Morphological and functional evaluation of the superior salivatory nucleus in rabbits

Horseradish peroxidase (HRP) was applied to the submandibular ganglion of the rabbit to determine the locus of the parasympathetic preganglionic neurons in the medulla. Labeled cells were recognized in the ipsilateral bulbar reticular formation at the level between the caudal end of the facial genu and the caudal part of the root of the facial nerve. The size of the labeled cells were distributed from 150 to 1150 μm² with a variety of forms such as spindle shape, triangular, and polygonal. Moreover, these cells of different sizes and forms were evenly scattered in the superior salivatory nucleus. To evaluate the physiologic functions of the bulbar salivatory nucleus, electrical stimulation was applied to the medulla, and salivary secretion and thermal change of the submandibular gland were measured simultaneously after bilateral cervical sympathectomy. A very good parallelism between the volume of salivary secretion and the magnitude of temperature change at each stimulating point suggests that secretory and vasodilator cells are intermingled with each other in the salivatory nucleus.