Modification of superior cervical ganglion transmission, by changes of carotid bifurcation pressure

Abstract

We investigated the effect of alterations in carotid bifurcation pressure on transmission in the superior cervical ganglion of pentobarbital-anaesthetized rabbits. Compound action potentials were evoked in the internal and external carotid nerves (post-ganglionic fibres) by electrical stimulation of the decentralized cervical sympathetic trunk. Pressure in the ipsilateral isolated carotid bifurcation (CBP) was maintained at a control value of 100 mmHg. Increases of CBP to between 125 and 200 mmHg caused graded reductions in the height and increases in the time to speak (TTP) of the S 2 wave of the compound action potential recorded from the extarnal carotid nerve (mean ± SEM: −5.8 ± 0.9% and +3.0 ± 0.5%, respectively, at 200 mmHg, P < 0.05). In the same nerve, reductions in CBP to between 25 and 75 mmHg caused graduated increases in the height and decreases in TTP of the S 2 wave (+6.3 ± 0.8% and −2.8 ± 0.4% at 25 mmHg, P < 0.05). Similar responses were obtained from the internal carotid nerve. The response of the S 2 wave in the external carotid nerve to a step increase of CBP from 100 to 175 mmHg was examined before and after section of either the ganglioglomerular or carotid sinus nerve. Section of the ganglioglomerular nerve abolished the response (height and TTP of the S 2 wave: before −10.7 ± 0.8% and +5.9 ± 0.9%; after −0.6 ± 0.6% and +0.2 ± 0.5%, P < 0.05). Section if the carotid sinus nerve had no effect on the S 2 wave response. It appears that a population of ganglioglomeruklar nerve fibres, with pressure-sensitive endings located in the wall of the carotid bifurcation, from the afferent limb of a reflex integrated in the superior cervical ganglion of the rabbit. The efferent limb includes postganglionic fibres in the internal and external carotid nerves.