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This Article Full Text Full Text (PDF) All Versions of this Article: 294/5/R1435    most recent 00012.2008v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Google Scholar Articles by Orer, H. S. Articles by Barman, S. M. PubMed PubMed Citation Articles by Orer, H. S. Articles by Barman, S. M.

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Physiological and Molecular Mechanisms Implicated in the Neural Control of Circulation

Role of serotonergic input to the ventrolateral medulla in expression of the 10-Hz sympathetic nerve rhythm

¹Department of Pharmacology and Toxicology, Michigan State University, East Lansing, Michigan; and ²Department of Pharmacology, Faculty of Medicine, Hacettepe University, Ankara, Turkey

Submitted 7 January 2008 ; accepted in final form 10 March 2008

We studied the changes in inferior cardiac sympathetic nerve discharge (SND) produced by unilateral microinjections of 5-hydroxytryptamine (5-HT) receptor agonists and antagonists into the ventrolateral medulla (VLM) of urethane-anesthetized, baroreceptor-denervated cats. Microinjection of the 5-HT2 receptor antagonist LY-53857 (10 mM) into either the rostral or caudal VLM significantly reduced (P 0.05) the 10-Hz rhythmic component of basal SND without affecting its lower-frequency, aperiodic component. The selective depression of 10-Hz power was accompanied by a statistically significant decrease in mean arterial pressure (MAP). Microinjection of LY-53857 into the VLM also attenuated the increase in 10-Hz power that followed tetanic stimulation of depressor sites in the caudal medullary raphé nuclei. Microinjection of the 5-HT2 receptor agonist 1-(2,5-dimethoxy-4-iodophenyl)2-amino-propane (DOI; 10 µM) into the VLM selectively enhanced 10-Hz SND, and intravenous DOI (1 mg/kg) partially reversed the reduction in 10-Hz SND produced by 5-HT2 receptor blockade in the VLM. Microinjection of the 5-HT1A receptor agonist, 8-hydroxy-2-(di-n-propylamino)tetralin (8-OHDPAT; 10 mM), into either the rostral or caudal VLM also selectively attenuated 10-Hz SND and significantly reduced MAP. The reduction in 10-Hz SND produced by 8-OHDPAT was partially reversed by intravenous WAY-100635 (1 mg/kg), which selectively blocks 5-HT1A receptors. These results support the view that serotonergic inputs to the VLM play an important role in expression of the 10-Hz rhythm in SND.

5-HT1A receptors; 5-HT2 receptors; caudal medullary raphé; caudal ventrolateral medulla; mean arterial pressure; rostral ventrolateral medulla; sympathetic nerve discharge