A M Allen

University of Melbourne, Melbourne, Victoria, Australia

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Publications (101)412.05 Total impact

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    ABSTRACT: Genetic tools that permit functional or connectomic analysis of neuronal circuits are rapidly transforming neuroscience. The key to deployment of such tools is selective transfection of target neurons, but to date this has largely been achieved using transgenic animals or viral vectors that transduce subpopulations of cells chosen according to anatomical rather than functional criteria. Here, we combine single-cell transfection with conventional electrophysiological recording techniques, resulting in three novel protocols that can be used for reliable delivery of conventional dyes or genetic material in vitro and in vivo. We report that techniques based on single cell electroporation yield reproducible transfection in vitro, and offer a simple, rapid and reliable alternative to established dye-labeling techniques in vivo, but are incompatible with targeted transfection in deep brain structures. In contrast, we show that intracellular electrophoresis of plasmid DNA transfects brainstem neurons recorded up to 9 mm deep in the anesthetized rat. The protocols presented here require minimal, if any, modification to recording hardware, take seconds to deploy, and yield high recovery rates in vitro (dye labeling: 89%, plasmid transfection: 49%) and in vivo (dye labeling: 66%, plasmid transfection: 27%). They offer improved simplicity compared to the juxtacellular labeling technique and for the first time offer genetic manipulation of functionally characterized neurons in previously inaccessible brain regions. © 2015 The Authors. Physiological Reports published by Wiley Periodicals, Inc. on behalf of the American Physiological Society and The Physiological Society.
    01/2015; 3(1). DOI:10.14814/phy2.12246
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    ABSTRACT: Obesity is associated with increased blood pressure (BP), which in turn increases the risk of cardiovascular diseases. We found that the increase in leptin levels seen in diet-induced obesity (DIO) drives an increase in BP in rodents, an effect that was not seen in animals deficient in leptin or leptin receptors (LepR). Furthermore, humans with loss-of-function mutations in leptin and the LepR have low BP despite severe obesity. Leptin's effects on BP are mediated by neuronal circuits in the dorsomedial hypothalamus (DMH), as blocking leptin with a specific antibody, antagonist, or inhibition of the activity of LepR-expressing neurons in the DMH caused a rapid reduction of BP in DIO mice, independent of changes in weight. Re-expression of LepRs in the DMH of DIO LepR-deficient mice caused an increase in BP. These studies demonstrate that leptin couples changes in weight to changes in BP in mammalian species. Copyright © 2014 The Authors. Published by Elsevier Inc. All rights reserved.
    Cell 12/2014; 159(6):1404-16. DOI:10.1016/j.cell.2014.10.058 · 33.12 Impact Factor
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    ABSTRACT: Brainstem catecholaminergic neurons play key roles in the autonomic, neuroendocrine, and behavioral responses to glucoprivation, yet the functions of the individual groups are not fully understood. Adrenergic C3 neurons project widely throughout the brain, including densely to sympathetic preganglionic neurons in the spinal cord, yet their function is completely unknown. Here we demonstrate in rats that optogenetic stimulation of C3 neurons induces sympathoexcitatory, cardiovasomotor functions. These neurons are activated by glucoprivation, but unlike the C1 cell group, not by hypotension. The cardiovascular activation induced by C3 neurons is less than that induced by optogenetic stimulation of C1 neurons; however, combined stimulation produces additive sympathoexcitatory and cardiovascular effects. The varicose axons of C3 neurons largely overlap with those of C1 neurons in the region of sympathetic preganglionic neurons in the spinal cord; however, regional differences point to effects on different sympathetic outflows. These studies definitively demonstrate the first known function of C3 neurons as unique cardiovasomotor stimulatory cells, embedded in the brainstem networks regulating cardiorespiratory activity and the response to glucoprivation.
    The Journal of Neuroscience : The Official Journal of the Society for Neuroscience 11/2014; 34(45):15110-22. DOI:10.1523/JNEUROSCI.3179-14.2014 · 6.75 Impact Factor
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    ABSTRACT: Chronic low dose systemic infusion of angiotensin II induces hypertension via activation of the angiotensin II type 1A receptor (AT1AR). Previously, we have demonstrated that expression of the AT1AR on catecholaminergic neurons is necessary for the full development of angiotensin-dependent hypertension. In the present study, we examined the mechanism by which selective deletion of the AT1AR from these cells affects the development of hypertension. We also tested the hypothesis that AT1AR expressed by catecholaminergic C1 neurons in the rostral ventrolateral medulla play an important role in angiotensin II hypertension. A Cre-lox approach was used to delete AT1AR from all catecholaminergic cells or from C1 neurons selectively. Subcutaneous administration of angiotensin II induced hypertension in all mice, with delayed onset and reduced maximal response in the global AT1AR catecholaminergic knockout. The AT1AR catecholamine knockout mice had decreased renal fluid and electrolyte retention and urinary noradrenaline excretion. The blood pressure response was only reduced during the second week of angiotensin II infusion in the selective C1 AT1AR deletion, demonstrating that AT1AR expression by C1 neurons plays a moderate role in angiotensin-induced hypertension. The difference in the time course of hypertension development between the global AT1AR knockout from catecholaminergic cells and the C1 AT1AR deletion mice suggests that other catecholamine neurons are important.This article is protected by copyright. All rights reserved
    Experimental physiology 09/2014; 99(12). DOI:10.1113/expphysiol.2014.082073 · 2.87 Impact Factor
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    ABSTRACT: Coordinated modulation of sympathetic and parasympathetic nervous activity is required for physiological regulation of tissue function. Anatomically, whilst the peripheral sympathetic and parasympathetic pathways are separate, the distribution of premotor neurons in higher brain regions often overlaps. This co-distribution would enable coordinated regulation and might suggest individual premotor neurons could project to both sympathetic and parasympathetic outflows. To investigate this one submandibular gland was sympathectomized. One of two isogenic strains of the pseudorabies virus, expressing different fluorophores, was injected into the cut sympathetic nerve and the other into the submandibular gland. Independent labeling of the peripheral sympathetic and parasympathetic pathways was observed. Dual-labeled neurons were observed in many CNS regions known to be involved in regulating salivary function. We propose these observations highlight a common pattern of organization of the CNS, providing the anatomical framework for the fine control of organ function required for homeostatic regulation and the coordination of organ responses to enable complex behaviors.
    Brain Structure and Function 05/2014; DOI:10.1007/s00429-014-0781-1 · 4.57 Impact Factor
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    ABSTRACT: Therapeutic targets for male contraception are associated with numerous problems due to their focus on disrupting spermatogenesis or hormonal mechanisms to produce dysfunctional sperm. Here we describe the dual genetic deletion of α1A-adrenergic G protein-coupled receptors (adrenoceptors) and P2X1-purinoceptor ligand gated ion channels in male mice, thereby blocking sympathetically mediated sperm transport through the vas deferens during the emission phase of ejaculation. This modification produced 100% infertility without effects on sexual behavior or function. Sperm taken from the cauda epididymides of double knockout mice were microscopically normal and motile. Furthermore, double knockout sperm were capable of producing normal offspring following intracytoplasmic sperm injection into wild-type ova and implantation of the fertilized eggs into foster mothers. Blood pressure and baroreflex function was reduced in double knockout mice, but no more than single knockout of α1A-adrenoceptors alone. These results suggest that this autonomic method of male contraception appears free of major physiological and behavioral side effects. In addition, they provide conclusive proof of concept that pharmacological antagonism of the P2X1-purinoceptor and α1A-adrenoceptor provides a safe and effective therapeutic target for a nonhormonal, readily reversible male contraceptive.
    Proceedings of the National Academy of Sciences 12/2013; 110(51). DOI:10.1073/pnas.1318624110 · 9.81 Impact Factor
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    ABSTRACT: The baroreceptor reflex dampens the short-term fluctuations in blood pressure by feedback modulation of heart rate (HR) and vascular resistance. Impairment of this reflex has been observed in hypertension and heart failure. Angiotensin II, a blood borne hormone, acts via its type 1A receptor to attenuate the baroreceptor reflex and this reflex is reported to be dramatically altered in angiotensin type 1A receptor knockout mice. This study sought to further investigate changes in the arterial and cardiopulmonary baroreceptor reflex control of HR in angiotensin II type 1A receptor knocked out mice. In artificially ventilated, isoflurane anesthetized mice, the arterial and cardiopulmonary baroreceptor reflexes were activated via injection or slow infusions, respectively, of phenylephrine and sodium nitroprusside through the jugular vein. We observed no impairment of either the arterial or cardiopulmonary baroreceptor reflex control of HR in angiotensin type 1A receptor knockout mice.
    11/2013; 1(6):e00171. DOI:10.1002/phy2.171
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    ABSTRACT: Hypertension contributes to multiple forms of cardiovascular disease and thus morbidity and mortality. The mechanisms inducing hypertension remain unclear although the involvement of homeostatic systems, such as the renin-angiotensin and sympathetic nervous systems, is established. A pivotal role of the angiotensin type 1 receptor in the proximal tubule of the kidney for the development of experimental hypertension is established. Yet, other systems are involved. This study tests whether the expression of angiotensin type 1A receptors in catecholaminergic cells contributes to hypertension development. Using a Cre-lox approach, we deleted the angiotensin type 1A receptor from all catecholaminergic cells. This deletion did not alter basal metabolism or blood pressure but delayed the onset of angiotensin-dependent hypertension and reduced the maximal response. Cardiac hypertrophy was also reduced. The knockout mice showed attenuated activation of the sympathetic nervous system during angiotensin II infusion as measured by spectral analysis of the blood pressure. Increased reactive oxygen species production was observed in forebrain regions, including the subfornical organ, of the knockout mouse but was markedly reduced in the rostral ventrolateral medulla. These studies demonstrate that stimulation of the angiotensin type 1A receptor on catecholaminergic cells is required for the full development of angiotensin-dependent hypertension and support an important role for the sympathetic nervous system in this model.
    Hypertension 09/2013; 62(5). DOI:10.1161/HYPERTENSIONAHA.113.01474 · 7.63 Impact Factor
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    ABSTRACT: The nucleus of the solitary tract (NTS) is important for cardiovascular regulation and contains angiotensin type 1A receptors (AT1AR). To assess function, we examined the effect of expressing in AT1AR in the NTS of mice lacking these receptors. Bilateral microinjections of lentivirus expressing AT1AR (AT1Av mice, n=6) or green fluorescent protein (GFPv, n=8, control) under the control of the PRSx8 promotor, were made into the NTS of AT1AR null mice (AT1A-/-). Telemetry devices recorded blood pressure (BP), heart rate (HR) and locomotor activity. Expression of AT1AR in the NTS increased BP by 11.2±4 mmHg (P<0.05) at 2 and 3 weeks, while GFPv mice remained at pre-injection BP. Ganglion blockade reduced BP to similar levels pre- and post-transfection in GFPv and AT1Av mice. Greater pressor responses to cage-switch stress were observed following AT1AR expression (+18±2 mmHg pre- to +24±2 mmHg post-virus, P<0.05) with similar stress-induced pressor responses pre- and post-virus in GFPv mice. Pressor responses to restraint stress pre- and post-virus were similar in AT1Av but were 20% less post GFPv (P<0.001). The lack of attenuation in BP to restraint was associated with 4-fold greater Fos-expression in AT1AR mice. AT1AR expression in the NTS did not alter baroreflex gain differently between groups. The results suggest that transfection of AT1AR on neurons in the NTS elevates BP independent of the SNS and pressor responses to aversive stimuli are associated with greater Fos-expression in forebrain regions. This study suggests a novel mechanism by which the NTS may modulate MAP in the long-term via AT1AR.
    Cardiovascular Research 07/2013; DOI:10.1093/cvr/cvt183 · 5.81 Impact Factor
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    ABSTRACT: Following its generation by both systemic and tissue-based renin-angiotensin systems, angiotensin II interacts with specific, G-protein coupled receptors to modulate multiple physiological systems, including the cardiovascular system. Genetic models in which the different components of the renin-angiotensin system have been deleted show large changes in resting blood pressure. Interruption of the generation of angiotensin II, or its interaction with these receptors, decreases blood pressure in hypertensive humans and experimental animal models of hypertension. Whilst the interaction of angiotensin II with the kidney is pivotal in this modulation of blood pressure, an involvement of the system in other tissues is important. Both systemic angiotensins, acting via the blood-brain barrier deficient circumventricular organs, and centrally-generated angiotensin modulate cardiovascular control by regulating fluid and electrolyte ingestion, autonomic activity and neuroendocrine function. This review discusses the pathways in the brain that are involved in this regulation of blood pressure as well as examining the sites in which altered angiotensin function might contribute to the development and maintenance of high blood pressure.
    Autonomic neuroscience: basic & clinical 02/2013; DOI:10.1016/j.autneu.2013.01.010 · 1.37 Impact Factor
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    ABSTRACT: The caudal ventrolateral medulla (CVLM) is important for autonomic regulation and is rich in angiotensin II type 1A receptors (AT(1A)R). To determine their function, we examined whether the expression of AT(1A)R in the CVLM of mice lacking AT(1A)R (AT(1A)(-/-)) alters baroreflex sensitivity and cardiovascular responses to stress. Bilateral microinjections into the CVLM of AT(1A)(-/-) mice of lentivirus with the phox-2 selective promoter (PRSx8) were made to express either AT(1A)R (Lv-PRSx8-AT(1A)) or green fluorescent protein (Lv-PRSx8-GFP) as a control. Radiotelemetry was used to record mean arterial pressure (MAP), heart rate (HR), and locomotor activity. Following injection of Lv-PRSx8-GFP, robust neuronal expression of GFP was observed with ∼60% of the GFP-positive cells also expressing the catecholamine-synthetic enzyme tyrosine hydroxylase. After 5 weeks, there were no differences in MAP or HR between groups, but the Lv-PRSx8-AT(1A)- injected mice showed reduced baroreflex sensitivity (-25%, P = 0.003) and attenuated pressor responses to cage-switch and restraint stress compared with the Lv-PRSx8-GFP-injected mice. Reduced MAP mid-frequency power during cage-switch stress reflected attenuated sympathetic activation (Pgroup × stress = 0.04). Fos-immunohistochemistry indicated greater activation of forebrain and hypothalamic neurons in the Lv-PRSx8-AT(1A) mice compared with the control. The expression of AT(1A)R in CVLM neurons, including A1 neurons, while having little influence on the basal blood pressure or HR, may play a tonic role in inhibiting cardiac vagal baroreflex sensitivity. However, they strongly facilitate the forebrain response to aversive stress, yet reduce the pressor response presumably through greater sympatho-inhibition. These findings outline novel and specific roles for angiotensin II in the CVLM in autonomic regulation.
    Cardiovascular Research 08/2012; 96(2):330-9. DOI:10.1093/cvr/cvs252 · 5.81 Impact Factor
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    ABSTRACT: C3 neurons constitute one of three known adrenergic nuclei in the rat central nervous system (CNS). While the adrenergic C1 cell group has been extensively characterized both physiologically and anatomically, the C3 nucleus has remained relatively obscure. This study employed a lentiviral tracing technique that expresses green fluorescent protein behind a promoter selective to noradrenergic and adrenergic neurons. Microinjection of this virus into the C3 nucleus enabled the selective tracing of C3 efferents throughout the rat CNS, thus revealing the anatomical framework of C3 projections. C3 terminal fields were observed in over 40 different CNS nuclei, spanning all levels of the spinal cord, as well as various medullary, mesencephalic, hypothalamic, thalamic, and telencephalic nuclei. The highest densities of C3 axon varicosities were observed in Lamina X and the intermediolateral cell column of the thoracic spinal cord, as well as the dorsomedial medulla (both commissural and medial nuclei of the solitary tract, area postrema, and the dorsal motor nucleus of the vagus), ventrolateral periaqueductal gray, dorsal parabrachial nucleus, periventricular and rhomboid nuclei of the thalamus, and paraventricular and periventricular nuclei of the hypothalamus. In addition, moderate and sparse projections were observed in many catecholaminergic and serotonergic nuclei, as well as the area anterior and ventral to the third ventricle, Lamina X of the cervical, lumbar, and sacral spinal cord, and various hypothalamic and telencephalic nuclei. The anatomical map of C3 projections detailed in this survey hopes to lay the first steps toward developing a functional framework for this nucleus.
    The Journal of Comparative Neurology 08/2012; 520(11):2352-68. DOI:10.1002/cne.23041 · 3.51 Impact Factor
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    ABSTRACT: The role of the renin-angiotensin system (RAS) in vasoregulation is well established, but a localized RAS exists in multiple tissues and exerts diverse functions including autonomic control and thermogenesis. The role of the RAS in the maintenance and function of skeletal muscle is not well understood, especially the role of angiotensin peptides, which appear to contribute to muscle atrophy. We tested the hypothesis that mice lacking the angiotensin type 1A receptor (AT(1A)(-/-)) would exhibit enhanced whole body and skeletal muscle function and improved regeneration after severe injury. Despite 18- to 20-wk-old AT(1A)(-/-) mice exhibiting reduced muscle mass compared with controls (P < 0.05), the tibialis anterior (TA) muscles produced a 25% higher maximum specific (normalized) force (P < 0.05). Average fiber cross-sectional area (CSA) and fiber oxidative capacity was not different between groups, but TA muscles from AT(1A)(-/-) mice had a reduced number of muscle fibers as well as a higher proportion of type IIx/b fibers and a lower proportion of type IIa fibers (P < 0.05). Measures of whole body function (grip strength, rotarod performance, locomotor activity) were all improved in AT(1A)(-/-) mice (P < 0.05). Surprisingly, the recovery of muscle mass and fiber CSA following myotoxic injury was impaired in AT(1A)(-/-) mice, in part by impaired myoblast fusion, prolonged collagen infiltration and inflammation, and delayed expression of myogenic regulatory factors. The findings support the therapeutic potential of RAS inhibition for enhancing whole body and skeletal muscle function, but they also reveal the importance of RAS signaling in the maintenance of muscle mass and for normal fiber repair after injury.
    AJP Regulatory Integrative and Comparative Physiology 06/2012; 303(3):R321-31. DOI:10.1152/ajpregu.00007.2012 · 3.53 Impact Factor
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    ABSTRACT: In heart failure (HF), cardiac sympathetic nerve activity (SNA; CSNA) is increased, which has detrimental effects on the heart and promotes arrhythmias and sudden death. There is evidence that the central renin-angiotensin system plays an important role in stimulating renal SNA in HF. Because SNA to individual organs is differentially controlled, we have investigated whether central angiotensin receptor blockade decreases CSNA in HF. We simultaneously recorded CSNA and renal SNA in conscious normal sheep and in sheep with HF induced by rapid ventricular pacing (ejection fraction: <40%). The effect of blockade of central angiotensin type 1 receptors by intracerebroventricular infusion of losartan (1 mg/h for 5 hours) on resting levels and baroreflex control of CSNA and renal SNA were determined. In addition, the levels of angiotensin receptors in central autonomic nuclei were determined using autoradiography. Sheep in HF had a large increase in CSNA (43±2 to 88±3 bursts per 100 heart beats; P<0.05) and heart rate, with no effect on renal SNA. In HF, central infusion of losartan for 5 hours significantly reduced the baseline levels of CSNA (to 69±5 bursts per 100 heart beats) and heart rate. Losartan had no effect in normal animals. In HF, angiotensin receptor levels were increased in the paraventricular nucleus and supraoptic nucleus but reduced in the area postrema and nucleus tractus solitarius. In summary, infusion of losartan reduced the elevated levels of CNSA in an ovine model of HF, indicating that central angiotensin receptors play a critical role in stimulating the increased sympathetic activity to the heart.
    Hypertension 03/2012; 59(3):634-41. DOI:10.1161/HYPERTENSIONAHA.111.181131 · 7.63 Impact Factor
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    ABSTRACT: The rise in blood pressure during an acute aversive stress has been suggested to involve activation of angiotensin type 1A receptors (AT(1A)Rs) at various sites within the brain, including the rostral ventrolateral medulla. In this study we examine the involvement of AT(1A)Rs associated with a subclass of sympathetic premotor neurons of the rostral ventrolateral medulla, the C1 neurons. The distribution of putative AT(1A)R-expressing cells was mapped throughout the brains of three transgenic mice with a bacterial artificial chromosome-expressing green fluorescent protein under the control of the AT(1A)R promoter. The overall distribution correlated with that of the AT(1A)Rs mapped by other methods and demonstrated that the majority of C1 neurons express the AT(1A)R. Cre-recombinase expression in C1 neurons of AT(1A)R-floxed mice enabled demonstration that the pressor response to microinjection of angiotensin II into the rostral ventrolateral medulla is dependent upon expression of the AT(1A)R in these neurons. Lentiviral-induced expression of wild-type AT(1A)Rs in C1 neurons of global AT(1A)R knock-out mice, implanted with radiotelemeter devices for recording blood pressure, modulated the pressor response to aversive stress. During prolonged cage-switch stress, expression of AT(1A)Rs in C1 neurons induced a greater sustained pressor response when compared to the control viral-injected group (22 ± 4 mmHg for AT(1A)R vs 10 ± 1 mmHg for GFP; p < 0.001), which was restored toward that of the wild-type group (28 ± 2 mmHg). This study demonstrates that AT(1A)R expression by C1 neurons is essential for the pressor response to angiotensin II and that this pathway plays an important role in the pressor response to aversive stress.
    The Journal of Neuroscience : The Official Journal of the Society for Neuroscience 02/2012; 32(6):2051-61. DOI:10.1523/JNEUROSCI.5360-11.2012 · 6.75 Impact Factor
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    ABSTRACT: Obesity increases the risk of hypertension and cardiovascular diseases developing. Our research shows that elevated leptin levels are essential in development of obesity associated hypertension. Obese leptin deficient children have significantly(p<0.01) lower blood pressure(BP) compared to weight and aged matched subjects. Obese male mice fed a high fat diet(HFD) are hypertensive(113.7+/-1.1mmHg) and tachycardic(577.5+/-4.8BPM) compared to weight matched leptin deficient(ob/ob:100.7+/-3.0mmHg,510+/-7.0BPM) and leptin receptor deficient db/db:103.5+/-1.7mmHg,519.7+/-8.0BPM) mice measured via radiotelemetry. The Dorso Medial Hypothalamus(DMH) region in the brain is critical for obesity associated hypertension as blocking leptin actions here with both a leptin receptor antagonist or Adeno Associated Viral/shRNA knockdown of DMH leptin receptors reduces the elevated BP. Female mice fed HFD develop metabolic syndrome, including insulin insensitivity and hypertension much slower compared to males, despite leptin levels in females being substantially higher per each gram of body fat. Why are females protected? Unlike female mice, obese male mice fed a HFD have (p<0.01) higher sympathetic nerve activity (SNA) indirectly measured as brown adipose tissue temperature(36.73+/-0.1[degrees]C) compared to lean male mice(35.96+/-0.1[degrees]C) and this is leptin driven. In female mice thermogenesis is significantly(p<0.05) increased once mice have all endogenous estrogen removed, via ovariectomy. Ovariectomized female mice that have been replaced with exogenous estrogen have significantly lower thermogenesis, most likely driven by reduced SNA. Interestingly every neuron expressing estrogen receptors in the hypothalamus(the region including the DMH) also expresses a leptin receptor. While leptin increases SNA in obesity, estrogen may counteract leptin's actions through neurons in higher brain regions, decreasing SNA and protecting from the development of hypertension.
    Journal of Hypertension 01/2012; 30:e68-e69. DOI:10.1097/01.hjh.0000420051.11769.2f · 4.22 Impact Factor
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    ABSTRACT: Dietary deficiency of ω-3 fatty acids (ω-3 DEF) produces hypertension in later life. This study examined the effect of ω-3 DEF on blood pressure and hypothalamic gene expression in young rats, before the development of hypertension, and in older rats following the onset of hypertension. Animals were fed experimental diets that were deficient in ω-3 fatty acids, sufficient in short-chain ω-3 fatty acids or sufficient in short- and long-chain ω-3 fatty acids, from the prenatal period until 10 or 36 weeks-of-age. There was no difference in blood pressure between groups at 10 weeks-of-age; however, at 36 weeks-of-age ω-3 DEF animals were hypertensive in relation to sufficient groups. At 10 weeks, expression of angiotensin-II(1A) receptors and dopamine D(3) receptors were significantly increased in the hypothalamic tissue of ω-3 DEF animals. In contrast, at 36 weeks, α(2a) and β(1) adrenergic receptor expression was significantly reduced in the ω-3 DEF group. Brain docosahexaenoic acid was significantly lower in ω-3 DEF group compared with sufficient groups. This study demonstrates that dietary ω-3 DEF causes changes both in the expression of key genes involved in central blood pressure regulation and in blood pressure. The data may indicate that hypertension resulting from ω-3 DEF is mediated by the central adrenergic system.
    Hypertension Research 11/2011; 35(4):381-7. DOI:10.1038/hr.2011.194 · 2.94 Impact Factor
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    Autonomic Neuroscience 09/2011; 163(1):53-53. DOI:10.1016/j.autneu.2011.05.047 · 1.37 Impact Factor
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    ABSTRACT: Astrocytes are the major source of angiotensinogen in the brain and play an important role in the brain renin-angiotensin system. Regulating brain angiotensinogen production alters blood pressure and fluid and electrolyte homeostasis. In turn, several physiological and pathological manipulations alter expression of angiotensinogen in brain. Surprisingly, little is known about the factors that regulate astrocytic expression of angiotensinogen. There is evidence that angiotensinogen production in both hepatocytes and cardiac myocytes can be positively regulated via the angiotensin type 1 receptor, but this effect has not yet been studied in astrocytes. Therefore, the aim of this project was to establish whether angiotensin II modulates angiotensinogen production in brain astrocytes. Primary astrocyte cultures, prepared from neonatal C57Bl6 mice, expressed angiotensinogen measured by immunocytochemistry and real-time PCR. Using a variety of approaches we were unable to identify angiotensin receptors on cultured astrocytes. Exposure of cultured astrocytes to angiotensin II also did not affect angiotensinogen expression. When astrocyte cultures were transduced with the angiotensin type 1A receptor, using adenoviral vectors, angiotensin II induced a robust down-regulation (91.4% ± 1.8%, p < 0.01, n = 4) of angiotensinogen gene expression. We conclude that receptors for angiotensin II are present in extremely low levels in astrocytes, and that this concurs with available data in vivo. The signaling pathways activated by the angiotensin type 1A receptor are negatively coupled to angiotensinogen expression and represent a powerful pathway for decreasing expression of this protein, potentially via signaling pathways coupled to Gα(q/11) .
    Journal of Neurochemistry 07/2011; 119(1):18-26. DOI:10.1111/j.1471-4159.2011.07406.x · 4.24 Impact Factor
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    ABSTRACT: All components of the renin angiotensin system necessary for ANG II generation and action have been reported to be present in renal proximal convoluted tubules. Given the close relationship between renal sodium handling and blood pressure regulation, we hypothesized that modulating the action of ANG II specifically in the renal proximal tubules would alter the chronic level of blood pressure. To test this, we used a proximal tubule-specific, androgen-dependent, promoter construct (KAP2) to generate mice with either overexpression of a constitutively active angiotensin type 1A receptor transgene or depletion of endogenous angiotensin type 1A receptors. Androgen administration to female transgenic mice caused a robust induction of the transgene in the kidney and increased baseline blood pressure. In the receptor-depleted mice, androgen administration to females resulted in a Cre recombinase-mediated deletion of angiotensin type 1A receptors in the proximal tubule and reduced blood pressure. In contrast to the changes observed at baseline, there was no difference in the blood pressure response to a pressor dose of ANG II in either experimental model. These data, from two separate mouse models, provide evidence that ANG II signaling via the type 1A receptor in the renal proximal tubule is a regulator of systemic blood pressure under baseline conditions.
    AJP Regulatory Integrative and Comparative Physiology 07/2011; 301(4):R1067-77. DOI:10.1152/ajpregu.00124.2011 · 3.53 Impact Factor

Publication Stats

4k Citations
412.05 Total Impact Points

Institutions

  • 1986–2015
    • University of Melbourne
      • • Department of Physiology
      • • Department of Medicine
      Melbourne, Victoria, Australia
  • 2001–2007
    • Victoria University Melbourne
      Melbourne, Victoria, Australia
  • 1986–1996
    • Austin Health
      Melbourne, Victoria, Australia
  • 1988
    • Universität Heidelberg
      Heidelburg, Baden-Württemberg, Germany
  • 1987
    • The Royal Children's Hospital
      Melbourne, Victoria, Australia