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Stroke. 1997;28:1035-1042

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(Stroke. 1997;28:1035-1042.)
© 1997 American Heart Association, Inc.

Articles

Genetic Susceptibility to Experimental Cerebral Aneurysm Formation in the Rat

Michèle Coutard, PhD; Mary Osborne-Pellegrin, PhD

From the Institut National de la Santé et de la Recherche Médicale, INSERM U 367, Paris, France.

Correspondence to Michèle Coutard, INSERM U 460, CHU Xavier Bichat, 16 rue Henri Huchard BP 416, 75870-Paris Cedex 18, France.


*    Abstract
up arrowTop
 *Abstract
down arrowIntroduction
 down arrowMaterials and Methods
 down arrowResults
 down arrowDiscussion
 down arrowReferences
 
Background and Purpose The susceptibility to experimental cerebral aneurysm formation in arteries of the circle of Willis was studied in four strains of rats presenting different susceptibilities to the spontaneous rupture of the internal elastic lamina in extracerebral arteries: Brown-Norway (BN)>Wistar>Long-Evans (LE)>LOU.

Methods Rats (150 g body weight) of the four strains were subjected to hypertension and a change in local cerebral blood flow by ligation of one common carotid artery for about 7 months. Six-month-old BN and LE rats were subjected to carotid ligation only for 11 to 13.5 months and treated or not (from 3 to 7 months of age) with an inhibitor of connective tissue fiber maturation, ß-aminopropionitrile (BAPN).

Results Aneurysmal structures (AS) occurred mainly in the anterior cerebral/anterior communicating arterial complex and proximal part of the posterior artery. In hypertensive rats, the AS incidence was LE, 56%; Wistar, 33%; BN, 17%; and LOU, 11%. When normotensive and subjected to carotid ligation only, LE rats showed an even greater susceptibility to AS formation (86%) than BN (7%). BAPN treatment did not influence AS formation: LE (60%) versus BN (8%).

Conclusions These results suggest that genetic factors are involved in cerebral aneurysm formation in the rat. The susceptibility of the internal elastic lamina of extracerebral arteries to spontaneous rupture does not appear to be a determinant genetic trait in the propensity to develop aneurysms in arteries of the circle of Willis. The comparison of these different rat strains may be very useful for studying factors contributing to cerebral aneurysm pathogenesis.


Key Words: cerebral aneurysm • genetics • rats


*    Introduction
up arrowTop
 up arrowAbstract
 *Introduction
down arrowMaterials and Methods
 down arrowResults
 down arrowDiscussion
 down arrowReferences
 
Although the etiology of cerebral aneurysms is still not established, aneurysms appear to result from the interplay between hemodynamics and structural properties of the arterial wall.1 A degenerative process in the arterial wall consecutive to the fatigue imposed by hemodynamic forces has been proposed as determinant.2 3 4 Medial gaps, which represent areas lacking medial smooth muscle cells, have been proposed by some5 6 7 as localizing factors in aneurysm formation, although this is still controversial.2 8 The earliest features observed in susceptible areas of experimental aneurysm development are damage to endothelial cells followed by alterations in the IEL and the media9 and changes in the medial elastic skeleton preceding morphological changes in the IEL.10 In a majority of reports concerning the etiology of cerebral aneurysms, the disintegration of the IEL was considered as an early key event.4 5 8 11 12

Intimal lesions characterized by the interruption of the IEL, with in some cases subsequent damage to endothelium and the underlying media, develop spontaneously with age in the caudal and renal arteries of the rat.13 14 Different susceptibilities to rupture of the IEL in the caudal artery between inbred rat strains have been established.15 BN rats are highly prone to IEL rupture because they develop large numbers of IEL interruptions in several arteries, particularly in the abdominal aorta.16 Recent observations on four strains of rats from sources different from those of the above studies have shown that BN rats are still the most susceptible to IEL rupture, the Wistar is intermediate, and the LE and LOU strains are the least, with the LE being slightly more susceptible than the LOU (M. Coutard, unpublished observations, 1994).

BAPN, which is a specific inhibitor of the enzyme lysyl oxidase17 involved in the cross-linking of elastic and collagen fibers,18 increases the incidence of experimental cerebral aneurysms in the rat.19 20 In addition, BAPN is able to increase the formation of arterial IEL interruptions21 and of aneurysmal-like structures in the testicular artery22 in the rat. Together these data suggest that the propensity to develop IEL interruptions may be determinant in cerebral aneurysm formation. We have thus investigated the incidence of experimental cerebral aneurysms in different rat strains with various susceptibilities to rupture of the IEL in extracerebral arteries (BN>Wistar>LE>LOU). First, we studied aneurysm formation in these four different rat strains with the previously described experimental model of cerebral aneurysm induction in the arteries of the circle of Willis in the rat,19 20 23 which associates experimental hypertension and ligation of one common carotid artery. By this procedure, hemodynamics were altered in two ways: an increase in intramural pressure and a modification of blood flow in some arteries that function as a shunt after carotid ligation.24 Although we did not measure blood flow within these arteries, it can be considered that an increase in local blood flow occurs,24 which may only be transient since arteries can adapt and local blood flow can return to normal values.

In this first experiment, we did not treat hypertensive rats with BAPN, since our purpose was to determine an eventual difference in aneurysm formation in rats pre-senting intrinsic differences in susceptibility to rupture of the IEL. Data from this first experiment showed that LE rats displayed the highest incidence of cerebral AS but also the highest level of blood pressure. Thus, to eliminate the possibility that these results might be due to the higher blood pressure levels in LE, we studied aneurysm formation in normotensive BN and LE rats subjected only to a modified local blood flow in cerebral arteries. It may be assumed that in these conditions aneurysm formation would be very low. Because, as reported above, the incidence of experimental cerebral aneurysms in rats is enhanced by BAPN treatment, in this second series of experiments we attempted to enhance aneurysm formation by treatment of half of these BN and LE rats with BAPN.


*    Materials and Methods
up arrowTop
 up arrowAbstract
 up arrowIntroduction
 *Materials and Methods
down arrowResults
 down arrowDiscussion
 down arrowReferences
 
Incidence of Cerebral Aneurysms in Different Strains of Experimental Hypertensive Rats
Animals
Inbred BN rats (n=20) and outbred Wistar rats (n=20) (Iffa-Credo, L'Arbresle, France), outbred LE rats (n=20) (CEJ, Le Genest Saint-Isle, France), and inbred LOU rats (n=28) (originally from CNRS and maintained in our laboratory) of about 150 g body weight were used.

The procedure for the care and euthanasia of studied animals was in accordance with European community standards on the care and use of laboratory animals.

Experimental Procedure
A clip of 0.2 mm in diameter was placed on the left renal artery to activate the renin-angiotensin system and consequently produce a sustained hypertension (two-kidney, one clip Goldblatt model).25 One week later, the left common carotid artery was ligated in two locations 5 mm apart and cut between the two ligatures to avoid an eventual revascularization. These two surgical procedures were performed with rats under ether anesthesia. Rats were fed normal laboratory chow and given tap water ad libitum. Systolic blood pressure was recorded weekly by the indirect tail-cuff transducer method (Narco Bio-systems). Several rats of each strain did not show any increase in blood pressure several weeks after renal artery clipping. Their blood pressure was then measured less frequently, and these rats were thereafter considered as normotensive and sham operated. Several rats died very soon postoperatively and were autopsied when possible.

At about 7 months after carotid ligation, animals were anesthetized with pentobarbital (40 mg/kg; Nembutal, Abbot). A catheter was inserted into the aorta toward the heart just above the renal arteries. Procaine 1% (2 mL) was injected through the vena cava to induce cardiac arrest. The vena cava was cut for outflow of perfusates. About 2 mL of NaCl 0.9% and 10 mL of fixative solution (3% buffered glutaraldehyde) were perfused, and the brain was removed from the skull. The brain was postfixed for several hours in glutaraldehyde solution and rinsed in 150 mmol/L cacodylate buffer overnight. Under a dissecting microscope, the ventral part of the brain was exposed, and the arteries of both the anterior and posterior parts of the brain were gently removed. These two arterial networks then were postfixed in 1% OsO4 for 2 hours and processed for routine electron microscopy. Just before embedding in epoxy resin, arteries were observed under a dissecting microscope to check for the presence of AS, which are more easily detectable when arteries have been previously slightly blackened with osmium. Arteries were cut with a razor blade into small pieces of about 5 mm in length and embedded in sequence as recorded on a diagram made of the arteries of the ventral surface of the brain. Semithin sections of about 1.5 µm in thickness were made of several AS (n=15). In addition, we performed detailed microscopic examination of sections from the bifurcation of the AA and OA of both sides from normotensive and hypertensive BN (n=6) and LE (n=7) rats. This bifurcation, on the side opposite to carotid ligation, has been reported to be one of the sites most susceptible to experimental cerebral aneurysm development in the rat.26

Incidence of Aneurysms in Normotensive BN and LE Rats
In a second experiment, 32 BN and 32 LE rats aged 3 months were given normal laboratory chow, and from 4 to 7 months of age, half of them received the same diet supplemented with 0.12% BAPN (Janssen Labs). All rats were maintained in the above-described conditions. At about 6 months of age, the left common carotid artery was ligated with rats under ether anesthesia. Several rats died (8 LE and 14 BN) from different causes unrelated to the aim of the experiment and were autopsied when possible.

Because we had no reference about cerebral aneurysm formation in these experimental conditions, first we killed 2 BN and 2 LE rats treated with BAPN 9 months after carotid ligation (at 15 months of age), then 3 BN and 2 LE BAPN-treated rats at 11 months after carotid ligation, and thereafter the remaining 7 BN and 5 LE BAPN-treated rats and the 9 BN and 9 LE untreated rats at 12.5 to 13.5 months after carotid ligation.

Arteries of the ventral part of the brain were processed as described above.

Statistical Analysis
To test the significance of differences between mean values from the four strains of rats, one-way ANOVA was used, followed by Fisher's test. For comparisons between only two groups of rats, Student's t test was used.


*    Results
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 up arrowAbstract
 up arrowIntroduction
 up arrowMaterials and Methods
 *Results
down arrowDiscussion
 down arrowReferences
 
Incidence of Cerebral Aneurysms in Different Strains of Experimental Hypertensive Rats
In the four strains, several rats died early (3 LE, 8 BN, 3 LOU, and 3 Wistar). In some of them (3 LE, 3 LOU, and 2 Wistar), the brains could not be examined. The brains that could be examined (8 BN, 1 Wistar) did not show AS, probably because the duration of the experiment was not sufficient for inducing them. However, half of these BN rats showed signs of hemorrhage in the cortex on the side contralateral to carotid ligation (right side). Three BN clipped rats showed small, round hemorrhagic spots, and one showed two important areas of hemorrhage. Although the level of blood pressure rose very quickly in several rats (reaching about 240 mm Hg 2 weeks after the clip had been placed on the renal artery) and the majority of rats that died had elevated arterial pressure, the rat that displayed the greatest hemorrhagic signs did not have the most elevated blood pressure (about 185 mm Hg), at least at 15 days after clipping (first record of blood pressure). Only one Wistar rat could be autopsied and showed a hemorrhagic spot in its right cerebral cortex. In the two other rat strains, no brains were in observable condition.

In our hands, the induction of experimental renovascular hypertension by placement of a clip on one renal artery was not 100% reliable. A variable number of rats in each strain showed no or only a transient increase in their systolic blood pressure, probably due to displacement of the clip. Thus, we considered rats with a mean systolic blood pressure of <170 mm Hg during the experimental period as normotensive.

Fig 1Down summarizes the incidence of cerebral AS and levels of blood pressure in the four strains of both normotensive (<170 mm Hg) and hypertensive (>=170 mm Hg) groups of clipped rats. In normotensive rats, only one individual showed an AS in the LE, Wistar, and BN strains, whereas in the LOU strain none occurred. In hypertensive rats, LE showed the greatest incidence of AS, Wistar was intermediate, and BN and LOU showed a low incidence. However, the mean systolic blood pressure of LE was significantly higher than those of the three other strains of rats. When comparing normotensive and hypertensive groups of rats, hypertension increased the incidence of AS in LE, Wistar, and LOU but not in the BN rats. However, it should be recalled that 8 BN rats with elevated blood pressure died early after clipping, and in the remaining BN rats the mean level of blood pressure was not very high.



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  		Figure 1. Incidence of AS (expressed as the percentage of the total number of rats presenting with at least one AS) and mean systolic blood pressure throughout the experimental period (expressed as mean±SD). Numbers in the bars represent the total number of rats studied. ***P<=.001, **P<=.01, *P<=.02 compared with LE. W indicates Wistar rats.

In this study, we found the sites of predilection for AS formation to be the complex of the AA and ACoA (Fig 2aDown) and the proximal segment of the PA (Fig 2bDown). Fig 2cDown illustrates the morphology of one AA/ACoA complex showing arterial bends. At a microscopic level, a small curved artery from an AA/ACoA complex showed AS changes at the internal side of the bend (Fig 2dDown) very similar to those observed in the convoluted rat testicular artery,7 where spontaneous aneurysmal changes mainly occur at the lesser curvature (Fig 2eDown). The left (ligated side) PA was often elongated and in numerous cases showed the presence of a loop compared with the PA of the nonligated side. As discussed later, this peculiar morphology may be of importance in the development of AS at these sites.



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  		Figure 2. a, Anterior part of the circle of Willis from a clipped LE rat with a saccular aneurysm in the AA/ACoA complex; b, posterior part of the circle of Willis from a normotensive BAPN-treated LE rat with a fusiform aneurysm in the proximal segment of the PA; c, anterior part of the circle of Willis from a clipped BN rat with a small artery in the AA/ACoA complex showing curves (arrow). Note the buttonholelike morphology of the AA. a through c, bars=1 mm. d and e, AS occurring at the internal part of bends: d, cerebral artery of the AA/ACoA complex from a clipped LE rat (bar=50 µm); e, testicular artery from a spontaneously hypertensive rat from a previous study (bar=200 µm). aa indicates anterior cerebral artery; ba, basilar artery; mca, middle cerebral artery; oa, olfactory artery; and sca, superior cerebellar artery.

The microscopic observation of a bilobed saccular aneurysm from an LE rat showed in one lobe the presence of cellular and fibrous components (Fig 3aDown) and the accumulation of plasma infiltrates and of numerous leukocytes in the other lobe (Fig 3bDown). The latter probably represents a more recent stage of aneurysmal development.



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  		Figure 3. a and b, Bilobed saccular aneurysm in the AA/ACoA complex from a normotensive LE rat with carotid ligation only: a, lobe filled with fibrous and cellular material; b, second lobe with numerous inflammatory cells and plasma infiltrates on the luminal side of the aneurysmal wall. c through e, PAs from normotensive LE rats with only carotid ligation: c, ligated side, with areas of dilatation (arrow); d, nonligated side; e, ligated side in a BAPN-treated rat. a through e, same magnification, bar=100 µm. iel indicates internal elastic lamina.

The great majority of the AS observed present less developed aneurysmal features than saccular aneurysms, representing microaneurysms and mild dilatations. Fig 3cUp shows the left PA from a hypertensive LE rat with a very thin wall and areas of dilatation consisting of either a decreased number of medial cells and lack of the IEL or of only endothelial cells lying on thin adventitial tissue. No such structural changes occurred in the PA of the nonligated side (Fig 3dUp).

In the first experiment, we did not observe macroscopic AS at the bifurcation of the AA and OA on the side opposite to the carotid ligation, a site previously described to be one of the sites of predilection for cerebral aneurysm formation in the rat.26 We thus further investigated this AA/OA bifurcation at the microscopic level in the two strains of rats with the highest (LE-clipped) and the lowest (BN-clipped) incidence of macroscopic AS. In the majority of these sites on both sides, at the apex of the bifurcation an intimal cushion was present, and under this structure the IEL was either absent, duplicated, or fragmented. In a great number of cases, sections showed the absence of the IEL over a short length in the vicinity of the intimal cushion (Fig 4aDown). No obvious difference was observed between the two strains of rats; only two "early aneurysmal lesions" with the absence of an intact IEL and a slightly dilated, thin media were observed in normotensive LE rats (Fig 4bDown), although as noted by Futami et al,27 these structural features may be observed even in normal bifurcations. No apparent saccular aneurysms, defined as dilated areas with only endothelial cells and fibrous adventitia, were observed at the AA/OA bifurcation of these rats when studied at the microscopic level.



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  		Figure 4. a and b, Bifurcation of AA/OA on the nonligated side: a, normotensive BN clipped rat; b, normotensive LE clipped rat (same magnification, bar=100 µm). c and d, BAPN-treated LE rat: c, microaneurysm at the apex of a buttonholelike formation of the AA; d, "preaneurysmal lesion" on the anterior cerebral artery (same magnification, bar=50 µm).

Incidence of AS in Normotensive BN and LE Rats Treated or Not With BAPN
The TableDown summarizes the number of rats showing different AS in arteries of the anterior and posterior parts of the circle of Willis in LE and BN rats treated or not with BAPN. The level of blood pressure at the time of death in these normotensive rats was slightly more elevated in LE than BN in controls and in BAPN-treated rats (TableDown), although these differences were not statistically significant (P>.2 for controls and P>.3 for BAPN-treated rats).


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  		Table 1. Incidence of Different Cerebral AS in Carotid-Ligated Normotensive LE and BN Rats Treated or Not With BAPN

LE rats showed a much greater total incidence of AS than BN, whether treated with BAPN or not. In contrast to the first experiment, a difference in AS incidence between normotensive LE and BN rats could be seen, probably due to different experimental conditions from using older rats and a longer duration of carotid occlusion.

In our experimental conditions, BAPN did not increase the incidence of AS. It may be noticed that several BAPN-treated rats were killed earlier than untreated rats (see "Materials and Methods"). However, at this time, only 1 of 4 LE rats displayed an AS compared with 4 of 5 about 3 months later. Thus, BAPN did not accelerate aneurysmal formation in our experimental conditions.

In 1 BAPN-treated LE rat, a saccular microaneurysm (Fig 4cUp) with a very thin wall occurred at the apex of a branching of the AA, forming a buttonholelike structure (as shown in Fig 2cUp), and in the same animal a preaneurysmal lesion with a decreased medial thickness was observed at the AA/OA bifurcation (Fig 4dUp).

In the PA of BAPN-treated rats, AS often appear macroscopically as white and opaque structures. At a microscopic level, more cell proliferation and a thicker adventitial tissue could be observed (Fig 3eUp) compared with untreated rats (Fig 3aUp).


*    Discussion
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 up arrowAbstract
 up arrowIntroduction
 up arrowMaterials and Methods
 up arrowResults
 *Discussion
down arrowReferences
 
The present study clearly showed that the LE rat strain was more susceptible to the development of cerebral AS than the BN rat, while it is clearly less prone to spontaneous rupture of the IEL in extracerebral arteries.16 In addition, LE and LOU rats showed very different susceptibilities to AS formation, whereas they present similar susceptibilities to IEL rupture. This suggests that the propensity of the IEL from extracerebral arteries to spontaneously rupture is not a major genetic determinant of the susceptibility to cerebral aneurysmal formation and that other factors may be of higher contributing importance. However, this does not exclude that the IEL degradation locally in cerebral arteries may be a very important early step in cerebral aneurysm pathogenesis.

In contrast to the results of the present study, in which LE rats showed a higher susceptibility to cerebral AS than BN rats, we have previously reported in the testicular artery a higher incidence in BN compared with LE of spontaneous aneurysmal-like structures, characterized in part by the absence of the IEL.22 This suggests that the testicular artery behaves like other systemic arteries for rupture of the IEL. In contrast, the situation in the cerebral arteries appears to be very different because genetic susceptibility to IEL rupture in extracerebral arteries does not correlate with cerebral aneurysm formation. This discrepancy between data obtained at cerebral and testicular levels leads us to reconsider our previous suggestion, proposing on a morphological basis the testicular artery as an eventual model for studying cerebral aneurysm pathogenesis.

In our experimental conditions, the light microscopic study of the bifurcation of the AA/OA did not reveal the presence of morphological alterations related to aneurysmal or even preaneurysmal changes, whereas other authors using this model of experimental induction of cerebral aneurysms in rats have reported this arterial bifurcation to be one of the most susceptible sites for aneurysm development.26 However, we used LE and BN rats instead of Sprague-Dawley rats and the two-kidney one clip Goldblatt model instead of deoxycorticosterone acetate–salt or ischemic renal models of experimental hypertension. Both the rat strain and the level and the course of hypertension induced by the different models used may account for the differences observed. From our experiments, we can conclude that when only hemodynamic parameters are modified, the sites with the highest susceptibility for AS development are very small arteries with a peculiar configuration that have to sustain an increase, at least transiently, in blood flow.

The difference in the susceptibility to AS formation between strains of rats strongly suggests that genetic factors may be involved in the pathogenesis of cerebral aneurysms. Among them, the arterial configuration, which itself may influence hemodynamic parameters, may play a role. Although in humans anatomic variations in the circle of Willis are considered by some to be normal and no more prevalent in subjects with intracranial aneurysms, certain variations may be commonly found with aneurysms of the ACoA28 and in other sites.29 30 In the rat, the morphology of the circle of Willis is not very different between individuals apart from two areas, the AA/ACoA complex and the origin of the PAs,31 which are also the arteries where AS develop. The comparison of the PA of the ligated side, which at least transiently receives an increased blood flow after carotid ligation, with that of the nonligated side showed an increase in the arterial diameter and an elongation with the frequent presence of a loop in the former. The morphology of the AA/ACoA complex is different in each individual and is characterized by a very irregular course of the arteries that may present various branchings, curves, and loops. We have previously shown that in the highly convoluted testicular artery of the spontaneously hypertensive rat, AS, sharing numerous characteristics with experimental cerebral aneurysms in rats, developed spontaneously at the internal part of the curves, whereas in the straight spermatic artery, of which the testicular artery is the continuity, no structural changes occurred.7 We did not observe any consistent difference in arterial configuration of the AA/ACoA complex between the different rat strains but a great range of variety within each strain. In addition, only some rats within any one (even inbred) strain developed AS at both susceptible arterial sites.

In humans, the presence of several affected members in the same family32 33 34 35 and in identical twins36 and the presence of multiple aneurysms in the same individual also suggest the implication of genetic factors. However, the familial aggregation of intracranial aneurysms is low (ie, less than 2%37 to 6.7%38 ) and considered by some to concern a specific small subpopulation,37 while that of multiple aneurysms is more elevated (ie, about 20%33 ). Thus, as previously suggested, if inherited factors are causal, they probably are multiple and/or require other associated conditions to be symptomatic. This view is supported in the present study by the occurrence of AS within only some individuals in outbred but also in inbred strains of rats.

The involvement of defective components of the extracellular matrix, mainly collagen,39 40 41 42 43 44 has been suggested in cerebral aneurysm formation in humans but still remains controversial.45 46 In the rat, the previously reported increased incidence of experimental cerebral aneurysms in BAPN-treated animals19 20 suggests that defective connective tissue may favor aneurysm development. We recently reported that the LE rat showed higher amounts of elastin and lower amounts of collagen than the BN.47 In addition, a lower level of tropoelastin mRNA in growing BN rats was observed in both abdominal and thoracic aorta, suggesting an intrinsic decreased synthesis of elastin in BN. No difference between the two strains was observed in {alpha}1-type I collagen mRNA in young and adult rats, although at 6 weeks of age, {alpha}1-type III collagen mRNA was lower in the abdominal segment in LE compared with BN. Thus, it appears that the lower content of aortic collagen in LE rats is not related to a generalized decrease in mRNA collagen transcripts. In our experimental conditions, we did not observe any increase in the incidence of cerebral AS between BN and LE rats treated with BAPN, which inhibits the maturation of connective tissue fibers. However, the treatment was given in adult rats when the bulk of elastin synthesis had already occurred, thus probably affecting this protein very little. As for collagen, the turnover is greater and continues in adult life, and its synthesis was probably more affected by BAPN in our experiments. This effect of BAPN on connective tissue even in adult rats is suggested by the increased occurrence of cerebral aneurysms when BAPN is given from 4 months of age in hypertensive rats.20 In our experiment, BAPN was given to normotensive rats subjected to carotid ligation only. It is possible that the increase in blood flow without associated hypertension was not sufficient to induce additional aneurysmal changes even on a structurally different artery. In addition, the duration of BAPN treatment (4 months) may have been insufficient. In one BAPN-treated LE rat, we observed a preaneurysmal lesion at the AA/OA bifurcation and a microaneurysm at another AA branching. We did not observe structural changes in these areas in untreated rats, suggesting that the use of BAPN may increase the susceptibility to aneurysmal changes at the apex of these bifurcations.

As for the presence of hemorrhagic signs within the cortex of several hypertensive rats, mainly in BN and also in one Wistar rat, this confirms a previous observation that when rendered hypertensive, BN rats showed a particular cerebrovascular fragility.16

Results of the present study suggest a genetic predisposition to cerebral aneurysm formation in the rat. The comparison of various biological parameters in strains of rats with high and low susceptibilities to aneurysm formation may point to eventual mechanisms involved in the pathogenesis of cerebral aneurysms.


*    Selected Abbreviations and Acronyms
 
AA = anterior cerebral artery
ACoA = anterior communicating artery
AS = aneurysmal structure(s)
BAPN = ß-aminopropionitrile
BN = Brown-Norway
IEL = internal elastic lamina
LE = Long-Evans
OA = olfactory cerebral artery
PA = posterior artery


*    Acknowledgments
 
This work was supported by INSERM. We thank Catherine Chollet for her excellent technical assistance.

Received December 2, 1996; revision received February 14, 1997; accepted February 28, 1997.


*    References
up arrowTop
 up arrowAbstract
 up arrowIntroduction
 up arrowMaterials and Methods
 up arrowResults
 up arrowDiscussion
 *References
 

  1. Sekhar LN, Heros RC. Origin, growth, and rupture of saccular aneurysms: a review. Neurosurgery. 1981;8:248-260.[Medline] [Order article via Infotrieve]
  2. Stehbens WE. Etiology of intracranial berry aneurysms. J Neurosurg. 1989;70:823-831.[Medline] [Order article via Infotrieve]
  3. Kayembe KNT, Kataoka H, Hazama F. Early changes in cerebral aneurysms in the internal carotid/posterior communicating artery junction. Acta Pathol Jpn. 1987;37:1891-1901.[Medline] [Order article via Infotrieve]
  4. Hazama F, Kataoka H, Yamada E, Kayembe K, Hashimoto N, Kojima M, Kim C. Early changes of experimentally-induced cerebral aneurysms in rats: light microscopic study. Am J Pathol. 1986;124:399-404.[Abstract]
  5. Forbus WD. On the origin of miliary aneurysms of the superficial cerebral arteries. Bull Johns Hopkins Hosp. 1930;47:239-284.
  6. Carmichael R. The pathogenesis of non-inflammatory cerebral aneurysms. J Pathol Bacteriol. 1950;62:1-19.[Medline] [Order article via Infotrieve]
  7. Coutard M, Osborne-Pellegrin MJ. The rat testicular artery: a model of spontaneous aneurysmal-like structure formation. Am J Pathol. 1992;141:1053-1061.[Abstract]
  8. Glynn LE. Medial defects in the circle of Willis and their relation to aneurysm formation. J Pathol. 1940;51:213-222.
  9. Kim C, Cervos-Navarro J, Kikuchi H, Hashimoto N, Hazama F. Alterations in cerebral vessels in experimental animals and their possible relationship to the development of aneurysms. Surg Neurol. 1992;38:331-337.[Medline] [Order article via Infotrieve]
  10. Yamazoe N, Hashimoto N, Kikuchi H, Hazama F. Elastic skeleton of intracranial cerebral aneurysm in rats. Stroke. 1990;21:1722-1726.[Abstract/Free Full Text]
  11. Cajender S, Hassler O. Enzymatic destruction of the elastic lamella at the mouth of cerebral berry aneurysm? Acta Neurol Scand. 1976;53:171-181.[Medline] [Order article via Infotrieve]
  12. Kim C, Kikuchi H, Hashimoto N, Kojima M, Kang Y, Hazama F. Involvement of internal elastic lamina in development of induced cerebral aneurysms in rats. Stroke. 1988;19:507-511.[Abstract/Free Full Text]
  13. Osborne-Pellegrin MJ. `Spontaneous' lesions of the intima in the rat caudal artery: principal morphologic characteristics and occurrence as a function of age and sex. Lab Invest. 1979;40:668-677.[Medline] [Order article via Infotrieve]
  14. Osborne-Pellegrin MJ. Natural incidence of interruptions in the internal elastic lamina of caudal and renal arteries of the rat. Acta Anat. 1985;124:188-196.[Medline] [Order article via Infotrieve]
  15. Osborne-Pellegrin MJ. Etude D'interruptions Spontanées de la Limitante élastique Interne dans Quelques Artères du Rat: Incidence sur la Morphologie Artérielle, et Formation dans des Conditions Naturelles et Expérimentales. Paris, France: University of Paris VI; 1986. Thesis.
  16. Capdeville M, Coutard M, Osborne-Pellegrin MJ. Spontaneous rupture of the internal elastic lamina in the rat: the manifestation of a genetically determined factor which may be linked to vascular fragility. Blood Vessels. 1989;26:197-212.[Medline] [Order article via Infotrieve]
  17. Tang SS, Trackman PC, Kagan HM. Reaction of aortic lysyl oxidase with ß-aminopropionitrile. J Biol Chem. 1983;258:4331-4338.[Abstract/Free Full Text]
  18. Eyre DR, Paz MA, Gallop PM. Cross-linking in collagen and elastin. Ann Rev Biochem. 1984;53:717-748.[Medline] [Order article via Infotrieve]
  19. Hashimoto N, Handa H, Hazama F. Experimentally-induced cerebral aneurysms in rats. Surg Neurol. 1978;10:3-8.[Medline] [Order article via Infotrieve]
  20. Hashimoto N, Handa H, Hazama F. Experimentally-induced cerebral aneurysms in rats, part II. Surg Neurol. 1979;11:243-246.[Medline] [Order article via Infotrieve]
  21. Osborne-Pellegrin MJ. Spontaneous arterial lesions involving breaks in the internal elastic lamina in the rat: effect of ß-aminopropionitrile and familial distribution. Exp Mol Pathol. 1986;45:171-184.[Medline] [Order article via Infotrieve]
  22. Coutard M, Osborne-Pellegrin MJ. Effect of defective connective tissue on the formation of aneurysmal-like structures in the rat testicular artery. Int J Exp Pathol. 1996;77:53-62.[Medline] [Order article via Infotrieve]
  23. Hashimoto N, Handa H, Nagata I, Hazama F. Saccular cerebral aneurysms in rats. Am J Pathol. 1983;110:397-399.[Medline] [Order article via Infotrieve]
  24. Hashimoto N, Handa H, Nagata I, Hazama F. Experimentally induced cerebral aneurysm in rats, V: relation of hemodynamics in the circle of Willis to formation of aneurysms. Surg Neurol. 1980;13:41-45.[Medline] [Order article via Infotrieve]
  25. Michel JB, Dussaule JC, Choudat L, Auzan C, Nochy D, Corvol P, Menard J. Effects of antihypertensive treatment in one-clip, two-kidney hypertension in rats. Kidney Int. 1986;29:1011-1020.[Medline] [Order article via Infotrieve]
  26. Kojima M, Handa H, Hashimoto N, Kim C, Hazama F. Early changes of experimentally induced cerebral aneurysms in rats: scanning electron microscopic study. Stroke. 1986;17:835-841.[Abstract/Free Full Text]
  27. Futami K, Yamashita J, Tachibana O, Higashi S, Ikeda K, Yamashima T. Immunohistochemical alterations of fibronectin during the formation and proliferative repair of experimental cerebral aneurysms in rats. Stroke. 1995;26:1659-1664.[Abstract/Free Full Text]
  28. Stehbens WE. Aneurysms and anatomical variation of cerebral arteries. Arch Pathol. 1963;75:45-76.[Medline] [Order article via Infotrieve]
  29. Alpers BJ, Berry RG. Circle of Willis in cerebral vascular disorders: the anatomical structure. Arch Neurol. 1963;8:398-402.
  30. Hashimoto I. Familial intracranial aneurysms and cerebral vascular anomalies. J Neurosurg. 1977;46:419-427.[Medline] [Order article via Infotrieve]
  31. Brown JO. The morphology of circulus arteriosus cerebri in rats. Anat Rec. 1966;156:99-106.[Medline] [Order article via Infotrieve]
  32. Bannerman RM, Ingall GB, Graf CJ. The familial occurrence of intracranial aneurysms. Neurology. 1970;20:283-292.[Free Full Text]
  33. Lozano AM, Leblanc R. Familial intracranial aneurysms. J Neurosurg. 1987;66:522-528.[Medline] [Order article via Infotrieve]
  34. Schievink WI, Schaid DJ, Rogers HM, Piepgras DG, Michels VV. On the inheritance of intracranial aneurysms. Stroke. 1994;25:2028-2037.[Abstract]
  35. Leblanc R, Melanson D, Tampieri D, Guttmann RD. Familial cerebral aneurysms: a study of 13 families. Neurosurgery. 1995;37:633-639.[Medline] [Order article via Infotrieve]
  36. Schon F, Marshall J. Subarachnoid haemorrhage in identical twins. J Neurol Neurosurg Psychiatry. 1984;47:81-83.[Abstract]
  37. Toglia IU, Samii AR. Familial intracranial aneurysms. Dis Nerv Syst. 1972;33:611-613.[Medline] [Order article via Infotrieve]
  38. Norrgard O, Angquist K-A, Fodstad H, Forsell A, Lindberg M. Intracranial aneurysms and heredity. Neurosurgery. 1987;20:236-239.[Medline] [Order article via Infotrieve]
  39. Schievink WI, Limburg M, Oorthuys JWE, Fleury P, Pope M. Cerebrovascular disease in Ehlers-Danlos syndrome type IV. Stroke. 1990;21:626-632.[Abstract/Free Full Text]
  40. Pope FM, Narcisi P, Neil-Dwyer G, Nicholls AC, Bartlett J, Doshi B. Some patients with cerebral aneurysms are deficient in type III collagen. Lancet. 1981;1:973-975.[Medline] [Order article via Infotrieve]
  41. De Paepe A, Van Landegem W, De Keyser F, De Reuck J. Association of multiple intracranial aneurysms and collagen III deficiency. Clin Neurol Neurosurg. 1988;90:53-56.[Medline] [Order article via Infotrieve]
  42. Majamaa K, Myllyla VV. A disorder of collagen biosynthesis in patients with cerebral artery aneurysm. Biochim Biophys Acta. 1993;1225:48-52.[Medline] [Order article via Infotrieve]
  43. Neil-Dwyer G, Bartlett JR, Nicholls AC, Narcisi P, Pope M. Collagen deficiency and ruptured cerebral aneurysms: a clinical and biochemical study. J Neurosurg. 1983;59:16-20.[Medline] [Order article via Infotrieve]
  44. Ostergaard JR, Oxlund H. Collagen type III deficiency in patients with rupture of intracranial saccular aneurysms. J Neurosurg. 1987;67:690-696.[Medline] [Order article via Infotrieve]
  45. Leblanc R, Lozano AM, van der Rest M, Guttmann RD. Absence of collagen deficiency in familial cerebral aneurysms. J Neurosurg. 1989;70:837-840.[Medline] [Order article via Infotrieve]
  46. Kuivaniemi H, Prockop DJ, Wu Y, Madhatheri SL, Kleinert C, Earley JJ, Jokinen A, Stolle C, Majamaa K, Myllyla VV, Norrgard O, Schievink WI, Mokri B, Fukawa O, ter Berg HWM, De Paepe A, Lozano AM, Leblanc R, Ryynanen M, Baxter BT, Shikata H, Ferrell RE, Tromp G. Exclusion of mutations in the gene for type III collagen (COL3A1) as a common cause of intracranial aneurysms or cervical artery dissections by sequence analysis of the coding sequence of type III collagen in 55 unrelated patients. Neurology. 1993;43:2652-2658.[Abstract/Free Full Text]
  47. Sauvage M, Jacob MP, Osborne-Pellegrin M. Aortic elastin and collagen content and synthesis in two strains of rats with different susceptibilities to rupture of the internal elastic lamina. J Vasc Res. 1997;34:126-136.[Medline] [Order article via Infotrieve]



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