[Show abstract][Hide abstract] ABSTRACT: The nucleus tractus solitarii (NTS) controls the cardiovascular system during exercise, and alteration of its function may underlie exercise-induced cardiovascular adaptation. To understand the molecular basis of the NTS's plasticity in regulating blood pressure (BP) and its potential contribution to the anti-hypertensive effects, we characterized the gene expression profiles at the level of the NTS after long-term daily wheel running in spontaneously hypertensive rats (SHRs). Genome-wide microarray analysis was performed to screen for differentially expressed genes in the NTS between exercise-trained (12 weeks) and control SHRs. Pathway analysis using the Kyoto Encyclopedia of Genes and Genomes (KEGG) database revealed that daily exercise altered the expression levels of NTS genes that are functionally associated with metabolic pathways (5 genes), neuroactive ligand-receptor interactions (4 genes), cell adhesion molecules (3 genes), and cytokine-cytokine receptor interactions (3 genes). One of the genes that belonged to the neuroactive ligand-receptor interactions category was histamine receptor H(1). Since we confirmed that the pressor response induced by activation of this receptor is increased after long-term daily exercise, it is suggested that functional plasticity in the histaminergic system may mediate the facilitation of blood pressure control in response to exercise, but may not be involved in the lowered basal BP level found in exercise-trained SHRs. Since abnormal inflammatory states in the NTS are known to be pro-hypertensive in SHRs, altered gene expression of the inflammatory molecules identified in this study may be related to the anti-hypertensive effects in exercise-trained SHRs, although such speculation awaits functional validation.
Preview · Article · Nov 2012 · Physiological Genomics
[Show abstract][Hide abstract] ABSTRACT: The brainstem nucleus of the solitary tract (nucleus tractus solitarii, NTS) is a pivotal region for regulating the set-point of arterial pressure, the mechanisms of which are not fully understood. Based on evidence that the NTS exhibits O2-sensing mechanisms, we examined whether a localized disturbance of blood supply, resulting in hypoxia in the NTS, would lead to an acute increase in arterial pressure.
Male Wistar rats were used. Cardiovascular parameters were measured before and after specific branches of superficial dorsal medullary veins were occluded; we assumed these were drainage vessels from the NTS and would produce stagnant hypoxia. Hypoxyprobe-1, a marker for detecting cellular hypoxia in the post-mortem tissue, was used to reveal whether vessel occlusion induced hypoxia within the NTS.
Following vessel occlusion, blood flow in the dorsal surface of the medulla oblongata including the NTS region showed an approximately 60% decrease and was associated with hypoxia in neurons located predominantly in the caudal part of the NTS as revealed using hypoxyprobe-1. Arterial pressure increased and this response was pronounced significantly in both magnitude and duration when baroreceptor reflex afferents were sectioned.
These results suggest that localized hypoxia in the NTS increases arterial pressure. We suggest this represents a protective mechanism whereby the elevated systemic pressure is a compensatory mechanism to enhance cerebral perfusion. Whether this physiological mechanism has any relevance to neurogenic hypertension is discussed.
No preview · Article · Jun 2011 · Journal of Hypertension
[Show abstract][Hide abstract] ABSTRACT: Axons of histamine (HA)-containing neurons are known to project from the posterior hypothalamus to many areas of the brain, including the nucleus tractus solitarii (NTS), a central brain structure that plays an important role in regulating arterial pressure. However, the functional significance of NTS HA is still not fully established. In this study, we microinjected HA or 2-pyridylethylamine, a HA-receptor H(1)-specific agonist, into the NTS of urethane-anesthetized Wister rats to identify the potential functions of NTS HA on cardiovascular regulation. When HA or H(1)-receptor-specific agonist was bilaterally microinjected into the NTS, mean arterial pressure (MAP) and heart rate (HR) were significantly increased, whereas pretreatment with the H(1)-receptor-specific antagonist cetirizine into the NTS significantly inhibited the cardiovascular responses. The maximal responses of MAP and HR changes induced by HA or H(1)-receptor-specific agonist were dose dependent. We also confirmed gene expression of HA receptors in the NTS and that the expression level of H(1) mRNA was higher than that of the other subtypes. In addition, we found that H(1) receptors are mainly expressed in neurons of the NTS. These findings suggested that HA within the NTS may play a role in regulating cardiovascular homeostasis via activation of H(1) receptors expressed in the NTS neurons.
Preview · Article · May 2011 · AJP Heart and Circulatory Physiology
[Show abstract][Hide abstract] ABSTRACT: Metabolic parameters in WKY and SHR. [Note that the data in this table were derived from the same animals represented in Figure 1C.] The levels of glucose, insulin, leptin, and free fatty acids (FFA) in the blood were determined in 8- to 9-week-old animals fed ad libitum. Blood was collected at 4-hr intervals over a 24-hr period from the hearts of WKY (n = 6 per time point) and SHR (n = 6 per time point). The data were pooled to provide an average level of each metabolic parameter over a 24-hr period. Values are presented as means ± SEM.
[Show abstract][Hide abstract] ABSTRACT: The loss of diurnal rhythm in blood pressure (BP) is an important predictor of end-organ damage in hypertensive and diabetic patients. Recent evidence has suggested that two major physiological circadian rhythms, the metabolic and cardiovascular rhythms, are subject to regulation by overlapping molecular pathways, indicating that dysregulation of metabolic cycles could desynchronize the normal diurnal rhythm of BP with the daily light/dark cycle. However, little is known about the impact of changes in metabolic cycles on BP diurnal rhythm.
To test the hypothesis that feeding-fasting cycles could affect the diurnal pattern of BP, we used spontaneously hypertensive rats (SHR) which develop essential hypertension with disrupted diurnal BP rhythms and examined whether abnormal BP rhythms in SHR were caused by alteration in the daily feeding rhythm. We found that SHR exhibit attenuated feeding rhythm which accompanies disrupted rhythms in metabolic gene expression not only in metabolic tissues but also in cardiovascular tissues. More importantly, the correction of abnormal feeding rhythms in SHR restored the daily BP rhythm and was accompanied by changes in the timing of expression of key circadian and metabolic genes in cardiovascular tissues.
These results indicate that the metabolic cycle is an important determinant of the cardiovascular diurnal rhythm and that disrupted BP rhythms in hypertensive patients can be normalized by manipulating feeding cycles.
[Show abstract][Hide abstract] ABSTRACT: Food intake and body weight in SHR under free and restricted feeding conditions. SHR were maintained on a 12∶12 LD cycle and exposed either to a free feeding condition or to a restricted feeding (RF) regimen in which food was provided only during the active (dark) period. On the fifth day of the feeding regimens, total food intake over a 24-hr period and body weight were determined in SHR fed ad libitum (n = 6) and SHR exposed to RF (SHR-RF, n = 6). Note that the data in this table were derived from animals 1 to 2 weeks older than those represented in table S1 because the animals in this table were exposed to feeding paradigms for nearly 1 week. All data are expressed as means ± SEM.
[Show abstract][Hide abstract] ABSTRACT: Cardiovascular parameters in WKY and SHR. [Note that the data in this table were derived from the same animals represented in Figure 4.] Systolic and diastolic blood pressure (BP) and heart rate (HR) were telemetrically monitored in freely moving WKY (n = 6) and SHR (n = 6). Data were collected for the first 5 min of every 60 min for 2 consecutive days and pooled to determine an overall mean (± SEM) value for the 12-hr light and 12-hr dark periods.
[Show abstract][Hide abstract] ABSTRACT: Effects of restricted feeding on the Cry gene expression in cardiovascular tissues of SHR. The levels of Cry1 and Cry2 mRNA expression in the heart and aorta were determined by real time PCR. Animals were either fed ad libitum or exposed to an RF regimen, in which food was provided exclusively during the dark period, for 5 consecutive days. On the fifth day, heart and aortic tissues were harvested from animals at 4-hr intervals. For visual clarity, only data from ad libitum-fed WKY (black lines, n = 4 per time point) and SHR (red lines, n = 4 per time point) and RF-fed SHR (blue lines, n = 4 per time point) are shown. Values for mRNA expression are displayed as relative expression levels normalized to β-actin. The 12∶12 LD cycle is indicated by the bars at the bottom of the figure. All data are expressed as means ± SEM. #, SHR versus WKY; *, SHR fed ad libitum versus RF; p<0.05.
[Show abstract][Hide abstract] ABSTRACT: Food intake and body weight in WKY and SHR. Food intake (grams) was determined for the 12-hr light, 12-hr dark and total 24-hr periods in the same set of WKY (n = 6) and SHR (n = 6) represented in Figure 1A. Body weight was also compared between these animals. Values are displayed as means ± SEM.
[Show abstract][Hide abstract] ABSTRACT: Effects of restricted feeding on diurnal rhythms of serum free fatty acids levels in SHR. Animals maintained under a 12∶12 LD cycle were fed ad libitum or maintained under restricted feeding (RF) conditions for 5 consecutive days. Under the RF condition, food was available only during the active (dark) period. On the fifth day of the feeding regimen, blood was collected every 4 hr from the free-fed WKY (black lines, n = 4 per time point) and SHR (red lines, n = 4 per time point) and the RF-fed SHR (blues lines, n = 4 per time point). The levels of free fatty acids (FFA) were determined by the enzymatic colorimetric method. Note that the results for WKY (black lines) and SHR (red lines) fed ad libitum were reproduced from data used in Figure 1C to clarify the difference in diurnal patterns between groups. Values are expressed as means ± SEM.
[Show abstract][Hide abstract] ABSTRACT: Since the nucleus tractus solitarii (NTS) is a pivotal region for regulating the set-point of arterial pressure, we propose here its role in the development of neurogenic hypertension. Given the findings of recent studies suggesting that the NTS of spontaneously hypertensive rats (SHR) exhibits a specific inflammatory state characterized by leukocyte accumulation within the NTS microvasculature, we hypothesized that gene expression levels of apoptotic factors are altered in the NTS of SHR compared to normotensive Wistar-Kyoto rats (WKY). To test this hypothesis, we used RT(2) Profiler PCR arrays targeting apoptosis-related factors. We found that gene expression of the death receptor Fas (tumor necrosis factor receptor superfamily, member 6) and the cysteine-aspartic acid protease caspase 12 were down-regulated in the NTS of both adult hypertensive and young pre-hypertensive SHR compared to age-matched WKY. On the other hand, an anti-apoptotic factor, neuronal apoptosis inhibitory protein, was highly increased in the NTS of SHR. These results suggest that the NTS of SHR exhibits an anti-apoptotic condition. Furthermore, this profile appears not to be secondary to hypertension. Whether this differential gene expression in the NTS contributes to the hypertensive state of the SHR via alteration of neuronal circuitry regulating cardiovascular autonomic activity awaits elucidation.
No preview · Article · Feb 2011 · Autonomic neuroscience: basic & clinical
[Show abstract][Hide abstract] ABSTRACT: Recent studies have demonstrated that pro-inflammatory molecules such as junctional adhesion molecules-1 are highly expressed in the nucleus tractus solitarii (NTS) of the spontaneously hypertensive rat (SHR), compared to normotensive rats (Wistar-Kyoto rats: WKY), suggesting that the NTS of SHR may exhibit an abnormal inflammatory state. In the present study, we tested whether gene expression of inflammatory markers such as cytokines and chemokines is altered in the NTS of SHR and whether this contributes to the hypertensive phenotype in the SHR.
We have performed RT Profiler PCR arrays in the NTS of SHR and WKY, which were designed to specifically target major cytokines/chemokines and their receptors. To validate PCR array results quantitative RT-PCR was performed. Microinjection studies using anesthetized rats were also carried out to examine whether validated inflammatory molecules exhibit functional roles on cardiovascular regulation at the level of the NTS.
Five inter-related transcripts were identified to be differentially expressed between the NTS of SHR and WKY. They include chemokine (C-C motif) ligand 5 (Ccl5), and its receptors, chemokine (C-C motif) receptor 1 and 3. All of them were down-regulated in the NTS of SHR compared to WKY. Moreover, we found that the protein Ccl5 microinjected into the NTS significantly decreased baseline arterial pressure and that the response was greater in the SHR compared to the WKY (-33.2±3.2 vs. -8.8±1.6 mmHg, P<0.001), demonstrating that its down-regulation in the NTS may contribute to hypertension in the SHR.
We suggest that gene expression of specific chemokines may be down-regulated to protect further inflammatory reactions in the NTS of SHR at the expense of arterial hypertension.
No preview · Article · Feb 2011 · Journal of Hypertension
[Show abstract][Hide abstract] ABSTRACT: Recent gene array and molecular studies have suggested that an abnormal gene expression profile of interleukin-6 (IL-6) in the nucleus tractus solitarii (NTS), a pivotal region for regulating arterial pressure, may be related to the development of neurogenic hypertension. However, the precise functional role of IL-6 in the NTS remains unknown. In the present study, we have tested whether IL-6 affects cardiovascular control at the level of the NTS. IL-6 (1, 10, and 100 fmol) was microinjected in the NTS of Wistar rats (280-350 g) under urethane anesthesia. Although the baseline levels of arterial pressure and heart rate did not change following IL-6 injections, the cardiac baroreflex in response to increased arterial pressure was dose-dependently attenuated. In addition, IL-6 (100 fmol) microinjections also attenuated l-glutamate-induced bradycardia at the level of the NTS. Immunohistochemical detection of IL-6 in naïve rats demonstrated that it was predominantly observed in neurons within the brain stem, including the NTS. These findings suggest that IL-6 within the NTS may play an important role for regulating cardiovascular control via modulation of input signals from baroreceptor afferents. Whether the abnormal gene expression of IL-6 in the NTS is associated in a causal way with hypertension remains to be resolved.
No preview · Article · Nov 2009 · AJP Regulatory Integrative and Comparative Physiology
[Show abstract][Hide abstract] ABSTRACT: Although both alpha(1)- and alpha(2)-adrenergic receptors (ARs) are known to be expressed in the nucleus of the solitary tract (NTS), the functional significance of these receptors is still not fully established. In this study, we microinjected alpha(1)- and alpha(2)-AR agonists into the NTS of urethane-anaesthetized Wister rats to study the cardiovascular effects in response to their activation. When the alpha(1)-AR agonist phenylephrine was microinjected into the area where barosensitive neurons are dominantly located (baro-NTS), mean arterial pressure (MAP) and heart rate (HR) were significantly elevated. When tested in the area where chemosensitive neurons are dominantly located (chemo-NTS), however, MAP and HR were significantly decreased. Pretreatment with the non-specific alpha-AR antagonist phentolamine into the NTS inhibited the phenylephrine-induced cardiovascular responses. In contrast, microinjection of the alpha(2)-AR agonist clonidine into either the baro-NTS or the chemo-NTS decreased MAP and HR; they were also inhibited by the alpha(2)-adrenergic antagonist yohimbine. Moreover, we immunohistochemically identified that cardiovascular responses induced by alpha(1)-ARs may be mediated by NTS neurons while those induced by alpha(2)-ARs may be mediated by astrocytes located in the barosensitive and chemosensitive areas of the NTS. These results suggest that both types of alpha-AR expressed in the NTS may be involved in regulating cardiovascular homeostasis via modulation of input signals from baroreceptor and chemoreceptor afferents; however, cardiovascular responses produced by stimulation of alpha(1)-ARs are strictly location specific within the NTS.