HT Rats Research Articles

Potential antihypertensive activity of novel peptides from green basil leaves

Hypertension is among the risk factors of death globally. Novel antihypertensive peptides are alternative choices of antihypertensive assistance. This study aimed to discover novel antihypertensive peptides from green basil leaves. Two bioactive peptides with high angiotensin-converting enzyme inhibition (Asp-Leu-Ser-Ser-Ala-Pro; peptide 1) and antioxidant (Asp-Ser-Val-Ser-Ala-Ser-Pro; peptide 2) activities were gavaged to male Wistar rats induced with NG-nitro-l-arginine methyl-ester (L-NAME). L-NAME-treated rats (HT) had decreased body weights and levels of nitrite and nitrate, which are metabolites of nitric oxide. The levels of their glucose and liver function indicators increased as compared to normal rats. HT rats receiving antihypertensive drugs (HTD) showed higher low-density lipoprotein and low-density lipoprotein/high-density lipoprotein levels than HT rats. Peptide 1 seems to benefit the rat lipid profiles, liver functions, antioxidant, nitrite, nitrate, and angiotensin II peptide levels but not peptide 2. In conclusion, our findings indicate the antihypertensive potential related to vasodilation of peptides from green basil leaves.Graphical

Activation of the NLRP3/IL-1β/MMP-9 pathway and intracranial aneurysm rupture associated with the depletion of ERα and Sirt1 in oophorectomized rats.

Subarachnoid hemorrhage (SAH) due to intracranial aneurysm (IA) rupture is often a devastating event. Since the incidence of SAH increases especially in menopause, it is crucial to clarify the detailed pathogenesis of these events. The activation of vascular nucleotide-binding oligomerization domain-like receptor family pyrin domain-containing 3 (NLRP3) inflammasomes has been studied in ischemic stroke and cardiovascular disease. However, the role of NLRP3 in IA rupture still needs to be explained. The authors sought to test their hypothesis that, under estrogen-deficient conditions, activation of NLRP3 inflammasomes via downregulation of the estrogen receptor (ER) facilitates IA rupture. Ten-week-old female Sprague Dawley rats with and without oophorectomy were subjected to hemodynamic changes and hypertension (OVX+/HT and OVX-/HT, respectively) and fed a high-salt diet. Separately, using human brain endothelial cells (HBECs) and human brain smooth muscle cells (HBSMCs), the authors tested the effect of NLRP3 under estrogen-free conditions and in the presence of estradiol or of ER agonists. In OVX+/HT rats, the frequency of IA rupture was significantly higher than in OVX-/HT rats (p = 0.03). In the left posterior cerebral artery prone to rupture in OVX+/HT rats, the levels of the mRNAs encoding ERα and Sirt1, but not of that encoding ERβ, were decreased, and the levels of the mRNAs encoding NLRP3, interleukin-1β (IL-1β), and matrix metalloproteinase 9 (MMP-9) were elevated. Immunohistochemical analysis demonstrated that the expression profiles of these proteins correlated with their mRNA levels. Treatment with an ER modulator, bazedoxifene, normalized the expression profiles of these proteins and improved SAH-free survival. In HBECs and HBSMCs under estrogen-free conditions, the depletion of ERα and Sirt1 and the accumulation of NLRP3 were counteracted by exposure to estradiol or to an ERα agonist but not to an ERβ agonist. To the authors' knowledge, this work represents the first demonstration that, in an aneurysm model under estrogen-deficient conditions, the depletion of ERα and Sirt1 may contribute to activation of the NLRP3/IL-1β/MMP-9 pathway, facilitating the rupture of IAs in the estrogen-deficient rat IA rupture model.

In vivo Molecular Imaging Stratifies Rats with Different Susceptibilities to Hyperoxic Acute Lung Injury

ObjectivesAcute Respiratory Distress Syndrome (ARDS) is one of the most frequent causes of admission to medical intensive care units. It carries a mortality rate >30%, due to lack of early detection tools, inability to identify patients at risk for progression, and limited therapies. Previously, we demonstrated the utility of 99mTc‐hexamethylpropyleneamine oxime (HMPAO) and 99mTc‐duramycin in vivo imaging to detect oxidative stress and endothelial cell death in rats exposed to 100% O2 (hyperoxia) as a model of human ARDS. Pre‐exposure to hyperoxia for 48 hrs followed by 24 hr in room air (H‐T) protects against ARDS in that, when subsequently re‐exposed to hyperoxia, rats are tolerant of and survive the otherwise lethal effects of hyperoxia. Thus, the objective of this study was to evaluate the ability of 99mTc ‐HMPAO and ‐duramycin to track the protection of hyperoxia pre‐exposure and to identify mechanisms involved as potential therapeutic targets.MethodsSprague‐Dawley rats were exposed to either room air, hyperoxia (100% O2) for 60 hr, hyperoxia for 48 hr followed by 24 hr of room air (H‐T), or H‐T followed by 60 hr of hyperoxia (H‐T+60). Rats were anesthetized and imaged using either 99mTc‐HMPAO or 99mTc‐duramycin (37‐74 MBq) (n=4‐6 per group). In vivo scintigraphy images were acquired 20 min post i.v. injection and lung uptake was determined from the images as mean lung activity normalized to mean forelimb blood activity. Rat lung endpoints including wet‐to‐dry weight ratio, volume of pleural effusion in the chest cavity, expression of 3‐nitrotyrosine (3NT), and histological H&E and cleaved caspase 3 positive‐cells (apoptosis marker) were also measured as indices of injury/protection.ResultsLung 99mTc‐HMPAO uptake increased by 200% in hyperoxia‐exposed rats, whereas uptake in H‐T+60 rats was 24% less than in H‐T rats. Lung uptake of 99mTc‐duramycin increased by 167% in hyperoxia‐exposed rats, but uptake in H‐T+60 rats was only 17% greater than H‐T rats. Lung wet/dry weight ratio increased by 21% in hyperoxia‐exposed rats, but by only 15% in H‐T+60 versus HT rats. Similarly, pleural effusion was reduced significantly (66%) in the H‐T+60 rats compared to the hyperoxia rats. 3NT expression, as a measure of oxidative stress, was increased ~300% with hyperoxia, but no significant increase was detected in H‐T+60 rats compared to H‐T. Histological analysis indicates that neutrophilic influx, edema, and apoptotic cells were increased with hyperoxia, but this increase was small or not observed with H‐T+60.ConclusionsLung uptake of 99mTc‐HMPAO and 99mTc‐duramycin, reflecting oxidative stress and cell death, respectively, is reduced significantly in rats preconditioned to tolerate hyperoxia compared to those without the preconditioning. This tolerance is also reflected in lung functional and histological endpoints measured independently. Overall these results suggest the potential utility of 99mTc‐HMPAO and 99mTc‐ duramycin imaging as a tool for identifying those hosts that are more or less susceptible to progressing to severe ARDS following mild symptoms of lung injury.

A Blunted Sympathetic Function and an Enhanced Nitrergic Activity Contribute to Reduce Mesenteric Resistance in Hyperthyroidism.

We aimed to determine whether an experimental model of hyperthyroidism could alter the function of sympathetic and nitrergic components of mesenteric innervation. For this purpose, male Wistar rats were divided into (1) control rats (CT) and (2) rats infused with L-Thyroxine (HT). Body weight gain and adipose tissue accumulation were lower in HT rats, while systolic blood pressure and citrate synthase activity in the soleus muscle were increased by HT. In segments from the superior mesenteric artery, the application of an electrical field stimulation (EFS) induced a vasoconstrictor response, which was lower in arteries from HT animals. The alpha-adrenoceptor antagonist phentolamine diminished EFS-induced vasoconstriction to a lower extent in HT arteries, while the purinergic receptor antagonist suramin reduced contractile response to EFS only in segments from CT. In line with this, noradrenaline release, tyrosine hydroxylase expression and activation and dopamine β hydroxylase expression were diminished in HT. The unspecific nitric oxide synthase (NOS) inhibitor L-NAME increased EFS-induced vasoconstriction more markedly in segments from HT rats. NO release was enhanced in HT, probably due to an enhancement in neuronal NOS activity, in which a hyperactivation of both PKC and PI3K-AKT signaling pathways might play a relevant role. In conclusion, perivascular mesenteric innervation might contribute to reduce the vascular resistance observed in hyperthyroidism.

Влияние электромагнитных излучений на ориентировочно-исследовательскую активность и когнитивные функции крыс с контрастной возбудимостью нервной системы

In recent years, the mechanisms of influence that technogenic sources of electromagnetic radiation and the change in the natural electromagnetic field have on biological objects have been actively investigated. Nevertheless, the role of ancestral conditional characteristics of the nervous system in susceptibility towards and resilience against electromagnetic field oscillations has been virtually ignored. The objective of our research is to investigate the impact of the UHF band radiation emitted by a standard Wi-Fi router and the impact of external magnetic and electric fields weakened by shielding on animals’ innate behaviour which reflects orientational and exploratory activity and emotional response in an Open Field Test, and also on the cognitive functions (retention of the conditioned response of passive avoidance) of male rats from two selected strains: HT and LT — with high and low thresholds of nervous system excitability, and control Wistar rats. The outcomes of the study confirm the negative impact of weak external electric and magnetic fields, as well as EMR of the UHF band, on innate behaviour and memory in rats regardless of the selected strain, although HT rats were more sensitive to changes in magnetic and electric fields and electromagnetic radiation in comparison with LT rats.

Red palm oil supplementation does not increase blood glucose or serum lipids levels in Wistar rats with different thyroid status.

Red palm oil (RPO) is a rich natural source of antioxidant vitamins, namely carotenes, tocopherols and tocotrienols. However, it contains approximately 50 % saturated fatty acids the regular consumption of which could negatively modify lipid profile. The aim of our study was to test whether 7 weeks of RPO supplementation (1 g/kg body weight/day) would affect blood glucose and lipid metabolism in adult male Wistar rats with altered thyroid status. We induced hypothyroidism and hyperthyroidism in rats by oral administration of either methimazole or mixture of thyroid hormones. Different thyroid status (EU - euthyroid, HY - hypothyroid and HT - hyperthyroid) was characterized by different serum thyroid hormones levels (total and free thyroxine and triiodothyronine), changes in the activity of a marker enzyme of thyroid status - liver mitochondrial glycerol-3-phosphate dehydrogenase, and altered absolute and relative heart weights. Fasting blood glucose levels were higher in HT rats in comparison with EU and HY rats, but the changes caused by RPO supplementation were not significant. The achievement of the HY status significantly increased serum levels of total cholesterol, as well as with high-density lipoprotein-cholesterol and low-density lipoprotein-cholesterol: 2.43+/-0.15, 1.48+/-0.09, 0.89+/-0.08 mmol/l, compared to EU: 1.14+/-0.06, 0.77+/-0.06, 0.34+/-0.05 mmol/l and HT: 1.01+/-0.06, 0.69+/-0.04, 0.20+/-0.03 mmol/l, respectively. RPO supplementation did not increase significantly levels of blood lipids but tended to increase glutathione levels in the liver. In conclusion, RPO supplementation did not induce the presumed deterioration of glucose and lipid metabolism in rats with three well-characterized alterations in thyroid status.

Therapeutic mild hypothermia improves early outcomes in rats subjected to severe sepsis

AimsTherapeutic hypothermia has shown beneficial effects in sepsis. This study focused on its mechanism. Main methodsSixteen male Sprague-Dawley rats underwent cecal ligation and perforation and subsequently were treated with either hypothermia (HT; body temperature cooled and maintained at 34 °C by ice pad for 10 h; n = 8) or normothermia (NT; n = 8). Three additional rats underwent sham surgery. The body temperatures of the sham-operated and NT groups were maintained at 38 °C with a thermal pad. After the hypothermia treatment, the HT rats were rewarmed for 2 h. The groups were compared for circulating cytokines (IL-6, IL-10), lactate, high mobility group box-1 protein (HMGB1), and lung and intestinal lesions. Animals were observed for 24 h. Key findingsCompared with the sham-operated group, the 2 sepsis group rats had significantly higher circulating IL-6, HMGB1, and lactate levels, and tissue injury. In the HT rats, the levels of IL-6, HMGB1, and lactate, the lung wet-to-dry ratio, and lung and intestinal damage were significantly lower than that of the NT group. Circulating IL-10 levels increased significantly after 12 h in the sepsis groups compared with sham animals, while that of the NT and HT groups were comparable. The survival rates of the NT and HT rats were also comparable. SignificanceTherapeutic hypothermia in a rat model of sepsis was associated with lower levels of circulating IL-6 and HMGB1, and less capillary leakage and tissue edema. These results suggest that mild hypothermia has potential as a therapy in sepsis.

Bazedoxifene, a selective estrogen receptor modulator, reduces cerebral aneurysm rupture in Ovariectomized rats

BackgroundEstrogen deficiency is thought to be responsible for the higher frequency of aneurysmal subarachnoid hemorrhage in post- than premenopausal women. Estrogen replacement therapy appears to reduce this risk but is associated with significant side effects. We tested our hypothesis that bazedoxifene, a clinically used selective estrogen receptor (ER) modulator with fewer estrogenic side effects, reduces cerebral aneurysm rupture in a new model of ovariectomized rats.MethodsTen-week-old female Sprague-Dawley rats were subjected to ovariectomy, hemodynamic changes, and hypertension to induce aneurysms (ovariectomized aneurysm rats) and treated with vehicle or with 0.3 or 1.0 mg/kg/day bazedoxifene. They were compared with sham-ovariectomized rats subjected to hypertension and hemodynamic changes (HT rats). The vasoprotective effects of bazedoxifene and the mechanisms underlying its efficacy were analyzed.ResultsDuring 12 weeks of observation, the incidence of aneurysm rupture was 52% in ovariectomized rats. With no effect on the blood pressure, treatment with 0.3 or 1.0 mg/kg/day bazedoxifene lowered this rate to 11 and 17%, almost the same as in HT rats (17%). In ovariectomized rats, the mRNA level of ERα, ERβ, and the tissue inhibitor of metalloproteinase-2 was downregulated in the cerebral artery prone to rupture at 5 weeks after aneurysm induction; the mRNA level of interleukin-1β and the matrix metalloproteinase-9 was upregulated. In HT rats, bazedoxifene restored the mRNA level of ERα and ERβ and decreased the level of interleukin-1β and matrix metalloproteinase-9. These findings suggest that bazedoxifene was protective against aneurysmal rupture by alleviating the vascular inflammation and degradation exacerbated by the decrease in ERα and ERβ.ConclusionsOur observation that bazedoxifene decreased the incidence of aneurysmal rupture in ovariectomized rats warrants further studies to validate this response in humans.

Decreases in 15-lipoxygenase metabolites in Olmsted syndrome model rats

BackgroundOlmsted syndrome (OS) is a congenital dermatosis characterized by palmoplantar keratoderma and periorificial keratotic plaque. TRPV3 (transient receptor potential vanilloid subtype 3) encodes a thermosensitive Ca2+ channel and is the causative gene of OS. However, the molecular mechanism that causes the pathological development of OS is unclear. ObjectiveWe aimed to investigate the molecular mechanisms underlying OS pathology from the perspective of lipid metabolism. MethodsComprehensive lipidomics and microarray analyses were conducted on tissue samples from a non-lesional skin area of OS model rats (Ht rats) and from wild type (WT) rats as the control. ResultsInfiltration of leukocytes such as eosinophils and neutrophils and an increase in the fibrotic region were detected in the unaffected skin area of Ht rats compared with the WT rats. Among about 600 lipid species examined, the levels of 15-lipoxygenase (LOX) metabolites, the precursors of anti-inflammatory and pro-resolving lipid mediators, and dihydroceramides decreased by ≥16-fold in Ht rats compared with WT rats. Consistent with the decreases in the 15-LOX metabolites, expression levels of the genes that encode the 15-LOXs, Alox15 and Alox15b, were largely reduced. Conversely, increased expression levels were detected of Il36b, Ccl20, Cxcl1, and Cxcl2, which encode cytokines/chemokines, and S100a8 and S100a9, which encode the Ca2+ binding proteins that are implicated in epidermal proliferation. ConclusionThe pro-inflammatory state in the unaffected skin of Ht rats caused by decreases in 15-LOX metabolites and increases in cytokines/chemokines may contribute to the pathogenesis of OS.

Involvement of the Median Preoptic Nucleus in the arterial blood pressure regulation

Studies have been shown that Median Preoptic Nucleus (MnPO) neurons have a great influence in the cardiovascular responses induced by changes in circulating volume. The present study sought to determine the participation of MnPO in the cardiovascular control. Male Wistar normotensive (NT) and spontaneously hypertensive (SH) rats (280–320g) were anesthetized with urethane (1.2 g/kg, i.v.) and instrumented for mean arterial blood pressure (MAP) and renal blood flow (RBF) recordings. Renal vascular conductance (RVC) was calculated as the ratio RBF/MAP and expressed as percentage of baseline. In NT rats (n=7), inhibition of MnPO nucleus produced a significant hypotension (−7 ± 1.5 mmHg) and renal vasodilation (5.3 ± 1.2% above baseline). In SH rats (n=8), hypotension response was significantly greater (−15 ± 2.7 mmHg, p<0.05) than NT rats. We also observed an increase of RVC (8.4 ± 2.4% above baseline) in HT rats. Analysis of the spread of dye nanoinjected at the end of the experiment showed that the drug injection sites were confined to the MnPO. We conclude that the MnPO nucleus is involved in the tonic regulation of blood pressure in NT rats. Moreover, the increase of neuronal activity in the MnPO may contribute to sympathoexcitation and maintenance of hypertension in SH rats. Supported by CNPq (477832/2010‐5; GRP).

Cytokines in the Hypothalamic Paraventricular Nucleus (PVN) are Not Required for Maintenance of Angiotensin II‐Salt Hypertension

Rats consuming high salt and treated with systemic angiotensin II (Ang II) develop neurogenic hypertension mediated by elevation of sympathetic nerve activity (SNA) derived from a forebrain‐hypothalamic circuit. Cytokines are proposed to increase SNA and arterial blood pressure (ABP) and we therefore sought to determine their role within PVN in maintenance of AngII+salt hypertension. We first focused on tumor necrosis factor α (TNFα), which was microinjected into the PVN (0.3 pmol in 50 nl/side) of anesthetized normotensive (NT, 0.4% NaCl diet, n=10) rats. Although this increased lumbar SNA (18±7%), splanchnic SNA (49±9%) and mean ABP (4±2 mmHg) compared to vehicle (P<0.05), interfering with TNFα binding by PVN injection of etanercept (20 μg in 100 nl/side) did not affect recorded variables either in NT rats or in Ang II (150 ng/kg/min, sc) + salt (2% NaCl diet) hypertensive (HT, n=12) rats. Given this apparent lack of TNFα “tone” in PVN, we next non‐selectively inhibited local cytokine release by microinjection of minocycline (1 μg in 100 nl/side). This too failed to alter lumbar SNA (HT: 13±9% vs NT: 0±3%), splanchnic SNA (HT: 12±4% vs NT: 6±2%) or mean ABP (HT: 3±2 mmHg vs NT: −1±1 mmHg) in NT or HT rats. These findings indicate that whereas TNFα can act in PVN to increase SNA; maintenance of Ang II‐salt hypertension does not depend on either PVN actions of TNFα or microglia derived cytokines. Support: HL102310 & HL 088052 (GMT)

Hypoxic training increases metabolic enzyme activity and composition of α-myosin heavy chain isoform in rat ventricular myocardium

Cardiac muscle adaptation is essential for maintaining physical capacity after ascending to high altitude. This study examines the effects of high altitude training on myocardial metabolic enzyme activity and composition of alpha-myosin heavy chain (MHC). Rats were randomly divided into normobaric sedentary (NS) and training (NT) groups, and hypobaric sedentary (HS) and training (HT) groups. HS and HT rats were exposed to hypobaric hypoxia (simulated 4,000-5,000 m) for 5 weeks (24 h/day), and HT rats simultaneously received swim training. Hypoxia exposure for 5 weeks led to a decrease in succinate dehydrogenase (SDH) and citrate synthase (CS) activities in the left ventricle (LV), and a decrease in CS, hexokinase (HK) and total lactate dehydrogenase (LDH) activities in the right ventricle (RV) (p < 0.05, HS vs. NS). Furthermore, 1 h/day swim training during hypoxia exposure enhanced the CS activity in LV and the SDH and CS activities in RV (p < 0.05, HT vs. HS). The percentages of alpha-MHC in both ventricles in HT were higher than those in HS (p < 0.05). We conclude that exercise training at high altitude is beneficial for cardiac muscle adaptation to hypoxia by increasing activities of enzymes and percentage of alpha-MHC. This may contribute to improved cardiac function and work capacity at high altitude.

Biomechanical performance of diaphyseal shafts and bone tissue of femurs from hypothyroid rats

The bone changes in hypothyroidism are characterized by a low bone turnover with a reduced osteoid apposition and bone mineralization rate, and a decreased osteoclastic resorption in cortical bone. These changes could affect the mechanical performance of bone. The evaluation of such changes was the object of the present investigation. Hypothyroidism was induced in female rats aged 21 days through administration of propylthiouracil in the drinking water for 70 days (HT group). Controls were untreated rats (C group). Right femur mechanical properties were tested in 3-point bending. Structural (load bearing capacity and stiffness), geometric (cross-sectional area and moment of inertia) and material (modulus of elasticity) properties were evaluated. The left femur was ashed for calcium content determination. Plasma T(4) concentration was significantly decreased in HT rats. Body and femur weight and length in HT rats were also reduced. Femoral calcium concentration in ash was higher in HT than in C rats. However, the femoral calcium mass was significantly lower in HT than in C rats because of the reduced femoral size seen in the former. The stiffness of bone material was higher in HT than in C rats, while the bone geometric properties were significantly lower. The "load capacity" was between 30 and 50% reduced in the HT group, although, the differences disappeared when the values were normalized per 100-g body weight. The lowered biomechanical ability observed in the femoral shafts of HT rats seems to be the expression of a diminished rate of growth. Qualitative alterations in the intrinsic mechanical properties of bone tissue were observed in HT rats, probably because the mineral content and the modulus of elasticity were positively affected. The cortical bone of the HT rat thus appears as a bone with a higher than normal strength and stiffness relative to body weight, probably due to improvement of bone material quality due to an increased matrix calcification.

DECREASED SMALL CONDUCTANCE, CALCIUM‐ACTIVATED POTASSIUM (SK) CURRENT UNDERLIES INCREASED EXCITABILITY OF PVN‐RVLM NEURONS AND SYMPATHOEXCITATION IN ANG II‐SALT HYPERTENSIVE (HT) RATS

A neural mechanism responsible for sympathoexcitation in HT rats was investigated. We hypothesized that reduced SK current in PVN neurons projecting to RVLM (PVN‐RVLM) could contribute to increased excitability and sympathetic outflow in HT rats. In voltage‐clamp recordings, the amplitude of SK current in neurons from HT rats (12±6 pA, n=5) was significantly (p&lt;0.01) less than that from neurons of normotensive (NT) rats (73±12 pA, n=5). In current‐clamp recordings, graded current injections evoked graded increases in discharge frequency. Maximum discharge was evoked by +200 pA injections in neurons from HT rats (47±5 Hz, n=10). This response was significantly greater (P&lt;0.001) than that of neurons from NT rats (25±2 Hz, n=10). The SK channel blocker UCL1684 (100 nM) significantly increased (p&lt;0.05) discharge in neurons from NT rats (39±4 Hz, n=6), but had no effect on neurons from HT rats (46±2 Hz, n=10). The contribution of SK channel activity in regulating ongoing sympathetic activity was assessed by microinjecting UCL1684 into the PVN of anesthetized rat. UCL1684 significantly (P&lt;0.05) increased RSNA by 58±14 % and MAP by 10±1 mmHg in NT rats (n=4), but was without effect in HT rats (n=4). We conclude that increased excitability of PVN‐RVLM neurons may contribute to sympathoexcitation and maintenance of hypertension. Reduced SK current in these neurons may constitute an underlying neural mechanism. Support: AHA0865107F (QHC) &amp; HL076312 (GMT)

Cytogenesis in the dentate gyrus after neonatal hyperthermia‐induced seizures: What becomes of surviving cells?

Febrile seizures (FS) are early-life seizures thought to play a role in epileptogenesis. By labeling cells that were dividing immediately following experimental FS, we previously demonstrated that significantly more of these newborn cells in the dentate gyrus (DG) survived 8 weeks later, relative to animals that did not experience FS. The purpose of the present study was to determine the long-term fate of these newborn cells. On postnatal day (PN) 10, hyperthermia-induced seizures (HT, +/-42 degrees C core temperature) were evoked in Sprague-Dawley rats and littermates were used as normothermia controls (NT, +/-35 degrees C core temperature). From PN11 to PN16, rats were injected with bromodeoxyuridine (BrdU) to label dividing cells. At PN66, we evaluated the number of BrdU-labeled cells in the DG that colocalized with the neuronal marker NeuN, glial marker glial fibrillary acidic protein (GFAP), neuronal excitatory amino acid transporter 3 (EAAT3), GABAergic neuronal marker glutamic acid decarboxylase 67 (GAD67) or microglia marker tomato lectin (TL). In all rats, almost all BrdU-labeled cells in the DG, that showed double-labeling, colocalized with NeuN, and rarely with GFAP, GAD67, or TL. In NT controls and HT rats that did not experience seizures ("HT-no seizures"), approximately 23% of BrdU-labeled cells colocalized with EAAT3, which was significantly different from 14% in HT rats that did experience seizures (HT + FS). Early-life seizures decrease the population of newborn cells that survive and mature into EAAT3-positive neurons and do not affect the GABAergic cell population. This may affect hippocampal physiology in young adulthood.

Ultrastructural Immunolocalization of Cartilage Oligomeric Matrix Protein, Thrombospondin-4, and Collagen Fibril Size in Rodent Achilles Tendon in Relation to Exercise

Fourteen 3-week-old Sprague-Dawley rats were housed in pairs in standard cages (5 controls) and in individual cages with a running wheel. Four of these rats had run 27–36 km/week (low training—LT) and 5 had run 56–92 km/week (high training—HT). After 4 weeks, the rats were euthanized and Achilles tendons were fixed for electron microscopy. The ultrastructural distribution of cartilage oligomeric matrix protein (COMP) and thrombospondin (TSP)-4 and collagen fibril thickness in two different extracellular compartments were studied. The immunolabeling of COMP decreased with longer running distance and was significantly lower in both the pericellular (p = 0.009) and interterritorial (p = 0.03) compartments of the HT rats compared with the controls. TSP-4 immunolabeling was higher in the pericellular compared with the interterritorial compartments in all rats (p = 0.013) but was not correlated with COMP immunolabeling. No alterations in collagen fibril size were found in relation to running; however, the gold markers representing COMP and TSP-4 were mostly found at the dark bands, representing the gap region of the fibril.

Effects of high-altitude exercise training on contractile function of rat skinned cardiomyocyte

Previous studies have questioned whether there is an improved cardiac function after high-altitude training. Accordingly, the present study was designed specifically to test whether this apparent blunted response of the whole heart to training can be accounted for by altered mechanical properties at the cellular level. Adult rats were trained for 5 weeks under normoxic (N, NT for sedentary and trained animals, respectively) or hypobaric hypoxic (H, HT) conditions. Cardiac morphology and function were evaluated by echocardiography. Calcium Ca2+ sensitivity of the contractile machinery was estimated in skinned cardiomyocytes isolated from the left ventricular (LV) sub-epicardium (Epi) and sub-endocardium (Endo) at short and long sarcomere lengths (SL). Cardiac remodelling was harmonious (increase in wall thickness with chamber dilatation) in NT rats and disharmonious (hypertrophy without chamber dilatation) in HT rats. Contrary to NT rats, HT rats did not exhibit enhancement in global cardiac performance evaluated by echocardiography. Stretch- dependent Ca2+ sensitization of the myofilaments (cellular index of the Frank-Starling mechanism) increased from Epi to Endo in N rats. Training in normoxic conditions further increased this stretch-dependent Ca2+ sensitization. Chronic hypoxia did not significantly affect myofibrilar Ca2+ sensitivity. In contrast, high-altitude training decreased Ca2+ sensitivity of the myofilaments at both SL, mostly in Endo cells, resulting in a loss of the transmural gradient of the stretch-dependent Ca2+ sensitization. Expression of myosin heavy chain isoforms was affected both by training and chronic hypoxia but did not correlate with mechanical data. Training at sea level increased the transmural gradient of stretch-dependent Ca2+ sensitization of the myofilaments, accounting for an improved Frank-Starling mechanism. High-altitude training depressed myofilament response to Ca2+, especially in the Endo layer. This led to a reduction in this transmural gradient that may contribute to the lack of improvement in LV function via the Frank-Starling mechanism.

Exercise training improves lung gas exchange and attenuates acute hypoxic pulmonary hypertension but does not prevent pulmonary hypertension of prolonged hypoxia

Our laboratory has previously shown an attenuation of hypoxic pulmonary hypertension by exercise training (ET) (Henderson KK, Clancy RL, and Gonzalez NC. J Appl Physiol 90: 2057-2062, 2001), although the mechanism was not determined. The present study examined the effect of ET on the pulmonary arterial pressure (Pap) response of rats to short- and long-term hypoxia. After 3 wk of treadmill training, male rats were divided into two groups: one (HT) was placed in hypobaric hypoxia (380 Torr); the second remained in normoxia (NT). Both groups continued to train in normoxia for 10 days, after which they were studied at rest and during hypoxic and normoxic exercise. Sedentary normoxic (NS) and hypoxic (HS) littermates were exposed to the same environments as their trained counterparts. Resting and exercise hypoxic arterial P(O2) were higher in NT and HT than in NS and HS, respectively, although alveolar ventilation of trained rats was not higher. Lower alveolar-arterial P(O2) difference and higher effective lung diffusing capacity for O2 in NT vs. NS and in HT vs. HS suggest ET improved efficacy of gas exchange. Pap and Pap/cardiac output were lower in NT than NS in hypoxia, indicating that ET attenuates the initial vasoconstriction of hypoxia. However, ET had no effect on chronic hypoxic pulmonary hypertension: Pap and Pap/cardiac output in hypoxia were similar in HS vs HT. However, right ventricular weight was lower in HT than in HS, although Pap was not different. Because ET attenuates the initial pulmonary vasoconstriction of hypoxia, development of pulmonary hypertension may be delayed in HT rats, and the time during which right ventricular afterload is elevated may be shorter in this group. ET effects may improve the response to acute hypoxia by increasing efficacy of gas exchange and lowering right ventricular work.

Attention-deficit and hyperactive neurobehavioural characteristics induced by perinatal hypothyroidism in rats

Thyroid hormone is essential for the proper development of the mammalian central nervous system (CNS). In the present study, we examined behavioural alterations caused by transient perinatal hypothyroidism induced by an anti-thyroid drug, propylthiouracil (PTU). This drug produces perinatal disruption of the thyroid system and subsequent behavioural changes, which we investigated using a series of behavioural tests and focusing particularly on attention-deficit/hyperactivity disorder (ADHD)-like behaviours. In the open field test, both male and female rats that had experienced perinatal hypothyroidism (HT rats) showed an increased percent of locomotion behaviour and reduced grooming behaviour, suggesting that HT rats may be hyperactive and show fewer anxiety characteristics. Neither male nor female HT rats showed retention in the passive avoidance test. Male HT rats showed a significantly lower rate of correct avoidance responses than control rats in earlier sessions in the active avoidance test. In addition, we observed significant increases in the number of times that rats crossed the partition during inter-trial intervals and the percent of failure of avoidance during 5 s electrical stimuli in HT rats, suggesting that HT rats are restless, have a shortened attention span and panic easily. In measuring spontaneous motor activity during a period of darkness, male HT rats appeared to plunge into active phase with short, quick steps, while male control rats showed only long active phases during a stress-free period of darkness. These abnormal behavioural characteristics in HT rats might coincide with those found in some cases of ADHD.

Responses to GABA(A) receptor activation are altered in NTS neurons isolated from renal-wrap hypertensive rats.

The inhibitory amino acid GABA is a potent modulator of the spontaneous discharge and the responses to afferent inputs of neurons in the nucleus of the solitary tract (NTS). To determine if responses to activation of GABA(A) receptors are altered in hypertension, GABA(A) receptor-evoked whole cell currents were measured in enzymatically dispersed NTS neurons from 33 normotensive (NT, 109+/-4 mm Hg, n=7) and 24 hypertensive (HT, 167+/-5 mm Hg, n=24) rats. GABA(A) receptor-evoked currents reversed at the calculated equilibrium potential for chloride and were blocked by bicuculline (n=6). Membrane capacitance was the same in neurons from NT (7.5+/-0.6 pF, n=62) and HT (6.8+/-0.6 pF, n=51) rats. The EC50 for peak GABA-evoked currents cells was significantly greater in neurons from HT (21.0+/-2.6 micromol/L, n=16) compared with NT rats (13.0+/-1.8 micromol/L, n=14, P=0.01). The EC50 of neurons exhibiting DiA labeling of presumptive aortic nerve terminals was no different than that observed in the nonlabeled cells (19.0+/-4.9 micromol/L, n=4). The time constant for desensitization of GABA(A)-evoked currents was the same in neurons from HT (4.5+/-0.3 seconds, n=17) and NT rats (3.8+/-0.3 seconds, n=17, P>0.05). Repetitive pulse application of GABA revealed a more rapid decline in the evoked current in neurons from HT compared with NT rats. The amplitude of the 5th pulse of GABA (5-second duration, 2-second interval) was 21+/-2% the amplitude of the 1st pulse in NT rats (n=10) and 14+/-2% in HT rats (n=11, P<0.05). These alterations in GABAA-receptor evoked currents could render the neurons less sensitive to GABA(A) receptor inhibition and influence afferent integration by NTS neurons in HT.