No abstract

Ulex europaeus agglutinin I (UEA-I) is a plant lectin with an affinity for L-fucosyl residues in the chains of lactoseries oligosaccharides associated with medium- and smaller-diameter dorsal root ganglion neurons and their axonal processes. These enter Lissauer's tract and terminate within the superficial laminae of the spinal cord overlapping projections known to have a nociceptive function. This implies that the surface coatings of neuronal membranes may have a relationship with functional modalities. The present investigation further examined this concept by studying a neuronal projection with a nociceptive function to determine whether fucosyl-lactoseries residues were incorporated in its primary afferent terminals. Transganglionic transport of horseradish peroxidase (HRP) following injection into tooth pulp chambers was employed to demonstrate dental pulp terminals in the trigeminal spinal complex, while peroxidase and fluorescent tags were used concomitantly to stain for UEA-I. Double immunolabeling for substance P (SP) and gamma-aminobutyric acid (GABA) using peroxidase and colloidal gold allowed a comparison of the distribution of a known excitatory nociceptive transmitter with that of UEA-I binding in specific subnuclei. Synaptic interrelationships between UEA-I positive dental pulp primary afferent inputs and specific inhibitory terminals were also examined. SP immunoreactivity occurred in laminae I and outer lamina II (IIo) of subnucleus caudalis (Vc) and in the ventrolateral and lateral marginal region of the caudal half of subnucleus interpolaris (Vi), including the periobex area in which Vi is slightly overlapped on its lateral aspect by cellular elements of Vc. The adjacent interstitial nucleus (IN) also showed an intense immunoreactivity for this peptide antibody. UEA-I binding displayed a similar distribution pattern in both Vc and Vi, but extended into lamina IIi and the superficial part of Lamina III in Vc. Dental pulp terminals were found to have a comparable distribution; however, many extended into the dorsal portion of the caudal half of Vi and the ventromedial quadrant of rostral Vi. Electron-microscopic analysis showed that transganglionically labeled dental pulp terminals contained ovoid, complex membrane-bound vacuoles laden with transported HRP. The preterminal axon and synaptic membranes of those dental pulp terminals located in zones of Vc and Vi displaying an affinity for UEA-I were usually characterized by a patchy, electron-dense coating of the peroxidase tag. SP was demonstrated ultrastructurally with Protein-A colloidal gold (3-nm particles), whereas GABA immunoreactivity was revealed by the avidin-biotin-peroxidase method.(ABSTRACT TRUNCATED AT 400 WORDS)

No abstract

Pain processing in the trigeminal complex has been thought to reside primarily in the spinal subnucleus caudalis (Vc). However, trigeminal tractotomies eliminating primary afferent input to Vc and severance of secondary trigemino-thalamic fibers from Vc do not disturb pain perception from the central face and oral cavity. Furthermore, large numbers of neurons that are highly responsive to noxious stimuli and suppressed by inputs from the periaqueductal gray and raphe complex have been identified in subnuclei interpolaris (Vi) and oralis (Vo). Therefore, the purpose of this study was to assess the distribution and spatial arrangements of nociceptive modulatory transmitters with nociceptive afferents and trigemino-thalamic relay cells in the rostral portion of the spinal trigeminal nuclear complex. The dental pulp contains predominantly nociceptors that project to all three subdivisions of the trigeminal spinal complex. These projections were visualized by anterograde transganglionic transport of horseradish peroxidase or by degeneration following administration of toxic ricin to the pulp chambers. The spatial arrangements of dental primary afferents with enkephalinergic (ENK) and serotoninergic (5HT) inputs was then assessed by employing avidin-biotin peroxidase and protein-A colloidal gold double-labeling immunocytochemistry. Trigemino-thalamic relay cells were also labeled by retrograde transport of HRP after stereotaxic injections into the ventrobasal thalamus. ENK and 5HT immunoreactivity was found in the ventrolateral quadrant and lateral margin of Vi, together with the adjacent interstitial nucleus (IN). This activity extended from the caudal pole of Vi and the periobex region, where it was most dense, rostrally to a position approximately 2.9 mm from the Obex. Neither ENK nor 5HT immunoreactivity was observed in Vo. Primary dental afferents projected into the ventromedial quadrant of rostral Vi and were found in the ventrolateral quadrant and dorsal aspect of the subnucleus farther caudally. They appeared as simple boutons with single contacts or as larger, sometimes scalloped terminals that formed multiple contacts. Postsynaptic elements were usually small dendritic profiles, although relay cell somata rarely received primary afferent inputs. Many primary afferents entered areas of synaptic clustering and contacted enkephalinergic dendrites, some of which were also postsynaptic to serotoninergic synapses. Alternatively, primary afferents contacted unlabeled processes that were also postsynaptic to the enkephalinergic element to form a triad arrangement. The least common occurrence was axo-axonic contacts in which enkephalinergic synapses were presynaptic to primary afferents. Both enkephalinergic and serotoninergic synaptic categories displayed round vesicles and generally formed asymmetric junctions.(ABSTRACT TRUNCATED AT 400 WORDS)