Autonomic innervation of the tongue: a horseradish peroxidase study in the dog

Abstract

Autonomic ganglia have been found along the lingual nerve in the rostral two-thirds of the canine tongue and along the glossopharyngeal nerve in the caudal glandular third of the tongue [4,17,18]. A 30% horseradish peroxidase (HRP) solution was injected throughout these ganglionated areas in order to identify the origin of the preganglionic fibers to the lingual ganglia. These injections resulted in ipsilateral retrograde labeling of small multipolar neurons in the lateral reticular formation of the medulla oblongata. The same injections labeled neurons in the ipsilateral cranial cervical ganglion, but preganglionic sympathetic neurons in the thoracic spinal cord were not labeled. These findings indicated that the lingual ganglia consist of parasympathetic neurons which receive preganglionic projections from the medulla. The lingual preganglionic neurons were located within the nucleus reticularis parvicellularis and, in this location, were co-extensive with salivatory neurons that labeled after HRP injections in the mandibular and sublingual salivary glands. A degree of somatotopic organization within the lingual preganglionic group was indicated by the results of regional injections of enzyme and was confirmed by performing unilateral chorda tympani and glossopharyngeal neurectomies prior to extensive bilateral injections of HRP.