Studies on the afferent pathway of the carotid sinus nerve

The afferents of the carotid sinus nerve were studied physiologically and morphologically using the dog. I. The sinus nerve was dissected into small groups of fibers, the electrical activty of which was observed oscillographically. The activation of the sinus nerve could be induced by several procedures, such as suffocation caused by tracheal obstruction, or intravenous injection of Lobelin as well as Theraptique. However, the modalities of the activation of afferents appeared to vary by the kind of stimulation. From the vagal and sympathetic branches to the carotid body, no spontaneous discharges were obtained. II. The sinus nerve was stimulated by the rectangular wave (100 per sec. in frequency, I msec. pulse duration and 15 volts), and the responses of respiration and blood pressure were recorded on the smoked paper. By the intracranial section of the rootlet of IX th nerve, the blood pressure response subsequent to electrical stimulation of the sinus nerve was reduced in most part, and after the additional section of the rostral rootlets of the vagal nerve the responses disappeared completely. The section of the solitary tract at the level of the entrance of the rootlet of IX th nerve resulted in the disappearance of blood pressure responses subsequent to the electrical stimulation of the sinus nerve, and the section at the level of obex showed normal blood pressure responses. The section of the solitary tract between the above-mentioned 2 levels reduced the blood pressure responses moderatly. Accordingly, th sinus nerve afferents appeared to terminate in the bulb via the solitary tract, their caudal limits being at the level of obex.