Abstract
In order to pursue further the possible localization of the functional centres which belong to the group of the glossopharyngeal, vagus and accessory nerves, the motoneurons of these nerves and their major branches in the rat were examined by the retrograde degeneration method and the horseradish peroxidase (HRP) method.
The results obtained are based on the examination of 62 rats which were divided into five groups. The results obtained are as follows: (A) The vagus nerve arises from 80-90% of neurons of the dorsal motor nucleus of the vagus (DMV), the total neurons of the ambiguus nucleus (AM) except for a few cells occupying the ventral part of its rostral region, the neurons of the reticular formation between the DMV and the AM, and the neurons of the lateral reticular formation ventrolateral to the AM. (B) The motoneurons of the superior laryngeal nerve innervating the laryngeal muscles comprise 20% of the total cells in the DMV and 50% of the neurons in the rostral one-third of the AM, but the motoneurons of the recurrent nerve are present only in the caudal two-thirds of the AM. (C) Fifty to 60% of the neurons of the DMV supply the abdominal organs. The cell mass forms a series of columns, which is located in the lateral part of the rostral region, the central and medial parts of the middle region and the medial part of the caudal region of the DMV. (D) The glossopharyngeal nerve does not arise from the DMV but from the neurons which are located at a more rostral level than the DMV and from the most rostral and the ventro-rostral parts of the AM. (E) The results also indicate that the vagus nerve consists of elements not only from the vagus nerve but also from the internal branch of the accessory nerve. The neurons of the internal branch of the accessory nerve are scattered in the caudal region of the DMV and the AM. The external branch of the accessory nerve does not arise from the DMV and the AM, but from neurons located in the lateral area of the anterior horns extending from the first to the fourth cervical segments of the spinal cord. These findings were consistently ipsilateral to the side operated on.
