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This Article Full Text Full Text (PDF) All Versions of this Article: 92/4/757    most recent expphysiol.2007.037481v1 Alert me when this article is cited Alert me if a correction is posted 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 Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Curran, A. K. Articles by Leiter, J. C. Search for Related Content PubMed PubMed Citation Articles by Curran, A. K. Articles by Leiter, J. C.

Departments of ¹ Physiology² Medicine, Dartmouth Medical School, 1 Medical Center Drive, Lebanon, NH 03756, USA

Inhibition of neurones in the ventral medulla accentuates the respiratory inhibition associated with acute blood pressure elevation in piglets. Activation of presynaptic 5-HT_1A receptors inhibits serotonergic neurones in the ventral medulla and caudal raphé, and we tested the hypothesis that administration of 8-hydroxydipropylaminotetralin (8-OH-DPAT), a 5-HT_1A agonist, within the rostroventral medulla and caudal raphé would enhance baroreceptor-mediated inhibition of respiratory activity in decerebrate, neonatal piglets. Baroreceptor stimulation was achieved by inflating a balloon in the distal aorta to elevate carotid blood pressure. After two to four control trials of baroreceptor stimulation, each piglet was given either a single intravenous (I.V.) dose of 10 µg kg^–1 8-OH-DPAT or treated by adding 10 or 30 mM 8-OH-DPAT to the dialysate for 10 min to inhibit serotonergic neurones, after which the baroreceptor stimulation trials were repeated. Baroreceptor stimulation reduced respiratory activity, particularly the respiratory frequency, which diminished from 35.7 ± 3.3 to 33.8 ± 3.1 breaths min^–1 (P < 0.02) and, following I.V. 8-OH-DPAT, baroreceptor-mediated inhibition of respiratory output was significantly accentuated (P < 0.05); the respiratory frequency declined from 34.5 ± 3.6 to 26.5 ± 2.9 breaths min^–1. Increasing aortic blood pressure reduced the respiratory frequency (P < 0.01), but focal dialysis of 10 or 30 mM 8-OH-DPAT had, on average, no effect on the ventilatory inhibition associated with an acute elevation of blood pressure. We conclude that activation of 5-HT_1A receptors after systemic administration of 8-OH-DPAT enhanced baroreflex-mediated inhibition of ventilation, but this effect cannot be attributed to 5-HT_1A receptor activation within the rostroventral medulla and caudal raphé.

(Received 26 February 2007; accepted after revision 12 March 2007; first published online 28 March 2007)
Corresponding author J. C. Leiter: Department of Physiology, Dartmouth Medical School, Lebanon, NH 03756, USA. Email: james.c.leiter{at}dartmouth.edu