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Central pathways activated by cardiac vagal afferent fibres in the rat

Bulmer, David Colin Eric; (2002) Central pathways activated by cardiac vagal afferent fibres in the rat. Doctoral thesis (Ph.D), UCL (University College London). Green open access

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Abstract

The heart receives a rich innervation of afferent vagal nerve fibres. The majority of these fibres are chemosensitive and unmyelinated and terminate in the left ventricle. Research into the central pathways activated by cardiac vagal afferent fibres has focused mainly on the mechanosensitive myelinated vagal afferent fibres originating from endings in the atrium of the heart, which are thought to play a role in the control of blood volume. The aim of this study was to investigate the pathways involved in relaying chemosensitive cardiac vagal afferent fibre input within the CNS of the rat. Within this thesis the experimental evidence derived from in vivo experiments using electrophysiological and immunohistochemical methods designed to demonstrate these projections is presented and critically evaluated. Initial experiments examined the pharmacology of the coronary chemoreflex or Bezold-Jarisch reflex in the rat. Activation of this reflex has been shown to produce a bradycardia and hypotension. The afferent limb of this reflex is carried by chemosensitive unmyelinated vagal afferent fibres from the heart. On the basis of the cardiovascular and respiratory effects observed following left ventricular drug administration both before and after vagotomy, the 5- HT3 agonist pheny1biguanide (PBG) was selected as the most suitable chemical stimulant of cardiac C-fibres in the rat. The expression of the activity dependent protein product of the c-fos oncogene throughout the CNS was determined in response to electrical stimulation of the cardiac branch of the vagus. A large increase in c-fos expression was observed in the parabrachial nucleus (PBN). The PBN has previously been shown to act as a major relay of afferent vagal input from the nucleus tractus solitarii (NTS) to other higher centres of the CNS. To investigate whether the PBN receives cardiac vagal afferent input via a direct projection from the NTS, single unit extracellular recordings were made from NTS neurones. A population of neurones were found that responded to both electrical and chemical stimulation of cardiac vagal afferent fibres and were activated antidromically following electrical stimulation of the PBN, indicating that they both received input from cardiac vagal afferent fibres and sent direct projections to the PBN. The results of this thesis demonstrate that the PBN is activated by cardiac vagal afferent fibre stimulation and that it receives input from cardiac vagal afferent fibres via a monosynaptic projection from the NTS.

Type: Thesis (Doctoral)
Qualification: Ph.D
Title: Central pathways activated by cardiac vagal afferent fibres in the rat
Open access status: An open access version is available from UCL Discovery
Language: English
Additional information: Thesis digitised by ProQuest.
Keywords: Biological sciences; Cardiac vagal afferent fibres
URI: https://discovery.ucl.ac.uk/id/eprint/10107242
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