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Microglial number is related to the number of tyrosine hydroxylase neurons in SHR and normotensive rats. Auton Neurosci 2016; 198:10-8. [PMID: 27260963 DOI: 10.1016/j.autneu.2016.05.005] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2016] [Revised: 05/19/2016] [Accepted: 05/20/2016] [Indexed: 01/30/2023]
Abstract
Microglia are ubiquitously distributed throughout the central nervous system (CNS) and play a critical role in the maintenance of neuronal homeostasis. Recent advances have shown that microglia, never resting cells of the CNS, continuously monitor and influence neuronal/synaptic activity levels, by communicating with neurons with the aid of their dynamic processes. The brainstem contains many catecholaminergic nuclei that are key to many aspects of brain function. This includes C1 neurons of the ventrolateral medulla that are thought to play a critical role in control of the circulation. Despite the role of catecholaminergic brainstem neurons in normal physiology, the presence of microglia that surrounds them is poorly understood. Here, we investigate the spatial distribution and morphology of microglia in catecholaminergic nuclei of the brainstem in 3 strains of rat: Sprague-Dawley (SD), Wistar-Kyoto (WKY) and spontaneously hypertensive rats (SHR). Our data reveal that microglia are heterogeneously distributed within and across different strains of rats. Interestingly, intra-strain comparison of tyrosine hydroxylase-immunoreactive (TH-ir) neuronal and microglial number reveals that microglial number varies with the TH-ir neuronal number in the brainstem. Even though microglial spatial distribution varies across brainstem nuclei, microglial morphology (% area covered, number of end point processes and branch length) does not differ significantly. This work provides the first evidence that even though microglia, in their surveilling state, do not vary appreciably in their morphology across brainstem areas, they do have a heterogeneous pattern of distribution that may be influenced by their local environment.
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Head GA. Proceedings of the Symposium ‘Angiotensin AT1 Receptors: From Molecular Physiology to Therapeutics’: ROLE OF AT1 RECEPTORS IN THE CENTRAL CONTROL OF SYMPATHETIC VASOMOTOR FUNCTION. Clin Exp Pharmacol Physiol 2007; 23 Suppl 3:S93-8. [DOI: 10.1111/j.1440-1681.1996.tb02820.x] [Citation(s) in RCA: 62] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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Saigusa T, Granger NS, Godwin SJ, Head GA. The rostral ventrolateral medulla mediates sympathetic baroreflex responses to intraventricular angiotensin II in rabbits. Auton Neurosci 2003; 107:20-31. [PMID: 12927223 DOI: 10.1016/s1566-0702(03)00104-8] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
The present study examined the role of the rostral ventrolateral medulla (RVLM) in mediating the pressor and renal sympathetic baroreflex effects of intraventricularly administered angiotensin II (Ang II) in urethane anaesthetised rabbits. Microinjection of Ang II over a wide range of medullary sites showed that pressor responses were observed only in the RVLM. Ang II was particularly potent in producing a transient pressor response at this site with a half maximal dose of 9 fmol. The administration of the Ang II antagonist Sar(1)-Ile(8)-Ang II (10 pmol) bilaterally into the RVLM inhibited the pressor response to local and fourth ventricular Ang II, but not the pressor response to RVLM applied glutamate. To determine the contribution of the RVLM to the renal sympathetic baroreflex effects of Ang II, blood pressure-renal sympathetic nerve activity (RSNA) curves were constructed with intravenous infusion of phenylephrine or nitroprusside before and after Ang II, vehicle or glutamate infusions into the RVLM. Ang II infusion of 4 pmol/min into the RVLM increased blood pressure by 8+/-3 mm Hg and shifted the renal sympathetic baroreflex curve to the right. The maximum RSNA evoked by lowering blood pressure increased by 36+/-6%, similar to the effect seen with fourth ventricular Ang II and RVLM glutamate. These studies suggest that the major medullary pressor site of action of Ang II when injected into the hindbrain cerebro-spinal fluid of anaesthetized rabbits is the RVLM where it facilitates baroreflex control of RSNA.
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Affiliation(s)
- Takeshi Saigusa
- Department of Physiology, Faculty of Medicine, University of Yamanashi, Tamaho, Nakakoma, Yamanashi 409-3898, Japan.
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Parkin ML, Godwin SJ, Head GA. Importance of imidazoline-preferring receptors in the cardiovascular actions of chronically administered moxonidine, rilmenidine and clonidine in conscious rabbits. J Hypertens 2003; 21:167-78. [PMID: 12544449 DOI: 10.1097/00004872-200301000-00027] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
OBJECTIVE To determine the involvement of central imidazoline receptors in the cardiovascular actions of the chronically administered antihypertensive agents moxonidine, rilmenidine and clonidine. DESIGN AND METHODS In 21 rabbits with implanted fourth-ventricular catheters, we investigated the central effects of three cumulative doses of an I(1)-imidazoline/alpha(2)-adrenoceptor antagonist, efaroxan, and of an alpha(2)-adrenoceptor antagonist, 2-methoxyidazoxan (2-MI), on the changes in blood pressure and heart rate (HR) elicited by chronic subcutaneous administration of moxonidine, rilmenidine and clonidine, after 1 and 3 weeks of treatment. A low, medium and high dose of 2-MI was matched to three doses of efaroxan, such that each produced equal reversal of the hypotension induced by fourth-ventricular alpha-methyldopa and hence produced a similar degree of alpha(2)-adrenoceptor blockade. RESULTS Clonidine and moxonidine, at doses of 1 mg/kg per day, and rilmenidine at 5 mg/kg per day, produced sustained reductions in mean arterial pressure of 13 +/- 3, 15 +/- 2 and 13 +/- 2 mmHg, respectively over the 3-week treatment period, but did not alter HR. Central administration of efaroxan on day 9 and day 23 of treatment produced a greater increase in blood pressure than did 2-MI with all three antihypertensive agents. Blood pressure reached levels that were significantly above the original control values. By contrast, the alpha(2)-adrenoceptor antagonist 2-MI only induced a rebound blood pressure effect in clonidine- and to a lesser extent in rilmenidine-treated rabbits. Both efaroxan and 2-MI produced a similar degree of tachycardia in moxonidine-, rilmenidine- and clonidine-treated animals.(2) CONCLUSIONS The greater effect of efaroxan compared to the alpha(2)-adrenoceptor antagonist 2-MI suggests that the hypotension induced by chronic subcutaneous administration of moxonidine, rilmenidine and clonidine is mediated predominantly via an action on central imidazoline receptors. Furthermore, all agents showed a propensity to produce rebound hypertension with imidazoline receptor blockade. However, only clonidine showed a rebound phenomenon when challenged by acute central alpha(2)-adrenoceptor blockade
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Affiliation(s)
- Monique L Parkin
- Neuropharmacology Laboratory, Baker Heart Research Institute, Commercial Road Prahran, St Kilda Road Central, Melbourne, Victoria 8008, Australia
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Maiorov DN, Malpas SC, Head GA. Influence of pontine A5 region on renal sympathetic nerve activity in conscious rabbits. Am J Physiol Regul Integr Comp Physiol 2000; 278:R311-9. [PMID: 10666130 DOI: 10.1152/ajpregu.2000.278.2.r311] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The effects of inhibiting the neural activity in the pontine A5 region on renal sympathetic responses to baroreflex and/or chemoreflex activation were examined in conscious rabbits. Eight rabbits were chronically instrumented with guide cannulas for bilateral microinjections into the A5 area and an electrode for measuring renal sympathetic nerve activity (RSNA). Baroreflex curves were obtained under conditions of normoxia and hypoxia (10% O(2) + 3% CO(2)) after injections into the A5 region of the GABA receptor agonist muscimol or vehicle solution. Under normoxia, injections of muscimol did not affect resting RSNA or blood pressure but increased the range of the RSNA baroreflex by 24 and 33% at doses of 175 or 875 pmol, respectively, without affecting the reflex gain. Hypoxia alone increased resting RSNA by 63%, as well as the range and gain of the RSNA baroreflex by 53 and 89%, respectively, without affecting blood pressure. However, under hypoxia, muscimol increased resting RSNA by 37 and 47% but decreased the gain of the RSNA baroreflex by 19 and 34% at doses of 175 or 875 pmol, respectively, without affecting the reflex range. The effects of muscimol on RSNA were mediated via changes in the amplitude of the sympathetic bursts, whereas burst frequency remained unaffected. These data suggest that the A5 region has a little tonic influence on RSNA in conscious rabbits but serves to limit the renal sympathetic responses to baroreceptor unloading or chemoreceptor stimulation. The different changes in the baroreflex range and gain evoked by muscimol under normoxia and hypoxia indicate that the A5 modulatory action may depend on the activity of the afferent inputs to this region.
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Affiliation(s)
- D N Maiorov
- Baker Medical Research Institute, Prahran, Victoria 3181, Australia
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Shafton AD, Ryan A, McGrath B, Badoer E. Volume expansion does not activate neuronal projections from the NTS or depressor VLM to the RVLM. THE AMERICAN JOURNAL OF PHYSIOLOGY 1999; 277:R39-46. [PMID: 10409256 DOI: 10.1152/ajpregu.1999.277.1.r39] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
We investigated whether a monosynaptic connection from the nucleus tractus solitarius (NTS) or the depressor ventrolateral medulla (VLM) to the pressor region of the rostral VLM (RVLM) constituted part of the reflex pathway activated by cardiopulmonary baroreceptors. Volume expansion in the conscious rabbit, which elicits renal nerve inhibition predominantly via cardiac mechanoreceptors, was used as the stimulus. The protein Fos was used as a marker of neuronal activation. The retrogradely transported tracer rhodamine-tagged microspheres, previously injected into the pressor region of the RVLM, identified medullary neurons that projected to that region. Volume expansion significantly increased the number of Fos-positive cell nuclei in the NTS and in the depressor VLM. Neurons that projected to the RVLM were found throughout the depressor region of the VLM and in the NTS but were not activated by volume expansion. Thus, although the central reflex pathways activated by volume expansion include the NTS and the depressor region of the VLM, we could not find evidence for a monosynaptic connection between those regions and the RVLM.
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Affiliation(s)
- A D Shafton
- Department of Medicine, Monash Medical Centre, Monash University, Clayton 3168, Melbourne, Victoria, Australia
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Maiorov DN, Wilton ER, Badoer E, Petrie D, Head GA, Malpas SC. Sympathetic response to stimulation of the pontine A5 region in conscious rabbits. Brain Res 1999; 815:227-36. [PMID: 9878751 DOI: 10.1016/s0006-8993(98)01150-0] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
Studies in anaesthetized animals have shown that the pontine A5 noradrenergic region plays an important role in the sympathetic control of arterial pressure (AP). The aim of this study was to develop, in conscious rabbits, a technique for microinjections into the A5 region and examine the effects of stimulation of this region on renal sympathetic nerve activity (RSNA). In preliminary mapping experiments on four anaesthetized rabbits, electrical stimulation of the A5 region induced a pressor response ranging between 25 and 75 mmHg while unilateral injection of glutamate (100 nmol) did not change AP. The mapping experiments were used to enable guide cannulae implantation for subsequent microinjections into the A5 region. In six conscious rabbits, unilateral injection of glutamate (100 nmol) caused a consistent increase in RSNA (+45%) but did not change AP. In another eight rabbits, bilateral injection of glutamate (0.3, 3, 30 nmol) into the A5 region dose-dependently increased RSNA by 13%, 30% and 40%, respectively. In four rabbits, angiotensin II (0.3, 3, 30 pmol) injected bilaterally into the A5 region increased RSNA by 5%, 22% and 28%, respectively. In all animals the increase in RSNA was mainly mediated by increasing amplitude of sympathetic synchronized bursts while their frequency remained unchanged. However, both glutamate and angiotensin II did not change AP indicating that the sympathoexcitatory response to the A5 stimulation might be relatively confined to the renal bed. Using a novel microinjection technique developed for conscious rabbits, we found that the A5 region may provide an important excitatory and possibly selective input to the renal sympathetic preganglionic neurons.
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Affiliation(s)
- D N Maiorov
- Baker Medical Research Institute, Prahran, P.O. Box 6492, St. Kilda Rd. Central, Melbourne, Victoria 8008, Australia
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Godwin SJ, Tortelli CF, Parkin ML, Head GA. Comparison of the baroreceptor-heart rate reflex effects of moxonidine, rilmenidine and clonidine in conscious rabbits. JOURNAL OF THE AUTONOMIC NERVOUS SYSTEM 1998; 72:195-204. [PMID: 9851569 DOI: 10.1016/s0165-1838(98)00105-2] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
In 10 conscious rabbits, the baroreceptor-heart rate (HR) reflex effects of centrally acting antihypertensive agents with high affinity for imidazoline receptors (IRs), moxonidine and rilmenidine, were compared with clonidine which acts predominantly via central alpha2-adrenoceptors. Dose regimens were chosen to give similar hypotension (-17+/-1 mm Hg) and bradycardia (-27+/-2 b/min) for all three agents given into the fourth ventricle. Baroreceptor-HR reflex curves were assessed by i.v. drug induced changes in blood pressure. With all treatments, the baroreflex curves with both vagal and sympathetic effectors intact were shifted to the left, corresponding to the hypotension, and the bradycardia plateau was reduced. Rilmenidine and moxonidine also reduced the upper plateau such that the curves were shifted parallel down the HR scale with no change in the HR range. By contrast, clonidine only decreased the lower plateau, and thus increased HR range (+19+/-6%). Moxonidine, but not rilmenidine, reduced the baroreflex gain by reducing the curvature. Clonidine also decreased curvature but this did not result in a reduction in gain as it was offset by the increase in HR range. The gain and range of the cardiac sympathetic component, as assessed after vagal blockade, was reduced by rilmenidine by 53 and 40% respectively, but was not affected by the other agents. The calculated vagal component of the curves showed that all agents produced a greater vagal bradycardia in response to a rise in pressure and that both rilmenidine and clonidine increased vagal HR range. The present study results show that many of the baroreflex effects of clonidine, such as facilitating cardiac vagal responses, are shared by the second generation agent rilmenidine, suggesting that they are primarily due to alpha2-adrenoceptor activation. In addition, the inhibition of the sympathetic component of the baroreflex, observed with rilmenidine, and not clonidine suggests that this effect may involve IRs. By contrast moxonidine, the most specific agent for I1 receptors, produces mainly a baroreflex independent inhibition of cardiac sympathetic activity with little effect on vagal activity.
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Affiliation(s)
- S J Godwin
- Neuropharmacology Laboratory, Baker Medical Research Institute, Melbourne, Victoria, Australia
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Gaudet EA, Godwin SJ, Head GA. Role of central catecholaminergic pathways in the actions of endogenous ANG II on sympathetic reflexes. THE AMERICAN JOURNAL OF PHYSIOLOGY 1998; 275:R1174-84. [PMID: 9756548 DOI: 10.1152/ajpregu.1998.275.4.r1174] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
In the present study, we examined the effect of blockade of the brain stem renin-angiotensin system on renal sympathetic baroreflexes and chemoreflexes in conscious rabbits and examined the role of central catecholaminergic pathways in these responses. Eleven rabbits underwent preliminary surgical instrumentation and pretreatment with central 6-hydroxydopamine (6-OHDA, 500 micrograms/kg) or ascorbic acid 6 wk before the commencement of the experiments. Baroreflex curves were determined under conditions of normoxia and hypoxia (10% O2 + 3% CO2) before and after central administration of either Ringer solution, the ANG II receptor antagonist losartan (10 micrograms), or the angiotensin-converting enzyme inhibitor enalaprilat (500 ng) on separate days. Losartan increased the upper plateau and the range of the mean arterial pressure (MAP)-renal sympathetic nerve activity (RSNA) curve (79 and 78%, respectively) in intact rabbits, whereas this effect was not observed in 6-OHDA-pretreated rabbits. Hypoxia elicited an increase in resting RSNA (111% in intact rabbits and 74% in 6-OHDA-injected rabbits) and elevated the upper plateau of the RSNA-MAP curve in both groups (89% in intact rabbits and 114% in 6-OHDA-injected rabbits). During hypoxia, losartan and enalaprilat increased the RSNA upper plateau in intact rabbits but had no effect in 6-OHDA-pretreated rabbits. No effects on the MAP-heart rate baroreflex curves were observed. Thus the effect of losartan to increase RSNA, particularly during hypoxia and baroreceptor unloading, being abolished by central noradrenergic depletion suggests that the endogenous ANG II which normally causes an inhibition of renal sympathetic motoneurons is dependent on the integrity of central catecholaminergic pathways.
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Affiliation(s)
- E A Gaudet
- Baker Medical Research Institute, Victoria, Australia
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Akama H, McGrath BP, Badoer E. Volume expansion fails to normally activate neural pathways in the brain of conscious rabbits with heart failure. JOURNAL OF THE AUTONOMIC NERVOUS SYSTEM 1998; 73:54-62. [PMID: 9808371 DOI: 10.1016/s0165-1838(98)00124-6] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
Immunohistochemical detection of the protein, Fos, was used to identify neurons in the brain activated following a volume load in conscious rabbits with doxorubicin-induced congestive cardiomyopathy. The plasma expander, Haemaccel, was infused intravenously into rabbits for 60 min and significantly increased right atrial pressure, blood pressure and heart rate. The rabbits were perfusion fixed 90 min after the start of the infusion and the distribution of Fos-positive cell nuclei was examined. Compared to control rabbits with heart failure, there was a small significant increase in the number of Fos-positive cell nuclei in the organum vasculosum of the lamina terminalis following volume expansion. In other regions of the brain that were studied in detail, there were no significant increases in Fos production. These included the parvocellular paraventricular nucleus (PVN) of the hypothalamus, the midbrain periaqueductal gray, the nucleus tractus solitarius (NTS), area postrema and the ventrolateral medulla (VLM). In the supraoptic nucleus and the magnocellular PVN, no Fos-positive cell nuclei were present as expected. The median preoptic nucleus, the bed nucleus of the striae terminalis and the diagonal band of Broca contained some Fos but there was no marked difference between volume expanded and control animals. In the anterior cortical and medial subnuclei of the amygdala there was a high concentration of Fos but there was no consistent difference between the two groups. The present findings in heart failure rabbits suggest that most brain regions are not activated sufficiently by the stimulus to elicit Fos expression. The results are in accord with findings showing that sympathetic reflexes initiated by volume expansion are attenuated in heart failure.
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Affiliation(s)
- H Akama
- Department of Medicine, Monash University, Monash Medical Centre, Melbourne, Victoria, Australia
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11
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Head GA, Burke SL. Relative importance of medullary brain nuclei for the sympatho-inhibitory actions of rilmenidine in the anaesthetized rabbit. J Hypertens 1998; 16:503-17. [PMID: 9797196 DOI: 10.1097/00004872-199816040-00012] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
OBJECTIVE To determine the contribution of the rostral ventrolateral medulla and the nucleus of the solitary tract in mediating the attenuation of the renal sympathetic baroreflex produced by administration of rilmenidine to anaesthetized rabbits and to examine the relative contribution of alpha2-adrenoceptors and imidazoline receptors at these sites to the cardiovascular effects of rilmenidine. METHODS AND RESULTS Rilmenidine micro-injected into the rostral ventrolateral medulla produced hypotension and inhibition of renal sympathetic nerve activity with doses an order of magnitude lower than those required in the nucleus tractus solitarius. Alpha-methylnoradrenaline, however, was similarly potent at producing hypotension when it was injected into the rostral ventrolateral medulla or nucleus tractus solitarius but, unlike rilmenidine, did not lower renal sympathetic nerve activity when it was injected into the nucleus tractus solitarius. The alpha2-adrenoceptor antagonist 2-methoxyidazoxan partially reversed the hypotension and renal sympathetic nerve activity inhibition due to alpha-methylnoradrenaline when it was administered into the rostral ventrolateral medulla, whereas the mixed alpha2-adrenoceptor/imidazoline receptor antagonists, idazoxan and efaroxan, did not. 2-Methoxyidazoxan, but not idazoxan, also reversed the hypotension when alpha-methylnoradrenaline was administered into the nucleus tractus solitarius. The hypotension induced by rilmenidine in the rostral ventrolateral medulla was completely reversed both by 2-methoxyidazoxan and by idazoxan, as was the sympathetic inhibition. To assess any interaction between the nucleus tractus solitarius and the rostral ventrolateral medulla in mediating the baroreflex effects of rilmenidine, we injected rilmenidine into the rostral ventrolateral medulla, the nucleus tractus solitarius or both nuclei and determined renal baroreflex responses of sympathetic nerve activity using drug-induced changes in blood pressure. Injection of 0.5 nmol rilmenidine into the rostral ventrolateral medulla reduced mean arterial pressure and basal renal sympathetic nerve activity as well as renal sympathetic baroreflex range (by 27%) and gain (by 35%). In contrast, injection of rilmenidine into the nucleus tractus solitarius had no effect on basal renal sympathetic nerve activity and renal sympathetic baroreflex parameters. The effect of combined injection was similar to that of administration into the rostral ventrolateral medulla alone. CONCLUSION Our results show that the rostral ventrolateral medulla, rather than the nucleus tractus solitarius, is the major site involved in the hypotension and inhibition of the renal sympathetic baroreflex by rilmenidine. Comparison of the actions of alpha2-adrenoceptor and imidazoline receptor antagonists on the effects of rilmenidine and alpha-methylnoradrenaline suggests that these agents are acting at different receptors, presumably imidazoline and alpha2-adrenoceptors receptors, respectively, and that both are important in lowering sympathetic tone and blood pressure in the rostral ventrolateral medulla.
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Affiliation(s)
- G A Head
- Neuropharmacology Laboratory, Baker Medical Research Institute, Prahran, Victoria, Australia.
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Badoer E, McKinlay D, Trigg L, McGrath BP. Distribution of activated neurons in the rabbit brain following a volume load. Neuroscience 1997; 81:1065-77. [PMID: 9330368 DOI: 10.1016/s0306-4522(97)00232-7] [Citation(s) in RCA: 47] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Immunohistochemical detection of the protein, Fos, was used to identify neurons in the brain activated following a volume load. The plasma expanders, Haemaccel and 6% dextran, were infused intravenously in conscious rabbits for 60 min. Compared to control animals both stimuli significantly increased right atrial pressure but had no effect on blood pressure. Heart rate was significantly elevated with dextran only. Volume expansion with Haemaccel also reduced renal sympathetic nerve activity by about 50% from the pre-infusion resting level. Ninety minutes after the start of the infusion, the rabbits were perfusion fixed and the distribution of Fos-positive cell nuclei was examined. Following Haemaccel infusion there were significant increases in the number of Fos-positive cell nuclei in the organum vasculosum of the lamina terminalis, parvocellular paraventricular nucleus and in specific rostrocaudal levels of the nucleus tractus solitarius and ventrolateral medulla. Following dextran similar effects were observed in the medulla but Fos-positive cell nuclei were not significantly elevated above controls in the forebrain. After Haemaccel or dextran areas such as the supraoptic nucleus, the magnocellular paraventricular nucleus, the bed nucleus of the stria terminalis, diagonal band of Broca and amygdala either did not produce Fos or were not consistently different from the control group. The results suggest that specific brain regions, that are known to be important in cardiovascular control, are activated by a volume load. These areas are likely to play an important role in the reflex responses initiated by that particular stimulus.
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Affiliation(s)
- E Badoer
- Department of Medicine, Monash University, Melbourne, Victoria, Australia
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Drolet G, Chalmers J, Blessing W. Vasodepressor neurons in medulla alter cardiac contractility and cardiac output. Hypertension 1993; 21:210-5. [PMID: 8094070 DOI: 10.1161/01.hyp.21.2.210] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
We injected neuroexcitatory and neuroinhibitory agents into the depressor region of the caudal ventrolateral medulla of anesthetized rabbits and determined the effect on arterial pressure, myocardial contractility, cardiac output, and plasma catecholamines and neuropeptide Y. Brief excitation of the sympathoinhibitory neurons with medullary injection of L-glutamate reduced arterial pressure, peripheral vascular resistance, and myocardial contractility. Cardiac output was unaffected. Prolonged inhibition of the sympathoinhibitory neurons with medullary injection of muscimol increased arterial pressure, peripheral vascular resistance, and myocardial contractility. There was a progressive fall in cardiac output. These changes were accompanied by an increase in plasma neuropeptide Y and plasma norepinephrine, but no change in plasma epinephrine. Our findings indicate that the sympathoinhibitory vasomotor neurons in the caudal ventrolateral medulla tonically suppress the activity of sympathetic preganglionic neurons controlling myocardial contractility as well as peripheral vasomotor tone. Dysfunction of these medullary neurons could underly some forms of experimental hypertension.
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Affiliation(s)
- G Drolet
- Department of Medicine, Flinders University of South Australia, Bedford Park
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Denoyer M, Sallanon M, Buda C, Kitahama K, Jouvet M. Neurotoxic lesion of the mesencephalic reticular formation and/or the posterior hypothalamus does not alter waking in the cat. Brain Res 1991; 539:287-303. [PMID: 1675907 DOI: 10.1016/0006-8993(91)91633-c] [Citation(s) in RCA: 67] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
In order to re-evaluate the role of two putative waking systems, we injected a neural cell body toxin, ibotenic acid (IA) (45 micrograms/microliters), into the mesencephalic reticular formation (MRF) and/or the posterior hypothalamus (PH). On the one hand, when the cell body destruction was only restricted to the MRF, the IA microinjection was followed by a temporary high voltage and slow neocortical electroencephalogram (EEG) during the first 24 postoperative hours and by a subsequent long term increase in waking which lasted 8-12 h. After the first postoperative day, there were no motor disturbances, no aphagia nor adypsia, no alteration of cortical activation and no modification of thermoregulation or of the sleep-waking cycle. On the other hand, the IA microinjection into the PH induced a hypothermia during the first postoperative night and a dramatic transient hypersomnia immediately after the disappearance of the anesthesia (14-24 h after the IA injection). On the third day, all cats recovered control level of paradoxical sleep (PS), slow wave sleep (SWS) and cerebral temperature. They presented normal motor behavior but they were not able to eat by themselves during the first postoperative week. Finally, when the lesions of the MRF and the PH were realized in one single operation, the cats were first motionless in a comatose state for 2-3 days. This state was accompanied by a transitory hypothermia and the suppression of a spontaneous or evoked cortical low voltage fast activity. However, from the 2nd postoperative week, both behavioral and EEG waking re-occurred. By contrast, the two successive operations (MRF followed by PH) did not induce a comatose state. We did not observe any deficit in motor behavior, and the sleep-waking cycle was quite normal as from the second postlesion day. In the MRF-PH-lesioned cats, the injection of alpha-methyl-p-tyrosine (150 mg/kg) induced a large decrease in waking and a moderate increase in PS. In the MRF-lesioned cats, IA produced a large area of cell body loss, centered in the MRF, that extended from levels A2 to A6 of stereotaxic planes and sometimes encroached upon the red nucleus and the substantia nigra. In the PH-lesioned cats, the histological analysis revealed a great loss of cell bodies in the PH extended from levels A8 to A12.5. The damage included the lateral and posterior hypothalamic areas and sometimes the tuberomamillary nucleus. In MRF- and PH-lesioned cats, the cell body loss extended from levels A2 to A12.5.(ABSTRACT TRUNCATED AT 400 WORDS)
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Affiliation(s)
- M Denoyer
- Département de Médecine Expérimentale, I.N.S.E.R.M. U 52, C.N.R.S. URA 1195, Université Claude Bernard, Lyon, France
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Elghozi JL, Head GA, Wolf WA, Anderson CR, Korner PI. Importance of spinal noradrenergic pathways in cardiovascular reflexes and central actions of clonidine and alpha-methyldopa in the rabbit. Brain Res 1989; 499:39-52. [PMID: 2508991 DOI: 10.1016/0006-8993(89)91133-5] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
We have examined in conscious rabbits the chronic effects of 6-hydroxydopamine (6-OHDA)-induced local lesions of the spinal noradrenaline (NA) pathways on (i) resting mean arterial pressure (MAP) and heart rate (HR), (ii) the nasopharyngeal pressor response, (iii) the sympathetic component of the baroreceptor-heart rate reflex (iv) the acute responses to intracisternal (i.c.) clonidine and alpha-methyldopa (alpha-MD), and (v) the acute NA release response produced by i.e. 6-OHDA. One month after injection of 6-OHDA (40 nmol in 4 microliters) into the first cervical spinal cord segment (C1), the NA content was reduced to 29% in C2, 45% in T4 and 61% in L3 with little non-specific damage. Basal MAP was 14% higher (P less than 0.05) than in sham-operated rabbits suggesting increased vasoconstrictor tone. Basal cardiac sympathetic tone was enhanced, but a corresponding increase in cardiac vagal tone resulted in little net effect on resting HR in the spinal NA-depleted group. Spinal NA lesions attenuated the nasopharyngeal pressor reflex by 27% in baroreceptor-intact rabbits and by 38% in sino-aortically denervated (SAD) animals. The lesion did not affect HR range, gain and BP50 of the sympathetic baroreflex. In SAD rabbits, the acute MAP responses to i.c. 6-OHDA (early hypotension, late hypertension) were not affected by spinal NA depletion, but the early fall in HR (cardiac sympathetic inhibition) was abolished. The hypotension produced by i.c. clonidine or alpha-MD was not affected by the lesion, probably because many of the NA terminals in the lower thoracic and upper lumbar cord were still intact. Our results suggest that intraspinal NA fibers have a tonic inhibitory action on spinal preganglionic vasoconstrictor and cardiac motoneurons. The spinal NA neurons affecting vasomotor tone (but not cardiac sympathetic tone) are in turn inhibited by higher vasomotor centers receiving projections from the arterial and trigeminal afferents and thereby participate in vasoconstrictor reflexes.
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Affiliation(s)
- J L Elghozi
- Baker Medical Research Institute, Prahran, Vic Australia
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Saad MA, Huerta F, Trancard J, Elghozi JL. Effects of middle cerebral artery occlusion on baroreceptor reflex control of heart rate in the rat. JOURNAL OF THE AUTONOMIC NERVOUS SYSTEM 1989; 27:165-72. [PMID: 2778268 DOI: 10.1016/0165-1838(89)90098-2] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
Neurons in the insular cortex have recently been shown to innervate medullary autonomic nuclei such as the nucleus tractus solitarii (NTS). The present study examines the effect of lesioning the insular cortex on baroreceptor-heart rate reflex in conscious rats. We did this by occluding the stem of the left proximal middle cerebral artery which causes a lesion of the insular and adjacent lateral frontoparietal cortices. Nine and 10 days after lesioning or sham operation, reflex heart rate responses were recorded following i.v. doses of the pressor agent phenylephrine and the depressor agent sodium nitroprusside. Baroreceptor reflex parameters were determined by computerized sigmoidal curve-fitting. The overall contribution of the sympathetic and the cardiac vagus were assessed by using peripherally acting muscarinic and beta-adrenoceptor antagonists, respectively. Lesioned rats were compared to sham-operated rats. Lesioning the insular cortex did not affect mean blood pressure and heart rate. However, the lesion selectively enhanced reflex vagal bradycardia that occurred when mean blood pressure was artificially elevated. A greater vagal bradycardia with no change in the upper plateau indicated that ischemia was acting entirely on the baroreflex-dependent vagal cardiac motoneurons. There was no effect on the sympathetic heart rate range but the normalized gain of the sympathetic component was increased in those lesioned rats. These observations suggest that the unilateral cortical lesion chronically affected the baroreceptor control of heart rate through mechanisms differentially affecting the vagus and the cardiac sympathetic nerves.
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Affiliation(s)
- M A Saad
- Department of Pharmacology, INSERM U7, Faculty of Medicine Necker, Paris, France
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17
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Blessing WW, Li YW. Inhibitory vasomotor neurons in the caudal ventrolateral region of the medulla oblongata. PROGRESS IN BRAIN RESEARCH 1989; 81:83-97. [PMID: 2694225 DOI: 10.1016/s0079-6123(08)62000-2] [Citation(s) in RCA: 52] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
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18
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Korner PI, Badoer E, Head GA. Cardiovascular role of the major noradrenergic cell groups in the rabbit: analysis based on 6-hydroxydopamine-induced transmitter release. Brain Res 1987; 435:258-72. [PMID: 2892575 DOI: 10.1016/0006-8993(87)91609-x] [Citation(s) in RCA: 34] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
We examined the role of the noradrenergic (NA) neurons of the A1, A2, A1 + A2, A5 and A6 + A7 regions on mean arterial pressure (MAP) and heart rate (HR), by comparing the acute responses of chronically lesioned and sham-operated rabbits to intracisternal 6-hydroxydopamine (6-OHDA, 600 micrograms/kg) which induces central release of transmitter. We studied rabbits (1) with intact arterial baroreceptors (non-denervated) and (2) after sino-aortic denervation (SAD). The acute transmitter release response consisted of an early fall in MAP (observed in SAD rabbits) and a late rise in MAP (observed in both non-denervated and SAD rabbits). Medullary lesions had no effect on either MAP component, but A5 and A6 + A7 lesions attenuated both pressor and depressor responses. Normally the transmitter release-induced MAP responses are modified by baroreceptor feedback. The 6-OHDA-induced HR changes were vagal in non-denervated rabbits and were sympathetically mediated in SAD rabbits. In non-denervated rabbits, A1, A2 and A1 + A2 lesions affected mainly the early vagal component, whilst A6 + A7 lesions affected the late vagal component. In SAD rabbits the early bradycardia was due to sympathetic inhibition and the late tachycardia due to sympathetic excitation; A1 + A2 lesions and A5 lesions attenuated the sympathetic bradycardia. We conclude that the various components of the MAP and HR responses are mediated through distinctive NA pathways; the deficits of a given lesion could be due to either to loss of NA cell bodies or of NA fibers of passage.
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Affiliation(s)
- P I Korner
- Baker Medical Research Institute, Melbourne, Australia
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Head GA, Badoer E, Korner PI. Cardiovascular role of A1 catecholaminergic neurons in the rabbit. Effect of chronic lesions on responses to methyldopa, clonidine and 6-OHDA induced transmitter release. Brain Res 1987; 412:18-28. [PMID: 2886185 DOI: 10.1016/0006-8993(87)91435-1] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
We confirmed the findings of previous investigators that bilateral anodal lesions of the A1 region were associated with hypertension, bradycardia, pulmonary edema and a high mortality. All these sequelae (except the bradycardia) no longer occurred after cathodal lesions and these were therefore used to investigate the role of the catecholaminergic (CA) neurons of the A1 region in circulatory regulation. Conscious rabbits were studied 2-4 weeks after A1 lesions or sham-operation, when resting mean arterial pressure (MAP) and heart rate (HR) were closely similar in both groups. We tested for differences in MAP and HR responses between lesioned and sham-operated groups: to intracisternal (i.c.) alpha-methyldopa (MD) and to clonidine; and to the acute effects of i.c. 6-hydroxydopamine (6-OHDA) which elicits central CA release. Since these tests depend on the integrity of the central CA neurons, response differences between lesioned and sham-operated groups denote participation by the CA neurons of the A1 region in the central circulatory pathways. The bradycardia responses in the above tests were all smaller in lesioned than sham-operated rabbits, but there were no differences in MAP responses. Electrical stimulation of the region under alfathesin anaesthesia produced depressor responses at low frequencies and pressor responses at high frequencies. From the results in conscious rabbits CA neurons of the A1 region mainly influence the pathways regulating HR, rather than blood pressure. The changes in MAP during electrical stimulation are thus probably mediated through non-CA neurons.
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