Cephalic carotid pressure as a measure of transmission through cervical ganglion.

Cephalic or cranial pressure, i.e., pressure recorded craniad from the external carotid artery, was recorded in the cat during stimulation of the pre- and postganglionic trunks of the superior cervical ganglion (SCG) as was tension developed by the nictitating membrane under these situations. The influence of distension of the carotid sinus and of metoprolol on hemodynamic and tension responses was compared with control responses. Distension of the sinus with an indwelling balloon produced an increase of cephalic pressure evoked by stimulation of the SCG. Tension developed by the nictitating membrane was unaffected. Metoprolol reduced the increase in pressure resulting from stimulation of the preganglionic trunk of the SCG at 1.0 Hz but enhanced the pressure increase in the cranial circulation evoked by postganglionic stimulation of the SCG at 5.0 Hz. Action potentials, recorded postganglionically from the SCG, could be roughly grouped by height and latency into three populations. The height of the M3 population increased with distension of the carotid sinus. This study provides evidence that cephalic pressure can be used as a measure of the influence of various factors on the transmission of impulses through the SCG. This parameter appears to be a more sensitive measure of transmission than that of tension developed by the nictitating membrane. Distension of the carotid sinus is one factor that facilitates ganglionic transmission, whereas the beta-adrenoceptor antagonist metoprolol depresses it.