Jacqueline K. Phillips

Hand-held Dynamometry Correlation With the Gold Standard Isokinetic Dynamometry: A Systematic Review

To examine the current evidence regarding the reliability and validity of hand‐held dynamometry for assessment of muscle strength in the clinical setting.

Heterogeneous control of blood flow amongst different vascular beds.

The control and maintenance of vascular tone is due to a balance between vasoconstrictor and vasodilator pathways. Vasomotor responses to neural, metabolic and physical factors vary between vessels in different vascular beds, as well as along the same bed, particularly as vessels become smaller. These differences result from variation in the composition of neurotransmitters released by perivascular nerves, variation in the array and activation of receptor subtypes expressed in different vascular beds and variation in the signal transduction pathways activated in either the vascular smooth muscle or endothelial cells. As the study of vasomotor responses often requires pre‐existing tone, some of the reported heterogeneity in the relative contributions of different vasodilator mechanisms may be compounded by different experimental conditions. Biochemical variations, such as the expression of ion channels, connexin subtypes and other important components of second messenger cascades, have been documented in the smooth muscle and endothelial cells in different parts of the body. Anatomical variations, in the presence and prevalence of gap junctions between smooth muscle cells, between endothelial cells and at myoendothelial gap junctions, between the two cell layers, have also been described. These factors will contribute further to the heterogeneity in local and conducted responses.

Differential expression of catecholamine biosynthetic enzymes in the rat ventrolateral medulla

Adrenergic (C1) neurons located in the rostral ventrolateral medulla are considered a key component in the control of arterial blood pressure. Classically, C1 cells have been identified by their immunoreactivity for the catecholamine biosynthetic enzymes tyrosine hydroxylase (TH) and/or phenylethanolamine N‐methyltransferase (PNMT). However, no studies have simultaneously demonstrated the expression of aromatic L‐amino acid decarboxylase (AADC) and dopamine β‐hydroxylase (DBH) in these neurons. We examined the expression and colocalization of all four enzymes in the rat ventrolateral medulla using immunohistochemistry and reverse transcription‐polymerase chain reaction (RT‐PCR) analysis. Retrograde tracer injected into thoracic spinal segments T2–T4 was used to identify bulbospinal neurons. Using fluorescence and confocal microscopy, most cells of the C1 group were shown to be double or triple labeled with TH, DBH, and PNMT, whereas only 65–78% were immunoreactive for AADC. Cells that lacked detectable immunoreactivity for AADC were located in the rostral C1 region, and approximately 50% were spinally projecting. Some cells in this area lacked DBH immunoreactivity (6.5–8.3%) but were positive for TH and/or PNMT. Small numbers of cells were immunoreactive for only one of the four enzymes. Numerous fibres that were immunoreactive for DBH but not for TH or PNMT were noted in the rostral C1 region. Single‐cell RT‐PCR analysis conducted on spinally projecting C1 neurons indicated that only 76.5% of cells that contained mRNA for TH, DBH, and PNMT contained detectable message for AADC. These experiments suggest that a proportion of C1 cells may not express all of the enzymes necessary for adrenaline synthesis. J. Comp. Neurol. 432:20–34, 2001.

Unravelling the pathophysiology of complex regional pain syndrome : focus on sympathetically maintained pain

1 In diseases such as complex regional pain syndrome (CRPS), where neuropathic pain is the primary concern, traditional pain classifications and lesion descriptors are of limited value. To obtain better treatment outcomes for patients, the underlying pathophysiological mechanisms of neuropathic pain need to be elucidated and analysed so that therapeutic targets can be identified and specific treatments developed. 2 In the present review, we examine the current literature on sympathetically maintained pain (SMP), a subset of neuropathic pain, within the context of CRPS. Evidence from both human and animal studies is presented and discussed in terms of its support for the existence of SMP and the mechanistic information it provides. 3 We discuss three current hypotheses that propose both a site and method for sympathetic–sensory coupling: (i) direct coupling between sympathetic and sensory neurons in the dorsal root ganglion; (ii) chemical coupling between sympathetic and nociceptive neuron terminals in skin; and (iii) the development of a‐adrenoceptor‐mediated supersensitivity in nociceptive fibres in skin in association with the release of inflammatory mediators. 4 Finally, we propose a new hypothesis that integrates the mechanisms of chemical coupling and a‐adrenoceptor‐mediated supersensitivity. This hypothesis is based on previously unpublished data from our laboratory showing that a histological substrate suitable for sympathetic–sensory coupling exists in normal subjects. In the diseased state, the nociceptive fibres implicated in this substrate may be activated by both endogenous and exogenous noradrenaline. The mediating a‐adrenoceptors may be expressed on the nociceptive fibres or on closely associated support cells.

Upregulation of angiotensin AT1 receptor and intracellular kinase gene expression in hypertensive rats.

1 Activation of angiotensin II AT1 receptors (AT1R) stimulates catecholamine systems within both central and peripheral tissues that are associated with blood pressure control. In the present study, we sought to determine whether the hypertensive phenotype of the spontaneously hypertensive rat (SHR) is associated with changes in AT1R gene expression and whether gene expression of downstream signalling molecules was coupled to catecholamine gene expression, both in key brainstem nuclei and in peripheral sites implicated in cardiovascular control. 2 Gene expression levels of AT1R, extracellular signal‐regulated kinase (ERK) 1 and 2 and phosphatidylinositol 3‐kinase (PI3‐K) were quantified in Wistar‐Kyoto (WKY) rats and SHR. Messenger RNA expression levels were quantified using real time reverse transcription–polymerase chain reaction. In addition, we investigated whether there was a relationship between gene expression and systolic blood pressure. 3 The gene expression levels of AT1R, ERK2 and PI3‐K were significantly higher in the paraventricular nucleus of the hypothalamus (4.12‐, 1.40‐ and 1.38‐fold, respectively), rostral ventrolateral medulla (2.71‐, 1.33‐ and 2.73‐fold, respectively), spinal cord (30.5‐, 2.72‐ and 1.53‐fold, respectively), adrenal medulla (1.68‐, 1.55‐ and 1.76‐fold, respectively) and coeliac ganglion (1.39‐, 1.35‐ and 1.12‐fold, respectively) in SHR compared with WKY rats. There was no significant difference in the level of ERK1 gene expression between the two strains. The gene expression levels of AT1R and ERK2 were positively correlated with blood pressure in all central nervous tissues investigated in the SHR, but not in WKY rats. Gene expression levels of the AT1R in the coeliac ganglion and adrenal medulla were also positively correlated with increased systolic blood pressure. 4 The present data suggest that a defect in AT1R expression (that may further alter downstream signalling pathways) in the SHR may be responsible, at least in part, for the hypertensive phenotype.

Aortic stiffness is associated with vascular calcification and remodeling in a chronic kidney disease rat model

Increased aortic pulse-wave velocity (PWV) reflects increased arterial stiffness and is a strong predictor of cardiovascular risk in chronic kidney disease (CKD). We examined functional and structural correlations among PWV, aortic calcification, and vascular remodeling in a rodent model of CKD, the Lewis polycystic kidney (LPK) rat. Hemodynamic parameters and beat-to-beat aortic PWV were recorded in urethane-anesthetized animals [12-wk-old hypertensive female LPK rats (n = 5)] before the onset of end-stage renal disease and their age- and sex-matched normotensive controls (Lewis, n = 6). Animals were euthanized, and the aorta was collected to measure calcium content by atomic absorption spectrophotometry. A separate cohort of animals (n = 5/group) were anesthetized with pentobarbitone sodium and pressure perfused with formalin, and the aorta was collected for histomorphometry, which allowed calculation of aortic wall thickness, medial cross-sectional area (MCSA), elastic modulus (EM), and wall stress (WS), size and density of smooth muscle nuclei, and relative content of lamellae, interlamellae elastin, and collagen. Mean arterial pressure (MAP) and PWV were significantly greater in the LPK compared with Lewis (72 and 33%, respectively) animals. The LPK group had 6.8-fold greater aortic calcification, 38% greater aortic MCSA, 56% greater EM/WS, 13% greater aortic wall thickness, 21% smaller smooth muscle cell area, and 20% less elastin density with no difference in collagen fiber density. These findings demonstrate vascular remodeling and increased calcification with a functional increase in PWV and therefore aortic stiffness in hypertensive LPK rats.

Temporal relationship between renal cyst development, hypertension and cardiac hypertrophy in a new rat model of autosomal recessive polycystic kidney disease

Background/Methods: We have examined the hypothesis that cyst formation is key in the pathogenesis of cardiovascular disease in a Lewis polycystic kidney (LPK) model of autosomal-recessive polycystic kidney disease (ARPKD), by determining the relationship between cyst development and indices of renal function and cardiovascular disease. Results: In the LPK (n = 35), cysts appear at week 3 (1.1 ± 0.1 mm) increasing to week 24 (2.8 ± 2 mm). Immunostaining for nephron-specific segments indicate cysts develop predominantly from the collecting duct. Cyst formation preceded hypertension (160 ± 22 vs. Lewis control 105 ± 20 mm Hg systolic blood pressure (BP), n = 12) at week 6, elevated creatinine (109 ± 63 vs. 59 ± 6 µmol/l, n = 16) and cardiac mass (0.7 vs. 0.4% bodyweight, n = 15) at week 12, and left ventricular hypertrophy (2,898 ± 207 vs. 1,808 ± 192 µm, n = 14) at week 24 (all p ≤ 0.05). Plasma-renin activity and angiotensin II were reduced in 10- to 12-week LPK (2.2 ± 2.9 vs. Lewis 11.9 ± 4.9 ng/ml/h, and 25.0 ± 19.1 vs. 94.9 ± 64.4 pg/ml, respectively, n = 26, p ≤ 0.05). Ganglionic blockade (hexamethonium 3.3 mg/kg) significantly reduced mean BP in the LPK (52 vs. Lewis 4%, n = 9, p ≤ 0.05). Conclusion: Cyst formation is a key event in the genesis of hypertension while the sympathetic nervous system is important in the maintenance of hypertension in this model of ARPKD.

A novel mutation causing nephronophthisis in the Lewis polycystic kidney rat localises to a conserved RCC1 domain in Nek8

BackgroundNephronophthisis (NPHP) as a cause of cystic kidney disease is the most common genetic cause of progressive renal failure in children and young adults. NPHP is characterized by abnormal and/or loss of function of proteins associated with primary cilia. Previously, we characterized an autosomal recessive phenotype of cystic kidney disease in the Lewis Polycystic Kidney (LPK) rat.ResultsIn this study, quantitative trait locus analysis was used to define a ~1.6Mbp region on rat chromosome 10q25 harbouring the lpk mutation. Targeted genome capture and next-generation sequencing of this region identified a non-synonymous mutation R650C in the NIMA (never in mitosis gene a)- related kinase 8 ( Nek8) gene. This is a novel Nek8 mutation that occurs within the regulator of chromosome condensation 1 (RCC1)-like region of the protein. Specifically, the R650C substitution is located within a G[QRC]LG repeat motif of the predicted seven bladed beta-propeller structure of the RCC1 domain. The rat Nek8 gene is located in a region syntenic to portions of human chromosome 17 and mouse 11. Scanning electron microscopy confirmed abnormally long cilia on LPK kidney epithelial cells, and fluorescence immunohistochemistry for Nek8 protein revealed altered cilia localisation.ConclusionsWhen assessed relative to other Nek8 NPHP mutations, our results indicate the whole propeller structure of the RCC1 domain is important, as the different mutations cause comparable phenotypes. This study establishes the LPK rat as a novel model system for NPHP and further consolidates the link between cystic kidney disease and cilia proteins.

Tyrosine hydroxylase gene expression in ventrolateral medulla oblongata of WKY and SHR: a quantitative real-time polymerase chain reaction study

The aims of this study were, first, to determine quantitatively the levels of tyrosine hydroxylase (TH) gene expression in both peripheral and central sites related to blood pressure regulation, and to compare the level of expression in Wistar Kyoto (WKY) and spontaneously hypertensive rats (SHR). Second, to see if any relationship exists between TH gene expression and systolic arterial blood pressure. Total RNA was isolated from adrenal glands and from tissue punches taken from the C1 and A1 cell groups in the rostral and caudal ventrolateral medulla oblongata of the brainstem, respectively. Total RNA was reverse-transcribed into cDNA followed by quantitative fluorescence detection polymerase chain reaction for TH cDNA. The levels of TH gene expression measured as a percentage of the house-keeping gene glyceraldehyde-3-phosphate dehydrogenase (GAPDH), in SHR, were significantly higher ( approximately 2.5-fold) compared to WKY in all sites examined (P<0.01). There was a positive and significant relationship between systolic blood pressure and TH gene expression in the C1 area of the brainstem in both WKY (n = 5, P<0.05) and SHR (n=6, P<0.05). Taken together, these results suggest that elevated gene expression of the TH gene is associated with the phenotypic characteristic of SHR.

PATHOGENESIS OF HYPERTENSION IN RENAL FAILURE: ROLE OF THE SYMPATHETIC NERVOUS SYSTEM and RENAL AFFERENTS

1. The kidney receives a dense innervation of sympathetic and sensory fibres and can be both a target of sympathetic activity and a source of signals that drive sympathetic tone. In the normal state, interactions between the kidney and sympathetic nervous system (SNS) serve to maintain blood pressure and glomerular filtration rate within tightly controlled levels. In renal failure, a defect in renal sodium excretory function leads to an abnormal pressure natriuresis relationship and activation of the renin–angiotensin–aldosterone system, contributing to the development of hypertension and progression of kidney disease.