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Activity of aortic chemoreceptors in the anaesthetized rat
Author(s) -
Brophy Sarah,
Ford Tim W.,
Carey Michael,
Jones James F. X.
Publication year - 1999
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1111/j.1469-7793.1999.821ad.x
Subject(s) - methoxamine , chemoreceptor , baroreceptor , hyperoxia , chemistry , anesthesia , sodium cyanide , agonist , chloralose , blood pressure , aorta , endocrinology , medicine , anatomy , receptor , heart rate , cyanide , lung , inorganic chemistry
1 It has been widely accepted that the rat aortic depressor nerve contains only baroreceptors. However, the experiments which have provided these negative data have employed whole aortic nerve recording. In the present study, the technical difficulties associated with recording single fibres in vivo , from the rat aortic nerve (diameter 25‐50 μm), have been surmounted using a small tip, glass suction electrode technique. 2 Upon switching from normocapnic hyperoxia to hypercapnic hypoxia, irregularly firing units ( n = 13 ) appeared and these were significantly excited by intravenous injections of sodium cyanide (20 μg) but not by rises in arterial blood pressure induced by methoxamine (an α 1 ‐adrenoreceptor agonist; 10 μg). Inhalation of 100 % oxygen rapidly and reversibly silenced, or profoundly reduced, ongoing activity. 3 Intravenous injection of phenylbiguanide (PBG; a 5‐HT 3 receptor agonist; 8 μg) strongly stimulated the chemoreceptors and was followed by a period of chemodepression (3‐21 s). In contrast none of the single fibre baroreceptors recorded ( n = 15 ) were excited by PBG but all significantly increased their discharge in response to the increases in arterial blood pressure associated with methoxamine and cyanide. Both the excitatory and inhibitory effects of PBG on the chemoreceptor fibres were abolished by ondansetron (a 5‐HT 3 receptor antagonist: 1 mg kg −1 i.v.; n = 5 animals) whilst the chemoexcitatory action of cyanide was preserved. 4 It is concluded that there are chemoreceptor afferents contained in the aortic nerve of the Sprague‐Dawley rat. The 5‐HT 3 receptor appears not to be a pre‐requisite for aortic body chemoexcitation.