Long-Term High-Fat Diet Consumption Depletes Glial Cells and Tyrosine Hydroxylase–Containing Neurons in the Brain of Middle-Aged Rats

Epidemiologic studies have indicated that dyslipidemia may facilitate the progression of neuronal degeneration. However, the effects of chronic dyslipidemia on brain function, especially in older individuals, remain unclear. In this study, middle-aged 37-week-old male Wistar-Kyoto rats were fed a normal diet (ND) or a 45% high-fat diet (HFD) for 30 weeks (i.e., until 67 weeks of age). To study the effects of chronic dyslipidemia on the brain, we analyzed spontaneous locomotor activity, cognitive function, and brain tissues in both groups of rats after 30 weeks. Compared with age-matched rats fed a ND, Wistar-Kyoto rats fed a HFD had dyslipidemia and showed decreased movement but normal recognition of a novel object. In our brain analyses, we observed a significant decrease in astrocytes and tyrosine hydroxylase–containing neurons in the substantia nigra and locus coeruleus of rats fed a HFD compared with rats fed a ND. However, hippocampal pyramidal neurons were not affected. Our findings indicate that the long-term consumption of a HFD may cause lipid metabolism overload in the brain and damage to glial cells. The decrease in astrocytes may lead to reduced protection of the brain and affect the survival of tyrosine hydroxylase–containing neurons but not pyramidal neurons of the hippocampus.

Intravital microscopic observation of the microvasculature during hemodialysis in healthy rats

Hemodialysis (HD) provides life-saving treatment for kidney failure. Patient mortality is extremely high, with cardiovascular disease (CVD) being the leading cause of death. This results from both a high underlying burden of cardiovascular disease, as well as additional physiological stress from the HD procedure itself. Clinical observations indicate that HD is associated with microvascular dysfunction (MD), underlining the need for a fundamental pathophysiological assessment of the microcirculatory consequences of HD. We therefore successfully developed an experimental small animal model, that allows for a simultaneous real-time assessment of the microvasculature. Using in-house built ultra-low surface area dialyzers and miniaturized extracorporeal circuit, we successfully dialyzed male Wistar Kyoto rats and combined this with a simultaneous intravital microscopic observation of the EDL microvasculature. Our results show that even in healthy animals, a euvolemic HD procedure can induce a significant systemic hemodynamic disturbance and induce disruption of microvascular perfusion (as evidence by a reduction in the proportion of the observed microcirculation receiving blood flow). This study, using a new small animal hemodialysis model, has allowed direct demonstration that microvascular blood flow in tissue in skeletal muscle is acutely reduced during HD, potentially in concert with other microvascular beds. It shows that preclinical small animal models can be used to further investigate HD-induced ischemic organ injury and allow rapid throughput of putative interventions directed at reducing HD-induced multi-organ ischemic injury.

Perfusion of Brain Preautonomic Areas in Hypertension: Compensatory Absence of Capillary Rarefaction and Protective Effects of Exercise Training

Remodeling of capillary rarefaction and deleterious arteries are characteristic hallmarks of hypertension that are partially corrected by exercise training. In addition, experimental evidence showed capillary rarefaction within the brain cortex and reduced cerebral blood flow. There is no information on hypertension- and exercise-induced effects on capillary profile and function within preautonomic nuclei. We sought now to evaluate the effects of hypertension and exercise training (T) on the capillary network within hypothalamic paraventricular (PVN) and solitary tract (NTS) nuclei, and on the remodeling of brain arteries. Age-matched spontaneously hypertensive rats (SHR) and Wistar-Kyoto (WKY), submitted to moderate T or kept sedentary (S) for three months, were chronically cannulated for hemodynamic recordings at rest. Rats were anesthetized for i.v. administration of fluorescein isothiocyanate (FITC)-dextran (capillary volume/density measurements) or 4% paraformaldehyde perfusion (basilar, middle, and posterior arteries' morphometry) followed by brain harvesting and processing. Other groups of conscious rats had carotid blood flow (CBF, ultrasound flowmeter) acquired simultaneously with hemodynamic recordings at rest and exercise. SHR-S exhibited elevated pressure and heart rate, reduced CBF, increased wall/lumen ratio of arteries, but no capillary rarefaction within the PVN and NTS. T improved performance gain and caused resting bradycardia in both groups; reduction of pressure and sympathetic vasomotor activity and normalization of the wall/lumen ratio were only observed in SHR-T. T groups responded with marked PVN and NTS capillary angiogenesis and augmented CBF during exercise; to avoid overperfusion at rest, reduced basal CBF was observed only in WKY-T. Data indicated that the absence of SHR-S capillary rarefaction and the intense SHR-T angiogenesis within autonomic areas associated with correction of deleterious arteries' remodeling are essential adjustments to hypertension and exercise training, respectively. These adaptive responses maintain adequate baseline perfusion in SHR-S and SHR-T preautonomic nuclei, augmenting it in exercised rats when a well-coordinated autonomic control is required.

Sex-Specific Behavioral Response to Early Adolescent Stress in the Genetically More Stress-Reactive Wistar Kyoto More Immobile, and Its Nearly Isogenic Wistar Kyoto Less Immobile Control Strain

Genetic predisposition and environmental stress are known etiologies of stress-related psychiatric disorders. Environmental stress during adolescence is assumed to be particularly detrimental for adult affective behaviors. To investigate how genetic stress-reactivity differences modify the effects of stress during adolescence on adult affective behaviors we employed two inbred strains with differing stress reactivity. The Wistar Kyoto More Immobile (WMI) rat strain show increased stress-reactivity and despair-like behaviors as well as passive coping compared to the nearly isogenic control strain, the Wistar Kyoto Less Immobile (WLI). Males and females of these strains were exposed to contextual fear conditioning (CFC) during early adolescence (EA), between 32 and 34 postnatal days (PND), and were tested for the consequences of this mild EA stress in adulthood. Early adolescent stress significantly decreased anxiety-like behavior, measured in the open field test (OFT) and increased social interaction and recognition in adult males of both strains compared to controls. In contrast, no significant effects of EA stress were observed in adult females in these behaviors. Both males and females of the genetically less stress-reactive WLI strain showed significantly increased immobility in the forced swim test (FST) after EA stress compared to controls. In contrast, immobility was significantly attenuated by EA stress in adult WMI females compared to controls. Transcriptomic changes of the glucocorticoid receptor (Nr3c1, GR) and the brain-derived neurotrophic factor (Bdnf) illuminate primarily strain and stress-dependent changes, respectively, in the prefrontal cortex and hippocampus of adults. These results suggest that contrary to expectations, limited adolescent stress is beneficial to males thru decreasing anxiety and enhancing social behaviors, and to the stress more-reactive WMI females by way of decreasing passive coping.

Glucose dynamics during ozone exposure measured using radiotelemetry: Stress drivers and human concordance

Background. Stress-related neurobehavioral and metabolic disorders are associated with altered circulating adrenal-derived hormones and hyperglycemia. Temporal assessment of glucose and these hormones is critical for insights on an individuals health. Objectives. Here we use implantable-telemetry in rats to assess real-time changes in circulating glucose during and after exposure to the air pollutant ozone, and link responses to circulating neuroendocrine stress and metabolic hormones. We also proposed to compare rodent glucose and corticosterone (cortisol in humans) responses to humans exposed to ozone. Methods. First, using a cross-over design, we monitored glucose levels during single or repeated ozone exposures (0.0, 0.2, 0.4 and 0.8-ppm) and non-exposure periods in male Wistar-Kyoto-rats implanted with glucose-telemeters. A second cohort of un-implanted rats was exposed to ozone (0.0, 0.4 or 0.8-ppm) for 30-min, 1-hour, 2-hour, or 4-hour with hormones measured immediately after exposure. Then we assessed glucose metabolism in sham and adrenalectomized rats with or without pharmacological interventions of adrenergic and glucocorticoid receptors. Finally, we assessed glucose and cortisol in serum samples form a clinical study involving exposure of human volunteers to air or 0.3 ppm ozone. Results. Ozone (0.8-ppm) caused hyperglycemia and hypothermia beginning 90-min into exposure, with reversal of effects 4-6 hours post-exposure. Glucose monitoring during four daily 4-hour ozone exposures revealed duration of hyperglycemia, adaptation, and diurnal variations. Ozone-induced hyperglycemia was preceded by increased adrenocorticotropic hormone, corticosterone, and epinephrine, but depletion of thyroid-stimulating, prolactin, and luteinizing hormones. Hyperglycemia was inhibited in rats that are adrenalectomized and/or treated with glucocorticoid inhibitor. There was coherence among rats and humans in ozone-induced corticosterone/cortisol increases. Discussion. We demonstrate for the first time the temporality of neuroendocrine-stress-mediated biological sequalae responsible for ozone-induced metabolic dysfunction as exposure occurs. Real-time glucose monitoring with stress hormones assessment may be useful in identifying interactions among pollutants and stress-related illnesses.

Differences in Distribution and Biological Effects of F3O4@PEG Nanoparticles in Normotensive and Hypertensive Rats—Focus on Vascular Function and Liver

We investigate the distribution and biological effects of polyethylene glycol (PEG)-coated magnetite (Fe3O4@PEG) nanoparticles (~30 nm core size, ~51 nm hydrodynamic size, 2 mg Fe/kg/day, intravenously, for two days) in the aorta and liver of Wistar–Kyoto (WKY) and spontaneously hypertensive rats (SHR). Fe3O4@PEG had no effect on open-field behaviour but reduced the blood pressure (BP) of Fe3O4@PEG-treated SHR (SHRu) significantly, compared to both Fe3O4@PEG-treated WKY (WKYu) and saline-treated control SHR (SHRc). The Fe3O4@PEG content was significantly elevated in the aorta and liver of SHRu vs. WKYu. Nitric oxide synthase (NOS) activity was unaltered in the aorta, but significantly increased in the liver of SHRu vs. SHRc. In the aorta, Fe3O4@PEG treatment increased eNOS, iNOS, NRF2, and DMT1 gene expression (considered main effects). In the liver, Fe3O4@PEG significantly elevated eNOS and iNOS gene expression in SHRu vs. SHRc, as well as DMT1 and FTH1 gene expression (considered main effects). Noradrenaline-induced contractions of the femoral arteries were elevated, while endothelium-dependent contractions were reduced in SHRu vs. SHRc. No differences were found in these parameters in WKY rats. In conclusion, the results indicated that the altered haemodynamics in SHR affect the tissue distribution and selected biological effects of Fe3O4@PEG in the vasculature and liver, suggesting that caution should be taken when using iron oxide nanoparticles in hypertensive subjects.

Evolution of Brain Morphology in Spontaneously Hypertensive and Wistar-Kyoto Rats From Early Adulthood to Aging: A Longitudinal Magnetic Resonance Imaging Study

The influence of hypertension and aging alone on brain structure has been described extensively. Our understanding of the interaction of hypertension with aging to brain morphology is still limited. We aimed to detect the synergistic effects of hypertension and aging on brain morphology and to describe the evolution patterns of cerebral atrophy from spatial and temporal perspectives. In 8 spontaneously hypertensive rats (SHRs) and 5 Wistar-Kyoto rats, high-resolution magnetic resonance imaging scans were longitudinally acquired at 10, 24, 52, and 80 weeks. We analyzed the tissue volumes of gray matter, white matter, cerebral spinal fluid, and total intracranial volume (TIV), and then evaluated gray matter volume in detail using voxel-based morphometry (VBM) and region of interest-based methods. There were interactive effects on hypertension and aging in tissue volumes of gray matter, white matter, and TIV, of which gray matter atrophy was most pronounced, especially in elderly SHRs. We identified the vulnerable gray matter volume with combined effects of hypertension and aging in the septal region, bilateral caudate putamen, hippocampus, primary somatosensory cortex, cerebellum, periaqueductal gray, right accumbens nucleus, and thalamus. We automatically extracted the septal region, anterior cingulate cortex, primary somatosensory cortex, caudate putamen, hippocampus, and accumbens nucleus and revealed an inverted-U trajectory of volume change in SHRs, with volume increase at the early phase and decline at the late phase. Hypertension interacts with aging to affect brain volume changes such as severe atrophy in elderly SHRs.

Sympathetic Nerve Activity and Baroreflex are Strongly Altered in a Context of Severe Hypertension Using the Spontaneously Hypertensive Rat Model Associated with Chronic Reduction of Nitric Oxide

The aim of our study is to investigate the sympathetic output and baroreflex via renal sympathetic nerve activity (RSNA) recording in a model of severe hypertension which exhibits arterial, cardiac, and renal damages, the spontaneously hypertensive rat (SHR) under lowered NO bioavailability. SHR are treated from 18 to 20 weeks of age with a low dose of L-NAME, a NO synthase inhibitor, in drinking water (SHRLN) and compared to SHR and normotensive Wistar Kyoto (WKY) rats. After the two-week treatment, rats are anesthetized for RSNA, mean blood pressure (MBP), and heart rate (HR) recording. MBP is higher in SHR than in WKY and higher in SHRLN than in SHR. Compared to WKY, SHR displays an alteration in the baroreflex with a displacement of the sympathoinhibition curve to highest pressures; this displacement is greater in SHRLN rats. The bradycardic response is reduced in SHRLN compared to both SHR and WKY. In hypertensive rats, SHR and SHRLN, basal RSNA is modified, the maximal amplitude of burst is reduced, but minimal values are increased, indicating an increased basal RSNA with reduced bursting activity. The temporal correlation between RSNA and HR is preserved in SHR but altered in 10 SHRLN out of 10. The RSNA inhibition triggered by the Bezold–Jarisch reflex activation is not modified in hypertensive rats, SHR or SHRLN, in contrast to that triggered by the baroreflex. Histological analysis of the carotid bifurcation does not reveal any abnormality in SHRLN at the level of the carotid sinus. In conclusion, data indicate that the sympathetic outflow is altered in SHRLN with a strong reduction of the baroreflex sympathoinhibition and suggest that its central pathway is not involved. These additional results on SHRLN also confirm the usefulness of this model of severe hypertension with multiple target organ damages.

Renal AT 2 Receptors Mediate Natriuresis via Protein Phosphatase PP2A

Background: How signals from activated angiotensin type-2 receptors (AT 2 R) mediate inhibition of sodium ion (Na+) reabsorption in renal proximal tubule cells (RPTCs) is currently unknown. Protein phosphatases including protein phosphatase 2A (PP2A) have been implicated in AT2R signaling in tissues other than kidney. We investigated whether inhibition of protein phosphatase PP2A reduced AT 2 R-mediated natriuresis and evaluated changes in PP2A activity and localization after renal AT 2 R activation in normal 4- and 10-week-old control Wistar-Kyoto rats (WKY) and 4-week-old pre-hypertensive and 10-week-old hypertensive spontaneously hypertensive rats (SHR). Methods and Results: In WKY, direct renal interstitial (RI) administration of selective AT 2 R non-peptide agonist Compound-21 (C-21) increased RI cyclic GMP (cGMP) levels, urine Na + excretion (U Na V), and simultaneously increased PP2A activity ≅ 2-fold in homogenates of renal cortical tubules. The cGMP and natriuretic responses were abolished by concurrent RI administration of protein phosphatase inhibitor calyculin A (CAL). In RPTCs in response to C-21, PP2A subunits A, B55α and C, but not B56γ, were recruited to apical plasma membranes together with AT 2 Rs. CAL treatment abolished C-21-induced translocation of both AT 2 R and PP2A regulatory subunit B55α to apical plasma membranes. Immunoprecipitation of AT 2 R solubilized from renal cortical homogenates demonstrated physical association of AT 2 R with PP2A A, B55α, and C but not B56γ subunits. In contrast, in SHR, administration of C-21 did not alter UNaV or PP2A activity and failed to translocate AT 2 Rs and PP2A subunits to apical plasma membranes. Conclusions: In RPTCs of WKY, PP2A is activated and PP2A subunits AB55αC are recruited to C-21-activated AT 2 Rs during induction of natriuresis. This response is defective in pre-hypertensive and hypertensive SHR, presenting a potential novel therapeutic target for treating renal Na+ retention and hypertension.

Skeletal myopathy in a rat model of postmenopausal heart failure with preserved ejection fraction

Heart failure with preserved ejection fraction (HFpEF) accounts for ~50% of all patients with heart failure and frequently affects postmenopausal women. The HFpEF condition is phenotype-specific, with skeletal myopathy that is crucial for disease development and progression. However, most of the current preclinical models of HFpEF have not addressed the postmenopausal phenotype. We sought to advance a rodent model of postmenopausal HFpEF and examine skeletal muscle abnormalities therein. Female, ovariectomized, spontaneously hypertensive rats (SHR) were fed a high fat, high sucrose diet to induce HFpEF. Controls were female sham-operated Wistar-Kyoto rats on a lean diet. In a complementary, longer-term cohort, controls were female sham-operated SHRs on a lean diet to evaluate the effect of strain difference in the model. Our model developed key features of HFpEF that included increased body weight, glucose intolerance, hypertension, cardiac hypertrophy, diastolic dysfunction, exercise intolerance, and elevated plasma cytokines. In limb skeletal muscle, HFpEF decreased specific force by 15-30% (p < 0.05) and maximal mitochondrial respiration by 40-55% (p < 0.05), increased oxidized glutathione by ~2-fold (p < 0.05), and tended to increase mitochondrial H2O2 emission (p = 0.10). Muscle fiber cross-sectional area, markers of mitochondrial content, and indices of capillarity were not different between control and HFpEF in our short-term cohort. Overall, our model of postmenopausal HFpEF recapitulates several key features of the disease. This new model reveals contractile and mitochondrial dysfunction and redox imbalance that are potential contributors to abnormal metabolism, exercise intolerance, and diminished quality of life in patients with postmenopausal HFpEF.