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Studies on the respiratory modulation of sympathetic activity

Zhou, Shi-Yi; (1995) Studies on the respiratory modulation of sympathetic activity. Doctoral thesis (Ph.D), UCL (University College London). Green open access

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Abstract

Sympathetic activity is modulated by central respiratory drive. Studies using whole nerve recordings in the rat have demonstrated different patterns of respiratory modulation in various sympathetic nerves. These regional differences in the discharge patterns of sympathetic outflows may result from either varying proportions of sympathetic neurones with a particular respiratory-related discharge pattern contributing to each whole-nerve activity or sympathetic preganglionic neurones (SPNs) projecting into different nerves having characteristic respiratory modulations. The present study has investigated the respiratory-related discharge patterns of a group of SPNs projecting to the lumbar sympathetic chain (LSC). Furthermore, the hypothesis that caudal raphe nuclei (raphe obscurus, pallidus and magnus) convey central respiratory drive onto sympathetic outflow has been examined. In anaesthetized and vagotomized rats extracellular recordings were made from identified SPNs projecting to or through the lumbar sympathetic chain between L4 and L5 ganglia, and from caudal raphe neurones with axons projecting to the spinal cord. The respiratory-related firing patterns were analysed. Differences in patterns of respiratory modulation and the proportion of SPNs with a certain pattern of respiratory modulation were found between SPNs recorded in the present study and SPNs located in upper thoracic spinal segments reported previously. These findings provide an explanation of the regional differences of respiratory modulation in various sympathetic nerves. Many caudal raphe-spinal neurones with respiratory-related activity could be activated antidromically from the area of the intermediolateral cell column (IML) and activity in some of these neurons correlated to the 2 to 6 Hz rhythm of cervical sympathetic activity. The findings are consistent with the idea that caudal raphe neurones within the region from which I recorded in this study are part of a supraspinal network that contributes to the 2 to 6 Hz component of sympathetic nerve activity. Therefore some raphe-spinal neurones may relay both "respiratory" and "sympathetic" rhythmic components to the sympathetic outflow. These spinally- projecting neurones in caudal raphe nuclei are different from those in the rostral ventrolateral medulla (RVLM) as they have no baroreceptor-related activity. Additionally, they do not have the "typical" characteristics of 5-HT containing neurones which have slow conduction velocities, and slow regular firing characteristics: the majority had small myelinated axons as indicated by their conduction velocities and relatively high discharge rates and irregular firing characteristics.

Type: Thesis (Doctoral)
Qualification: Ph.D
Title: Studies on the respiratory modulation of sympathetic activity
Open access status: An open access version is available from UCL Discovery
Language: English
Additional information: Thesis digitised by ProQuest.
Keywords: Biological sciences
URI: https://discovery.ucl.ac.uk/id/eprint/10103270
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