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Lindqvist A, Jalonen J, Laitinen LA, Seppälä T, Strömberg C. The effects of midazolam and ephedrine on post-exercise autonomic chronotropic control of the heart in normal subjects. Clin Auton Res 1996; 6:343-9. [PMID: 8985623 DOI: 10.1007/bf02556305] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
Benzodiazepines may induce hypotension by inhibiting the pressor response. Ephedrine has adrenergic effects on the circulation. After exercise, changes in cardiovascular control impair orthostatic tolerance. The impaired pressure response can be compensated for by chronotropic control of the heart. We studied the effect of midazolam and ephedrine on post-exercise cardiac autonomic chronotropic control in six 21-year-old female volunteers, who received single doses of 15 mg midazolam, 50 mg ephedrine, or placebo orally according to a placebo-controlled, double-blind, crossover design. After exercise, the subjects assumed the supine position for rest, then a -10 degrees head-down position followed by a 70 degrees head-up position. Power spectral analysis of heart rate variability for 7 min and steady-state brachial arterial blood pressure were measured in each position. After administration of midazolam, three subjects had an abnormal fall in their arterial blood pressure (with one presyncope) as a response to head-up tilt. Changes in heart rate variability exceeded those seen during placebo treatment (p < 0.01) and involved oscillations, suggesting activation of both sympathetic and parasympathetic dynamics. After ephedrine administration, arterial blood pressure increased during head-down tilt, but parasympathetic dynamics to the heart were dampened. Head-up tilt induced increased sympathetic stimulation of the heart and a sympathicotonic cardiovascular response (p < 0.01). In conclusion, midazolam induced unexpectedly great changes in dynamic cardiac control during cardiovascular stimulation. Ephedrine increased tonic sympathetic activity and stabilized the neural circulatory control of the heart by immobilizing dynamic parasympathetic activation.
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Affiliation(s)
- A Lindqvist
- Research Institute of Military Medicine, Central Military Hospital, Helsinki, Finland
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Smit AA, Wieling W, Voogel AJ, Koster RW, van Zwieten PA. Orthostatic hypotension due to suppression of vasomotor outflow after amphetamine intoxication. Mayo Clin Proc 1996; 71:1067-70. [PMID: 8917291 DOI: 10.4065/71.11.1067] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
Ten hours after ingestion of amphetamines, a previously healthy 17-year-old female adolescent experienced dizziness on standing. Examination revealed pronounced drowsiness and severe orthostatic hypotension. Assessment of arterial baroreflex function suggested that suppressed sympathetic vasomotor drive was the cause of the orthostatic hypotension. Within 3 days, the baroreflex failure resolved spontaneously. To our knowledge, suppressed vasomotor outflow after ingestion of amphetamines has been previously observed only in animal studies.
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Affiliation(s)
- A A Smit
- Department of Internal Medicine, University of Amsterdam, The Netherlands
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Liu W, Varner KJ. Characterization of the sympathetic nerve responses to amphetamine: role of central alpha 2-adrenergic receptors. J Cardiovasc Pharmacol 1996; 28:712-22. [PMID: 8945686 DOI: 10.1097/00005344-199611000-00015] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
Although amphetamine has profound cardiovascular actions, the role of the sympathetic nervous system in these responses is largely unknown. The purpose of this study was to characterize the sympathetic nerve responses to amphetamine and to determine whether these neural responses involve an action of amphetamine in the rostral ventrolateral medulla (RVLM). In sinoaortically denervated (SAD) and sham-SAD rats, amphetamine dose-dependently increased mean arterial pressure (MAP) and heart rate (HR), while decreasing (-87 +/- 5%, max) renal sympathetic nerve discharge (SND) for 57 +/- 5 min. Comparison of the SND responses in SAD and sham-SAD rats revealed a small but significant contribution of the baroreceptor reflex to the sympathoinhibitory response. In separate studies, the bilateral microinjection of amphetamine into RVLM decreased HR, MAP, and SND. The magnitude and duration of the decrease in SND elicited by amphetamine were significantly attenuated by the prior intravenous (i.v.) administration of idazoxan (alpha 2-adrenergic antagonist). The prior bilateral microinjection of idazoxan or piperoxan into RVLM significantly attenuated the duration of the sympathoinhibitory responses elicited by i.v. amphetamine. Idazoxan and piperoxan also tended to decrease the magnitude of the SND response; however, this reduction was significant at only the highest doses. The MAP and HR responses were unaffected by idazoxan treatment. The microinjection of terazosin (alpha 1-adrenergic antagonist) or propranolol (beta-adrenergic antagonist) into RVLM did not alter the HR, MAP, or SND responses to i.v. amphetamine. We conclude that i.v. amphetamine decreases SND in anesthetized rats, in large part, by a mechanism involving the activation of alpha 2-adrenergic receptors in RVLM.
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Affiliation(s)
- W Liu
- Department of Pharmacology and Experimental Therapeutics, Louisana State University Medical Center, New Orleans 70112, USA
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Hey JA, Ito T, Koss MC. alpha-Methyldopa produces mydriasis in the rat by stimulation of CNS alpha 2-adrenoceptors. Br J Pharmacol 1988; 94:834-8. [PMID: 2902894 PMCID: PMC1854015 DOI: 10.1111/j.1476-5381.1988.tb11594.x] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
Abstract
1. The effects of i.v. administration of alpha-methyldopa (MD) on rat pupil diameter were investigated. All experiments were carried out in rats in which vagosympathetic nerve trunks were sectioned bilaterally at the cervical level. 2. In anaesthetized rats MD produced a marked dose-related increase in pupil diameter. The onset of pupillary response to MD was gradual and reached maximal levels 2-3 h after administration. 3. Pretreatment with alpha 2-adrenoceptor antagonists yohimbine (1.5 mg kg-1, i.v.) or idazoxan (0.5 mg kg-1, i.v.) blocked the pupillary response to MD. In contrast, the alpha 1-antagonists prazosin (1.0 mg kg-1, i.v.) and phenoxybenzamine (1.5 mg kg-1, i.v.) did not significantly alter the pupillary effects of MD. 4. Selective enzymatic blockade with 3-hydroxy-benzyl-hydrazine (NSD-1015; 25 mg kg-1, i.p.), a dopa-decarboxylase inhibitor, as well as bis (4-methyl-homopiperazinyl-thiocarbonyl) disulphide (FLA-63, 5.0 mg kg-1, i.p.), a dopamine-beta-hydroxylase inhibitor, prevented the mydriatic effect of MD. 5. The above findings support the hypothesis that MD produces a clonidine-like CNS mydriasis in the rat. This effect appears to be mediated primarily by the MD metabolite, alpha-methylnoradrenaline. 6. These results indicate that MD produces mydriasis in the rat by a CNS action. The mydriatic action of MD appears to be produced by its metabolite alpha-methylnoradrenaline which in turn stimulates CNS postsynaptic alpha 2-adrenoceptors.
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Affiliation(s)
- J A Hey
- Department of Pharmacology, University of Oklahoma Health Sciences Center, Oklahoma City
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Kobinger W. Rudolf Buchheim lecture. Drugs as tools in research on adrenoceptors. NAUNYN-SCHMIEDEBERG'S ARCHIVES OF PHARMACOLOGY 1986; 332:113-23. [PMID: 3010138 DOI: 10.1007/bf00511400] [Citation(s) in RCA: 35] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
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6
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Koss MC. Pupillary dilation as an index of central nervous system alpha 2-adrenoceptor activation. JOURNAL OF PHARMACOLOGICAL METHODS 1986; 15:1-19. [PMID: 2869190 DOI: 10.1016/0160-5402(86)90002-1] [Citation(s) in RCA: 124] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
In recent years there has been increasing evidence that some antihypertensive drugs like clonidine and alpha-methyldopa (after conversion in the brain to alpha-methylnorepinephrine) may decrease sympathetic tone by stimulating central nervous system (CNS) alpha 2-adrenoceptors. These same drugs also produce pupillary dilation in cats and rats. In this review, evidence is presented supporting the hypothesis that clonidinelike drugs act either directly or indirectly on CNS postsynaptic alpha 2-adrenoceptors to cause pupillary dilation by reduction of parasympathetic neural tone to the iris. It is further suggested that the underlying physiologic mechanism for this mydriatic action is activation of an ascending pathway that provides tonic inhibitory input by releasing norepinephrine on neurons in the Edinger-Westphal complex. Yohimbine-sensitive pupillary dilation in these species may provide a simple and effective model for quantitatively accessing CNS alpha 2-adrenoceptor activity.
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Greitz T, Andreen M, Irestedt L. Effects of ephedrine on haemodynamics and oxygen consumption in the dog during high epidural block with special reference to the splanchnic region. Acta Anaesthesiol Scand 1984; 28:557-62. [PMID: 6496016 DOI: 10.1111/j.1399-6576.1984.tb02119.x] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
High lumbar epidural block was induced in seven dogs with 0.5% bupivacaine, causing a fall in mean arterial blood pressure (AP) from 19.2 +/- 3.2 to 10.5 +/- 3.2 kPa, owing to equal reductions in cardiac output (QT) and systemic vascular resistance (SVR). After the administration of ephedrine (a single injection of 200-300 micrograms X kg-1 b.w. followed by a continuous infusion of 10-20 micrograms X kg-1 b.w. X min-1) AP, QT and SVR rose to pre-epidural values. Furthermore, the hypokinetic circulation following the epidural block returned to normokinetic levels. Portal venous blood flow was increased from 16.5 +/- 6.2 to 25.5 +/- 4.3 ml X kg-1 b.w. X min-1 by ephedrine, while the hepatic arterial blood flow was unchanged and remained at its pre-epidural level. In spite of a slight rise in hepatic oxygen consumption from 1.2 +/- 0.4 to 1.6 +/- 0.6 ml X kg-1 b.w. X min-1, the percentages of oxygen extracted from the portal vein and the hepatic artery decreased significantly. It is concluded that ephedrine restores central and splanchnic haemodynamics in a desirable manner during high epidural anaesthesia.
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Koss MC. Methyldopa produces central inhibition of parasympathetic activity in the cat. NAUNYN-SCHMIEDEBERG'S ARCHIVES OF PHARMACOLOGY 1980; 314:135-9. [PMID: 6256665 DOI: 10.1007/bf00504529] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
alpha-Methyldopa (10-100 mg/kg i.v.) produced a dose-dependent pupillary dilation in anaesthetized cats which was antagonized by subsequent administration of yohimbine hydrochloride (0.5 mg/kg i.v.). The peak effects were observed approximately 2-3 h after injection. This alpha-methyldopa-induced mydriasis was present only when the parasympathetic innervation to the iris was intact. Prior treatment with yohimbine (0.5 mg/kg i.v.) 30 min before alpha-methyldopa also antagonized the mydriatic effect, whereas pretreatment with phenoxybenzamine (2.5 mg/kg i.v.) did not. In contrast, phenoxybenzamine, but not yohimbine, effectively antagonized the pupillary dilation produced by adrenaline (0.3-10.0 microgram/kg i.v.). These results suggest that alpha-methyldopa produces mydriasis in the cat by means of CNS inhibition of tonic outflow from the oculomotor nucleus and that an alpha-adrenergic inhibitory mechanism may be involved. This conclusion is supported further by experiments in which direct measurements of ciliary nerve activity were made.
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Langer SZ, Cavero I, Massingham R. Recent developments in noradrenergic neurotransmission and its relevance to the mechanism of action of certain antihypertensive agents. Hypertension 1980; 2:372-82. [PMID: 6105128 DOI: 10.1161/01.hyp.2.4.372] [Citation(s) in RCA: 142] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Abstract
This report reviews a number of significant developments in the fields of noradrenergic transmission and adrenergic receptors which suggest that, in addition to the classical postsynaptic adrenoceptors, there are also presynaptic adrenoceptors that help modulate the release of norepinephrine (NE) from peripheral as well as central noradrenergic nerve endings during nerve stimulation. In particular, stimulation of presynaptic alpha-adrenoceptors reduces this release of transmitter and the reverse is observed after blockade of these receptors. Clearcut pharmacological differences exist between the postsynaptic alpha 1-adrenoceptors that mediate the responses of certain organs and the presynaptic alpha 2-adrenoceptors that modulate the NE release during nerve stimulation. Therefore, subclassification of alpha-adrenoceptors into alpha 1 and alpha 2 subtypes is warranted but must be considered to be independent of the anatomical location of these receptors. Some noradrenergic nerve endings have also been shown to possess beta-adrenergic receptors, the stimulation of which increases the quantity of transmitter released by nerve impulses. Physiologically, these receptors could be activated by circulating epinephrine (E) and be involved in essential hypertension. A third type of catecholamine receptor found at the noradrenergic nerve ending is the inhibitory dopamine (DA) receptor, which might be of significance in the development of new antihypertensive agents. Application of these new concepts of noradrenergic neurotransmission and the subclassification of alpha-adrenoceptors to the treatment of hypertension is presented. Clonidine, for example, appears to be a potent alpha 2-adrenoceptor agonist; the central receptor involved in its antihypertensive action is pharmacologically an alpha 2-type but located postsynaptically. Clonidine also induces activation of peripheral presynaptic alpha 2-adrenoceptors, which might contribute to its cardiovascular action. The antihypertensive effects of alpha-methyldopa are related to the formation of alpha-methylnorepinephrine, a preferential alpha 2-adrenoceptor agonist, which can stimulate peripheral presynaptic alpha 2-adrenoceptors leading to a decrease of NE release and a reduction in sympathetic tone. Prazosin is a new antihypertensive agent the mechanism of action of which involves a selective blockade of postsynaptic alpha 1-adrenoceptors. This drug does not antagonize several effects of clonidine that are mediated via alpha 2-adrenoceptors. The mechanisms presently considered to account for the antihypertensive activity of beta-adrenoceptor blocking agents are numerous. It is proposed that blockade of peripheral presynaptic facilitatory beta-adrenoceptors could be of significance in the antihypertensive action of these drugs.
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Koss MC. Clonidine mydriasis in the cat. Further evidence for a CNS postsynaptic action. NAUNYN-SCHMIEDEBERG'S ARCHIVES OF PHARMACOLOGY 1979; 309:235-9. [PMID: 530304 DOI: 10.1007/bf00504755] [Citation(s) in RCA: 27] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
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11
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Koss MC, Christensen HD. Evidence for a central postsynaptic action of clonidine. NAUNYN-SCHMIEDEBERG'S ARCHIVES OF PHARMACOLOGY 1979; 307:45-50. [PMID: 481609 DOI: 10.1007/bf00506550] [Citation(s) in RCA: 45] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
Intravenous administration of clonidine (1--100 micrograms/kg) produces a dose-dependent mydriasis in cats by inhibition of parasympathetic tone to the iris. The magnitude of CNS-induced pupillary dilation was similar in both normal anaesthetized cats and in anaesthetized preparations pretreated with reserpine (5 mg/kg i.p.) and alpha-methyl-p-tyrosine (2 x 300 mg/kg i.p.). Pretreatment reduced the concentrations of noradrenaline, dopamine and serotonin to less than 3% of that control levels in most parts of the CNS in which these amines were measured. Clonidine produced bradycardia in control animals but not in pretreated cats. In amine depleted animals in which only one eye was innervated by the ciliary nerves (parasympathetic), clonidine produced mydriasis only on the innervated side. These experiments confirm our previous observations that clonidine produces mydriasis in the cat by means of inhibition of parasympathetic tone to the iris. It is concluded that if clonidine produces this effect by stimulating noradrenergic, dopaminergic or serotonergic receptors, then clonidine exerts its centrally-induced mydriatic effect by acting on post-synaptic mechanisms.
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12
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13
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Wellens DL, Wouters LJ, De Reese RJ, Beirnaert P, Reneman RS. The cerebral blood distribution in dogs and cats. An anatomical and functional study. Brain Res 1975; 86:429-38. [PMID: 1116007 DOI: 10.1016/0006-8993(75)90893-8] [Citation(s) in RCA: 44] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
On the basis of corrosion preparations and of microsphere studies, the following characteristics of the canine and feline cerebral circulation were observed. (1) In cats, a greater part of the vertebral arterial blood goes to the brain and it is more specifically restricted to the ponto-medullary and cerebellar structures. These structures received approximately 3 times more microspheres in cats than in dogs. (2) In dogs, an important amount of vertebral blood goes to the neck muscles, and the intracranial vertebral blood supply is spread over a greater area of the brain, including the thalamo-hypothalamic and posterior cortical zone. (3) In cats the thalamo-hypothalamic area receives a greater amount of blood via the common carotid artery than in dogs. (4) In both animal species, the vascular connections between the left and right side of the brain are more extensive in the vertebral than in the carotid bed. However, for either vascular bed, a more important left to right transmission was found in the dog.
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de Jong W, Zandberg P, Bohus B. Central inhibitory noradrenergic cardiovascular control. PROGRESS IN BRAIN RESEARCH 1975; 42:285-98. [PMID: 1197726 DOI: 10.1016/s0079-6123(08)63671-7] [Citation(s) in RCA: 38] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
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15
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Pelton EW, Chase TN. L-Dopa and the treatment of extrapyramidal disease. ADVANCES IN PHARMACOLOGY AND CHEMOTHERAPY 1975; 13:253-304. [PMID: 1106161 DOI: 10.1016/s1054-3589(08)60233-1] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
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Struyker Boudier HA, Smeets GW, Brouwer GM, van Rossum JM. Hypothalamic alpha adrenergic receptors in cardiovascular regulation. Neuropharmacology 1974; 13:837-46. [PMID: 4610445 DOI: 10.1016/0028-3908(74)90039-2] [Citation(s) in RCA: 87] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
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Haeusler G. Clonidine-induced inhibition of sympathetic nerve activity: no indication for a central presynaptic or an indirect sympathomimetic mode of action. NAUNYN-SCHMIEDEBERG'S ARCHIVES OF PHARMACOLOGY 1974; 286:07-111. [PMID: 4281069 DOI: 10.1007/bf00499107] [Citation(s) in RCA: 173] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
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Thoenen H. Sympathetic nervous system and hypertension. VERHANDLUNGEN DER DEUTSCHEN GESELLSCHAFT FUR INNERE MEDIZIN 1974; 80:124-8. [PMID: 4454386 DOI: 10.1007/978-3-642-85449-1_20] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
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Kobinger W, Walland A. Modulating effect of central adrenergic neurones on a vagally mediated cardioinhibitory reflex. Eur J Pharmacol 1973; 22:344-50. [PMID: 4147333 DOI: 10.1016/0014-2999(73)90036-8] [Citation(s) in RCA: 42] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
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