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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Naunyn-Schmiedeberg's archives of pharmacology 349 (1994), S. 549-554 
    ISSN: 1432-1912
    Keywords: Kynurenate ; Excitatory amino acid receptor ; Vasopressin ; Chemoreceptor ; Vasopressin antagonist ; Rostral ventrolateral medulla ; Carotid body ; Rat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The rostral ventrolateral medulla (RVLM) is involved in the mediation of cardiovascular responses to peripheral chemoreceptor stimulation. To investigate whether excitatory amino acid inputs in the RVLM are related to the responses to chemoreceptor stimulation, we microinjected kynurenate, an amino acid antagonist, unilaterally into the RVLM and examined its effects on the pressor response to stimulation of carotid body chemoreceptors. Male Wistar rats were anesthetized with urethane, paralyzed and artificially ventilated. The carotid chemoreceptors were stimulated with isotonic solutions of inorganic phosphate solution. Stimulation of carotid body chemoreceptors produced increases in blood pressure. Kynurenate injected ipsilaterally but not contralaterally into the RVLM markedly inhibited the pressor response to chemoreceptor stimulation. In rats with spinal transection, stimulation of carotid body chemoreceptors also produced increases in blood pressure. The pressor response in rats with spinal transection was inhibited by intravenous injection of a vasopressin antagonist or by kynurenate injected ipsilaterally into the RVLM. Kynurenate injected into the RVLM inhibited the pressor response to NMDA, AMPA and kainate but not to acetylcholine in intact rats. These findings indicate that excitatory amino acid receptors are involved in mediating the pressor response to carotid body chemoreceptor stimulation in the rat RVLM. It appears that the chemoreceptor stimulation produces an increase in vasopressin release and the enhancement of vasopressin release is also mediated by an increase in excitatory amino acid inputs in the RVLM.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Naunyn-Schmiedeberg's archives of pharmacology 343 (1991), S. 46-51 
    ISSN: 1432-1912
    Keywords: Aortic baroreceptor reflex ; Excitatory amino acid receptors ; Caudal ventrolateral medulla ; Kynurenate ; Muscimol ; Rat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The caudal ventrolateral medulla (CVLM) contains vasodepressor neurons which, when activated, decrease vasomotor tone. To investigate whether excitatory amino acid receptors in the CVLM of the rat are involved in mediation of the aortic baroreceptor reflex, we microinjected amino acid antagonists unilaterally into the CVLM and examined their effects on the depressor response to electrical stimulation of the aortic nerve which contains mainly baroreceptor afferent fibers in rats. Male Wistar rats were anaesthetized with urethane, paralyzed and artificially ventilated. To block reflex vagal effects, methylatropine (1 mg/kg) was given intravenously. Kynurenate (227 ng), an excitatory amino acid antagonist, injected ipsilaterally but not contralaterally into the CVLM markedly inhibited the depressor response to aortic nerve stimulation, while both injections produced a similar small increase in basal blood pressure. Muscimol (1 ng), a GABA receptor agonist, injected ipsilaterally into the CVLM partly inhibited the baroreflex response, while it produced a moderate increase in basal blood pressure. 2-Amino-5-phosphonovalerate (APV) (10 ng), a N-methyl-d-aspartate (NMDA) receptor antagonist, and MK-801 (30 ng), a NMDA receptor channel blocker, partly inhibited the baroreflex response. MK-801 (30 ng) injected into the CVLM reduced the depressor response to the NMDA receptor agonist NMDA (0.3 ng) but not to the quisqualate receptor agonist quisqualate (0.1 ng) and the kainate receptor agonist kainate (0.1 ng), while kynurenate (227 ng) inhibited the depressor response to all three excitatory amino acid receptor agonists. These findings provide further evidence for the presence of excitatory amino acid receptors involved in mediating the aortic baroreceptor reflex in the rat CVLM. It appears that neurons other than the vasodepressor neurons in the CVLM, at least in part, play a role in transmitting the aortic baroreceptor reflex. In addition, both NMDA and non-NMDA receptors may be responsible for the mediation of the reflex.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Naunyn-Schmiedeberg's archives of pharmacology 343 (1991), S. 317-322 
    ISSN: 1432-1912
    Keywords: Aortic baroreceptor reflex ; Excitatory amino acid receptor ; Nucleus tractus solitarii ; Kynurenate ; MK-801
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Excitatory amino acid receptors and l-glutamate in the nucleus tractus solitarii (NTS) may be involved in the regulation of baroreceptor reflexes. To evaluate this hypothesis, we microinjected amino acid antagonists unilaterally into the rat NTS, and examined their effects on cardiovascular responses to electrical stimulation of the aortic nerve and on depressor responses to excitatory amino acid agonists microinjected into the NTS. Male Wistar rats were anesthesized with urethane, paralyzed, and artifically ventilated. Kynurenate (227 ng), an excitatory amino acid antagonist, injected ipsilaterally but not contralaterally into the NTS, markedly inhibited the depressor response to aortic nerve stimulation. l-Glutamate diethylester (GDEE, 3 μg), another excitatory amino acid antagonist, injected ipsilaterally into the NTS, also markedly inhibited both reflex depressor and bradycardic responses. MK-801 (30 ng), an N-methyl-d-aspartate (NMDA) receptor channel blocker, slightly inhibited the baroreflex responses, while Joro spider toxin JSTX-3 (17 ng), a glutamate receptor antagonist, did not affect them. Kynurenate (227 ng) and GDEE (3 μg) markedly inhibited the depressor response to the NMDA receptor agonist NMDA (0.3 ng), the quisqualate receptor agonist quisqualate (0.1 ng), the kainate receptor agonist kainate (0.1 ng), and l-glutamate (10 ng), microinjected into the NTS, while MK-801 (30 ng) reduced only the depressor response to NMDA (0.3 ng), and JSTX-3 (17 ng) reduced only the depressor response to kainate (0.1 ng). These findings provide evidence for the presence of excitatory amino acid receptors involved in mediating the aortic baroreceptor reflex in the rat NTS. In addition, these observations are consistent with the hypothesis that l-glutamate or a related excitatory amino acid may be the neurotransmitter of baroreceptor information in the NTS. It appears that both NMDA and non-NMDA receptors in the rat NTS are responsible for the mediation of baroreflexes.
    Type of Medium: Electronic Resource
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