Permeability of intracranial extracerebral vessels in stroke-prone SHR

Is the spontaneously hypertensive stroke prone rat a pertinent model of sub cortical ischemic stroke? A systematic review

The spontaneously hypertensive stroke prone rat is best known as an inducible model of large artery stroke. Spontaneous strokes and stroke propensity in the spontaneously hypertensive stroke prone rat are less well characterized; however, could be relevant to human lacunar stroke. We systematically reviewed the literature to assess the brain tissue and small vessel pathology underlying the spontaneous strokes of the spontaneously hypertensive stroke prone rat. We searched systematically three online databases from 1970 to May 2010; excluded duplicates, reviews, and articles describing the consequences of induced middle cerebral artery occlusion or noncerebral pathology; and recorded data describing brain region and the vessels examined, number of animals, age, dietary salt intake, vascular and tissue abnormalities. Among 102 relevant studies, animals sacrificed after developing stroke-like symptoms displayed arteriolar wall thickening, subcortical lesions, enlarged perivascular spaces and cortical infarcts and hemorrhages. Histopathology, proteomics and imaging studies suggested that the changes not due simply to hypertension. There may be susceptibility to endothelial permeability increase that precedes arteriolar wall thickening, degeneration and perivascular tissue changes; systemic inflammation may also precede cerebrovascular changes. There were very few data on venules or tissue changes before hypertension. The spontaneously hypertensive stroke prone rat shows similar features to human lacunar stroke and may be a good spontaneous model of this complex human disorder. Further studies should focus on structural changes at early ages and genetics to identify factors that predispose to vascular and brain damage.

Therapeutic effects of AE0047, a novel calcium antagonist, on progression of brain damage after stroke in stroke-prone spontaneously hypertensive rats

1. The potential of AE0047, a novel calcium antagonist, to remedy brain damage of stroke-prone spontaneously hypertensive rats (SHRSPs) with signs of stroke was compared with those of nicardipine and hydralazine. 2. AE0047 (1 and 3 mg/kg/day) given daily to diseased SHRSPs prevented mortality and improved neurological symptoms. Histological examination also supported the effectiveness of AE0047 against the progression of the disease. 3. Nicardipine (10 mg/kg/day) and hydralazine (10 mg/kg/day) were less effective than AE0047 in a dose equal to or more than the hypotensive dose, respectively. 4. AE0047 may be beneficial for treating the acute stage of stroke in humans by virtue of its long-lasting hypotensive action and undefined direct actions on the cerebral vasculature.

Chromosomal mapping of quantitative trait loci contributing to stroke in a rat model of complex human disease

Stroke is a complex disorder with a poorly understood multifactorial and polygenic aetiology. We used the stroke-prone spontaneously hypertensive rat (SHRSP) as a model organism, mated it with the stroke-resistant spontaneously hypertensive rat (SHR) and performed a genome-wide screen in the resultant F2 cohort where latency until stroke, but not hypertension (a major confounder) segregated. We identified three major quantitative trait loci, STR1-3, with lod scores of 7.4, 4.7 and 3.0, respectively, that account for 28% of the overall phenotypic variance. STR2 colocalizes with the genes encoding atrial and brain natriuretic factor, peptides with important vasoactive properties. Our results demonstrate the existence of primary, blood pressure-independent genetic factors predisposing to a complex form of stroke.

Effects of a selective endothelin A-receptor antagonist, BQ-123, in salt-loaded stroke-prone spontaneously hypertensive rats

1. We examined the effects of a selective endothelin A (ETA)-receptor antagonist, BQ-123, on the development of hypertension and organ damage in stroke-prone spontaneously hypertensive rats (SHRSP) given 1% NaCl for 6 weeks. 2. BQ-123 at doses of 0.7, 2.1 and 7.1 mg/day was continuously administered for 6 weeks to 8 week old salt-loaded SHRSP, who were given water containing 1% NaCl for the following 6 weeks, via a subcutaneous osmotic minipump. 3. Development of high blood pressure was accelerated in salt-loaded SHRSP compared with that in non-salt-loaded SHRSP. After 6 weeks of salt-loading, incidence of cerebral infarction, renal sclerosis and renal fibrosis were greater in salt-loaded than non-salt-loaded SHRSP. 4. BQ-123 attenuated the age-related rise in blood pressure in a dose-dependent manner. The effect coincided with reduction in the incidence of cerebral infarction and prevention of renal sclerosis and fibrosis. Kidney function was improved as observed by an increase in glomerular filtration rate and decreases in urinary protein excretion, blood urea nitrogen and fractional sodium excretion. Furthermore, BQ-123 prevented increases in the heart weight/bodyweight ratio and aortic wall thickness in salt-loaded SHRSP. 5. These results suggest that endogenous endothelin-1 (ET-1) and ETA-receptors may be, at least in part, involved in the pathogenesis of hypertension and organ damage in salt-loaded SHRSP.

Demonstration of hereditarily accelerated proliferation in astrocytes derived from spontaneously hypertensive rats

1. We examined the proliferative rates of cultured astrocytes isolated from stroke-prone spontaneously hypertensive rats (SHRSP) and stroke-resistant spontaneously hypertensive rats (SHRSR). Wistar-Kyoto rats (WKY) were used as a control for SHRSP and SHRSR. 2. In the presence of 10% fetal bovine serum (FBS), the doubling time for astrocytes from SHRSP and SHRSR was significantly shorter than WKY. 3. When quiescent astrocytes derived from SHRSP or SHRSR were released from serum-deprivation, the DNA synthesis was stimulated 13.3-fold and 12.5-fold, respectively, whereas only a 7.76-fold increase was observed in WKY astrocytes. 4. Further we studied the effects of two growth factors, epidermal growth factor (EGF) and fibroblast growth factor (FGF) on astrocytes proliferation. EGF induced greater DNA synthesis in SHRSP and SHRSR astrocytes compared with WKY astrocytes, although FGF had little or no effect. 5. Total cholesterol levels in SHRSP astrocytes and SHRSR astrocytes were significantly lower than that of WKY astrocytes, which was consistent with our previous observations in cultured vascular smooth muscle cells. 6. There was no difference in morphology among the cultured astrocytes from the three strains. 7. The abnormality of growth rate and cell membranes composition of astrocytes might be closely related to the genetic phenotypes (acute death of neurons and oedema of astrocytes) of SHRSP or SHRSR.

Detailed disease processes of cerebral pericytes and astrocytes in stroke-prone SHR

We examined ultrastructurally cerebral pericytes and astrocytes in 20 normotensive Wistar Kyoto rats and 60 asymptomatic stroke-prone spontaneously hypertensive rats, which were sequentially killed at 4-52 weeks of age. Another 30 SHRSP were killed soon after they showed symptoms of stroke. We found two kinds of pericytes around the capillaries; granular pericytes and filamentous pericytes. Granular pericytes possibly serve as scavenger cells in the central nervous system and became active and grew in size with time. In contrast, filamentous pericytes degenerated during the development of hypertension. Degeneration of the filamentous pericytes was involved in an increase of endothelial permeability. Increased permeability caused focal and then circumferential swelling of the astrocytes around the capillaries. Swelling of the astrocytes seemed to accelerate the production of attachment plaques. Following this increase in the number of attachment plaques, numerous astrocytic filaments were produced within the cytoplasm. As a result, fibrous astrocytes were fully developed. Adjacent to the fibrous astrocytes we detected opening of the interendothelial junctions as well as dead neurons. From these observations we propose that astrocytes perform the main function in trophic interactions among cerebral endothelial cells, astrocytes, and neurons and that dysfunction of astrocytes disturbs the neural environment, resulting in neuronal death.