBF) was monitored by laser Doppler flowmetry. The measured c-CBF was below 20% of control (P < 0.001) during ischemia. A c-CBF of 227.5 +/- 54.1% (P < 0.001) was obtained during reperfusion hyperemia. A c-CBF of 59.7 +/- 8.8% (P < 0.001) occurred at the nadir of postischemic hypoperfusion, and this was followed by a second hyperemia. The cytoarchitecture of the vascular smooth muscles and pericytes was assessed by scanning electron microscopy. Samples were prepared using a KOH-collagenase digestion method. In control rats, arteriolar muscle cells showed smooth surfaces. Capillary pericytes were closely apposed to the endothelium. Immediately after reperfusion, transverse membrane creases were observed on the smooth muscle surfaces. During maximal hyperemia the creases disappeared. When c-CBF started to decrease the creases became visible again. Throughout the postischemic hypoperfusion the creases remained. Capillary endothelial walls became tortuous in the late phase of hypoperfusion. During the second hyperemia most arteriolar muscle cells showed smooth surfaces. Some pericytes appeared to have migrated from the vascular wall. The morphological changes of smooth muscle membranes suggest that they are related to specific perfusional disturbances during ischemia and reperfusion.

Pericytes as Inducers of Rapid, Matrix Metalloproteinase-9-Dependent Capillary Damage during Ischemia

“…Both male and female mice were used, and all mice used were between 2 and 5 months of age. To induce transgene expression in NG2-CreER mice, tamoxifen dissolved in corn oil/ethanol (9:1) was injected intraperitoneally at a dose of 100 mg/kg, every 24 h for 5 consecutive days (Madisen et al, 2010). These mice were then imaged within 2 weeks after the final tamoxifen injection.…”

“…tdTomato reporter mice (Ai14) on a C57BL/6 background were purchased from The Jackson Laboratory (stock #007914; Madisen et al, 2010). These mice were bred with the following two different Cre driver lines to achieve transgene expression in pericytes: PDGFR␤-Cre mice (a gift from Volkhard Lindner, Maine Medical Center Research Institute, Portland, Maine;Cuttler et al, 2011) and neural/glial antigen 2 (NG2)-CreER mice (stock #008538, The Jackson Laboratory; Zhu et al, 2011).…”

“…Increased BBB permeability worsens stroke outcome by exposing neurons to blood components, increasing tissue edema (Larrue et al, 1997) and limiting the window for thrombolytic treatment (Hawkins and Davis, 2005;Desilles et al, 2013). Cerebral pericytes may play a role in BBB changes after stroke, as they are essential for the proper formation and maintenance of the BBB in the normal brain (Winkler et al, 2011;Liu et al, 2012). Their continuous signaling with the endothelium promotes normal tight junction development, and regulates vesicular trafficking and immune cell infiltration across the endothelium (Armulik et al, 2005;Daneman et al, 2010;Ben-Zvi et al, 2014).…”

“…Cultured pericytes have recently been shown to produce matrix metalloproteinases (MMPs;Thanabalasundaram et al, 2011;Takahashi et al, 2014), which are key mediators of BBB disruption during stroke (Yang et al, 2007;Barr et al, 2010) and during small-vessel disease in dementia (Weekman and Wilcock, 2015). In particular, various inflammatory signaling cascades can induce pericyte MMP-9 expression in vitro (Takata et al, 2011;Machida et al, 2015) and in vivo (Gurney et al, 2006;Bell et al, 2012). This suggests that, unlike their supportive roles during normal brain function, pericytes may open a route for vascular leakage by enhancing MMP activity during ischemia.…”

Highly Enhanced Permeability of Blood‐Brain Barrier Induced by Repeated Administration of Endothelin‐1 in Dogs and Rats

“…On the other hand, it was observed that pericytes migrated from the vascular wall indicating morphological changes in response to brain damage such as ischaemia and traumatic brain injury (Takahashi et al 1997;Dore-Duffy et al 2000;Walski & Gajkowska 2001). Although we have no evidence for the involvement of capillary pericytes in the disruption of blood-brain barrier permeability caused by endothelin-1, the possibility cannot be entirely ruled out.…”