Selective age-related changes in neuronal markers and smooth muscle reactivity in cerebrovascular beds of Fischer 344 rats

Extent of collateralization predicting symptomatic cerebral vasospasm among pediatric patients: correlations among angiography, transcranial Doppler ultrasonography, and clinical findings

OBJECT

Although the development and prevalence of cerebral vasospasm (CV) has been extensively investigated in adults, little data exist on the development of CV in children. The authors hypothesized that even though children have highly vasoreactive arteries, because of a robust cerebral collateral blood flow, they rarely develop symptomatic CV.

METHODS

The authors retrospectively reviewed their university hospital's neurointerventional database for children (that is, patients ≤ 18 years) who were examined or treated for aneurysmal or traumatic subarachnoid hemorrhage (SAH) during the period 1990-2013. Images from digital subtraction angiography (DSA) were analyzed for the extent of CV and collateralization of the cerebral circulation. Results from transcranial Doppler (TCD) ultrasonography were correlated with those from DSA. Cerebral vasospasm on TCD ultrasonography was defined according to criteria developed for adults. Clinical outcomes of CV were assessed with the pediatric modified Rankin Scale (mRS).

RESULTS

Among 37 children (21 boys and 16 girls ranging in age from 8 months to 18 years) showing symptoms of an aneurysmal SAH (comprising 32 aneurysms and 5 traumatic pseudoaneurysms), 17 (46%) had CV confirmed by DSA; CV was mild in 21% of these children, moderate in 50%, and severe in 29%. Only 3 children exhibited symptomatic CV, all of whom had poor collateralization of cerebral vessels. Among the 14 asymptomatic children, 10 (71%) showed some degree of vessel collateralization. Among 16 children for whom TCD data were available that could be correlated with the DSA findings, 13 (81%) had CV according to TCD criteria. The sensitivity and specificity of TCD ultrasonography for diagnosing CV were 95% and 59%, respectively. The time to CV onset detected by TCD ultrasonography was 5 ± 3 days (range 2-10 days). Twenty-five (68%) of the children had good long-term outcomes (that is, had mRS scores of 0-2).

CONCLUSIONS

Children have a relatively high incidence of angiographically detectable, moderate-to-severe CV. Children rarely develop symptomatic CV and have good long-term outcomes, perhaps due to robust cerebral collateral blood flow. Criteria developed for detecting CV with TCD ultrasonography in adults overestimate the prevalence of CV in children. Larger studies are needed to define TCD ultrasonography-based CV criteria for children.

Association of a younger age with an increased risk of angiographic and symptomatic vasospasms following subarachnoid hemorrhage

Object

Vasospasm is a leading cause of morbidity and death following aneurysmal subarachnoid hemorrhage (SAH). It is important to predict which patients are at risk for vasospasm so that interventions can be made. There are several potential risk factors for vasospasm, one of which is age. However, the effect of age on vasospasm, particularly symptomatic vasospasm, remains controversial.

Methods

Three hundred ninety-one patients were retrospectively identified from a prospective observational database of patients with SAH who had been admitted to a single center. Demographic and clinical data were recorded, and cerebral angiograms obtained at admission and between 5 and 10 days later were compared. The relationship between age and angiographic and symptomatic vasospasms was examined using logistic regression techniques.

Results

Mild (86 patients), moderate (69 patients), severe (56 patients), and no angiographic vasospasms (180 patients) were documented by comparing admission and follow-up angiograms in each patient. Symptomatic vasospasm was identified in 69 patients (17.6%). Angiographic vasospasm was more frequent as age decreased. Except in patients < 30 years old, the frequency of symptomatic vasospasm also increased with decreasing age (p = 0.0001). After adjusting for variables known to be associated with vasospasm, an advanced age was associated with a reduced incidence of any angiographic vasospasm (OR 0.96, 95% CI 0.94–0.97), severe angiographic vasospasm (OR 0.96, 95% CI 0.95–0.98), and symptomatic vasospasm (OR 0.98, 95% CI 0.96–0.99).

Conclusions

Results in this study show that a younger age is associated with an increased incidence of angiographic and symptomatic vasospasm.

Cerebral vessels in ageing and Alzheimer's disease

The integrity of the cerebral vasculature is crucial to the maintenance of cognitive functions during ageing. Prevailing evidence suggests that cerebrovascular functions decline during normal ageing, with pronounced effects in Alzheimer's disease (AD). The causes of these changes largely remain unknown. While previous studies recorded ageing-related impairments, such as atherosclerosis and loss of innervation in basal surface arteries of the brain, it only recently has been realized that a number of subtle alterations in both the intracranial resistance vessels and the smaller capillaries is apparent in both ageing animals and humans. The dominant changes include alterations in composition of connective tissues and smooth muscle of large vessel walls, thickening of the vascular basement membrane, thinning of the endothelium in some species, loss of endothelial mitochondria and increased pericytes. Some of these attributes appear more affected in AD. Other abnormalities entail profound irregularities in the course of microvessels, unexplained inclusions in the basement membrane and changes in unique proteins and membrane lipids associated with the blood-brain barrier. Brain imaging and permeability studies show no clear functional evidence to support the structural and biochemical anomalies, but it is plausible that focal and transient breach of the blood-brain barrier in ageing, and more notably in AD, occurs. Thus, circumscribed neuronal populations in certain brain regions could become vulnerable. Furthermore, the characteristic deposition of amyloid in vessels in AD may exacerbate the decline in vascular function and promote chronic hypoperfusion. Although not explicit from current studies, it is likely that the brain vasculature is continually modified by growth and repair mechanisms in attempts to maintain perfusion during ageing and disease.

Cholinergic and vasoactive intestinal polypeptidergic innervation of the cerebral arteries

Acetylcholine and vasoactive intestinal polypeptide are not only two vasoactive agonists that predominantly induce a vasodilatation of the cerebral arteries, but also correspond to neurotransmitters that innervate the various anatomical segments of the cerebral vasculature. The distinct patterns of the cerebrovascular cholinergic and vasoactive intestinal polypeptidergic innervation, their neurochemistry, in vitro and in vivo pharmacology, as well as the putative pathophysiological implications of these neurotransmission systems are critically summarized on the basis of the most recently published literature.

Potential mechanisms of the age-related changes in the blood-brain barrier

A variety of age-related changes in the blood-brain barrier transport processes have been identified. These include reduced hexose and butyrate transport, reduced choline transport, reduced triiodothyronine transport without a change in the transport of neutral and basic amino acids. The potential mechanisms underlying these age-related changes include hemodynamic alterations in the cerebral circulation of aged rats, notably increased occurrence of arteriovenous shunting. Additional age-related changes in cerebral microvessels include alterations in protein composition, and increased accumulation of lipid peroxidation byproducts, along with changes in membrane fluidity of isolated cerebral microvessels. In addition, neurotransmitter activity notably beta adrenergic neurotransmission, is significantly reduced in cerebral microvessels of aged rats. These alterations taken together may account for some of the age-related changes in the blood-brain barrier.

A statistical analysis of factors related to symptomatic cerebral vasospasm

A retrospective review of patients presenting to our institution with aneurysmal subarachnoid hemorrhage between 1980-1990 was accomplished. Eleven variables were examined as to their relationship to clinical vasospasm: age, sex, clinical grade, amount of subarachnoid blood on CT, aneurysm location, incidence of vasospasm, incidence of complications, use of calcium channel blockers, time to surgery, length of stay, and outcome. Data were analyzed with univariate and multivariate logistical regression methodology. By univariate analysis, age under 20, amount of subarachnoid hemorrhage, and clinical grade were associated with a higher risk of vasospasm. Using multivariate logistic regression, these factors, along with age under 35, were correlated as being predictive of clinical vasospasm. When all patients are grouped into either good or bad outcome, and a similar analysis is performed, only in the poor outcome group is the amount of subarachnoid hemorrhage and clinical grade correlated with vasospasm. This suggests that there is a group of patients with a predisposition to vasospasm that is independent of subarachnoid hemorrhage and clinical grade, and that these patients may have a more favorable outcome.

Somatostatin-induced contraction mediated by endothelial TXA2 production in canine cerebral arteries

Whether somatostatin causes endothelium-dependent contraction (EDC) in isolated canine basilar arteries was examined. Somatostatin (10(-8)-10(-6) M) caused transient contractions in a dose-dependent manner. These contractions were abolished by removal of the endothelium, while the contractile response to neuropeptide Y occurred even after removal of the endothelium. The EDC induced by somatostatin (10(-7) M) was affected by neither atropine (10(-6) M) nor cyclo-somatostatin (10(-5) M), which suggests that the EDC is not due to release of endogenous acetylcholine and that the endothelial somatostatin receptor is different from hormonal somatostatin receptors. The somatostatin-induced EDC was attenuated by cyclooxygenase inhibitors (aspirin and indomethacin), thromboxane A2 (TXA2) synthetase inhibitors (OKY-064 and RS-5186), and TXA2 antagonists (ONO-3708 and S-145), which suggests that the endothelium-derived contracting factor is TXA2. These findings demonstrate that somatostatin causes EDC via activation of TXA2 synthesis in canine cerebral arteries.

In vivo microscopic studies of age-related changes in the structure and the reactivity of cerebral microvessels

To determine if hemodynamic changes in cerebral microvessels could contribute to the age-related changes in the blood-brain barrier (BBB) function, the cerebral microvessels of male Fischer 344 rats at different ages were studied using intravital fluorescence microscopy. Aging in rats was associated with significant arteriovenous shunting in the cerebral microvessels without alterations in blood flow characteristics or changes in vascular permeability to FITC dextran (150 kDa). The basal diameter of terminal arterioles examined in 24- to 27-month-old (aged) rats (28.6 +/- 2.8 microns) was not different from that in 12- to 15-month-old (intermediate age) rats (32.5 +/- 2.5 microns) or in 3- to 6-month-old (young) rats (28.6 +/- 3.0 microns). At 3 s following addition of 5% BaCl2 there was 23.3 +/- 3.47% constriction of arterioles in young rats and 14.8 +/- 5.16% constriction in intermediate age rats, but only a 3.43 +/- 5.69% change in aged rats (P less than 0.03). This initial brief constriction phase was followed by a dilatory response which was similar in all age groups. One minute following suffusion with artificial cerebrospinal fluid, the arteriolar diameter essentially returned to baseline in all rats examined. It is concluded that aging in rats is associated with alterations in cerebral microvascular reactivity in vivo along with arteriovenous shunting. These changes may contribute to age-related alterations in the BBB function.