Ultrastructure of transganglionic degeneration in brain stem trigeminal nuclei during normal primary tooth exfoliation and permanent tooth eruption in the cat.

Electron microscopy is used to study changes in the axons and terminals in the cat brain stem trigeminal nuclei, main sensory, and partes interpolaris and caudalis, during the process of natural tooth shedding. Areas previously showing light optical argyrophilic degeneration products and adjacent areas lacking this degeneration are included. Various types of alteration occur early during tooth loss, including increased presumed glycogen, increased cytoplasmic density, flocculence, lucency, and neurofilamentous hyperplasia. By the stage of maximum exfoliation, terminals and axons of marked density become prominent in areas showing argyrophilia, whereas nondense forms occur elsewhere. By late eruption ages, all forms of degenerated terminals and axons are rare, but phagocytes are heavily laden with similar forms of debris. The sequence of ultrastructural events is discussed in light of recent studies of transganglionic degeneration, their correlation with light microscopic findings, and the potential implications for central plasticity in this system.

Congenital insensitivity to noxious stimuli.

Cerebral-evoked potentials were used to study a 25-year-old man, the older of two siblings with congenital insensitivity to all noxious stimuli, gross impairment of temperature perception, and anhidrosis. Electrical stimulation of tooth pulp consistently eliciting pain and cerebral responses in normal subjects evoked neither cerebral potentials nor painful or other sensations in our patient. However, ordinarily painful electric shocks to the skin of his face evoked cerebral responses as well as sensations lacking disagreeable qualities. Those cerebral potentials elicited by electrical stimulation of the median nerve, clicks, and light flashes were within normal limits. These findings strongly suggest that a defect in transmission of noxious impulses presumably involving first order sensory neurons exists in our patient.

Cerebral responses to electrical tooth pulp stimulation in man. An objective correlate of acute experimental pain.

The pulp of individual teeth of 17 normal adult volunteers was electrically stimulated via pairs of electrodes implanted into dentine. Computer-summated responses recorded from the surface of the head were composed of two concurrent sequences of events, one of which was seen maximally over midline areas and the other over the lower portions of the postcentral regions. Appropriate tests demonstrated that these wave forms represented cerebral tooth pulp-evoked potentials. Because tooth pulp-evoked potentials represent objective, quantifiable, nonverbal concomitants of central events associated with the perception of noxious stimuli, they may prove helpful in investigating acute experimental pain in man.

Toxic ricin demonstrates a dual dental projection.

Toxic ricin was used to study the central distribution of dental afferents in the cat. Following intrapulpal ricin injections ganglion cell degeneration is seen in the II and III ganglion divisions. Central argyrophilic degeneration occurs in the dorsal portion of all ipsilateral trigeminal nuclei. Ventral degeneration is seen in the pars interpolaris and pars caudalis. No contralateral degeneration was observed. The results are discussed with regard to previous studies of the central location of dental afferents.

Projections from dental structures to the brain stem trigeminal complex as shown by transganglionic transport of horseradish peroxidase.

Horseradish peroxidase (HRP) was implanted in one maxillary canine of cats and the transganglionic transport to the brain stem studied and mapped. HRP-positive fibers and terminal granules are distributed ipsilaterally to each subdivision of the trigeminal complex but are heaviest in the main sensory nucleus, adjacent pars oralis and pars interpolaris near obex with somewhat less in the rest of pars oralis and least in pars caudalis. The distribution indicates a wider central representation than previous anatomical reports and corresponds well with certain physiological studies.

Electron microscopy of degenerating axons and terminals in spinal trigeminal nucleus after tooth pulp extirpations.

Following multiple tooth pulp extirpations, electron microscopic preparations show degenerating axons and synaptic terminals in the same region of the brain stem trigeminal nucleus previously demonstrating degeneration by light-optical methods. The observations confirm the phenomenon of transganglionic degeneration in this system and identify the class of central nervous system axons and synapses specifically related to innervation of the teeth.

Ultrastructural study of transganglionic degeneration following dental lesions.

Transganglionic degeneration in the trigeminal main sensory nucleus (MSN) and pars interpolaris (PI) was studied in cats following dental lesions. At early survival times, three types of terminal alteration were seen in both MSN and PI: (1) flocculent degeneration, (2) neurofilamentous hyperplasia and, (3) glycogen accumulation. With longer survival times, the magnitude of these terminal alterations increases. Electron dense degeneration was only seen in the ventral half of PI. Phagocytosis of the altered terminals was also observed. The study suggests a plausible explanation for the variations observed in the CNS projection of primary afferents with degeneration and with HRP transport studies.

Ultrastructure of degenerative changes following ricin application to feline dental pulps.

The ultrastructure of degenerative changes within the ipsilateral trigeminal ganglion, and partes caudalis and interpolaris of the spinal trigeminal nucleus in the cat is described following the application of the potent toxin ricin to the tooth pulps of unilateral maxillary and mandibular posterior teeth, including the cuspids. Survival times ranged from 6 to 10 days. Typical changes identified within the ipsilateral trigeminal ganglion included myelin fragmentation and 'compartmentalization' of the axoplasm of medium-sized myelinated axons, while small myelinated and unmyelinated axons underwent a more variable response ranging from electron-lucent to electron-dense changes. The affected cell body was characterized by the presence of swollen, electron-lucent mitochondria, a reduction of cytoplasmic ribosomes and a filamentous hyperplasia. Other changes often included an eccentric nucleus and satellite cell proliferation. Degenerative changes often occurred in isolated elements surrounded by normal profiles, suggesting specificity of ricin within the trigeminal ganglion. Changes within brainstem axons showed both an electron-dense and a lucent, fragmenting type of axonal alteration. Terminal changes ranged from electron-dense to lucent and also included filamentous hyperplasia and 'hyperglycogenesis'. The altered axonal knobs contained round synaptic vesicles that were presynaptic to dendritic profiles and postsynaptic to terminals containing flattened synaptic vesicles. The above brainstem alterations were identified specifically in the following areas: ventrolateral, medial and dorsomedial pars interpolaris; the ventrolateral and mid-dorsal to dorsomedial areas of the marginalis and outer substantia gelatinosa layers of pars caudalis; and in ventral pockets corresponding to lamina V of the medullary dorsal horn. Dense alterations within terminals containing flattened synaptic vesicles that are typically presynaptic to primary afferents in these areas were rare findings, but along with vacuolization of dendritic profiles suggest a trans-synaptic effect possibly due to the exocytosis of ricin. The results are discussed in relation to different reports of dental projections and with regards to patterns of transganglionic degeneration.