Chang, Hong-Shiu; (1999) Dynamic synchronization of sympathetic oscillators. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Synchronous activity of single postganglionic sympathetic neurones (PGNs) underlies rhythmical or semi-rhythmical burst discharges recorded from peripheral sympathetic nerves. It is still controversial whether this rhythmicity is generated by an autonomous sympathetic oscillator. Previous studies have demonstrated that activity of single PGNs innervating the caudal ventral artery (CVA) of the rat's tail has a dominant rhythm (T-rhythm). The frequency of T- rhythm is different from the cardiac frequency and can be different from those of ventilatory and respiratory rhythms, suggesting that T-rhythm is generated by an oscillator independent of periodic drives originating from the arterial baroreceptors, the ventilation afferents and the respiratory network. Using the rat's tail circulation as a model, the purpose of the present study is: 1) to determine whether activity from different single PGNs is generated by multiple oscillators. 2) to establish whether synchronization of single PGNs is an obligatory feature and if not, how it is regulated. 3) to determine whether periodically driven single PGN oscillators exhibit dynamics as predicted by the theory of nonlinear coupled oscillators. 4) to explain the discharge behaviour of whole nerve activity based on the findings at single PGN level. The experiments were conducted in anaesthetized Sprague-Dawley rats. Population PGN activity was recorded from the ventral collector nerve (VCN) of the tail. Single PGN activity was recorded focally from the surface of the CVA. The interaction between two single PGNs was studied by recording two units simultaneously. The discharge behaviours of PGNs in response to a periodic input were studied using the central respiratory drive (CRD) and lung-inflation cycle (LlC)-related activity as the driving forces. The findings from the present study suggest that: 1) Activity of CVA PGNs is generated by multiple oscillators independent of CRD, LIC-related activity and cardiac activity. 2) The multiple PGN oscillators are capable of dynamic synchronization. 3) When subjected to frequency changes of LICs, single PGNs exhibit dynamics, such as 1:1 entrainment, relative coordination, high order rational frequency-lock, asynchrony, characterising nonlinear coupled oscillators. 4) Population PGN activity should be considered as output activity from a pool of dynamically interactive multiple oscillators rather than that from a single oscillator.

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