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Fast (3 Hz and 10 Hz) and slow (respiratory) rhythms in cervical sympathetic nerve and unit discharges of the cat

Wu-Xin Huang, Qiping Yu and Morton I. Cohen

1. In seven decerebrate cats, recordings were taken from the preganglionic cervical sympathetic (CSy) nerves and from 74 individual CSy fibres. Correlation and spectral analyses showed that nerve and fibre discharges had several types of rhythm that were coherent (correlated) between population and unit activity: respiratory, '3 Hz' (2-6 Hz, usually cardiac related), and '10 Hz' (7-13 Hz).

2. Almost all units (73/74) had respiratory modulation of their discharge, either phasic (firing during only one phase) or tonic (firing during both the inspiratory (I) and expiratory (E) phases). The most common pattern consisted of tonic I-modulated firing. When the vagi were intact, lung afferent input during I greatly reduced CSy unit and nerve discharge, as evaluated by the no-inflation test.

3. The incidence of unit-nerve coherent fast rhythms (3 Hz or 10 Hz ranges) depended on unit discharge pattern: they were present in an appreciable fraction (30/58 or 52 %) of tonic units, but in only a small fraction (2/15 or 13 %) of phasic units.

4. When baroreceptor innervation (aortic depressor amd carotid sinus nerves) was intact, rhythms correlated to the cardiac cycle frequency were found in 20/34 (59 %) of units. The cardiac origin of these rhythms was confirmed by residual autospectral and partial coherence analysis and by their absence after baroreceptor denervation.

5. The 10 Hz coherent rhythm was found in 7/34 units when baroreceptor innervation was intact, where it co-existed with the cardiac-locked rhythm; after barodenervation it was found in 9/50 neurones. Where both rhythms were present, the 10 Hz component was sometimes synchronized in a 3:1 ratio to the 3 Hz (cardiac-related) frequency component.

6. The tonic and phasic CSy units seem to form distinct populations, as indicated by the differential responses to cardiac-related afferent inputs when baroreceptor innervation is intact. The high incidence of cardiac-related correlation found among tonic units suggests that they are involved in vasomotor regulation. The high incidence of respiratory modulation of discharge suggests that the CSy units may be involved in regulation of the nasal vasculature and consequent ventilation-related control of nasal airway resistance.

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