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Shen S, Ingenito AJ. Synergistic centrally mediated cardiovascular effects of a kappa opioid agonist and an alpha2-adrenoceptor agonist. GENERAL PHARMACOLOGY 1999; 33:449-56. [PMID: 10647770 DOI: 10.1016/s0306-3623(99)00041-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Abstract
In this study, we determined possible additive and synergistic centrally mediated hypotensive and bradycardic effects of U-62,066E, a nonpeptide kappa opioid agonist acting on the hippocampal formation (HF), and guanabenz, an alpha2-adrenoceptor agonist acting on the rostral ventrolateral medulla (RVLM), the nucleus tractus solitarius (NTS), or the locus coeruleus (LC). The drugs were microinjected at various doses into these areas of alpha-chloralose-anesthetized Sprague-Dawley rats. There were synergistic hypotensive and bradycardic effects between low, noneffective doses of U-62,066E acting on the HF and guanabenz acting simultaneously on the RVLM. Higher doses of each agent, which themselves caused hypotension and bradycardia acting on each brain area alone, did not lead to synergistic effects when the drugs were injected simultaneously into those areas. There were no synergistic effects between U-62,066E acting on the HF and guanabenz acting on the NTS or the LC.
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Affiliation(s)
- S Shen
- Department of Pharmacology, School of Medicine, East Carolina University, Greenville, NC 27858-4353, USA
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2
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Kuo T, Yang C, Chan J, Tsai HF, Chan S. Further Characterization of Nociception-Related and Arterial Pressure-Related Neuronal Responses in the Nucleus Reticularis Gigantocellularis of the Rat. J Biomed Sci 1996; 3:338-347. [PMID: 11725116 DOI: 10.1007/bf02257964] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022] Open
Abstract
The present study was undertaken to further characterize the nucleus reticularis gigantocellularis (NRGC) of the medulla oblongata in the central processing of nociceptive and cardiovascular signals, and its modulation by met-enkephalin. In Sprague-Dawley rats anesthetized with pentobarbital sodium, we found that all 125 spontaneously active NRGC neurons that responded to noxious stimuli (tail clamp) also exhibited arterial pressure-relatedness. Forty neurons additionally manifested cardiac periodicity that persisted even during nociceptive responses. While maintaining their cardiovascular responsive characteristics, the nociception-related NRGC neuronal activity was blocked, naloxone-reversibly (0.5 mg/kg, i.v.), by morphine (5 mg/kg, i.v.). Microiontophoretically applied met-enkephalin suppressed the responsiveness of NRGC neurons to individually delivered tail clamp or transient hypertension induced by phenylephrine (5 &mgr;g/kg, i.v.). Interestingly, in NRGC neurons that manifested both nociception and arterial pressure relatedness, the preferential reduction in the response to noxious stimuli upon simultaneous elevation in systemic arterial pressure was reversed to one that favored nociception in the presence of met-enkephalin. All actions of met-enkephalin were discernibly blocked by the opioid receptor antagonist, naloxone. Our results suggest that individual NRGC neurons may participate in the processing of both nociceptive and cardiovascular information, or in the coordination of the necessary circulatory supports during nociception. In addition, neuropeptides such as met-enkephalin may exert differential modulation on neuronal responsiveness according to the prevailing physiologic status of the animal. They also showed that NRGC may be a central integrator for pain and cardiovascular-related functions. Copyright 1996 S. Karger AG, Basel
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Affiliation(s)
- T.B.J. Kuo
- Center for Neuroscience, National Yang-Ming University, Veterans General Hospital-Taipei, Taipei, Taiwan
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3
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Len WB, Tsou MY, Chan SH, Chan JY. Participation of presynaptic noradrenergic fibers in the suppression of alpha 2-adrenoceptor activity by substance P at the nucleus reticularis gigantocellularis of the rat. Synapse 1995; 21:357-63. [PMID: 8869166 DOI: 10.1002/syn.890210411] [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: 02/02/2023]
Abstract
We applied reverse microdialysis and high performance liquid chromatography (HPLC) analysis to evaluate the participation of presynaptic noradrenergic neurotransmission in the suppression by substance P (SP) of alpha 2-adrenoceptor activity at the nucleus reticularis gigantocellularis (NRGC) in Sprague-Dawley rats anesthetized with pentobarbital sodium. Microinfusion of SP (600 microM/min) into the NRGC through a stereotaxically positioned microdialysis probe attenuated the hypotensive and bradycardiac actions of the alpha 2-adrenoceptor agonist, guanabenz (100 micrograms/kg, i.v.). This inhibitory effect correlated positively with the time course of elevation in the estimated extracellular concentrations of SP and norepinephrine (NE) in the NRGC. Direct microinfusion of NE (50 nM/min) into the NRGC also lessened the cardiosuppressant effects of guanabenz. These circulatory and NE responses to SP were, however, significantly blunted in rats in which the noradrenergic innervation in the NRGC was depleted with N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine hydrochloride (DSP4) pretreatment. Microinfusion of NE into the NRGC of DSP4-pretreated animals restored the attenuation of guanabenz-induced cardiovascular suppression. These results suggest that SP may depress the activity of alpha 2-adrenoceptor at the NRGC that are involved in circulatory regulation by increasing the extracellular concentration of NE via a presynaptic modulation of noradrenergic neurotransmission.
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Affiliation(s)
- W B Len
- Department of Medical Research, Veterans General Hospital-Taipei, Taiwan, Republic of China
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4
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Chen C, Lin K, Chan S. Further Elucidation of a Pertussis Toxin-Sensitive Transmembrane Signaling Mechanism Involved in Central alpha(2)-Adrenoceptor Activation in the Rat. J Biomed Sci 1994; 1:13-18. [PMID: 11725002 DOI: 10.1007/bf02258335] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022] Open
Abstract
In adult male Sprague-Dawley rats anesthetized with pentobarbital sodium, we elucidated the molecular consequence of central alpha(2)-adrenoceptor activation. The hypotensive and negative chronotropic and inotropic actions of the alpha(2)-adrenoceptor agonist guanabenz were used as our experimental index. Intracerebroventricular administration of pertussis toxin (2.5 &mgr;g) significantly attenuated the cardiovascular suppressant effects of the aminoguanidine compound (100 &mgr;g/kg i.v.). However, application of N-ethylmaleimide (0.125 or 0.250 &mgr;g), phorbol 12-myristate 13-acetate (1.25 or 2.50 &mgr;g), cholera toxin (1.25 or 2.50 &mgr;g) or forskolin (12.5 or 25.0 &mgr;g) into the lateral cerebral ventricle elicited no appreciable blunting effect on the circulatory depression produced by guanabenz. These results were essentially duplicated when pertussis toxin (0.125 or 0.250 &mgr;g), N-ethylmaleimide (0.0125 or 0.05 &mgr;g), phorbol 12-myristate 13-acetate (0.125 or 0.25 &mgr;g), cholera toxin (0.125 or 0.25 &mgr;g) or forskolin (1.25 or 2.50 &mgr;g) was microinjected bilaterally to the nucleus reticularis gigantocellularis, a medullary site believed to be intimately related to the antihypertensive action of guanabenz. These findings suggest that stimulation of the alpha(2)-adrenoceptors in the medulla oblongata may result in the activation of a pertussis toxin-sensitive GTP-binding regulatory protein. They further suggest that the biologic signals subsequent to this action may not be linked to Gs, Gi or Gp but possibly Go. Copyright 1994 S. Karger AG, Basel
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Affiliation(s)
- C.H. Chen
- Institute of Pharmacology, National Yang-Ming Medical College, Taipei, Taiwan, ROC
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5
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Tsou MY, Len WB, Lee TY, Chan SH, Pan WH, Chan JY. Participation of noradrenergic neurotransmission in the suppression by substance P of alpha 2-adrenoceptors at the nucleus reticularis gigantocellularis involved in central cardiovascular regulation in the rat. Brain Res 1994; 653:183-90. [PMID: 7526958 DOI: 10.1016/0006-8993(94)90388-3] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
We applied reverse microdialysis and HPLC analysis to quantify the participation of noradrenergic neurotransmission in the modulation by substance P of alpha 2-adrenoceptors at the nucleus reticularis gigantocellularis involved in cardiovascular regulation, using Sprague-Dawley rats anesthetized with pentobarbital sodium. The efficacy of circulatory suppression of a centrally acting alpha 2-adrenoceptor agonist, guanabenz, was used as the experimental index. Continuous infusion of substance P (600 or 1200 pmol/microliters/min) into the nucleus reticularis gigantocellularis through a stereotaxically positioned microdialysis probe (active exchange length: 500 microns, diameter: 220 microns) for 80 min elicited a reduction in the hypotensive and bradycardiac actions of guanabenz (100 micrograms/kg, i.v.). This implied suppression of alpha 2-adrenoceptor activity correlated positively with the time-course of increase in the estimated extracellular concentration of the undecapeptide and norepinephrine in the nucleus reticularis gigantocellularis. Experimentally elevating the concentration of norepinephrine at this reticular nucleus via microinfusion by reverse microdialysis also decreased the efficacy of the cardiovascular suppression of the aminoguanidine compound. These results suggest that substance P may depress the activity of the alpha 2-adrenoceptors in the nucleus reticularis gigantocellularis that are involved in central cardiovascular regulation via an increase in the extracellular concentration of norepinephrine at this reticular nucleus.
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Affiliation(s)
- M Y Tsou
- Department of Anesthesiology, Veterans General Hospital-Taipei, Taiwan, ROC
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6
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Chan JY, Tsai HF, Kuo TB, Chan SH. Modulation by angiotensin III of nociception-related and arterial pressure-related neuronal responsiveness in the nucleus reticularis gigantocellularis of the rat. REGULATORY PEPTIDES 1994; 50:247-57. [PMID: 8016409 DOI: 10.1016/0167-0115(94)90005-1] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
We evaluated possible modulation by angiotensin III (AIII) of the interactive effect of noxious stimuli and elevation in systemic arterial pressure on the responsiveness of neurons in the nucleus reticularis gigantocellularis (NRGC) of the medulla oblongata. Combined extracellular single-neuron recording and microiontophoresis were carried out on male, adult Sprague-Dawley rats anesthetized with pentobarbital sodium. The responsiveness of NRGC neurons to nociception (tail clamp) and/or transient hypertension elicited by phenylephrine (5 micrograms/kg, i.v.), in the absence or presence of AIII, was used as the experimental index. Microiontophoretic application of the heptapeptide suppressed the responses of spontaneously active NRGC neurons to individually delivered nociception or hypertension. Interestingly, the preferential reduction in responsiveness to tail clamp upon simultaneous elevation in arterial pressure was reversed to one that favored nociception in the presence of AIII. These actions of the heptapeptide appeared to be receptor-specific, since they were discernibly blocked by its selective antagonist, Ile7-angiotensin III. Our results reveal that neuropeptides such as AIII may differentially modulate neuronal responsiveness according to the prevailing physiologic input(s) to the central nervous system of the animal.
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Affiliation(s)
- J Y Chan
- Institute of Physiology, National Yang-Ming Medical College, Taipei, Taiwan, ROC
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7
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Len WB, Tsou MY, Chan SH, Chan JY. Substance P suppresses the activity of alpha 2-adrenoceptors of the nucleus reticularis gigantocellularis involved in cardiovascular regulation in the rat. Brain Res 1994; 638:227-34. [PMID: 7515321 DOI: 10.1016/0006-8993(94)90654-8] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
We evaluated possible interactions between substance P (SP) and the alpha 2-adrenoceptors in the nucleus reticularis gigantocellularis (NRGC) of the medulla oblongata involved in cardiovascular regulation. Adult, male Sprague-Dawley rats anesthetized with pentobarbital sodium (40 mg/kg, i.p., with 10 mg/kg/h i.v. supplements) were used. The circulatory suppressant efficacy of a centrally acting alpha 2-adrenoceptor agonist, guanabenz, was used as the experimental index. Bilateral microinjection of SP (300 or 600 pmol) into the NRGC, a medullary site that is critically involved in the cardiovascular depressive actions of guanabenz, significantly diminished the hypotensive and bradycardiac efficacy of the aminoguanidine compound (100 micrograms/kg, i.v.). This implied reduction in alpha 2-adrenoceptor activity in the NRGC by SP was antagonized by its selective receptor antagonist, [D-Pro2,D-Trp7,9]-SP (1200 pmol). Similarly, attenuation by SP of the cardiovascular suppressant effects of guanabenz was also reversed by immunocytochemically verified depletion of dopamine-beta-hydroxylase-immunoreactive nerve terminals in the NRGC, elicited by the selective noradrenergic neurotoxin, DSP4 (50 micrograms). These data suggest that SP may exert an inhibitory action on the alpha 2-adrenoceptors in the NRGC that are involved in central cardiovascular regulation, possibly via a presynaptic modulation on noradrenergic neurotransmission.
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Affiliation(s)
- W B Len
- Department of Medical Research, Veterans General Hospital-Taipei, Taiwan, Republic of China
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8
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Yen JC, Chan SH. Passive biophysical membrane properties of nucleus reticularis gigantocellularis neurons in brain slices from the rat. Neurosci Lett 1993; 159:5-8. [PMID: 8264977 DOI: 10.1016/0304-3940(93)90784-i] [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: 01/29/2023]
Abstract
This study employed intracellular recording coupled with the current clamp technique to characterize the passive biophysical membrane properties of neurons in the nucleus reticularis gigantocellularis (NRGC) of brain slices from adult, male Sprague-Dawley rats. We found that NRGC neurons possessed highly depolarized transmembrane potentials (-22.9 +/- 0.6 mV, n = 189). The 29 NRGC neurons that received further evaluation showed that they could be separated into two clusters, with significantly different membrane input resistances (3.51 +/- 0.89 vs 77.50 +/- 8.82 M omega) and membrane time constants (0.56 +/- 0.05 vs 1.27 +/- 0.12 ms). These membrane properties, which resembled qualitatively those we observed previously in cats in vivo, will form the basis for further evaluation of the ionic mechanisms that may underlie the actions of pharmacologic agents on the NRGC neurons.
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Affiliation(s)
- J C Yen
- Institute of Pharmacology, National Yang-Ming Medical College, Taipei, Taiwan, ROC
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9
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Chan JY, Lee HC, Chan SH. Reduction in postsynaptic alpha 2-adrenoceptor activity by endogenous angiotensin III in the nucleus reticularis gigantocellularis of the rat. Neurosci Lett 1991; 133:81-5. [PMID: 1686483 DOI: 10.1016/0304-3940(91)90062-x] [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: 12/28/2022]
Abstract
We investigated in adult, male Sprague-Dawley rats anesthetized with pentobarbital sodium the synaptic location of the interaction between endogenous angiotensin III (AIII) and the alpha 2-adrenoceptors in the medulla oblongata that are involved in cardiovascular regulation. The circulatory suppressant efficacy of a centrally acting alpha 2-adrenoceptor agonist, guanabenz, was used as the experimental index. Direct bilateral microinjection of AIII (40 pmol) into the nucleus reticularis gigantocellularis (NRGC), a medullary site believed to be intimately related to the cardiovascular inhibitory actions of guanabenz, attenuated, whereas the selective AIII receptor antagonist, Ile7-AIII (20 nmol), potentiated, the circulatory suppressant effects of guanabenz (100 micrograms/kg, i.v.). These two respective actions were essentially unaffected by immunocytochemically verified depletion of noradrenergic nerve terminals in the NRGC, elicited by a selective noradrenergic neurotoxin, DSP4. These data suggest that endogenous AIII may exert a tonic inhibitory action on the alpha 2-adrenoceptors located postsynaptically on neurons in the NRGC that are involved in central cardiovascular regulation.
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Affiliation(s)
- J Y Chan
- Department of Medical Research, Veterans General Hospital-Taipei, Taiwan, Republic of China
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10
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Yen CT, Hwang JC, Su CK, Lin YF, Yang JM, Chai CY. Differential actions of the medial region of caudal medulla on autonomic nerve activities. Clin Exp Pharmacol Physiol 1991; 18:743-51. [PMID: 1685946 DOI: 10.1111/j.1440-1681.1991.tb01392.x] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
1. The inhibitory effects produced by activation of the medial region of caudal medulla on activities of the left and right cardiac sympathetic, vagus and greater splanchnic nerves were studied in chloralose-urethane anaesthetized cats. 2. Electrical stimulation of the medial region produced an 80-92% inhibition of the sympathetic nerve activities, and a 45% and 58% inhibition of the left and right cardiac vagal nerve activities, respectively. There were no significant differences between effects elicited in the left and right autonomic nerves. Similar but smaller inhibitory effects were produced by micro-injection of sodium glutamate (0.5 mol/L) or DL-homocysteic acid (50 mmol/L) to the same medullary sites. 3. These data suggest that neurons residing in the medial medullary region exert strong inhibitory effects on autonomic nerve activities. Since the vasculature is principally innervated by sympathetic nerves, inhibition of sympathetic nerve activities might be the principal factor responsible for the depressor effects caused by activation of the medial region of caudal medulla. The heart is innervated both by sympathetic and parasympathetic nerves. Thus, their simultaneous inhibition during activation of the medial region elicits only a weak and variable inhibition of the heart.
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Affiliation(s)
- C T Yen
- Department of Zoology, National Taiwan University, Taipei, Republic of China
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11
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Yin DC, Chan JY, Chan SH. Interaction between angiotensin III and alpha 2-adrenoceptors of the medulla oblongata involved in cardiovascular regulation in the rat. REGULATORY PEPTIDES 1990; 29:59-72. [PMID: 2167505 DOI: 10.1016/0167-0115(90)90109-a] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
We evaluated, in adult, male Sprague-Dawley rats anesthetized with pentobarbital sodium, possible interaction between angiotensin III (AIII) and the alpha 2-adrenoceptors in the medulla oblongata that are involved in cardiovascular regulation. The hypotensive and negative chronotropic and inotropic actions of the alpha 2-adrenoceptor agonist, guanabenz, were used as our experimental index. Intracerebroventricular (i.c.v.) administration of AIII (100 or 200 pmol) significantly attenuated the cardiovascular suppressive effects of the aminoguanidine compound (25 or 50 micrograms/kg, i.v.). Bilateral microinjection of AIII (20 or 40 pmol) to the nucleus reticularis gigantocellularis (NRGC), a medullary site believed to be intimately related to the antihypertensive action of guanabenz, produced similar results. In addition, i.c.v. administered AIII (200 pmol) altered the effects of guanabenz on the arterial pressure-related neurons in the NRGC, in a manner that paralleled the blunted vasodepressive action of the aminoguanidine compound by the heptapeptide. When applied microiontophoretically, AIII also significantly decreased the responsiveness of arterial pressure-related neurons in the NRGC to guanabenz. These findings suggest that AIII may interact with the alpha 2-adrenoceptors located in the NRGC that are involved in central cardiovascular regulation.
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Affiliation(s)
- D C Yin
- Institute of Pharmacology, National Yang-Ming Medical College, Taipei, Taiwan, Republic of China
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12
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Chen CH, Chan SH. Involvement of postsynaptic alpha 2-adrenoceptors and guanine nucleotide-binding protein in guanabenz-induced cardiovascular suppressant effects in the rat. Neurosci Lett 1989; 105:183-8. [PMID: 2562061 DOI: 10.1016/0304-3940(89)90034-7] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
In adult, male Sprague-Dawley rats anesthetized with pentobarbital sodium, pretreatment with the catecholamine-depleting agent, reserpine (150 micrograms, i.c.v.) significantly antagonized the hypotensive and negative inotropic and chronotropic effects of guanabenz, either given intravenously (100 micrograms/kg) or microinjected bilaterally (5 micrograms) into the nucleus reticularis gigantocellularis (NRGC), a medullary site of action for this centrally acting antihypertensive agent. Pretreating animals with microinjection of the selective norepinephrine neurotoxin, DSP4 (50 micrograms), into the bilateral NRGC, on the other hand, did not appreciably blunt the cardiovascular suppressive actions of the aminoguanidine compound. I.c.v. administration of pertussis toxin (2.5 micrograms), which potentially blocks the action of two guanine nucleotide-binding proteins (Gi and Go), significantly antagonized the circulatory inhibitory effects of guanabenz (100 micrograms/kg, i.v.). More specifically, this blocking effect was still apparent upon microinjecting pertussis toxin (250 ng) into the bilateral NRGC. These data suggest that both pre- and postsynaptic alpha 2-adrenoceptors, and a pertussis toxin sensitive G-protein(s) (Gi and/or Go), in the NRGC are crucial to the expression of the cardiovascular suppressant actions of guanabenz.
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Affiliation(s)
- C H Chen
- Department of Psychiatry, Veterans General Hospital, Taipei, Taiwan
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13
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Chan JY, Chan SH. Passive electrical properties of spontaneously active neurons in the nucleus reticularis gigantocellularis of the cat. Neurosci Lett 1989; 97:169-74. [PMID: 2919002 DOI: 10.1016/0304-3940(89)90158-4] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
We evaluated in chloralose-urethane anesthetized cats the passive electrical properties of 25 spontaneously active neurons in the nucleus reticularis gigantocellularis (NRGC) of the medulla oblongata. Compared to other mammalian brain regions, these reticular cells in general possessed higher input resistance, shorter membrane time constant and first equalizing time constant, and longer somatodendritic electrotonic length factor. It is discussed that, by providing a synaptic machinery for quick and sensitive response to afferent inputs and an efficacious interplay between temporal and spatial summation, these electrical membrane properties may account for the spontaneous and irregular discharge pattern characteristic of the NRGC neurons.
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Affiliation(s)
- J Y Chan
- Department of Pharmacology, National Yang-Ming Medical College, Taipei, Taiwan
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14
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Lim HC, Chong OK, Chan SH. Characterization of alpha-adrenoceptors in the nucleus reticularis gigantocellularis involved in the cardiovascular depressant effects of guanabenz in the rat. Neuropharmacology 1988; 27:243-9. [PMID: 2897642 DOI: 10.1016/0028-3908(88)90040-8] [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: 01/03/2023]
Abstract
The participation of alpha-adrenoceptors in the nucleus reticularis gigantocellularis in the hypotensive, negative inotropic and chronotropic effects induced by guanabenz, was examined in rats anesthetized with pentobarbital sodium (40 mg/kg, i.p.). Pretreatment with alpha-adrenoceptor antagonists yohimbine (10 micrograms), phentolamine (2.5 micrograms) and phenoxybenzamine (20 micrograms), which were injected bilaterally into the nucleus reticularis gigantocellularis, significantly antagonized the cardiovascular suppressant effects normally produced by systemic administration of guanabenz (10 micrograms/kg, i.v.). Pretreatment with prazosin (0.25 microgram) did not affect the vasodepressive, but significantly attenuated the bradycardic actions of guanabenz. The general trend of "antagonization potency" shown by the alpha-adrenergic blockers, against the cardiovascular effects of guanabenz, was in the order: yohimbine greater than phentolamine greater than phenoxybenzamine greater than prazosin. It is concluded that while the alpha 2-adrenoceptors in the nucleus reticularis gigantocellularis are more critically involved in the antihypertensive actions of guanabenz, the possibility exists that alpha 1-adrenoceptors may also participate, in part.
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Affiliation(s)
- H C Lim
- Department of Physiology, Faculty of Medicine, National University of Singapore, Kent Ridge
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15
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Chan SH, Lin AM. Correlated effects of guanabenz on single-neuron activity in the nucleus reticularis gigantocellularis, systemic arterial pressure and heart rate in the rat. Neuropharmacology 1988; 27:157-62. [PMID: 3352872 DOI: 10.1016/0028-3908(88)90165-7] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
The simultaneous effects of guanabenz on the activity of single-neurons in the nucleus reticularis gigantocellularis of the medulla oblongata, systemic arterial pressure and heart rate were assessed in Sprague-Dawley rats, anesthetized with pentobarbital sodium (40 mg/kg, i.p.). Of the 35 arterial pressure-related neurons (neurons that temporally altered their spike rhythm subsequent to fluctuations in arterial pressure) which were evaluated in this reticular nucleus, 32 changed their discharge frequencies that exhibited a degree and time-course parallel to the hypotension promoted by the amino-guanidine compound (5, 10 or 20 micrograms/kg, i.v.). More importantly, these alterations neuronal activity preceded the occurrence of the induced vasodepression, signifying a causative relationship between the two events. Four of the 5 non-arterial pressure-related neurons in the gigantocellular reticular nucleus, on the other hand, manifested no basic modification in their spike frequencies in relation to the hypotension induced by guanabenz. These observations provided further support for the idea that the nucleus reticularis gigantocellularis participates actively in the cardiovascular suppressive actions of the aminoguanidine compound.
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Affiliation(s)
- S H Chan
- Institute of Pharmacology, National Yang-Ming Medical College, Taipei, Taiwan, Republic of China
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16
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Chan JY, Chan SH, Chen CF, Barnes CD. Effects of bestatin on the central cardiovascular regulatory mechanisms in the rat. REGULATORY PEPTIDES 1987; 18:75-84. [PMID: 3628868 DOI: 10.1016/0167-0115(87)90037-1] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
We evaluated the effects of bestatin, the specific aminopeptidase-B and leucine aminopeptidase inhibitor, on the central cardiovascular regulatory mechanisms in Sprague-Dawley rats anesthetized with pentobarbital sodium (40 mg/kg, i.p.). Intracerebroventricular injection of bestatin (100 or 200 nmol/5 microliters) consistently elevated the basal systemic arterial pressure and heart rate. At the same time, this degradative enzyme blocker increased the sensitivity of the baroreceptor reflex responses as well as the efficacy of the modulatory actions of the medullary nucleus reticularis gigantocellularis on these reflexes. We speculate that enhancing the tonic activities of the endogenous neuropeptides in the brain by protecting them from their catabolic enzymes may affect the central cardiovascular regulatory machinery by modifying the operations of the baroreceptor feedback controls and their modulatory mechanisms.
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Chan SH, Ong BT. A simple experimental index for the evaluation of inotropic responses. JOURNAL OF PHARMACOLOGICAL METHODS 1987; 18:23-9. [PMID: 3626567 DOI: 10.1016/0160-5402(87)90014-3] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
The validity of the first derivative of systemic arterial pressure (SAdP/dt) as an indirect experimental index for the evaluation of inotropic responses was ascertained in rats anesthetized with pentobarbital sodium (40 mg/kg, i.p.), using the first derivative of left ventricular pressure (LVdP/dt) as the reference. We observed highly significant qualitative and quantitative (p less than 0.001) correlations between these two parameters, under five well-established experimental cardiovascular perturbations that are known to promote inotropic actions, viz, vagosympathetic trunk stimulation; intravenous administration of pentobarbital, epinephrine, or phenylephrine; and temporary common carotid artery occlusion. Preliminary experiments using isometric ventricular contraction as the reference also confirmed these observations. It is suggested that the SAdP/dt may qualify, at the systemic level, as an easily accessible experimental index for ventricular contractility.
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Chan JY, Chan SH. Interactions between guanabenz and clonidine in their antinociceptive effects in the rat. Exp Neurol 1987; 96:233-6. [PMID: 3556516 DOI: 10.1016/0014-4886(87)90186-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
Based on the hot-plate algesiometric assay in conscious Sprague-Dawley rats, we observed that both guanabenz and clonidine, at a subcutaneous dose of 5 and 1 mg/kg, respectively, exhibited significant antinociceptive potencies. Paradoxical actions on the hot-plate responses, however, were exerted by guanabenz at lower doses, varying from hyperalgesia (1 mg/kg) to no effect (2 mg/kg). A pretreatment of clonidine (1 mg/kg) substantially potentiated the antinociceptive efficacy of the two latter doses, but failed to further augment the pain-suppressive action of guanabenz at 5 mg/kg. These interactive effects of the two alpha-adrenoceptor agonists suggest that they may share a common mechanism(s) in their analgesic actions.
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Chan SH, Chan JY, Ong BT. Anatomic connections between nucleus reticularis rostroventrolateralis and some medullary cardiovascular sites in the rat. Neurosci Lett 1986; 71:277-82. [PMID: 3796885 DOI: 10.1016/0304-3940(86)90633-6] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
Based on wheat germ agglutinin-conjugated horseradish peroxidase histochemistry in Sprague-Dawley rats, we identified a reciprocal and bilateral connection between the nucleus reticularis rostroventrolateralis (NRRVL) and the nucleus ambiguus. The rostral ventrolateral medulla also received bilateral inputs from the nucleus reticularis gigantocellularis (NRGC) and nucleus reticularis medullae oblongatae, a projection from the caudal ventrolateral medulla, and had a close relationship with the NRGC pars lateralis. Thus, apart from its well-established projection to the spinal sympathetic preganglionic neurons and innervation from the nucleus tractus solitarius, the NRRVL may also have rich connections with many medullary sites that participate in cardiovascular regulations.
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Chan JY, Chan SH, Ong BT, Barnes CD. Anatomic and physiologic evaluation of a link between the nucleus reticularis gigantocellularis and nucleus ambiguous in the rat. Neurosci Lett 1986; 67:31-6. [PMID: 3725198 DOI: 10.1016/0304-3940(86)90203-x] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
Localized microinjection of wheat germ agglutinin-conjugated horseradish peroxidase into the nucleus ambiguous (NA) of Sprague-Dawley rats retrogradely labeled neurons that were bilaterally located within the confine of the nucleus reticularis gigantocellularis (NRGC). These cells conformed with the Golgi description of cytoarchitectonic configurations and size distributions for neurons in this reticular nucleus. Furthermore, field potentials antidromically evoked at the NA by stimulating the vagus nerve were augmented by concurrent activations of bilateral NRGC sites that were themselves capable of eliciting hypotension and bradycardia. We conclude that the gigantocellular reticular nucleus may at least employ the cardiac vagal preganglionic neurons in the NA to exert its actions on the heart.
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Lim HC, Chan SH. The roles of alpha 2-adrenoceptors in the nucleus reticularis gigantocellularis and vagal mechanism in the cardiovascular suppressive effects of guanabenz in the rat. Neurosci Lett 1986; 63:45-50. [PMID: 3005924 DOI: 10.1016/0304-3940(86)90010-8] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
In pentobarbital-anesthetized rats, pretreatment with yohimbine (10 micrograms), which was microinjected into the bilateral nucleus reticularis gigantocellularis (NRGC), significantly antagonized the reduction in arterial pressure, and the force and rate of heart contraction normally promoted by systemic administration of guanabenz (10 micrograms/kg, i.v.). At the same time, the vasodepressive as well as negative inotropic and chronotropic effects of direct application of guanabenz (500 ng) into the NRGC were attenuated by bilateral cervical vagotomy or atropine sulfate (1 mg/kg, i.v.). We conclude that guanabenz may promote antihypertension by activating the alpha 2-adrenoceptors in the NRGC, which in turn elicits cardiovascular suppression by at least facilitating the vagal outflows to the heart.
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