The central respiratory‐drive‐related inputs to antidromically identified cervical sympathetic preganglionic neurones have been investigated, in the rat, using extracellular recording techniques, the ionophoretic application of an excitatory amino acid (glutamate) to increase their excitability, and phrenic nerve discharge as an indicator of central respiratory drive. Three distinct firing patterns of sympathetic preganglionic neurones are described: maximal discharge during phrenic nerve activity, maximal discharge during phrenic silence, and a firing pattern unrelated to phrenic nerve discharge. Both spontaneously active and glutamate‐activated silent cervical sympathetic preganglionic neurones had similar, if not identical, firing patterns. The application of glutamate, using ionophoretic currents of up to 100 nA, did not disrupt central respiratory‐drive‐related discharge patterns indicating that these inputs are an important contribution in the regulation of the firing pattern of a proportion of sympathetic preganglionic neurones. On the basis of these observations it is proposed that some sympathetic preganglionic neurones may receive central respiratory drive potentials similar to those received by respiratory motoneurones.

In 21 conscious unrestrained rabbits, arterial pressure was continuously recorded up to 11 wk by an indwelling catheter placed in the thoracic aorta. The average and standard deviation of the 24-h mean arterial pressure (MAP) were calculated and compared before and after sinoaortic denervation, sham operation, or cervical sympathectomy. At the time of sinoaortic denervation, the cervical sympathetic nerve was always disrupted bilaterally to remove possible arterial barosensory afferents contained in it. Subsequent to sinoaortic denervation performed on 12 rabbits, the average 24-h MAP was initially elevated but invariably returned to the predenervation level in 5-36 days (average 14 days). Meanwhile, the standard deviation remained elevated in all but one animal. In five sham-operated or four cervical-sympathectomized animals, neither the average 24-h MAP nor the standard deviation was significantly altered from that of controls. Our results are consistent with the view that the arterial baroreceptor reflex by itself does not play a critical role in determining the long-term level of arterial pressure.

No abstract

No abstract

No abstract