Proceedings of the Physiological Society and the Societa Italiana Di Fisiologia, 11‐13 July 1985, Oxford Meeting: Communications

Abstract

(1932) first noted a respiratory grouping of cervical sympathetic nerve discharge. Recordings from single fibres in the cervical sympathetic nerve of the cat (Preiss, Kirchner & Polosa, 1975) show that some neurones fire maximally during inspiration and others during expiration. Furthermore, shifts in antidromic latency indicate that both spontaneously active and silent preganglionic neurones receive an input related to central respiratory drive (Lipski, Coote & Trzebski, 1977). In the present investigation the activity of spontaneously active and glutamate-activated silent sympathetic preganglionic neurones has been analysed for firing patterns related to central respiratory drive in order to determine whether they receive similar phasic inputs.In 19 ac-chloralose-(100 mg/kg i.v.) anaesthetized rats the activity of fifty-two antidromically identified cervical sympathetic preganglionic neurones was recorded in Th2 segment of the spinal cord using multibarrelled micropipettes as described by Gilbey, Coote, Fleetwood-Walker & Peterson (1982). The animals were paralysed with gallamine triethiodide and artificially ventilated with 02-enriched room air. Phrenic nerve discharge was recorded as an indication of central respiratory drive. Some animals were given a pneumothorax and were vagotomized. End-tidal CO2 and blood gases were monitored. Thirty-two neurones were shown to have a phrenic-related discharge pattern on the basis of phrenic-triggered histograms. One group of twelve neurones fired maximally during phrenic nerve activity; of these, four were silent but were induced to fire by the ionophoresis of glutamate. The other group of twenty neurones fired maximally during phrenic silence, of which six were glutamate-activated. In each group spontaneously active and glutamate-activated neurones had similar firing patterns.The present experiments show that, in the rat as in the cat, some sympathetic preganglionic neurones receive phasic inputs related to central respiratory drive which exert a marked control over their output. By raising their excitability, by the ionophoresis of glutamate, the central respiratory-drive-related inputs to silent sympathetic preganglionic neurones have been shown to be similar, if not identical, to those received by spontaneously active neurones.