Activation of 5-hydroxytryptamine-1A receptors suppresses cardiovascular responses evoked from the paraventricular nucleus
ABSTRACT Activation of central 5-hydroxytryptamine-1A (5-HT(1A)) receptors powerfully inhibits stress-evoked cardiovascular responses mediated by the dorsomedial hypothalamus (DMH), as well as responses evoked by direct activation of neurons within the DMH. The hypothalamic paraventricular nucleus (PVN) also has a crucial role in cardiovascular regulation and is believed to regulate heart rate and renal sympathetic activity via pathways that are independent of the DMH. In this study, we determined whether cardiovascular responses evoked from the PVN are also modulated by activation of central 5-HT(1A) receptors. In anesthetized rats, the increases in heart rate and renal sympathetic nerve activity evoked by bicuculline injection into the PVN were greatly reduced (by 54% and 61%, respectively) by intravenous administration of (±)-8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT), an agonist of 5-HT(1A) receptors, but were then completely restored by subsequent administration of WAY-100635, a selective antagonist of 5-HT(1A) receptors. Microinjection of 8-OH-DPAT directly into the PVN did not significantly affect the responses to bicuculline injection into the PVN, nor did systemic administration of WAY-100635 alone. In control experiments, a large renal sympathoexcitatory response was evoked from both the PVN and DMH but not from the intermediate region in between; thus the evoked responses from the PVN were not due to activation of neurons in the DMH. The results indicate that activation of central 5-HT(1A) receptors located outside the PVN powerfully inhibits the tachycardia and renal sympathoexcitation evoked by stimulation of neurons in the PVN.
SourceAvailable from: Glenn M Toney[Show abstract] [Hide abstract]
ABSTRACT: Circulating angiotensin II (Ang II) combined with high salt intake increases sympathetic nerve activity (SNA) in some forms of hypertension. Ang II-induced increases in SNA are modest, delayed, and specific to certain vascular beds. The brain targets for circulating Ang II are neurons in the area postrema (AP), subfornical organ (SFO), and possibly other circumventricular organs. Ang II signaling is integrated with sodium-sensitive neurons in the SFO and/or organum vasculosum of the lamina terminalis (OVLT) and drives sympathetic premotor neurons in the rostral ventrolateral medulla (RVLM) via the paraventricular nucleus (PVN). It is likely that, over time, new patterns of gene expression emerge within neurons of the SFO-PVN-RVLM pathway that transform their signaling properties. This transformation is critical in maintaining increased SNA. Identification of a novel gene supporting this process may provide new targets for treatment of neurogenic hypertension.Current Hypertension Reports 07/2007; 9(3):228-35. DOI:10.1007/s11906-007-0041-3 · 3.90 Impact Factor
[Show abstract] [Hide abstract]
ABSTRACT: Experimental evidence indicates that the hypothalamic paraventricular nucleus modulates sympathetic vasomotor tone and blood pressure and that this modulation is altered in some cardiovascular diseases. This study tested the hypothesis that this nucleus exerts a more significant tonic excitatory modulation of basal sympathetic vasomotor activity in spontaneously hypertensive rats. In anesthetized, artificially-ventilated rats, bilateral microinjections of the GABA(A) receptor agonist, muscimol (1 to 1.5 nmoles per side), into the paraventricular nucleus produced a depressor and sympathoinhibitory response that did not recover. When compared with normotensive rats, this response was more marked in spontaneously hypertensive rats, where lumbar sympathetic nerve discharge was reduced by 75 +/- 3% and mean arterial pressure fell from 119 +/- 7 mm Hg to 58 +/- 3 mm Hg. Blockade of excitatory and inhibitory amino acid receptors in the rostral ventrolateral medulla significantly attenuated this response. Microinjections of small volumes (<20 nL) of GABA were used to localize precisely the responsive region of the paraventricular nucleus. Unilateral injections of GABA into the dorsomedial cap of the paraventricular nucleus induced a brisk depressor (decrease of 42 +/- 4 mm Hg), sympathoinhibitory (decrease by 72 +/- 2%), and bradycardic (decrease of 77 +/- 16 bpm) response. The mechanisms underlying the sympathoinhibition after inactivation of the paraventricular nucleus are not elucidated, but evidence discussed suggests the involvement of a supracollicular sympathoinhibitory pathway. The results presented demonstrate that the paraventricular nucleus exerts a powerful, tonic effect on the control of sympathetic vasomotor tone under basal conditions in anesthetized rats and that this is enhanced in spontaneously hypertensive rats.Hypertension 03/2002; 39(2):275-80. DOI:10.1161/hy0202.104272 · 7.63 Impact Factor
[Show abstract] [Hide abstract]
ABSTRACT: It is now nearly 5 years since the last of the currently recognised 5-HT receptors was identified in terms of its cDNA sequence. Over this period, much effort has been directed towards understanding the function attributable to individual 5-HT receptors in the brain. This has been helped, in part, by the synthesis of a number of compounds that selectively interact with individual 5-HT receptor subtypes--although some 5-HT receptors still lack any selective ligands (e.g. 5-ht1E, 5-ht5A and 5-ht5B receptors). The present review provides background information for each 5-HT receptor subtype and subsequently reviews in more detail the functional responses attributed to each receptor in the brain. Clearly this latter area has moved forward in recent years and this progression is likely to continue given the level of interest associated with the actions of 5-HT. This interest is stimulated by the belief that pharmacological manipulation of the central 5-HT system will have therapeutic potential. In support of which, a number of 5-HT receptor ligands are currently utilised, or are in clinical development, to reduce the symptoms of CNS dysfunction.Neuropharmacology 09/1999; 38(8):1083-152. DOI:10.1016/S0028-3908(99)00010-6 · 4.82 Impact Factor