Nerve growth factor receptor (p75)-immunoreactivity in the normal adult feline trigeminal system and following retrogasserian rhizotomy.

The 75 kDa protein nerve growth factor receptor [NGFr(p75)] is a neurotrophin receptor that is able to bind different members of the neurotrophin family of molecules implicated in affecting neuronal survival. Here we describe the light microscopic distribution of NGFr(p75)-immunoreactivity (IR) within the feline trigeminal brainstem sensory nuclear complex and trigeminal ganglion of normal adult subjects and in subjects 10 and 30 days following retrogasserian rhizotomy. Within the trigeminal ganglion of normal subjects, numerous fibers and most of the neuronal cell bodies showed NGFr(p75)-IR that varied in intensity, while cells and fibers with NGFr(p75)-IR were less numerous within the mesencephalic trigeminal nucleus. Within the main sensory and spinal trigeminal nuclei, NGFr(p75)-IR formed a reproducible pattern that varied between the different subnuclei. The NGFr(p75)-IR consisted both of dense pockets and a low level NGFr(p75)-IR that was selective to the trigeminal neuropil. Following rhizotomy, most of the NGFr(p75)-IR was lost from the main sensory and spinal trigeminal nuclei, except in regions where the upper cervical roots and cranial nerves VII, IX, and X project. In contrast, examination of the central root that was still attached to the trigeminal ganglion showed increased NGFr(p75)-IR in fibers and supporting cells, as did the motor root within the peripheral mandibular division. These results indicate that the majority of the NGFr(p75)-IR within the main sensory and spinal trigeminal nuclei originates from primary trigeminal afferents and that retrogasserian rhizotomy leads to an up-regulation of NGFr(p75)-IR in the part of the central root that is contiguous with the ganglion.

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.

Enhanced ultrastructural visualization of the horseradish peroxidase-tetramethylbenzidine reaction product.

Ultrastructural visualization of the horseradish peroxidase-tetramethylbenzidine (HRP-TMB) reaction product within trigeminal ganglion cells and brain stem axons and terminals following HRP injections into the pulpal chambers of cat teeth is enhanced by utilization of a modified osmication procedure that converts the reaction product to a markedly stable and electron-dense form. The results following the use of the modified osmication procedure (pH 5.0 phosphate buffer at 20 degrees C for 12 hours) are compared to results obtained by following Carson's osmication protocol (Carson KA, Mesulam M-M: J Histochem Cytochem 30:425, 1982; Carson KA, Mesulam M-M: In Tracing Neural Connections with Horseradish Peroxidase. Edited by M-M Mesulam. J Wiley, Chichester, England, 1982, p 153-184) (pH 6.0 phosphate buffer at 45 degrees C for 45 min). The results suggest that the conversion of the HRP-TMB reaction product to an electron-dense form during osmication is intimately associated with the pH of the phosphate buffer and the total time of osmication.

Brain stem degeneration patterns following tooth extractions: visualization of dental and periodontal afferents.

The terminal central nervous system distribution of those primary afferent neurons from the teeth and periodontium in cats was studied by degeneration methods. Lesions were created by combinations of tooth extractions and the brain stem was examined at 14, 30 and 60 days survival for degeneration patterns, with 30 days being the optimal survival time. Degenerating axons and terminals are seen bilaterally, but somewhat less on the side contralateral to the lesions and are concentrated in the ventral half of pars interpolaris and pars caudalis near obex. The results are discussed with regard to the current controversies concerning the primary central termination of these trigeminal neurons.

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.

Central representation of dental structures in the kitten, including projections to the mesencephalic trigeminal nucleus.

Horseradish peroxidase (HRP) was injected into either a single maxillary or a single mandibular primary (deciduous) cuspid tooth of 8- to 10-week-old kittens. The large apex of the primary cuspid allowed for some leakage of the HRP from the pulpal chamber to the periodontal ligament (PDL). Thus, the injection procedure resulted in the application of HRP to the PDL as well as to the pulpal tissues. The transganglionic transport of HRP resulted in discrete terminal fields within the spinal trigeminal nucleus (STN) and the main sensory nucleus (MSN). These projections were clearly somatotopically organized within the STN, but less so within MSN. Within pars oralis (PO) and pars interpolaris (PI), mandibular cuspid dental structures (MdCDS) were represented in a dorsal position relative to the maxillary cuspid dental structures (MxCDS), whereas within pars caudalis (PC) and the adjacent reticular formation the somatotopic representation was not dorsoventral, but rather mediolateral, with the MdCDS represented more medially than the MxCDS. Areas of overlap between MxCDS and MdCDS were found within MSN and to a lesser degree within the superficial laminae of PC. In addition, the fiber pathway leading to labeled somata in the mesencephalic trigeminal (Mes V) nucleus was clearly identified. The majority of the fibers traced to the Mes V nucleus exited the spinal trigeminal tract at the level of the transition from PO to the MSN and traversed the nuclear region in a position dorsal to and separate from the trigeminal motor tract. As in STN, fibers within the caudal Mes V tract appeared to be somatotopically organized, with the fibers from the MdCDS generally more dorsal than the ones from the MxCDS. Labeled fibers, some with terminal arbors, were also identified in close association with the trigeminal motor tract. The findings show a complex pattern of central representation in the immature feline central nervous system for deciduous dental structures.

Light- and electron-microscopic localization of primary dental afferents to medullary dorsal horn (pars caudalis).

Light-microscopic (LM) and ultrastructural (electron-microscopic, or EM) identification of primary dental afferents to medullary dorsal horn (MDH) was demonstrated in the cat following injections of horseradish peroxidase (HRP) into pulpal chambers of unilateral maxillary and mandibular posterior teeth, including the cuspids. Use of a new osmication protocol improved and simplified the EM localization of reaction product within the brain stem terminals. LM examination showed that the projection pattern varied between the different levels of MDH. At caudal levels, the labeling was primarily confined to a narrow band consisting of a dense projection to the dorsomedial portion of laminae I and superficial II and a less intense projection to lamina V. The pattern to rostral levels became increasingly more dense and extensive within these same laminae. LM examination of the tooth apex region showed that a limited spread to the periodontal ligament occurred in some cases. EM investigation of the ipsilateral MDH demonstrated reaction product in terminals with synaptic vesicles that are presynaptic to small and medium-sized dendrites. Labeled axonal endings in close association with cell bodies were also observed. No labeled structures were identified in the contralateral MDH. Some of the reaction product found with EM was below the LM limit of resolution, and thus ultrastructural investigation is necessary for a complete analysis of any pathway when using HRP.

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.

Mapping of the normal distribution of substance P-like immunoreactivity in the spinal trigeminal nucleus of the cat.

Although a recent preliminary report indicated a pattern of substance P-like immunoreactivity within the spinal trigeminal nucleus that is similar to the projection sites for dental afferent fibers, details of this substance P distribution are lacking. Our purpose was to describe in cats the complete normal pattern of this immunoreactivity within each of the spinal trigeminal subnuclei. Special emphasis was given to the distribution of substance P-like immunoreactive axons and terminals located in the rostral subnucleus caudalis and the periobex region of subnucleus interpolaris, as these are regions shown to receive dental afferent fibers. Careful mapping in normal cats showed, within the resolution of the light microscope, a consistent pattern of distribution that included only a portion of the previously identified dental relay sites, but was somewhat broader in certain levels and more restricted in others. The results are compared with those provided by others from regions such as the dorsal horn and subnucleus caudalis of the spinal trigeminal nucleus. The findings also provide an anatomical basis for a recent physiologic report on specific cell types associated with dental nociceptive afferent fibers. This study also provides a baseline control for future investigations of possible changes in substance P-like immunoreactivity that follows various peripheral, including dental and central, lesions.

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.

Localization of nerve growth factor receptor immunoreactivity in the trigeminal nucleus of kittens.

A monoclonal antibody raised against the human nerve growth factor receptor (NGFr) was used to map the distribution of NGFr-immunoreactivity (IR) in the trigeminal nuclear complex of 8- to 10-week-old, immature felines. Somata and fibers show NGFr-IR within the trigeminal ganglion and the mesencephalic trigeminal nucleus. NGFr-IR is also found in fibers within the trigeminal root entry zone, the spinal trigeminal tract, and in fibers and terminals within all the central trigeminal sensory nuclei. The NGFr-IR found within the trigeminal sensory nuclei typically occurs in circumscribed zones that vary in position for the different subnuclei. NGFr-IR is found in the dorsomedial and ventrolateral subdivisions of the main sensory nucleus, in the dorsomedial and occasionally in ventral positions within pars oralis, in dorsal and ventral regions within pars interpolaris, and primarily in outer lamina II with fibers that project to lamina V within pars caudalis/medullary dorsal horn. These results show some overlap with the central distribution of trigeminal primary afferent nociceptive fibers such as those found from the tooth pulp and overlap with the central distribution of such peptides as calcitonin gene-related peptide and substance P, but NGFr-IR is more restricted. Thus, it appears that NGFr-IR is associated with the endings of primary afferent fibers in the brain stem, and that these fibers may represent a certain subclass of primary afferent nociceptors. It is speculated that fibers showing NGFr-IR may have the ability to alter their response to peripheral deafferentation when compared to fibers lacking NGFr-IR.