[Show abstract][Hide abstract] ABSTRACT: In response to an osmotic challenge, the synthesis of the antidiuretic hormone arginine vasopressin (AVP) increases in the hypothalamus, and this is accompanied by extension of the 3′ poly(A) tail of the AVP mRNA, and the up-regulation of the expression of RNA binding protein Caprin-2. Here we show that Caprin-2 binds to AVP mRNAs, and that lentiviral mediated shRNA knockdown of Caprin-2 in the osmotically stimulated hypothalamus shortens the AVP mRNA poly(A) tail at the same time as reducing transcript abundance. In a recapitulated in vitro system, we confirm that Caprin-2 over-expression enhances AVP mRNA abundance and poly(A) tail length. Importantly, we show that Caprin-2 knockdown in the hypothalamus decreases urine output and fluid intake, and increases urine osmolality, urine sodium concentration, and plasma AVP levels. Thus Caprin-2 controls physiological mechanisms that are essential for the body's response to osmotic stress. DOI: http://dx.doi.org/10.7554/eLife.09656.001
[Show abstract][Hide abstract] ABSTRACT: Sympathetic nerve activity (SNA) exhibits respiratory modulation. This component of SNA is important - being recruited under cardiorespiratory reflex conditions and elevated in the spontaneously hypertensive (SH) rat - and yet, the exact influence of this modulation on vascular tone is not understood, even in normotensive conditions. We constructed a mathematical model of the sympathetic innervation of an arteriole, and used it to test the hypothesis that respiratory modulation of SNA preferentially increases vasoconstriction compared to a frequency-matched tonic pattern. Simulations supported the hypothesis, where respiratory modulated increases in vasoconstriction were mediated by a noradrenergic mechanism. These predictions were tested in vivo in adult Wistar rats. Stimulation of the sympathetic chain (L3) with respiratory-modulated bursting patterns, revealed that bursting increases vascular resistance (VR) more than tonic stimulation (57.8 ± 3.3% vs 44.8 ± 4.2%; P < 0.001; n = 8). The onset of the VR response was also quicker for bursting stimulation (rise time-constant = 1.98 ± 0.09 s vs 2.35 ± 0.20 s; P < 0.01). In adult SH rats (n = 8), the VR response to bursting (44.6 ± 3.9%) was not different to tonic (37.4 ± 3.5%; P = 0.57). Using both mathematical modelling and in vivo techniques, we have shown that VR depends critically on respiratory modulation and revealed that this pattern-dependency in Wistar rats is due to a noradrenergic mechanism. This respiratory component may therefore contribute to the ontogenesis of hypertension in the pre-hypertensive SH rat - raising VR and driving vascular remodelling. Why adult SH rats do not exhibit a pattern-dependent response is not known, but further modelling revealed that this may be due to dysfunctional NA reuptake. This article is protected by copyright. All rights reserved.
The Journal of Physiology 10/2015; DOI:10.1113/JP271253 · 5.04 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Central apnoeas and respiratory irregularity are a common feature in Rett syndrome (RTT), a neurodevelopmental disorder most often caused by mutations in the methyl-CpG-binding protein 2 gene (MECP2). We used a MECP2 deficient mouse model of RTT as a strategy to obtain insights into the neurobiology of the disease and into mechanisms essential for respiratory rhythmicity during normal breathing. Previously, we showed that, systemic administration of a GABA reuptake blocker in MECP2 deficient mice markedly reduced the occurrence of central apnoeas. Further, we found that, during central apnoeas, post-inspiratory drive (adductor motor) to the upper airways was enhanced in amplitude and duration in Mecp2 heterozygous female mice. Since pontine Kölliker-Fuse (KF) region drives post-inspiration, suppresses inspiration, and can reset the respiratory oscillator phase, we hypothesized that synaptic inhibition in this area is essential for respiratory rhythm regularity. In this study, we found that: (i) Mecp2 heterozygous mice show deficiency of GABA perisomatic bouton-like puncta and processes in the KF; (ii) blockade of GABA reuptake in the KF of RTT mice reduced breathing irregularity; (iii) conversely, blockade of GABAA receptors in the KF of healthy rats mimicked the RTT respiratory phenotype of recurrent central apnoeas and prolonged post-inspiratory activity. Our results show that reductions in synaptic inhibition within the KF induce rhythm irregularity whereas boosting GABA transmission reduces respiratory arrhythmia in a murine model of RTT. Our data suggest that manipulation of synaptic inhibition in KF may be a clinically important strategy for alleviating the life threatening respiratory disorders in RTT. This article is protected by copyright. All rights reserved.
The Journal of Physiology 10/2015; DOI:10.1113/JP270966 · 5.04 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Healthy ageing and alterations in respiratory-sympathetic coupling have been independently linked with heightened sympathetic neural vasoconstrictor activity. We investigated how age influences the respiratory related modulation of muscle sympathetic nerve activity (MSNA), and the association between the rhythmic fluctuations in MSNA and blood pressure that occur with respiration (Traube-Hering Waves; THW). Ten young (22 ± 2 years, mean±SD) and ten older (58 ± 6 years) healthy men were studied while resting supine and breathing spontaneously. MSNA, blood pressure and respiration were simultaneously recorded. Resting values were ascertained and respiratory cycle triggered averaging of MSNA and blood pressure measurements performed. MSNA burst incidence was higher in older individuals (22.7 ± 9.2 vs. 42.2 ± 13.7 bursts·100 heartbeats(-1) P<0.05), and was similarly reduced in the inspiratory to post-inspiratory period in young and older subjects (by ∼25% compared to mid-to-late expiration). A similar attenuation of MSNA burst frequency (bursts per minute), amplitude and total activity (burst frequency × mean burst amplitude) was also observed in the inspiratory to post-inspiratory period in both groups. A significant positive correlation between respiratory related MSNA and THW magnitude was observed in all young (100%) and most older (80%) subjects. These data suggest that the strength of the cyclical inhibition of MSNA during respiration is similar between young and older individuals and thus alterations in respiratory-sympathetic coupling appear not to contribute to the age-related elevation in MSNA. Furthermore, central respiratory-sympathetic coupling plays a role in the generation of THW in both healthy young and older humans. This article is protected by copyright. All rights reserved.
This article is protected by copyright. All rights reserved.
[Show abstract][Hide abstract] ABSTRACT: Electrocardiograph (ECG) criteria for left ventricular hypertrophy (LVH) are a widely used clinical tool. We recalibrated six ECG criteria for LVH against gold-standard cardiac magnetic resonance (CMR) and assessed the impact of obesity. One hundred and fifty consecutive tertiary hypertension clinic referrals for CMR (1.5 T) were reviewed. Patients with cardiac pathology potentially confounding hypertensive LVH were excluded (n=22). The final sample size was 128 (age: 51.0±15.2 years, 48% male). LVH was defined by CMR. From a 12-lead ECG, Sokolow-Lyon voltage and product, Cornell voltage and product, Gubner-Ungerleidger voltage and Romhilt-Estes score were evaluated, blinded to the CMR. ECG diagnostic performance was calculated. LVH by CMR was present in 37% and obesity in 51%. Obesity significantly reduced ECG sensitivity, because of significant attenuation in mean ECG values for Cornell voltage (22.2±5.7 vs 26.4±9.4 mm, P<0.05), Cornell product (2540±942 vs 3023±1185 mm • ms, P<0.05) and for Gubner-Ungerleider voltage (18.2±7.1 vs 23.3±1.2 mm, P<0.05). Obesity also significantly reduced ECG specificity, because of significantly higher prevalence of LV remodeling (no LVH but increased mass-to-volume ratio) in obese subjects without LVH (36% vs 16%, P<0.05), which correlated with higher mean ECG LVH criteria values. Obesity-specific partition values were generated at fixed 95% specificity; Cornell voltage had highest sensitivity in non-obese (56%) and Sokolow-Lyon product in obese patients (24%). Obesity significantly lowers ECG sensitivity at detecting LVH, by attenuating ECG LVH values, and lowers ECG specificity through changes associated with LV remodeling. Our obesity-specific ECG partition values could improve the diagnostic performance in obese patients with hypertension.Journal of Human Hypertension advance online publication, 4 June 2015; doi:10.1038/jhh.2015.58.
Journal of human hypertension 06/2015; DOI:10.1038/jhh.2015.58 · 2.70 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Hypertensive patients and experimental models of hypertension showed a marked sympatho-excitation. The mechanisms responsible for this sympathetic activation in arterial hypertension (AHT) are not completely elucidated.Our working hypothesis is that the increased sympathetic activity observed in AHT is a result from an elevated sympathetic drive from the rostroventrolateral medulla (RVLM) and the paraventricular nucleus of the hypothalamus (PVN). Both areas are included in the autonomic network and have an increased neuronal activity in hypertensive conditions.
A decrease in neuronal excitability in PVN and RVLM was promoted to modulate the central sympathetic activity in spontaneously hypertensive rats (SHR) by the over-expression of a potassium-channel induced by a lentivirus. Telemetry blood pressure (BP) values, autonomic output, baro- and chemoreceptor function and molecular signalling in hypertensive target organ were evaluated.
Chronic over-expression of potassium-channels in the PVN and RVLM caused a sustained decrease in systolic (26mmHg, 39mmHg), diastolic (22mmHg, 40mmHg) and mean BP (22mmHg,40mmHg) in conscious unrestrained SHR. This BP decrease were accompanied by a decrease in sympathetic-output as revealed indirectly by a decrease in the low frequencies band of systolic BP (from 0.79 ± 0.13 to 0.42 ± 0.09mmHg2 and from 0.69 ± 0.11 to 0.42 ± 0.10mmHg2,p < 0.05) in PVN and RVLM, respectively, at 60 days post-microinjection.In the PVN the baro- and chemoreceptor function were restored but no changes were observed in the RVLM. Signalling changes occurred in heart, kidney and vessels, mainly through the up-regulation of angiotensinogen and AT-2 genes in the kidney and down-regulation of AT-1 receptors in the heart.
These results give support to PVN and RVLM role as powerful sites to control BP in neurogenic hypertension and we expect, by identifying the role of these central areas, to provide realistic targets for therapeutic interventions.
[Show abstract][Hide abstract] ABSTRACT: The polyamines spermidine and spermine are small cations present in all living cells. In the brain, these cations are particularly abundant in the neurons of the paraventricular (PVN) and supraoptic nuclei (SON) of the hypothalamus, which synthesise the neuropeptide hormones arginine vasopressin (AVP) and oxytocin (OT). We recently reported increased mRNA expression of antizyme inhibitor 1 (Azin1), an important regulator of polyamine synthesis, in rat SON and PVN as a consequence of 3 days of dehydration (DH). Here, we show that Azin1 protein is highly expressed in both AVP and OT positive magnocellular neurons of the SON and PVN, together with antizyme 1 (AZ1), ornithine decarboxylase (ODC) and polyamines. Azin1 mRNA expression increased in the SON and PVN as a consequence of DH, salt loading (SL) and by acute hypertonic stress. In organotypic hypothalamic cultures, addition of the irreversible ODC inhibitor DL-2-(Difluoromethyl)-ornithine hydrochloride (DFMO) significantly increased the abundance of heteronuclear AVP (hnAVP), but not hnOT. To identify the function of Azin1 in vivo, lentiviral vectors that either over-express or knockdown Azin1 were stereotaxically delivered into the SON and/or PVN. Azin1 shRNA delivery resulted in decreased plasma osmolality and had a significant effect on food intake. The expression of AVP mRNA was also significantly increased in the SON by Azin1 shRNA. In contrast, Azin1 overexpression in the SON decreased AVP mRNA expression. We have therefore identified Azin1, and hence by inference polyamines, as novel regulators of the expression of the AVP gene.
[Show abstract][Hide abstract] ABSTRACT: Arginine vasopressin (AVP) is synthesised in magnocellular neurons (MCNs) of supraoptic nucleus (SON) and paraventricular nucleus (PVN) of the hypothalamus. In response to the hyperosmotic stressors of dehydration (complete fluid deprivation, DH) or salt loading (drinking 2% salt solution, SL), AVP synthesis increases in MCNs, which over-burdens the protein folding machinery in the endoplasmic reticulum (ER). ER stress and the unfolded protein response (UPR) are signaling pathways that improve ER function in response to the accumulation of misfold/unfold protein. We asked whether an ER stress response was activated in the SON and PVN of DH and SL rats. We observed increased mRNA expression for the immunoglobulin heavy chain binding protein (BiP), activating transcription factor 4 (Atf4), C/EBP-homologous protein (Chop), and cAMP responsive element binding protein 3 like 1 (Creb3l1) in both SON and PVN of DH and SL rats. Although we found no changes in the splicing pattern of X box-binding protein 1 (Xbp1), an increase in the level of the unspliced form of Xbp1 (Xbp1U) was observed in DH and SL rats. CREB3L1, a novel ER stress inducer, has been shown to be activated by ER stress to regulate the expression of target genes. We have previously shown that CREB3L1 is a transcriptional regulator of the AVP gene; however, a role for CREB3L1 in the response to ER stress has yet to be investigated in MCNs. Here, we used lentiviral vectors to introduce a dominant negative form of CREB3L1 (CREB3L1DN) in the rat SON. Expression of CREB3L1DN in the SON decreased Chop and Xbp1U mRNA levels, but not BiP and Atf4 transcript expression. CREB3L1 is thus implicated as a transcriptional mediator of the ER stress response in the osmotically stimulated SON.
PLoS ONE 04/2015; 10(4):e0124956. DOI:10.1371/journal.pone.0124956 · 3.23 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: A great deal of basic and applied physiology and pharmacology in sensory and autonomic neuroscience has teased apart mechanisms that drive normal perception of mechanical, thermal and chemical signals and convey them to CNS, the distinction of fiber types and receptors and channels that mediate them, and how they may become dysfunctional or maladaptive in disease. Likewise, regulation of efferent autonomic traffic to control organ reflexes has been well studied. In both afferent and efferent limbs, a wide array of potential therapeutic mechanisms has surfaced, some of which have progressed into clinic, if not full regrastration. One conversation that has been less well progressed relates to how the afferent limb and its sensitization shapes the efferent outputs, and where modulation may offer new therapeutic avenues, especially for poorly addressed and common signs and symptoms of disease.Therapeutics for CV disease (HF, hypertension), respiratory disease (asthma, COPD), urological disease (OAB), GI disease (IBS), and inter alia, have largely focused on the efferent control of effector cells to modulate movement, contraction and secretion; medicinal needs remain with limits to efficacy, AEs and treatment resistance being common. We now must turn, in the quest for improved therapeutics, to understand how sensation from these organs becomes maladapted and sensitized in disease, and what opportunities may arise for improved therapeutics given the abundance of targets, many pharmacologically untapped, on the afferent side. One might look at the treatment resistant hypertension and the emerging benefit of renal denervation; or urinary bladder overactivity / neurogenic bladder and the emergence of neuromodulation, capsaicin instillation or botox injections to attenuate sensitized reflexes, as examples of merely the start of such progress. This review examines this topic more deeply, as applies to four major organ systems all sharing a great need from unsatisfied patients.
[Show abstract][Hide abstract] ABSTRACT: Why sympathetic activity raises in neurogenic hypertension remains unknown. It has been postulated that changes in the electrical excitability of medullary pre-sympathetic neurones are the main causal mechanism for the development of sympathetic over activity in experimental hypertension. Herein, we review recent data suggesting that enhanced sympathetic activity in neurogenic hypertension is, at least in part, dependent on alterations in the electrical excitability of medullary respiratory neurones and their central modulation of sympatho-excitatory networks. We also present results showing a critical role for carotid body tonicity in the etiology of enhanced central respiratory modulation of sympathetic activity in neurogenic hypertension. We propose a novel hypothesis of respiratory neurone channelopathy induced by carotid body over activity in neurogenic hypertension that may contribute to sympathetic excess. Moreover, our data support the notion of targeting the carotid body as a potential novel therapeutic approach for reducing sympathetic vasomotor tone in neurogenic hypertension. This article is protected by copyright. All rights reserved.
This article is protected by copyright. All rights reserved.
The Journal of Physiology 04/2015; 593(14). DOI:10.1113/JP270423 · 5.04 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Systemic arterial hypertension has been previously suggested to develop as a compensatory condition when central nervous perfusion/oxygenation is compromised. Principal sympathoexcitatory C1 neurons of the rostral ventrolateral medulla oblongata (whose activation increases sympathetic drive and the arterial blood pressure) are highly sensitive to hypoxia, but the mechanisms of this O2 sensitivity remain unknown. Here, we investigated potential mechanisms linking brainstem hypoxia and high systemic arterial blood pressure in the spontaneously hypertensive rat. Brainstem parenchymal PO2 in the spontaneously hypertensive rat was found to be ≈15 mm Hg lower than in the normotensive Wistar rat at the same level of arterial oxygenation and systemic arterial blood pressure. Hypoxia-induced activation of rostral ventrolateral medulla oblongata neurons was suppressed in the presence of either an ATP receptor antagonist MRS2179 or a glycogenolysis inhibitor 1,4-dideoxy-1,4-imino-d-arabinitol, suggesting that sensitivity of these neurons to low PO2 is mediated by actions of extracellular ATP and lactate. Brainstem hypoxia triggers release of lactate and ATP which produce excitation of C1 neurons in vitro and increases sympathetic nerve activity and arterial blood pressure in vivo. Facilitated breakdown of extracellular ATP in the rostral ventrolateral medulla oblongata by virally-driven overexpression of a potent ectonucleotidase transmembrane prostatic acid phosphatase results in a significant reduction in the arterial blood pressure in the spontaneously hypertensive rats (but not in normotensive animals). These results suggest that in the spontaneously hypertensive rat, lower PO2 of brainstem parenchyma may be associated with higher levels of ambient ATP and l-lactate within the presympathetic circuits, leading to increased central sympathetic drive and concomitant sustained increases in systemic arterial blood pressure.