DISTRIBUTION OF ACTIVATING NEURONS IN MEDULLA OBLONGATA BY STIMULATION OF THE VAGUS NERVE

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Abstract
The potential pattern and topographical arrangement of vagal neurons in the medulla of the decerebrated cat were studied by the unit response analysis, employing microelectrodes.1) Stimulation of the vagus nerve between the ganglion nodosum and the ramification of the recurrent nerve evoked the potential in the following regions in the medulla; i.e., the area in the vicinity of the solitary tract, the triangular nucleus of the vestibular nerve, the nucleus of the spinal tract of the trigeminal nerve, and the ambiguus nucleus. By the use of double stimulation method, it was concluded that the responses obtained in the vicinity of the solitary tract, trigeminal nucleus and triangular nucleus of vestibular nerve were due to orthodromic conduction of impulses and those in the ambiguus nucleus due to antidromic one.2) Conduction velocities of these afferents ranged from 18 to 92 meters per second. Spontaneous discharges synchronous with respiratory cycle or discharges induced by a traction of the lung were frequently encountered in vagal units located in the ventral part of the nuclei of the solitary tract.3) Cajal's commissure of the vagus nerve was the only portion where responses could be obtained to stimulation of the contralateral vagus nerve.4) The responses to vagal stimulation which were antidromic in nature were encountered in the caudal part of ambiguus nucleus. Conduction velocities ranged from 40 to 110 meters per second, the maximal value of responses being 500μV in magnitude. Some units located medially in this area displayed often impulse discharge synchronous with respiratory cycle.5) When the vagus nerve was stimulated in the thoracic cavity, evoked potentials could be obtained only in the vicinity of the solitary tract and triangular nucleus of vestibular nerve.

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