Properties of the inspiration‐related activity of sympathetic preganglionic neurones of the cervical trunk in the cat.

Abstract

SUMMARY1. The experiments reported here have examined some temporal characteristics of the inspiration-related sympathetic discharge of the cat in control conditions and during forcing of the respiratory oscillator into marked deviations from its natural frequency. The purpose of these experiments was to establish whether or not the relation of sympathetic to phrenic nerve activity shows properties consistent with the hypothesis that the inspiration-related sympathetic discharge is driven by a neural oscillator, independent of, but coupled and stably entrained to, the brain-stem respiratory oscillator.2. The electrical activity of the whole cervical sympathetic trunk (n = 26) or of small strands of the cervical trunk containing single units (n = 20) and of the phrenic nerve was recorded in pentobarbitone-anaesthetized, paralysed, artificially ventilated, sino-aortic denervated cats. Most of the cats were bilaterally vagotomized.3. The onset of the inspiratory burst of the sympathetic preganglionic neurones had a fixed delay from the onset of the phrenic nerve burst. The level of activity within the burst, in whole cervical trunk recording, reached a maximum in early inspiration and then was maintained at approximately this level for the rest of inspiration (twenty-two out of twenty-six cats). In four cats the activity level increased throughout the burst. Individual sympathetic preganglionic neurones displaying inspiration-related burst firing were characteristically recruited in early inspiration and thereafter maintained an approximately constant firing frequency for the rest of inspiration.4. Electrical stimulation of afferents in the superior laryngeal nerve during various phases of the respiratory cycle caused equivalent, phase-dependent, resetting patterns of both phrenic nerve and inspiration-related sympathetic discharge.5. In cats with intact vagus nerves, entrainment of the brain-stem respiratory oscillator to the frequency of the respiratory pump was used to change the frequency of the former, within limits, by changing the frequency of the latter. Over the range of frequencies tested, the pump-to-phrenic delay varied as a function of frequency, while the delay between phrenic and sympathetic burst onset was essentially independent of frequency.6. In hyperthermic, hypocapnic cats phrenic nerve burst frequency increased up to about 300 bursts/min from a value of 15 bursts/min in normothermia-18 PHY 385 M. BACHOO AND C. POLOSA normocapnia. At all frequencies within this range the sympathetic burst maintained a delay, with respect to the phrenic burst, which was essentially independent of frequency.7. The fact that phrenic nerve and sympathetic burst maintained a 1: 1 relation with essentially constant delay over all frequencies tested is inconsistent with the known behaviour of coupled neural oscillators. Therefore, the equality of period of phrenic nerve burst and inspiration-related sympathetic discharge is unlikely to result from the activity of an autonomous sympathetic oscillator coupled to the bra...

Relationship between breathing and cardiovascular function at rest: sex‐related differences

“…This has led to the proposal of regulatory models in which the activities of respiratory and cardiovascular neurones control (Bachoo & Polosa 1987), or are coupled to (Barman & Gebber 1976), cardiovascular neuronal activities. Alternatively, respiratory and cardiovascular neurones are governed by a common pool of ‘cardiorespiratory’ interneurones (Richter & Spyer 1990) which may be located in the caudal ventrolateral medulla (Mandel & Schreihofer 2006).…”

“…The interaction between respiratory and cardiovascular mechanisms has been investigated mostly with regard to the rhythmic interplay between breathing and autonomic neural and/or cardiovascular function over the respiratory cycle. Studies in anaesthetized animals suggest that respiratory and autonomic neural rhythms originate in the same brainstem area or are driven from a common oscillator in the brainstem (Bachoo & Polosa 1987, Guyenet et al 1990). In humans, the close relationships between variations of breathing, sympathetic nerve traffic and cardiovascular measures have been interpreted in terms of a central respiratory gate, rather than baroreflex-related phenomena (Eckberg 2003).…”

Burst‐patterned stimulation promotes nicotinic transmission in isolated perfused rat sympathetic ganglia.

“…Under combined conditions of hypercapnia and hypoxia these units fire with 10-40 Hz bursts during inspiration separated by periods of relative silence during expiration (Bachoo & Polosa, 1987). Birks (1978Birks ( , 1979Birks ( , 1982 has shown in the perfused cat superior cervical ganglion (SCG) that repetitive stimulation with short high-frequency bursts at intervals of several seconds produces a larger potentiation of acetylcholine (ACh) release than continuous stimulation at the same frequency, and that this potentiation is stable during many tens of minutes of stimulation.…”

Role of Respiratory Motor Output in Within-Breath Modulation of Muscle Sympathetic Nerve Activity in Humans

“…In these deafferented animal preparations, sympathetic neurons fire mainly during inspiration (ie, in synchrony with phrenic discharge), with their minimum activity occurring during expiration. 1,2 The close temporal relationship between phrenic discharge and sympathetic activity recorded in anesthetized, paralyzed, and vagotomized animals has led to the hypothesis that the 2 neural outputs either arise from the same brain stem neurons or are driven by a common oscillator. 1,3 However, in the intact human, sympathetic outflow to skeletal muscle (muscle sympathetic nerve activity; MSNA) declines during inspiration, reaching its nadir at end inspiration/early expiration, and then rises, reaching its peak at end expiration.…”

“…1,2 The close temporal relationship between phrenic discharge and sympathetic activity recorded in anesthetized, paralyzed, and vagotomized animals has led to the hypothesis that the 2 neural outputs either arise from the same brain stem neurons or are driven by a common oscillator. 1,3 However, in the intact human, sympathetic outflow to skeletal muscle (muscle sympathetic nerve activity; MSNA) declines during inspiration, reaching its nadir at end inspiration/early expiration, and then rises, reaching its peak at end expiration. 4,5 The influence of central respiratory motor output on the within-breath modulation of MSNA has not been studied in humans.…”