Andrew D. Dixon

Somatotopic organization of the trigeminal ganglion in the rat

Abstract Forty adult rats underwent simple transection of one of ten different branches of the maxillary and mandibular nerves. All animals were killed on the tenth postoperative day and the trigeminal ganglia were removed for routine histological processing. After staining for Nissl substance, the positions of chromatolytic perikarya were plotted on overlays of photographic enlargements of serial sections. The percentages of chromatolytic cells for all ganglion regions and all nerve lesions were determined and used to construct histograms. Results showed a series of somatotopic columns arranged longitudinally within the ganglion. The laterally placed cell columns corresponded to lateral fields of orofacial innervation supplied by the auriculo-temporal nerve and branches to the molar teeth. The antero-medial cell columns corresponded to more medial orofacial structures, supplied by the maxillary incisor and external nasal nerves. The dorso-ventral organization was more complex although, in general, intraoral structures were represented in the more ventral nerve-cell masses.

A histological study of chromatolytic cell groups in the trigeminal ganglion of the rat

Abstract A detailed description of chromatolytic cell group locations was derived from experimental lesions in young adult Wistar rats. Surgical division of the inferior alveolar, mental, infraorbital, external nasal or superior labial nerves was performed on four rats for each type of nerve lesion. The animals were sacrificed 10 days postoperatively, the heads fixed in Bouins fluid, and histologic sections prepared. Tracings of trigeminal ganglia were made from photomicrographic enlargements of alternate sections in each slide series selected for study. The locations of chromatolytic cells were plotted. External nasal and superior labial cells were located respectively at the medial and lateral sides of the ophthalmic-maxillary part of the ganglion, with some overlap ventrally. Inferior alveolar nerve cell bodies were closely arranged in a posterolateral protuberance at the side of the ganglion, with the mental nerve cells concentrated in the dorsal part of this group.

Epithelial Changes in the Presumptive Regions of Fusion During Secondary Palate Formation

Specific epithelial changes before fusion of the palatal processes and nasal septum of human fetuses were studied at the fine structural level and were compared with the changes in rodents and chick cervical sinus formation.

Acid phosphatase in the Golgi apparatus of cells forming extracellular matrix of hard tissues

SummaryHistochemical studies using cryostat sections of fixed rodent fetal and newborn tissues indicated that acid phosphatase (APase) staining of the Golgi apparatus (GA) of cells secreting matrix for hard tissue formation was a general phenomenon. The enzyme was chiefly observed in the GA of tall secretory ameloblasts involved in enamel formation and in the GA of odontoblasts forming dentine; lysosome-like granules reactive for this enzyme were also observed in these cells. Activity was also intense in the GA and lysosomes of osteoblasts involved in intramembranous and endochondral bone formation.High levels of APase in the GA of extracellular matrix-forming cells appeared to correlate with secretory activity. The GA of most other cells, even chondroblasts forming cartilage matrix, had much less marked APase activity. Contrary to previous suggestions, it appears that APase may have a more direct role in osteogenesis than the osteolytic or resorptive action usually cited.

The role of the cartilaginous nasal septum in midfacial growth

Abstract 1. 1. The prenatal development of the cranial base and cartilaginous nasal septum in the midsagittal plane was investigated in normal A/Jax mice and A/Jax mice with spontaneous bilateral clefts of the lip and palate. 2. 2. The emergence of the snout as a prominent rodent characteristic coincided with the extension of the angulated cranial base and was most rapid prior to and during closure of the palatal shelves. 3. 3. There was no significant difference in the amount of extension of the cranial base between the normal fetuses and those with bilateral clefts of the lip and palate. Therefore, the amount of extension of the cranial base was not identified as the important etiologic factor in the formation of a cleft secondary palate in A/Jax mice with bilateral cleft lip. 4. 4. No morphologic or chronologic differences in development of the cranial base were detected between the normal and cleft fetuses. 5. 5. The cartilaginous nasal septum was significantly shorter in the fetuses with bilateral clefts of the lip and palate. This shortness appeared to be the result of a localized anteroposterior deficiency in the anterior third of the septal cartilage. 6. 6. This finding in cleft A/Jax fetuses does not support the view that the nasal septum acts as a “growth center” which set the pace for the downward and forward thrust of the midfacial skeleton during early facial growth.

Distribution of Mast Cells and Their Reactivity to a Histamine Liberator in the Trigeminal Ganglion of the Rat

Mast cell locations were plotted on tracings of photomicrographs of histologic sections of rat trigeminal ganglia. Mast cells were found infrequently in the root and proximal parts of the ganglion, but they were observed in increasing numbers distally. Ganglionic endoneurial mast cells in proximity to the cell bodies of chromatolytic neurons were degranulated by intraperitoneal injections of compound 48/80; this suggests that mast cells play a role in injury responses of the peripheral trigeminal system.

Introduction to the Conference

The Dental Research Center of the University of North Carolina at Chapel Hill was completed in the summer of 1967, coincident with funding from the National Institute of Dental Research as one of a small number of regional dental research centers and institutes. The facilities and fiscal support have created an environment that has attracted outstanding scientists for research into problems of oral health, and we are indebted to the unprecedented efforts by the dental profession and their associates in North Carolina who initiated these developments. Based on the belief that dental research centers should build on and extend existing institutional research strengths, the interrelated and cohesive approach within specified areas of research interests has sought to use effectively the scientific strengths of the entire university community and neighboring institutions. During the initial years, the research effort has been concentrated on a greater understanding of aspects of growth and development of the craniofacial region; areas of research interest include neural mechanisms, mechanisms of mineralization, speech mechanisms, immunologic mechanisms, growth mechanisms, biomaterials, and hemostasis research. Specifically, the neural mechanisms group is seeking to develop effective means for the control of oral and facial pain based on more basic studies of the trigeminal sensory pathway. The role of mineralization in the formation of the hard tissues of the craniofacial region provides opportunities for applied studies of dental and skeletal formation. The growth and speech mech-