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|Title:||Activation of 5-HT1A receptors attenuates tachycardia induced by restraint stress in rats|
|Citation:||American Journal of Physiology-Regulatory Integrative and Comparative Physiology, 2008; 294(1):R132-R141|
|Publisher:||Amer Physiological Soc|
|Sukonthar Ngampramuan, Mathias Baumert, Mirza Irfan Beig, Naiphinich Kotchabhakdi, and Eugene Nalivaiko|
|Abstract:||To better understand the central mechanisms that mediate increases in heart rate (HR) during psychological stress, we examined the effects of systemic and intramedullary (raphe region) administration of the serotonin-1A (5-HT1A) receptor agonist 8-hydroxy-2-(di-n-propylamino)tetraline (8-OH-DPAT) on cardiac changes elicited by restraint in hooded Wistar rats with preimplanted ECG telemetric transmitters. 8-OH-DPAT reduced basal HR from 356 ± 12 to 284 ± 12 beats/min, predominantly via a nonadrenergic, noncholinergic mechanism. Restraint stress caused tachycardia (an initial transient increase from 318 ± 3 to 492 ± 21 beats/min with a sustained component of 379 ± 12 beats/min). β-Adrenoreceptor blockade with atenolol suppressed the sustained component, whereas muscarinic blockade with methylscopolamine (50 µg/kg) abolished the initial transient increase, indicating that sympathetic activation and vagal withdrawal were responsible for the tachycardia. Systemic administration of 8-OH-DPAT (10, 30, and 100 µg/kg) attenuated stress-induced tachycardia in a dose-dependent manner, and this effect was suppressed by the 5-HT1A antagonist WAY-100635 (100 µg/kg). Given alone, the antagonist had no effect. Systemically injected 8-OH-DPAT (100 µg/kg) attenuated the sympathetically mediated sustained component (from +85 ± 19 to +32 ± 9 beats/min) and the vagally mediated transient (from +62 ± 5 to +25 ± 3 beats/min). Activation of 5-HT1A receptors in the medullary raphe by microinjection of 8-OH-DPAT mimicked the antitachycardic effect of the systemically administered drug but did not affect basal HR. We conclude that tachycardia induced by restraint stress is due to a sustained increase in cardiac sympathetic activity associated with a transient vagal withdrawal. Activation of central 5-HT1A receptors attenuates this tachycardia by suppressing autonomic effects. At least some of the relevant receptors are located in the medullary raphe-parapyramidal area.|
|Keywords:||serotonin; psychological stress; heart rate; sympathetic; medullary raphe|
|Rights:||Copyright © 2008 by the American Physiological Society.|
|Appears in Collections:||Electrical and Electronic Engineering publications|
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