MRI Characterization of Age‐Associated Changes to the Cerebral Arteries in a Rodent Model of Aging and Hypertension

Abstract

Cerebral blood vessel remodeling occurs in response to aging and hypertension. Of importance are structural changes that occur to the circle of Willis and the impact of these changes on blood flow within the brain, especially in regions associated with learning and memory, such as the hippocampus. In the present study, we apply MRI to a rodent model of aging and hypertension to elucidate changes in the circle of Willis during aging and age‐associated hypertension.HypothesisWe hypothesized that arteries comprising the circle of Willis in hypertensive Dahl‐salt sensitive rats (Dahl‐S) will exhibit age‐related volume changes, these changes will impact metabolite levels in the hippocampus and the effects will differ between Dahl‐S and age‐matched Sprague‐Dawley rats (SD).MethodsWhole brain time‐of‐flight (TOF) 3D MRI and MRS (spectroscopy) of the hippocampus were acquired using a 7 Tesla 30 cm Bruker Biospec scanner in SD and Dahl‐S male rats on normal 0.5% NaCl intake at 3, 6 and 12‐mo of age (n=5/group). Cerebral arteries comprising the circle of Willis (cerebral arterial circle (CAC), caudal communicating artery (CCA) and rostral communicating artery (RCA)) were manually segmented using AMIRA. MRS data were processed using LCmodel. Systolic blood pressure (SBP) was measured via the tail‐cuff method at each time point before MRI scans. Data were analyzed using 2‐way ANOVA followed by a Tukey's posthoc test, and are presented as mean ± standard deviationResultsAt 3‐mo, SBP did not differ between Dahl‐S vs SD (134.6±14.1 vs 131.4±8.8 mmHg). However, Dahl‐S had higher SBP vs SD at 6‐mo (165.8±20.6 vs 123.7±8.8 mmHg) and 12‐mo (166.1±16.9 vs 142.2±12.8 mmHg). The CAC volume was greater in SD vs Dahl‐S at 3 and 12‐mo but did not differ at 6‐mo (Table). Importantly, the CAC was not visible by MRI in Dahl‐S at 12‐mo of age, except in one animal. The CCA volume was greater in SD vs Dahl‐S at 12‐mo and did not differ at 3 or 6‐mo. The RCA volume did not differ between strains at any time point. No arterial volume differed with age in SD. In Dahl‐S, the CCA and RCA volumes were larger at 6‐mo compared to 3 and 12‐mo (Table). Total N‐acetylaspartate (NAA) in the hippocampus was lowest at 6‐mo in both strains, compared to 3 and 12‐mo, but did not differ between strains at any time point (Table).ConclusionWe observed variations with strain and age in the volume of arteries in the circle of Willis in normotensive SD and hypertensive Dahl‐S. Hypertensive Dahl‐S at 6‐mo of age may experience increased metabolic demand and blood volume requirements in the brain.Support or Funding InformationThis work was supported solely by the NIH/NIA Intramural Research Program.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.