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Pressor effects following microinjection of 5‐HT 1A receptor agonists into the raphe obscurus of the anaesthetized rat
Author(s) -
Dreteler Gea H.,
Wouters Wout,
Saxena Pramod R.,
Ramage Andrew G.
Publication year - 1991
Publication title -
british journal of pharmacology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.432
H-Index - 211
eISSN - 1476-5381
pISSN - 0007-1188
DOI - 10.1111/j.1476-5381.1991.tb12172.x
Subject(s) - endocrinology , raphe , medicine , 5 ht1a receptor , blood pressure , raphe nuclei , chemistry , heart rate , bradycardia , microinjection , pindolol , stimulation , 5 ht receptor , propranolol , receptor , serotonin , serotonergic
1 The effects of electrical stimulation and microinjections (90 nl) of the 5‐HT 1A receptor agonists, flesinoxan and 8‐hydroxy‐2‐(di‐n‐propylamino) tetralin (8‐OH‐DPAT), and glutamate into the raphe obscurus on blood pressure, heart rate and phrenic nerve activity (central inspiratory drive) were investigated in rats anaesthetized with α‐chloralose. 2 Electrical stimulation of the raphe obscurus caused a rise in blood pressure which was associated with bradycardia, while glutamate (2.7 nmol) caused only a rise in blood pressure. 3 Flesinoxan (1.3 nmol) and 8‐OH‐DPAT (0.7 nmol) increased blood pressure by 9 ± 1 and 14 ± 2 mmHg, respectively and did not affect heart rate. For both agonists the effect on blood pressure was shown to be dose‐dependent; again no effect on the heart rate was observed over the dose‐ranges chosen. 4 Microinjections of the non‐selective 5‐HT 1A receptor antagonists, (±)‐pindolol (2.7 nmol) or methiothepin (5.2 nmol), into the raphe obscurus prevented the increase in blood pressure caused by microinjection of flesinoxan. However, (±)‐pindolol caused a sustained rise in blood pressure of 15 ± 1 mmHg while methiothepin caused a transient rise in blood pressure. Neither drugs affected heart rate. The ability of methiothepin to attenuate the pressor effect of flesinoxan was found to be partially reversed after 30 min. 5 It is suggested that activation of 5‐HT 1A receptors within the raphe obscurus can cause sympathoexcitation.